Environmental Modeling

Assessing the potential effects on natural communities, ecosystems, and individual organisms, or selected groups of organisms, within ecosystems is becoming integral to the regulation of pesticides and industrial chemicals. In certain cases, potential effects on the environment drive the decisions regarding uses of a chemical. Exponent specializes in solving challenging ecological risk and environmental issues. When necessary, Exponent can draw on additional in-house expertise to conduct higher-tier modeling and assessments, including probabilistic assessments, or higher-level statistical analyses of data, such as monitoring data, to address regulatory issues. 

The Exponent team can also conduct higher-tier evaluations of the available toxicity data that makes use of the full data sets, rather than the limited use and extrapolations of toxicity data that are typically used by regulators in a screening-level assessment. Combining this with more detailed, realistic estimates of exposure often results in a very different picture of potential risk than is provided by the standard regulatory screening-level assessment.

In the U.S., the legal framework for evaluating uses and potential environmental effects and risks of chemicals includes the Federal Insecticide, Fungicide, and Rodenticide Act, the Toxic Substances Control Act, and other federal and state environmental statutes. The U.S. EPA has primary responsibility for overseeing and administering many of these requirements. Similar legislation exists in the EU, including the Plant Protection Products Directive (919/414/EEC) and the BIocidal products Directive (98/8/EC).

The processes and methods for conducting environmental and ecological assessments are becoming increasingly complex, both in terms of estimating potential exposures, and in utilizing toxicity data generated on different types of non-target organisms. These organisms include mammals, birds, fish, aquatic and terrestrial invertebrates, soil micro- and macro-organisms, and aquatic and terrestrial plants. These two basic components—estimated exposure and toxicity data—are integrated for conducting an ecological risk assessment that evaluates the potential for adverse effects to organisms, communities, or ecosystems from the use or release of a chemical.

The estimates for potential exposure of non-target organisms to a chemical are increasingly reached by computer modeling. A variety of models are used to estimate potential exposure of non-target organisms to chemicals in different environmental media, such as soil, sediment, surface water, groundwater, and feed items. Some of these models are also used to estimate human exposure to chemicals in drinking water. For example, the U.S. EPA uses models such as GENEEC, FIRST, PRZM-EXAMS, T-rex, SciGrow, and TerrPlant. In the EU, the models PRZM, PELMO, PEARL, MACRO, TOXSWA, and SWASH are used routinely. The results of these modeled exposures are then matched with appropriate toxicity data to conduct both acute and long-term (subchronic, chronic) ecological risk assessments, or as inputs for human dietary assessments.

Exponent’s specialists are familiar with all the models used in regulation (either by regulators or notifiers), and are skilled in all aspects of ecological risk assessment and human dietary assessment derived in part through environmental fate modeling. As part of the EU system, notifiers must supply their own dossiers and risk assessments in their regulatory submission, and Exponent has many years of experience in writing these documents and conducting the risk assessments. Exponent staff also participate in various EU expert technical groups developing guidance (e.g., FOCUS) and hence are well-suited to advise clients on forthcoming changes to the system. Exponent routinely conducts the types of modeling done by U.S. regulatory agencies, and therefore can conduct all the exposure modeling and related ecological assessments a priori, to support submissions to regulatory agencies, to provide a client with a thorough up-front understanding of how regulatory agencies will evaluate a chemical, and to evaluate potential mitigation measures, if needed. Exponent’s environmental specialists can also efficiently evaluate and respond to the conservative, screening-level assessments conducted by regulatory agencies.

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