Comparative Phytotoxicity Assays of the Herbicide Alloxydim and Its Main Identified Photoproduct in Cereal and Broadleaves Crops

Abstract

When herbicides are sprayed in the field, a proportion of the herbicide falls onto leaves and soil surfaces, where it can be exposed to sunlight, generating photoproducts that can be more toxic and/or persistent than the parent substance and affect human health and the environment. The aim of this study was to identify the photoproducts of the herbicide alloxydim in leaf and soil model systems and to perform phytotoxicity studies. Alloxydim was rapidly photodegraded in systems simulating plant cuticles and soil surfaces, with half-lives ranging from 1 to 30 min. The main by-product, identified by LC-Qtof-MS as deallyoxylated alloxydim, was more stable than the active substance. The EC50values on root lengths of different varieties of wheat plants and one grass weed ranged from 0.38 to 0.50 mg L−1for alloxydim. In contrast, the EC50values for deallyoxylated alloxydim ranged from 94 to 600 mg L−1in the same species and in crops where the herbicide was applied. Special attention should be given to alloxydim degradation products because of the rapid degradation of this herbicide. Comparative bioassay studies between alloxydim and its photostable by-product showed that the by-product presents low phytotoxicity, whereas alloxydim can cause injury to neighboring and succeeding cereal crops.

Assessing the Effects of Alloxydim Phototransformation Products by QSAR Models and a Phytotoxicity Study

“…Although the results may be overestimations of risk, they may be useful as they offer a safety margin when extrapolating plant sensitivity to the field and the effect on crop production [ 27 , 28 ]. In a previous work of our research group, we observed that the main photoproduct of alloxydim shows a low phytotoxic effect on the germination of different seeds species [ 19 ].…”

“…The heterogeneity of the surfaces and the complex light phenomena make experiments quite difficult. Previous studies by our group showed that alloxydim rapidly photodegrades in water [ 17 , 18 , 19 ]. However, before entering into the aqueous compartments, the herbicide, after spraying, comes in contact with soil and plant leaf surfaces and is subjected to sunlight irradiation.…”

Assessing the Effects of Alloxydim Phototransformation Products by QSAR Models and a Phytotoxicity Study

“…Although the results may be overestimations of risk, they may be useful as they offer a safety margin when extrapolating plant sensitivity to the field and the effect on crop production [27,28]. In a previous work of our research group, we observed that the main photoproduct of alloxydim shows a low phytotoxic effect on the germination of different seeds species [19]. www.videleaf.com…”

“…The heterogeneity of the surfaces and the complex light phenomena make experiments quite www.videleaf.com difficult. Previous studies by our group showed that alloxydim rapidly photodegrades in water [17][18][19]. However, before entering into the aqueous compartments, the herbicide, after spraying, comes in contact with soil and plant leaf surfaces and is subjected to sunlight irradiation.…”