Study of the Photocatalytic Degradation of Highly Abundant Pesticides in Agricultural Soils

Organic pesticides are major sources of soil pollution in agricultural lands. Most of these pesticides are persistent and tend to bio accumulate in humans upon consumption of contaminated plants. In this study, we investigate different natural soil samples that were collected from agricultural lands. The samples revealed the presence of 18 pesticides that belong to four different groups including organochlorines (OCP), organophosphorus (OPP), carbamates (Carb), and pyrethroids (Pyrth). The photocatalytic degradation of the five most abundant pesticides was studied in the presence and absence of 1% TiO2 or ZnO photocatalysts under UV irradiation at a wavelength of 306 nm. The five abundant pesticides were Atrazine (OCP), Chlorpyrifos methyl (OPP), Dimethoate (OPP), Heptachlor (OCP), and Methomyl (Carb). The results showed that photolysis of all pesticides was complete under UV radiation for irradiation times between 64-100 h. However, both photocatalysts enhanced photocatalytic degradation of the pesticides in comparison with photolysis. The pesticides were photocatalytically degraded completely within 20-24 h of irradiation. The TiO2 photocatalyst showed higher activity compared to ZnO. The organochlorine heptachlor, which is very toxic and persistent, was completely degraded within 30 h using TiO2 photocatalyst for the first time in soil. The mechanism of photocatalytic degradation of the pesticides was explained and the effects of different factors on the degradation process in the soil were discussed.

Automated summary

Organic pesticides are significant sources of soil pollution in agricultural lands, and their accumulation in human bodies is concerning. In this study, the presence of 18 pesticides in natural soil samples from agricultural lands was investigated, revealing the effectiveness of photocatalytic degradation using TiO2 or ZnO photocatalysts under UV radiation. The results showed that the five most abundant pesticides could be completely degraded within 20-24 hours using these photocatalysts, with TiO2 demonstrating higher activity. Notably, the persistent and toxic organochlorine pesticide heptachlor was completely degraded within 30 hours for the first time in soil using TiO2 photocatalyst.