Ecokinetics: A study of the fate and distribution of chemicals in laboratory ecosystems

Abstract

The anticipated kinetic behavior of different amounts or forms of a chemical in the environment can be studied by introducing the chemical into a laboratory ecosystem, collecting samples of the different components of the system at various times, and obtaining a sequence of concentrations of the chemical and/or its metabolites. Conventional compartmental models can be used to characterize this concentration-time data in order to better predict the distribution and ultimate fate of a chemical introduced into the environment, to provide a quantitative measure for helping assess the environmental impact of different chemicals, and to reduce the cost of expensive laboratory testing and field work. SCOPEMost progressive industrial companies are committed to exercising responsible care for all products both during manufacture and later in their use by the customer. This product stewardship concept makes it necessary to collect and interpret meaningful data to assess the environmental impact of each new or existing product so that appropriate steps can be taken to protect employee and public health as well as the environment as a whole. One method being pursued is to build laboratory ecosystems which simulate typical environmental conditions. Then the kinetic behavior of different amounts or form of chemical is examined by introducing it into the simulated ecosystem, collecting samples of the different components of the system at various times, and obtaining a sequence of concentrations or amounts of the chemical and/or its metabolites. Collection of kinetic data is a departure from the standard practice of determining the residue at one or at most two time periods remote from the exposure time. In this paper we show that a conventional compartmental analysis can be used to characterize this data. The parameters of the characterizing model make it possible to compare the potential environmental impact of different chemicals. The model itself makes it possible to predict the time distribution in the environment for different modes of exposure (for example, slow release, accidental spill, etc.) so that proper exposure levels and handling procedures can be determined even before environmental testing is initiated.Two major problems are associated with the use of compartmental models. The first is the development of plausible models for a particular ecosystem. This requires considerable background in the field from which the problem arises. Accumulated knowledge must provide some justification for the model selected and the parameters selected must have meaning in terms of known processes and the structure of the real system. The second problem is the socalled "inverse" of the first. That is, given one or more plausible models for an ecosystem, what data should be collected to decide which model is the most suitable and to obtain meaningful estimates of the model parameters. Recently developed model discrimination and nonlinear parameter estimation techniques are combined in an iterative computer-based model building proce...

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