Identification, Elucidation, and Toxicity Assessment of Nontarget Disinfection By-products from Fipronil Chlorination

In the present study, fipronil degradation was evaluated in typical chlorination conditions (fipronil: 20 μg L −1 ; free chlorine concentration: 2 mg L −1 ; pH 7.5; 25 ○ C). Fipronil was quickly degraded by chlorination with half-time life of 2.08 min, achieving 95% of degradation in 15 min of reaction. For identification and elucidation of its disinfection by-products, fipronil solutions (2.0 mg L −1 ) were chlorinated at different contact times. Six by-products were identified and their structural formulas were elucidated by high-resolution mass spectrometry. Lastly, the toxicity of the unreacted and chlorinated solutions was evaluated using in vitro, in vivo, and in silico assays. Unreacted and chlorinated solutions were toxic to Artemia salina nauplii with an increase on toxic effects after 24 h of reaction time. No estrogenicity and cytotoxicity were observed for the tested solutions using re-engineered bioluminescent yeast estrogen screen and colorimetric MTT assays, respectively. According to quantitative structure-activity relationship methodology, chlorination may produce a more mutagenic compound than the precursor fipronil. The generated disinfection by-products also proved to be developmental toxicant, although it was not possible to measure their relative potency in relation to the parent compound.