Photolysis Methoxychlor

Methoxychlor. Methoxychlor is strongly adsorbed to the soil and does not leach, and volatilization is slow. There is no evidence for oxidation, and although photolysis is rapid in aquatic systems, it is assumed not to occur in the soil environment. The hydrolysis half-life is a year in aquatic systems (33) and probably longer in soil systems because of adsorption. Biodegradation does occur in soil systems, however, with a half-life of from 1 to 3 weeks (34). Methoxychlor would not persist in the soil environment. 

Photolytic. In air-saturated distilled water, direct photolysis of methoxychlor by >280 nm light produced l,l-bis(p-methoxyphenyl)-2,2-dichloroethylene (DMDE), which photolyzed to p-meth-oxybenzaldehyde. The photolysis half-life was estimated to be 4.5 months (Zepp et al., 1976). 

Methoxychlor-DDE and p,p-dimethoxybenzophenone were formed when methoxychlor in water was irradiated by UV light (Paris and Lewis, 1973). Compounds reported from the photolysis of methoxychlor in aqueous, alcoholic solutions were p,p-dimethoxybenzophenone, p-methoxybenzoic acid, and 4-methoxyphenol (Wolfe et al., 1976). However, when methoxychlor in milk was irradiated by UV light (A. = 220 and 330 nm), 4-methoxyphenol, methoxychlor-DDE, p,p-dimethoxybenzophenone, and l,l,4,4-tetrakis(p-methoxyphenyl)-l,2,3-butatriene were formed (Li and Bradley, 1969). 

Zepp, R.G., Schlotzhauer, P F. (1983) Influence of algae on photolysis rates of chemicals in water. Environ. Sci. Technol. 17,462-468. Zepp, R.G., Wolfe, N.L., Gordon, J.A., Fincher, R.C. (1976) Light-induced transformation of methoxychlor in aquatic systems. 

Z pp and co-workers (1976) found that photolysis of methoxychlor, although much more rapid than that of DDT, is still a very slow environmental process. The major product of light-induced transformation is l,l-bis(p-methoxyphenyl)-2,2-dichloroethylene (DMDE, 24). This product is subject to rapid photodegradation in both aqueous and hydrocarboi) media. 

Figure 6.9 Comparison of calculated and observed half-lives for direct photolysis of several pesticides and pesticide derivatives quantum yields given in parentheses. 1. N-Nitrosoatrazine in water (4> = 0.30) 2. trifuralin in water (4> = 0.0020) 3. DDE analogue of methoxychlor, DMDE, in water (4> = 0.30) 4. DMDE in hexadecane (4> = 0.20) 5. DDE in hexadecane (4> = 0.26) 6. diphenylmercury in water (4> = 0.27) 7. phenylmercuric acetate in water (4> = 0.25) 8. 2,4-D-butoxyethyl ester in hexadecane (4> = 0.17) 9. carbaryl in water (4> = 0.0060) 10. 2,4-D-butoxyethyl ester in water (4> = 0.056). [Reproduced with permission from R. G. Zepp and D. M. Cline, Environ. Sci. Technol. 11, 359 (1977). Copyright 1977, American Chemical Society.]...

Substantial rate enhancement for the photolysis of the pesticide methoxychlor... 

---