Passive sampling in support of biota monitoring of hydrophobic substances under the Water Framework Directive

This paper presents an approach to apply aquatic passive sampling (PS) in regulatory chemical water quality monitoring in Europe. Absorption-based passive sampling is well developed and suitable for the sampling of hydrophobic chemicals, some of which are European Water Framework Directive priority substances with Environmental Quality Standards (EQS) derived for biota. Considering a chemical activity approach to chemical risk assessment, we propose equilibrium concentration in lipids (from passive water sampling) as a reference value for measured concentrations in biota. Through existing PS-fish datasets, we show a growing body of evidence supporting the use of lipid-based contaminant concentrations at equilibrium with water derived from PS as a conservative proxy of levels of these chemicals in fish. We propose a procedure that includes PS as a first, animal-free screening step of a tiered approach, followed by more conventional fish analyses when PS indicates these are needed to confirm EQS_biota exceedance. This paper reviews fish-passive sampler datasets, provides a reasoning for the proposed procedure and discusses how to broadly put it into monitoring practice. PS offers the possibility of well-defined standardised monitoring approaches that can help overcome the natural variability challenges associated with measurements in biota across member states and simplify EQS_biota compliance.