United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Las Vegas, NV 89193-3478
Research and Development
EPA/540/SR-94/502
August 1994
EPA Project Summary
Potential Use of Ultrasound in
Chemical Monitoring
Grazyna E. Orzechowska, Edward J. Poziomek, and William H. Engelmann
EPA has been examining the poten-
tial of combining sonication with exist-
ing measurement technologies for
monitoring specific classes of organic
pollutants in water. The research spe-
cifically addressed using ultrasound (ul-
trasonic) processors to decompose
aqueous organochlorine compounds
into ions as a screening method for
organochlorine pollutants in water.
The approach in using sonication is
applicable to other organic compounds
that contain other halides, phospho-
rus, nitrogen, and sulfur that, when re-
leased, could be easily quantified. An-
ions specific to the inorganic compo-
nents would be produced in sonica-
tion. Changes in ion concentrations
before and after sonication would be
used in monitoring for the pollutants.
The organochlorine compounds tested
were those usually found as volatile
organic compounds (VOCs) at hazard-
ous waste sites. The success with com-
pounds, such as trichloroethylene
(C2HCI3), chloroform (CHCI3), and car-
bon tetrachloride (CCI4) served as proof-
of-principle and forms a rationale for
expanding the research to other pollut-
ant classes.
This Project Summary was developed
by ERA'S Environmental Monitoring
Systems Laboratory, Las Vegas, NV, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
The research described in the full re-
port (based on the Master of Science the-
sis of the first author, G. E. Orzechowska)
relates to a search for new concepts for field
screening methods applicable to hazardous
waste sites with emphasis on in situ ground-
water monitoring.
Field screening involves the use of rapid,
low-cost test methods to determine whether
a parameter of interest was present or ab-
sent, above or below a predetermined thresh-
old at a given site, or at a concentration within
a predetermined range of interest. Screening
methods can be used in the field to identify
the nature and extent of contamination at
individual sites.
The overall challenge of field screening
involves dealing with numerous com-
pounds within many classes (organic, in-
organic, biomarker, and radionuclide),
across various media, and in complex mix-
tures. The detection limits of field meth-
ods are not always as low as laboratory
methods and the accuracy of field meth-
ods is not always as reliable as laboratory
methods. This is especially critical, for ex-
ample, if the detection limit of the field
method does not meet water quality crite-
ria or regulatory requirements. Neverthe-
less, less accurate methods can be useful
to screen samples before confirmatory
laboratory analyses. The advantage is in
cost savings by limiting the number of
samples sent for laboratory analyses.
A few field screening methods are avail-
able now and more are being developed.
The most mature are judged to be those
based on gas chromatography and x-ray
fluorescence. One of the clear trends is to
miniaturize. Methods that are still in vari-
ous stages of development include the
use of fiber optic sensors and chemical
microsensors, such as piezoelectric quartz
microbalances and surface acoustic wave
Printed on Recycled Paper
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(SAW) probes. The technologies devel-
oped as field screening methods are rel-
evant to the monitoring and measurements
needs of many U.S. Environmental Pro-
tection Agency programs. The need for
ground-water monitoring relates to pro-
tecting public water supply wells, well
fields, springs, and hazardous waste sites
as well.
Ground water contains a variety of natu-
ral constituents; the various chemical spe-
cies and concentrations depend on fac-
tors such as the specific geochemical en-
vironment and the source of the ground
water. The major anions that are usually
analyzed to indicate general water quality
include bicarbonate, chloride, nitrate, and
sulfate. Other general indicators of water
quality include electrical conductivity, tem-
perature, pH, dissolved oxygen (DO), bio-
chemical oxygen demand (BOD), chemi-
cal oxygen demand (COD), total organic
carbon (TOG), oxidation reduction (redox)
potential, total suspended solids (TSS),
total dissolved solids (TDS), and turbidity.
The central idea brought forward in this
research was to measure the significant
parameters such as pH, electrical con-
ductivity, and specific anion concentration
before and after sonication of a water
sample.
The current research combines sonica-
tion with commercially available probes
and offers a simple and low-cost approach
toward field screening and monitoring.
Description of Ultrasound
Ultrasound is defined as any sound that
is of frequency beyond response of the
human ear, i.e., generally above 16 kHz.
Physical as well as chemical changes are
caused by ultrasound and are categorized
Into two frequency ranges: (1) high fre-
quency or diagnostic ultrasound (2-10
MHz) that causes temporary physical
changes in the medium and (2) low fre-
quency or power ultrasound (20-100 kHz)
that affects chemical reactivity by cavita-
tion (formation of microbubbles). Average
temperatures of 5,000°K and pressures of
the order of 1,000 atmospheres are gen-
erated by the collapse of cav'rtation bubbles
resulting from the ultrasound power.
Sonochemistry
Sonochemical reactions can be catego-
rized as (1) 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 and (2) secondary
reactions Involving radicals from primary
reactions and other species.
The topics most relevant to this research
are homogeneous aqueous sonochemistry
and the sonochemistry of organochlorine
compounds.
Principal products from ultrasonic irra-
diation of water are H2O2 and H2. The
formation of H* and HO- was attributed to
the thermal dissociation of water vapor
present in the cavities during the com-
pression phase. The wide range of oxida-
tions and reductions that occur with aque-
ous sonochemistry is often a consequence
of secondary reactions of these high en-
ergy intermediates.
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. The sonica-
tion of aqueous solutions of organochlo-
rine compounds leads to different prod-
ucts. However, the common product was
HCI, as the result of C-CI bond cleavage,
as in CCI4 + H2O —> CI2 + CO + 2 HCI.
Reviewing the literature on sonochemistry
of organochlorine compounds did not lead
to any reports on the use of ultrasound for
chemical monitoring. However, the reported
sonochemistry of organochlorine com-
pounds in water gave much support for
using sonication in combination with
changes in chloride ion, conductivity, and/
or pH as a way of monitoring for the
presence of the compounds in water.
Research Design Elements
The following materials and equipment
were used:
• Four VOC analytes (3-40 ppm) CCI4,
CHCI3, C2HCI3, C6H5-CI
• One polychlorinated biphenyl (PCB)
analyte:
(5-55 ppm in methanol-H2O with
1% surfactant)
• Ultrasound systems with cup-horn and
1/2-inch diameter horn-probe
• Commercially available probes such
as:
ion selective electrodes (ISEs), con-
ductivity cells, and a pH electrode
The following parameters were investi-
gated:
• Sonication times (1-90 minutes)
• Continuous vs. pulsed ultrasonic
• Sample temperatures (constant 30°C)
• Sample volumes (8-15 ml_)
• Water sources (deionized, tap, well)
Summary and Conclusions
The common denominator in the aque-
ous sonochemistry of organochlorine com-
pounds is HCI. However, the mechanism
and rate of the reaction may differ mark-
edly depending on the conditions under
which the sonication was performed. Elu-
cidation of reaction mechanism was not
part of the objectives of the present work.
However, nothing was encountered that
would counter the expectation that the
major mechanism involves hydrogen and
hydroxyl radical reactions with the pollut-
ants. Under the conditions of the present
experiments, HCI was the major ionic
product. Small amounts of formate ions
(HCOO-) were detected as well. How-
ever, the formate ions may have origi-
nated from the sonochemistry of the
methanol solvent. Another possibility might
be the oxidation of methanol by secondary
sonochemistry reaction products such as
chlorine (Cl) or hypochlorite ion (OCI").
Use of ultrasound in combination with
chloride ISE appears more applicable to
monitoring nonaromatic organochlorine
compounds such as C2HCI , CHCI3 and
CCI4. As discussed in the full report, rela-
tively low yields of chloride ion were ob-
tained from chlorobenzene (Ph-CI) and
PCBs. Low yield of chloride ion does not
necessarily mean that the aromatic com-
pounds did not react. A logical explana-
tion is that hydroxyl radicals oxidized Ph-
CI and the PCB mixture without
dehalogenation. Such a reaction scheme,
though applicable to decomposition of
Ph-CI and PCBs, does not lead to the
immediate formation of chloride ion.
Sufficient chloride ion was formed un-
der the sonication conditions examined to
allow measurement using commercially
available chloride ISE. It was apparent
that 5 minutes sonication with the cup
horn at 60% pulse mode or 1 minute soni-
cation with the 1/2" horn probe resulted in
close to 3% or higher yields of chloride
ion. This was sufficient to achieve detec-
tion with the commercial chloride ISE for
37-40 ppm of C2HCI3 CHCI3 and CCI4.
Lower concentrations of these compounds
should be detectable by increasing the
chloride-ion yield.
It was speculated that pH may be use-
ful in driving the reaction toward HCI as
the final product. Results from the present
research confirmed the pH decreases. It
also appears from the work that the
sonolysis of organochlorine compounds
was inhibited at higher pHs. Bicarbonate
and carbonate may act as hydroxyl radi-
cal scavengers, thus inhibiting the orga-
nochlorine compound decomposition. In
any event, more research is needed on
real-world samples to better understand
the implications of pH for monitoring meth-
ods development using ultrasound.
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Conductivity changes were higher than
expected based on measured chloride ion.
Ion chromatography of solutions before
and after sonication showed that formate
Ion was produced by the sonication. 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 com-
pounds represented by Ph-CI and PCBs,
respectively, did not form chloride ion as
readily as did CCI4, CHCI3> and C2HCI3.
Molecular decomposition may have oc-
curred through sonication by other mecha-
nisms but did not result in high yields of
chloride ion. The PCB solutions produced
no measurable changes in chloride ion,
conductivity, or pH under sonication.
The potential of combining sonication
with commercially available measurement
technologies for monitoring specific pollut-
ants in water is judged to be high. The
results achieved with the organochlorine com-
pounds CCI4 CHCI and C2HCI3 serve as
proof-of-principle and form a base of informa-
tion that can be used to develop ultrasonic
monitoring methods for these compounds.
Srazyna E. Orzechowska is a graduate student at the University ofNevada-L V, Las
Vegas, NV 89154-4009 and Edward J. Poziomek is with the Harry Reid Center
for Environmental Studies, University of Nevada-LV, Las Vegas, NV 89154-4009.
The EPA author, William H. Engelmann, (also the EPA Project Officer, see
below), iswith the Environmental Monitoring Systems Laboratory, Las Vegas, NV
89193-3478.
The complete report, entitled "Potential Use of Ultrasound in Chemical Monitoring,"
(Order No. PB94-188190; Cost: $17.50, subjectto change) will be available only
from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Las Vegas, NV 89193-3478
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
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PERMIT No. G-35
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Penally for Private Use $300
EPA/S40/SR-94/502
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