Unveiling transformation processes of cardiovascular pharmaceuticals in wastewater based on nontarget screening

Cardiovascular pharmaceuticals were extensively detected and generally coexist with their transformation products (TPs) in wastewater. However, knowledges on TPs and transformation processes for cardiovascular pharmaceuticals remained largely unclear. To fill this knowledge gap, nontarget screening combined with batch experiments were employed to reveal the transformation of five cardiovascular pharmaceuticals (atenolol, metoprolol, propranolol, bezafibrate and candesartan) in aerobic activated sludge. The removal rate constants per unit of biomass ranged from 0.0105 to 0.0571 L g SS^-1 h^-1 for five cardiovascular pharmaceuticals. Atenolol and bezafibrate exhibited more excellent removal efficiency (over 99 %) than other three cardiovascular pharmaceuticals. Subsequently, 33 TPs were tentatively identified and 16 of them were not reported in previous studies. Based on identified TPs, transformation pathways of five cardiovascular pharmaceuticals were proposed, which suggested acetylation, ammoniation, carboxylation, dealkylation, decarboxylation, dihydroxylation, demethylation, epoxidation, formylation, hydrogenation, hydrolysis, hydroxylation, methylation and oxidation were involved in the transformation of cardiovascular pharmaceuticals in wastewater. Notably, N- dealkylation at the site of secondary and tertiary amine, acetylation at the site of primary amine and dehydrogenation at the site of linear alkyl were summarized as the specific transformation patterns across different cardiovascular pharmaceuticals. Furthermore, the predicted results suggested that about 30 % TPs have higher persistence and bioaccumulation than parent compounds while about 40 % TPs harbored higher toxicity than parent compounds of cardiovascular pharmaceuticals. Collectively, this study unveiled the fate and transformation pathways of five cardiovascular pharmaceuticals and summarized the specific transformation patterns for them in aerobic activated sludge, which is theoretically useful to effectively remove pharmaceuticals from wastewater.