UV and temperature effects on chloroacetanilide and triazine herbicides degradation and cytotoxicity

The purpose of this study was to explore the stability and toxicity of the herbicides and their degradation byproduct after exposure to different environmental factors. Triazines (atrazine, propazine, simazine) and chloroacetanilides (acetochlor, alachlor, metolachlor) which are commonly used herbicides were evaluated for cytotoxicity in different UV (254 nm and 365 nm) and temperature (4 °C, 23 °C, and 40 °C) conditions as well as degradation rates. Atrazine with the highest LD₅₀ (4.23 μg mL^-1) was less toxic than the other tested triazine herbicides Chloroacetanilides tested were more toxic than tested triazines, with LD₅₀ 0.08-1.42 μg mL^-1 vs 1.44-4.23 μg mL^-1, respectively. Alachlor with LD₅₀ 0.08 μg mL^-1 showed the strongest toxic response as compared with other tested herbicides. Temperatures only did not alter cytotoxicity of the tested herbicides, except for acetochlor and alachlor showing about 45 % more cell death after exposure to 40 °C for 2 h. At all 3 tested temperatures, 2 h of UV treatments did not affect cytotoxic effects of the tested herbicides, except for acetochlor and alachlor. At 4 °C, acetochlor toxicity was attenuated about 63 % after UV 365 nm exposure; but alachlor toxicity was enhanced after either UV 254 or 365 nm exposure for about 40 % and 24 %, respectively. At 23 °C, acetochlor toxicity was enhanced about 35 % after UV 254 nm exposure, but attenuated about 48 % after UV 365 nm exposure. Alachlor toxicity was enhanced about 34 % after UV 254 nm and 23 °C exposure. In combination of UV 254 nm and 40 °C, acetochlor toxicity was lowered by 63 % and alachlor toxicity was no change as compared with 4 °C, no UV group. After co-treatment with UV 365 nm and 40 °C both acetochlor and alachlor toxicity was enhanced 55 % and 80 %, respectively. Through degradation analysis by LC-MS/MS, alachlor showed the most dramatic degradation (only 0.58 %-10.58 % remaining) after heat and UV treatments.