United States       Prevention, Pesticides    EPA712-C-98-048
         Environmental Protection    and Toxic Substances    January 1998
         Agency        (7101)
&EPA   Fate, Transport and
         Transformation Test
         OPPTS 835.1220
         Sediment and Soil

     This guideline is one  of a  series  of test  guidelines that have been
developed by the Office of Prevention, Pesticides and Toxic Substances,
United States Environmental  Protection Agency for use  in the testing of
pesticides and toxic substances, and the  development of test data that must
be submitted to the Agency  for review under Federal regulations.

     The Office of Prevention, Pesticides and Toxic Substances (OPPTS)
has  developed this guideline through  a process of harmonization that
blended the testing  guidance  and requirements that  existed in the Office
of Pollution Prevention and  Toxics  (OPPT) and appeared in Title  40,
Chapter I,  Subchapter R of the Code of Federal Regulations  (CFR),  the
Office of Pesticide Programs (OPP) which appeared in publications of the
National Technical  Information Service (NTIS) and the guidelines pub-
lished by the Organization  for Economic Cooperation and Development

     The purpose of harmonizing these  guidelines  into a single set of
OPPTS  guidelines is to minimize variations among the testing procedures
that must be performed to meet the data  requirements of the U. S. Environ-
mental Protection Agency  under the Toxic  Substances  Control Act  (15
U.S.C. 2601) and the Federal Insecticide, Fungicide and Rodenticide Act
(7U.S.C. I36,etseq.).

     Final  Guideline Release: This guideline  is available from the U.S.
Government Printing Office, Washington, DC 20402 on The Federal Bul-
letin  Board.   By  modem  dial   202-512-1387,  telnet   and   ftp:
fedbbs.access.gpo.gov  (IP, or  call 202-512-0132 for disks
or paper copies.  This  guideline is also available electronically in ASCII
and PDF (portable document format) from EPA's World Wide Web  site
(http://www.epa.gov/epahome/research.htm) under the heading "Research-
ers and  Scientists/Test Methods and Guidelines/OPPTS  Harmonized Test

OPPTS  835.1220   Sediment  and  soil adsorption/desorption  iso-
     (a) Scope—(1) Applicability. This guideline is intended to meet test-
ing  requirements  of both  the  Federal  Insecticide,  Fungicide,   and
Rodenticide Act (FIFRA) (7 U.S.C. 136, et seq.) and the Toxic Substances
Control Act (TSCA) (15 U.S.C. 2601).

     (2) Background. The source material used in developing this har-
monized OPPTS test guideline are 40 CFR 796.2750 Sediment and Soil
Adsorption Isotherm and OECD 106 Adsorption/Desorption.

     (b) Guidance information—(1) Prerequisites. Water solubility data;
suitable analytical method; boiling point; vapor pressure curve.

     (2) Qualifying statements, (i) This method as described is not appli-
cable to substances  which are not soluble in  water to  an  extent which
can be measured analytically. It is also not applicable to compounds which
are unstable in the time scale of the test.

     (ii) Although the methods can be applied to pure and commercial
grade substances, the possible  effects of impurities on the results should
be considered.

     (3) Recommendations,  (i) It is emphasized that although three  soil
types are  broadly described  under paragraph (c)(4)(i)  of this guideline,
there is a wide variation of the  soils used in different laboratories through-
out the world and variation in  the test results is to be expected. It is not
possible to prescribe exactly the soils to be used, and experience with a
central store of so-called "standard soil" indicates that this approach also
presents problems.

     (ii) This test has promised to give preliminary information on the
soil leaching behavior of substances. Therefore, substances of known soil
leaching behavior should be investigated. For reference substances in order
to establish this possibility see paragraph (g)(4) of this guideline.

     (4) Standard documents. The  following  test guideline is based on
the references under paragraph  (g) of this guideline. Certain modifications
have been introduced to minimize the disparity in the references with re-
gard to materials used, laboratory methodology, data presentation, and data

     (c) Method—(1) Purpose, relevance, application, and limits of test.
(i) Adsorption-desorption data are necessary for the evaluation of the mi-
gratory tendency of chemicals into  the air, water, and  soil or  sediment
compartments of our environment. They are needed to estimate, for exam-
ple,  leaching   through  the   soil,  volatility  from water and  soil,
photodegradation in the adsorbed state on aerosol surfaces, and concentra-
tion in water or run-off from land surfaces into natural waters. Adsorption/

desorption processes  (=  sorption processes) of chemicals have an  effect
on transport processes and on their bioavailability. In the natural environ-
ment adsorption reduces  the concentration of a chemical in aqueous solu-

     (ii) Since  soils have varying capacities for ion-exchange as well as
differing surface areas, pH, and redox potential, interaction with chemical
substances in an aqueous system is  a complex process and cannot be com-
pletely defined by a simple testing scheme.

     (iii)  The resulting distribution between the adsorbed and solution
phase depends  upon chemical parameters, properties of the adsorbent  and
environmental parameters  such  as  temperature, the ratio of soil to  water
and  ionic strength. The  present test  method is based upon a  simplified
model  which can serve as an initial  sorption screening  test for chemical
substances. When warranted, more extensive testing can be performed to
more accurately define the effect of a specific soil or environmental vari-
able (for  instance  to obtain isotherm  data)—and these possibilities  are
pointed out in this guideline.

     (iv) The experimental procedure  measures the decrease in concentra-
tion when aqueous solutions of a chemical substance are in contact with
three different soil types at room temperature.

     (v) A CaCi2 solution (0.01 M) is used as the aqueous solvent  phase
to improve centrifugation and minimize cation exchange.

     (2) Definitions and  abbreviations,  (i) The definitions in section 3
of the  Toxic Substances  Control Act (TSCA)  and  the  definitions  in 40
CFR Part 792—Good Laboratory  Practice  Standards apply to this  test
guideline. The following definitions also apply to this test guideline.

     Soil is the unconsolidated mixed mineral and organic material of the
earth which consists  of  the  three-phase  system: Mineral and/or organic
material/water/air,  and which serves as a natural medium for the growth
of plants.

     Sediment is the  unconsolidated material deposited  at  the bottom of
natural water  and  which consists  of the phases mineral material/water/

     Adsorption in  the present method does not distinguish between  sur-
face adsorption and such processes as surface catalyzed  degradation, bulk
adsorption, or chemical reaction.

     (ii) The following abbreviations and units used in this guideline:

     a is concentration in soil blank, in milligrams per liter (mg/L).

     c is  decrease in  concentration (Q  = Ce)  in milligrams per  liter
     Ci is initial concentration (= weight of test substance/volume solution)
in milligrams per liter (mg/L).
     Ce is final concentration, in milligrams per liter (mg/L).
     Co  is  concentration in  no-soil  control,  in milligrams  per  liter
     Ce is final concentration after correction, (Ce' = a) in milligrams per
liter (mg/L).
     d is volume of solution and of each wash, in liters (L).
    / is concentration in first desorption extraction (wash),  in milligrams
per liter (mg/L).
     GA  is quantity in no-soil  control [Cid(l,000)] in  micrograms (jig).
     GD  is total quantity desorbed [(l,000)(j  +  1)] in  micrograms (jig).
     GR  is  quantity  remaining  on  soil  after  desorption  (x  - GD)  in
micrograms (jig).
     h is quantity in first wash (g x d) in milligrams (mg).
     / is quantity in v, [Ce x v(l/l,000)], in milligrams (mg).
    j is quantity desorbed by first wash (h - i) in milligrams  (mg).
     k is concentration in second wash, in milligrams per liter (mg/L).
     / is quantity in second wash (k x d) in milligrams (mg).
     m is quantity of soil (oven-dried equivalent), in grams (g).
     m is oven dried weight of soil (q = pq) in grams (g).
     p is fraction of moisture in soil.
     q is air dried weight of soil used, in grams (g).
     S is soil as described under paragraph (c)(4)(i) of this guideline.
     t is temperature at which test was run in degrees Celsius (°C).
     T is  quantity in solution at equilibrium  [Ced( 1,000)] in micrograms
     x is quantity adsorbed [(c  x d)( 1,000)] (or,  GA =  T) in micrograms

           x/m is concentration adsorbed in micrograms per gram (|ig/g).
           V is volume of solution recovered from adsorption test in milliliters

           v is volume of solution remaining in soil (d - 1,000 - V) in milliliters

           (3) Reference substances. The following reference compounds need
      not be employed in  all cases when investigating a new  substance. They
      are listed so that the method can be calibrated from time to time and to
      offer the  chance to compare  the results when  another method is applied.
      The values presented in the  following Table  1. are not necessarily rep-
      resentative of the results which can be obtained with this  test guideline,
      as they have been derived from an earlier version of it.
                           Table 1.—Reference Substances2

Soil I
Soil II
Soil III
2.4-Dichlorophenoxy acetic
Soil I 	
Soil II
Soil III 	
Soil character
very strongly-strongly acid sandy soil
moderately or slightly acid loamy soil
slightly alkaline loamy soil
very strongly-strongly acid sandy soil
moderately or slightly acid loamy soil
sliahtlv alkaline loamv soil
4205 (739-7671)
7382 (772-20 088)
17009 (1441-32577)
175.9 (119.0-231.0)
1084 (693-1444)
225.6 (62.1 - 389.0)
  1 Total mean and range of mean values (in parentheses) reported by the participants of the OECD/
EEC Laboratory Intercomparison Testing, Part II.
  2 p-Chloroaniline is suggested in addition to the above.
           (4) Principle of the test method, (i) Three soils which vary signifi-
      cantly in cation exchange capacity,  clay content, organic matter content,
      exchangeable cations, and pH are selected:

           (A) Very strongly to strongly acid sandy soil (pH 4.5-5.5, clay con-
      tent 5 percent, organic matter content 0.6-3.5 percent (e.g. Spodosol).

           (B) Moderately or slightly acid loamy  soil, pH 5.6-6.5; clay content
      15-25 percent, organic carbon content 0.6-2.3 percent (e.g. Alfisol).

           (C) Slightly alkaline loamy soil, pH 7.1-8.0; CaCO3 1-10 percent;
      clay content 11-25  percent, organic carbon content 0.6-2.3 percent (e.g.

           (D) All soils should be classified in terms  of the US comprehensive
      soil classification system (on the level of the soil family)  and additional
      information may be included (e.g.  the national soil  classification). The
      physical and chemical properties of Alfisol are given by:

               Physical and Chemical Properties of Alfisol
        Soil order:  	  Alfisol
        Soil series: 	  Crider
        Location: 	  Gallatin County, Illinois, California
        Classification: 	  typic  paleudalf,  fine-silty,  mixed,
        Horizon:  	  A
        percent sand: 	  1.2
        percent silt: 	  86.6
        percent clay: 	  12.2
        percent organic carbon 	  1.0
        carbonate as CaCOS 	  -
        pH (1:1 H20): 	  7.2
        cation      exchange     capacity  13.5
          (meq/100 g).
        extractable cations (meq/100 g).
            Ca	  8.4
            Mg 	  2.8
            Na 	  -
            K  	  0.7
            H  	  1.6
        Clay Fraction Mineralogy: 	  >50%   Montmorillonite;    5-20%
                                             mica; <5% kaolinite (36-120 cm

     (ii) All three soils are common in temperate zones, but are not rep-
resentative of arid or tropical regions. They may also be used for  further
testing designed to study behavior in sedimentary systems.

     (iii) The method first establishes  that a suitable analytical procedure
exists, then proceeds to answer  the question whether the chemical sub-
stance has a tendency to be strongly, weakly or nonadsorbed from a dilute
aqueous solution by any of the three soil types. If little or no adsorption
occurs, no  further sorption tests are performed because the chemical will
not be retained  in soil media.

     (iv) If adsorption is moderate or high (A > 25%), a single desorption
test  is performed to  establish whether or not this chemical is likely to
be retained in soil media. If it is readily desorbed  (D > 75%),  no  further
sorption tests are required; if only poorly desorbed  (D < 75%), the screen-
ing test is considered to be complete  and the investigator has the option
of proceeding to the secondary or advanced phase  in which an adsorption
isotherm is determined and a mass balance established.

     (v) Under the  advanced test, the  absorption kinetics are determined.
If neither a plateau value nor a mass balance value is obtained,  check
for biotic  and  abiotic  degradation. If  a plateau value or a mass balance
value is obtained, the absorption isotherms are determined. If the soil envi-

ronment is not considered a likely as a trap for the substance, no further
tests are needed because  the soil media are of minimal importance. The
information should be considered for hazard assessment of the substance.
If the soil environment seems to be a likely trap,  consider the fate of the
substance in soil,  and consider  the information for hazard assessment of
the substance.

     (5)  Quality  criteria—(i)  Repeatability.  The  repeatability  of the
measurement is not well  known at present,  as is  indicated with two ref-
erence compounds named under paragraph (c)(3) of this guideline. Stand-
ard deviation of the mean  should be determined.

     (ii)  Sensitivity.  The sensitivity  of the  test method depends  on the
water solubility of the test substance.

     (iii) Specificity. This method as described is not applicable to water
insoluble gases, hydrolytically unstable  compounds, chemicals which may
suffer catalytic decomposition on soil surface, or in cases where analytical
methods are unavailable in the 0.01 mg/L range.

     (iv) Possibility of standardization. The method itself can be stand-
ardized,  but the soils probably cannot. There is no possibility of automa-

     (d)  Description of the test procedure—(1) Preparations. The ad-
sorption test should be run using sieved soil to be less than or equal to
2 mm (N°  10 mesh)  soil which has either been stored damp since collec-
tion or  air-dried  and reequilibrated with approximately twice its  weight
of water before use. (This reequilibration should be carried out for a mini-
mum of 24 h by gently tumbling the soil and water together.)  In either
case the dry weight content (100 °C for approximately 12 h) of the soil
should be determined.

     (2)  Test conditions,  (i) The three soil samples selected for this study
should have  a pH between 4 and 8, an organic carbon content between
0.6 and  3.5 percent.  Suggested soil types are described under paragraph
(c)(4)(i)  of this guideline.

     (ii)  Distilled or deionized water are used to prepare the CaCk solution
(0.01 M) as the solvent.

     (iii) Containers  should be  made of materials that adsorb negligible
amounts of the chemical to be tested.  Other details of container design
are not critical, although handling and transfer errors are minimized by
using centrifuge tubes. The test solutions listed under paragraph  (d)(3)(ii)
through (iv) of this guideline should be added to their respective  test con-
tainers and  equilibrated (without  soil sample). The containers should be
closed during agitation and centrifugation to avoid volatility losses.

     (iv) The actual determination should be carried out in duplicate using,
e.g. 1:5 w/w soil/solution ratio.

     (v) The experiment should be run at room temperature.

     (3) Performance of the tests — (i) Preliminary test.  (A) To assure
applicability  of the method, especially the analytical method, to a given
chemical substance the following test should be performed.
     (B) The soil is equilibrated with the aqueous phase (0.01 M
as described under paragraph (d)(3)(ii)(A) of this guideline. The  aqueous
phase is separated by centrifugation,  and sufficient test chemical is added
to form a solution of approximately one-half saturation and not exceeding
5 mg/L, unless the  analytical method cannot be operated at this level.  The
solution is then subjected to chemical  analysis and, if satisfactory, the
screening test  can  be  performed. A satisfactory, reproducible analytical
method is essential  to this method.

     (ii) Screening test:  Adsorption. (A)  The solution of test chemical
is prepared in 0.01  m CaCl2 at a level of one-half saturation but less than
5 mg/L maximum, unless otherwise dictated by the analytical method.

     (B) The adsorption  step is  performed in duplicate upon this single
concentration solution using the three  soil types.
     (C) Blanks include each of the  three soils with only 0.01 M
solution (no test chemical) and a single control of the test chemical  solu-
tion with no soil. These blanks permit correction for analytical interference
due to soil extracts as well as correction for interaction between chemical
and container or handling losses.

     (D) The soil is added to the test solution and agitation is begun imme-
diately. Agitation  must be continuous  and sufficient to maintain the ad-
sorbent (soil)  in suspension, but should not be so vigorous as to cause
the breakdown of the soil structure.

     (E) Agitation  is continued for 16 h.

     (F) After agitation, this  suspension is centrifuged  to obtain a  clear
solution. The volume of clear aqueous solution is measured and either ana-
lyzed immediately for parent compound concentration or stored under re-
frigeration (5 °C) to minimize biodegradation.

     (G) The three blanks and control are  subjected to precisely the  same
steps as the test systems and appropriate correction is applied as necessary.

     (H) The  volume of equilibrium test solution retained in the  solid
phase following centrifugation and the volume, V, of the supernatant must
be recorded for subsequent correction of the desorption data.

     (iii) Screening test: Desorption. (A) If no significant adsorption (ap-
proximately 25 percent or less) occurs, the desorption part of the test is
not called for.

     (B) If medium to high adsorption occurs (A > 25%),  desorption test-
ing is carried out.

     (7)  To  each solid  phase is added a  volume V  (see paragraph
(d)(3)(ii)(H) of this guideline) of 0.01 M  CaCk solution and this mixture
gently agitated for 16 h. It is then  centrifuged and the supernatant retained
for analysis. The whole desorption procedure is then repeated on the solid
phase with a further quantity of fresh 0.01  M CaCk solution.

     (2) The solute retained in the entrained equilibrium test solution under
paragraph (d)(3)(ii)(H) is assumed to be  completely removed  in the two
washings  along with  the desorbed material and an appropriate correction
applied to decrease the measured  concentration by the calculated amount
of retained solute.

     (3) The  determination of the  amount and the characterization of the
chemical remaining in the aqueous solution phase should be accomplished
by appropriate analytical methods.

     (iv) Advanced  test:  Adsorption.  (A)  If the  screening test dem-
onstrates  a  significant  degree  of chemical   adsorptivity,  adsorption
isotherms may be helpful in predicting mobility in soil/water systems.

     (B) To ascertain that equilibrium conditions will be met in the ad-
vanced test, a series of samples of each soil is prepared using one conven-
ient concentration of test chemical. These samples are analyzed after ap-
propriate time intervals. If no decomposition  of the test chemical occurs,
its  concentration in the aqueous  phase  will eventually reach a plateau
value.  The time required to reach this plateau  value is the minimum agita-
tion time. If no plateau value can be reached  abiotic or biotic degradation
must be considered.

     (C) For the adsorption isotherm determination, four initial concentra-
tions, Ci,  of approximately 0.04, 0.20, 1.00, and 5.00 mg/L are prepared
and the adsorption test performed on each as described under paragraph
(d)(3)(ii) of this  guideline. In some  cases the low solubility  of the test
chemical will prohibit the  use  of some  of the above concentrations.  In
these cases the adsorption isotherm is measured using high and low (other
than 0.00) equilibrium solution  concentrations of the chemical that are at
least 1 order of magnitude apart.

     (D) Blanks  are  identical with  those  described  under paragraph
(d)(3)(ii)(C) of this guideline.

     (E) An analytical control sample (no soil)  should also be run at a
convenient test concentration, not to exceed approximately  1 mg/L.


    (F) Analysis and correction are as before.
    (v) Mass balance. (A) A mass balance should be performed by deter-
mining, in addition to the concentrations in the solutions, the concentration
of the  substance in the  soil. This additional measurement needs only be
performed after reaching the equilibrium plateau and only for one con-
centration with each soil.
    (B) The adsorbed chemical substances remaining on the soil particles
are removed so that a mass balance can be attempted. The extraction me-
dium  should be a suitable solvent  in which  the chemical of interest is
very soluble (minimum 1 mg/L). A volume of suitable  solvent equal to
the volume  of  aqueous solution originally used to attain equilibrium is
added to the adsorbent and shaken vigorously for 10 min.
    (C) The mixture is centrifuged to obtain a clear solution.
    (D)  The extraction procedure is performed  3  times  with  equal vol-
umes of fresh solvent which are then analyzed.
    (E) The aqueous solution phase is analyzed for the  parent chemical
under test.
    (e) Data and reporting—(1) Treatment  of results—(i) Soil charac-
terization. Report data on soil using the format provided under paragraph
(f) of this guideline, DATA SHEET FOR SEDIMENT AND SOIL AD-
SORPTION/DESORPTION ISOTHERM, part A.  Soils used as adsorbents.
    (ii) Screening test. (A) The data required  are:
    (7) m = dry weight of soil employed (g)
    (2) Ce = concentration of substance remaining in solution (V) in the
adsorption step (g/L)
    (3) Ci  = concentration of substance in solution in the first wash (g/
    (4) C2  = concentration of substance in solution in the second wash
    (5) Vo = original volume of solution employed (mL)
    (6) V = volume of solution obtained after the adsorption step (mL)
    (7) G = quantity of material recovered from the soilless control (g)
    (B) The calculations to be carried out are as follows:
    (7) The percent of the chemical adsorbed is calculated as:
                  A = (G - Ce xV0)/G x 100  = x/G x 100

     (2) The percent of the adsorbed material which is  desorbed is cal-
culated as

                  D = [(Ci + C2)V - (V0 - V)Ce]/x x 100

     (3) The percent of the adsorbed material which is not desorbed is
calculated as:

                     R = [G - (Ce + Ci + C2)V]/x x 100

     (4) The adsorption coefficient for the determination is calculated as:

                  K' = (x/m)/Ce

     (5) The adsorption coefficient should also be calculated as a function
of the organic carbon content of the soil:

                  K'oc = K'(100/percent organic carbon)

     (iii) Advanced  test. (A)  The time required to reach the equilibrium
concentration, Ce, should be determined.

     (B) In addition to using  the data to perform the calculations in the
screening test under paragraph (e)(l)(ii) of this guideline, the data should
be plotted according to the Freundlich equation. While the equation is em-
pirical it is widely used  and  has been found to describe adequately the
adsorption  process in dilute solution. The equation has the form:

                     (x/m) = (K) + (Ce^)

K and 1/n are  empirical constants characteristics of the test compound and
the  sorbent used in the test.  Graphically, K is the x/m intercept of the
isotherm plot at Ce = 1  and  1/n is the  slope of the  line when log x/m
is plotted on the ordinate (vertical axis) and log Ce is plotted on the ab-
scissa (horizontal axis). The intercept is an indicator of sorption capacity
and the slope of sorption intensity.

     (iv) Mass balance. A mass balance should be performed for the par-
ent  compound. The combined  concentrations of the parent chemical in the
aqueous phase and the organic solvent  extracts are subtracted from the
initial concentrations of parent compound and reported.  A reasonable hy-
pothesis should be submitted to account for any  discrepancy significantly
greater than the experimental error.

     (v) Adsorption  isotherm and mass balance data  format. (A) The
following format is used for presenting adsorption isotherm data:
                         Adsorption Isotherm Data


log (x/m)

log Ce


                           Adsorption Isotherm Data—Continued


log (x/m)

log Ce

           (B) Format for graphing adsorption isotherm data for sediment or soil

           (7) Graph 1.—Abscissa is Ce  (jig in solution); ordinate is x/m (jig
       adsorbed per gram of soil).

           (2)  Graph  2.—Abscissa  is   log  Ce;   ordinate  is  log   (x/m).
       (Log (x/m)  =  log  K  + 1/n  log Ce;  intercept =  log  K; slope = 1/n;  R2 =
       coefficient of determination for the regression analysis.

           (C)  The following  format should be used for presentation  of mass
       balance data.
                                  Mass Balance Data
Original amount (u,g)
Amount absorbed at plateau (u,g)
Amount in equilibrium solution (u,g)
Unaccounted material [u,g/(a — (b — c))]
Percentaae of unaccounted material [(b + cVa x 100 = %1
Soil I

Soil II

Soil III

           (2) Test  report.  Information should be submitted for the soils  se-
      lected using the data sheet provided under paragraph (f) of this guideline.

           (i) Screening test. Report the percent of chemical adsorbed, A, and
      if necessary, the percent of adsorbed material which is desorbed, D, and
      the percent  of the adsorbed  material  which  is not desorbed, R, for each
      soil. Also report K' and K'oc and the concentration Ce used in the calcula-
      tion (refer to paragraph (e)(l)(ii)(B) of this guideline).

           (ii) Adsorption/desorption test  report  The following Tables 2. and
      3. list the data required.
                               Table 2.—Adsorption Test
Soil I
Soil III
concentration of test substance (mg/L) 	
  after contact of... hours with soil 	
  correction for blank with soil 	
  correction for blank without soil 	
       final corrected concentration (mg/L)

                   Table 2.—Adsorption Test—Continued
initial concentration of test solution (mg/L)
decrease in concentration (mg/L)
quantity adsorbed (u,g) 	
quantity of soil (g of oven-dried equivalent) 	
quantity adsorbed (u,g) per gram of soil
temperature of test (°C)
volume of solution recovered after centrifugation (ml) 	
volume of solution not recovered (ml) 	
corresoondina auantitv of test substance (ma) 	
Soil 1

Soil II

Soil III

                        Table 3.—Desorption Test
concentration in combined washings (mg/L) 	
corresponding quantity of test substance (mg) 	
auantitv desorbed (ma) 	
Soil 1

Soil II

Soil III

     (iii) Advanced test.  (A) The time for reaching the plateau value
should be recorded together with the raw data.

     (B) The amount of adsorbed chemical (x) per unit amount of adsorb-
ent (m) (usually expressed as micrograms per gram (|ig/g) soil) is defined
as x/m.  This value  is calculated from the  difference between the initial
concentration of the chemical in the solution and the equilibrium solution
concentration  of the chemical (Ce), the volume  of the solution and the
weight of the soil (see paragraph (e)(2)(ii) of this guideline.

     (C) Average values of the adsorbed chemical, x/m, are plotted graphi-
cally as a function of equilibrium concentration, Ce, for each soil.

     (D) The results can  also be  evaluated  by plotting log (x/m) versus
log Ce. If the relationship is linear then the Freundlich isotherm

                    x/m = K x Ce 1/n

may be applied in its logarithmic form

                    log x/m = log K + 1/n log Ce

and  the  linear  regression  calculated. If the  regression is  significant  (for
N = 5,  P = 5%,  R2 >  0.77), the adsorption constant K and the constant
1/n should  be  reported  along with  all  raw data (see  Mass Balance under
paragraph (e)(l)(iv) of this guideline).

     (E) KOC should be determined from K and recorded.


    (f) Data report forms. Sample data sheets for reporting test results
are attached, and may be duplicated.

                  DESORPTION ISOTHERM


Test Substance:.

    Name (IUPAC):.
A. Soils used as adsorbents

Soil order 	
Soil series
percent sand
percent silt 	
percent clay 	
percent organic matter
percent organic carbon 	
carbonate as CaCOS
percent insoluble carbonates
pH (1:1 Ho) 	
Cation exchange cap (MEQ/100 g)
Extractable cations (MEQ/100 g)



Special Chemical/Mineralogical Features:
Clay Fraction Mineralogy:

B. Results of preliminary test
     Test substance:	
     Sample purity:	
     Saturation concentrations:
     Concentration of the test solution (show calculation):
     Description of a suitable analytical method:

C. Results of screening test

     1. Adsorption

C control 	


il 1


1 II



    2. Desorption


il 1


1 II



    3. Final data

temperature t °C
initial concentration, Ci 	
percent of chemical adsorbed on adsorbent, A 	
percent desorbed D
percent of the original quantity found in the control sample
remaining on adsorbent after desorption, R 	
adsorption coefficient K'
adsorption coefficient based on organic carbon content K'00
final concentration after correction. C,, 	




D. Results of advanced test
     1. Adsorption kinetics
Soil Type I:
Time for reaching Ce	

Soil Type II:
Time for reaching Ce

Soil Type III:
Time for reaching Ce


2. Adsorption Isotherms for each concentration (Ci)











     (g) References. The following references should be consulted for ad-
ditional background material on this test guideline.

     (1) Aharonson, N. and U. Kafkafi. Adsorption, mobility and persist-
ence of thiabendazole and methyl  2-benzimidazole carbamate in  soils.
Journal of Agrcultural and Food Chemistry 23:720-724 (1975).

     (2) Environmental Protection Agency, Office of Pesticide  Programs.
Guidelines for registering pesticides in the United States. FEDERAL REG-
ISTER 40, No. 123, 26881 (1975).

     (3) FEDERAL REGISTER 44 FR 16257-16264 (1979).

     (4) Hamaker, J.W. The interpretation of soil  leaching experiments,
in Environmental Dynamics of Pesticides  (ed. R. Hague and V.H. Freed),
pp 115-134, Plenum, N.Y. (1975).

     (5) Harvey, R.G.  Soil adsorption and  volatility of dinitroaniline herbi-
cides. Weed Science 22:120-124 (1974).

     (6) Laskowski  & McCall, Communication  to W.M.J. Strachan, July

     (7) Murray, D.S., P.W. Santlemann, and J.M. Davidson. Comparative
adsorption, desorption, and mobility of disporpetryn and prometryn in soil.
Journal of Agricultural and Food Chemistry 23:578-582 (1975).

     (8) Saltzman, S. et al. Adsorption-desorption of parathion as  affected
by soil  organic matter. Journal of Agricultural  and Food Chemistry 20:
1224-1226 (1972).

     (9) Unweltbundesamt (Draft: Test protocol for the determination of
adsorbability. Sept.  1979. with comments from Prof. Brummer, Kiel,  and
Prof Lagally, Kiel).

     (10) Weber, J.B. Model soil system, herbicide leaching, and sorption.
P. 145-60. In R.E.  Wilkinson, ed., Research methods in weed  science.
Southern Weed Science Society (1971).

     (11) Wu.  C.H.  et al. Napropamide adsorption, desorption, and move-
ment in soils. Weed Science 23: 454-457 (1975).