Tier-testing environmental chemicals

U.S. Environmental Protection Agency Toxic Substances Control Act (U.S. EPA TSCA) Chemical Inventory and Test Submission Data Base, 13 694 U.S. EPA Tier 2 specification, gasoline sulfur content, 10 54. See also Environmental Protection Agency (EPA)... 

Tier 2 PRA process involved developing environmental exposure data and chronic toxicity data distributions for individual POPs. The mean concentrations of POPs in local marine water measured at various locations were used as exposure data in the construction of the exposure distribution. The chronic toxicity data distribution was established based on published international acute toxicity data (LC50, EC50) on a variety of aquatic organisms tested in many jurisdictions, drawn primarily from the USEPA ECOTOX database (2002) (available at http //www.epa.gov/ ecotox). If the upper 5th centile of the measured chemical exposure data distribution did not exceed the lower 5th centile of its estimated chronic toxicity distribution, the potential ecological risk posed by the chemical was judged to be tolerable (Hall and Giddings, 2000). 

Along with the toxicity test battery, physico-chemical analysis of waste and each leachate produced either in the prerequisite study (i.e. Tier I in Figure 2) or in the WASTOXHAS procedure are useful to understand the main processes that can influence release (and rate of release) of pollutants from a solid matrix. In this sense, ecotoxicological and physico-chemical approaches are complementary to ensure a sound and reliable assessment of the potential environmental impacts of solid wastes. 

A similar application of ecotoxicological data is hazard assessment. Unlike risk assessment, hazard assessment is nonprobabilistic and relies upon indices rather than probabilities. One such index is the hazard quotient , which is the ratio of the expected environmental concentration (based upon field surveys or simulation models) divided by a benchmark concentration. The benchmark concentration is derived from some measure of toxicity such as the LC50 or no-observed-effect level. Hazard assessments are often conducted at different levels or tiers of increasing complexity and specificity if a chemical is identified as potentially hazardous by tier (the least complex and specific test), a decision is made to take action or, if more information is needed, to proceed to tier 2 tests. After tier 2 tests, a decision is made whether to take action or proceed to tier 3 tests, and so on. This process is repeated until it is decided that there is enough information to determine whether or not there is significant ecological hazard. If there is, then regulatory action is taken. 

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