John Wiley & Sons, Ltd.

iSTREEM®: An approach for broad‐scale in‐stream exposure assessment of “down‐the‐drain” chemicals

The iSTREEM® model (“in‐stream exposure model”), a web‐based model made freely available to the public by the American Cleaning Institute, provides a means to estimate concentrations of “down‐the‐drain” chemicals in effluent, receiving waters, and drinking water intakes across national and regional scales under mean annual and low flow conditions. We provide an overview of the evolution and utility of the iSTREEM® model as a screening‐level risk assessment tool relevant for down‐the‐drain products. The spatial nature of the model, integrating point locations of facilities along a hydrologic network, provides a powerful framework to assess environmental exposure and risk in a spatial context. A case study was conducted comparing national distributions of modeled concentrations of HHCB (fragrance) and DEET (insect repellent) to available monitoring data at comparable flow conditions. The iSTREEM® low flow model results yielded a conservative distribution of values, while the mean flow model results more closely resembled the concentration distribution of monitoring data. We demonstrate how model results can be used to construct a conservative estimation of the distribution of chemical concentrations for effluents and streams leading to the derivation of a “predicted environmental concentration” (PEC) using the high end of the concentration distribution (e.g., 90th‐percentile). Data requirements, assumptions and applications of iSTREEM® are discussed in the context of other “down‐the‐drain” modeling approaches to enhance understanding of comparative advantages and uncertainties for prospective users interested in exposure modeling for ecological risk assessment. This article is protected by copyright. All rights reserved

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