Fate of aldicarb, aldicarb sulfoxide, and aldicarb sulfone in Floridan groundwater

Abstract

The fate of aldicarb, aldicarb sulfoxide, and aldicarb sulfone in Floridan groundwater microcosms was determined. One reaction mechanism observed was base hydrolysis and degradation rates decreased in the order sulfone > sulfoxide » aldicarb. Appearance of oximes followed the disappearance of corresponding parent compounds while appearance of nitriles was minor and rarely observed. Microcosms amended with crushed limestone showed rates of hydrolysis that were 4-5 times slower than microcosms without limestone. Oxidation of aldicarb to the sulfoxide was minimal within 70 days whereas in separate experiments, the reduction of the sulfoxide to aldicarb was significant over the same time period. The sorption of aldicarb, aldicarb sulfoxide, and aldicarb sulfone onto limestone was not observed.Recently, several studies have discussed the degradation

The Geochemistry of Pesticides

“…The varying tendencies of different buffers to accelerate hydrolysis and dehydrohalogenation are consistent with reactivity trends predicted by the HSAB model (Barbash, 1993) and, for hydrolysis, may be predicted quantitatively using a method introduced by Perdue and Wolfe (1983). Relatively few laboratory studies have accounted for buffer effects (e.g., Reinhard, 1989a, 1992b;Burlinson et al, 1982;Li and Felbeck, 1972;Miles and Delfino, 1985;Smolen and Stone, 1997), but failing to make such corrections may lead to overestimates in the rates at which these reactions are likely to occur in natural waters.…”

“…This is consistent with observations regarding the effects of ionic strength on the rates of hydrolysis of pesticide compounds over the range of salinities encountered in most natural waters. As predicted by transition-state theory, these effects have been found to be minor over the pH range (if any) within which a given pesticide compound is subject only (or primarily) to reaction with H 2 O (Barbash and Reinhard, 1992b;Bondarenko et al, 2004;Liqiang et al, 1994), but substantial both at higher pH for those compounds that are subject to base catalysis (Bondarenko et al, 2004;Miles and Delfino, 1985) and at lower pH for those subject to acid catalysis (Wei et al, 2000). Also consistent with transition-state theory is the observation by Miles and Delfino (1985) that the effect of salt concentration on the rate of aldicarb sulfone hydrolysis is more pronounced (on a molar basis) for the divalent Ca 2þ than for the monovalent Na þ .…”

“…As predicted by transition-state theory, these effects have been found to be minor over the pH range (if any) within which a given pesticide compound is subject only (or primarily) to reaction with H 2 O (Barbash and Reinhard, 1992b;Bondarenko et al, 2004;Liqiang et al, 1994), but substantial both at higher pH for those compounds that are subject to base catalysis (Bondarenko et al, 2004;Miles and Delfino, 1985) and at lower pH for those subject to acid catalysis (Wei et al, 2000). Also consistent with transition-state theory is the observation by Miles and Delfino (1985) that the effect of salt concentration on the rate of aldicarb sulfone hydrolysis is more pronounced (on a molar basis) for the divalent Ca 2þ than for the monovalent Na þ . The effects of ionic strength on photochemical reactions do not appear to be extensively documented (e.g., Mill and Mabey, 1985), but Walse et al (2004) observed a significant increase in the rate of photolysis of the insecticide fipronil upon the addition of 3% NaCl, suggesting that the rate of this reaction is likely to be higher in marine waters (which typically have salinities of approximately 3.5%) than in freshwater environments.…”

“…Reduction reactions, by contrast, may result in products that are less water soluble than their parent compound. Examples include the reduction of aldicarb sulfoxide to aldicarb (Lightfoot et al, 1987;Miles and Delfino, 1985) and the reduction of phorate sulfoxide to phorate (Coats, 1991). The reactivity of transformation products may be either higher or lower than that of their parent compounds.…”

“…One-way arrows denote essentially irreversible reactions, two-way arrow denotes a reversible reaction, and multiple arrows in sequence denote multistep reactions. References cited: a:Egli et al (1988), b: Picardal et al (1995, c:Wang and Arnold (2003), d:Novak et al (1997), e:Milligan and Häggblom (1999), f:Tesoriero et al (2001), g:Klecka et al (1990), h:Gibson and Suflita (1986), i: Adrian andSuflita (1990), j:Miles and Delfino (1985), k:Lightfoot et al (1987), l:Nair and Schnoor (1992), m:Papiernik and Spalding (1998), n:Rügge et al (1999), o:Larsen et al (2000), p:Agertved et al (1992).…”