Bromoxynil Octanoate a Herbicide Widely Used After Atrazine Banning: Microbial Degradation in Different Soil Types

Bromoxynil, frequently applied as bromoxynil octanoate, is a post-emergence herbicide, widely used for control of broad-leaved weeds on a variety of crops, particularly since the banning of atrazine in most countries. This study analysed the degradation of bromoxynil octanoate by microorganisms from non-organically managed agricultural soils developed over granite (G) and schist (S) as well as from an organically managed agricultural soil developed over granite (Go). As a means of analysing the role of the most abundant members of the soil microbial community, degradation of bromoxynil octanoate was evaluated in microcosms incubated with distinct amounts of soils. Furthermore, the effect of the herbicide on soil microbial communities (community level physiological profiles, CLPP) was analysed. Bromoxynil octanoate was rapidly degraded by microorganisms from the 3 soils and was no longer detectable three days after initiating the experiment. At this time, about half of the herbicide applied was present as the active compound, bromoxynil. Thereafter, bromoxynil was degraded more rapidly in G and S than in Go, in which the herbicide was still detectable 2 weeks after its application. In the short-medium term (3-15 days), the metabolites 3,5-dibromo-4-hidroxybenzamide (DBHB amide) and/or 3,5-dibromo-4- hidroxybenzoic acid were detected in all three soils. The most abundant members of the soil microbial communities were also able to degrade bromoxynil and its ester, though this degradation was slower, or incomplete, and bromoxymil and/or DBHB amide were detected 6 weeks after application. The herbicide had little effect on the functionality of the microbial communities in the soils.