Methoxychlor and DDT Degradation in Water: Rates and Products N. Lee Wolfe', Richard G. Zepp, Doris F. Paris, George L. Baughman, and Reginald C. Hollis Environmental Research Laboratory, U.S. Environmental Protection Agency, Athens, Ga. 3060 1
in water at pH 7 and 9. In natural water samples, however, the w Methoxychlor [2,2-bis(p-methoxyphenyl)-l,l,l-trichlo- half-life was as short as 7 days. While hydrolytic degradation roethane] and DDT [2,2-bis(p-chlorophenyl)-l,l,l-trichloroethane] undergo different hydrolytic degradation pathways in water a t pH's common to the aquatic environment. For methoxychlor a t common aquatic pH's, the reaction is pH independent, and a t 27' the half-life is about 1year. On the other hand, for DDT the reaction is pH dependent, and a t 27' and p H 7 the half-life is about 8 years. The major products of methoxychlor hydrolysis a t p H 7 are anisoin, anisil, and DMDE [2,2-bis(p-methoxyphenyl)-l,l-dichloroethylene]; the major product of DDT is DDE [2,2-bis-(p-chlorophenyl)1,l-dichloroethylene]. Hydrolytic degradation half-lives of metabolites and reported breakdown products are estimated and compared with the parent compounds. The contribution of hydrolysis is dependent on the amount of methoxychlor and DDT in aqueous solution. Calculations with partition coefficients indicate that even though high concentrations of these two compounds are present in the sediment and biota, a large fraction can be in solution.
might be slow when compared with the rates of alternative degradative pathways, however, it can still be environmentally significant in view of the long life times in the environment. For example, methoxychlor is termed a moderately persistent pesticide, but DDT is long lived in the environment with a life time estimate of up to 20 years (6). Based on these facts, the chemical behavior of methoxychlor and DDT in water was examined-with emphasis placed on rates of hydrolytic degradation, pH effects, and products. In addition, structure reactivity relationships were used to estimate the hydrolytic degradative half-life for metabolites and other reported breakdown products.
Experimental Equipment. All melting points were obtained on a Fisher Johns melting point apparatus and were uncorrected. Infrared (IR) spectra were obtained with a Perkin-Elmer 621 grating infrared spectrophotometer. Nuclear magnetic resonance (NMR) spectra were obtained on a Varian T-60A NMR Methoxychlor [2,2-bis(p-methoxypheny1)-l,l,l-tri- spectrometer. chloroethane] is a popular substitute for DDT [2,2-bis(pGas-liquid chromatographic (GLC) analysis was carried out chlorophenyl)- l,l,l-trichloroethane] in the control of many on a Tracor MT-220 gas chromatograph equipped with 63Ni insects. I t has a low mammalian toxicity and is considered to electron capture and flame ionization detectors (FID) and be moderately biodegradable (1).Although many reports on fitted with a 1.8 m X 3.5 mm i.d. column packed with 3% SE-30 the biodegradation of methoxychlor are available, few data on 80-100 mesh Chromosorb W. Gas chromatographic-mass exist concerning its chemical behavior not only in aquatic spectrometric (GC-MS) analyses were performed with a ecosystems but also in water. An investigation, therefore, was Varian Aerograph Model 1532-B gas chromatograph interinitiated into the chemical reactivity of methoxychlor in water faced with a Finnigan 1015 SL quadrupole mass spectrometer to help delineate the contribution of hydrolysis. to its envihaving a Gohlke glass jet separator and a Systems Industries ronmental degradation and to identify products. In addition, 150 digital computer. its chemical reactivity in water was compared with that of Liquid chromatographic (LC) analysis was performed on DDT, a related compound for which extensive environmental a Micromeritics 7000 liquid chromatograph employing ODS background data exist. as the stationary phase and 45% methanol-water as the mobile In a quantitative study to assess microbial contribution to phase. Analysis was carried out using a variable wavelength methoxychlor degradation, Paris et al. ( 2 ) examined four UV detector a t 245 nm; pressure, 1200 psi; flow rate, 2.5 bacterial populations. Only one isolate was reported to demL/min. The thin-layer techniques employed have been grade methoxychlor, and a second-order degradative rate previously described by Kapoor et al. (7). constant of (1.1f 0.6) X lOP13 L org-l h-' was reported, which Chemicals. The synthesis and purification of methoxyis low compared with that found for other pesticides investichlor, DDT, DMDE, and DDE have been previously described gated. (3).Anisoin and anisil were obtained from Pfaltz and Bauer Zepp et al. (3) reported pseudo-first-order rate constants and recrystallized from chloroform-hexane before use. All of 5.3 X day-' and
