Phorate

Abstract: Phorate {O,O-diethyl S-[(ethylthio)methyl] phosphorothioate; trade name: thimet} is an organophosphate compound used agriculturally, primarily in the production of corn, cotton, and potatoes, to control sap-feeding insects including various beetles, mites, grubs, and worms. There are no registered residential uses. Phorate was first registered for use in the United States in 1959 [U.S. Environmental Protection Agency (EPA) 2001]. In the United States, almost 2.5 million acres are treated annually with 2–3 million pounds of phorate, making it the sixth most common organophosphate used (Donaldson et al. 2002). The currently limited body of literature does not provide evidence to suggest that phorate is mutagenic, genotoxic, or carcinogenic (Bingham et al. 2001; California Department of Pesticide Regulation 1996; Lin et al. 1987; Pandita 1986). However, several epidemiologic studies have found associations between exposure to organophosphate pesticides and non-Hodgkin lymphoma (NHL) (Cantor et al. 1992; Zahm et al. 1993) as well as leukemia (Brown et al. 1990; Clavel et al. 1996), and the International Agency for Research on Cancer (IARC) considers insecticide application to be an exposure that is probably carcinogenic in humans (Group 2A) (IARC 1991). Recent findings from the Agricultural Health Study (AHS) linking lung cancer with exposure to diazinon and chlorpyrifos (Alavanja et al. 2004) and prostate cancer with exposure to chlorpyrifos, coumaphos, fonofos, and phorate among applicators with a family history of prostate cancer (Alavanja et al. 2003) prompted us to examine risk for all cancers among phorate users in the same cohort over a longer follow-up period. The aforementioned insecticides belong to the organothio-phosphate subgroup, are similar to phorate in chemical structure, and must be converted in the body to their bioactive, neurotoxic oxon forms, which irreversibly inhibit acetylcholine esterase by phosphorylating a serine hydroxyl group in the active site of the enzyme (Pope 1999; Sultatos 1994). Little is known of the carcinogenicity of the oxon species. To our knowledge, this is the largest epidemiologic examination of an occupational group exposed to phorate.

Abstract: Pesticides are potential risk factors for respiratory disease among farmers, but farmers are also exposed to other respiratory toxicants. To explore the association of pesticides with wheeze in a population without other farming exposures, the authors analyzed data from 2,255 Iowa commercial pesticide applicators enrolled in the Agricultural Health Study. Controlling for age, smoking status, asthma and atopy history, and body mass index, the authors calculated odds ratios for the relationship between wheeze and 36 individual pesticides participants had used during the year before enrollment (1993-1997). Eight of 16 herbicides were associated with wheeze in single-agent models; however, the risk was almost exclusively associated with the herbicide chlorimuron-ethyl (odds ratio (OR) = 1.62, 95% confidence interval (CI): 1.25, 2.10). Inclusion of chlorimuron-ethyl in models for the other herbicides virtually eliminated the associations. The odds ratios for four organophosphate insecticides (terbufos, fonofos, chlorpyrifos, and phorate) were elevated when these chemicals were modeled individually and remained elevated, though attenuated somewhat, when chlorimuron-ethyl was included. The association for dichlorvos, another organophosphate insecticide, was not attenuated by chlorimuron-ethyl (OR = 2.48, 95% CI: 1.08, 5.66). Dose-response trends were observed for chlorimuron-ethyl, chlorpyrifos, and phorate; the strongest odds ratio was for applying chlorpyrifos on more than 40 days per year (OR = 2.40, 95% CI: 1.24, 4.65). These results add to the emerging literature linking organophosphate insecticides and respiratory health and suggest a role for chlorimuron-ethyl.

Abstract: An aquatic, multicomponent microcosm simulating a northern prairie wetland was used to assess the potential effects of six extensively used agricultural pesticides on this important wildlife habitat. Using a nested experimental design, 16 4-liter aquatic microcosms were treated with three concentrations of each of the pesticides carbofuran, fonofos, phorate, atrazine, treflan and trial-late. The microcosm units were incubated for 30 d in an environmental chamber, with a 16-h light:8-h dark cycle, maintained at 20°C. Specific limnological, biological and toxicological parameters were monitored over time by observing the interactions of water, animals, sediment and plants with the pesticides. The laboratory protocol was designed as an initial, rapid, economical screening test to determine the effect, but not the fate, of chemical contaminants in terms of toxicity, impaired productivity and community biochemical functions. Static acute toxicity tests with Daphnia magna and Chironomus riparius suggested that carbofuran, fonofos, phorate and triallate were very toxic to aquatic invertebrates. For D. magna the 48-h EC50 values were 48, 15, 19 and 57 μg/L, respectively. Invertebrate viability tests indicated rapid changes in the toxicological persistence of these pesticides after microcosm interaction. Populations of D. magna were established in the 10 μg/L test concentration of carbofuran, phorate, triallate and fonofos at 1, 1, 14 and 28 d, respectively. Preexposure of the wetland sediments to either triallate or fonofos did not appear to change the relative toxicological persistence of each compound in the water column. Changes in pH, alkalinity, conductivity, dissolved oxygen, total nitrogen and total phosphorus were also observed with different pesticide treatments. Atrazine significantly reduced gross primary productivity and inhibited algal and macrophytic growth. In general, there was no evidence of significant inhibition of microbial functions in the water or hydrosoil of the treated microcosms. The respiratory electron transfer system, phosphatase activity, oxygen consumption and mineralization of dissolved organic carbon were not significantly impacted by any of these pesticides in hydrosoils. However, the impact of atrazine, fonofos and triallate on invertebrates and plants in the microcosm—both key elements in wetland productivity—would suggest that caution be used in application of these pesticides in or near wetland habitats.