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Title: ISOPROTURON DEGRADATION AS AFFECTED BY THE GROWTH OF TWO ALGAL SPECIES AT DIFFERENT CONCENTRATIONS AND PH VALUES

Author
item MOSTAFA, FADWA - OICD
item HELLING, CHARLES

Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2001
Publication Date: 7/24/2001
Citation: N/A

Interpretive Summary: Evaluation of the potential risk of an agricultural pesticide includes determination of its metabolic fate in the systems where it is released. In most cases, this main repository becomes the soil. Although various microbial species can act to break down pesticides, one important group has been relatively overlooked-soil algae. In this research, two predominant algal species were found to degrade the important phenylurea herbicide isoproturon to at least three identified products. This was the first known report of isoproturon metabolisms by algae, and the process is expected to be significant in both soil and water environments. The pathway of breakdowns was very similar for both algae (Chlorella and Anabaena) despite their large taxonomic difference; this commonality extends to other microorganisms, plants, and even mammals, suggesting a relatively predictable fate for isoproturon and perhaps for other pesticides of this class. This research will be useful to pesticide regulatory agencies and scientists concerned with pesticide fate in the environment.

Technical Abstract: The metabolism of [14C-u-phenyl]isoproturon [3-(4-isopropylphenyl)-1, 1-dimethylurea] by two soil and freshwater microorganisms, green alga Chlorella kesslerei and cyanobacterium Anabaena inaequalis, was studied as a function of pH, pesticide concentration, and incubation time. Metabolized isoproturon, in the media, ranged from 0 percent (Chlorella at pH 5.5 after 1 d) to 22 percent (Anabaena at pH 5.5 after 10 d). Twenty-five percent faster degradation of isoproturon by Anabaena occurred at pH 5.5 versus pH 7.5, when measured over 10 d. Increased 14C incorporation into tissue, with time and at lower pH, was due mainly to bioaccumulation of [14C]isoproturon and/or its metabolites in the cells. Metabolic degradation resulted in four identifiable metabolites. Based on this, a degradation pathway is proposed, involving mono and di-N-demethylation, hydroxylation of the isopropyl moiety, and hydrolysis (in Anabaena only) to 4-isopropylaniline. Resemblance among the metabolites produced, suggests that the enzyme systems responsible for metabolizing isoproturon are similar in both photosynthetic micro-algae.