xvEPA
               ted States
              Environmental Protection
              Agency
               fice of Pesticides
              and Toxic Substances
              Washington, DC 20460
EPA-560/11-80-
October 1980
              Toxic Substances
Support Document
Test Data Development
Standards

Physical/Chemical and
Persistence Characteristics :

Density/Relative Density
Melting Temperatures
Vapor Pressure
Octanol/Water Partition Coefficient
Soil Thin  Layer Chromatography

Proposed Rule, Section 4
Toxic Substances Control Act

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                               EPA 560/11-80-02?

SUPPOET  DOCUMENT
TEST DATA DEVELOPMENT STANDARDS
PHYSICAL/CHEMICAL & PERSISTENCE CHARACTERISTICS:

DENSITY/RELATIVE DENSITY
MELTING TEMPERATURES
VAPOR PRESSURE
OCTANOL/WATER PARTITION COEFFICIENT
SOIL THIN LAYER CHROMATOGRAPHY

PROPOSED RULE, SECTION 4
TOXIC SUBSTANCES CONTROL ACT
Exposure Evaluation Division
Office of Toxic Substances
OCTOBER 1980
U. S. Environmental Protection Agency
Office of Pesticides & Toxic Substances
Washington, D.C. 202^60

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TABLE   OF   CONTENTS


[Numbers Refer to Those at Top of Page]




Density/Relative Density	  1


Melting Temperatures	27


Vapor Pressure	51
Octanol/Water Partition
Coefficient	79
Soil'fMn Layer
Chromatography	121

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DENSITY/RELATIVE DENSITY

STANDARD FOR TEST DATA DEVELOPMENT
PROPOSED RULE, SECTION 4, TSCA

Refers to

Part 772 -- Standards for Development of Test Data
    Subpart I.  Physical, Chemical and Environmental
                Persistence Characteristics
       Section 772.122-1 Density/Relative Density

October 1980

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                             CONTENTS
                                                        Paqe
1.  NEED FOR THE TEST	 1


2 .  SCIENTIFIC ASPECTS	 4

    2.1.  Selection of Test Conditions	 4

          2.1.1.  Equipment	 4

          2.1.2.  Materials	 5

    2.2.  Selection of Test Procedures	 5

          2.2.1.  Temperature of Test	 5

          2.2.2.  Selection of Measurement Technique... 6

          2.2.3.  Calculation of Ideal Gas Density	10

    2.3.  Test Data Required	10


3 .  ECONOMIC ASPECTS	12


4.  COMPATABILITY WITH OTHER TEST STANDARDS	13

    4.1.  TSCA/FIFRA Compatibility	14

    4.2.  OECD Compatibility	14

    4.3.  IRLG Compatibility	14


5.  RESPONSES TO COMMENTS RECEIVED ON  PROPOSED
    GUIDANCE FOR PREMANUFACTURE TESTING	15

    5.1.  General	15

    5.2.  Responses to Specific Comments	15


6.  REFERENCES	19

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1.        NEED FOR THE TEST






     The purpose of this test  is to develop  data  on  density and



relative density (specific gravity) of  chemical substances  and



mixtures.






     EPA will use the data obtained from  testing  of  density and



relative density to evaluate the potential for human and



environmental exposure to chemicals.  Data also will be used as a



screening test in order to determine what additional testing will



be required for physical and chemical characteristics and for



effects on the various portions of the  living and nonliving



environment.






     Density is an important factor affecting the path that a



chemical will take in moving through the  environment and



affecting where the material may eventually  accumulate.  As



chemical substances enter the  atmosphere  or  water, as a result of



normal practices of manufacture, transportation,  use, ultimate



disposal, or accidental spill, they will  tend to  rise, sink, or



disperse as a function of their density.  In water,  for example,



low density substances  (liquid or solid)  will float  to the



surface, dense substances will tend to  sink  to the bottom,  and



materials with approximately the same density as  the water  will



tend to become dispersed.  EPA, therefore will use information on



density to determine if principal exposure may be to bottom-



dwelling organisms (e.g., shellfish), to  plants or animals



(e.g., waterfowl) that live at the surface,  to swimmers who use



the shallow beach areas, or to swimming fish which contact  the






                               -1-

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dispersed chemicals.  The  information will be used  in  selecting



which types of plants or animals to test  for toxic  effects,  and



it will be used  in the ultimate evaluation of risk  to  the human



and nonhuman environment.






     Similar considerations need to be made for materials that



enter the atmosphere through any of a number of ways,  intentional



or accidental.   Dense gases will tend to  accumulate near the



surface of the earth.  An  example  is chlorine, which occasionally



is spilled as a  result of  train, barge, or truck  wrecks  or  the



rupture of storage vessels.  Because of its density, the gas



remains near the surface and causes a great risk  to nearby  human



and animal populations.  Light gases, on  the other  hand, tend to



rise and diffuse in the atmosphere where  they may be subject to



photochemical degradation.  However, if they are  not degraded



they may be transported great distances and ultimately be



redeposited through various processes of  atmospheric deposition.





     One way that EPA will use data  from  density  testing is as



part of the input to several mathematical models  for assessing



transport and fate of chemicals in the  environment.  These



models, which consider movement in the  atmosphere,  surface



waters, and ground water,  all require information on density to



evaluate the movement of materials, their ultimate  deposition,



and the biological and chemical processes of transformation that
                                -2-

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will affect them.  Results  from the modeling work  are  then




combined with the results of toxicity  and  other hazard



evaluations in order to assess the total human and environmental



risk from the chemicals.
                                -3-

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2.        SCIENTIFIC ASPECTS








2.1.      Selection of Test Conditions








2.1.1.    Equipment






     The use of calibrated ASTM-specification  thermometers is




required.  The particular type of thermometer  is  usually



specified in the  standard technique  identified in Table  1  of the




Test Standard.






     Widespread laboratory experience has  found that  manufactured



thermometers are  sometimes inaccurate by several  degrees.   Such



inaccuracy may result in incorrect density values that would



adversely affect  EPA's ability to use the  data in models.   A



minimal, satisfactory, easily attainable traceability to NBS is a



comparison by the manufacturer or the analyst  with a  thermometer




that has been calibrated by NBS.  Compliance with this condition



of the test is relatively easy, but  it  is  an important factor



that often is overlooked.






     The other apparatus required is fully described  in  the




methods and procedures referenced in Table 1 of the Standard.



EPA has reviewed  and adopted these procedures  with their




appropriate equipment requirements.
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2.1.2.    Materials






     The reference materials, water, mercury, cyclohexane,  and



toluene have been recommended by the IUPAC Commission on



Physicochemical Measurements and Standards (1975,  1976), and



recommended density values have been given.  These, or other



appropriately selected substances, are to be used  in this



procedure for calibrating the apparatus as described in several



of the techniques.





     The suggested immersion liquids are water and a series of



organic compounds useful in the event that the substance is



soluble in water.  The liquids listed are representative and have



been recommended in one or more of the techniques  requiring



immersion of the specimen.  The immersion liquids  include  several



of high density, to be used in the sink-float technique.   The



comparison gases are  for use with the gas-comparator pycnometer




technique.
2.2.      Selection of Test Procedures
2.2.1.    Temperature of test





     The IUPAC has  for many years  recommended  (IUPAC  1972)  the



reporting of physical-chemical-properties measurements  at the



convenient temperature of  25°C,  and  this is  the  preferred



temperature.  Testing at this temperature will provide  the



reliable data that  EPA requires  for  use in its modeling



techniques for evaluating  environmental fate and exposure.   A





                               -5-

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                               10
temperature of 25°C is slightly above  customary  laboratory



temperature, which makes for convenient  adjustment  and



maintenance of a constant temperature  bath  at  25°C  for



measurements.





     However, engineering groups,  such as the  American Petroleum



Institute and the American Gas Association  have  established a



much lower  reference temperature.   Their most  common reference



temperature for many years had been 60°F (15.55°C).   Within the



last few years, with the shift to  SI units,  and  to  harmonize



their standards with the European  standards (through ISO)  they



have agreed to shift to 15°C as the reference  temperature.  This



temperature is representative of many  environmental temperatures



and EPA will be able to adjust its evaluating  techniques to use



density data determined at 15°C.





     The CIPAC group has adopted  (Raw  1970) 20°C as the standard



reporting temperature  for the properties of pesticides.  A



substantial body of data on pesticides has  been  determined at



this temperature and the results are useable by  EPA.  Pesticides



are commonly used at temperatures  which  are somewhat warmer than



annual temperature because they are generally  used  during the



growing season or indoors.








2.2.2.    Selection of a Measurement Technique






     The procedure for testing chemicals under the  Toxic



Substances  Control Act (TSCA) must be  broad enough  to cover the



entire range of chemicals subject  to the law.   Measurement of






                               -6-

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                               11






density, in itself, is not a complicated problem  for  most




chemicals, however, the techniques  for handling different  kinds



of chemicals are quite different because of  different physical



characteristics.






     Many simple procedures have been developed for making



measurements on common classes of chemicals.  These are based on



well known physical principles, such as Archimedes' principle



(see, for example Bauer and Lewin [1971], p.91) or on the



definition of density itself.  The  different techniques have



specific limitations because of the shapes of the measuring



devices, the incompatibility of certain chemicals with immersion



liquids, the viscosity and the volatility of the  test substance,



or the  size of the particles that may have to be  tested.






     EPA has reviewed a broad  range of methods from the



scientific literature and has  adopted the large number of



standardized protocols listed  in Table 1 of  the Standard.  Each



method  has been evaluated for  suitability for use with different



types of substances as described by characteristics given  in



Table 2 of the Standard.  Section (e)(l)(ii)  of the Standard



specifies which types of techniques EPA has  judged suitable for



use with the different types of substances.   The  person doing the



testing then is free to choose from among the appropriate



standardized protocols listed  in Table 1.






     Some contingencies may not be  covered by the identified



techniques in this procedure.  In these cases the method to be



used will be specified in the  test  rule.






                               -7-

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                               12






     An important feature of Table  1  is  its  application  to  the




choice of a technique that is  suitable to the  physical



characteristics of the material to  be tested.   For  assistance in




this process, Table 2 of the Test Standard has been developed to




give the important characteristics  that  must be taken into




account in making the selection of  a  technique.   If further



guidance is necessary, EPA recommends the book by Bauer  and Lewin




(1971), Table 2.7, which outlines recommended  techniques for




various special problems.






     For gaseous substances the principal decision  is whether to



calculate or measure the density.   In consideration of the



relatively small differences between  results produced by the two



techniques, the Agency will accept  a  calculation based on the



ideal  gas law as adequate.  This method  is suitable for



assessment purposes, as indicated by  a comparison of real gas and



ideal  gas densities of several typical industrial gases  (allene,



ammonia, 1,3-butadiene, chlorine, methylamine,  helium,




fluoromethane, and nitrous oxide),  at atmospheric pressure  and




ambient temperatures.  The real gas density  is higher than  the



ideal  gas density in all cases but  one.  However, the average




relative error is only 3.0 percent, with a standard deviation in




the  relative error of 4.7 percent.  However, because easily used




devices are available commercially  for measuring gas density,



[ANSI/ASTM D 1070] the option  is given of measuring rather  than



calculating the density.
                                -8-

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                              13






     For liquids, the volatility  and  viscosity are factors in the



selection of a method.  The  sensitivity  of  the techniques to



these factors is not very great,  however, so  for  certain ranges



of volatilities and viscosities,  one  technique or another may



work equally well.  For volatilities,  this  range  is defined by 15



kPa  < P° < 80 kPa, where 1  kPa = 0.00987 atm.  and P°  is the



vapor pressure of the pure  liquid at  25°C.  Similarly  there is a



range of viscosities in which  one technique or another may



equally well be used.  This  range is  defined  by 15 cST <  T



(258C) < 400 St where  T     is the viscosity.   The viscosity



primarily affects the ease with which the liquid  flows through



capillary tubes used in some techniques.  Table 2 of the



Standards accounts for the  range  of overlap.






     For solids, the size of particles,  the interfacial tension



with water, and the solubility in water  affect the choice of



method.  The selection is not  strongly dependent  on the



characteristic, however, so  the Standard leaves room for the



judgment of the analyst.






     Solubility of the solid in water in amounts  greater than 1



mass percent precludes use of  water as an immersion liquid,  and



some other liquid must be chosen.   Also,  immersion methods in



which the change in weight of  an  object  is  used as a measure of



its density, require pieces  large enough to be handled



individually.  Wettability  is  another important parameter,



particularly for powders, if the  density is to be determined by



displacement of water.
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                              14






     Table 2 lists the characteristics  of  interest  in  a




systematic way for convenience, but  it  gives  limits only in some



cases for which quantitative  criteria  seem to be useful.  Within




the scope of this Table and Table  1, the  sponsor is expected to




determine which technique to  use and to apply it appropriately in




making the test.






     The accuracies obtainable  by  the  standard techniques are




stated in the published descriptions of the techniques.  In every



case they meet or exceed the  requirements  of  the Agency.




Techniques for exposure assessment used by EPA generally accept



an accuracy within 5 percent  as adequate,  except in the region of



relative density from  0.95 to 1.05.  Here,  in order to determine




how a chemical will act in water,  the  relative density needs to



be known to 0.01.








2.2.3.    Calibration






     Calibration of laboratory  equipment  has  long been a



standard requirement for testing or  research.   The  step, while




not burdensome, assures that  the data  will not be affected by



equipment that is damaged or  has drifted  out  of calibration.








2.2.4.    Calculations of Ideal Gas  Density








          The density, p, is  calculated from  the formula








p                             = pM/RT
                               -10-

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                              15





in which p is the pressure, M the molar mass,  R the  thermodynamic




gas constant, and T the thermodynamic temperature.   Using  T  =



298.15 K (25°C) and R = 8.3143  J mol^R-1,  and with  the  mass M



expressed in grams and the pressure  in kilopascals,  the  gas



density can be calculated in kilograms per  cubic meter.






     The relative density of an ideal gas with respect to  air is



calculated from the ratio of the molecular  weight of the gas to



the average molecular weight of air.  For the  average molecular



weight of air, we have taken 28.964  from Weast (1978-1979).








2.3.      Data Required






     The sponsor is allowed the option of reporting  either the



density or the relative density because the calculation  from one



to the other is simple and unambiguous.  The sponsor is  also



asked for a statement of the technique that was chosen and for



calibration information.  Because, in some  instances, the  density



of the material tested may not  indicate the range of acceptable



densities in a material of variable  composition,  a statement of



the acceptable range of densities is requested.
                               -11-

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                               16






3.        ECONOMIC ASPECTS






     A survey of commercial  laboratories  to estimate costs for




performing the tests outlined  in  the  Standard found a range of



$15 to $75, with four of  the five estimates having a top range of




$30, and with a "best estimate" of $28  based on the survey.  A



cost estimate also was made  by separating the protocol into




components and estimating the  cost of each component, including



direct labor cost, overhead  cost, other direct cost, general and




administrative costs, and profit  or fee.   The protocol best



estimate of cost was  $72, with an estimated range of $36 to $109



based on ± 50 percent of  the best estimate.  An analysis of the



discrepancy between the protocol  estimate and the survey pointed




out that the nature of the chemical to  be analyzed has an impact



on  the cost of analysis.  The  physical  state of the compound



 (e.g., liquids versus chunk  or particulate -old'3-* determines the



method to be used.  Different  methods will cause variations in



cost.  The number  of  samples for  analysis may also affect the



cost per  sample.   Discounts  are offered by some laboratories




based on the number of samples to be  analyzed.






     The above cost estimates  were made assuming that all the




requirements of Good  Laboratory Practice Standards, as specified




in  section  (c) of  the Density Standard, are being satisfied.




Details of the cost estimates  are contained in a report by Enviro



Control, Inc.  (1980).
                               -12-

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                                17


4.        COMPATABILITY WITH OTHER TEST STANDARDS



4.1.      TSCA/FIFRA Compatibility


     Methods for determining density given  in  FIFRA  guidelines

(USEPA 1978) refer to techniques as follows: CIPAC MT3; ASTM  D

941-55; ASTM D 1480-62; ASTM D  1481-62; and ASTM D 1217-54.   No

guideline is given as to which  technique  should be used.  All of

the above techniques are offered in the present test protocol,  as

well as some additional techniques which  may be needed because  of

the greater variety of chemicals to which TSCA applies.   In

addition instructions are given in the TSCA Standard for  the

selection of an appropriate technique.


     The FIFRA guidelines (USEPA 1978) specify the reporting  only

of density for solids and only  of relative  density  (specific

gravity)* for liquids.  We offer a broader  option of either

density or relative density for both solids and liquids.  Either

type of information is equally  suitable for use in the type of

exposure analysis used for TSCA chemicals.


     The FIFRA guidelines (USEPA 1978) specify a reporting

temperature of 20°C.  The TSCA  protocol includes that temperature
*The IUPAC  (McGlashan  et  al.  1979) has  recommended  the  term
relative density in preference  to  specific  gravity;  preferring to
reserve the word "specific" to  refer  to a quantity  per  unit mass,
as in specific volume.  The term  "specific  gravity," with the
same meaning as relative  density  is therefore  obsolescent.   This
practice has been adopted also  by  ASTM  (1978)  for their
standards.
                               -13-

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                                18





among three options, all  of which are  used to some extent in




nationally and internationally  standardized tests.  The 20°C



reference temperature  is  adopted  by CIPAC (Raw 1970),  and this




provides the  justification  for  its use.   However,  as explained in




Section III,  there  is  substantial justification for allowing




other reporting temperatures.   In summary, the TSCA protocol is




compatible with the FIFRA guidelines (and with proposed




revisions) but is somewhat  broader in  scope and both more



specific and  more flexible  in  its requirements.








4.2.      OECD Compatibility






     An OECD  Test Guideline for Density (OECD Expert Group



Physical chemistry,  1978) lists many of the same standard



techniques.   We believe  the present document is entirely



compatible with the OECD standard,  but to assure adequate



selection of  applicable  techniques, the TSCA Standards specify



which protocol is to be  used  for  specific types of materials.








C.        IRLG Compatibility






     The IRLG has not  proposed  a  standard for density.



We  expect to  submit this  standard to IRLG as a proposed



standard.
                               -14-

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                                19
among three options, all of which are used  to  some  extent  in



nationally and internationally standardized tests.   The  20°C



reference temperature is adopted by CIPAC  (Raw 1970),  and  this



provides the justification for its use.  However, as explained  in



Section III, there  is substantial justification for allowing



other reporting temperatures.  In summary,  the TSCA protocol is



compatible with the FIFRA guidelines  (and with proposed



revisions) but is somewhat broader in scope and both more



specific and more flexible in its requirements.








4.2.      OECD Compatibility






     An OECD Test Guideline for Density  (OECD  Expert Group



Physical chemistry. 1978) lists many of  the same standard



techniques.  We believe the present document is entirely



compatible with the OECD standard, but to assure adequate



selection of applicable techniques, the  TSCA Standards specify



which protocol is to be used for specific types of  materials.








4.3.      IRLG Compatibility





     The IRLG has not proposed a standard  for  density.



We expect to submit this standard to  IRLG as a proposed



standard.
                               -14-

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                                 20






5.        RESPONSES TO COMMENTS  RECEIVED ON PROPOSED GUIDELINES




          FOR PREMANUFACTURE TESTING  (USEPA 1979).








5.1.      General






     Following publication  of  the Guidelines a reconsideration




of the variety of chemical  materials  requiring testing and of the




availability of standardized procedures  for such testing brought




us to the conclusion that the  techniques proposed then were




inadequate to cover the multiplicity  of  identifiable situations




that would arise.  As a result this proposed Test Standard goes



into considerably more detail  with respect to the characteristics




of materials that influence the  selection of a technique,  and it



specifies appropriate techniques for  handling materials with



these characteristics.  The requirement  for the temperature at



which the test is to be carried  out was  also changed to allow



selection of one of three options.








5.2.      Responses to specific  comments






     In  response to the Proposed Guidelines,  comments dealing



specifically with density/relative density were received from six



respondents.








5.2.1.    General Approval






     The largest group of responders  who commented on the test




expressed general approval  of  the test requirement,  on the basis
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                                21





that the test can be and  routinely  is  made  on materials  for use




in marketing and handling, and  can  be  done  with  the  accuracy



required here.








5.2.2.    Marginal Utility






     One comment was that the test  result is  useful  in



understanding the general nature of a  specific chemical  but is  of



marginal utility in determining its environmental  effects.   The



Agency position is that the  information  is  needed  to evaluate



environmental fate, and therefore plays  an  important part  in risk



assessment.  The usefulness  in  determining  environmental fate is



discussed in Section I of this  document.








5.2.3.    Limitations on  Materials  to  Which the  Test



          Should Be Applied.





     One respondent stated that testing  would be unneccessary



if the relative density had  already been determined  to be  less



than 0.97 or more than 1.03  in  the  temperature range between 10



and 30°C, or if the solubility  in water  is  10 percent or more.






     The criteria as to whether testing  is  to be required  under a



Section 4 Test Rule are somewhat different  from  the  criteria for



testing under Section 5 Premanufacture Test Guidelines.   It might



indeed be decided that for a particular  chemical which available



information put within the bounds suggested by the respondent,  no



test requirement would be made.  On the  other hand,  for  other



material testing may be required.   An  example might  be a dense






                               -16-

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                                   22






material that may be expected to get  into  flowing water where  it




would be transported in turbulent  suspension, as sand  is



transported.  For such material, knowledge of density  is  required




to apply equations of turbulent transport  to estimate  where  and




how the material will move  in the  environment.








5.2.4.    Limitations on Accuracy  and Care Required






     One responder suggested that  special  care  cited  in the



Proposed Guideline is not required if the  accuracy specified for



the test is only ± 0.1 g cm"3.  This  is  an editorial  comment and




an appropriate change has been made.








5.2.5.    Additional Test Procedures  Suggested






     Individual respondents suggested as alternatives:  (1)   a



microsyringe method developed by Burroughs and  Goodrich  (1974);




(2)  Volumetric flask  (Class A)  (NBS  1959);  (3) Simpler



techniques approved by the  Association of  Official Analytical




Chemists (AOAC 1975).






     The first response to  these suggestions  is that  the  number




of specified acceptable test procedures  in this Test  Standard is



substantially larger than the number  in  the  Guidelines (USEPA




1979), but that EPA still has not  attempted  to  include all of the



available tests that may be acceptable.  While  some  techniques




that might be acceptable are not included  here, EPA  feels that it



has included a broad range  of tests that are widely  accepted and




in common use.  Many laboratories  use the  techniques,  and their






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                               23






applicability, limitations, and special precautions  necessary




will not present a hardship or increase the  cost  of  testing.   The




exclusions of other methods are considered to be  of  minor  impact




in view of the large number of acceptable techniques and the  long




period of time over which they have been developed.






     The microsyringe technique (Burroughs and Goodrich 1974)  is




not included, principally because  no  evidence was found that  it




has been found generally useful enough to be widely  adopted.   It




seems most useful for rare or  research chemicals  that are




available only in very  small amounts.  This  criterion does  not




apply to chemicals subject to  control under  TSCA.  The use  of a




calibrated volumetric flask is included in the specified array of




acceptable techniques for the  present Test Standard.   The




standards of AOAC (1975) included  several techniques,  all  of




which are also found in the specified array  of techniques,  though




not specifically identified as AOAC standards.








5.2.6.    Temperature of the test






     One respondent suggested  that the temperature range




(20 ± 3)°C proposed by  EPA (1979)  be modified to  (25 ± 3)°C in




order to include most common laboratory temperatures without  the




need for a thermostated water  bath or laboratory  air-




conditioning.  The present test standard specifies one of  three




temperatures, 15°C, 20°C, or 25°C, discussed and  justified in




section II.B.(l) of this document.
                               -18-

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                                24
6.
REFERENCES
ASTM.  1978 .  American Society  for  Testing  and  Materials.
Annual book of ASTM Standards, books  1-47.   Philadelphia,  PA:
American Society for Testing  and Materials.

AOAC.  1975.  Association of  Official Analytical Chemists.
Official methods of analysis  of  the  association  of official
analytical chemists, 12th ed.  Washington,  DC:  Association of
Official Analytical Chemists.

Bauer N, Lewin SZ. 1971.  The determination  of density.   In:
Weissberger A, Rossiter BW, eds.  Techniques of  chemistry.   New
York:  Wiley-Interscience, Vol.  I, Part  IV,  Chapter 2.

Burroughs VE, Goodrich CP- 1974.  Rapid  method for determining
densities of  liquids using microsyringes.  Anal. Chem.  46:
1614.

Enviro Control, Inc.  1980.   Cost analysis methodology  and
protocol estimates:  environmental standards.  Rockville,  MD:
Enviro Control, Inc., Borriston  Laboratories,  Inc.

IUPA.  1975.  International Union of  Pure  and Applied
Chemistry.  Commission on Physicochemical  Measurements  and
Standards.  Herrington EFG, ed.   Recommended reference  materials
for  the  realization of physicochemical properties.   Pure Appl.
Chem. 40:393-472.

IUPAC.   1976.  International  Union of Pure and Applied  Chemistry,
Commission on Physicochemical Measurements and Standards.
 (a)Herrington EFG, ed.  Recommended  reference materials for the
realization of physicochemical properties.   Brown J,  Lane  JE,
collators.  Section:  Density.   Pure  Appl. Chem. 45:1-9.
 (b)  Physicochemical measurements:  Catalogue of  reference
materials  from national laboratories.  Pure  Appl. Chem.  48ROS-
SIS.

IUPAC.   1972.  International  Union of Pure and Applied  Chemistry,
Commission on Thermodynamics  and Thermochemistry.  A guide to
procedures  for the publication of thermodynamic  data.  Pure Appl.
Chem. 29:397-407.
*As a matter of  good  practice,  the  most recent available edition
that contains the  desired  Standard  should  be  used.
                               -19-

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                                25


McGlashan ML, Paul MA, Whiffen  DH,  eds.  1979.   Manual  of Units,
2nd revised 1973 edition.  New  York:  Pergamon  Press.   See
also:  Pure Appl. Chem.  51:1-41.

NBS.  1959.  National Bureau of Standards.   Capacity tolerances
for volumetric flasks.   National Bureau  Standards   Circular  602.
Washington, DC:  U.S. Government Printing Office.

OECD.  1978.  Organization for  Economic  Cooperation and
Development Expert Group Physical  Chemistry.  Test  guidelines  for
density.  Draft October  11, Berlin,  FRG:  Umweltbundesamt.

Raw, GR, ed. 1970.   CIPAC handbook,  Ashworth RdeB,  Henriet J,
Lovett JF, compilers. Volume I.  Analysis of technical and
formulated pesticides.   Herpender,  Herts.   UK.   Collaborative
International Pesticides Council,  Ltd.   (Obtain from National
Agricultural Chemicals Association,  Washington  DC).  Method  MT-
3.  pp. 830-839.

USEPA.  1978.  U.S.  Environmental  Protection Agency.   Proposed
guidelines for registering pesticides in the United States.  Fed.
Regist., July 10, 1978,  43 29695-29741.

USEPA.  1979.  U.S.  Environmental  Protection Agency.   Toxic
substances control.  Discussion of premanufacture testing Policy
and technical issues; request  for  comment,  Fed.  Regist.  March  16,
1979, 44 16240-16292.

Weast RF, ed. 1978-79.   Handbook of chemistry and physics, 59th
edition.  Cincinnati, OH: CRC  Publishing Co.
                               -20-

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                   27
MELTING TEMPERATURES

STANDARD FOR TEST DATA DEVELOPMENT
PROPOSED RULE, SECTION 4, TSCA


Refers to
Part 772 — Standards for Development of Test Data
  Subpart 1.  Physical, Chemical and Environmental
            Persistence Characteristics
    Section 772.122-2  Melting Temperatures
October  1980

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                                29




                             CONTENTS



                                                             Page


    INTRODUCTION AND SUMMARY OF THE STANDARD	 1




1.   NEED FOR THE TEST	 3




2.   SCIENTIFIC ASPECTS	 4



    2.1.  Melting Behavior of Materials	 4



    2.2.  Test Material	 5



    2.3.  Good Laboratory Practices	 6


                             i
    2.4.  Test Conditions	 7
          2.4.1.  Thermometers	 7



          2.4.2.  Apparatus	 8



          2.4.3.  Reference Materials	 8



    2.5.  Test Procedures	 9



          2.5.1.  Visual Technique	 9



          2.5.2.  Preliminary Examination	 9



          2.5.3.  Selection of a Standard Technique	 10



          2.5.4.  Precise Study	 12



    2.6.  Test Data Required	 12

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                                30
                       CONTENTS (continued)
3 .   ECONOMIC ASPECTS	  14
4.  TSCA/FIFRA COMPATIBILITY	  15
5.  DISCUSSION OF COMMENTS SUBMITTED  IN  RESPONSE  TO
      PROPOSED GUIDELINES FOR PREMANUFACTURE  TESTING	  17
    5.1   General	  17
    5. 2   Specific Comments	  17
6 .  REFERENCES	  19

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                                31
             INTRODUCTION AND SUMMARY OF THE STANDARD






     The Support Document to this  test  summarizes  the  scientific



basis of the melting temperature test and  its  applicability in



the assessments of chemicals.






     The proposed test  standard, when applied  through  a  testing



rule will require sponsors to determine melting  temperature of



the test chemical, or the range of temperature over  which  it



melts, within the range from -30°C to +250°C.  The standard is



written in  a general way to permit selection of  a  technique



appropriate to the particular chemical  from a  variety  of



available techniques.   The techniques proposed are limited to



visual techniques in which the actual melting  process  is



observed.





     A preliminary examination of  the chemical is  required in



order to provide information for the  selection of  an appropriate



technique.  Criteria include:  (1)  decomposition  on melting;



(2) volatility;  (3) reactivity with air or with  possible



apparatus material;  (4) lack of sharpness  of melting;  and



(5) melting outside the range specified.





     A variety of standardized techniques  are  stipulated for the




test, but at the option of the sponsor  techniques  of greater



accuracy than is required by the Agency are allowed.  Under this



standard, persons subject to TSCA  physical properties  test rules



would develop and submit to the Agency  the following kinds of




information.
                                -1-

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                           32
(1)  Information and results obtained from the test,
    including a numerical value of the melting temperature;
    range of melting temperatures, or pour point; and a
    statement of special characteristics of the substances
    that influenced the selection of technique such as
    volatility, chemical decomposition, or range of
    softening temperature;


(2)  Information relating to the technique used;
    justification for the technique selection, if a
    technique was used that is not specified in the
    standard; and
(3) Information relating to good laboratory practices, such
    as nature and purity of the test substance,
    qualifications of personnel conducting the measurement
    and of the laboratory in which the test was made, and
    quality control practice in the laboratory.

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                                33
1.        NEED FOR THE TEST






     The normal melting temperature describes  quantitatively  the



conditions under which a chemical substance or mixture will be



solid or fluid under ambient pressure.   It therefore  provides



information on the physical form in which the  chemical will be



found when in the free state.






     Information on the physical form of a chemical in the



environment, as solid or liquid, is important  in order to assess



the movement and fate of the chemical and the  human and



environmental exposure to  it.  Physical  form determines whether



the chemical will stand in place or flow away  from spills.  When



combined with density information and solubility information  it



determines how the chemical will move in a waterway.  When



combined with other information such as  volatility and particle



size, it determines the distribution resulting from dispersal of



the material.  All of this information,  when assessed together,



is used to determine what  human populations, classes  of



organisms, or sectors of the environment will  be affected.






     Knowledge of physical form also is  of value in assessing the



mode of interaction and speed of interaction at interfaces, which



is strongly dependent on whether a substance is solid or



liquid.  A liquid, for instance may wet  the skin and  cause an



inflammation or absorption much more rapidly than a solid.
                               -3-

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                               34
2.        SCIENTIFIC ASPECTS








2.1.      Melting Behavior of Materials






     Melting temperature is the temperature  at which  the  change




from solid to liquid takes place.  The term  "melting  point"  is




often used instead.






     The melting temperature of a material is affected  by its




composition.  Impurities added to a pure  substance  cause  a



lowering of the melting temperature if the impurities are soluble



in  the liquid and if the mixed substances segregate on



solidifying.  If the mixed substances form a liquid solution and




do  not segregate on solidifying, the melting temperature  will



usually be a weighted average of the melting temperatures of the



substances in the mixture.






     Other materials that form glasses have  special melting



behavior because of complex intermolecular forces,  and  the



distinction between solid and liquid is not  clear cut.






     Thus, in practice, many materials, particularly  those that




are mixtures or form glasses, do not melt sharply at  a  well




defined temperature, but rather soften and liquefy  over a range




of  temperatures.  Under some circumstances the melting




temperature is lowered many kelvins  (degrees Celsius) by




impurities.  For these materials other terms are used,  including



pour point, congealing temperature, drop  melting temperature,




initial and final melting temeprature, or melting range.   Such
                                -4-

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                                35
parameters are included  in this  test  standard  and  are defined in



the standard.






     Definitions related to  normal melting  temperature are  given



to allow for more precision  of statement  in describing the



results of tests on  impure materials  and  materials that do  hot



have sharp melting temperatures.  They  also are  useful in



describing tests that  inherently do not strictly determine  the



true melting temperature, but only an approximation to it.   These



terms are in common  practice in  test  laboratories  and test



standards.






     The term  "normal"  is often  used  to specify  that the phase



change occurs  at 1 atm pressure.  Because the  effect of pressure



changes is rather small, we  do not emphasize the use of this



term.  The term  "melting temperature" is  used  instead of "melting



point" to specify that it is the temperature rather than pressure



or volume that is of interest, and to emphasize  the fact that



"point" refers to a  "point"  on a phase  diagram (i.e.,  an



invariant), while the  melting temperature is a variable depending



on pressure and  composition.








2.2.      Test Material






     The type  or grade of material to be  tested  is not specified



in this Standard, but  will be specified in  Test  Rules that



incorporate the  Standard.  The following  discussion relates to



the choice of material to be tested.
                                -5-

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                                36
     The normal melting temperature of a pure material  is  one



means of characterizing the substance and usually  is  considered a



worthwhile standard reference datum.






     The technical grade of substance is often  a mixture of the



substance with other substances that are not easily separated and



do not interfere with the technological applications  of the



material.  Because of the phase behavior of materials briefly



outlined in earlier parts of this Standard, the technical  grade



material will usually have a melting temperature different from



that of the pure substance and melt over a range of temperature,



rather than sharply at a single temperature.  These effects may



amount to several kelvins, and may not be the same from one batch



of technical material to the next.  The technical  grade is the



material that will normally be found in commerce,  and the



temperature differences that will be encountered are  within the



range of fluctuations that occur periodically in the



environment.








2.3.      Good Laboratory Practices





     Laboratories that do not have proper quality  control



sometimes produce data that are less than adequate for  supporting



sound analyses and decisions.  Good Laboratory  Practice



Standards, cited in section (c) of the test standard, are



designed to ensure that all data generated in response  to  Test



Rules will be valid.  For further discussion of the details



contained in Good Laboratory Practice Standards see the Preamble
                                -6-

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                                37
for Good Laboratory Practice  Standards  for  Physical,  Chemical,



Persistence, and Ecological Effects Testing (Section  772.110-2)



proposed in the same  issue of the  Federal Register  in which this



proposed Standard for density is proposed.








2.4.      Test Conditions
2.4.1.    Thermometers
     A good thermometer  is the most  important  item  of  equipment



needed for measuring melting  temperature.   Specifications  for  all



the thermometers needed  for the  techniques  listed are  given  by



ASTM.






     Thermometers  frequently  are inaccurate because of errors  in



manufacture or accidents which damage  them, such as by separation



of the mercury or  fluid  column.   They,  therefore, invariably need



to be calibrated if they are  to  be accurate indicators of



temperature.





     The U.S. temperature scale  is maintained  at the National



Bureau of Standards, and measurement accuracy  is propagated



throughout the nation by calibrations  of  thermometers  originating



at the National Bureau of Standards.   Traceability  to  the



National Bureau of Standards  may be  by comparison of thermometers



of which one was calibrated at the National Bureau  of  Standards,



or by measurement of the melting temperature of a substance



certified for melting temperature at the  National Bureau of



Standards, or by a longer sequence of  comparisions. The






                               -7-

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                                38
comparison can be done by the manufacturer  or  by  the  laboratory




doing the testing.  If this traceability  is  not available  for the




thermometer being used, there is no way to  verify readings that




are taken during the course of testing.








2.4.2.    Apparatus






     See the discussion of test procedures  (section 2.5. of this




document) for a description of how specific  test  procedures were



selected and adopted from among standardized methods.   Published




protocols for the standardized methods generally  include



descriptions of specific pieces of equipment or apparatus  and



accessories required for the test.  The equipment, as  specified



in the protocol, is considered to be  an integral  part  of the




standardized test, and therefore is required by EPA as one of the



conditions of this Standard.








2.4.3.    Reference Materials
     See the discussion of the use  of  reference  materials  for the



calibration of thermometers  in a previous  paragraph  in  this  same



section (2.4.) of this support document.   In  addition,  the



reference materials should be available  and should be used for



the calibration of the total apparatus and procedure used.  Some



of the standardized protocols adopted  in this  standard



specifically require a calibration  step  with  a standard reference



material.   Several recommended materials are  listed  in  the



standard,  and should be selected by the  analyst  according  to the

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                                39






method used and the type of material  being  tested.   The standard




also allows for the selection of  other materials  as  the analyst



may judge necessary.








2.5.      Test Procedures
2.5.1.    Visual Technique^






     The criterion of visual  evidence  of melting  is  necessary  to



establish that the transition reported is  actually that between



solid and liquid.  This  is because  of  the  pronounced difference



in the behavior of solids  and liquids  in dispersion,  in rate of



reaction, and in kind of surface  interaction  with other



materials.






     The list of acceptable techniques could  be expanded  by



including nonvisual techniques  such as differential  scanning



calorimetry  (DSC).  This would  be permissible only after  evidence



was obtained in preliminary visual  examination that  the melting



occurred in a general temperature range within which a single



DSC-observed transition  could be  indentified.  This  seemed to



constitute a more complex  test  than those  adopted and was thus




rejected.








2.5.2.    Preliminary Examination






     The purpose of the  preliminary examination required  by  this



Test Standard (Section  (e)(2))  is to identify special features of



the test material that would  invalidate a  test of melting






                                -9-

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                                40
temperatures and to guide the selection  of  a  suitable




technique.  The following section describes how  the  information



from the preliminary examination is  applied in the  selection of




one of the standard techniques referenced in  the Test  Standard.








2.5.3.    Selection of a Standard Technique






     Section (e)(3) and Table 1 of the Test Standard require the



use of certain standardized protocols to be selected according to



the information determined from the  preliminary  examination.






     In selecting the many standardized  techniques  listed  in




Table 1, EPA reviewed many published protocols,  and  determined




that those selected were capable of  producing good  and reliable



data for the broad range of substances that are  expected to be



tested under the provisions of TSCA.  These protocols  are



believed to be widely used for the routine  determination of




melting temperature, and therefore provide  economical  and



suitable means of producing the data that EPA requires for



evaluation of environmental exposure.






     Paragraphs (e)(3)(i)-(iv) of the Standard specify which type




of technique(s) (e.g., Thiele tube,  cooling curve,  pour point,




etc.) is(are) to be used according to the type of melting




characteristics which different types of materials  have.   These




specifications were based on a detailed  review of the  protocols




and their stated or EPA's judgment of their applicability.   For



material for which the standard gives several types  of suitable




techniques, the analyst is free to select the most  applicable






                               -10-

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                                41
type, and likewise, where Table  1  lists  several  suitable



protocols for a type of test, the  analyst may  select  the  most



convenient or suitable standard  method to follow.






     The following several paragraphs give  additional detail as



to how the stipulated techniques in  sections  (e)(3)(i)-(iv)



relate to the melting characteristics of the test materials.






     Softening temperatures  are  best determined  by  techniques  not



suitable for materials with  sharp  melting temperatures.   If



decomposition or other chemical  reaction occurs  on  melting, the



temperature observed depends  strongly on the rate of  heating.



This is because the properties of  products  of  the reaction affect



the results.  Therefore, the  technique must take  account  of this



possibility-  Vaporization might cause disappearance  of the



sample and excessively volatile  substances  should be  enclosed  for



the test.





     Techniques designed for  substances  that melt sharply are



unsuitable for substances that have  an extended  softening



interval.  This is because the techniques will show a broad range



of melting temperature or will give  results which have



considerable uncertainty.  Techniques that  rely  on  physical



appearance or movement under  rigorously  standardized  conditions



narrow the range of uncertainty  for  such substances.






     For materials that decompose  on melting,  a  technique needs



to be used in which decomposition  does not  influence  the



results.  For example, the Kofler  hot bench technique effectively
                               -11-

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                               42
divides a lot of material into  small  sublets,  each of which is




exposed to a different temperature  and  is  separately




observable.  Thus, the decomposition  at one  temperature does not




unduly influence the state of an  adjacent  substance which is at a




slightly lower temperature.  Volatilization,  reaction with air,




or other reactions tend to invalidate the  test;  hence,  this




limits the kind of measurement  technique that can  be used.








2.5.4.    Precise Study






     A well established research  and  development facility or a




quality control laboratory may  very accurately determine the



melting temperature using procedures  referenced in section (e)(4)



of the Standard.  The results of  these  more  accurate tests




certainly satisfy the Agency's  needs, and  therefore are



acceptable in lieu of the standardized  tests  specified in section
2.6.      Test Data Required






     No melting temperature measurement  is  required for




substances that sublime or decompose  at  normal  pressure because



the melting process does not  occur  under real world conditions.






     Information about any nonspecified  test procedure is needed




to determine that acceptable  data have been generated and that




the testing laboratory had good  reason for  using a nonstandard



method .
                               -12-

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                               43
     The level of accuracy required  in  reporting  is  1  to 2°C.   In



general this level of accuracy  is  inherent  in  the technique,  is



easy to determine, and  is approximately the accuracy with which



ambient temperatures are known.  This point is discussed further



in section 5.2.(2).





     Sections  (f)(4)-(ll) specify  the observable  end points  which



are to be reported for  the different types  of  testing



techniques.  These reportable end  points have  been specified in



the standard to assure  that  data from the different  techniques



are reported in similar manners that are suitable for  use in



EPA's data storage systems,  are suitable for comparison  from



chemical to chemical, and are correctly reported  for checking the



performance of the method when  used  with standard reference



materials.
                               -13-

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                               44
3.        ECONOMIC ASPECTS






     A survey of three commercial  laboratories  to estimate costs




for performing the tests outlined  in this  Standard found a range




of $25 to $75, with a "best estimate"  of  $50.   A cost estimate




also was made by separating the protocol  into components and




estimating the cost of each component,  including direct labor




cost, overhead cost, other direct  costs,  general and




administrative costs, and profit or  fee.   The protocol best



estimate of cost was $83, with an  estimated  range of $42 to $125




based on ± 50 percent of the best  estimate.  An analysis of the



discrepancy between the protocol estimate  and the survey pointed




out that the nature of the chemical  to be  analyzed has an impact




on the cost of analysis.  The actual melting temperature of the



compound has an influence on cost.   For example,  a compound




melting at 250°C will take longer  to analyze than one with a



lower melting point.  Separate methods also  are required for




compounds that decompose or melt,  compounds  that show extended



softening, and compounds that react  or volatilize.   Differences



in the methods will cause variations in the  cost.






     The above cost estimates were made assuming that all the



requirements of Good Laboratory Practice  Standards,  as specified




in section (c) of the melting temperature  standard,  are being




satisfied.  Details of the cost estimate  are in a report by




Enviro Control, Inc.  (1980).
                               -14-

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                               45
4.        TSCA/FIFRA/IRLG/OECD  COMPATIBILITY






     In Pesticides Guidelines  (USEPA  1978)  Section  163.61  8(c)(3)



a melting temperature  or melting  range  in  °C is  required for a



solid technical chemical unless the technical chemical  sublimes



or decomposes.  This criterion  is consistent with the present



Test Standard.






     In Pesticides Guidelines  (USEPA  1978)  Section  163.61,



Appendix to Product Chemistry calls for CIPAC test  MT 2.   This is



one of the standard tests  using the Thiele  tube  to  which we



refer.  Any data acceptable  under Pesticide Guildlines  would



therefore be acceptable under this Test Standard, provided that



the test substance was appropriate and  did  not require  use of one



of the specialized methods specified  in Section  (e)(3)(i),  (ii),



or (iii) of the Standard.






     There is a difference in the scope of  requirements for  FIFRA



and TSCA in that the FIFRA applies solely to pesticides, which



are a more uniform chemical  group than  those to  which TSCA



applies.  The CIPAC test is  an  adequate test for many pesticides;



it is not adequate for the whole  range  of chemicals to  which TSCA



applies.  Therefore, this Test  Standard appropriately includes a



broader range of tests than  Pesticide Guidelines because the



greater range of chemical types requires a  greater  range of




techniques.





     The OECD (1979) has issued a Draft Test Guideline  for




Melting Point/Melting Range.  This OECD draft guideline includes
                               -15-

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                               46
a variety of techniques, allowing  for  making  the  determination on



materials with various melting  characteristics, and  in this way



it is comparable to the proposed TSCA  standard.   The OECD draft



is considerably longer and gives many  experimental details and



other parameters that are included in  the  proposed TSCA standard



only by reference to ASTM or other standards.  A  technique-tay-



technique comparison shows that the OECD guideline and the EPA



proposed standard have scopes which seem to differ principally in



the inclusion in the EPA standard  of provision for materials that



soften and melt only over an extended  range,  and  giving a drop



melting temperature or pour point.   The proposed  TSCA Standard



does not discuss automated methods,  whereas the OECD standard



discusses the applicability of  automation  to  several,  and



includes one  (photocell detection)  that is only offered as an



automated technique.  From EPA's point of  view, automation is a



peripheral factor because TSCA  tests fundamentally are not



production-line processes.  The EPA standard  outlines to a much



greater degree how the testing  of  a particular substance is to be



approached but avoids many of the  details  found in the OECD



standard.
                               -16-

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                               47
5.        DISCUSSION OF COMMENTS SUBMITTED  IN RESPONSE TO
            PROPOSED GUIDELINES FOR PREMANUFACTURE TESTING
            (USEPA 1979).
5.1.      General
     Following publication of EPA's Proposed Guidelines  for

Premanufacture Testing, the Agency reconsidered the variety of

chemical materials requiring testing under  Section 4  of  TSCA  and

the availability of standardized procedures for determining

melting temperature.  EPA concluded that the techniques

originally proposed were inadequate to  cover the multiplicity of

identifiable situations that would arise.   As  a result,  this

proposed Test Standard gives considerably more detail with

respect to the special characteristics  of materials that

influence the selection of a technique, and it specifies

appropriate techniques for handling materials  with these

characteristics.



5.2.      Specific Comments


     In response to the Proposed Guidelines  (USEPA 1979) comments

referring specifically to melting temperature  were received  from

10 responders.  Their comments  may be grouped  in  five categories:
      (1)   General concurrence.   Three  responders  expressed
           general approval  of  the  tests  and  the  reference to
           standardized procedures  such as  those  of ASTM.

      (2)   Precise measurements  are not needed.   We concur.
           However, we do not believe the requirement of accuracy
           can be relaxed so far as to  allow  a range of 12°C as
           suggested by one  responder.  While environmental
                               -17-

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                         48
      temperatures sometimes fluctuate daily by this amount
      and seasonal changes are even larger, the physical
      state of the chemical will also fluctuate if it
      happens to have a melting temperature within the daily
      or seasonal fluctuation range.  Thus, for a reasonably
      good assessment of the state and manner of movement of
      the chemical in a -particular environment the
      temperature of melting should be known with
      approximately the same certainty as the temperature of
      the environment is known, 1 to 2°C.

(3)    Measurement is redundant and should be omitted.  Three
      responders made this argument on the basis that
      melting and boiling temperature were lumped together
      for discussion in the Proposed Guidelines.  They
      argued that vapor pressure measurement gives the
      essential information contained in a boiling
      temperature measurement.  An examination of the
      argument reveals that it must have been directed
      toward the boiling temperature alone and is invalid
      when applied to the melting temperature.  The boiling
      temperature is a rapidly varying function of pressure,
      while melting temperature is a slowly varying function
      and futhermore, melting temperature cannot be derived
      from the vapor pressure alone.

(4)    Measurement as described is inapplicable to
      polymers.  We concur with the two responders making
      the point that the Proposed Guideline (USEPA 1979) was
      inadequate in this respect.  We believe the present
      proposed Test Standard with additional protocols is
      versatile enough to provide for the necessary
      softening or melting temperatures that are useful for
      characterizing polymers.

(5)    Refer to specific test techniques.  One responder
      indicated that their laboratory regularly used
      differential thermal analysis (d.t.a.) for this test
      and that a test costs $2500.  The d.t.a. method was in
      the Proposed Guidelines (USEPA 1979), but d.t.a. has
      been omitted from the current Test Standard because of
      excessive cost.  The fact that the responder quotes a
      cost of $2500,  compared to costs for traditional
      melting temperature tests in the range of less than
      $125 (Section III) supports our contention that the
      d.t.a./d.s.c. technique is more elaborate and costly
      than the techniques specified.  At the sponsor's
      option,  however, the d.t.a./d.s.c. techniques still
      could be used under provisions of section (e)(4).
                         -18-

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                               4,9
6.         REFERENCES

Enviro Control, Inc.  1980.  Cost analysis methodology  and
protocol estimates:  environmental  standards.  Rockville, MD.
Enviro Control, Inc., Borriston Laboratories,  Inc.  April 28.

OECD.  1979.  Organization  for Economic Cooperation and
Development.  Draft test guideline  for melting point/melting
range.  Berlin: Umweltbundesamt.  June 20.

USEPA.  1979.  U.S. Environmental Protection Agency.  1979.  Toxic
substances control.  Discussion of  premanufacture  testing policy
and technical issues; request  for comment.  Fed. Regist., March
16, 1979,  44 16240-16292.

USEPA.  1978.  U.S. Environmental Protection Agency.  Proposed
guidelines for registering  pesticides in  the United States.  Fed.
Regist., 1978,  43 29696 -  29713.
                               -19-

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                  51
VAPOR PRESSURE

STANDARD FOR TEST DATA DEVELOPMENT
PROPOSED RULE, SECTION 4, TSCA


Refers to
Part 772 — Standards for Development of Test Data
  Siibpart L.  Physical, Chemical and Environmental
            Persistence Characteristics
    Section 772.122-3  Vapor Pressure
October 1980

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                               53







                             CONTENTS








                                                             PAGE








1.    Need for the Test	  1








2.    Scientific Aspects	  5








     2.1.  Test methods	  5



     2.2.  Test procedures	  9



           2.2.1.  Temperature of the test	  9



           2.2.2.  Sorbent for gas saturation procedure	  10



           2.2.3.  Gas flow  rates in gas saturation procedure  11



           2.2.4.  Calculations of vapor pressure in gas



                   saturation procedure	  11



     2.3.  Test data required	  12








3.    Economic Aspects	  14








4.    Replies to comments on  March 16, 1979 document	  16








5.    TSCA/FIFRA Compatibility	  20








6.    TSCA/OECD Compatibility	  21








7.    References	 22

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                              55
1.      NEED  FOR THE  TEST





     The vapor pressure  of  a  chemical  is  an  important parameter



in determining the environmental  fate  of  the  chemical.





     The atmosphere  is a major  route  for  the  widespread  distribu-



tion of chemicals.  There are several  ways by which  chemicals  may



become airborne and subsequently  be  transported  by wind  currents.



Airborne solids and foamy emulsions  are commonly observed,  but



these are not believed to be  major  factors in atmospheric  trans-



port because  they involve particulate  matter  which settles  out in



a relatively  short time  (Seiber et  al.  1975). Aerosols,  from



spray applications, manufacturing and  formulation sites, and



aerated waste treatment  systems may  constitute more  important



sources of chemical for  air transport  since very small droplets



(5 micrometers or less in diameter)  may be formed and carried



considerable  distances (Edwards 1973).  However,  it  appears that



volatilization from land and  water  surfaces  is the most  important



source of material for airborne transport  (Hartley 1969, Lich-



tenstein 1971, MacKay and Wolkoff 1973, Seiber et al. 1975).





     Volatilization is the  evaporative  loss of a chemical  com-



pound.  Volatilization rates  are  dependent on the vapor  pressure



of the chemical and the  environmental  factors which  influence



diffusion from the evaporative  surface.   Harper  et al. (1976,  p.



236) noted that "volatilization is  probably  the  single largest



means by which pesticides are lost  and  transported over  wide



areas and into bodies of water  far  from the application





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                               56
 location."   The  airborne  vapors of a hazardous chemical may



 present  a  threat to  plant and  animal life exposed to those



 vapors,  not  only in  the  area of chemical release but also at



 sites  remote from the  volatilization site.  This occurs when



 vapors are removed from  the  air, primarily by precipitation with



 rain or  snow.





     Volatilization  rates are  related to vapor pressure, which



 varies with  temperature.   However,  volatilization from soil or



 water  is influenced  by other environmental conditions and the



 effective  vapor  pressure  may be considerably lower than the



 potential  vapor  pressure. Nevertheless, vapor pressure is the



 one common factor governing  the tendency of a compound to



 volatilize.





     According  to kinetic theory there is a continuous flight of



 molecules  from  the surface of  a liquid or solid into the free



 space  above  it.   At  the  same time vapor molecules return to the



 surface  at a rate depending  on the  concentration of the vapor.



 If there is  no  removal of vapor from the surface (for example, by



 air currents), equilibrium will be  established where the rate of



 vaporization is  exactly  equal  to the rate of condensation.  The



pressure exerted by  the equilibrium vapor is known as the vapor



pressure (Daniels and  Alberty  1955) and is dependent upon



temperature.





     Knowledge of the  vapor  pressure of a compound allows the



ranking  of a chemical  as  relatively nonvolatile, highly volatile,



or of  some intermediate  volatility-  When vapor pressure data are



combined with solubility  data  to calculate Henry's Law constants,





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                               57
as described by MacKay and Leinonen  (1975) and Dilling  (1977),



rates of the evaporation of dissolved chemicals from water can be



estimated.






     Evaporation from an exposed surface will depend upon other



factors such as wind speed (which reduces the vapor density above



the surface) and adsorption (which may act to hold the substance



on the surface).  Volatilization from aqueous systems depends



also on the solubility of the compound and its movement to the



water surface.  In soils the rate of volatilization of a chemical



will depend upon such factors as adsorption on soil, solubility



in soil water, and on the amount of soil water and its rate of



evaporation.  Volatilization from soils can become a diffusion



controlled process as mass transfer to the soil surface is



reduced by low water evaporation due to high humidity or to the



lack of soil water in a dry soil (Bailey et al. 1974).






     Chemicals that have relatively low vapor pressures and that



sorb readily to solids or dissolve readily in water are not



likely to vaporize significantly at ambient temperatures.  For



that reason, airborne transport is not a major transport mecha-



nism for these chemicals and assessment of them should be focused



on their chemical fate and environmental effects in soils,



sediments, and water.  However, chemicals with high vapor pres-



sures or with relatively low water solubility and low adsorptiv-



ity to solids are less likely to reside only in soils, sediments



or water,  since volatilization can be a potentially significant



factor in their environmental transport.  Chemicals that are
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                               58
gases at ambient temperatures and that have low water solubility



and low adsorptive tendencies will be transported to a



significant degree in the atmosphere and are prime candidates for



photolysis and for involvement in adverse atmospheric effects



such as smog formation or stratospheric alterations.  Further-



more, effects testing of those chemicals should also focus on



inhalation and surface contact as potential routes for direct



exposure.





     An understanding of how a chemical is likely to partition



among the various environmental media (air, water, soil, and



sediment) is needed in judging whether or not a chemical will be



subject to various transformation possibilities, such as



oxidation by hydroxyl ion or ozone in the atmosphere.  Vapor



pressure data can influence decisions on whether or not it is



appropriate to conduct photolysis, adsorption/desorption,



partition coefficient, and certain biodegradation tests.  Vapor



pressure data are an important consideration in the design of



other fate and effects tests, for example in preventing or



accounting for the loss of volatile materials during the course



of the test.  Clearly, a knowledge of vapor pressure combined



with information on water solubility and adsorptive tendencies is



necessary in predicting environmental transport and in providing



guidance as to which persistence and effects tests need to be



considered and how those tests should be designed.
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                               59
2.      SCIENTIFIC ASPECTS







2.1.    -Test Methods





     A procedure  for measuring  the  vapor  pressure  of  materials



released to the natural environment ideally  would  cover  a  range



of vapor pressure values, at  ambient temperatures,  of about 10~5



Pa to 10  Pa  (approximately 10~7  to 760 Torr).   Because  no single



procedure can cover this  range,  two different procedures are



described, each suited for a  different part  of  the  range.   The



isoteniscope procedure  (ASTM  1978)  is for pure  liquids with vapor



pressures from 0.1 to 100k Pa.   For vapor pressures of 10    to



103 Pa, a gas saturation  procedure  is to  be  used.   The Knudsen



effusion procedure (Thomson and  Douslin 1971) may  be  used  for  low



vapor pressure values.





     Each of the  tests must be  performed  under  conditions  of



normal laboratory room temperatures in order to allow for  careful



control of the temperatures in  thermostated  baths  or  chambers



containing the test apparatus.





     The isoteniscope procedure  uses a standardized technique



that was developed to measure the vapor pressure of certain



liquid hydrocarbons.  It  is applicable to pure  liquids with vapor



pressures of 0.1 kPa (0.75 Torr)  or more  at  ambient temper-



atures.  The sample is purified  within the equipment  by  removing



dissolved and adsorbed gases  until  the measured vapor pressure is



constant.  This process is called "degassing."   The procedures do





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                               60





not remove higher boiling impurities, decomposition products, or



compounds that boil close to or form azeotropes with the material



under test.  If compounds that boil close to or form azeotropes



with the test material are present, it is necessary to remove the



interfering compounds and use pure test material.  Impurities



more volatile than the sample will tend to increase the observed



vapor pressure above its true value but the purification steps



will tend to remove these impurities.  Soluble, nonvolatile



impurities will decrease the apparent vapor pressure.  However,



because the isoteniscope procedure is a static, fixed-volume



method in which an insignificant fraction of the liquid sample is



vaporized, it is subject to only slight error for samples



containing nonvolatile impurities.  That is, the nonvolatile



impurities will not be concentrated due to vaporization of the



sample.





     Gas saturation (or transpiration) procedures use a current



of inert gas passed through or over the test material slowly



enough to ensure saturation and subsequent analysis of either the



loss of material or the amount (and sometimes kind) of vapor



generated (Bellar and Lichtenberg 1974, Thomson and Douslin



1971).






     The gas saturation procedures have been described by Spencer



and Cliath (1969).  Results are easy to obtain and can.be quite



precise.  The same procedures also can be used to study



volatilization from laboratory scale environmental simulations.



Vapor pressure is computed on the assumption that the total
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                              61
pressure of a mixture  of  gases  is  equal  to the sum of the
pressures of the  separate or  component gases.   The partial
pressure of the vapor  under  study  can be calculated from the
total gas volume  and the  weight  of the material vaporized.  If v
is the volume which contains  w  grams  of  the vaporized material
having a molecular weight M,  and if p is the pressure of the
vapor in equilibrium at  temperature T (K), then the vapor
pressure, p, of the sample is calculated by

                          p =  (w/M)(RT/v)

where R is the gas constant  (8.31  Pa  m mol  K  )  when the
pressure is in pascals  (Pa)  and  the volume in  cubic meters.   As
noted by Spencer  and Cliath  (1970), direct vapor pressure
measurements by gas saturation  techniques are  more directly
related to the volatilization of chemicals than are other
techniques.

     In an effort to improve  upon  the procedures described by
Spencer and Cliath and to determine the  applicability of the gas
saturation method to a wide  variety of chemical types and
structures, EPA is sponsoring research and development work  at
SRI International (EPA Contract  No. 68-01-5117).  The procedures
described in Appendix A are  those  developed under  that contract
and currently being evaluated with a  wide variety  of chemicals of
differing structure and vapor pressures.
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                               62





      In  addition  to  the  above  methods,  other procedures have been



described  for  the measurement  of  vapor  pressure (Daniels et al.



1956,  Glasstone  1946,  Nesmeyanou  1963,  Thomson and Douslin



1971).   These  include  boiling  point  procedures, effusion



techniques,  and  many highly  specialized techniques that are



restricted  to  the determination of very precise vapor pressure



values or  to the  measurement of vapor pressures of specific kinds



of materials.  These highly  specialized methods were rejected by



EPA  because  they  do  not  have general applicability to either a



wide  variety of  chemicals  or a relatively broad range of vapor



pressure values  at ambient temperatures.





      EPA rejected boiling  point procedures,  such as that using



Ramsey and  Young  apparatus,  because  the accuracy is very poor



below 10  Pa (Thomson  and  Douslin 1971) and  because boiling point



methods  provide  inaccurate estimates of the  vapor pressures at



ambient  temperatures if  there  is  a change of state or a



transition  temperature between the boiling temperature and



ambient  temperatures.






      Effusion  techniques,  particularly  those employing the



Knudsen  effusion  apparatus,  are used to measure vapor pressures



from  about  10~5  to 1 Pa  and  have  provided some good data (Hamaker



and Kerlinger  1969).   Those  procedures  were  rejected because they



require  working with systems under vacuum and because it is



necessary to saturate  the  capsule space with vapor during the



measurement  periods.   The  lack of equilibrium saturation has been



postulated as  a reason for inaccurate published vapor pressures



data  (Spencer  and Cliath 1970).   However, it must be recognized
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                               63





that there are laboratories which have employed Knudsen effusion



techniques successfully and which have considerable experience



with the method, especially for determining very low vapor




pressure values, such as 10~5 to 10~3 Pa.  For such laboratories,



the Knudsen effusion methods are a satisfactory alternative to



the gas saturation method in the determination of low vapor



pressure values.  However, it seems reasonable to require that



the laboratory using effusion methods supply documentation to



substantiate  successful utilization of the effusion procedures



with other compounds.








2.2.    Test  Procedures
2.2.1.  Temperature






     The test procedures generally require a thermostated bath or



test chamber temperature of 25 ± 0.5° C.  Laboratories should be



able to carry out vapor pressure measurements without the need



for elaborate temperature control devices.  Control of the bath



or chamber to ±0.5°C will permit substantial confidence in the



data without requiring unnecessarily costly apparatus.





     The International Union of Pure and Applied Chemistry has



for many years  (IUPAC 1972) recommended the reporting of



physical-chemical properties measurements at the temperature of



25°C.  A temperature of 25°C is slightly above most laboratory



room temperatures and this allows for convenient adjustment and



maintenance of constant temperature baths and enclosures.
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                               64





Because of the nature of the isoteniscope procedure, it is




necessary in that test to conduct some measurements at




temperatures above and/or below  25°C in order to determine




whether the sample needs further degassing.  Also, for some



chemicals, it may be necessary to require vapor pressure  data  at



temperatures other than 25°C and, in such cases, this requirement




will be noted in Test Rules for  specific chemicals.  Examples  of




when this requirement may be applicable include situations where




there  is evidence that the vapor pressure may change signi-



ficantly with relatively small changes in ambient temperature  or




when the boiling temperature for a chemical is at an ambient



temperature below 25°C.








2.2.2.  Sorbent for Gas Saturation Procedure








     The choice of sorbent and desorption solvent are dictated by




the nature of the compound being evaluated.  Charcoal sorbent  is




inexpensive and may be desorbed with carbon disulfide, a  conven-



ient solvent for use with flame ionization detector.  Many com-



pounds, however, do not desorb efficiently from charcoal  and more



expensive sorbents, such as Tenax GC and XAD-2, must be used.



The desorption efficiency of a particular compound from a sorbent



with a solvent is defined as the weight of the compound which  can




be recovered from the sorbent divided by the weight of the com-




pound originally adsorbed.  It must be measured for every combi-




nation of sample,  sorbent, and solvent used.  Desorption



efficiency may vary with concentration, so it is important to
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                               65




measure it at or near the concentration of the actual sample.  It



is sometimes necessary to interpolate between two measured



efficiencies.








2-2.3.  Gas Flow Rates in Gas  Saturation Procedure






     Accurate control of gas flow rates is essential to assure



that a known volume of carrier gas is passed through the system.



Very long sampling times are required for compounds with low



vapor pressures, and it is difficult to control very low flow



rates for very long times.  It is necessary to use fine needle



valves to control the flow rates and to measure the flow rates



frequently during the test period in order to make corrections



for variation which can occur, e.g. due to changes in atmospheric



pressure.








2.2.4.  Calculations of Vapor  Pressure in the Gas Saturation



        Procedure





     The calculation of vapor  pressure is straightforward.  The



weight of the sample desorbed  from a sorbent section is divided



by the desorption efficiency to give the weight of the sample



collected by the sorbent trap.  With the volume of carrier gas



calculated from the flow rate, the ideal gas law is used to



calculate the vapor pressure of the sample.  To assure that the



carrier gas is indeed saturated with the compound vapor, each



compound is sampled at three different gas flow rates.  If the



vapor pressure calculated shows no dependence on flow rate, then
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the gas is assumed to be saturated.  The method also assumes that




there are no interactions between vaporized sample and the




carrier gas and that the molecular weight of the vaporized  sample




is the same as for the sample liquid or solid.  If there are any




indications that these may not be valid assumptions, the vapor



should be analyzed both qualitatively and quantitatively using



such techniques as gas chromatography combined with mass




spectrometry (Heller et al. 1975).








2.3.    Test Data Required






     The average calculated vapor pressure for the test material




at each required test temperature must be reported. The reported




data must also include the individual values from triplicate



determinations and the calculated standard deviation for each



average calculated vapor pressure.  It might be preferable  for




assessment purposes to require that each vapor pressure



determination be made in sufficient replication to provide  a




given degree of reproducibility.  However, the precision




attainable will vary not only with the number of replications but



also with the procedure employed and the test chemical.  For a




given chemical, the only way to determine how many replications



of a given procedure are necessary to provide vapor pressure data



with some specified precision is to repeat the procedure until




the data provide that precision.  This may take a few or many




replications and a requirement for numerous replications is not



justified unless the specified precision is needed for assessment




purposes with an individual chemical.  The minimum requirement






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                               67





EPA would impose would be a statistical analysis of vapor




pressure data to provide standard deviation calculations based on



triplicate determinations.






     For the isoteniscope method, the vapor pressure data



generated during the degassing operation, including a plot of log



p vs 1/T, must be included to provide evidence of successful



degassing.  For the gas saturation method, the data showing that



vapor pressure does not vary with flow rate must be included to



provide evidence of saturation of the carrier gas with the sample



vapor.  The data also must include a complete description of all



analytical techniques and results, a description of the sorbents



and desorption solvents used and the desorption efficiency




calculations.
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                              68
3.      ECONOMIC ASPECTS

     A survey of commercial  laboratories  to  estimate costs for
performing the tests outlined  in  this  Standard  predicted a range
of $64 to $193 per substance  for  the  isoteniscope  method and $185
to $554 for the gas saturation method.  The  "best  estimate"
costs, based on the survey,  were  $129  for the  isoteniscope method
and $369 for the gas saturation method.   The cost  estimates were
made assuming that all  the requirements of Good Laboratory
Practice Standards (GLPs), as  specified in section (c)  of the
Test Standard, are being  satisfied.   Details of the  cost
estimates are contained in a  report by Enviro Control,  Inc.
(1980).

     The cost estimates in the Enviro  Control report do not
include the costs associated  with  specialized analytical
methodology or for analytical  method  development that may be
required for vapor pressure  analysis  by the  gas saturation
method.  It is not possible  to estimate the  cost of  such special
analytical requirements since  the  costs are  related  to the nature
of the chemical to be analyzed and because such cost may be
prorated among the analytical  needs related  to  other Test
Standards.  Also, the nature  of the chemical to be tested for
vapor pressure may cause  drastic variations  in  price when, for
example, very long sampling  times  are  required  in  the gas
saturation method for substances with  very low  vapor pressures.
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                               69
     In reviewing the state of technology concerning this area of



testing, the Agency has not identified any adequately developed



tests that would be significantly less costly while providing



comparable information.
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                              70





4,      REPLIES TO FEDERAL REGISTER OF MARCH  16





     The Fedegal- Register of March 16, 1979,  (EPA  1979)  presented



a discussion of policy issues,  alternative  approaches,  and  test



methods under consideration as  guidance  for premanufacture



testing.  Included in the test  methods was  a  section  on vapor



pressure (pp. 16256-16257) which discussed  the isoteniscope



procedure and the gas saturation procedure  as potential methods



for use in developing information on new chemicals.   Among  the



comments received in response to the discussion were  several



comments related to the vapor pressure methods.





     Several commentors contended that a requirement  for vapor



pressure measurements at each of three ambient temperatures (10,



20, and 30°C) would be unnecessarily time consuming and too



costly for the needs of a chemical fate  assessment.   There  were



two reasons for obtaining vapor pressure data at each of three



temperatures.  First, it seemed desirable to  obtain vapor



pressure data at representative environmental temperatures  to



determine if vapor pressure changed significantly  over  that range



of temperatures.  Second, the determination of vapor  pressure at



each of three temperatures provides a check on the validity of



the data.  If the vapor pressure data are determined  correctly,



then a plot of log p vs 1/T (where p = vapor  pressure as Pa and T



= test temperature as K) will produce a  straight  line.   However,



for most substances it will not be necessary  to have  knowledge  of



the vapor pressure at each of three rather  closely spaced



temperatures and a requirement  for the determination  of vapor
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                               71




pressure at each of three temperatures solely as a check on the




validity of the method would be unduly time consuming.




Therefore, the requirement has been changed to a determination of




vapor pressure at one temperature, 25°C, unless otherwise noted



in a specific Test Rule.






     For some chemicals there may be indications that the vapor




pressure changes significantly over the range of environmental



temperatures or there may be evidence that there is a change of




state at an environmental temperature.  Either of these




circumstances may justify a requirement for vapor pressure




measurements at temperatures in addition to 25°C.  Note, also,




that the isoteniscope method requires a determination at 25°C




plus a sufficient number of other temperatures to ascertain




whether or not further degassing is needed.  Although the vapor



pressure determinations at temperatures other than 25°C need not




be made in triplicate (unless they are temperatures specified in




a Test Rule), the data can serve to confirm the validity of the




vapor pressure results.






     Some commentors suggested that the investigator should be




able to use any technique, even employing high temperatures for



the vapor pressure measurement and an Antoine equation nomograph




to determine the vapor pressure at ambient temperatures.  The




problem with this appraoch is that there may be a change of state




or a transition temperature between the test temperature and




ambient temperatures.  If this is the case, extrapolation will




yield incorrect and misleading results.  The use of differential




thermal analysis and thermal evolution analysis, suggested by one
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                               72




commentor, involves variations on the melting point/boiling point




procedures for estimating vapor pressures and are subject to the




same errors described above.  It may be appropriate to use such



estimation techniques to provide guidance in performing the vapor




pressures measurements but those estimated values for vapor




pressure would not be sufficiently reliable to be used in




estimating volatility using water solubility and calculating the




Henry's law constant.  Such predictions of volatility based on




Henry's law constant will be an important consideration in



evaluating the environmental fate of a chemical.






     It was commented that ionizable and highly soluble compounds



should be exempt from the requirements for vapor pressure data.




This would be a reasonable suggestion if it could be demonstrated



that the chemical in question would reside exclusively in the




aqueous environment upon release to the environment.  If the     ,




chemical can occur in non-aqueous environments, such as soils or



on solid surfaces, its vapor pressure is needed regardless of



whether or not it is ionizable or highly soluble in water.






     It was stated that there should be no need to determine




vapor pressure as low as 10"^ Pa.   Unfortunately, experience has




shown that compounds with very low vapor pressures can volatilize




to a significant extent when low vapor pressure is combined with




low water solubility.  Examples include DDT and the




polychlorinated biphenyls (PCBs).   When dealing with the wide




variety of chemical compounds which exist in the commercial



chemical inventory,  it is necessary to conclude a concern for



those which have low vapor pressures and low water solubilities
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                               73



and which may, as a result of these factors, evaporate from water


bodies and become airborne contaminants.




     One commentor suggested simply determining the weight loss
                                                          /

at 1 Torr  (about 102 Pa) and 30°C in place of a determination of


vapor pressure.  This  simplistic sort of procedure can provide


some information on the tendency of a compound to evaporate from


a non-adsorptive surface, provided the vapor pressure is


sufficiently high to observe results in a relatively short time,


but no quantitative information  is obtained which is of value in


assessing  environmental fate.
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                              74
5.      TSCA/FIFRA COMPATIBILITY






     In the 1978 Proposed Pesticide Guidelines  (EPA  1978)  it is



suggested that vapor pressure be determined by ASTM  Method D-



3074-72.  This method measures the pressure within an  aerosol can



and is related to packaging.  It is not applicable to  environ-



mental fate considerations.  In the 1975 Proposed Guidelines (EPA



1975), it was suggested that vapor pressure should be  determined



by the Knudsen effusion or the gas saturation  (transpiration)



procedures, both of which are discussed in this document.   The



FIFRA proposed guidelines have not contained any reference to a



vapor pressure prcedure which would be applicable to compounds



with relatively high vapor pressures, in excess, say,  of 1 kPa at



environmental temperatures.  This may be because the FIFRA



concern is primarily with compounds of low vapor pressure,



although there are some pesticides which do not fit  that picture,



such as fumigants.  Since TSCA must deal with  the entire range of



chemicals, the Test Standards available must include methodology



suitable for chemicals with high vapor pressures, such as  the



isoteniscope procedure.
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                             75





6.      TSCA/OECD  COMPATIBILITY






     The Organization  for  Economic  Cooperation and Development



(OECD) has been developing a testing  plan  for  toxic chemicals



which will aid  in  assessing environmental  fate and effects.   The



plan, which has not yet  been published,  will  include recommended



methodology for vapor  pressure.   The  approach  being considered by



OECD is similar to that  proposed  by TSCA in  the Fede-r-al- Reqi-ster



discussion document of March 16,  1979,  (EPA  1979).  The isoteni-



scope method  and the gas saturation method are recommended for



the determination  of vapor pressure at  30°C.   OECD also



recommends a  vapor pressure balance method which seems  to be



similar in principle to  the Knudsen effusion  method and which



measures the  pulse generated on a sensitive  balance by  a vapor



jet in a high vacuum.  This appears to  be  a  rather complicated



procedure employing delicate apparatus.   There are no literature



references to its  use  in the OECD draft  reports.  The equipment



and expertise may  be readily available  in  Europe but it does not



seem to be a  procedure in  common  use  in  the  United States.  For



laboratories  which have  the equipment and  successful application



experience, the Vapor  Pressure Balance  method  may be an



acceptable procedure for determining  relatively low vapor



pressure values, but EPA would need to  have  more information on



the method and  its use before acceptance.  Finally, the OECD



suggests the  use of a  boiling point method which EPA believes



would not provide  acceptable data,  because of  poor repro-



ducibility and  the possibilty of  gross  inaccuracies, as noted



earlier.
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                             76
7.      REFERENCES


ASTM.  1978.  American Society for Testing and Materials Annual
book of standards, part  24.  Philadelphia, PA.  pp. 740-745.

Bailey GW, Swank RR, Jr., and Nicholson HP.  1974.  Predicting
pesticide runoff of agricultural land:  a conceptual model.  J.
Environ. Qual. 3:95-102.

Balson EW.  1947.  Studies  in vapor pressure measurement,  Part
III—An effusion manometer  sensitive to 5 x 10   mm Hg:  Vapor
pressure of DDT and other slightly volatile substances.  Trans.
Fara. Soc. 43:54-60.

Bellar TA and Lichtenberg JJ.  1974.  Determining volatile
organics at microgram-per-litre levels by gas chromatography.  J.
Am. Water Works Assn., 66:739-744.

Daniels F and Alberty RA.   1955.  Physical Chemistry, New York:
John Wiley and Sons, p. 157.

Daniels F, Mathews JH, Williams JW, Bender P, and Alberty  RA.
1956.  Experimental physical chemistry. New York:  McGraw-Hill
Book Co., pp. 47-511, 370-373.

Enviro Control Inc.  1980.  Cost analysis methodology and
protocol estimates:  environmental standards.  Rockville, MD:
Enviro Control, Inc., Borriston Laboratories, Inc.

Dilling WL.  1977.  Interphase transfer processes.  I.
Evaporation rates of chloromethanes, ethanes, ethylenes, pro-
panes, and propylenes from  dilute aqueous solutions.  Comparisons
with theoretical predictions.  Env. Sci. Tech. 11:405-409.

Edwards CA.  1973.  Persistent pesticides in the environment.
Cleveland:  CRC Press,  p.  21.

USEPA. 1975.  U.S. Environmental Protection Agency, Office of
Pesticide Programs.  Proposed guidelines for registering
pesticides in the  United States.  Fed. Regist., June 25,  1975,
40 p. 26889.

USEPA.  1978.  U.S. Environmental Protection Agency, Office of
Pesticide Programs.  Proposed guidelines for registering
pesticides in the United States.  Fed. Regist., July 10, 1978 43
p. 29711- 29712.

USEPA.  1979.  U.S. Environmental Protection Agency, Office of
Toxic Substances.  Discussion of premanufacture testing policy
and technical issues, Fed.  Regist. March 16, 1979 44 p. 16240-
16292.
                               -22-

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                               77
Glasstone S.  1946.  Textbook of physical chemistry, 2nd ed. New
York:  D. Van Nostrand Co., p. 446-449.

Hamaker JW and Kerlinger WO.  1969.  Vapor pressure of
pesticides.  Adv. Chem. Series 86:39-54.

Harper LA, White AW, Jr., Bruce RR, Thomas AW, and Leonard RA.
1976.  Soil and micro climate effects of trifluralin
volatilization.  J. Environ. Qual. 5:236-242.

Hartley GS.  1969.  Evaporation of pesticides.  Adv. Chem. Series
86:115-134.

Heller SR, McGuire JM and Budde WL.  1975.  Trace organics by
GC/MS. Environ. Sci. Tech. 9:210-213.

International Union of Pure and Applied Chemistry.  IUPAC,
1972.  Commission on Thermodynamics and Thermochemistry- 1972.  A
guide to procedures for the publication of thermodynamic data.
Pure and Appl. Chem. 29:397-407-

Lichtenstein EP.  1971.  Environmental factors affecting fate of
pesticides in Degradation of Synthetic Organic Molecules on the
Biosphere.  Washington, DC:  National Academy of Sciences, p.192.

MacKay D and Leinonen PJ.  1975, Rate of evaporation of low-
solubility contaminants from water bodies to atmosphere.
Environ. Sci. Technol. 9:1178-1180.

MacKay D and Wolkoff AW.  1973.  Rate of evaporation of low-
solubility contaminants from water bodies to atmosphere.
Environ. Sci. Technol.  7:611-614.

Seiber JM, Shafik TM and Enoa HF.  1975.  Determination of
pesticides and their transformation products in water.  In Haque
R and Fried VH eds. Environmental dynamics of pesticides, New
York:  Plenum Press, p.18.

Spencer WF and Cliath MM.  1969.  Vapor density of dieldrin J.
Agric. Food Chem. 3:664-670.

Spencer WF and Cliath MM.  1970.  Vapor density and apparent
vapor pressure of lindane.  J. Agric. Food Chem.  18:529-530.

Thomson GW and Douslin DR.  1971.  Vapor pressure.  In: _Physical
methods of chemistry. Vol. I. Part V., Weissberger A and Rossiter
BW, eds.  New York:  Wiley-Interscience, p. 46-89.
                               -23-

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                 79
OCTANOL/WATER PARTITION COEFFICIENT

STANDARD FOR TEST DATA DETOOIMENT
PROPOSED RULE, SECTION 4, TSCA
Refers to
Part 772 — Standards for Development of Test Data
  Subpart L.  Physical, Chemical and EnyirpnmBntal
            Persistence Characteristics
    Section 772.122-4  Octanol/Water Partition Coefficient
October 1980

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                                  81


                        TABLE OF  CONTENTS


1.    NEED FOR THE TEST	  1

2 .    SCIENTIFIC ASPECTS	  3

     2.1.  Rationale for the Use  of the Octanol/Water Partition
           Coefficient  to Estimate Bioconcentration  Potential	  3

     2.2.  Rationale for the Selection of the Test Method	  4

           (2.2.1.)  The Conventional Method of Determining  the
                     Octanol/Water Partition Coefficient KOW	  4

           (2.2.2.)  Other Experimental Methods of Determining KQW....  5

                     (1)  Reverse-Phase High-Pressure Liquid Chro-
                          matography as a Method  of  estimating KQW....  5

                     (2)  Thin-Layer Chromatography  as a Method  of
                          Estimating KQW	<	  7

                     (3)  Estimation of K_,T from  Water Solubility
                          Data	?V	  7

     2.3.  Rationale for the Selection of the Test Conditions	  9

           (2.3.1.)  Theory of  the Distribution Law  and the
                     Octanol/Water Partition Coefficient	  9

           (2.3.2.)  Factors which Affect the Value  of KQW	  12

                     (1)  Effect  of Temperature	  12

                     (2 )  Purity  of the Solvents	  13

                     (3)  Concentration of Solute	  13

                     (4)  Equilibration Time	  14

                     (5)  Octanol/Water Volume Ratio	» ...  14

                     (6)  Chemical Analysis of the Octanol and
                          Water Phases	  17

                     (7)  Emulsification and Ultracentrifugation	  18

                     (8)  Equilibration Vessel	  18

                     (9)  Speciation Effects	  19

                     (10) Presaturation of the Solvents	*  20

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                                 82


                                                                       PAGE

     2.4.  Reference Compounds	  20

     2.5.  Test Data Required	  21

     2.6,  Statistical Analysis of the Data	  23

3 .    ECONOMIC ASPECTS	  25

4i    REPLIES TO THE COMMENTS ON THE PUBLISHED SECTION 5
     TESTING GUIDELINES	» .  27

5 .    TSCA/FIFRA COMPARABILITY	  32

6.    TSCA/OECD COMPARABILITY	  33

7.    REFERENCES	  35

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                                 83






1.        NEED FOR THE TEST






     Bioconcentration, the accumulation  of  a  substance  in  living



tissues or other organic matter  as a  result of  net  chemical



uptake from the medium  (e.g., water),  is a  factor in  determining



the movement of a chemical in the environment and the potential



effects of the chemical on biota.  Hydrophobia  chemicals which -



are present in the aqueous environment at subtoxic  concentrations



may accumulate to toxic levels once inside  organisms, presumably



through diffusion into nonpolar  cell  components where they



accumulate because of their  greater solubility.  Further movement



of the substance in  living tissues may occur  as a result of



ingestion of lower trophic level organisms, i.e., food  chain



effects.






     The octanol/water partition coefficient  KQW has  been  shown



to be a good predictor of the tendency of chemicals to



bioconcentrate in fish  (Neely et al.  1974).   Since  1974, KQW has



been used as a measure of bioconcentration  potential  in fatty



tissues in aquatic and other living organisms.  The numerical



value of the octanol/water partition  coefficient is one factor to



be considered in determining whether  to  conduct fish  biocon-



centration studies.  Other factors must  also  be taken into



account.  For example, transformation rates (e.g.,  rates of



biodegradation, hydrolysis,  photolysis,  and oxidation)  must also



be considered.  If a chemical transforms readily by one of these

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                                 84






processes, the potential for bioconcentration will  be  reduced




significantly and fish bioconcentration  studies may not  be



needed.






     The octanol/water partition coefficient has  been  introduced




by Hansch to correlate biological  activity and chemical  structure




(Hansch 1969; Hansch and Fujita 1964).   Numerous  papers  have  been




published by Hansch and his coworkers on this subject  in the



ensuing years.  A monograph has been published on the  Hansch



approach (Gould 1972).






     A recent publication has indicated  that the  sorption of



several hydrophobic pollutants on  natural sediments can  be



related to the octanol/water partition coefficient.  Karickhoff



et al. (1979) showed that a reasonable estimate (within  a factor



of two) of the sorption behavior of hydrophobic pollutants  can be



made from knowledge of the particle size distribution  and



associated organic content of the  sediment and the  octanol/water



partition coefficient.






     A recent publication has described  a novel method for  esti-




mating the distribution of a chemical in the environment (Mackay




1979).  KOW is used in this partitioning analysis.   This parti-



tioning analysis will be used as a guide to ecological and  health



effects testing.

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                                  85





2.        Scientific Aspects








2.1.      Rationale for the Use  of the  Octanol/Water  Partition



          Coefficient to Estimate Bioconcentration  Potential






     Intuitively, the absorption and  fat  storage  of xenobiotic



chemicals in living organisms  seem to be  related  to lipophilicity



or preferential  solubility in  fats as compared  to water.   By



definition, the  octanol/water  partition coefficient KQW  expresses



the equilibrium  concentration  ratio of  an organic chemical



partitioned between octanol and  water in  dilute solution.   If  one



assumes that octanol simulates fats in  its solubilizing  effect on



organic chemicals, then KOW should be a potential measure  of the



ease of storage  of organic chemicals  in fats.   For  example, a



large value of KQW indicates that an  organic  chemical is not very



soluble in water but soluble in  octanol.   Hence,  this would



suggest the potential for a large storage of  the  organic chemical



in fats.  Davies et. al.  (1975)  reported  human  pesticide



poisoning by a fat-soluble organophosphate, dichlofenthion.  The



octanol/water partition coefficient KQW was found to  be  very high



(1.37x10^) which correlated with the  high fat storage of this



chemical.





     Neely et al. (1974) found a pronounced correlation  between



K   and the bioconcentration in  trout muscle.   Specifically,
 ^J\w


these researchers obtained a linear correlation between  the log

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                                 86
of bioconcentration and the log of calculated K    for  a  series  of
organic chemicals.  Since that time, KQW has been  used by
researchers as an index of bioconcentration potential  in living
organisms.  The Office of Pesticide Programs  (OPP)  [EPA  1975,
1978] has proposed, and the Organization for Economic  Cooperation
and Development (OECD 1978) is considering the use  of  Kow  as  a
measure of bioconcentration potential in aquatic organisms.


2.2.      Rationale for the Selection of the Test  Method


2.2.1.    The Conventional Method of Determining the
          Octanol/Water Partition Coefficient Kow

     The conventional method for determining a distribution
coefficient is carried out by distributing a chemical  between two
immiscible liquids in a vessel and measuring the concentration  of
the chemical in the two liquid phases after equilibration
(Glasstone 1946; Leo et al. 1971).  This method can be applied  to
the determination of the octanol/water partition coefficient
KQW.  Numerous researchers use the conventional method of
determining KQW and have published papers using this method
(e.g., Fujita et al. 1964; Hansch and Anderson 1967; Leo et al.
1971; Chiou et al. 1977).  OPP (EPA 1975, 1978) has proposed, and
OECD  (1978) is considering the conventional method  of  determining
K_,7.  Most chemical companies that determine octanol/water
 Ovv
partitioning use the conventional method of determining  K   .

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                                 87
Hence, the proposed test  standard  utilizes  the  conventional
method of determining the octanol/water  partition  coefficient
KQW.  it should be noted  that  there  is no validated  standard test
method for determining KQW  (e.g.,  an ASTM method).   The  proposed
method in this standard was  developed  from  a  thorough  review of
the research  literature on  the experimental determination  of Kow
and by talking to researchers  who  have considerable  experience  in
carrying out  these experiments.

2.2.2.    Other Experimental Methods of  Determining  KQW
          (1)  Reverse-Phase High-Pressure  Liquid  Chromatography
               as a Method  of  Estimating KOW.   A rapid method
based on reverse-phase high-pressure liquid Chromatography has
been developed by Veith  (Veith and Morris 1978;  Veith  et al.
1979) to estimate the octanol/water  partition coefficient  of
organic chemicals.  Using the  solvent  mixture water/methanol
(15/85 v/v) as the elutant,  the log  of the  retention time  [log
(tR)] of organic chemicals  on  a permanently bonded (C-18)
reverse-phase high-pressure liquid chromatographic system  has
been found to be linearly related  to log KQW.   This  relationship
has been expressed by the equation
                  1Q9 Kow  =  A J-ogftR)  - B'                   (1)
where A and B are constants determined from the experimental data
for some organic chemicals.  Using a mixture  of the  chemicals
benzene, bromobenzene, biphenyl, p,p -DDE [2,2-bis(p-

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                                  88




chlorophenyl)-l,l-dichloroethylene]  and  2,4,5,2',5*-




pentachlorobiphenyl, A and B were  found  to be  5.106 and 1.258,



respectively, with a correlation  coefficient of  0.975.   It must



be emphasized that this correlation  is limited with respect to




being representative of the organic  chemicals  encountered.  This




calibration mixture was selected  largely on  the  basis  of the log




KQW values reported in the literature, and the correlation is




linear over five orders of magnitude of  Kow-   To determine the



accuracy of this method of estimating log KQW  by comparison with



data reported in the literature, Veith and coworkers measured the




retention time of 18 chemicals, and  the  standards and  log KQW



values were calculated from the regression equation  (1)-   The




results indicated that log KQW can be estimated  to within  (22.8



± 20.0) percent when compared with the values  reported in the




literature from measurements using other methods. The percent




error was calculated assuming the  literature value is  the correct




log KQW/ an assumption these researchers had some reservations



about.  It should be noted that some of  the  greatest relative



errors were observed with polar chemicals which  dissociate in




water (e.g.,  m-chlorobenzoic acid, 2,4,5-trichlorophenol,  and




diphenylamine).  This method has  a definite  advantage  since the




estimation of KQW can be made rapidly and relatively easily in




comparison to the determination of K  by the  conventional




method.  Futhermore, KQW can be estimated for  individual



chemicals in complex mixtures (e.g., solid wastes) without




knowing the specific chemical structure  of each  chemical.



Further work is being carried out by Veith (at the Duluth EPA

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                                 89




Laboratory), and others, to develop  this  method  so  that  it  may be




applicable to a large number of organic chemicals with a wide



range of different organic structures.  If  this  research is



successful, this high-pressure liquid  chromatographic method of



estimating KQW will be  proposed as a test standard.






     Other researchers  have developed  high-pressure  liquid



chromatographic methods to determine KQW  (Mirrless  et al. 1976;



Yamana et al. 1977; Carlson et al. 1975;  Hulshoff and Perrin



1976; McCall 1975).  However, these  methods are  based on a  very



limited number of experiments and considerably more  work is



needed to develop them.








          (2)  Thin-Layer Chromatography  as a Method of



               Estimating KOW.  It has been reported that thin-



layer chromatography can be used to  estimate KQW (Mirrless  et



al., 1976; Hulshoff and Perrin 1976).  However,  high-pressure



liquid chromatography  (HPLC) is far  superior to  thin-layer



chromatography (TLC) because of its  accuracy (i.e.,  definition of



the peak), reproducibility. ease of  detection in many cases, and



above all the range of  applicability (HPLC  is applicable over  5



order of magnitude of KQW while TLC  is only applicable over 1.5



orders of magnitude of  KQW\ ( Mirrless et al. 1976).








          (3)  Estimation of K^.lT from  Water Solubility Data.



The octanol/water partition coefficient is  defined  as the ratio



of the equilibrium molar concentation  of  the chemical in octanol



and water.  Thus, low molecular mass (i.e.,  molecular weight)

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                                 90




organic chemicals with a low water solubility  should have a high




value of Kow (e.g., hydrophobic organic chemicals).   Therefore,




there should be a correlation between KQW and  water  solubility.




Chiou et al. (1977) studied the relationship between KQW and the



water solubility, S, and found that for 34 organic chemicals,  an




excellent linear correlation was observed between log Kow and log



S which extended to more than eight orders of  magnitude in water




solubility  (10~3 to 104 ppm), and six orders of  magnitude in Kow



(10 to 107).  Chiou et al. (1977) found the following regression




equation



                  log KQW = 5.00 - 0.670 log S,                (2)



where Kow is the octanol/water partition coefficient,  S is the



water solubility in ymol/L, and the correlation  coefficient (r )




was 0.970 for these 34 chemicals.  Thus, KQW can be  estimated



from the experimental value of the water solubility  of an organic



chemical.  This method would have a definite advantage in that




KQW could be estimated directly from water solubility data



without having to experimentally measure K  .  Thus,  the



octanol/water test standard could eventually be  eliminated,




thereby reducing the cost of testing.  However,  considerably more




experimental work is necessary to extend the correlation to a



large number of organic chemicals with different structures




before it can be used as a test standard.  EPA will  sponsor



research work to develop this method.
                                8

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                                 91




2.3.      Rationale for the Selection of  Test  Conditions






     A detailed study of the theory of the  distribution  law,  the



partition coefficient, and the published  literature  on the




conventional determination of KQW  indicates that  it  is extremely



important that numerous factors  (or test  conditions) be



standardized.  In order to establish these  factors clearly,  the



theory of the distribution law and its relation to these  factors



are discussed in detail in the following  sections.








2.3.1.    Theory of the Distribution Law  and the  Octanol/Water



          Partition Coefficient






     The distribution coefficient  or partition coefficient  can be



derived using thermodynamic theory  (Glasstone  1946).  Consider a



mixture of two immiscible liquids  which is  shaken with a  solute



(organic chemical).  The solute  distributes itself between  the



two liquids in such a way that at  equilibrium, in dilute



solution, the ratio of the concentrations of the  solute  in  the



two layers is a constant at a given temperature.  The tendency of



a chemical to distribute itself  between two immiscible liquids



with a constant concentration ratio, in dilute solution,  is a



direct consequence of the thermodynamic requirements for



equilibrium.  To illustrate this,  consider  a pair of immiscible



liquids A and B in contact with  each other  containing the same



solute in solution.  The chemical  potential of a  solute  in




solvent A is given by

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                                  92
                      y»   =   y°    +  RT in a.  ,                 (3)
                      A       A            A


where  y  is the  chemical  potential of the solute in solvent
       A


A, y°   is the standard chemical  potential of the solute in the



same solvent  (i.e., the value of  y  at a,.  = 1),  while aA, the



activity of the  solute in the solvent A is the  effective



concentration taking  into account intermolecular interactions of



the solute in the  solvent.   R is  the gas constant and is equal to



8.314  joules/°K/mol,  while T is the absolute  temperature in °K.



Similarly, for solvent B



                      UB  = y°B  +  RT in aB,                     (4)
where all the quantities have  the  same  significance as in equa-



tion (3).  At equilibrium between  the layers  Ay = 0;  hence



                        Ay = y  —  y  =  O,



and




                            UR - WA.                           (5)
                             D    f\






Using equations  (3) and (4) in (5) yields



                   y°B  +  RT In aB = y°A   +  RT In aft         (6)
                      in
                            ft             RT


However, at a given temperature,  u°B  and  u°A are constants for a



given solute in a particular solvent; hence
                        ln
                                10

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                                 93


and,

                               !*  =   K.                       (7)
                               aA
Equation (7) is the mathematical statement  of  the  distribution

law which states that a  substance  will distribute  itself between

two solvents until at equilibrium  and  the ratio  of the  activities

of a chemical  in the two layers  is a constant  at a fixed

temperature, irrespective of  the absolute values of aA  or aB.

The activity aA can be written as

                           aA  =  YA CA  ,                        (8)



where YJ> is the activity coefficient and takes into account the

interaction between molecules A  in solution, and CA is  the molar

concentration.  In dilute solution as

                            CA  *  o ,
hence,
                            YA  *   1  ;                          (9)
                                limit

                               CA  *  °    (aA>   =  CA*
    The same argument  follows  for  the  solute  in solvent B and
 limit
 C* O  (a_) = C_.   Using  these  results  in equation (7),  the
  B      B     is

distribution coefficient K,  in dilute  solution,  becomes
                           0      limit      Cn
                         K°   =   C  >  O   (  -?£- }  .             (11)
    For the specific  case  for  the  octanol/water partition

coefficient, B  is the solvent  n-octanol,  A is the solvent water,

and K° = KQW.   Thus,  equation  (11)  becomes
                                11

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                                 94
                          =            .                       (12)
                      ow     C  ^
                              water
    According to Nernst, the distribution  law  applies  only to


individual molecular species in solution.   If  a  molecule


dissociates or associates in octanol and water,  then equation


(12) must be modified.  In general, if  a represents the  fraction


of the total solute that is dissociated or  associated, assuming


that either association or dissociation occurs in  each solvent,


then
                (1  —  n    \ f
        K    -          Oct.' UOCt.
        K
         OW      l  _          c
                        water   water
since  (1-a) gives the fraction of unchanged molecules  in  each



phase.  For the special case where no association  takes place in


octanol, equation (13) reduces to

              °»          -  War




2.3.2.    Factors Which Affect the Value of Kow






          (1) Effect of Temperature.  From the theory  of  the


distribution law as outlined in section 2.3.1., the distribution


coefficient K is a function of the temperature (equation  (6)),


and is a constant at a fixed temperature (equation  (7)).   Since


KQW is a distribution coefficient, it should also vary with


temperature and is a constant at a fixed temperature.  Hence,  in


carrying out octanol/water partition coefficient experiments  by
                                12

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                                 95
the conventional method,  the  temperature  should be controlled.



However, variations due  to  temperature  are  small compared to



those inherent  in  the  errors  in  the  other measurements,  e.g.,  the



errors in measuring the  concentration of  solute in octanol and



water.  Therefore, for reasonably accurate  determinations of KQW,



it is sufficient to control the  temperature to ± 1°C.   Since most



physical properties of chemicals are reported at 25°C,  the



proposed standard  requires  that  KQW  be  determined at this



temperature.








           (2)   Purity  of the  Solvents.  Trace amounts of



impurities present in  n-octanol  tend to produce emulsions and



must be removed (Fujita  et  al. 1964; Hansch and Anderson 1967;



Chiou et al. 1977).  Emulsions give  poor  phase separation and



result in a wide scatter in the  value of  KQW.  in addition,  im-



purities in octanol may  affect the analysis for the solute.



Hence, the proposed test standard required  that the octanol  be



_>99.9% pure.  Distilled  or  reagent grade  water (ASTM Type II)



should be used.








           (3)   Concentration  of  Solute.  From the theory of  the



distribution law,  as outlined in section  2.3.1., equations (12),



(13), and  (14)  only apply in  dilute  solution.  Hence the proposed



test standard requires that all  experiments be carried out at



molar concentration C  <  0.01M in octanol  and water.
                                13

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                                 96
          (4)  Equilibration Time.  For many  chemicals,  5 minutes



of gentle agitation of the two phase  system established



equilibrium and produced consistent results  (Leo  et al.  1971).



Studies by Craig and Craig (1950) indicated that  when  the phases



were of about equal volume, equilibrium was rapidly attained.



When high ratios of water to octanol  (>100:1) were  used,  longer



shaking was necessary to establish equilibrium. High ratios  of



water to octanol are used to determine KQW for very hydrophobia



organic chemicals  (sections 2.3.2.(5) and  (8)) as described



below.  Therefore, for most chemicals, gentle agitation  for  1



hour should be adequate to reach equilibrium.  For  surfactants,



at least 16 hours  of agitaton is necessary to reach



equilibrium.  This is an empirical observation obtained  by



researchers who have carried out experiments with surfactants.



It is undoubtedly  due to the nature of surfactant chemicals.








          (5)  Octanol/Water Volume Ratio.  Depending  upon the



solubility of the  solute in octanol and water, the  ratio of  the



volume of octanol  to water should be  adjusted.  For hydrophobic



solutes, which are very insoluble in  water, considerably more



water than octanol should be used.  Adjustment of solvent volumes



can decrease the effect of analytical errors  and  consequently



decrease the error in determining KQW  (Leo et.al.  1971). The



following example will illustrate this point.  Consider  a



chemical with a molecular mass  (i.e., molecular weight)  MW



(mg/mmol). KQW = 200.  Twenty mg of chemical  are  dissolved in  100



mL of octanol, and 100 mL of water are added  to this system.
                                14

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                                 97
After equilibration,  the  mass  of chemical  in each phase can be

calculated as  follows.  The  chemical will  partition with x mg in

the water phase  and  (20-x) mg  in the octanol phase.


                       (20-x)mg
                   MW (mg/mmol)     _  (20-x)  mmol  _  (20-x)  Molar
            oct.      100  mL         ~  100  MW   mL      100 MW

                           x  mg
                   	MW(mg/mmol)      _     x     mmol  _    x
          Cwater  =       100 mL         =  100 MW    mL      100 MW

Since

                       K
                               Cwater

                                   (20-x)
                                   100 MW         (20-x).
                         200  =  	Z	   =       	
                                                    x
                                  100 MW
            20
Then  x   =  	  = 0.0996 = 0.10 mg = mass of chemical in the
           201

water phase; and (20-x) = 19.9s: 20 mg = mass of chemical in the

octanol  phase.


      Consider  an analytical error of +_ 0.05 mg in the aqueous phase

 (i.e., 0.10 -  0.05 = 0.05 and 0.10 + 0.05 = 0.15).
                                      20
                                      MW
                                     100	      20
                        K0w  =  	^05"	  =  oTbT  = 40°
                                      MW
                                     100

                                      20
                                      MW
                                     100             20
                                     0.15      -    0.15
                                      MW
                                     100
                                 15

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                                 98
    Therefore, an analytical error  of  ±  0.05  mg in the aqueous phase

means that KQW can range  from 400 to 133,  and a very large error in

KQW occurs.


     Now consider the same example  as  above but now the solvents are

adjusted to 200 mL of water and 5 mL of  octanol.   After equilbration,

the mass of chemical in each phase  is  now:

                                  (20-x)
                                   MW
                       oct.
                                      X
                                     MW
                       vow
                      200  =
  200

coct.
cwater

(20-x)
 5 MW
  x
200 MW
           (20-x)
            5 MW
                                                200  MW
                                                        Molar
                                                       Molar
                                                 (20-x)
                    (40)
         20
Then x = — = 3.33 mg = mass of  chemical  in  the  water phase;  and
         6


(20-x) = 16.7 mg  =  mass of chemical  in  the octanol phase.


     Now consider the same analytical  error  of ^KD.05 mg in the aqueous

phase (i.e., 3.33 - 0.05 = 3.28  and  3.33  + 0.05  = 3.38)

                                     16.7
                                     MW
                      K
                       OW
3.28
 MW
200

16.7
 MW
                 16.7
                 3.38   (40) = 203
                      K,
                       ow
3.28
 MW
200
                  16.7
                  3.28 .(40) _  197.
                                16

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                                  99
Now the analytical error  of ±  0.05 mg  in  the  aqueous  phase means that




Kow can range from 197 to 203  and the  error in  Kow has  been reduced



dramatically.








          (6)  Chemical Analysis of  the Octanol



               and Water  Phases.  Consider a  partitioning experiment



in which a chemical  is dissolved in  octanol at  a  low  concentration



(less than 0.01 molar).   The conventional partitioning  experiment is



carried out and only one  phase is analyzed for  the molar  concentration



of the solute.  Using a mass balance,  the molar concentration of the



solute in the other  phase is obtained  by  difference.  However,  if



there is a loss of chemical by adsorption to  the  surface  of the glass



walls, a serious  error will occur at this low concentration.   This is



especially true for  very  hydrophobic chemicals  (Chiou et  al.  1977) and



for ionic solutes (Leo et al.  1971).  Therefore,  the  proposed test



standard requires that both the octanol and water phases  be analyzed.






     An analytical method should be  selected  that is  the  most



applicable to the analysis of  the specific chemical.  However,  large



errors can occur  as  a result of traces of more-water-soluble



contaminants that are not analytically distinguishable  from the parent



chemical.  This error is  very  significant when  the analytical method



is ultraviolet absorption spectroscopy or radiometry, since these



methods can be nonspecific for many  solutes.  Therefore,



chromatographic methods are preferable because  of their compound



specificity in analyzing  the parent  chemical  without  interference from
                                17

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                                100






impurities (Karickhoff and Brown 1979).  Whenever  practicable,  the




chosen analytical method should have a precision within  ±  5  percent.








          (7)  Emulsification and Ultracentrifugation.   Many chemicals




can cause troublesome emulsions to form between octanol  and  water and



emulsification can result in large errors  in KQW  (Leo  et al.  1971;



Chiou et al. 1977).  This is especially true for hydrophobia




chemicals.  Therefore, gentle shaking shall be used  to minimize the



formation of emulsions.  In addition, incomplete separation  of  the two




phases is one of the most serious sources  of error.  To  break any




emulsion formed and to completely separate the octanol and water



phases, the proposed test standard requires that the two phase  system




be ultracentrifuged at 25°C for 20 minutes.  The acceleration G value



required to break an emulsion and to completely separate the octanol



and water phases must be determined by trial-and-error




experimentation.  Since the clarity of the two phases  is not a



dependable criterion of the absence of an  emulsion and complete



separation of the two-phase system, the proposed test  standard




requires that a turbidimeter be used to make sure  that the emulsion is



broken and the octanol and water phases have been  completely



separated.








          (8)  Equilibration Vessel.  To simplify  the  experimental




procedure, equilibration should be carried out in  a  centrifuge  tube




(special glass tubes can be used up to approximately 12,000  G and




stainless steel centrifuge tubes can be used at higher G values)  with




a scalable cap.  This will avoid a transfer step and volatile
                                18

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                                101






chemicals can be handled easily.  The  centrifuge  tube  shall be almost



completely filled with the two phase mixture  to minimize  partitioning



with air.  This is especially important when  determining  KQW for



volatile chemicals (Hansch and Anderson 1967).






     Very hydrophobic chemicals, with  KQW  in  the  order of 104 to 106,



require relatively large volumes of the aqueous phase  (section 2.3.2.



(5)).  Hence, for these chemicals, the proposed test standard requires



that equilibration be carried out in a large  ground-glass stoppered



flask.








          (9)  Speciation Effects.  The details of  speciation have



been discussed in the theory of the distribution  law and  the



octanol/water partition coefficient, section  2.3.1.





     If the chemical does not associate or dissociate  in  octanol and



water, then the proposed test standard requires that equation (12)  be



used and Kow be determined at concentrations  C <  0.01M and C^ =



0.1C.  Under these experimental conditions, if KQW  is  constant,  then



association or dissociation has been minimized or eliminated.






     If the chemical associates in octanol or water or in both



liquids, then the proposed test standard requires that equation (13)



be used and KQW be determined at concentations C  <  0.01M,  C^ = 0.1C,



C2 = 0.01C, C3 = 0.001C, 	  When KQW  is constant  at two



concentrations differing by a factor of 10, then  the effect of



association has been minimized or eliminated.
                                19

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                                102





     For chemicals which reversibly  ionize  or  protonate (e.g.,




carboxylic acids, phenols or  anilines),  the proposed  test standard



requires that equation  (14) be used  with water buffered at pH 5.0,




7.0, and 9.0, the pHs of environmental  concern.








           (10)  Presaturation of the Solvents.   Presaturation of




octanol with water and  water  with  octanol is required for this  test




standard.  The preparation of these  saturated  solutions is very simple



to carry out.  This requirement is extremely important when




determining KQW for very hydrophobic chemicals since  the ratio  of



water to octanol will be very large.  In this  case, if the experiment



is carried out without  presaturation of  the water with octanol,  then




all the octanol will dissolve in the aqueous phase  and KQW cannot be



determined.








2.4.      Reference Compounds






     It would be very desirable to have  reference compounds which




cover a KQW range of 10 to 106.  These  reference compounds would



provide the experimenter with comparative reference values to




determine how well the  test has been conducted.  Unfortunately,  these



reference compounds are not available.   The EPA is  funding work at the




National Bureau of Standards  to develop  such reference compounds.



When this work is completed,  these reference compounds will be




recommended for use in  this test standard.   In the  interim, it  is




recommended that the book by  Hansch  and  Leo (1979)  be used for  the




selection of potential  reference compounds.
                                20

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                                103





2.5.      Test Data Required






     The tendency of an  organic chemical  to partition out of water



into other environmental compartments  containing hydrophobia



constituents  (e.g., aquatic organisms)  can be inferred from the values




of the octanol/water partition coefficient Kow.   Chiou et al.  (1977)



developed regression equations relating log KQW  with water solubility



S (in ymol/L) and bioconcentration  in  rainbow trout  (BF).   Assuming



log KQW is between 1 and 6, S and BF can  be calculated;  these  results



are summarized in Table  1 (note that S  has been  converted to mol/L).



Furthermore,  assuming  that the average  molecular mass (i.e.  molecular



weight) of an organic  chemical is 300  gm/mol,  the water  solubility can



be converted  to ppm; these results  are  also summarized in Table 1.  It



is apparent that for log Kow =6  (i.e., KOW = 106),  the  water



solubility will be extremely low  (9.7  x 10~^ ppm or  9.7  ppb) and



the predicted BF is 1.48 x 10  .  Hence, the data indicate that



the chemical  will partition out of  the  water phase and into the




fat of the fish (i.e., the hydrophobic  phase).   For  log  Kow =  1



(i.e., KQW =10), the  water solubility  will be very  high (2.80 x



105 mg/L or 280 gm/L)  and the predicted BF is 2.4.   Hence,  these



data indicate that the chemical will remain in the water phase



and will not  partition significantly into the fat of the fish



(i.e., the hydrophobic phase)-  Therefore, the proposed  test



standard is designed to  determine the  value of KOW in the range



10 to 106.  Low molecular mass organic  chemicals with a  KQW value



less than 10  will not  partition significantly into,  or tend to





                                21

-------
                                104
Table 1.  Summary of Calculated Values of  Water  Solubility and

Bioconcentration in Rainbow Trout as a Function  of  Log  Kowa
    KQW        S(mol/L)b        S(mg/L or ppm)c     BFd
   6           3.24 x 10~8      9.7 x 10~3        1.48  x  104



   5           1 x 10~6         0.30              2.57  x  103



   4           3.09 x 10~5      9.3               4.47  x  102



   3           9.77 x 10~4      2.93 x  102        7.76  x  101



   2           3.02 x 10~2      9.06 x  103        1.35  x  101



   1           9.33 x 10"1      2.80 x  105        2.4



a  Regression equations taken  from Chiou  et  al.  (1977).
"  Water solubility
c  Water solubility in ppm assuming a molecular  mass of  an
   organic chemical is 300 gm/mol.
   Bioconcentration in rainbow trout
                                22

-------
                                105





accumulate in, any hydrophobia  environmental  compartments.   Low




molecular mass organic chemicals with  KQW in  excess  of 106  will



tend to accumulate into  all hydrophobia  enviromental



compartments.  For low molecular mass  organic chemicals outside



the range 10 to 10 , the proposed  test standard  requires that



KQW  be characterized as < 10 or >  106 with no further



quantification.






     Specific analytical and recovery  procedures are needed to



determine whether acceptable data  have been generated.








2.6.      Statistical Analysis  of  the  Data






     Numerous researchers have  published data on the determina-



tion of the octanol/water partition coefficient  by the conven-



tional method (e.g., Chiou et al.  1977;  Davies et al.  1975;



Fujita et al. 1964; Hansch and  Anderson  1967; Leo et al. 1971).



However, none of these researchers has analyzed  the  data



statistically and the precision of KQW as determined by the



conventional method has  not be.en clearly established.   The  pre-



cision is, in part, a function  of  the  nature  of  the  specific



chemical.  As the hydrophobicity of the  chemical increases, KQW



increases and the precision of  Kow decreases.  Furthermore, the



precision is also a function of the analytical procedure used.



In general, the lower the concentration  to be measured, the



poorer is the precision  of the  analytical procedure.  Therefore,



no reliable precision can be stated at this time for determining




KQW.  Obviously, the precision  can be  improved by making numerous
                                23

-------
                                106
replicate determinations. However, in order  to minimize  cost,  it



has been decided to determine KOW with three replicates.   The



submitter of the test results must analyze the data  statis-



tically.  When a large number of chemicals have been determined



by the proposed method, the data will be  analyzed  statistically



and the level of precision can be defined for various ranges of




Kow'
                                24

-------
                                 107






3.        ECONOMIC ASPECTS






     A survey of three commercial  laboratories  to  estimate costs




for performing the test outlined in  this  Standard  found  a  range




of $100 to $1,400 and with a  "best estimate"  of $553.  A cost




estimate was also made by separating the  protocol  into components




and estimating the cost of each  component including  direct labor




cost, overhead cost, other direct  costs,  general and




administrative costs, and profit or  fee.   The estimated  range  for




this test ranged from $229 to $688 with a "best estimate"  of




$458.  The cost estimates were made  assuming  that  all the




requirements of Good Laboratory  Practice  Standards,  as specified




in section (c) of this Test Standard,  are being satisfied.




Details of the cost estimates are  contained in  a report  by Enviro




Control, Inc.  (1980).






     The cost estimates in the Enviro Control report do  not




include the costs for specialized  analytical  methodology or for



analytical method development that is required  to  determine the




concentration of the chemical in octanol  and  water at




equilibrium.  It is not possible to  estimate  the cost of such




special analytical methodology since the  costs  are related to  the




nature of the chemical to be  analyzed and related  because  such




method development costs may  be  prorated  among  the analytical




needs of other test standards.






     In reviewing the state of technology concerning this  area of




testing, the Agency has not identified any adequately developed
                                25

-------
                                108
tests that would be significantly less costly while providing
comparable information.
                             26

-------
                                 109





4. REPLIES TO THE COMMENTS ON  THE  PUBLISHED  SECTION 5




   TESTING GUIDELINES






     The Federal Register of March 16,  1979  (EPA 1979)  presented




a discussion of the policy issues,  alternative  approaches,  and




test methods under consideration as  guidance for premanufacture




testing.  Included in  the test methods  was a section on the




octanol/water partition  coefficient,  KQW (pages 16254-16256),



which discussed a method for determining this parameter for use




in developing information on new chemicals.   Among  the  comments




received in response to  the discussion  were  several comments




related to the determination of K_,..
                                 ^y Vr





     One commentor made  the following statement:   "The  rationale




for including this test  in the proposed premanufacture  testing




program is based upon  published data indicating that there  is  a




correlation of KQW with  bioconcentration or  biomagnification




potential of chemical  substances in  aquatic  and other living




organisms.  However, researchers (Chiou et al.  1977;  Lu and




Metcalf 1975; Metcalf  et al. 1975) have shown that  there is a




correlation between bioconcentration and aqueous solubility




suggesting that the assessment for bioconcentration potential  can




be obtained from water solubility  data.   Under  these circum-




stances, the determination of  KQW  would be redundant."   However,




K   has other uses in  addition to  predicting bioconcentration
potential. KQW  is  related  to  partitioning  into all  hydrophobic



environmental compartments (e.g.,  sediments).   In addition,  K




is an indicator of biological activity.  Therefore,  KQW is a very
                                27

-------
                                110
important and useful physical/chemical property-   The  research




work by Chiou is significant because KOW  can be  estimated from



water solubility data and this work has been thoroughly discussed




in section 2.2.2.  (3).  Research work will be  sponsored by EPA to




develop this method.






     Another commentor indicated that HPLC has been  overlooked as




an alternative method for determining KOW-  However, this method



has been addressed in the TSCA Federal Register  guidelines and




has been thoroughly discussed in section  2.2.2.  (1).   HPLC is



much simpler to run than the conventional method.  Hence,




research will be sponsored by EPA to develop this  method.






     Two commentors indicated that the range of  K    should be



limited.  One commentor suggested that the range should be 10 to




104 while another  commentor indicated that there is  very little



value in pushing the method to 10^ or to  very  low  values.  This



subject has been thoroughly discussed in  section 2.5.   The data




presented in this  section indicated that  the most  useful range of




KQW is 10 to 10^ and for values outside this range,  KQW should be



characterized by <10 or >106 without further quantification.   The




value of KQW proposed by one commentor  (i.e.,  104) is  too low




since a significant amount of a chemical  would still be in the




water phase, bioconcentration is moderate  (447), and partitioning




is not. complete.   It is only when KQW = 106 that the water solu-



bility is very low (9.7 ppb), bioconcentration is  high (1.48 x




104) and partitioning into a hydrophobic  environmental compart-



ment is essentially complete.
                                28

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                                Ill
     There were two comments  related  to  equilibration time.   One



commentor indicated that the  equilibrium time  of  1  hour is



entirely too short since it can  take  several weeks  or months to



establish equilibrium  in a water solublity  experiment for very



hydrophobia chemicals.  However,  in determining water solubility,



the equilibration is between  the molecules  in  the solid state and



in solution and this process  is  very  slow for  very  hydrophobia



chemicals.  On the other hand, in determining  Kow,  the chemical



is dissolved in octanol, water is added,  and equilibrium is



involved with molecules in solution.   Under these conditions,



equilibration is rapid (5-15  minutes).   Equilibrium has been



discussed in section 2.3.2.  (4).






     Another commentor indicated that in order to ensure that




equilibrium has been established,  several measurements of Kow are



necessary at different times, e.g., 1, 6,  16 hours.   However,



this procedure would be too costly since several  determinations



must be made.  As indicated in section 2.3.2.  (4),  equilibrium is



attained rapidly for most chemicals  (5-15 minutes)  and 1 hour is



sufficient to reach equilibrium.   For surfactants,  16 hours  is



sufficient to reach equilibrium.





     Three commentors  discussed  the determination of KQW at  pH 5,




7, and 9.  One commentor indicated that  the measurement Of KQW at



different pHs is inappropriate since  the objective of this



measurement is to simulate bioaccumulation  in  fatty tissues  under



physiological and surface water  conditions  (pH 7).   This state-



ment is not true.  In  general, the pH of surface  waters can  vary
                                29

-------
                                112






from 5 to 9 and is not necessarily at  7-  Hence  for  chemicals




which reversibly ionize or protonate,  the pH of  the  surface water



will determine the type of molecular species present and this




molecular species is the one which will be bioconcentrated.   In




addition, this test will give information on sorption into any




hydrophobic compartment (e.g., sediments) which  is a function of



the nature of these molecular species  and, therefore,  will have a




direct effect on partitioning in the environment.  Another




commentor suggested that it would be more than sufficient to



measure the partition coefficient of the chemical at the pH (5 or




9) that will give the lowest solubility since this will  most




likely yield the highest partition coefficient.  However,  Kow



will be used in a partitioning analysis and it is necessary to




know KQW at pH 5, 7, or 9, the pHs of  environmental  concern.   The



third commentor suggested that the same buffers  described in the




hydrolysis protocol (p. 16268) be used.  The buffers listed in




the hydrolysis procedure were designed to minimize buffer



effects.  Hence, these buffers have been recommended for use in



the proposed test standard.






     Two commentors discussed the use  of glass-stoppered centri-




fuge tubes at 37,000 G.  They indicated that currently there are



no glass-stoppered centrifuge tubes that can be  used at  37,000




G.  This suggestion has been incorporated in the proposed test




standard.  Special glass centrifuge tubes are available




commercially which can be used to approximately  12,000 G and



stainless steel centrifuge tubes can be used at  higher G values.
                                30

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                                 113






     One commentor discussed  the inadequacy of the sampling




procedure.  The commentor  indicated  that  since the octanol layer



is on top of the water  layer,  it would  be extremely difficult to



sample the aqueous phase without contaminating the sampling



device (the pipet) with the concentrated  octanol  phase.  The test



standard has incorporated  a method which  will  avoid this



problem.  The test standard requires that the  octanol  phase be




sampled first with a pipet.   Then the remainder of the octanol



phase and the interfacial  layer  can  be  removed and discarded.



Finally, a new pipet can be used to  sample the aqueous layer.






     One commentor discussed  the problem  of emulsification.  It



was indicated that even gentle shaking  for 1 hour could lead the



same horrendous emulsions  for certain chemicals.   This problem



has been recognized and thus  ultracentrifugation  is required to



break any emulsion and  to  separate the  octanol and water phases.
                                31

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                                114

5.         TSCA/FIFRA COMPARABILITY

     The methods for determining the octanol/water partition
coefficient described in the FIFRA Guidelines  (EPA 1975,  1978)
and this Test Standard are similar.  However,  the FIFRA Guide-
lines only give general guidance for determining K_t,   Because
                                                  tJW •
the determination of KQW is a difficult procedure, as  explained
above, a number of variables must be controlled in order  to
obtain a reliable result.  Therefore, detailed procedures  for
controlling these variables have been included in the  TSCA Test
Standard.  Furthermore,  adherence to these detailed procedure is
required to insure that a uniform method is used by all
submitters, thereby allowing the data to be compared.
                                32

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                                115
6.        TSCA/OECD COMPARABILITY



     The Organization  for Economic  Cooperation and Development


issued a draft of a test protocol  for  determining KQW (OECD,


1978).   This draft is  old but  is the only one  available for com-


parison with the TSCA  proposed test standard.   In general,  the


OECD test protocol and the TSCA proposed  standard are very  simi-


lar.  However, there are a few differences which  are  discussed


below.   OECD requires  that KQW be  determined quantitatively


regardless of the value for  a  specific chemical.   The TSCA  test


standard specifies that Kow  only be determined quantitatively in


the range 10 to 10^.   The justification for this  range is out-


lined in section 2.5.



     OECD indicates that KQW is "ideally" dependent on tempera-


ture.  Kow is, indeed, a function  of temperature  as discussed in


section 2.3.2.  However, OECD  indicates that the  effect of


temperature on KOW is  small  (i.e.,  approximately  0.01 logarithmic


units per degree Celsius and can be positive as well  as


negative).  Hence, OECD does not require  temperature  control  and


their test method specifies  that KQW be measured  at room


temperature.  However, no experimental data are given to support

                                     *
this finding.  Since KQW is  an equilibrium constant and is


dependent on temperature (section  2.3.2.), the TSCA proposed  test


standard requires that KQW be  determined at 25 +_ 1°C.  Precise


temperature control is not required as indicated  by the range of


temperature control of + 1°C.
                                33

-------
                                116
     OECD does not require that K   be determined  as  a  function



of pH for chemicals that reversibly ionize or protonate.   The




TSCA proposed test standard requires that chemicals that




reversibly ionize or protonate should be tested at pHs  5,  7, and




9, the pHs of environmental concern.  The effect of pH  is




discussed in section 2.3.2. (!).






     OECD does not indicate how to handle volatile chemicals or




very hydrophobia chemicals while the TSCA test standard gives



detailed procedures for handling these types of chemicals.  The




reasons for giving precise directions on handling  these types  of



chemicals are discussed in section 2.3.2. (8).






     OECD requires an equilibration time of 5 minutes while the



TSCA proposed standard requires an equilibrium time of  one hour




for most chemicals and 16 hours for surfactants.   Equilibration



time is discussed in section  2.3.2. and also has been discussed



in section 4.






     OECD indicates that the  reproducibility is in general




+_ 3 percent.  However, no data are given to substantiate this



finding.  A thorough literature search has been made  and no data




have been published which have established the precision of Kow



for a large number of chemicals.  Hence, no precision is




specified in the TSCA proposed test standard.  The statistical



analysis of the data is discussed in section 2.5.
                                34

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                                117
8.         REFERENCES
Carlson RM, Carlson RE, Kopperman  HL.   1975.   Determination of
partition coefficients by  liquid chromatography.   J.
Chromatogr.  107:219.

Chiou CT, Freed VH, Schmedding  DWf  Kohnert  RL.   1977.   Partition
coefficient and bioaccumulation of selected organic  chemicals.
J. Environ. Sci. Tech.  11:475.

Craig LC , Craig D.   1950.   In:  Technique  of  organic  chemistry,
Vol. Ill, pt. I, Chapter 4.  New York:   Interscience Publishers,
Inc.

Davies JE, Barquet A, Freed  V,  Haque  R,  Morgade  C, Sonneborn RE,
Vaclavek C.  1975.  Human  poisonings  by a fat-soluble  organo-
phosphate insecticide.  Arch. Environ.  Health  30:608.

Enviro Control, Inc.  1980.  Cost  analysis  methodology and
protocol estimates; Environmental  Review Division  standards.
Rockville, Md., Enviro Control, Inc.,  Borriston  Laboratories,
Inc.

USEPA.  1975.  U.S. Environmental  Protection Agency.   Office of
Pesticide Programs.   Proposed guidelines for registering
pesticides in the United States.   Fed.  Regist.  1975  40,  26802.

USEPA.  1978.  U.S. Environmental  Protection Agency, Office of
Pesticide Programs.   Proposed guidelines for registering
pesticides in the( United States.   Fed.  Regist.   1978 43,  29696.

Fujita T, Iwasa J, Hansch  C.  1964.   A new  substituent constant,
derived from partition coefficients.   J. Am. Chem. Soc.  86:5175.

Glasstone S.  1946.   Textbook of physical chemistry.   New York:
Van Nostrand Co.

Gould RF ed.  1972.   Biological correlations—the  Hansch
approach.  Adv. Chem. Ser. No.  114.   Washington, D.C.:  American
Chemical Society.

Hansch C.  1969.  A quantitative approach to biomedical
structure-activity relationships.   Ace.  Chem.  Res. 2:232.

Hansch C, Anderson SM.  1967.   The effect of intramolecular
hydrophobia bonding on partition coefficients.   J. Org.  Chem.
23:2583.
                                35

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                                118
Hansch C, Fujita T.  1964.    p-ot-ir anaysis. A  method  for the
correlation of biological activity and  chemical  structure.   J.
Am. Chem. Soc. 86:1616.

Hansch C, Leo A.  1979.  Substitueht  constants for  correlation
analysis in chemistry and biology.  New York:  J. Wiley & Sons.

Hulshoff A, Perrin JH.  1976.  A comparision of  the determination
of partition coefficients of  1,4-benzodiazepines by high-
performance liquid chromatography and thin-layer
chromatography.  J. Chromatogr. 129:263.

Karickhoff SW, Brown DS.  1979.  Determination of octanol/water
distribution coefficients, water solubilities, and
sediment/water partition coefficients for hydrophobic organic
pollutants.  EPA-600/4-79-032.

Karickhoff SW, Brown DS, Scott TA.  1979.   Sorption of
hydrophobic pollutants  on natural sediments.   Water Res.  13:241.

Leo A, Hansch C, Elkins D.  1971.  Partition coefficients and
their uses.  Chem. Rev. 71:525.

Lu PY, Metcalf RL.  1975.  Environmental fate  and
biodegradability of benzene derivatives as  studied  in a model
aquatic ecosystem.  Environ.  Health Perspect.  10:269.

Mackay D.  1979.  Finding fugacity feasible.   Environ.  Sci.  Tech.
13:1218.

Metcalf RL, Sanborn JR, Lu PY, Nye D.   1975.   Laboratory model
ecosystem studies of the degradation  and fate  of radiolabelled
tri-, tetra-, and pentachlorobiphenyl compared with DDE.   Arch.
Environ. Cont. 3:151.

McCall JM.  1975.  Liquid-liquid partition  coefficients by high-
pressure liquid chromatography.  J. Med. Chem.  18:549.

Mirrless MS, Moulton SJ, Murphy CT, Taylor  PJ.   1976.   Direct
measurement of octanol-water  partition  coefficients by high-
pressure liquid chromatography.  J. Med. Chem.  19:615.

Neely WB, Branson DR, Blau GE.  1974.   Partition coefficient to
measure bioconcentration potential of organic  chemicals in
fish.  Environ. Sci. Tech. 8:113.

OECD-Chemicals Testing  Program.  1978.  Draft  test  protocol for
the determination of the partition coefficient of solid and
liquid substances in the system water/n-octanol.

Veith GD, Morris RT.  1978.   A rapid  method for  estimating log P
for organic chemicals.  EPA-600/3-78-049.
                                36

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                                 119
Veith GD, Austin NM, Morris  RT.   1979.  A  rapid  method  for
estimating log P for organic chemicals.  Water Res.  13:43.

Yamana T, Tsuja A, Miyamoto  E, Kubo  O.  1977.  Novel method for
determination of partition coefficients of penicillins  and
cephalosporins by high-pressure  liquid chromatography.   J.  Pharm.
Sci. 66:747-
                                 37

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              121
SOIL THIN LAYER CHROMATOGRAPHY

STANDARD FOR TEST DATA DEVELOPMENT
PROPOSED RULE, SECTION $, TSCA


Refers to
Part 772 — Standards for Development of Test Data
  Subpart L.  Physical, Chemical and Environmental
            Persistence Characteristics
    Section 772.122-5  Soil Thin Layer Chromatography
October 1980

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                             123
                             CONTENTS


                                                           Page

1.    NEED FOR THE TEST	  1

2.    SCIENTIFIC ASPECTS OF SOIL LEACHING	  2

     2.1.  Introduction	  2

     2.2   Basic Processes Affecting Soil Leaching	  2

     2.3   Chemical Properties Affecting Leaching	  4

     2.4   Soil Properties Affecting Leaching	  4

     2 . 5   Types of Adsorptive Forces	  7

     2.6   Surface Transformations	  8

3.    ECONOMIC ASPECTS	 11

4.    SCIENTIFIC ASPECTS OF THE TEST	 12

     4.1   Development of Soil Thin Layer
           Chromatography (TLC)	 12

     4.2   Rationale for the Selection of Soil TLC	 15

     4.3   Rationale for Selection of Experimental
           Conditions and Procedures	 17

     4.4   Replies to Federal Register	 20

5 .    TSCA/FIFRA/OECD COMPARABILITY	 23

6.    REFERENCES	 24

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                                125
1.       NEED FOR THE TEST






     Leaching of chemicals through  soil  is  an important process



which affects a chemical's distribution  in  the environment.   If a



chemical is tightly adsorbed  to  soil  particles,  it will not  leach



through the soil profile but  will remain on the  soil  surface.   If



a chemical is weakly adsorbed, it will leach through  the soil



profile and may reach ground  waters and  then surface  waters.



Knowledge of the leaching potential is essential under  certain



circumstances for the assessment of the  fate of  chemicals in  the



environment.






     Chemical leaching  also affects the  assessment of ecological



and human health effects of chemicals.   If  a chemical reaches



ground water, deleterious human  health effects may arise due  to



the contamination of drinking water.  If a  chemical remains  at



the soil surface, deleterious environmental and  human health



effects may arise due to an increased concentration of  the



chemical in the zone of plant growth, possibly resulting in




contamination of human  food supplies.






     Soil thin layer chromatography (TLC) is a qualitative



screening tool suitable for obtaining an estimate of  chemical's



leaching potential.  This test is the first of several  tests



which will be used in obtaining  a rough  estimation of a



chemical's leaching potential and is  the test most amenable  to



standardization at the  present time.

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                                 126
2.       SCIENTIFIC ASPECTS OF SOIL LEACHING
2.1.     Introduction
     Since chemical leaching in soils is affected by  a  large
number of interacting processes, this section of the  support
document will discuss these processes as they relate  to this
phenomenon .

2.2.     Basic Processes Affecting Soil Leaching

     As it occurs in the real world, leaching through soil  is  a
complex phenomenon consisting of several major processes (Hamaker
1975).  These processes are operative in the soil TLC method and
will be discussed in detail below.

     The general equation  (Guenzi 1974) for chemical  movement
through porous media under steady state soil-water  flow
conditions is :

              --

where    B =  soil bulk density  (g/cm^)
         0 =  volumetric water content  (cm  'cm  '
         S =  amount of chemical adsorbed at  the
              soil/water interface  (g/g  soil).
         t =•  time ( sec. )
         C'=  solution concentration of  chemical
         D'=  dispersion coefficient (cm /sec)

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                                  127






         V =  average pore-water velocity  (cm/sec)



         X =  space coordinate measured  normal  to the



              section






     Most mass transport equations  represent  simplifications  of



"real world" conditions.  Equation  1  and similar mathematical



expressions try to describe the chromatographic distribution  of



the chemical in the soil profile and  are gross  simplifications  of



a phenomenon affected by a number of  complex  interacting



processes including but not limited to precipitation,



evaporation, evapotranspiration and hydrodynamic dispersion.






     In general, chemical leaching  is dependent upon three major



processes: the mass transport of water   (the  direction  and rate,



of water flow), diffusion, and the adsorption  characteristics  of



the chemical in soil  (Guenzi 1974).   Diffusion  is the transport



of matter resulting from random molecular  motion caused by



molecular thermal energy.  This random motion will  lead to the



uniform distribution of molecules in  a closed system since there



is net movement from regions of higher to  lower concentrations.



In this document, adsorption refers to the equilibrium



distribution of a molecule between  a  solid phase and a  solution



phase.  As the degree of adsorption increases the concentration



of the chemical in the soil water and the  soil  air  decreases.



This equilibrium process is governed  by  two opposing rate



processes.  The adsorption rate is  the rate to  which molecules



from the liquid phase transfer into the  adsorbed state  in the



solid phase.  The desorption rate is  the opposite process,  i.e..

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                                   128
the rate at which molecules transfer  from  the  adsorbed  state in



the solid phase into the liquid phase.   In general,  the mass



transport, diffusion, and adsorption  processes produce  the



observed leaching pattern of a chemical  in soil.








2.3.     Chemical Properties Affecting Leaching





     The main process of the three processes discussed  above



which determines a chemical's leaching potential  (as described



mathematically in equation 1) is adsorption.   Adsorption is



governed by the properties of both the adsorbent  and the



adsorbate.  The important properties  of  the absorbate affecting



adsorption by soil colloids (Bailey and  White  1970)  are:   (1)



chemical structure and conformation (2)  acidity or basicity  of



the molecule (pka or pkb), (3) water  solubility.  (4)  permanent



charge,  (5) polarity. (6) molecular size,  and  (7) polariz-



ability.  There are many ways in which each of these adsorbate



properties interact and are manifested in  the  overall adsorption



reaction (Bailey and White 1970).








2.4.     Soil Properties Affecting Leaching






     Soil is the unconsolidated organic  and mineral  material on



the immediate surface of the earth which serves as a natural



medium for the growth of plants.  The combined actions  of



climate, microorganisms and macroorganisms over long periods of



time on different parent geologic and bio£ic materials  form  soils



that differ widely in their physical, chemical, and  morphological

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                                    129
characteristics.  The wide variations  in  the  amounts  and types of



clay and organic matter, soil pH, primary and secondary minerals,



structure, texture, and exchange  capacity create  soils  of



substantial heterogeneity within  the United States.   There  are



currently 10 Soil Orders, at least  43  Suborders,  over 200 Great



Groups and over 7,000 soil series recognized  in the United  States



(Buckman and Brady 1969).  The  test rule  will specify the minimum



number of soils depending on the  number of sites  of manufacture,



distribution, use, and disposal of  the test chemical.   The  soil



physical/chemical property ranges for  pH,  organic matter and



cation exchange capacity will be  specified so that soils used in



the TLC method will be representative  of  U.S.  humid and semiarid



region mineral soils.






     The soil properties affecting  the adsorption and desorption



of organics include organic matter  content, type  and  amount of



clay, exchange capacity, and surface acidity  (Adams 1973; Bailey



and White 1970; and Helling 1970).  Soil  organic  matter is  a



primary soil parameter responsible  for the adsorption of many



pesticides.  Helling  (1970) lists many examples where the organic



matter primarily influenced the adsorption of pesticides.



Although organic matter and clay  are the  soil components most



often implicated in pesticide adsorption,  the individual effects



of either organic matter or clay  are not  easily  ascertained.



Since the organic matter in most  soil  is  intimately bound to the



clay as a clay-metal-organic complex  (Stevenson  1973),  two  major



types of adsorbing surfaces are normally  available to the



chemical, namely, clay-organic  and  clay alone.  Clay  and organic

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                                    130






matter function more as a unit than as separate  entities  and the




relative contribution of organic and inorganic surfaces to



adsorption will depend on the extent to which the  clay  is coated




with organic substances.  Comparative  studies between known clay




minerals and organic soils suggest that most, but  not all,



pesticides have a greater affinity for organic surfaces than for



mineral surfaces (Stevenson 1973).  Since typical  soil  studies




compare soils in which both clay and organic matter  increase and



do not utilize multiple regression analyses to isolate  the



governing parameter (Helling 1970), only generalizations




concerning the relative importance of  clay and organic  matter can



be made.






     The activity of protons in the bulk suspension  (i.e.,  as



measured by pH) and the activity of protons at or  in close



proximity to the colloidal surface (i.e., the acidity in  the




interfacial region) may differ significantly.  The term "surface



acidity" as applied to soil systems is the acidity at or  in close




proximity to the colloidal surface and reflects  the  ability of




the system to act as a Lewis acid.  Surface acidity  is  a



composite term which reflects both the total number  of  acidic



sites and their relative degree of acidity.  Surface acidity is




probably the most important property of the soil or  colloidal



system in determining the extent and nature of adsorption of




basic organic chemicals as well as determining if  acid-catalyzed



chemical transformation occurs (Bailey and White 1970).   There  is




overwhelming evidence, mainly from infrared studies, pointing to




the fact that there is protonation of  basic chemicals by  clays

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                                    131
having hydrogen and aluminum  as  the  predominant exchangeable



cation and by clays saturated with alkali,  alkaline  earth,  and



transition metal cations.  A  summary of  recent investigations



indicates that the protonation of chemicals in the  interfacial



region of clays is a  function of the basicity of the molecule,



the nature of the exchangeable cation on the clay, water  content



of the clay system, and  the origin of negative charge in  the



aluminosilicate clay  (Bailey  and White 1970).






     In summary, the  chemical properties discussed  in (c)  and the



soil properties discussed  in  (d) both govern the extent of



adsorption in soils.








2.5      Types of Adsorptive  Forces






     The specific type of  interaction of organic molecules with



soil will depend on the  specific chemical properties of the



organic molecule and  the type of soil.  These specific



interactions or adsorptive forces are usually classified  as:  van



der Waals forces, charge transfer, ion exchange,  and hydrophobic



bonding (Adams 1975,  Goring and  Hamaker  1972).






     The van der Waals forces arise  from the fluctuations  in a



molecule's electron distribution as  the  electrons circulate in



their orbitals.  These fluctuations  produce instantaneous  dipoles



which cause that molecule's attraction to other atoms and



molecules.  Charge transfer involves the formation of a  donor-



acceptor complex between an electron donor  molecule  and  an



electron acceptor molecule with  partial  overlap of their

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                                 132
respective molecular orbitals and a partial  exchange  of  electron



density.  Hydrogen bonding is an example of  a particular type  of



charge transfer.  Ion exchange refers to the exchange between



counterions balancing the surface charge on  the  soil  colloid and



the ions in the soil solution.  The driving  force  for this



interaction is the requirement for electroneutrality:  the



surface electric charge must be balanced by  an equal  quantity  of



oppositely charged counterions.  In general, ion exchange is



reversible, diffusion controlled, stoichiometric and, in most



cases, exhibits some selectivity or preferential adsorption for



one ion over another competing ion.  Hydrophobia bonding refers



to the preference of an organic molecule for a hydrocarbon



solvent or hydrophobia region of a colloid over  a  hydrophilic



solvent.  This preference is due to the fact that  hydrocarbon



regions of a molecule have greater solubility in liquid



hydrocarbons (or most organic solvents) than in water. In



general, one or more of these specific interactions or adsorptive



forces may occur at the same time depending  on the presence and



magnitude of the chemical and soil properties discussed  above.








2.6.     Surface Trans formations
     A special type of interaction between organic molecules  and



soils deals with the transformation of organic  chemicals  into new



compounds containing different chemical  structures through the



catalytic activity of the soil colloid surfaces. Although several



theories exist to account for the mechanism  of  these



transformations, no scheme predicting the occurrence  of such
                                8

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                                 133
surface reactions presently  exists.   Therefore,  parent compound



mass balances shall be performed  and  reported  as part of the



requirements of this soil TLC  Test  Standard  in order to ascertain



the extent of such transformations  during  soil leaching experi-



ments.  Also, the leaching pattern  (a diagram  or photograph of



the TLC plate showing the position  of the  chemical)  can give a



qualitative indication of the  extent  of  such transformations and



shall be reported.  The  scientific  literature  shows  that a  number



of chemicals and chemical classes undergo  colloid surface induced



chemical transformations.  Poly-(dimethylsiloxane)  fluids in



intimate contact with many soils  undergo siloxane bond redistri-



bution and hydrolysis, resulting  in the  formation of low mole-



cular weight cyclic and  linear oligomers (Buch and Ingebrightson



1979)-  S-triazines (White 1976)  and  organophosphorus pesticides



(Yaron 1978, and Mingelgrin  et al.  1977) undergo clay colloid



induced hydrolysis.  Benzene and  phenol  polymerize into high



molecular weight species by  adsorption and reaction  at the



surface of smectite saturated  with  transition  metal  cations



(Mortland and Halloran 1976).  Gallic  acid, pyrogallol,



protocatechuic acid, caffeic acid,  orcinol,  ferulic  acid,  p-



coumaric acid, syringic  acid,  vanillic acid  and p-hydroxybenzoic



acid undergo oxidative polymerization in the presence of various



clay minerals (Wang and  Li 1977 and Wang et  al.  1978).   In



general, testing methods that  do  not  take  into account surface

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                                 134
transformations should not be used in determining  the  leaching




potential of chemicals.






     In summary, the interfacial region is  important in




determining the adsorption mechanism, the energy by which  the



adsorbate is held, and in determining if the adsorbed  chemical is




transformed.  This information is important in determining the



persistence and ultimate toxicity of the molecule  since  the



transformation product(s) (1) may be more or less  toxic  than the



original compound, (2) may be more or less  tightly bound than  the



original compound, and (3) may have a water solubility either



greater than or less than the original compound, thereby




affecting its leaching and movement into the groundwater.
                                10

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                                  135


3.       ECONOMIC ASPECTS


     A survey of commercial  laboratories  to estimate costs for

performing the test outlined  in  this  standard  found a range of

$390-$850 with a "best  estimate"  of  $620.   A cost  estimate also

was made by separating  the standard  into  components and

estimating the cost of  each  component including direct labor

cost, overhead cost, other direct costs general and admini-

strative costs and profit or  fee.  The best estimate of cost was

$344 with an estimated  range  of  $172  to $516.   An  analysis of the
                    T
discrepancy between the price estimate and  survey  pointed out

that the nature of the  method of analysis,  after solvent

migration, has an impact on  the  cost  of analysis.   Different

methods will cause variations in cost.  Also,  the  price estimate

does not include costs  for any analytical work which may be

necessary before the test can be performed.  In practice,  testing

laboratories receive chemicals in a  pure  form,  and most identi-

fication and analytical methodology  has already been developed.

Extraction, GC, MS, etc. methodology may  be necessary,  however,

and it is estimated that this would  cost  less  than $1000 for 90

percent of the chemicals tested.


     The above cost estimates were made assuming that all the

requirements of Good Laboratory  Practice  Standards (GLPs) are

being satisfied.  Details of  the cost estimate are contained in a

report by Enviro Control, Inc. (1980).
                                11

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                                  136
4.       SCIENTIFIC ASPECTS OF THE TEST








4.1.     Development of Soil Thin Layer Chromatography (TLC)






     Before 1968, methods of investigating  the  mobility of



nonvolatile organic chemicals within  soils  were based  on the  use




of field analysis, soil adsorption isotherms, and  soil columns.




In 1968, Helling and Turner introduced soil thin layer



Chromatography  (soil TLC) as an alternate procedure.   It is



analogous to conventional TLC, with the use of  soil  instead of



silica gels, oxides, etc. as the adsorbent  phase.






     In their initial report. Helling and Turner used  Lakeland



sandy loam, Chillum silt loam, and Hagerstown silty  clay loam.




Medium sand (>250 pm dia.) was removed from Chillum  and



Hagerstown soils and coarse sand (>500  um  )  from  Lakeland soil



by dry-sieving.  Aqueous slurries were prepared and  500 um (silt




loam, silty clay loam) or 750 um (sandy loam) thick  layers were



spread on TLC plates using conventional TLC apparatus.  After



drying, six or  seven radiolabelled pesticides were applied near




the base of a 20 x 20 cm plate and developed ten cm  with water by




ascending Chromatography.  Pesticide  movement was  visualized  by



autoradiography.  Movement was expressed by the conventional  R




designation, although this referred to the  front of  pesticide



movement rather than its maximum concentration.  The soil TLC




data are most appropriately compared  with other mobility data



which indicate  the depth to which an  organic chemical  may be
                                12

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                                  137






leached.  The ranking of pesticides  in  order  of mobility is in



good agreement with general  trends previously reported.






     Absolute movement on  soil  TLC plates  cannot be transposed



directly to field or soil  column  experiments.  Since soil



structure in the TLC system  is  considerably more homogeneous that



in most other systems, band  spreading will be somewhat  less than



in field or column regimes.   Flow rates are also higher  than



those occurring naturally.   For example, infiltration into



Hagerstown silty clay loam was  equivalent  to  rainfall of about



1.2 cm/hr (Helling 1970).  High flow rates are usually associated



with increased mobility, as  later correlations (Helling  1968)



bore out. In spite of these  problems, monitoring data utilizing



certain reference chemicals  has provided the  necessary infor-



mation to relate soil TLC  data  to column and  field  data.   In



general, Helling and Turner  (1968) indicated  that soil TLC



offered a rapid, simple, and inexpensive procedure  for



establishing a general mobility classification of pesticides and



organic chemicals.






     Simple chromatographic  theory can  be  used to correlate




adsorption coefficients with soil TLC R£ values.   If



chromatographic movement through  a soil column is treated



according to the distillation theoretical  plate theory  (Block et



al. 1958, Martin and Synge 1941), a  formula for Rf is obtained in



terms of the relative cross-sectional areas of the liquid and



solid phases and partition of a chemical between solid  and liquid




phases  (Hamaker 1975):
                                13

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                                   138
        Rf = AL/(AL + AS) = i/[(i+ a  (AL + AS)]        (2)

where As and AL are cross-sectional areas of solid and  liquid
phases and a is the ratio of volume concentration in  the  solid
phase to that in the liquid phase . For saturated conditions which
will be assumed for a soil plate, AL + As = A  (cross-sectional
area), this can be written:
        Rf = i/[(i  + a (A/[AL - i])]                    (3)

     When reexpressed in terms of the pore  fraction of the
soil 6, density of soil solids (ds), and a  soil adsorption
coefficient K, this equation becomes:
        Rf =f(i + K(ds)(i/e-i)]-                    (4)

     This ratio, A/AL, is set equal to 1/6 '  by analogy  to  the
treatment of soil diffusion by Millington and Quirk  (1961) where
it serves to correct for the tortuosity of flow through the
porous medium.  In this case, it serves to relate  the  pore volume
to the cross sectional area of the liquid phase in a saturated
soil.  In general, equation 4 has shown that an inverse
relationship exists between the soil adsorption coefficient  K and
Rf (Hamaker 1975) .
                                14

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                                139
     Riley  (1976) presented a general  relationship between the



soil/solution distribution coefficient K  and  the  depth of



pesticide leaching.  Relating the  data of Riley (1976) with the



Rf values of Helling (1968, 1971a,  1971b,  1971c)  and the average



K values of Goring and Hamaker  (1972)  for selected pesticides,



the general relationship  shown  in  Table 1 was developed between



the soil/solution partition coefficient,  Rf,  and  soil mobility.








4.2      Rationale for Selection of Soil  TLC






     A number of laboratory tests,  the soil thin  layer



chromatography, soil adsorption isotherm,  and soil columns have



been developed to obtain  an estimate of a chemical's leaching



potential (Hamaker 1975).  Soil TLC is the first  of several tests



with will be recommended  for use.   It  is  the  least expensive of



the available tests which measures  leaching potential,is widely



used, and is the test most amenable to standardization at the



present time.





     The soil TLC offers  many desirable features.   First,



mobility results are reproducible.   Mass  transfer and diffusion



components are distinguishable.  The method has relatively modest



requirements for chemicals, soils,  laboratory space,  and



equipment.  It yields data that are amenable  to statistical



analyses.  A chemical extraction-mass  balance procedure to elicit



information on degradation and  chemical transformations occurring



at colloid interfaces can be incorporated into this test.   The




ease with which the Rf and mass balance are performed will depend
                                15

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Table 1.  The General Relationship Between the Soil/Solution




          Partition Coefficient K, R  and Soil Mobility
K Rf Mobility class
0.1 	 	 0.95 Very Mobile 	
1 	 0.60 	
10 	 0.25 Mobile 	
10^.. 	 	 	 0.10 Low mobility 	
102-5 	 0.00 	
103 	 0.00 	
104 	 0.00 Immobile 	
Distance surface applied chemical may leach

Much of chemical leaches through top 20 cm soil
into subsoil
. . Much of chemical leached Into soil but peak
concentration in top 20 cm soil.
. . Only small amount of leaching and peak
concentration normally In top 5 cm soil

No siqnificant leachinq.

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                                  141






upon the physical/chemical properties  of  the  test  chemical  and




the availability of suitable analytical techniques for  measuring



the chemical.








4.3.     Rationale for Selection  of Experimental Conditions



         and Procedures






     The papers by Helling  (1968,  1971a,  1971b,  1971c)  and



Helling and Turner (1968) were the basis  of this test standard.



The soil and colloid chemistry literature and the  analytical



chemistry literature substantiates the experimental conditions



specified in the suggested  standard as accepted, standard



procedures.  A few of these conditions will be discussed in



greater detail below.





     Soil TLC can be used to determine the soil mobility of



sparingly water soluble  to  infinitely  soluble chemicals.   In



general, a chemical having  a water solubility of less than  0.5



ppm need not be tested since the  literature indicates that  these



chemicals are, in general,  immobile  (Goring and  Hamaker,  1972).



However, this does not preclude  future soil adsorption/transfor-



mation testing of these  chemicals if more refined  data  are  needed




for the assessment process.






     Soil TLC may be used to test the  mobility of  volatile



chemicals by placing a clean plate over  the  spotted soil  TLC



plate and then placing both plates in  a  closed chromatographic




chamber.
                                17

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                                   142
     Soil TLC was originally designed  for  use with  soils.   The



literature shows no published use of this  method with  sediments



as the adsorbent phase, probably due to the  fact that  sediment



surface properties change significantly during  air  drying.   The



TLC plate with the adsorbent must be air dried  before  leaching



studies can be undertaken.





     The Test Rule will specify the minimum  number  of  soils to be



tested.  This number will depend upon  the  number of sites  of



manufacture, distribution, use, and disposal of the test



chemical.  Since there are currently 10 recognized  soil orders in



the United States containing soils with wide variations in the



amounts and types of clay, organic matter, pH,  primary and



secondary minerals, structure, texture, and  exchange capacity the



inclusion of a requirement to test soils representing  each major



order  for each chemical would make this standard prohibitively



expensive.






     Distilled-deionized I^O is required in  order to minimize



competition effects for soil exchange  sites  by  cationic and



anionic species normally present in tap and  distilled  H^O.





     The purity of the test chemical will  be specified in  the



test rule.  In general, however, the test  chemical  should  be of



the purest grade available.  Impurities may  produce migration



patterns on the TLC plate independent  of the parent chemical and



may be misinterpreted as transformation products.   Transformation



product identification is an expensive analytical procedure that
                                18

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                                 143






may be unnecessarily required  as  a  result  of  the presence of



impurities.






     The sieving of soils will remove  the  coarse (500-2,000 ym )



and medium (250-500 ym  ) sand  fractions.   Published"testing



results showed that removal of a  portion of sand had no affect on



the mobility of a test  compound but aided  in  achieving  a more



cohesive uniform soil layer and more reproducible results



(Helling 1971a).






     Gentle crushing and grinding must be  used  to reduce soil



aggregate size.  Fine particles (silt  and  clay)  in excess of the



amount originally present may  be  created if excessive pressure is



exerted on the aggregates.






     Application of the soil slurry to clean  glass plates must be



done quickly to prevent particle  size  segregration.   A  specific



method of soil slurry application was  not  identified since a



number of methods which produce the acceptable  layer thickness



are in use today.






     Replication of the basic  experimental unit was necessary  in



order to estimate the standard deviation of the treatment mean.



Three replicates are considered to  be  the  minimum number of



replicates for a statistically acceptable  estimation.  The soils



literature indicates that, in  general, the standard deviation




should be less than 0.01 Rf units for  soil TLC.





     Since the available literature indicated that pesticide



mobility on soil TLC plates did not significatly change when






                                19

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                                  144







temperature varied from 2° to 25°C  (Helling 197la), only  a  room




temperature range was suggested.






     The Soil Order, Series, and general clay fraction mineralogy




data may be found in Soil Survey Reports published after



approximately 1970.  Pre-1970 reports may not contain mineralogy




data.  Soil Survey Reports have been issued for most U.S.



counties and may be obtained from County Extension Offices;  the




State Office of the U.S. Department of Agriculture Soil



Conservation Service; or the USDA-Soil Conservation Service,



Publications and Information Division, P.O. Box 2890, Washington,



DC 20013.  If mineralogy data are not printed in  a report,  the



State Office of the U.S. Department of Agriculture Soil



Conservation Service may be contacted for assistance in obtaining



general clay mineral data of a particular soil.   The test



standard does not require test soil mineral analysis since




general clay mineralogy data may already exist for the test soil.








4.4.    Replies to Federal Register of March 16,  1979






     The Federal Register of March  16, 1979  (EPA  1979) presented



a discussion of policy issues, alternative approaches, and  test



methods under consideration for premanufacture testing.   Included




in the test methods was a soil thin  layer chromatography  test



method (pgs. 16257-16264).  Several  comments received on  this



method will be discussed in this section.






     One commentor suggested that it  is not possible to determine




the adsorption coefficients of organic compounds, having






                                20

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                                  145






solubilities less than 0.05 ppm, with any degree of accuracy.



Therefore, a 0.5 ppm solubility limit has been adopted  in  the



soil TLC test standard.






     Several commentors stated that the 95%  extraction  efficiency



in the mass balance section of the March 16,  1979, standard  is



too stringent and too costly to implement.   An 80 percent



extraction efficiency has been adopted in response to this



comment and is believed to be a more reasonable indicator  of a



chemicals propensity to transform.






     One commentor suggested that the high pressure liquid



chromatography technique HPLC be adopted instead of the soil TLC



for soil mobility testing.  Sections 2.3., 2.4., and  2.5.  of this



support document indicate that hydrophobia bonding is an



important effect governing soil mobility, but is not  the only



effect that must be considered for all chemicals.  HPLC measures



only the hydrophobia bonding potential of a  neutral organic



chemical.  Also section 2.6. indicates that  surface



transformations may occur but no scheme to predict the  occurence



of these reactions presently exists.  HPLC does not measure  this



effect.  For these reasons, the suggestion was not adopted.






     Several commentors stated that the use  of soil as  the



adsorption medium is impractical.  A substitute adsorbent such as



carbon, clay, humic substances, oxides, and  silica and/or alumina



plates could be used with  several  solvents  of different



polarity.  This suggestion was  not adopted  for  several  reasons.



First, water is the liquid  environmental  transport media of





                                21

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                                    146
concern.  Use of  different solvents would give  little insight

into the mobility of  chemicals in soils.  Second,  section 2.4.,

2.5., and 2.6.  of this  document indicate that soil is a

heterogeneous mixture of numerous inorganic and  organic phases.

The published literature does not substantiate  the use of one

substitute adsorbent  as an adequate replacement  for soils during

mobility tests.   Third, the literature does not  indicate how data

derived from these adsorbents can be extrapolated  to soils.
                                 22
                                              4 U. S. GOVERNMENT PRINTING OFFICE : 1880 341-085/3932

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                                   147






5.      TSCA/FIFRA/OECD COMPARABILITY






     Leaching data are required to  support  the  FIFRA  registration




of all formulated products intended  for  terrestrial noncrop,  tree




fruit/crop, and field/vegetable crop uses,  and  for




terrestrial/aquatic  (forest) uses.   One  preferred technique  to




support registration is soil TLC.   Data  derived for the  Office of




Pesticide Programs will be accepted  under TSCA  provided  chemical




mass balance data is submitted and  soil  physical/chemical




property guidance as discussed in the  test  rule have  been met.






     The Organization for Economic  Cooperation  and  Development




recognizes the importance of determining the  mobility of a




chemical in soils to assess the potential risk  to man and the




environment due to the manufacture,  distribution, use,  and




disposal of chemical products.  The  soil adsorption isotherm was




identified by OECD as a potential method for  determining the




leaching potential of chemicals in  soils.   This test  will be




proposed as a standard method in the future.
                                23

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                                   148





6.         REFERENCES








Adams Jr. RS.  1973.  Factors influencing  soil  adsorption and




bioactivity of pesticides. Residue Rev. 47:1-54.








Bailey GW, White JL.  1970.  Factors  influencing  the  adsorption,




desorption and movement of pesticides  in soil.  Residue  Rev.




32:29-92.








Block RJ, Durrum EL, Zweig G.  1958.   A manual  of paper




chromatography and paper electrophoresis.  Second Edition.



Academic Press, N.Y.








Buch RR, Ingebrigtson DN.  1979.  Rearrangement of poly-



(dimethyl/siloxane) fluids on soil.   Environ. Sci and Technology



13:676-679.








Buckman HO, Brady NC.  1969.  The nature and  properties  of




soils.  London:  The Macmillan Company








Enviro Control, Inc.  1980.  Cost analysis methodology and




protocol estimates:  environmental standards.   Submitted to the



Office of Regulatory Analysis, U.S. Environmental Protection



Agency,  Washington, DC
                                24

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                                  149







Goring CAI, Hamaker JW eds.  1972.  Organic chemicals in the soil




environment.  Vol. I & II.  New York:  Marcel Dekker, Inc.








Guenzi WD ed.  1974.  Pesticides in soil and water.  Madison, WI:




Soil Science Society of America, Inc.








Hamaker JW  1975.  The interpretation of soil leaching




experiments.  In Haque R and Freed VH eds.  Environmental  science




research Vol. 6:  Environmental dynamics of pesticides.








Helling CS  1968.  Pesticide mobility investigations using soil




thin-layer chromatography.  Amer. Soc. Agron. Abstracts p.   89.








Helling CS, Turner BC.  1968.  Pesticide mobility: Determination




by soil thin layer chromatography.  Science 162:562.








Helling CS.  1970.  Movement of s-triazine herbicides in  soils.




Residue Review 32:175-210.








Helling CS.  1971a.  Pesticide mobility in soils  I.  Parameters




of soil thin layer chromatography.  Soil Sci. Soc. Amer.  Proc.




35:732-737-








Helling CS.  1971b.  Pesticide mobility in soils  II.




Applications of  soil thin  layer chromatography.   Soil Sci. Soc.




Amer.  Proc.  35:737-743.
                                25

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                                  150
Helling CS.  1971c.  Pesticide mobility in soils  III.   Influence




of soil properties. Soil. Sci. Soc. Amer. Proc.   35:743-748.








Martin AJP , Synge RLM.  1941.  A new form of chromatogram




employing two liquid phases.  Biochem. J. 35:1358.








Millington RJ and Quirk JP  1961.  Permeability of porous solids.




Trans. Faraday Soc. 57:1200.








Mingelgrin U, Saltzman S, Yaron B.  1977.  A possible model  for




the surface induced hydrolysis of organophosphorus pesticides  on



kaolinite clays.  Soil Sci. Soc. Amer. Jour. 41:519-523.








Mortland MM, Halloran LJ.  1976.  Polymerization  of aromatic



molecules on smectite.  Soil Sci. Soc. Amer. Jour. 40:367-370.








Riley D.  1976.  Physical loss and redistribution of pesticides



in the liquid phase.  In:  British Crop Protection Council



Symposium Proceedings, p. 109-115.








Shearer RC, Letey J, Farmer WJ, Klute A.  1973.   Lindane




diffusion in soil.  Soil Sci. Soc. Amer. Proc. 37:189-193.








Stevenson FJ.  1973.  Organic matter reactions involving




pesticides in soil.  In Bound and conjugated pesticide




residues.  ACS Symposium Series Monograph 29/1976.
                                26

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                                   151






Wang TDC, Li,SW.  1977.  Clay minerals as heterogeneous  catalysts




in preparation of model humic substances.   Z. Pflanzenernaehr.



Bodenkd. 140:669-676.








Wang TSC, Li SW, Ferng YL.  1978.  Catalytic polymerization  of




phenolic compounds by clay minerals.  Soil  Sci.  126:15-21.








White JL.  1976.  Determination of susceptibility  of  s-triazine




herbicides to protonation and hydrolysis by mineral surfaces.




Arch. Environ. Contain. Toxicol. 3:461-469.








Yaron B.  1978.  Some aspects of surface interactions of clays




with organophosphorus pesticides.  Soil. Sci. 125:210-216.
                                27

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S0272-101	
 REPORT DOCUMENTATION
        PAGE
                                                153
                      1. REPORT NO.
                       EPA 560/11-80-02?
                                                                     3. Recipient's Accession No.
  Title and Subtitle
  Support Document,  Test Data Development  Standards, Physical/
  Chemical & Persistence Characteristics:  Density/Relative Density
  Melting Temperature,  Vapor Pressure. Octanol/Water Partition
                                                                     5. Report Date
                                                                         October 1980
                                                                    (6.
7. Authors  Coefficient, Soil Thin Layer Chromatography.
                       Geo.  T.  Armstrong. Robert H. Brink,
                                                                     8. Performing Organization Rept. No.
                                                             Asa Lei'er

9. Performing Organization Name and Address Jam6S
  U. S. Environmental  Protection Agency
  Office of Pesticides & Toxic Substances,
  Office of Toxic  Substances
  Exposure Evaluation  Division
  401 M Street.  S.W..  Washington. D.C., 20460
                                                                     10. Project/Task/Work Unit No.
                                                                     11. Contract(C) or Grant(Q) No.

                                                                     (0

                                                                     (G)
 12. Sponsoring Organization Name and Address
  U. S. Environmental Protection Agency
  401 M Street, S.W.,
  Washington, D.C.,  20/4-60
                                                                     13. Type of Report & Period Covered
                                                                     14.
 15. Supplementary Notes
  This is a Support Document to a Proposed Rule for Environmental Test Standards
  under the Toxic  Substances Control Act  (TSCA), published in the Federal Register October
 16. Abstract (Limit: 200 words)
  This technical Support Document provides  the rationale for the  development of test
  standards  to develop data on density/relative density, melting  temperature, vapor pressure
  octanol/water partition coefficient, and  soil thin layer chromatography of chemical sub-
  stances.   EPA will use the data on these  physical/chemical characteristics to evaluate
  the manner and extent of environmental  transport, fate and places of deposit as  *>n aid
  in assessing health and environmental effects of chemicals under TSCA.  For density/
  relative testing,  an analysis is given  of available methods  of  determining this  pro-
  perty of particular classes of materials  with different physical characteristics.  For
  melting temperature testing, available  methods are analyzed  in  terms of materials with
  different  physical characteristics.  For  vapor pressure, two procedures are given, the
  isoteniscope procedure for pressures of 0.1 to 100 kPa and a gas saturation (transpiration
  procedure  for pressures of 10"^ to 10*  Pa.  The Rnudsen effusion procedures are  also
  given.  How  to determine the numerical  values of the octanol/water partition coefficient
  are given.  Soil thin layer chromatography, an experimental  method for determining the
  relative mobility of ofcgsriie.'lehemicals  in soils, is discussed,  including scientific
 - aspects of soil  leaching, economic aspects of the method, and scientific history and
  the rationale for selection of experimental conditions for this method.
 17. Document Analysis  a. Descriptors
  Environmental Transport
   Environmental Exposure Pathway
                                                     Adsorption
                                                     Leaching
                                                     Soil ChemiBtry
   Chemical Tests
   Chemical Analysis
   Octanol/Water Partition Coefficient
   ta. Identifiers/Open-Ended Term*
  Density, Specific Gravity; Melting Point, Temperature;  Gas Saturation Procedure,
   Isoteniscope Procedures, Gas  Transpiration Procedures;  Bioaccumulation,  Ecological
   Concentration, Partitioning Measurement; Soil Mobility, Soil Thin Layer  Chromatography,
   Soil Tests.
   e. COSATI Field/croup Q^Q chemistry, Physical Properties
 18. Availability Statement
  This document is available for general public
  release.
                                                       19. Security Class (This Report)
                                                           none
                                                       20. Security Class (This Page)
21. No. of Pages
 ca.  200 pp
                                                                                22. Price
(See ANSI-Z39.18)
                                        See Instructions on Reverse
                                                                               OPTIONAL FORM 272 (4-77)
                                                                               (Formerly NTIS-35)
                                                                               Department of Commerce

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