Environmental hazard and risk assessment under the United States Toxic Substances Control Act

Abstract

The Toxic Substances Control Act (TSCA) was enacted in 1976 and provides for the regulation of industrial chemicals. TSCA allows for regulation of a chemical if there is an unreasonable risk towards human health or the environment, and it allows for testing if a chemical may present an unreasonable risk or has significant exposure towards humans or the environment. Risk assessment under TSCA consists of the integration of the hazard assessment for a chemical with the chemical's exposure assessment. The environmental hazard assessment consists of identifying all of the effects of a chemical towards organisms in the environment, and towards the populations, communitities, and ecosystems to which those organisms belong. Toxicity data for a chemical consists of effective concentrations (EC) which indicate the type of effect and the seriousness of that effect at a known concentration of chemical. Effective concentrations are either measured or predicted using structure activity relationships (SAR). SAR may consist of nearest analog analysis, member of a toxic chemical class, or quantitative SAR (QSAR). A collection of all of the ECs for a chemical is called a hazard profile or a toxicity profile. The environmental exposure assessment consists of measuring or predicting the environmental concentrations of a chemical from releases due to its production, processing, uses, and disposal. There are two types of exposure assessment most frequently used under TSCA: the Percentile Stream Flow Method and the Probability Dilution Model (PDM) Method. Environmental risk assessment under TSCA is performed by using the quotient method. This method simply compares an EC with the actual or predicted environmental concentrations (PEC). If the PEC is greater than the EC, then you have a potential risk. The risk assessment process usually consists of three steps: (i) worst case risk assessment, (ii) identification of the type or risk (e.g., acute and/or chronic risk), and (iii) quantification of the degree of environmental risk or the potential environmental impact expected for each type of risk. If the risk assessment determines that a chemical presents a potential risk to the environment, then the results of this assessment are integrated with the economic assessment, any relative risk factors, and governmental policy in order to decide whether a chemical present an unreasonable risk to the environment.