Contaminants of emerging concern (CECs) in the environment undergo many abiotic and biotic transformations resulting in various transformation products (TPs). The ecological risks of these TPs, such as demethylated or methylated derivatives, are largely unknown due to their different physicochemical properties from the parent compounds. In this study, we examined the influence of demethylation or methylation on the bioaccumulation and acute toxicity of typical CECs, as well as the interconversion between the selected CECs and their demethylated or methylated derivatives, in Daphnia magna. Preliminary results showed that naproxen and methylparaben accumulated significantly more than their demethylated TPs (p &lt; 0.05). Similarly, the methylated derivative of acetaminophen was relatively more bioaccumulative than its parent compound (acetaminophen, p &lt; 0.01). In contrast, the demethylated TP of diazepam (nordiazepam) exhibited greater bioaccumulation in D. magna compared with diazepam. After 1 d exposure in artificial freshwater spiked with 1 mg/L diazepam or nordiazepam, 58.4 ± 9.16 μg/g of diazepam and 96.7 ± 13.9 μg/g of nordiazepam accumulated in D. magna, respectively. Interconversion between nordiazepam and diazepam was observed and may effectively extend the persistence of chemicals in the organisms. This study provides substantial experimental data to help understand the ecological risks posed by the common demethylated or methylated TPs of CECs on aquatic invertebrates.

Demethylation or methylation induced changes in bioaccumulation and acute toxicity of typical emerging contaminants in Daphnia magna

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