ELEGANT ANALYTICAL CHEMISTRY APPLIED TO ENVIRONMENTAL PROBLEMS - A PRACTICAL SYMPOSIUM ppt

SELECTIVE MONITORING TO ASSESS THE BIOAVAILABILITY

OF ORGANIC CHEMICALS IN AQUATIC SYSTEMS

S. W. Morrall, C. A. Smith, W. M. Begley, D. J. Versteeg and J. M. Rawlings

Human and Environmental Safety Division, The Procter & Gamble Co.,

PO Box 538707, Cincinnati, OH 45253

The risk a chemical poses to the aquatic environment is a function of concentration,

toxicity, and bioavailability. The concentration of a chemical in the environment

represents a maximum dose that is potentially available to an organism. Bioavailability

describes the fraction of this potential dose that the organism actually encounters.

Bioavailability is determined to an extent by physical properties, such as aqueous

solubility, vapor pressure, and partitioning. However, the entire system; biota,

environmental compartment composition, and physico-chemical properties are

intimately related and their interaction ultimately defines the actual dose or

bioavailability of a chemical. We can do a reasonable job of estimating both toxicity,

via laboratory testing, and environmental concentration, by direct measurement and

modeling. However, accurate assessment of the bioavailability of organic compounds

in aquatic systems has remained elusive due to the complexity and variability inherent

to the environment.

In an aquatic system, organic compounds can be in molecular solution, associated

with dissolved organic carbon (DOC), sorbed to colloids, suspended particulates, and

sediment. The chemical is available to different organisms to varying degrees,

depending upon what form it is. For example partitioning from a dissolved phase to

sediment will reduce bioavailability to many fish, but increase availability to organisms

that “graze” on periphyton attached to the sediment. Additional variables that impact

effects to biological organisms and ultimately risk to the ecosystem, include the

physical properties and chemical composition of the aquatic system, route of chemical

exposure to organisms, and form of ionizable molecules. Integration of all these factors

Preprints of Extended Abstracts Vol. 41 No. 1

668

ELEGANT ANALYTICAL CHEMISTRY APPLIED TO ENVIRONMENTAL

PROBLEMS — A PRACTICAL SYMPOSIUM

Organized by

V. Turoski, S.D. Richardson and J. Plude

Symposia Papers Presented Before the Division of Environmental Chemistry

American Chemical Society

San Diego, CA April 1-5, 2001