Abstract
Once applied, an herbicide first makes contact with leaves and soil. It is known that photolysis can be one of the most important processes of dissipation of herbicides in the field. However, degradation does not guarantee detoxification and can give rise to byproducts that could be more toxic and/or persistent than the active substance. In this work, the photodegradation of alloxydim herbicide in soil and leaf cuticle surrogates was studied and a detailed study on the phytotoxicity of the main byproduct on sugar beet, tomato, and rotational crops was performed. Quantitative structure–activity relationship (QSAR) models were used to obtain a first approximation of the possible ecotoxicological and environmental implications of the alloxydim and its degradation product. The results show that alloxydim is rapidly degraded on carnauba and sandy loam soil surfaces, two difficult matrices to analyze and not previously studied with alloxydim. Two transformation products that formed in both matrices were identified: alloxydim Z-isomer and imine derivative (mixture of two tautomers). The phytotoxicity of alloxydim and the major byproduct shows that tomato possesses high sensitivity to the imine byproduct, while wheat crops are inhibited by the parent compound. This paper demonstrates the need to further investigate the behavior of herbicide degradation products on target and nontarget species to determine the adequate use of herbicidal products to maximize productivity in the context of sustainable agriculture.
Highlights
Public concern about the use of synthetic chemicals on crops is growing, and the legislative requirements from authorities for the registration of agrochemicals are becoming stricter [1,2].The use of pesticides is so intense around the world that pesticide residues can usually be found in environmental compartments [2,3,4]
This paper demonstrates the need to further investigate the behavior of herbicide degradation products on target and nontarget species to determine the adequate use of herbicidal products to maximize productivity in the context of sustainable agriculture
Alloxydim was applied at the field doses and the radiation intensity was similar to solar radiation in the region in order to mimic as much as possible the environmental conditions
Summary
The use of pesticides is so intense around the world that pesticide residues can usually be found in environmental compartments [2,3,4]. In this sense, the general trend of companies is to develop pesticides with low application doses and short-lived time to diminish their persistence in the environment. In some cases, this advantageous feature can present drawbacks including the generation of transformation products and metabolites by degradation processes, which can be more toxic and/or mobile than their parent pesticides [5,6,7,8]. Pesticides are intended to protect crops, they or their degradation products may affect nontreated neighboring crops, rotational crops, or successive crops (nontarget species), resulting in alterations of the equilibrium of agro systems in the mid to long term [9,10].
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