The influence of solvents on the acute toxicity of some lipophilic chemicals to aquatic invertebrates

Due to the difficulties encountered in dissolving lipophilic substances in aqueous media, solvents are often used in aquatic toxicity tests. Yet, in most cases the potential effect of the solvent is only assessed separately from that of the toxicant. In the present study, water-insoluble chemicals such as diazepam, digoxin, and malathion have been tested either in pure form or in combination with dimethylsulfoxide (DMSO), ethanol, methanol or acetone, for their acute toxicity to several aquatic invertebrates commonly used in ecotoxicology. The three former compounds are included in the first 20 “priority chemicals” of the Multicentre Evaluation of In Vitro Cytotoxicity (MEIC) programme. The results indicate that the use of solvent carrier gave differences in the acute effect of the three chemicals to 6 test species: the crustaceans Artemia salina, Streptocephalus proboscideus, and Daphnia magna, the rotifers Brachionus plicatilis and Brachionus calyciflorus, and the bacterium Photobacterium phosphoreum. Consequently, the toxicity resulting from the combination of test substance and solvent should be evaluated carefully, and the magnitude of interaction taken into consideration when comparing toxicity data from various sources.