Growth inhibition and fate of benzotriazoles in Chlorella sorokiniana cultures

Benzotriazoles are among the most commonly found organic micropollutants in the aquatic environment. In this study, toxicity experiments were conducted in order to investigate the effects of different benzotriazoles on Chlorella sorokiniana growth. Four compounds were tested; 1H-benzotriazole (BTR), xylytriazole (XTR), 5-methyl-1H-benzotriazole (5TTR) and 5-chlorobenzotriazole (CBTR). The fate of these micropollutants was also studied under batch conditions and the effect of different mechanisms on their elimination was investigated. According to the results, the EC₅₀ values in single-substance toxicity experiments were calculated to 8.3 mg L^-1 for BTR, 22 mg L^-1 for 5TTR and 38.7 mg L^-1 for CBTR. A slight inhibition on microalgae growth was noted at the maximum tested concentration of XTR (77 mg L^-1), while no inhibition was observed when a mixture of target BTRs was tested at 200 μg L^-1. Calculation of the Risk Quotient (RQ) showed no possible ecological threat in the presence of 5TTR, XTR and CBTR, while RQ values close or higher than 1 were estimated for BTR. All target contaminants were significantly eliminated in microalgae experiments that lasted 16 days. Their removal efficiency ranged between 42.2 ± 3.1% (XTR) to 97.2 ± 0.9% (XTR), while their half-life values were estimated to 2.4 ± 0.5 days for 5TTR, 6.5 ± 0.6 days for BTR, 15.2 ± 1.4 days for CBTR and 20.7 ± 2.0 days for XTR. Photodegradation was the main mechanism affecting BTR, XTR and CBTR removal, while bioremoval processes enhanced 5TTR elimination. The addition of sodium acetate decreased the removal efficiency of BTRs possibly due to catabolite repression. This is the first study investigating the toxicity and fate of BTRs in microalgae cultures.