Fate, transformation and toxicological implications of environmental diclofenac: Role of mineralogy and solar flux

Diclofenac is an emerging surface water contaminant, yet the environmental impact of its degradation products remains elusive. The current study focuses on mineralogy-controlled diclofenac photo-degradation and its po-tential health impacts. Under irradiated conditions, we studied the effects of kaolinite, hematite, and anatase on diclofenac degradation. Our results showed that kaolinite doubled the diclofenac degradation rate, which can be attributed to the high catalytic effect, mediated via increased surface area and pore size of mineral surface in the low pH. Conversely, anatase, a crystal phase of titanium dioxide (TiO2), diminished the diclofenac degradation compared to treatments without TiO2. Hematite, on the other hand, showed no effect on diclofenac degradation. Photo-degradation products also varied with the mineral surface. We further assessed in vitro toxicological ef-fects of photo-degraded products on two human cell lines, HEK293T and HepG2. Biological assays confirmed that photo-degraded compound 6 (1-(2,6-dichlorophenyl)indolin-2-one) decreased HEK293T cell survival signifi-cantly (p < 0.05) when compared to diclofenac in all concentrations. At lower concentrations, inhibition of HEK293T cells caused by compounds 4 (2-(8-chloro-9H-carbazol-1-yl)acetic acid), and 5 (2-(9H-carbazol-1-yl) acetic acid) was greater than diclofenac. Compound 7 (1-phenylindolin-2-one) was toxic only at 250 mu M. Additionally, compound 6 decreased HepG2 cell viability significantly when compared to diclofenac. Overall, our data highlighted that mineralogy plays a vital role in environmental diclofenac transformation and its photo -degraded products. Some photo-degraded compounds can be more cytotoxic than the parent compound, diclofenac.

Automated summary

This study investigates the impact of minerals on the degradation of diclofenac and its photo-degradation products, as well as their potential health effects. The results show that kaolinite enhances the degradation of diclofenac, while anatase diminishes its degradation. Some photo-degraded compounds are more cytotoxic than diclofenac itself.