An updated state of the science EQC model for evaluating chemical fate in the environment: Application to D5 (decamethylcyclopentasiloxane)

The EQuilibrium Criterion (EQC) model developed and published in 1996 has been widely used for screening level evaluations of the multimedia, fugacity-based environmental fate of organic chemicals for educational, industrial, and regulatory purposes. Advances in the science of chemical partitioning and reactivity and the need for more rigorous regulatory evaluations have resulted in a need to update the model. The New EQC model is described which includes an improved treatment of input partitioning and reactivity data, temperature dependence and an easier sensitivity and uncertainty analysis but uses the same multi-level approach, equations and environmental parameters as in the original version. A narrative output is also produced. The New EQC model, which uses a Microsoft Excel platform, is described and applied in detail to decamethylcyclopentasiloxane (D5; CAS No. 541-02-6). The implications of these results for the more detailed exposure and risk assessment of D5 are discussed. The need for rigorous evaluation and documentation of the input parameters is outlined.

► The EQC model calculates the fate of a chemical in air, water, soil and sediment.
► The model was revised to allow for more flexibility in input parameter selection.
► It includes guidance on estimating chemical properties at different temperatures.
► The model was applied to decamethylcyclopentasiloxane (D5).
► The mode of entry of D5 to the environment likely plays a key role in its fate.