Toxicological effects of mixtures of chemical pollutants at EQS concentrations
Abstract
Mixtures of 14 or 19 chemical substances of concern for the contamination of surface waters, each present at concentrations equivalent to their environmental quality standard (EQS) have been produced as a reference material and tested using biological effect-based tools. Around 30 bioassays covering the most relevant ecotoxicological endpoints and 13 organisms from different trophic levels have been included in the exercise in which 16 laboratories have participated. The chemicals selected for the mixtures were the substances atrazine, diuron, isoproturon and simazine (herbicides), benzo[a]pyrene and fluoranthene (polycyclic aromatic hydrocarbons), cadmium and nickel (metals), DEHP (plasticizer), 17β-estradiol (naturally occurring estrogen), 4-Nonylphenol (surfactant), diclofenac (pain killer), chlorphenvinphos and chlorpyrifos (insecticides), and the emerging compounds bisphenol A, carbamazepine, sulfamethoxazole, triclosan and DEET. The results from this exercise showed a general comparability between different bioassays targeting the same biological endpoint and classes of substances. The mixtures of chemicals at EQS concentrations originated effects on a few of the methods. These include changes in the algal-bacteria composition in a marine microcosm, effects on immobilization in Daphnia magna, fish embryo toxicity and effects on frog embryo development. Additionally, increased expression on reporter genes linked with oxidative stress was observed in both C. elegans and E. coli. An addictive effect was apparent for methods sensitive to estrogenic compounds and photosystem II inhibitors. The results indicate that some precaution on the chemical mixture assessment should be taken even in cases where individual compounds are present at seemingly harmless concentrations.