Modification of microalgae-based toxicity assessment by continuously updating the tested solution: taking sulfonamide toxicity as an example

Toxicity assessments using microalgae are commonly conducted to reflect the ecological risks posed by exogenous pollutants. In natural water, pollutant concentrations often remain constant due to continuous import from point or non-point sources. However, in the laboratory, pollutants are mixed with test organisms at the beginning of the toxicity assessment and are gradually biodegraded, which may not accurately reflect the continuous pollution present in natural conditions. Therefore, this study proposed a new method that fresh pollutants (three typical sulfonamides, SAs) were continuously provided to the testing organism (microalgae, Chlorella vulgaris ) in the detection system. The difference in algal growth ratio between test group and control group (named Δr) was applied to reflect the toxicity of antibiotics. It was revealed that the three SAs caused greater inhibition or less promotion effect on 5-7 days’ microalgae growth when using the proposed method, compared to the traditional method. This result demonstrated that the traditional test could under-estimate the antibiotic toxicity. Furthermore, a blueprint of the extended method and its corresponding device were proposed based on the idea of plug flow to determine the toxicity of antibiotics and their intermediate products generated during various treatment processes. • Pollutant concentrations in nature are commonly constant due to continuous input. • Toxicity tests based on traditional methods may not accurately reflect real situation. • Traditional toxicity tests under-estimated the antibiotic toxicity. • Plug flow of target solution in device provided constant condition for microbes. • A method and device were proposed for toxicity tests of antibiotics and by-products.