Does simplifying transport and exposure yield reliable results? An analysis of four risk assessment methods

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Four approaches for predicting the risk of chemicals to humans and fish under different scenarios were compared to investigate whether it is appropriate to simplify risk evaluations in situations where an individual is making environmentally conscious manufacturing decisions or interpreting toxics release inventory (TRI) data: (1) the relative risk method, that compares only a chemical's relative toxicity; (2) the toxicity persistence method, that considers a chemical's relative toxicity and persistence; (3) the partitioning, persistence toxicity method, that considers a chemical's equilibrium partitioning to air, land, water, and sediment, persistence in each medium, and its relative toxicity; and (4) the detailed chemical fate and toxicity method, that considers the chemical's relative toxicity, and realistic attenuation mechanisms such as advection, mass transfer and reaction in air, land, water, and sediment. In all four methods, the magnitude of the risk was estimated by comparing the risk of the chemical's release to that of a reference chemical. Three comparative scenarios were selected to evaluate the four approaches for making pollution prevention decisions: (1) evaluation of nine dry cleaning solvents, (2) evaluation of four reaction pathways to produce glycerine, and (3) comparison of risks for the chemical manufacturing and petroleum industry. In all three situations, it was concluded that ignoring or simplifying exposure calculations is not appropriate, except in cases where either the toxicity was very great or when comparing chemicals with similar fate. When the toxicity is low to moderate and comparable for chemicals, the chemicals' fate influences the results; therefore, we recommend using a detailed chemical fate and toxicity method because the fate of chemicals in the environment is assessed with consideration of more realistic attenuation mechanisms than the other three methods. In addition, our study shows that evaluating the risk associated with industrial release of chemicals (e.g., the toxics release inventory) may be misleading if only mass emissions are considered.

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Environmental Science and Technology