Effects of solvents and dosing procedure on chemical toxicity in cell-based in vitro assays

Due to the implementation of new legislation, such as REACh, a dramatic increase of animal use for toxicity testing is expected and the search for alternatives is timely. Cell-based in vitro assays are promising alternatives. However, the behavior of chemicals in these assays is still poorly understood. We set out to quantify the exposure and associated toxicity of chemicals with different physicochemical properties toward a fish gill cell line when different solvents and procedural steps are used to introduce test chemicals to cells. Three chemicals with a range of hydrophobicity and volatility were selected and delivered in three different solvents using two common dosing procedures. Toxicity tests were coupled with chemical analysis to quantify the chemical concentrations within culture wells. The impact of solvents and dosing procedure was greatest for the most volatile and hydrophobic test chemical. We show that certain combinations of the test chemical, solvent, and procedural steps can lead to inhomogeneous distribution of the test chemical and thus differing degrees of bioavailability, resulting in quantitative differences in apparent toxicity.