1. Methoxychlor Presentation By Dave Lewis

2. Structure and Properties Methoxychlor [1,1,1-trichloro-2,2-di(4- methoxyphenyl)ethane] is a bicycle aromatic DDT analog

3. Structure Compared to DDT Methoxychlor DDT

4. Physical & Chemical Properties Molecular Wt. 345.65 Molecular Wt. 345.65 ColorLight Yellow ColorLight Yellow Physical StateCrystalline Solid Physical StateCrystalline Solid Boiling Pt.Decomposes Boiling Pt.Decomposes Solubility in WaterVery slightly soluble 0.045 Mg./L Solubility in WaterVery slightly soluble 0.045 Mg./L Partition Coefficients Partition Coefficients Log K ow Lipophilic 4.7-5.1 Log K ow Lipophilic 4.7-5.1 Log K oc 4.9 Log K oc 4.9

5. Uses and Application, Production History etc This DDT analog was very heavily used after cancellation of DDT in the 1970s, although usage has declined more recently. In the early ‘90s about 300 to 500 thousand pounds of methoxychlor was used per year in the US (ATSDR, 1994). Compared to DDT, methoxychlor is rapidly metabolized both in the environment and in living organisms, so it does not produce the long-lasting toxicity and bioaccumulation, which led to the cancellation of DDT.

6. Uses and Application, Production History etc First synthesized by Elbs (1893), its insecticidal properties were described by Lauger et al. (1944) together with DDT, and it has been commercial insecticide for about 60 years. It has been used against houseflies, mosquitoes, cockroaches, chiggers, various arthropods found on field crops, and insect pests in stored grain or seed for planting. It has been registered for use on more than 85 crops, including fruits, vegetables, soybeans, nuts, and alfalfa. It is also approved for use on forests, ornamental plants, and for insect control around houses, barns, and other agricultural premises (ATSDR, 1994). It has often been formulated with other pesticide products, such as captan, diazinon, and malathion. It has been available in many forms, including technical-grade concentrate, wettable powders, dusts, granules, emulsifiable concentrates, and pressurized sprays for home use. It’s use was suspended in California in 1995 and use limited to stocks on hand. In 2000, the EPA did not reregister it for continued use.

7. Mode of Entry in Aquatic Environment Methoxychlor binds tightly to soils, but is not usually detectable in soil except in areas where it has been applied as a pesticide. Wind and rain can erode contaminated soils, resulting in the migration of methoxychlor-containing particulates. Some methoxychlor can persist in soils for more than a year after its application. However, most of it is degraded to dechlorinated, dehydrochlorinated, and demethylated products. These metabolites are more polar than methoxychlor and bind less tightly to soils which can contribute to wider dispersion. Methoxychlor can be released directly to surface waters on farms when used to control larvae of insects. Methoxychlor had prior approval for use on cranberries (EPA 1988b), which are grown in bogs, and therefore methoxychlor could be released directly to surface waters where cranberries are grown. Methoxychlor may be released to water from agricultural runoff from soil containing methoxychlor where it can be adsorbed onto suspended soil particles.

8. Chemical reactivity with water Methoxychlor undergoes a spontaneous elimination reaction in water to yield dehydrochlorinated products. The half-life is one year through this process. Methoxychlor can also undergo direct photolysis (half-life 4.5 months) or indirect "sensitized" photolysis (half-life <5 hours) depending upon the presence of photosensitizers Methoxychlor can also undergo direct photolysis (half-life 4.5 months) or indirect "sensitized" photolysis (half-life <5 hours) depending upon the presence of photosensitizers Half-life of Methoxychlor in Half-life of Methoxychlor in Sediments. Anaerobic >28 days Sediments. Anaerobic >28 days Aerobic >100 days Aerobic >100 days

9. Methoxychlor is very toxic to aquatic life. Reported 96 hour LC50 values are 20 ug/L for cutthroat trout, Atlantic salmon, brook trout, lake trout, northern pike and largemouth bass (Johnson and Finley 1980). Reported 96 hour LC50 values are 20 ug/L for cutthroat trout, Atlantic salmon, brook trout, lake trout, northern pike and largemouth bass (Johnson and Finley 1980). Reported 96 hour LC50 values are between 20 and 65 ug/L in rainbow trout, goldfish, fathead minnow, channel catfish, bluegill, and yellow perch (Johnson and Finley 1980). Reported 96 hour LC50 values are between 20 and 65 ug/L in rainbow trout, goldfish, fathead minnow, channel catfish, bluegill, and yellow perch (Johnson and Finley 1980). Aquatic invertebrates with 96- or 48-hour LC50, values of less than 0.1 mg/L include Daphnia, scuds, sideswimmers, and stoneflies (Johnson and Finley 1980 Aquatic invertebrates with 96- or 48-hour LC50, values of less than 0.1 mg/L include Daphnia, scuds, sideswimmers, and stoneflies (Johnson and Finley 1980 In comparison to mammals, rat oral 96 hour LC50 values In comparison to mammals, rat oral 96 hour LC50 values were >6000 mg per kg –much less sensitive. were >6000 mg per kg –much less sensitive.

10. Molecular mode of toxic interaction Acute: At the sodium gates of the axon, DDT exerts its toxic action by preventing the deactivation or closing of that gate after activation and membrane depolarization. The result is a lingering leakage of Na+ ions through the nerve membrane, creating a destabilizing negative afterpotential. The hyperexcitability of the nerve results in trains of repetitive discharges in the neuron after a single stimulus and/or occur spontaneously

11. Molecular mode of toxic interaction There are at least ten separate binding sites for ligands on the sodium channel There are at least ten separate binding sites for ligands on the sodium channel There are at least ten separate binding sites for ligands on the sodium channel The binding sites are accessible to the lipid bilayer and therefore to lipid-soluble insecticides. The binding of insecticides and formation of binding contacts across different channel elements could stabilize the channel when in the open state

12. Molecular mode of toxic interaction There are at least ten separate binding sites for ligands on the sodium channel There are at least ten separate binding sites for ligands on the sodium channel Flat topography of the Na+ channel The Methoxychlor binding site is thought to lie in a cavity formed between the D2 and D3 domains.

13. Toxic Effects (Endocrine Disruption) Activation of Methoxychlor to Estrogenic Metabolites. The rapid demethylation of methoxychlor decreases its neurotoxicity and leads to a rapid elimination from the body (Lehman 1952), making it significantly less toxic than its structural analogue, DDT. However, this detoxification pathway also is thought to act as an activation pathway for reproductive and developmental effects. Data from in vitro and in vivo studies indicate that the phenolic metabolites of methoxychlor resulting from demethylation (and contaminants in technical grade and laboratory grade methoxychlor) are responsible for most of the estrogenic activity rather than methoxychlor itself.

14. Toxic Effects (Endocrine Disruption) Methoxychlor has been shown to bind the androgen receptor and competitively displace testosterone from the receptor in goldfish testis (Antagonistic effect) Methoxychlor has been shown to bind the androgen receptor and competitively displace testosterone from the receptor in goldfish testis (Antagonistic effect) Methoxychlor treatment in channel catfish (Ictalurus punctatus) increased serum estradiol and vitellogenin (egg yolk protein) levels, demonstrating estrogenic activity. (Agonistic effect) Methoxychlor treatment in channel catfish (Ictalurus punctatus) increased serum estradiol and vitellogenin (egg yolk protein) levels, demonstrating estrogenic activity. (Agonistic effect) To determine the estrogenic capacity of MXC, adult zebrafish were exposed to 0, 0.5, 5, and 50 µg MXC/L for 14 d. Induction of vitellogenin ([VTG] measured with protein electrophoresis and Western blot) in males was detected at 5 and 50 µg MXC/L (Agonistic effect) To determine the estrogenic capacity of MXC, adult zebrafish were exposed to 0, 0.5, 5, and 50 µg MXC/L for 14 d. Induction of vitellogenin ([VTG] measured with protein electrophoresis and Western blot) in males was detected at 5 and 50 µg MXC/L (Agonistic effect)

15. Developmental Effects Environmental estrogens may interfere with hormone signaling during development. Xenopus laevis embryo treated with 1 μM methoxychlor developed a thin, poorly developed dorsal fin devoid of melanocytes, spotty melanocytes atop the spinal cord, crooked spine, and poorly defined somites melanocytes atop the spinal cord, crooked spine, and poorly defined somites Normal Methoxychlor treatment

16. Mode of entry into organisms Methoxychlor is absorbed through dermally, through gills and consumed in food. Methoxychlor is absorbed through dermally, through gills and consumed in food. Some organisms like Daphnia have the potential to bio-accumulate methoxychlor Some organisms like Daphnia have the potential to bio-accumulate methoxychlor

17. Biochemical metabolism and breakdown

18. Defense strategies available for detoxification by organism Methoxychlor is rapidly metabolized by CYP isoenzymes into less toxic metabolites which are not generally stored, and rapidly excreted. However, during chronic exposure or critical development, these mechanisms can fail to protect the organism.

19. Bibliography ATSDR (1994) Toxicological profile for methoxychlor. U.S. Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, Atlanta, GA. TP-93/11. Bevan.C, Porter.D, (2003) Environmental Estrogens Alter Early Development in Xenopus laevis.EnvironHealthPerspec pp. 488-496. Coats, J.R., (1990) Mechanisms of Toxic Action and Structure-Activity Relationships for Organochiorine and Synthetic Pyrethroid Insecticides. Environ Health Perspect Vol. 87, pp. 255-262, Cummings AM. (1997) Methoxychlor as a model for environmental estrogens. Crit Rev Toxicol Vol.27:4 pp.367-79. Johnson, W.W., and M.T. Finley. (1980). Handbook of acute toxicity of chemicals to fish and aquatic invertebrates. U.S. Fish Wildl. Serv. Resour. Publ. 137. pp 98. Lintelmann, J., Katayama, A.,. Kurihara, N., Shore, L. (2003) Endocrine Disrupters in The Environment. Pure Appl. Chem., Vol. 75: 5, pp. 631–681,. Nimrod, A.C. and Benson, W.H. (1997) Xenobiotic Interaction with and Alteration of Channel Catfish Estrogen Receptor Toxicology and Applied Pharmacology Vol.147:2 pp. 381-390 O’reilly, A., Khambay,B., (2006) Modelling insecticide-binding sites in the voltage-gated sodium channel Biochem. J. Vol. 396, pp. 255–263 Versonnen, B. J., Roose, P., Monteyne, E. M., Janssen, C. R. Estrogenic and toxic effects of methoxychlor on zebrafish (Danio rerio). Environmental Toxicology and Chemistry Vol. 23: 9 pp. 2194–2201 Wells, K. (1) ; Van Der Kraak. G. (2000) Differential binding of endogenous steroids and chemicals to androgen receptors in rainbow trout and goldfish Environmental Toxicology and Chemistry Vol.19 pp. 2059–2065,