Single- and mixture toxicity of three organic UV-filters, ethylhexyl methoxycinnamate, octocrylene, and avobenzone on Daphnia magna

- Single- and mixture toxicity of three organic UV-filters was conducted with concentration-combinations after binary or ternary exposure.
- Exposure to mixtures of three organic UV-filters was shown a reduced toxic effect when compared to the single toxicity tests.
- A reduced toxic effect was caused by the antagonistic interaction between components in the mixtures.
- Antagonistic interaction between components may rely upon chemical reaction or dissimilar mode of action on components when three organic UV-filters are combined.

In freshwater environments, aquatic organisms are generally exposed to mixtures of various chemical substances. In this study, we tested the toxicity of three organic UV-filters (ethylhexyl methoxycinnamate, octocrylene, and avobenzone) to Daphnia magna in order to evaluate the combined toxicity of these substances when in they occur in a mixture. The values of effective concentrations (ECx) for each UV-filter were calculated by concentration-response curves; concentration-combinations of three different UV-filters in a mixture were determined by the fraction of components based on EC25 values predicted by concentration addition (CA) model. The interaction between the UV-filters were also assessed by model deviation ratio (MDR) using observed and predicted toxicity values obtained from mixture-exposure tests and CA model. The results from this study indicated that observed ECxmix (e.g., EC10mix, EC25mix, or EC50mix) values obtained from mixture-exposure tests were higher than predicted ECxmix (e.g., EC10mix, EC25mix, or EC50mix) values calculated by CA model. MDR values were also less than a factor of 1.0 in a mixtures of three different UV-filters. Based on these results, we suggest for the first time a reduction of toxic effects in the mixtures of three UV-filters, caused by antagonistic action of the components. Our findings from this study will provide important information for hazard or risk assessment of organic UV-filters, when they existed together in the aquatic environment. To better understand the mixture toxicity and the interaction of components in a mixture, further studies for various combinations of mixture components are also required.

170