Studies on the metabolism of hydroxybenzonitrile herbicides: I. Mass spectrometric identification

Abstract

The biodegradation and transport of the herbicides bromoxynil and ioxynil during artificial groundwater recharge and bank filtration were investigated to allow further risk assessment. The main field of interest was the identification and the behaviour of metabolites of these herbicides. The behaviour of the phenoxy alkanoic acid mecoprop (MCPP) was also investigated, because in commercial products MCPP is often applied in combination with bromoxynil and ioxynil. A pilot plant at the Institut für Wasserforschung in Schwerte (Ruhr valley, NRW) was used for the experiments, simulating worst‐case situations during slow sand filtration and aerobic and anaerobic underground passage. Six metabolites of bromoxynil, seven of ioxynil and one of mecoprop could be identified using GC/MS with electron impact ionization. In addition MS/MS was used to confirm the results. Seven of these 14 metabolites are described for the first time. Two main pathways of metabolism can be proposed; one is the hydrolysis of the nitrile group, resulting in the benzoic acid amide and the corresponding benzoic acid respectively, the other is a remarkable replacement of bromine and iodine by chlorine when chloride is present in the matrix. The only metabolite of mecoprop which could be identified under these conditions was the corresponding 4‐chloro‐2‐methylphenol. After four weeks no further degradation of this phenol could be observed. Some of the metabolites could be identified even after four weeks, so that it is obvious that they are capable of reaching the groundwater in natural systems. © 2000 Society of Chemical Industry

Dehalogenation of the Herbicides Bromoxynil (3,5-Dibromo-4-Hydroxybenzonitrile) and Ioxynil (3,5-Diiodino-4-Hydroxybenzonitrile) by Desulfitobacterium chlororespirans

“…Studies investigating ioxynil's fate include the aerobic transformation of ioxynil to 3,5-diiodo-4-hydroxybenzamide by Agrobacterium radiobacter 8/4 (47, 49) and a report identifying seven ioxynil metabolites during groundwater recharge and bank infiltration (16). All seven ioxynil metabolites were halogenated, with two retaining the iodine groups and the others exchanging the iodine groups for other halogens.…”

“…However, one could hypothesize that ioxynil is subject to a similar pathway (also retaining the halogens) because of the structural similarity of these two herbicides. The most commonly reported aerobic bromoxynil transformation products are 3,5-dibromo-4-hydroxybenzamide and 3,5-dibromo-4-hydroxybenzoate (DBHB) (15,16,27,37,42,43,47,48). DBHB can be formed directly from the parent (27) or via 5-dibromo-4-hydroxybenzamide (15,43,48).…”

Study of Cytotoxic Effects of Benzonitrile Pesticides

“…Their concentrations are observed not only in water and soil, but also in the air and living organisms [ 24 ]. Ioxynil is well biodegradable in soil and detected metabolites ( Figure 1 ) are similar to those formed in the case of bromoxynil [ 25 ]. Complete mineralization of the ioxynil to CO 2 was also observed [ 26 ].…”

Insights into the microbial degradation pathways of the ioxynil octanoate herbicide

“…It was observed that the abiotic degradation of benzonitrile herbicides in soils and sediments has minor effects relative to biodegradation (Holtze et al, 2006(Holtze et al, , 2008Vesela et al, 2010). The main microbial enzymes responsible for ioxynil biodegradation, as is shown in Scheme 1, are the enzymes involved in nitrile metabolism: nitrile hydratase (EC 4.2.1.84), amidase (EC 3.5.1.4) and nitrilase (EC 3.5.5.1) (Vesela et al, 2012;Pasquarelli et al, 2015;Detzel et al, 2013;Nielsen et al, 2007, Grab et al, 2000.…”