Occurrence of Dicofol in the San Joaquin River, California

Joseph L. Domagalski

Bulletin of Environmental Contamination Toxicology (1996) 57:284-291

Abstract:
The San Joaquin River and its tributaries were sampled intensively for pesticides during the irrigation season--April through October of 1993. The purpose of the sampling was to determine the occurrence of pesticides defined operationally as those dissolved in the water column. A pesticide detected frequently in these samplings was dicofol (2,2,2-trichloro-1,1-bis(4-chlorophenyl)ethanol). Dicofol is similar in structure to DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane) (figure 1) and has been implicated as a compound that can induce endocrine disruption in wildlife populations and humans (Guillette Jr. et al, 1994, Colborn and Clement, 1992). Chlorinated hydrocarbons, including pesticides, represent one class of synthetic organic chemicals that are thought to have endocrine disrupting effects (Colborn et al, 1993, Hileman, 1993). Scientists' concern over these chemicals have been directed toward the different effects on the offspring of the exposed organism relative to the adult. The effects may be highly dependent on the timing of exposure, especially with respect to fetal development (Colborn and Clement, 1992). Low concentrations, such as those routinely detected in environmental samples, may result in the onset of undesirable effects. The San Joaquin River and its tributaries are known to have elevated concentrations of DDT and its degradation products in bed sediments (Gilliom and Clifton, 1990) and fish (Rasmussen and Blethrow, 1990). The bed sediment concentrations measured at the time were among the highest for any major river system in the United States (Gilliom and Clifton, 1990).

The structure of dicofol relative to DDT is sufficient to alter significantly some chemical properties, such as water solubility. Therefore, the type of exposure for aquatic organisms will be different. Dicofol is principally transported as a dissolved constituent in the San Joaquin River and its tributaries as opposed to DDT, which principally occurs in bed or suspended sediment or aquatic tissue. DDT can bioaccumulate because of its low water solubility, but dicofol should not. The presence of an endocrine disrupting chemical dissolved in the water column may have implications for aquatic organisms. At present the toxicology significance of dicofol, with respect to endocrine disruption, has not been fully evaluated.

The purpose of this paper is to present the results of dicofol occurrence in the San Joaquin River and its tributaries, during the irrigation season of 1993, and to relate that occurrence to land use within the basin and to the physical properties of dicofol.