Linking toxicity in algal and bacterial assays with chemical analysis in passive samplers deployed in 21 treated sewage effluents

Abstract

A diverse mix of micropollutants, including pesticides, biocides, and pharmaceuticals, reaches the aquatic environment through treated sewage effluents. We sampled 21 final effluents with polar organic chemical integrative samplers (POCIS) and investigated to what extent chemical analyses of six photosystem II (PS-II) inhibitors and 12 other chemicals explain the toxic burdens quantified with two bioassays. Baseline toxicity equivalent concentrations (TEQ) were determined with a bacterial bioluminescence inhibition assay using Vibrio fischeri (baseline-TEQ(bacteria)) and by assessing toxicity on algal growth using Pseudokirchneriella subcapitata (baseline-TEQ(algae)). Inhibition PS-II was also determined with algae and expressed using diuron equivalent concentrations (DEQ(bio)). Concentrations of chemicals and toxicities varied appreciably between effluents, typically spanning two orders of magnitude. Across 21 independent effluents, a DEQ calculated by concentration addition of PS-II inhibitors (DEQ(chem)) proved a very good predictor of DEQ(bio); DEQ(chem) explained 65% of DEQ(bio). However, baseline-TEQ(bacteria,bio) correlated poorly with baseline-TEQ(algae,bio), because baseline-TEQ(algae) were strongly influenced by PS-II inhibitors. Using data on the 18 quantified compounds, and their estimated toxicities in the bacterial assay, we calculated a baseline-TEQ(bacteria,chem). With one exception, a site with a high load of diclofenac, less than 1% of baseline-TEQ(bacteria,bio) was explained by the analyzed chemicals. We conclude that for the analyses of final effluents, DEQ(bio) is a robust endpoint and useful screening tool for PS-II inhibitors; in the presence of herbicides, baseline-TEQ(bacteria,bio) proves a more robust measure of baseline toxicity than baseline-TEQ(algae,bio).