Pulsed light treatment of pesticides induces high compound degradation and toxicity decrease

Pulsed light (PL) is a technology using high-intensity pulses of polychromatic light enabling the photolysis of various organic compounds. This study examined the photodegradation by PL of 18 pesticides commonly used in viticulture using both chemical and ecotoxicological approaches. Pesticide concentrations were monitored in treated and untreated samples, along with the formation of degradation products using HPLC-MS/MS. PL successfully degraded the 18 pesticides from initial concentrations between 304 and 561 µg/L to < 30 µg/L after a treatment at 91 J/cm² for 8.53 min duration. The concentrations of 14 pesticides were even reduced below their limit of quantification, and for 10 of them, below their limit of detection. Dimethomorph was the least degraded compound, with a 93.5 % reduction. Besides, 42 degradation products were observed. The study also showed that PL can degrade the degradation products themselves. The ecotoxicological approach assessed the acute toxicity of the pesticide mix before and after PL on three levels of the aquatic trophic chain: the bacteria Aliivibrio fischeri, the microalgae Raphidocelis subcapitata, and the fish Oryzias latipes. Acute toxicity was reduced two-fold for A. fischeri and 24-fold for R. subcapitata. For O. latipes, a mortality rate of 6.6 % was observed in treated samples, whereas it was 100 % in untreated samples. However, some sublethal effects, such as axial skeleton deformations appeared in 22.2 % of O. latipes, likely due to residual pesticides and degradation products. These results demonstrate that PL is a promising process to significantly lower both pesticide concentrations and acute toxicity.