A margin of safety approach for the assessment of environmentally realistic chemical mixtures in the marine environment based on combined passive sampling and ecotoxicity testing.

Organisms in the marine environment are being exposed to an increasing variety of chemicals. This research presents an effect-based monitoring method for the derivation of a margin of safety for environmentally realistic chemical mixtures. The method is based on a combination of passive sampling and ecotoxicity testing. First, passive sampling was performed using HO-philic divinylbenzene Speedisks during 3 sampling campaigns between 2016 and 2018 at 4 sampling locations in the Belgian part of the North Sea. Next, we exposed the marine diatom Phaeodactylum tricornutum to Speedisk extracts that were reconstituted in HPLC-grade water and defined the MoS of each sample as the highest no-observed effect concentration, expressed as relative enrichment factor (REF). A REF was defined by comparing the concentrations of 89 personal care products, pesticides and pharmaceuticals in the biotest medium with those measured in water grab samples to relate exposure concentrations in the tests to environmental concentrations. Across eight marine samples, diatom growth inhibition was observed at REF ≥ 3.2 and margins of safety were found between REF 1.1-11.0. In addition, we found that reconstitution of extracts in HPLC-water was suitable to overcome the solvent-related challenges in biotesting that are usually associated with passive sampler extract spiking, whilst it still allowed REFs up to 44 in the biotest medium to be achieved. This method, however, likely covers mainly the polar fraction of environmentally realistic chemical mixtures and less the non-polar fraction. Nevertheless, for 5 out of 8 samples, the Margin of Safety (MoS) was found to be lower than 10, which represents the typically lowest possible assessment factor applied to no effects ecotoxicological data in conventional environmental risk assessments, suggesting ecological risks for these samples.