Photolysis of Aqueous Chlorimuron and Imazaquin in the Presence of Phenolic Acids and Riboflavin

Abstract

Laboratory experiments were conducted to determine the effect of three phenolic acids, acetone, and riboflavin on aqueous photolysis of chlorimuron and imazaquin. The phenolic acids investigated were caffeic acid (CA), ferulic acid (FA), andp-coumaric acid (PCA). Treatment solutions were contained in quartz vessels and irradiated with 300 to 400 nm UV light in a photoreactor. The extrapolated photolysis half-life of chlorimuron in pure solution was 107 h, compared to a half-life of 0.42 h for pure aqueous imazaquin. Chlorimuron in solutions containing 10 ppmw riboflavin, acetone, CA, FA, or PCA exhibited half-lives of 9, 57, 58, 67, and 146 h, respectively. Imazaquin in solutions containing 10 ppmw riboflavin, acetone, CA, FA, or PCA had half-lives of 0.70, 0.55, 0.55, 0.48, and 0.55 h, respectively. The presence of PCA in aqueous media delayed chlorimuron photolysis, whereas all other compounds, especially riboflavin, sensitized chlorimuron photolysis. In contrast, imazaquin photolysis was delayed in the presence of the test compounds, with riboflavin having the greatest effect and causing in a 68% increase in imazaquin half-life over that of imazaquin alone. Quantum yields for sensitized photolysis of chlorimuron by riboflavin and for riboflavin by imazaquin were 0.1134 and 0.0477, respectively. These results suggest that some soluble and naturally occurring organic compounds may enhance chlorimuron photolysis yet delay imazaquin photolysis in surface waters.

Degradation of chlorimuron-ethyl byAspergillus nigerisolated from agricultural soil

“…Chlorimuron-ethyl degrades in the agricultural environment primarily via pH-and temperature-dependent chemical hydrolysis (Beyer et al, 1988;Brown, 1990;Hay, 1990), as observed for many sulfonylurea herbicides, such as sulfometuron-methyl (Harvey et al, 1985), chlorsulfuron (Sabadie, 1990), metsulfuron-methyl (Sabadie, 1991), rimsulfuron (Schneiders et al, 1993), nicosulfuron (Sabadie, 2002 and flazasulfuron (Bertrand et al, 2003). The phototransformation of chlorimuron by sunlight also takes place on the soil surface (Choudhury & Dureja, 1996 a) and in water (Venkatesh et al, 1993;Choudhury & Dureja, 1996 b). Within the surface soil chlorimuron is also considered to serve as a source of carbon, nitrogen and sulfur for microorganisms.…”

Light regime, riboflavin, and pH effects on 2,4-D photodegradation in water

“…The total UV energy emitted under each light regime was monitored during each 2,4-D PHOTODEGRADATION IN WATER 475 experiment by trifluralin-acetonitrile chemical actinometry (Draper, 1987;Venkatesh et al, 1993). The actinometer was calibrated in a merry-go-round photoreactor apparatus fitted with lamps having a known energy output and 300-400 ran wavelength distribution (Draper, 1987, Venkatesh et al, 1993.…”

“…The actinometer was calibrated in a merry-go-round photoreactor apparatus fitted with lamps having a known energy output and 300-400 ran wavelength distribution (Draper, 1987, Venkatesh et al, 1993.…”

“…Natural waters often contain significant concentrations of photoreactive compounds including flavins, plant pigments, phenolic acids, amino acids, humic 2,4-D PHOTODEGRADATION IN WATER 471 substances etc., which may act either as quenching agents or photosensitizers (Choudhry, 1984;Mopper and Zika, 1987;Venkatesh, et al, 1993). In addition to other photosensitizers or quenchers present in reaction media, photoproducts formed during pesticide photolysis can also influence subsequent rates of indirect photolysis by acting either as quenchers that inhibit (Choudry et al, 1979) or sensitizers that promote (Larson et al, 1992) further photolysis of the pesticide.…”

Growth and production of laccases by the ligninolytic fungi,Pleurotus ostreatus andBotryosphaeria rhodina , cultured on basal medium containing the herbicide, Scepter® (imazaquin)

“…Imazaquin can persist in the soil for up to seven months and can interfere with soil microbes sensitive to this chemical. Its degradation in the environment is partly through photo-decomposition (VENKATESH et al 1993) and microbial action, but its fate still remains unclear (RODRIGUES and ALMEIDA 1995). In Brazil, imazaquin is registered for use with soybean cultivation, and is commercially available as Scepter ® and Topgan ® in the form of soluble concentrate or dispersible granules, respectively.…”