Estimation of the contribution made to down-the-drain emissions of D5 by personal care product categories in the European Union.

Aquatic risk assessment of personal care chemicals requires quantifying the contribution of all product types containing the ingredient to down-the-drain emissions. We developed a probabilistic model framework embracing stochastic variability associated with individual consumers and their behaviours in the EU, as well as other sources of uncertainty related to losses following applications (e.g. volatilisation). The model was applied to decamethylcyclopentasoloxane (D5), an emollient used in wash-off (WO) and leave-on (LO) products. Quantifying contributions from each product category containing D5 to down-the-drain emissions is necessary to inform optimal risk management options. Simulation results for the baseline scenario (2012) supports the argument that leave-on products make up a minor contribution (7.1%) to the down-the-drain emissions of D5 with only 0.20% of the D5 used in LO products being released to wastewater. The most influential model parameters are the release factor from WO products and the time between application and use for various LO product types, stressing the importance of embracing stochastic variability across individuals' behaviour when assessing contributions of various product types to environmental emissions. The downward trend in WO use from 2010 to 2016 is reflected in declining concentrations in wastewater influent over the same period. Uncertainty remains about future levels of D5, once phasing out from WO products is complete. The probabilistic model in conjunction with high tier consumer habits data is a promising high tier tool for the characterisation of complex emission scenarios of personal care ingredients. This article is protected by copyright. All rights reserved.