Studies on photodegradation of chlorimuron-ethyl in soil

Abstract

: Photolysis of chlorimuron-ethyl was studied on a soil surface under sunlight and UV light. Eight photoproducts were isolated and characterised by spectroscopic methods. Major photoproducts are formed by cleavage of the sulfonylurea bridge and minor products are formed via dechlorination, hydrolysis and cyclisation. The rates of photodegradation of chlorimuron-ethyl on di †erent soils followed Ðrst-order rate kinetics, with half lives of 22É3 h, 9É4 h, 4É9 h (UV) and 20É7 days, 11É1 days and 11É1 days (sunlight) for alluvial, red and laterite soils, respectively. The di †erences in rates of photodegradation were dependent upon the soil pH.

Reviews of Environmental Contamination and Toxicology

“…Similar reduction of light has also been reported for sediments suspended in aqueous solutions of pesticides (Miller and Zepp 1979;Oliver et al 1979;. In contrast, soil organic matter reduced the photodegradation of chlorimuron ethyl (102) (Choudhury and Dureja 1997a), triasulfuron (100) and thifensulfuron-methyl (105) (Albanis et al 2002), and fipronil (220) (Bobe et al 1998b), indicating involvement of either quenching or a shielding effect. In contrast, soil organic matter reduced the photodegradation of chlorimuron ethyl (102) (Choudhury and Dureja 1997a), triasulfuron (100) and thifensulfuron-methyl (105) (Albanis et al 2002), and fipronil (220) (Bobe et al 1998b), indicating involvement of either quenching or a shielding effect.…”

“…For the Nformyl-N-methyl derivative, the excited carbonyl group was likely to initiate hydrogen abstraction from the N-methyl group followed by reaction with Oz. 20) (Choudhury and Dureja 1997a). By comparing the results in aerobic soil metabolism, photolysis was likely to be of minor importance for (54).…”

Fate of Pesticides in Soils: Toward an Integrated Approach of Influential Factors

“…For instance, fipronil photodegradation scheme presents only one pathway in soil instead of two in water (Bobé et al, 1998a). Soil characteristics may play a different role according to the pesticide and its own properties: photodegradation efficiency was found to decrease when adsorption (Kf) increased for fipronil (Bobé et al, 1998a), or when pH increased for the sulfonylurea chlorimuron-ethyl (Choudhury & Dureja, 1997). Humic substances tend to decrease direct photolysis through light screening, static quenching (inhibition of the PX* formation through complexation of the ground-state molecule) and dynamic quenching (energy transfer from PX* to humic substance) (Walse et al, 2004).…”

Photocatalytic degradation of polycyclic aromatic hydrocarbon benzo[a]pyrene by iron oxides and identification of degradation products

“…These methods have limitations such as containment is not a permanent solution, thermal desorption leads to high cost and microbial degradation of high molecular weight PAHs (more than 3-rings) is slow due to their high stability and requires an effective maintenance of optimised conditions (Henner et al, 1997). Photodegradation using a photocatalyst is a favourable path for the elimination of PAHs and other persistent organic pollutants like pesticides (Choudhury and Dureja, 1999;Faisal et al, 2010). TiO 2 in different available forms has been extensively used as a photocatalyst for PAH degradation in aqueous solutions and on soil surfaces (Sabate et al, 2001;Zhang et al, 2008).…”