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MOLINATE (ORDRAM)

Molinate is a selective herbicide used to control the germination of grasses and broadleaf weeds in rice fields. Its registered trade name is Ordram, and its chemical name is S-ethyl hexahydro-1H-azepine-1-carbothioate. The Chemical Abstract Service (CAS) Registry Number is 2212-67-1. Molinate is a clear to amber-colored liquid with an aromatic or spicy odor. Its water solubility is 970 mg/L at 25°C and its vapor pressure is 5.6 X 10^-3 mm Hg at 25°C, making it a volatile pesticide (HSDB, 2001).

During the years 1991 to 1997, an average of 1.35 million pounds of molinate was used yearly in California, the majority of which was used on rice (DPR, 1999a, 2000). The molinate products registered for use in California are Ordram 8-E (emulsifiable concentrate), which contains 8 pounds of active ingredient per gallon, and Ordram 15-GM (granules), which contains 15 pounds of active ingredient per 100 pounds (Zeneca Ag Products, 1999).

Molinate applied to rice paddies may volatilize into the air from both water and soil surfaces (HSDB, 2001). High temperatures and windy conditions increase the rate of volatilization. Molinate concentrations up to 23 µg/m³ have been measured in air sampled near rice fields in Colusa County (Baker et al., 1996). Molinate was not detected in California groundwater wells sampled between July 1, 1997, and June 30, 1999 (DPR, 1999b, 2000). Molinate was detected in surface waters in the Sacramento Valley in a 1995 survey (Bennett et al., 1998), including sites at the Colusa Basin Drain (2.8 to 25 µg/L), Butte Slough (2.1 to 8.5 µg/L), and the Sacramento Raw Water Intake (0.12 and 0.16 µg/L).

Human exposure may occur through inhalation in the vicinity of a molinate-treated rice field, by dermal contact during occupational use, or possibly through ingestion of contaminated water or food (HSDB, 2001). A federal tolerance level for molinate in or on raw rice grain and straw is 0.1 ppm (HSDB, 2001).

Molinate has been shown to cause adverse reproductive and neurological effects in laboratory species (DPR, 1996). The U.S. EPA Carcinogenicity Peer Review Committee recommended in 1992 that molinate should be classified under Group C (possible human carcinogen) (U.S. EPA, 1992a). This was based on an increased incidence of combined kidney tumors in male rats exposed to 300 ppm molinate in the diet over their lifetime. U.S. EPA estimated a unit risk, q₁* (in human equivalents), for molinate of 0.11 (mg/kg-d)^-1, based on the kidney tumors, using a body weight^2/3 extrapolation (U.S. EPA, 1992b).

A California MCL of 20 µg/L (20 ppb) was established for molinate in 1988 (DHS, 1988). A federal MCL has not been developed; however, molinate has been placed on the drinking water contaminant candidate list published by the U.S EPA (1998).

References

Baker LW, Fitzell DL, Seiber JN, Parker TR, Shibamoto T, Poore MW, Longley KE, Tomlin RP, Propper R, Duncan DW (1996). Ambient air concentrations of pesticides in California. Environ Sci Technol 30:1365-8.

Bennett KP, Singhasemanon N, Miller N, Galavan R (1998). Rice pesticides monitoring in the Sacramento Valley, 1995. Report No. EH 98-03. Environmental Hazards Assessment Program, California Department of Pesticide Regulation, Sacramento, California. February 1998.

DHS (1987). Proposed maximum contaminant level. Molinate (OrdramÒ). Hazard Evaluation Section, Department of Health Services (presently the Pesticide and Environmental Toxicology Section, Office of Environmental Health Hazard Assessment, California Environmental Protection Agency).

DHS (1988). Maximum contaminant levels for 1,1,2-trichloroethane, thiobencarb, molinate, bentazon, atrazine and simazine in drinking water (R-39-88). Notice of Proposed Rulemaking, California Department of Health Services, June 23, 1988.

DPR (1996). Molinate risk characterization document. Department of Pesticide Regulation, California Environmental Protection Agency, March 1, 1996.

DPR (1999a). Summary of pesticide use report data, 1997, Indexed by chemical. Department of Pesticide Regulation, California Environmental Protection Agency, Sacramento, California. June 1999. http://www.cdpr.ca.gov/docs/pur/pur97rep/97_chem.htm

DPR (1999b). Sampling for pesticide residues in California well water. 1999 Update of the well inventory database for sampling results reported from July 1, 1998 through June 30, 1999. Department of Pesticide Regulation, California Environmental Protection Agency, Sacramento, California. EH00-04. December 1999.

DPR (2000). Sampling for pesticide residues in California well water. 1998 Update of the well inventory database for sampling results reported from July 1, 1997 through June 30, 1998. Department of Pesticide Regulation, California Environmental Protection Agency, Sacramento, California. EH00-03. February 2000.

HSDB (2001). Molinate (CASRN 2212-67-1). Hazardous Substances Databank, a database of the National Library of Medicine's TOXNET system. Last revised April 26, 2001.

U.S. EPA (1992a). Carcinogenicity peer review of molinate. Memorandum from L. Taylor and E. Rinde, Health Effects Division, to R. Taylor, Registration Division, and J. Ellenberger, Special Review and Reregistration Division, U.S. Environmental Protection Agency, Washington, D.C. August 14, 1992.

U.S. EPA (1992b). Molinate, quantitative risk assessment, two-year Charles River Crl:CD(SD)BR rat dietary study. Memorandum from B. Fisher to L. Taylor, Health Effects Division, U.S. Environmental Protection Agency, Washington, D.C. December 4, 1992.

U.S EPA (1998). Announcement of the drinking water contaminant candidate list; notice. Part III, Environmental Protection Agency. Fed. Reg. 63(40):10273-87. March 2, 1998.

Zeneca Ag Products (1999). Pesticide labels for OrdramÒ 8-E selective herbicide and OrdramÒ 15-GM rice herbicide. www.syngenta.com (Formerly Zeneca Ag Products, now Syngenta).

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Last Updated August 13, 2003