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Case Study

Broad-Scale In-Stream Exposure Assessment of “Down-the-Drain” Chemicals

The iSTREEM® model (“in-stream exposure model”), a web-based model, 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 (7Q10) flow conditions. The spatial nature of the model, integrating point locations of facilities along a hydrologic network, provides a powerful framework to assess environmental risk in a spatial context.

Our Findings

A case study was conducted comparing national distributions of modeled concentrations of HHCB, triclosan and DEET, to available monitoring data at comparable flow conditions. It was determined that the iSTREEM® model yields reasonable to conservative exposure estimates. Low flow model results provided a conservative distribution of values and mean flow model results aligned more closely with the concentration distribution of monitoring data.

We demonstrated 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. 95th-centile).

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