vvEPA
             United States
             Environmental Protection
             Agency
              Office of Research and
              Development
              Washington, DC 20460
LPA/540/R-94/502
July 1994
Potential Use of
Ultrasound in Chemical
Monitoring

-------
User entered document, Key - 3404
ACCN
TYPE
DB
MTI
MYDATE
CALLNO
RN
LOCATION
1  3404
2  CAT
4  Potential use of ultrasound in chemical monitoring

5  0794
6  EPA-540-R-94-502
7  EPA-540-R-94-502
8  elad

-------
                                                      EPA/540/R-94/502
                                                      July 1994
             POTENTIAL USE OF ULTRASOUND
                 IN CHEMICAL MONITORING
                               by
            Grazyna E. Orzechowska and Edward J. Poziomek
              Harry Reid Center for Environmental Studies
                   University of Nevada-Las Vegas
                     Las Vegas, NV  89154-4009

                 Cooperative Agreement No CR818353
                          Project Officer

                       William H. Engelmann
                Advanced Monitoring Systems Division
              Environmental Monitoring Systems Laboratory
                     Las Vegas, NV  89193-3478
                              U.S. Environmental Protection Agency
                              Region 5, Library (PL-12J)
                              77 West Jackson Boulevard, 12th Floor
                              Chicago, IL 60604-3590
ENVIRONMENTAL MONITORING SYSTEMS LABORATORY-LAS VEGAS
            OFFICE OF RESEARCH AND DEVELOPMENT
           U.S. ENVIRONMENTAL PROTECTION AGENCY
                LAS VEGAS, NEVADA 89193-3478

                                                  Gyy Printed on Recycled Paper

-------
                                         NOTICE

       The U.S. Environmental Protection Agency (EPA), through its Office of Research and
Development (ORD), partially funded and managed the extramural research described here.  It has
been peer reviewed by the Agency and approved as an EPA publication.  Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.

-------
v                                                    ABSTRACT
i
K,
-j                  EPA has been examining the potential of combining sonication with other technologies for
           monitoring specific classes of organic pollutants in water. The research specifically addressed using
/i          ultrasonic processors to decompose organochlorine compounds into ions which could be detected using
^          a specific ion electrode as a screening method for organochlorine pollutants. Changes in chloride,
           conductivity, and pH were measured using commercially available equipment before and after
y         sonication in order to detect the presence of the organochlorine pollutant.  The results obtained are
           very promising.  Chloride ion could be  detected in aqueous solutions of low ppm concentrations of
           carbon tetrachloride, chloroform, and trichloroethylene after one minute sonication. The increases of
           chloride ion were accompanied by increases in conductivity and decreases of pH.  Ion chromatography
           of solutions before and after sonication  showed that formate ion was  also formed.  Aromatic and
           polyaromatic chloro compounds represented by chlorobenzene and polychlorobiphenyls,  respectively,
           did not  form chloride ion as readily as did carbon tetrachloride, chloroform, and trichloroethylene.
           The potential of combining sonication with commercially available measurement technologies for
           monitoring specific pollutants in water is judged to be high. The results achieved  with the
           organochlorine compounds tested serve  as proof-of-principle and form a base of information which can
           be used to develop ultrasound monitoring methods for these compounds.
                                                         111

-------
                                    CONTENTS



ABSTRACT	 iii

CHAPTER 1. INTRODUCTION	  1

CHAPTER 2. OBJECTIVE	  4

CHAPTER 3. DESCRIPTION OF ULTRASOUND	  5
       Ultrasound Definition	  5
       Cavitation 	  5
       Temperature and Pressure Phenomena	  6
       Practical Applications of Power Ultrasound	  6

CHAPTER 4. SONOCHEMISTRY	  8
       Water	  8
       Organochlorine Compounds	  9

CHAPTER 5. EXPERIMENTAL	   12
       Sample Preparation	   12
       Equipment	   12
       Sonication Procedures and Measurements  	   14
       Optimization of conditions with the cup-horn system  	   15

CHAPTER 6. RESULTS AND DISCUSSION	   18
       Ion Chromatography Analysis  	   18
       Changes in Conductivity	   23
       Changes in Cl~ Concentrations  	   25
       Changes in pH	   25
       Tap Water Samples  	   28
       Well Water Samples	   28
       Reaction Mechanism	   28
       Implications for Chemical Monitoring Methods Development  	   32

CHAPTER 7. SUMMARY AND CONCLUSIONS  	   35

BIBLIOGRAPHY 	   36

-------
                                         TABLES

Table 1.       Principal products from sonication of organochlorine compounds in water	   10
Table 2.       Principal products from sonication of organochlorine compounds in nonaqueous
              solvents	   10
Table 3.       Average levels of ion concentrations and pH in samples of deionized
              water and tap water before sonication	   15
Table 4.       Concentration of Cl~ obtained from ion chromatography and Cl~ ISE
              measurements. (Samples sonicated in the cup horn at 60% pulse mode at
              10 minutes.)	   18
Table 5.       Measurement data of conductivity, Cl~, and pH in well water samples.
              (Samples were sonicated in the cup horn system at 60% pulse mode, at 10
              minutes)	   30
Table 6.       Summary of Cl~ yields [%] under various sonication conditions	   34

                                         FIGURES

Figure 1.      Sketches of the cup horn and the W horn probe used in sonication experiments.  .   13
Figure 2.      Sonication reaction tube	   13
Figure 3.      Changes upon sonication of 37 ppm TCE vs. pulse mode	   17
Figure 4.      Changes upon sonication of 37 ppm TCE vs. time	   17
Figure 5.      Ion chromatograms of 37 ppm TCE	   19
Figure 6.      Ion chromatograms of 37 ppm CHC13	   19
Figure 7.      Ion chomatograms of 40 ppm CC14	   20
Figure 8.      Ion chromatograms of 94 ppm Ph-Cl	   20
Figure 9.      Ion chromatograms of 55 ppm PCB in  1% Triton-X-100	   21
Figure 10.     Ion chromatograms of 1% Triton-X-100	   21
Figure 11.     Ion chromatograms of Cl~ standard solutions	   22
Figure 12.     Ion chromatograms of deionized water	   22
Figure 13.     Ion chromatograms of 10 ppm HCOO~.	   22
Figure 14.     Changes in conductivity upon sonication vs. time	   24
Figure 15.     Changes in conductivity upon sonication vs. time and pulse mode	   24
Figure 16.     Changes in Cl~ concentration upon sonication vs. time	   26
Figure 17.     Changes in Cl~ concentration upon sonication vs. time and pulse mode	   26
Figure 18.     Changes in pH upon sonication vs. time	   27
Figure 19.     Changes in pH upon sonication vs. time and pulse mode	   27
Figure 20.     Changes upon sonication of 37 ppm CHC13 in tap and deionized water	   29
Figure 21.     Possible mechanisms in the sonochemistry of organochlorine compounds in water.   31
                                           vi

-------
                                          CHAPTER 1

                                        INTRODUCTION

        The U.S. Environmental Protection Agency has been examining the potential of combining
sonication with other technologies for monitoring specific classes of organic pollutants in water.  The
research described in this report relates to a search for new concepts for field screening methods
applicable to hazardous waste sites with emphasis on in situ groundwater monitoring.

        Field screening involves the use of rapid, low-cost test methods to determine whether a
parameter of interest is present or absent, above or below a predetermined threshold at a given site, or
at a concentration within a predetermined range of interest (1).  Screening methods can be used in the
field to identify the nature and extent of contamination at individual sites.  Although they may not be
as accurate or precise as laboratory methods, some are very accurate and precise as well as sensitive.
Field screening methods:

              allow rapid identification of contaminants present and  their relative levels;
              allow priorities to be set at a site and identification to  be made of hot  spots;
              help to either quickly establish  a more comprehensive monitoring program for a given
               site, or prioritize the site relative to other sites;
              have the potential to accelerate  site clean-up and to  reduce cost; and
              are  needed to support on-site monitoring and characterization activities.

        The technologies developed as field screening methods are relevant to the monitoring and
measurements needs of many U.S. Environmental Protection Agency (EPA) programs which may use
field screening data to support a variety of go/no-go environmental management decisions.  The
overall challenge of field screening involves dealing with numerous compounds within many classes
(organic, inorganic, biomarker, and radionuclide), across various  media, and in complex mixtures.

        Desirable characteristics of field screening devices are that they be:  sensitive, specific, user-
friendly, real-time, able to handle a broad range of samples, rugged, small in  size, lightweight, low in
cost, and reliable.  A proper blend of these characteristics is chosen to meet specific needs.

        A few field screening methods are available now, and more are being developed. The most
mature are judged to be those  based on gas chromatography, x-ray fluorescence, and infrared
spectroscopy. One of the clear trends is to miniaturize. Various hand-held vapor sensors can be
purchased which are applicable to field screening needs. These are  based on, for example,  tin oxide
catalytic oxidation, ion mobility spectrometry, and photoionization detection.  Hand-held colorimeters
are also available.  A recent overview of the state of the art of field screening and analysis
technologies was performed by Koglin and Poziomek (1).

       Methods which are still in various stages of development include the use of fiber optic sensors
and chemical microsensors, such as piezoelectric quartz microbalances and surface acoustic wave
(SAW) probes. The fiber optic technology typically involves the measurement of a chemical or
biochemical reaction and is relevant to in situ monitoring.  The use of a fiber optic system could also

-------
involve measurements of spectroscopic properties of the pollutant molecules using any one of several
techniques such as luminescence (including laser-induced fluorescence), UV-visible, near and mid
infrared absorption, spectrochemical emission, and surface-enhanced Raman.  The piezoelectric and
SAW microsensors require chemical/biological reactions or molecular association effects involving the
pollutant being measured. These techniques are still emerging.  They have the potential for achieving
sensitivities at the part-per-billion (ppb) level, and many are amenable to remote sensing and in situ
modes.  However, considerable research is still required, especially in developing sensor recognition
coatings for the devices.

        The need for ground-water monitoring has been discussed by Makeig (2).  A comprehensive
review highlighting potential wellhead protection field technologies is also available (3). This relates
to protecting public water supply wells, well fields, and springs  from contamination. The technologies
reviewed apply to ground-water monitoring at hazardous waste sites as well.  Methods are presented
which may be especially useful for field screening.

        The detection limits of field methods are not always as low as laboratory methods, and the
accuracy of field  methods is not always as reliable as laboratory methods. This is especially critical,
for example, if the detection limit of the field method does not meet water quality criteria or
regulatory requirements.  Nevertheless, less accurate methods might be useful to screen samples prior
to confirmatory laboratory analyses. The advantage is in cost savings by limiting the number of
samples sent for laboratory analyses.

        Groundwater contains  a variety of natural constituents, with the various species and
concentrations depending on factors such as the specific geochemical environment and the source of
the groundwater (4). The major anions that are usually analyzed to indicate general water quality
include bicarbonate, chloride (Cl^), nitrate, and sulfate.  Other general indicators of water quality
include electrical conductivity, temperature, pH, dissolved oxygen (DO), biochemical oxygen demand
(BOD), chemical oxygen demand (COD), total organic carbon (TOC), oxidation reduction (redox)
potential, total suspended solids (TSS), total dissolved solids (TDS), and turbidity.  The idea being
brought forward in this research is to measure several of these  general parameters such as pH,
electrical conductivity,  and specific anion concentration before and after sonication of a water sample.
An increase of Cl~ concentration after sonication, for example, could be an indicator that the water
was polluted with organochlorine compounds.  Commercially  available Cl~ electrodes have a
sensitivity limit at the low parts-per-million (ppm) level.  This is the sensitivity to be expected,
therefore, for organochlorine compound detection by combining sonication with ion selective electrode
(ISE) technology.

        This research complements approaches already being taken for characterizing hazardous sites.
The Resource  Conservation and Recovery Act (RCRA) interim status regulations, for example,
identified four indicator parameters for use in monitoring ground-water contamination in the detection
phase:  specific conductance, pH,  total organic carbon,  and total organic halides (5). Organic halide
monitoring, however, is difficult and not readily amenable to in  situ use.  In situ ground-water
monitoring has been identified as one of the  major technology needs in  field screening (1).  The
present research combines sonication with commercially available probes and offers a simple approach
toward field screening and monitoring.

        Success in this  monitoring approach requires destruction of neutral organochlorine pollutants
and formation of Cl~.  Formation of H+ and  other ions may be utilized or exploited as well.  A later
section describes  the known sonochemistry of water and organochlorine compounds.

-------
        The classical use of sonication with environmental samples has been to assist in the extraction
of semivolatile organic contaminants from soil (6).  Interest has also emerged recently in the
possibility of using sonication to remediate groundwater (7). Sulfate, nitrite, nitrate, p-nitrophenol,
phosphate, and oxalate were identified as products of parathion sonolysis (7).  No reports have been
published on use of ultrasound in monitoring.

-------
                                         CHAPTER 2

                                         OBJECTIVE

       The objective of this study was to examine the potential of combining sonication with existing
measurement technologies for monitoring specific classes of organic pollutants in water.  The research
specifically addressed using ultrasound processors to decompose organochlorine compounds into ions
as a screening method for organochlorine pollutants in water.

       The approach in using sonication is obviously applicable to other organic compounds which
contain other halides, phosphorus, nitrogen, and sulfur that, when released, could  be easily quantified.
Anions specific to the inorganic components would be produced in sonication.  Changes in anion
concentrations before and after sonication would be used in monitoring for the pollutants.  The
selection of organochlorine compounds was made because these compounds are the most common
pollutants found at hazardous waste sites. Success with compounds such as trichloroethylene (TCE),
chloroform (CHC13),  and carbon tetrachloride (CC14)  will serve as proof-of-principle and form  a base
for expanding the research to other pollutant classes.

-------
                                          CHAPTER 3

                               DESCRIPTION OF ULTRASOUND

        There are two compilations which give an excellent summary of the fundamentals of
ultrasound (8,9).

Ultrasound Definition

        Ultrasound is defined as any sound which is of frequency beyond that to which the human ear
can respond, i.e., above 16 KHz.  In the terms of frequency ranges, and physical as well as chemical
changes caused by ultrasound, there are two categories:

               high frequency or diagnostic ultrasound (2-10 MHz); such irradiation causes temporary
               physical changes in the medium; and
               low frequency or power ultrasound (20-100 kHz); this affects chemical reactivity.

        A whistle constructed by F. Gallon (10) 100 years ago was the first device generating
ultrasound.  It is an example of a transducer which can change one form of energy (gas motion) into
another (sound).  The whistle had an adjustable  resonance cavity capable of generating sounds of
known frequencies.  Gallon used the device to determine the threshold hearing frequencies of people
and animals.

Cavitation

        The term cavitalion was firsl used by Sir John Thornycraft and Sidney Barby (11) at ihe turn
of the 19th century during their observation of propeller inefficiency in destroyers. They observed that
water was "torn apart," producing tiny bubbles due to a tremendous reduction  in pressure on the
trailing  faces of the blades. It is the energy generated on the collapse of these bubbles which is ihe
underlying reason for the erosion damage of propellers.  The same cavitation bubbles can be produced
by the irradiation of a liquid with power ultrasound. The energy generated on the collapse of these
bubbles is given as the underlying reason for chemical enhancements and iransformalions which can
be achieved in sonochemistry (9).

        Sound is transmitted through any  liquid  as waves consisting of alternating compression  and
rarefaction cycles. If the rarefaction wave is sufficiently powerful, il can develop a negative pressure
large enough to overcome the intermolecular forces of bonds in fluids. In ihis situation, the  molecules
will be torn apart from each other to form tiny microbubbles throughout the medium.  In ultrasonic
cavitation, the compression cycle follows  rarefaction. This can cause the microbubbles to collapse
almosl instantaneously with ihe release of a large amounl of energy.

       Transienl cavilalion bubbles are voids or vapor-filled bubbles produced by ullrasonic
intensities in excess of 10 W cm"2.  They  exisl for one, or al most a few, acoustic cycles, expanding to
ihe radius of al leasl iwice their initial size, before collapsing violently in the compression phase. On
iheir collapse, they may be a source of nuclei for further cavitalion by disintegration into smaller

-------
bubbles.  Bubbles which oscillate in the acoustic field with a much longer lifetime give stable
cavitation.

Temperature and Pressure Phenomena

        The high temperatures and pressures created during transient cavitation are difficult to
calculate and measure experimentally.  Some models predict maximum temperature and pressure as
high as 10,000 K and 10,000 atmospheres, respectively.  More realistic estimates from increasingly
sophisticated hydrodynamic models yield estimates of approximately 5,000 K and 1,000 bars with
effective times of > 100 ns (8, p.130).

        Equations have been developed in the early 1950's for estimating the maximum temperature
and pressure developed within the bubble at the moment of collapse (9, p. 11):

                                                 Pm(h-l)
                                      T    = T f	-1
                                       ""     l    P   J                                    (1)

                                     P    - pr1^-1^                                   (2)
                                     Tmu.         p
where:
        Tmax    = the maximum temperature
        Pmax    = the maximum pressure
        T0     = the ambient (experimental) temperature
        h      = the ratio of specific heats of the gas (or gas/vapor) mixture
        P      = the pressure in the bubble at its  maximum size and is usually assumed to be equal
                      the vapor pressure of the liquid
        Pm     = liquid pressure at collapse.

        Calculations using these equations suggest that for water at 25C, the average temperatures of
5,000 K and pressures of the order of 1,000 atmospheres are generated by the collapse of cavitation
bubbles due to power ultrasound.

        Determination of the temperatures reached in a cavitating bubble has remained a challenging
problem.  Flint and Suslick (12) briefly reviewed various approaches including a laborious comparative
rate analysis of the decomposition of metal carbonyls involving a substantial extrapolation of kinetic
parameters (13).  The same authors  reported the use of sonoluminescence as more convenient and
desired  determination of the effective temperature  of cavitation bubbles collapse.  The methodology
was adapted from plasma  techniques based on rotational and vibrational diatomic emission spectra.
Sonoluminescence spectra from silicone oil were determined and analyzed.  The observed emission
was compared to synthetic spectra as a  function of rotational and vibrational temperatures.  The
effective cavitation temperature was found to be 5075  156 K based on this comparison.

        Regardless of the details of the  theoretical and experimental studies, it is clear that cavitational
collapse generates hot spots with effective temperatures of several  thousand  degrees.

Practical Applications of Power Ultrasound

        An overview of practical applications of power ultrasound  shows many  uses in automotive,
electronic, optical, semiconductor, biomedical, and other industries (14).  The widest application in
liquids is cleaning. The widest application in solids is plastic welding. Less established areas in

-------
liquids include:  soldering, cell disruption, inhalation therapy, degassing, and medical surgery.  There
is also some industrial use for debumng, erosion testing, extraction, emulsification, solids dispersion,
fuel atomization, and crystal growth.  Experimental use of ultrasound in liquids involves sterilization,
filtration, drying of textiles, and metal grain refinement.

       Other applications in solids include metal welding, metal forming, impact grinding, rotary
abrasive machining, metal cutting, fatigue testing, trimming of composites, and dental descaling.
Airborne applications include particle agglomeration, defoaming, and drying.

-------
                                         CHAPTER 4

                                     SONOCHEMISTRY

       The first account of the chemical effect of ultrasonic waves was published in 1927 by Richards
and Loomis (15). A number of phenomena were noted including acceleration of the explosion rate of
nitrogen triiodide, hydrolysis rate of methyl sulfate, and reduction rate of iodate by sulfite. Recent
updates of homogeneous and heterogeneous sonochemistry were provided by Suslick (16) and
Boudjouk (17). Sonochemical reaction can be categorized  as:

             primary reactions involving thermal decomposition of solvent, solute or gases present
              in solution as a result of high temperatures and pressures attained upon bubble collapse
              secondary reactions involving radicals from primary reactions and other species.

       The topics most relevant to the present research are homogeneous aqueous sonochemistry and
the sonochemistry of organochlorine compounds. These are discussed in the next sections.

Water
       The principal products from ultrasonic irradiation of water are H2O2 and H2. Various data
support the presence of hydroxyl radicals and hydrogen atoms as intermediates (8, p. 13 8).  The
sonolysis of water to produce hydrogen peroxide was first reported by Smith et al.  (18):
                             H,O  -> HO- +  H-
                                       H202
                                                                            (3)
       The formation of H- and HO- is attributed to the thermal dissociation of water vapor present
in the cavities during the compression phase.  The wide range of oxidations and reductions that occur
with aqueous sonochemistry is often a consequence of secondary reactions of these high energy
intermediates.

       Examples of reactions that appear to be involved in water sonolysis in the presence of gases:
Ar, O2, N2, and air (19, p.26) follow:
       1)
       2)
under Ar:
   H2O ->  H- + HO
   HO- +  H- -> H2O
   2 HO
   2 HO
                          O- + H2O
under 02:
   O2 -> 2 O-
   O, + H- -
                            H2O2
                            HO,
                               (4)
                               (5)
                               (6)
                               (7)
                              (12)
                              (13)
2H-  ->  H2              (8)
2O-  ->  O2              (9)
O2 + H- -> HO2-          (10)
HO2- + H- -* H2O + O-   (11)
                                                                2 HO2- - H2O2 + O2      (14)

-------
        3)      under N2:
                  N2 + HO- -> N2O + H-      (15)
                  N2 + O- * N2O              (16)
                  N2 + O * NO + N-         (17)

                  N2O + O- - N2 + O2        (18)
                  NO  + H- -> N- + HO-       (19)

        4)      under air:
                  as in 2  and 3 plus N2 + O2 -> 2 NO                                        (20)

        These reactions have been proposed to be analogous to combustion and shock tube chemistry.
In the absence of HO- scavengers (e.g., N2), the main product of the sonolysis of water is H2O2.

Organochlorine Compounds

        Various organochlorine compounds have been sonicated either as aqueous solutions, as
dispersions, or in nonaqueous solutions with the  formation of a wide range of highly degraded
products.

        Early investigations of the effects  of ultrasonic irradiation on aqueous solutions of
organochlorine compounds and KI were made in 1929 by Smith et al.  (18).  At the end of one minute
of sonication of an aqueous solution of CC14 in the presence of starch and KI, the solution became
opaque  a blue color formed which became much more intense than that obtained by three minutes
sonication of KI and starch alone. This was cited as evidence of C-C1 bond cleavage causing the
acceleration of iodine formation due to presence  of C12.

        In the early 1950's, Weissler et al. (20) carried out more detailed studies on ultrasonic
oxidation of KI by CC14 as an effect of C-C1 bond cleavage. It was also concluded that the main
reaction was between water and dissolved carbon tetrachloride to give  chlorine which then oxidized
iodide:

                               CC14  + H2O -> C12 + CO + 2 HC1                           (21)

                                    3 T + C12  -> V  +2  Cr                               (22)

        The oxidation of KI solution proceeded only about one-fifteenth as rapidly in the absence of
CC14 as  in its presence.

        A number of investigators have studied the sonochemistry  of organochlorine compounds.
Examples of the principal products found in aqueous and nonaqueous solutions are given in Tables 1
and 2, respectively.

        The sonication of aqueous solutions of organochlorine compounds leads to different products.
However, in each of the reported studies (Table 1), the common product is HC1.  Sonication of
organochlorine compounds, either neat  or in nonaqueous solution, should be expected to yield HC1 as
well.  This  would not be true for compounds such as CC14, in which no hydrogen is available
(Table 2).

-------
       Cheung and coworkers (23) reported preliminary results on the use of ultrasound to destroy
organochlorine compounds at the 100-1000 ppmv range in aqueous solution. Quantitative data with
120 ppm CH2C12 in water yielded a first-order rate constant of 3.93 x  10"2  2.7 x 10"3 min"1 under the
particular sonication experimental conditions.  No organochlorine species (other than CH^Cy  were
identified using GC/MS to follow the sonochemistry. Decreases in pH were noted as the CH2C12 was
destroyed. It was concluded that sonochemical destruction of organochlorine compounds appears to be
a potentially powerful method of remediation,  which may compete with or serve as  an adjunct to other
advanced oxidation processes. Personal communication established that Cheung was not considering
the potential use of ultrasound in chemical monitoring (31).
Table 1.
Principal Products from Sonication of Organochlorine Compounds in Water.
Organochlorine compound
CC14
RjCHa
a3CCH(OH)2
CH2a2
a3ccH3
a2ccna (TCE)
Product(s)
C12
CO2
na
QCl,
HOC1
R2CHOH
na
HC1
HO
BOO
HC1
a,
CO2
na
Reference
18, 19, 20, 21, 22, 23
24,25
26
23
22, 23, 27, 28
23
Table 2.       Principal Products from Sonication of Organochlorine Compounds in Nonaqueous
              Solvents.
   Organochlorine compound
                        Product(s)
        Reference
  CHO,
  CC14
               HO
               ca4
               CH2C12
               C13CCHC12
               ci2cca2
               C13CCC13
               C12CCHC1 (TCE)

               C12
               a3cca3
(8, p.  147; 29)
(30)
                                             10

-------
       Toy and coworkers (27) have considered the use of sonolysis to decompose C13CCH3 in water
at 1-10 ppm levels.  The interest was in defining process conditions. It was found that as the volume
of the same concentration of C13CCH3 was increased, the sonolysis digestion efficiency decreased.
Solution volumes were varied from 500 to 56,775 mL.  The sonolysis digestion was followed using
GC analysis (for decreasing C13CCH3), and ion chromatography (for increasing Cl~).

       Petrier and coworkers (32) examined the potential applications of sonochemical treatment as a
way to treat toxic wastes containing sodium pentachlorophenate (PCP). The main feature was rapid
cleavage of the C-C1 bond giving Cl~.

       Reviewing the literature on sonochemistry of organochlorine compounds as summarized above
did not lead to any reports on the use of ultrasound for chemical monitoring.  However, the reported
sonochemistry of organochlorine compounds in water gave much support for using sonication in
combination with changes in Cl~, conductivity and/or pH as a way of monitoring for the presence of
the compounds in water.
                                             11

-------
                                        CHAPTERS

                                      EXPERIMENTAL

Sample Preparation

       High purity (99%) chemicals were used for sample solution preparations. Methanol (MeOH),
chloroform (CHC13), carbon tetrachloride (CC14), and chlorobenzene (Ph-Cl) were purchased from
Burdick and Jackson Laboratories Inc. Trichlorethylene (TCE) was purchased from Baker Reagents.
3,3'-Dichlorobiphenyl (PCB) and 4,4'-dichlorobiphenyl (PCB) were obtained from Chem Service.
Triton X-100 and technical grade humic acid, sodium salt, were purchased from Aldrich Chemical
Company, Inc.  Potassium chloride (KC1) solution (1000 ppm CH was obtained from Orion.
       The stock solutions of analytes were prepared in MeOH.  Aliquots of stock solutions were
taken for preparation of aqueous samples (1:100 dilution).  PCB samples, a 1:1 combination of the
3,3'- and 4,4'- isomers, were diluted in 1% aqueous solution of Triton X-100.  Dilution of analyte
solutions was made to obtain roughly the same concentrations (ppm) of organic chlorine among
samples, except for those of PCBs, which were somewhat lower due to limited availability of reagents.

       The following deionized water solution samples were used in the experiments:
       TCE   3.7 ppm (3.0 ppm Cl) and 37 ppm (30 ppm Cl)
       CC14   4.0 ppm (3.7 ppm Cl) and 40 ppm (37 ppm Cl)
       CHC13 3.7 ppm (3.3 ppm Cl) and 37 ppm (33 ppm Cl)
       Ph-Cl  9.4 ppm (3.0 ppm Cl) and 94 ppm (30 ppm Cl)
       PCB   5.5 ppm (1.7 ppm Cl) and 55 ppm (17 ppm Cl)
Deionized water was used for the blanks.

       Tap water solutions of analytes, i.e., TCE (36.6 ppm), CC^ (39.7 ppm), CHC13 (37.1 ppm),
and Ph-Cl (94.1 ppm), were prepared from the same stock solutions in MeOH. Tap water was used
for the blanks.  Aqueous solutions of analytes were freshly prepared before analysis.

       Two well-water samples, Brad Ford (Ash Meadow, Nevada, sampled 4/16/93) and Hawaii
(Grand Canyon, Arizona, sampled 4/23/93), were stored at 4C in screw-cap glass bottles after they
had been used in another study in May 1993. They were used in the present study (August 1993)
without dilution or further processing.

Equipment

       A Branson Ultrasonic Corporation Sonifer Model 450 was used for sonication of samples.
The unit was equipped with a power supply, a soundproof box, a converter, a cup horn, and 1/2" horn
probe.  Figure 1 shows the cup horn and the 1/2" horn probe.   Sonication was performed in glass
screw-cap reaction tubes (Figure  2).  The tubes were modified from commercially available screw-cap
vials by rounding their bottoms and adding glass supporting rings. The design of the tubes allowed
them to be placed into the sonicator cup-horn at the same depth.
                                             12

-------
                 CUP HORN
  Coolant
  outlet port
                  1/2" HORN PROBE

                  To converter^
              and power supply
                                       Reaction tube
inlet port
                             To converter
                           and power supply
                           (Branson Ultrasonics Corporation)
Figure 1.  Sketches of the cup horn and the 1/2" horn probe used in sonication experiments.
                                             GP|
                                         thread finish
                                           20-400
                     Threads
                      3 mm
                                                     3 mm
                                                   thickness ~N
                                 -23 mm

                                 -29 mm
Figure 2.  Sonication reaction tube.
                                     13

-------
       A constant temperature circulator (Model 1160 of VWR Scientific Company) was used as a
cooling bath. The cooled liquid (commercial anti-freeze, polyethylene glycol) was pumped through
the cup-horn system with a peristaltic pump (Cole Farmer Instrument No.7520-25) equipped with an
easy-load pump head (Cole Farmer Instrument, Model 7518).

       The following measurement equipment was used:

              Conductivity Meter, Orion Model 180 C, Orion Cell No. 018010, temperature
              compensator, Orion No. 018870;
              pH/Ion Selective Electrode Meter (ISE), Orion Model EA 940, temperature
              compensator Orion No. 91700;
              Electrodes:  Cl~ Orion Solid State Combination (Cl~ ISE), No. 9617, and pH,
              Orion Ross Combination, No. 8103.
             Ion chromatograph Dionex -  Quick, lonPac AG4A Guard Column, lonPac AS4A
              Analytical Column, suppress  conductivity detector.

Sonication Procedures and Measurements

       Sonication of samples and blanks was performed using two ultrasound systems:  a cup-horn
and a 1/2" horn probe.  Both the cup horn and the 1/2" horn probe were placed in the soundproof box.
Sample solutions were pipetted into reaction tubes.  Each individual sample tube was closed and then
placed in the cup horn system for sonication.  In the case of the 1/2" horn probe system, the horn was
directly immersed in the  sample tube.  The tube was placed into the cup horn which also served as a
cooling bath. The coolant (polyethylene glycol) was pumped through the cup horn using a constant
temperature circulator.  The temperature of the circulator was set at -10C.  The cup horn and the 1/2"
horn probe operated at the maximum output control setting i.e., 10, during experiments.

       The following experimental parameters were investigated:

              continuous vs. pulse sonics (pulse mode 10%-90%)
              time of sonication  (1-90 min)
             sample volume (8-15 ml)
             different concentrations of analytes
             temperature of samples after  sonication
              different water sources  (deionized, tap, well)

       At least two series of three replicates of a sample  and  a blank were sonicated and measured.
The conductivity and pH/ISE meters  were calibrated daily for each series of experiments.  The limit of
detection for the Cl~ ISE electrode was 1.8 ppm. The conductivity meter and Cl~ ISE electrode were
calibrated in concentration units, i.e., mg/L (ppm) using Cl~ standard solutions.  Calibration curve
equations obtained with regression analysis had correlation coefficients of 0.998-0.999.  Standard
solutions used for calibrating the Cl~ ISE were in a range 1-15 ppm Cl~ for deionized water and 50-
250 ppm Cl~ for tap and well water. Though one of the points (1 ppm) was below the  sensitivity
limit of the C1~ISE, excellent correlation coefficients were obtained. This allowed estimates down to
0.5 ppm  Cl~. Calibrations of the conductivity meter were made with standard solutions of 1-25 ppm
Cl" for deionized water, and 100-1000  ppm Cl~ for tap and well water.  Measurements  of
conductivity, Cl~, and pH were made in samples before and after sonication. The effects of sonication
were noted as changes in these parameters.
                                              14

-------
       Relative errors of conductivity and Cl~ measurements ranged from 1% to 10% and were
concentration-related, i.e., higher errors were found at lower concentrations.  The errors were 1% or
less in pH measurements.

       Examples of levels of ion concentrations and pH in deionized water and tap water used for
sample preparations are presented in Table 3.  These represent blanks.
Table 3.        Average Levels of Ion Concentrations and pH in Samples of Deionized Water and Tap
               Water Before Sonication.
Water
Deionized
Tap
Conductivity
[ppm]
(6)a
0.00  0.00
(6)
330 4
cr
[ppm]
(6)
0.40  0.05b
(6)
98.3  1.1
pH
(6)
6.50  0.01
(6)
8.37  0.02
a Number of samples.
b Results below the limit of quantitation (Ref. 33)

       There were no changes in ion concentrations and pH after sonication of the deionized and tap
water blanks. However, there were some variations among different samples of tap water.  These
variations were  of no consequence since measurements were  always performed before and after
sonication.

       The sample volume used with the cup horn system was 8 mL.  That corresponded to the
minimum volume needed for measurements with the conductivity cell.  The optimum sample volume
for use with the 1/2" horn probe was 15 mL.  That allowed proper immersion of the probe.

       Continuous and pulse modes were utilized. In the pulse mode, ultrasonic vibrations are
transmitted to a solution at a rate of one pulse per second.  The pulse duration can be adjusted from
10% to 90%, enabling a solution to be processed at full ultrasonic intensity while limiting temperature
build-up.

       Changes in ion concentration and pH were not evident upon sonication at low concentration of
organochlorine compounds, i.e., 3.7 ppm TCE, 4.0 ppm CC14, 3.7 ppm  CHC13, 9.4 ppm Ph-Cl, and 5.5
ppm PCB for the sonication times examined.

Optimization of conditions with the  cup-horn system

       Changes in conductivity, Cl~ content, and pH of TCE solutions with the cup horn at various
pulse modes are shown in Figure 3. The sonication time was 10 minutes.  The greatest increase of ion
concentrations and the greatest decrease of pH were observed at the 60% pulse mode.  Much lower
changes were noticed at the constant mode (100%), which may be explained by losses of power output
during sonication. The same pattern of changes was found as the result of 5 and 20 minutes
sonication.  The longer the sonication time, the greater the observed changes.
                                              15

-------
       Sonication time - dependent changes with the cup horn system at the 60% pulse mode in TCE
solution are shown in Figure 4. The greatest changes in ion concentration were observed at the 60-
minute sonication time; however, the 5-minute sonication time was sufficient to allow increases of
conductivity and Cl~ as well as decreases of pH in the sample to be noted. Sonication times greater
than 60 minutes were not examined.
                                             16

-------
era
n

I
TO

o
5



I


8,
3

a
<   ^
                   A ppm Ion Concentration
                   A ppm Ion Concentration
n
w


Q
                                                       1
                                                       I
                                                       
                                                       1.
O


O
*-i>


3
a

o
I
8

o
8-
           ApH
           ApH

-------
                                         CHAPTER 6
                                 RESULTS AND DISCUSSION
Ion Chromatography Analysis
       Increases in Cl  in a sample after sonication were used as evidence that C-C1 bond cleavage
occurred.  Organic chlorine became measurable as chloride ion.  The increases in conductivity were
due to the formation of Cl~ and other ionic products.  Ion chromatography was used to identify
products resulting from cup horn sonication experiments at the 60% pulse mode and 10 minutes
sonication time.  Four sample solutions of each analyte were examined including a 1% aqueous
solution of Triton X-100 that served as the blank for PCB solutions.  One sample solution from each
set was analyzed by ion chromatography, and the remaining three were analyzed according to the
procedure described previously.  Ion chromatograms before and after sonication are presented in
Figures 5-10 for solutions of TCE, CHC13, CC14, Ph-Cl, PCB, and Triton X-100.  Data of Cl~
concentrations in samples after sonication obtained from ion chromatography and Cl" ISE
measurements are presented in Table 4.

       The data show very good agreement for Q~ between the two methods.  This  confirmed
credibility of Cl" ISE measurements in the present work.

       Five standard solutions of Cl~  (1-15  ppm) were used to prepare a calibration curve for the ion
chromatography experiments.  Heights  of peaks were used in the regression analysis.  The correlation
coefficient was 0.996.  Chromatograms for the standard solutions  are shown in Figure 11.

       Chloride ion was not detected by either method in the deionized water used for these
experiments.  Ion chromatograms of the deionized water blanks before and after sonication are shown
in Figure 12. No changes are evident.

Table 4.       Concentration of Cl~ Obtained from Ion Chromatography and Cl~ ISE Measurements.
              (Samples sonicated in the cup horn at 60% pulse mode at 10 minutes.)

Sample

TCE (37 ppm)
CC14 (40 ppm)
CHC13 (37 ppm)
Ph-Cl (94 ppm)
PCB (55 ppm)*
1% aq.sol.Triton X-100
Method
Ion Chromatography a
Cr [ppm]
2.80
3.74
4.55
0.50
0.30
0.30
ISEb
Cr [ppm]
2.67  0.18
3.81  0.50
4.37  0.25
0.40  0.05
0.20  0.08"
0.20  0.02"
  1 sample per compound
  3 samples per compound
PCB solution in 1% aqueous solution Triton X-100.
Results below limit of quantitation. (Ref. 33)
                                              18

-------
             Before sonication
                                     cr
After sonication
Cup-horn
Pulse mode, 60%
Time, 10 min
         HCOCT
         	A	
  cr

 1
           0                          40

                                 Retention Time (min)


Figure 5. Ion chromatograms of 37 ppm TCE.
      Before sonication
                           cr
 After sonication
 Cup-horn
 Pulse mode, 60%
 Time, 10 min
          HCOO-
            !\
                                                 "V
                                                                    _,_
                                                                    <*
                                                                    II
 !i
.I  L
                            4                  0

                              Retention Time (min)
Figure 6. Ion chromatograms of 37 ppm CHC^.
                                   19

-------
us




Before sonication



V"
After sonication
Cup-horn rr
Pulse mode, 60% .
Time, 10 min ||
II
II
 
HCOCT I I
j !
  , _^JL . .J L
^- ^ 	 v. 	
      0
         0          2

Retention Time (min)
Figure 7. Ion chromatograms of 40 ppm CCLj.
       Before sonicatlon
             After sonication
             Cup-horn
             Pulse mode, 60%
             Time, 10 min
                                                  HCOO'
                                   cr
                                    A
                                        0           2
                               Retention Time (min)
Figure 8. Ion chromatograms of 94 ppm Ph-Cl.
                                      20

-------



Before sonlcatlon
|
V HCOQ- cr
; VA- w
\f^
After sonlcatlon
Cup-horn
Pulse mode, 60%
Time, 10 mln
I
: /INCOG-' cr
rv
     0             2            40            2
                                Retention Time (mln)

Figure 9. Ion chromatograms of 55 ppm PCB in 1 % Triton-X-100.
                                   40             2
                                Retention Time (min)
Figure 10.  Ion chromatograms of 1 % Triton-X-100.
                                     21

-------
      us
          CALIBRATION CURVE EQUATION: y = 10.576 x + 2.461
          Correlation Coefficient:  r = 0.996
                1 ppm
2ppm
5 ppm
10 ppm
                              Retention Time (min)

Figure 11. Ion chromatograms of Cl" standard solutions.
15 ppm
                Before sonication
                       After sonication
                       Cup-horn
                       Pulse mode, 60%
                       Time, 10 min
                              Retention Time (min)

Figure 12.  Ion chromatograms of deionized water.
                           uS
                                     4-
                                     0           2
                               Retention Time (min)
 Figure 13. Ion chromatogram of 10 ppm HCOO".

                                     22

-------
        Formate ion (HCOO~) was not detected in samples before sonication except for PCB and
 Triton X-100. Formate ion was detected in all  samples after sonication.  See Figures 5-10.  No other
 major sonication products were noted in the ion chromatograms.

        A 10 ppm standard solution of HCOO~ was run in the ion chromatography system (Figure
 13).  The height of the peak was used in calculating HCOO~ concentration insample solutions.
 Formate ion concentrations after sonication were estimated to be: 0.29 ppm (TCE sample), 0.88 ppm
 (CC14 sample), 0.69 ppm (CHC13 sample), and 0.20 ppm (Ph-Cl sample). These results are
 semiquantitative at best but give an appreciation of the HCOO~ levels.  For the PCB and Triton X-
 100 samples, the concentration of HCOO~ was  the same before and after sonication and was estimated
 to be 0.39 ppm.  Clearly, the Triton X-100 solution contained ionic impurities including Cl~, HCOO~
 and another substance which were evident in the ion chromatograms in a relatively high concentration
 but not identified.

        The concentration ratios of HCOO7C1" using the ion chromatography results were calculated
 as follows:  0.10 (0.29/2.80) (TCE), 0.23 (0.88/3.74) (CCIJ, 0.15 (0.69/4.55) (CHC13), and 0.40
 (0.20/0.50) (Ph-Cl). The highest ratio was for Ph-Cl, a compound which did not give a high Cl~
 yield. Differences in sonication mechanisms might be reflected by the ratio variations; however, time
 did not allow a detailed study of this phenomenon. A source of formate ion could also be through the
 sonochemistry of methanol which was used to prepare solutions of anlaytes.

 Changes in Conductivity

        A.  Cup-horn system, 60% pulse mode.

        Changes in conductivity with  sonication time using the cup horn system at 60% pulse mode
 are shown in Figure 14. The greatest changes of ion concentration were observed at 20 minutes, the
 lowest at 5 minutes.  Changes in conductivity for Ph-Cl solutions were noted only after 10 and 20
 minutes sonication. The changes, however, were very small (1 ppm to 2.5 ppm). PCB solutions were
 sonicated for 10 minutes; no changes  in conductivity were noted.  The greatest changes of ion
 concentration were observed with solutions of CHC13 and CC14. The average output power for the
 cup-horn system  was 160 Watts.  Temperatures  of samples after sonication ranged from 27C to 30C.

        B.  1/2" Horn probe system.

        Sonication with the  1/2" horn  probe was performed at 2 minutes in constant and 60% pulse
 modes, and at  1 minute in constant and 80% pulse modes.  The changes in conductivity of sample
 solutions are shown in Figure 15. In contrast to the cup horn system,  it  was noted that the constant
 mode is more effective  than the 60% pulse mode.  The changes of ion concentration at 2 minutes
 sonication at the 60% pulse mode were at least half those observed at  the constant mode. There were
 no significant differences noted in conductivity changes between 1 minute sonication at the constant
 and 80% pulse modes; they were higher, however, than those found after 2 minutes sonication at the
 60% pulse mode.  In the 1/2" horn probe system, effectiveness of sonication seemed greater at the
 constant mode in comparison to the cup hom. For  both systems, effectiveness increased with
 sonication time.

       The greatest changes of ion concentration with the horn probe  were  noted with solutions of
 CC14, i.e., 21 ppm at 2 minutes, and 8.5 ppm at  1 minute at constant mode.  In contrast, the greatest
changes with the cup horn were observed for CHG3 solutions. This was surprising, but the results
were found to be repeatable.
                                             23

-------
                      A ppm Ion Concentration
c


fD
9
o



5'

o
o

D.

O
I
o'
o
tt


o
o.

'O


VI
n
o
o.
o
                    en
                                              ro
                                              o
ro
01
                                                               3
                                                               a5"
                                                                                  A ppm Ion Concentration
ro
o
ro
01
CO
o
1 1



1



1



1



1

_L
fo









BilB
"0 O O H



32
52
                                                               o
                                                               o


                                                               Q-


                                                               O
                                                               O


                                                               en
                                                               O


                                                               o'
                                                               SO


                                                               o'
                                                               3  ci.

-------
        Increases in ion concentrations were observed for TCE solutions with the horn probe, but there
 were no measurable changes for Ph-Cl solutions.

        The average output power in the 1/2" horn probe was 220 watts. The temperature of a
 sample after sonication was 30-35C.

 Changes in  Cl~ Concentrations

        A.  Cup-horn system, 60% pulse mode.

        Changes in Cl~ concentration versus sonication time in the cup horn system at 60% pulse
 mode are shown in Figure 16. The greatest relative increases of Cl~ were observed with CHC13
 solutions at  each sonication time. The longer the sonication time, the greater were the increases for all
 analyte solutions. There was measurable but low Cl~ (less than 0.40 ppm) in Ph-Cl solution after  10
 and 20 minutes sonication. Changes in Cl~ concentration in PCB solutions were not noted after
 sonication for ten minutes.

        B.  1/2" Horn-probe system.

        Changes in Cl~ concentration for sample solutions after sonication in the 1/2" horn probe
 system are presented in Figure 17. The greatest increase of Cl~ was noted for CC^;  smaller changes
 of Cl~ were observed for CHC13 and TCE.  This parallels conductivity changes (Figure  15).  There
 were measurable but very small increases of Cl~ concentration for Ph-Cl solutions (estimated lower
 than 0.3 ppm) after 2 minutes sonication at the constant mode.

 Changes in pH

        A. Cup-horn system, 60% pulse mode.

        Changes of pH in sample solutions upon sonication in the cup horn at 60% pulse mode versus
 sonication time are shown in Figure 18. The changes were greater with longer sonication times. At
 20 minutes the pH decreased by 2.3 units for CC14 solutions.  The smallest relative changes of pH
 were with solutions of Ph-Cl at sonication time of 10 and 20 minutes.  These changes, however, were
 much larger than would have been predicted based on Cl~ or conductivity results. The  implication is
 that Ph-Cl is reacting but  Cl~ is not a major product.  Hydroxylation may be occuring at an open
 position of the aromatic ring. pH changes were  measurable but small with solutions of PCB, and are
 not illustrated in Figure 18.  This parallel the lack of changes in Cl~ and conductivity for PCB
 solutions mentioned earlier.

       B.  1/2" Horn-probe system.

       Changes in pH upon sonication versus time and pulse mode in the 1/2" horn probe are
presented in Figure 19.  As noted with the cup horn, pH changes were larger with longer sonication
times.  Smaller changes were noted at the 60% pulse mode in comparison to the constant mode for the
same sonication time (2 minutes). There were no differences in pH changes between the constant and
80% pulse modes at 1 minute sonication. The changes in pH at 1 minute sonication in the horn-probe
were comparable with those using the cup horn for 10 minutes of sonication.  The greatest changes of
pH  were observed in CC14 solutions at 2 minutes of sonication. The change was  a decrease in 3.8
units of pH using the constant mode. There were measurable changes in pH of the Ph-Cl solution
after sonication.  It was interesting to find that the pH changes with Ph-Cl, though small (0.3 units),
                                             25

-------
      CUP-HORN
      PULSE MODE, 60%
       CSTCE
        CHCI3
       [S3 CCI4
          Ph-CI
                       Sonication Time (min)

Figure 16. Changes in CT concentration upon sonication vs. time.
      1/2" HORN PROBE
                                                  KSTCE
                                                  M CHCI3
                                                  ^ CCI4
                                                  E3 Ph-CI
        2min-100%      2 min-60%      1 min-100%      1 min-80%
               Sonication Time (min) & Pulse Mode (%)

Figure 17. Changes in CT concentration upon sonication vs. time and pulse mode.
                           26

-------
       CUP-HORN; PULSE MODE, 60%
  -0.5-
   -1-
o.
  -1.5-
   -2-
  -2.5
              5                 10

                        Sonication Time (min)
 Figure 18. Changes in pH upon sonication vs. time.


       1/2" HORN PROBE
   -4
         2min-100%     2 min-60%   '   1 min-100%   '   1 min-80%

                 Sonication Time (min) & Pulse Mode (%)

 Figure 19. Changes in pH upon sonication vs. time and pulse mode.
                             27

-------
were significant but much smaller than the pH changes for Ph-Cl solutions in the cup hom. No
explanation can be offered at the present time.

Tap Water Samples

       Solutions of TCE (37 ppm), CC^ (40 ppm), CHC13 (37 ppm), and Ph-Cl (94 ppm) were
prepared in tap water.  Sonication was performed in the cup horn system at 60% pulse mode at 10
minutes, and in the 1/2" horn probe at 80% pulse mode at 1 minute. Using tap water solutions,
changes in conductivity and pH were observed to be far lower than those in deionized water.  This
may be explained by the initial pH. As mentioned earlier, the tap water pH was on the average 8.4,
whereas the deionized  water pH was 6.5.  It is known that the rate of organochloro compound
sonolysis increases with lower pH (23).  Also, any bicarbonates and carbonates which are present may
act as buffering agents. Furthermore, bicarbonate and carbonate may serve as  hydroxyl radical
scavengers (19), thus possibly inhibiting sonochemistry processes involving such radicals.  Figure 20
shows the differences in sonication of 37 ppm CHC13 in tap and deionized water.

       The changes observed with the  horn probe were lower than those from the cup hom comparing
either tap or deionized water.  This was expected from previous experiments under similar condition.

Well Water Samples

       Two well-water samples were sonicated in the cup horn system  at 60% pulse mode at 10
minutes.  Measurement data of conductivity, Cl~ concentrations, and pH, before and after sonication,
are presented in Table  5.  No changes were noted as a result of the sonication  within experimental
errors.  Gas chromatography/mass spectrometry results showed the presence of CHC13 at 0.6 ppm in
the Hawaii well water  sample. This concentration would not be detectable using sonication in
combination with changes in Cl~, conductivity, and/or pH with the measurement equipment used in
this research. However, it was judged important to check real-world samples in the event there were
any unknown factors which might influence changes of the parameters being measured in the absence
of 1 ppm levels or higher of organochlorine compounds.  Ion  chromatographs  of the real-world
samples showed the presence of low ppm F~,  Br~, and NO3~, and high  ppm (94 and 176) of SC^"2
in addition to Cl~.  As shown in Table  5, their presence had no impact on Cl~ conductivity,  and pH
as a result of sonication.

       No organic anions (such as formate and acetate) were shown to  be present within the
sensitivity limits of the ion chromatograph.

       The results in Table 5 show how reproducible the measurements were  with the same  sample
and how well the Cl~ results with the ISE corresponded to those obtained with the ion chromatograph.

       The real world samples numbered only two.  Additional ones will have to be examined in the
development of an ultrasound method.  Samples of well water from soil areas  rich with humus would
be especially important; however, none  were available for the present proof-of-concept study.

Reaction Mechanism

       The common denominator in the aqueous sonochemistry of organochlorine compounds is HC1.
All reports indicate it to be among  the principal products (Table 1).  However, the mechanism and rate
of the reaction  may differ markedly depending on the conditions. As shown in Table 2, there may be
a variety of products.
                                             28

-------
               CUP-HORN
               PULSE MODE, 60%
               TIME, 10 MIN
                  1/2" HORN PROBE
                  PULSE MODE, 80%
                  SONICATION TIME, 1 MIN
                                                                   SS3 conductivity
                                                                   tm or
                                                                   ESSpH
                  Tap Water
Deionized Water
Tap Water
Deionized Water
       Figure 20.  Changes upon sonication of 37 ppm CHC13 in tap and deionized water.
       Elucidation of reaction mechanism was not part of the objectives of the present work.
However, nothing was encountered which would counter the expectation that the major mechanism
involves hydrogen and hydroxyl radical reactions with the pollutants.  Under the conditions of the
present experiments, HC1 was the major ionic product. Small amounts of HCOO~ were detected as
well.  However, the formate may have originated from the sonochemistry of methanol solvent.
Another possibility might be the oxidation of methanol by secondary sonochemistry reaction products
such as Cl2or HOC1.

       Use of ultrasound in combination with Cl~ ISE appears more applicable to monitoring
nonaromatic organochlorine compounds such as TCE, CHC13 and CC14.  As discussed earlier,
relatively low yields of Cl~ were obtained from  Ph-Cl and PCBs.  Low  yield of Cl~ does not
necessarily mean that the aromatic compounds did not react. A logical explanation is that hydroxyl
radicals oxidized Ph-Cl and the PCB mixture without dehalogenation.  Sedlak and Andren (34)
examined the oxidation of PCBs by hydroxyl radicals generated with Fenton's reagent. (This is a
buffered solution of H2O2 and Fe2+.)  It was found through GC/MS that  the halogenated sites were
unreactive but that hydroxyl attacked one of the PCB nonhalogenated sites. Such  a reaction scheme,
though applicable to decomposition of Ph-Cl and PCBs, does not lead to the immediate formation Cl~
                                            29

-------
 Table 5.       Measurement data of conductivity, Cl~  and pH in well water samples.  (Samples were
               sonicated in the cup horn system at 60% pulse mode, at 10 minutes).
Sample

Brad Ford
Ash Meadow
Nevada
4/16/93l)
Average+STD
IC>
Hawaii
Grand Canyon
Arizona
4/23/93
Average
1C
Before Sonication
Conductivity
ppm
308
309
308
305
308
.*>
308+2
180
175
178
cr
ppm
41.1
40.4
40.9
39.2
44.2
38.6
40.1
40.61.8
40.10.3
19.6
20.5
20.1
21.20.1
PH
8.64
8.60
8.63
8.66
8.58
8.68
8.76
8.6510.06
8.37
8.32
8.34
After Sonication
Conductivity
ppm
305
305
308
3062
173
178
177
cr
ppm
41.3
41.6
42.2
41.70.5
19.6
20.2
19.9
PH
8.60
8.64
8.39
8.540.13
8.35
8.36
8.35
a) Sampling date
b) Volume of a sample not sufficient to measure conductivity.
c) Ion chromatography data obtained from the Analytical Lab at HRC-UNLV.1

        Essentially no Cl~ was detected with the PCB sample.  However, Cl~ in relatively low yields
was detected with Ph-Cl. This may be due to its volatility. Kotronarou and coworkers (35) reviewed
the nature of sonochemical reactions and pointed out that they  are characterized by the simultaneous
occurrence of pyrolysis and free radical reactions.  Volatile solutes will participate in pyrolysis
reactions because of their presence inside the bubbles during the collapse of the cavities.  In the
solvent layer surrounding the hot bubble, both pyrolysis and free radical reactions are possible.
Pyrolysis in the interfacial region is predominant at high solute concentrations. Free radical reactions
are likely to predominate at low  solute concentrations.  The latter mechanism is more likely for the
low ppm concentrations of  pollutants used in the present research. The relatively low yields of Cl~
from Ph-Cl and PCB  are not unexpected.

        It is interesting to note that  photocatalytic oxidation (use of TiO^ of pentachloro-phenol
through hydroxyl radical attack proceeds through the para position of the aromatic ring to form
chloride (36).  Formate and acetate  were formed during the latter stages of photooxidation. Useful
information may be gained  in predicting the outcome of sonochemical reactions by examining the
literature on hydroxyl radical oxidation.

        Possible mechanisms in the  sonochemistry of organochlorine compounds in water are
illustrated in Figure 21.
       1 Ion chromatograph Dionex DX-300, conductivity detector.  Analytical method of EPA-300.0

                                               30

-------
        ENHANCED HYDROLYSIS
              1
           -CCI
              1
                    I
           u -* - COH + HCI
           M2U     |
        REACTION WITH HO
H20 J
1
-C-CI
1
^ H + H

+ HO- 

O*
1
>  C H
1


h HOCI

        SECONDARY REACTIONS SUCH AS WITH H,O2
                        2^2
   2HO- >  H2O

    I
2 - C-CI + H2O2
    I
                                   I
                               2 - C*  + 2 HOCI
                                   I
        C-CI BOND CLEAVAGE
            1
         -C-CI
                 H2O
                '
                C-
          EXAMPLE
          CCI4  +  H20
                  CI2 + CO + 2 HCI
          2CCI'  K,^T^  C^C|6   + Cl'
                 NoH2O
        REACTION WITH H
H20 
1
-C-CI
1
i- H-

+ H-

+ HO-
1
-^ -c- +
1


HCI

Figure 21. Possible mechanisms in the sonochemistry of organochlorine compounds in water.

                           31

-------
Implications for Chemical Monitoring Methods Development

       The use of sonication in combination with measuring changes in Cl~, conductivity, and pH in
real time is a very simple approach in monitoring organochlorine compounds in water.  However,
there are many parameters that may affect the rate of Cl~ production.  One may not necessarily be
able to provide controls in a field situation to optimize the course of sonochemical reactions. For field
screening, in situations in which the potential contaminants are known and in which the water system
characteristics are understood, optimization may not be needed.  Sonication experiments with water
from a particular location using potential pollutants of interest should allow an understanding of what
to expect in monitoring the well water and what the data obtained from that well water means.

       Design of the ultrasound  system and choice of equipment options are very important.  Such
choices impact on the sonochemistry. For example, in the present work, greater changes in Cl~ and
ionic conductivity occurred with CHC13 solutions using the cup horn. However, with the horn probe,
greater changes were observed with CC14. This remains unexplained and could not have been
predicted without performing the experiments.

       The ultimate goal for field measurements is to design an ultrasound system which would allow
a probe to be placed into  2" and 4" diameter monitoring wells.  Preliminary engineering designs were
not considered under the scope of this work, but the possibility of miniaturized ultrasound systems
appears feasible. For example, tapered microtip horns are commercially available with diameters of
3.2 mm.  These can be used for volumes ranging from 1-2 mL.  The design of a cell system
compatible for both sonolysis and reaction product measurements  present technical challenges, but
these do not appear insurmountable.

       The work by Toy (27), which showed that as the volume capacity of the  same concentration of
C13CCH3 increases, the sonolysis  efficiency decreases, has important implications for in situ sonolysis
cell design.  A  system is needed with the smallest possible volume allowing solution residence time to
be maximized and products to be measured. Special cells would not be needed for situations in which
water samples were brought to ultrasound systems  emplaced in the back of a field truck or contained
in field laboratories.  Rapid screening of many samples under such situations is judged to be feasible.

       Perhaps the most  important chemical parameter which needs to be taken into account in
developing ultrasound monitoring methods is  pH.   Cheung and coworkers (23) recorded pH data in
destroying organochlorine compounds in water. The pH decreased rapidly in all  cases.  In experiments
with CH2C12, the rate of HC1 formation seemed to peak at approximately pH  4.  It was speculated that
pH may be useful in driving the reaction toward HC1 as the final product.  Results from the present
research confirmed the pH decreases. It also  appears from our work that the sonolysis of
organochlorine  compounds  is inhibited at higher pHs. As mentioned earlier,  bicarbonate and carbonate
may act as hydroxyl radical scavengers, thus inhibiting the organochlorine compound decomposition
(see the discussion on tap water and reference 19).  In any event,  more research is needed on real-
world samples to better understand  the implications of pH for monitoring methods development using
ultrasound.

       It does  not appear that chemical additives need to be considered  to achieve organochlorine
compound degradation rates for monitoring applications.  Sufficient Cl~ was  formed under the
sonication conditions examined to allow measurement using commercially available Cl~ ISEs.
Table 6 contains a summary of Cl~ yields under various sonication conditions for the experiments
discussed previously.  It is apparent that 5 minutes sonication with the cup horn at 60% pulse mode or
1 minute sonication with the W horn probe resulted in close to 3% or higher yields of Cl~. This
                                              32

-------
was sufficient to achieve detection with the commercial Cl  ISE for 37-40 ppm of TCE CHC13 and
CC14.  Lower concentrations of these compounds should be detectable by increasing the Cl~ yield.
The simplest way   would be to increase sonication time.  Twenty minutes sonication of the CHC13
solution raised the yield to 25.3%.  Optimization of yield was not part of the current research and was
not pursued further.

       Destruction of hazardous substances, including organochlorine compounds, using ultrasound
has been proposed. References were cited earlier.  In such cases high reaction yields are important.
The application examined in the present research does not  require high yields.  This should be of
advantage in designing ultrasound systems for monitoring purposes that are smaller and require less
energy. The presence of some ions such as bicarbonate and carbonate might be expected to inhibit the
desired sonochemistry.  On the other hand, other ions may increase the rate. For example, I~ was
found to  accelerate both H2S oxidation and CC14 degradation (7).

       Another important question for sonolysis experiments in the real world for monitoring
applications relates to the effect of suspended particles.  Kotronarou (19) studied the effect of large
sand particles (500 urn average)  and fine particles (7 nm average) on the sonication rate of sulfide
oxidation.  Large particles might be expected to decrease the rate because of sound attenuation.  The
fine particles might enhance the rate by providing additional nuclei for bubble formation. The effects
of sand particles at the sizes and concentrations studied were insignificant.  This implies that no
problems should be encountered in chemical monitoring scenarios.
                                              33

-------
Table 6.       Summary of Cl~ Yields [%] Under Various Sonication Conditions.
Compound
(ppm)

TCE
(37)
CHC13
(37)
CC14
(40)
Ph-Cl
(94)
Cup Horn
W Horn Probe
Deionized Water Solutions
Sonication time, min & pulse mode (%)
5(60)
3.1
5.6
4.6
-
10 (60)
10.3
13.3
9.7
0.2
20 (60)
16.8
25.3
13.1
1.8
2 (const)
5.8
15.2
22.4
1.3
2(60)
3.4
8.2
8.9
0.6
1 (Const)
2.7
7.5
8.0
1.3
1(80)
2.6
8.2
6.6
1.8
Tap Water Solutions
TCE
(37)
CHC13
(37)
CC14
(40)
Ph-Cl
(94)
-
-
-
-
6.7
8.1
10.1
0.2
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
3.0
6.1
6.8
-
                                           34

-------
                                         CHAPTER 7

                               SUMMARY AND CONCLUSIONS

        The objective of this study was to examine the potential of combining sonication with other
technologies for monitoring specific classes of organic pollutants in water. The research specifically
addressed using ultrasonic processors to decompose organochlorine compounds into ions as a
screening method for organochloro pollutants.  Changes in Cl~, conductivity, and pH were measured
using commercially available equipment before and after sonication.

        The results obtained are very promising. Chloride ion could be detected in aqueous solutions
of low ppm CC14, CHC13, and TCE after one minute sonication. The increases of Cl~ were
accompanied by increases in conductivity and decreases of pH. The conductivity changes were higher
than expected based on measured Cl~. Ion chromatography of solutions before and after sonication
showed that formate  ion was also formed.  Other ions may have formed as well, but the concentrations
were too low to allow their detection relative to formate and chloride. Aromatic and polyaromatic
chloro compounds represented by Ph-Cl and PCBs, respectively, did not form chloride ion as readily
as did CC14, CHC13, and TCE.  Molecular decomposition may have occurred through sonication by
other mechanisms but not resulting in high yields of Cl~.  The PCB solutions gave no measurable
changes in either Cl~, conductivity, or pH.

       The potential of combining sonication with commercially available measurement technologies
for monitoring specific pollutants in water is judged to be high. The  results achieved with the
organochlorine compounds CC14, CHC13, and TCE  serve as proof-of-principle and form a base of
information which can be used to develop ultrasound monitoring methods for these compounds. The
probability of success of similar approaches in developing ultrasound monitoring methods for other
classes of pollutants is judged to be high.
                                              35

-------
                                      BIBLIOGRAPHY

(1)     Koglin, E.N., and Poziomek, E.J., Field Screening and Analysis Technologies:  An Overview
       of the State of the Art.  In: Monitoring and Measurement Technologies for Hazardous
       Substances.  Water Environment Federation, Alexandria, Virginia, 1993.  In press.

(2)     Makeig, K.S., Regulatory Mandates for Controls on Ground-Water Monitoring. In: Practical
       Handbook of Ground-Water Monitoring.  D.M. Nielson, ed., Lewis Publishers, Chelsea,
       Michigan, 1991.  697 pp.

(3)     Eschner, E., et al., Monitoring Technologies for Wellhead Protection.  U.S. Environmental
       Protection Agency, Environmental Monitoring Systems Laboratory, Las Vegas, Nevada,
       EPA/600/4-91/020, July  1991, 147 pp.

(4)     Todd, O.K., Tinlin, R.M., Schmidt, K.D., Everett, L.D., Monitoring Groundwater  Quality:
       Monitoring Methodology. EPA-600/4-76/026.  U.S. Environmental Protection Agency,
       Environmental Monitoring Systems Laboratory, Las Vegas, Nevada, 1976.

(5)     U.S. Environmental Protection Agency, Transport and Fate of Contaminants in the Subsurface
       (Seminar Publication). Center for Environmental Research Information and R.S. Kerr
       Research Laboratory. EPA-625/4-89/019.  R.S. Kerr Environmental Research Laboratory.
       Ada, Oklahoma,  1989.

(6)     U.S. Environmental Protection Agency.  Test Methods for Evaluating Solid Waste, 3rd ed.
       EPA SW-846, Method 3550, U.S. Government Printing Office, Washington, DC,  1990.

(7)     Kotronarou, A., Mills, G., and Hoffmann, M.R., Decomposition of Parathion in Aqueous
       Solution by Ultrasound Irradiation. Environ. Sci.  Technol. 1992, 26(7): 1460-1462.

(8)     Suslick, K.S., ed. Ultrasound:  Its Chemical, Physical, and Biological Effect.  VCH
       Publishers, Inc., New York,  1988, 336 pp.

(9)     Mason, T.J., Chemistry with Ultrasound.  Elsevier Applied Science, New York, 1990, 195 pp.

(10)    Gallon, F., Inquiries into Human Faculty and Development. MacMillan, London, 1883.

(11)    Atchley, A.A., and Crum, L.A., Acoustic Cavitation and Bubble Dynamics.  In: Ultrasound:
       Its Chemical, Physical and Biological Effects, K.S. Suslick, ed., VCH Publishers,  Inc., New
       York, 1988, pp. 1-64. (Thornycraft, J.; Bamaby, S.W.; Inst. Civ.  Eng. 122, 51, 1985.)

(12)    Flint, E.B.; Suslick, K.S., The Temperature of Cavitation.  Science 1991, 253, 1397-1399.

(13)    Suslick, K.S., Hammerton, D.A., and Cline, R.E., The Sonochemical Hot Spots. /. Am. Chem.
       Soc., 1986, 108, 5641-5642.
                                             36

-------
 (14)    Shoh, A., Industrial Applications of Ultrasound. In: Ultrasound: Its Chemical, Physical, and
        Biological Effects, K.S. Suslick, ed., VCH Publishers, Inc., New York, 1988, 336 pp.

 (15)    Richards, W.T., and Loomis, A.L., The Chemical Effects of High Frequency Sound Waves I.
        A Preliminary Survey., /. Am. Chem. Soc., 1927, 49, 3086-3099.

 (16)    Suslick, K.S., Homogeneous Sonochemistry.  In: Ultrasound:  Its Chemical, Physical and
        Biological Effects, K.S. Suslick, ed., VCH Publishers, Inc., New York, 1988, pp.  123-163.

 (17)    Boudjouk, P., Heterogeneous Sonochemistry, In: Ultrasound: Its Chemical, Physical and
        Biological Effects, K.S. Suslick, ed., VCH Publishers, Inc., New York, 1988, pp.  165-226.

 (18)    Smith, P.O., Johnson, C.H., Olson, A.R., Oxidation Promoted by Ultrasonic Radiation.  J. Am.
        Chem. Soc., 1929, 57, 370-377.

 (19)    Kotronarou, A., Ultrasonic Irradiation of Chemical Compounds in Aqueous Solutions.  Ph.D.
        Thesis, California Institute of Technology, Pasadena, California, 1992.

 (20)    Weissler, A., Cooper, H.W., and Snyder, S., Chemical Effect of Ultrasonic Waves: Oxidation
        of Potassium Iodide Solution by Carbon Tetrachloride.  /. Am. Chem. Soc., 1950,  72, 1769-
        1775.

 (21)    Spurlock, L.A., and Reifsneider, S.B., Chemistry of Ultrasound.  I. A Reconsideration of First
        Principles and the Applications to  a Dialkyl Sulfide. /. Am. Chem.  Soc. 1970, 92, 6112-6117.

 (22)    Chendke, P.K.,  and Fogler, H.S., Sonoluminescence and Sonochemical Reactions of Aqueous
        Carbon Tetrachloride Solutions. /. Phys. Chem., 1983, 87, 1362-1369.

 (23)    Cheung, M., Bhatnagar, A., and Jansen, G., Sonochemical Destruction of Chlorinated
        Hydrocarbons in Dilute Aqueous Solution.  Environm. Sci. Technol. 1991, 25, 1510-1512.

 (24)    Lorimer, J.P., and Mason, T.J., Effect of Ultrasonic Irradiation on the Solvolysis of 2-Cloro-2-
        methylpropane in Aqueous Ethanol Mixtures. J. Am. Chem. Soc. Chem. Commun. 1980, 1135-
        1136.

 (25)    Mason, T.J., Lorimer,  J.P., Mistry, B.P., The Effect of Ultrasound on the  Solvolysis of
        Methylpropane in Aqueous Media.  Tetrahedron Lett.,  1980, 23, 5363-5364.

 (26)    Sakai,  Y., Sadaoka, Y., Takamaru, Y., Decomposition of Chloral Hydrate in Aqueous Solution
        by Action of Ultrasound. J. Phys. Chem., 1977, 81, 509-511.

(27)    Toy, M.S.,  Stringham, R.S., and Passel,  T.O., Sonolysis Transformation of 1,1,1-
        Trichloroethane in Water and Its Process Analyses.  "Preprint Extended Abstract,"  Presented
        before the Division of Environmental Chemistry, American Chemical Society, Atlanta,
        Georgia, April 14-19, 1993, pp. 420-421.

(28)   Jennings, B.H.,  and Townsend, S.N., The Sonochemical Reactions of Carbon Tetrachloride and
       Chloroform in Aqueous Suspension in an Inert Atmosphere. J. Phys. Chem., 1961, 65,  1574-
        1579.
                                             37

-------
       (29)   Suslick, K.S., and Schubert P.P., Sonochemistry of Mn2(CO)10 and Re2(CO)10. J. Am. Chem.
              Soc., 1983, 705, 6042-6044.

       (30)   Weissler, A., Pecht, I., and Anabar, M., Ultrasound Chemical Effects on Pure Organic Liquids.
              Science, 1965, 150, 1288-1289.

       (31)   Poziomek, E.J., Personal Communication with H.M. Cheung, August 1993.

       (32)   Pettier, C., Micolle, M., Merlin, G., Luche, J.L., and Reverdy, G., Characteristic of
              Pentachlorophenate Degradation in Aqueous Solution by Means of Ultrasound.  Environ. Sci.
              TechnoL, 1992, 26, 1639-1642.

       (33)   Taylor, J.K., Quality Assurance of Chemical Measurements,  ed., Lewis Publishers, 1987.

       (34)   Sedlak, D.L., and Andren, A.W., Aqueous-Phase Oxidation of Polychlorinated Biphenyls by
              Hydroxyl Radicals.  Environ. Sci. TechnoL, 1991, 25,  1419-1427.

       (35)   Kotronarou, A., Mills, G., and Hoffman, M.R., Ultrasonic Irradiation of p-Nitrophenol in
              Aqueous Solution. J. Phys. Chem., 1991, 95, 3630-3638.

       (36)   Mills, G., and Hoffman, M.R., Photocatalytic Degradation of Pentachlorophenol on Ti2O
              Particles:  Identification of Intermediates and Mechanism of  Reaction. Environ. Sci. TechnoL,
              1993, 27, 1681-1689.
U.S. Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boulevard, 12th Floor
Chicago, IL  60604-3590
38
        &U.S. GOVERNMENT PRINTING OFFICE: 14*4 - S50-OOI/OOI69

-------