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National Hxposure Research Laboratory
Research Abstract

GPRA Goal 8 - (Sound Science)

Significant Research Findings:

Speciation of Complex Organic Contaminants in Water

Scientific	Environmental assessments of organic chemicals are generally conducted

Problem and	by the Agency with the assumption that only non-complexed, neutral

Policy Issues	chemicals exist in water and soil-water systems. However, many chemicals

of environmental concern are of such complexity, containing numerous
heteroatoms and ionizable groups, that this assumption does not hold.
Processes that determine the environmental fate and transport of chemicals
are altered greatly when neutral chemicals ionize or form complexes with
water. Also, metabolism and human and ecological toxicity differ greatly
for different ionization species of a given chemical. This situation
introduces large uncertainties in exposure and risk assessments. Prior to
this research, there has not been an experimental tool available that allows
determination of exact speciation of organic chemicals in aqueous or
biological systems.

Research	This research resulted in the development, testing, and application of an

Approach	analytical method by which a chemical that exhibits complex speciation can

be (for the first time) fully described in water. The approach is based on
modeling temperature- and pH-variant Raman spectra according to well-
established equations from physical chemistry. This research project was
subjected to two major peer reviews and each of the research products
(listed below) was subjected to extensive internal- and peer-review prior to
publication.

Results and
Implications

An acceptable analytical method for fully describing organic chemical
speciation must first inform the user as to the number of species present.
Second, it must allow qualitative identification of these species. Third, it
must inform the user of the concentration of each species (i.e., it must
provide the equilibrium constants that couple the species). Finally, it is
critical that the chemical equilibrium not be disturbed during the course of
the analytical measurement. No methods were available prior to this
research that met all of these criteria. This research was conducted under

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the hypothesis that a method based on modeling temperature- and pH-
variant data from a modern Raman spectrometer could meet these stringent
demands. Further, it was proposed that the method could be designed such
that the frequency and intensity fluctuations that accompany Raman spectra
could be minimized to the point that they are insignificant. As described in
the research products listed below, it was found that, indeed, the method
meets these stringent demands. Further it was found that results from the
method were robust and sufficiently insensitive to frequency and intensity
fluctuations. This method opens many new scientific doors. For example,
it is now possible to obtain quantitative and qualitative information on
individual tautomers, which are chemical species that cannot be physically
separated one from the other, although they differ in structure and, often to
a great extent, in behavior (e.g., toxicity, reactivity, etc.) Most importantly
for EPA, this method can be used to determine the exact form of a chemical
present in the aquatic environment, or present inside the body of humans or
other organisms. With this information, exposure and risk assessments can
be much more certain because risk from various forms of the same
chemical often differ dramatically.

This research was carried out entirely in-house at the Ecosystems Research
Division of NERL by Dr. Tim Collette and his collaborators (post-doctoral
associates, students). However, it is a component of a task with the larger
goal of forecasting chemical fate in the environment. This task includes
collaboration with about 10 other senior EPA scientists and several
colleagues at the University of Georgia.

Examples of recent publications from this study include:

A Method for the Measurement of Site-specific Tautomeric and
Zwitterionic Microspecies Equilibrium Constants. J.C. D'Angelo and T.W.
Collette, Anal. Chem. 69, 1642-1650 (1997).

Speciation of Complex Organic Contaminants with Raman Spectroscopy.
R. T. Bishop, J.C. D'Angelo, and T.W. Collette, in SPIE Proceedings 3534
Environmental Monitoring and Remediation Technologies, ed. T. Vo-Dinh
and R. L. Spellicy, February 1999.

Optimization of Raman Spectroscopy for Speciation of Organics in Water.
T.W. Collette, T.L. Williams, and J.C. D'Angelo, Appl. Spectros. 55,
750-766 (2001).

"Environmental Applications of Raman Spectroscopy to Aqueous
Systems," T.L. Williams and T.W. Collette, in Handbook of Raman
Spectroscopy, ed. I.R. Lewis and H.G.M. Edwards, Marcel Dekker: New

Research
Collaboration and
Publications

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York, NY, 2001, Chapter 17, pp. 683-731.

The Role of Raman Spectroscopy in the Analytical Chemistry of Potable
Water. T.W. Collette and T.L. Williams, J. Environ. Monitor. 4, 27-34
(2002).

Raman Spectroscopy for Speciation of Organics in Water. T.W. Collette,
T.L. Williams, and J.C. D'Angelo, in Raman Review: New Developments
in Raman Spectroscopy, Kaiser Optical Systems, Inc., Ann Arbor, MI,
Issue 1, 2003, pp. 1-3.

Also, Dr. Collette has presented, on invitation, eight lectures on this topic
at national and international conferences since 1997; and he, or his
coworkers, have presented about eight submitted talks during this time.

Future Research Current and future research is focused on two important areas - 1) applying
the method to key chemicals of environmental concern, and 2) improving
the method and extending its range of applicability. For example, at
present we are successfully improving the method by conducting
experiments at elevated pressure. This allows us to extend the range over
which the sample temperature can be varied, which improves method
accuracy and applicability.

Questions and inquiries can be directed to:

Timothy W. Collette, Ph.D.

U.S. EPA, Office of Research and Development
National Exposure Research Laboratory
Ecosystems Research Division
960 College Station Rd
Phone: 706/355-8211
E-mail: collette.tim@epa.gov

Funding for this project was through the U.S. EPA's Office of Research and
Development, National Exposure Research Laboratory, and the work was
conducted by the Ecosystems Research Division.

Contacts for

Additional

Information

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