Modelled environmental exposure to persistent organic chemicals is independent of the time course of emissions: Proof and significance for chemical exposure assessments

The fate and transport of organic pollutants in the environment is usually assessed with the help of multimedia models. A target variable calculated with these models is the environmental exposure to a substance. It indicates that part of the potential hazard of a chemical that is caused solely by the chemical’s fate and transport behaviour, regardless of toxicological substance properties. So far, pulse-emissions are usually assumed in order to arrive at an easy-to-compute expression for exposure. Here, we show that exposure does not depend on the shape of the emission function. Exposure calculated for the pulse release of a particular mass of contaminant is equal to exposure calculated for any arbitrary dynamic release of the same mass. This result extends the meaning of model evaluations at steady-state. It also allows for a more general interpretation of the persistence and the spatial range of a chemical, as well as of the toxicity potential used in life cycle impact assessment.