Pesticide exposure insecticides

Pesticides, including insecticides, herbicides, and fungicides, are widely used in agriculture, and the potential for these residues to accumulate in food has led to concern for human safety. Pesticide residues may enter food animals from environmental sources or from treated or contaminated feeds. Immunoassay development for pesticides has had major impacts for pesticide registrations, analysis of residues in foods, monitoring environmental contamination, determination of occupational exposure, and integration of pest management. 

Major questions that arise whenever a pesticide exposure evaluation is completed are how good are the data and how close to the real answer have we gotten For most commercially sold insecticides, there are no appreciable pharmacokinetic data in human systems, although some data normally exist for animal models. Because such pharmacokinetic data do not exist for most active insecticides, passive dosimetry measurements must be used to estimate the exposure and eventually dose. Once such passive dosimetry data exist, certain assumptions must be made to arrive at an estimate of dose. 

EPA research investments since 1995 in pesticide exposure and risk assessment methods have helped pioneer novel approaches to quantify risk levels. A team at the University of Washington s School of Public Health and Community Medicine found that 2-5 year olds consuming predominantly organic foods over a 3-day period had 8.5-fold lower mean levels of OP insecticide metabolites in their urine than children eating mosdy conventional (unlabeled) foods (Curl et al., 2003). The study was carefully designed to minimize potentially... 

It is difficult to obtain figures that accurately reflect the incidence of pesticide poisoning, and the number of documented cases of direct human poisoning in the USA varies from source to source. It was estimated that there are 100,000 nonfatal cases of human poisoning each year from pesticide exposure (7). In 1973 there were 1,A7A cases of occupational illness associated with pesticide exposure in California (8). Organophosphate insecticides are a major cause of occupational poisoning. 

Environmental Defence recently released Toxic Nation A Report on Pollution in Canadians (Environmental Defence 2005). Samples were collected from 11 people for the presence of 88 chemicals, including heavy metals, PBDEs, PCBs, perfluorinated chemicals, organochlorine pesticides, organophosphorus-insecticide metabolites, and VOCs. The study objectives included determining whether pollutants were present at measurable concentrations in Canadians, identifying chemicals of concern, and creating public awareness of methods for avoiding exposure. 

In Australia, the most extensive set of data involves 4640 blood samples analysed for OCPs at the New South Wales Workcare Authority from 1987 to 1989. The vast majority of samples contained less than the occupational limits 50ppb (pg L-1) of dieldrin and less than 20ppb (pg L-1) of heptachlor. Of the 49 samples above the occupational limit 44 of these were from pest control operators (NHMRC, 1992). An earlier NSW study by Siyali (1972) compared whole blood levels of organochlorine insecticides from persons with and without industrial pesticide exposure. Levels of HCB, total DDT, dieldrin and HCH (BHC) were substantially higher in the exposed group, particularly for dieldrin. 

APPENDIX 22 TOXIC MANIFESTATIONS OF CHRONIC EXPOSURE TO PESTICIDES AND INSECTICIDES... 

Indoor concentrations of pesticides in proximity to pesticide-treated farmland have been measured (Fenske et al., 2002). For example, it has been shown that pesticide exposure in children could potentially be increased if they live in homes in close proximity (60 m) to pesticide-treated farmland (Fenske et al., 2002). Clothing and cars of farm workers can also be a source of pesticide exposures for children. Usually, applications of insecticides and herbicides in and around the home are a more likely source for children s exposures. 

Pesticides include a broad range of substances most commonly used to control insects, weeds, and fungi. Insecticides are often subclassified by chemical type as organophosphates, organochlorines, carbamates, and pyrethroids [110]. Some studies have indicated that pesticide exposure is associated with chronic health problems or health symptoms such as respiratory problems, memory disorders, dermatologic conditions, cancer, depression, neurologic deficits, miscarriages, and birth defects [111]. 

Bosma H, van Boxtel MP, Ponds RW, et al Pesticide exposure and risk of mild cognitive dysfunction (letter). Lancet 356 912-913, 2000 Furst JB, Cooper A Failure of systematic desensitization in 2 cases of obsessive-compulsive neurosis marked by fears of insecticide. Behav Res Ther 8 203-206,1970 Gauthier E, Fortier I, Courchesne F, et al Environmental pesticide exposure as a risk factor for Alzheimer s disease a case-control study. Environ Res 86 37-45, 2001... 

Another area that would be of direct benefit to the medical personnel responsible for treating pesticide exposure in humans is the development of antidotal and symptomatic treatment for the various classes of pesticides. Although we have more specific antidotes available to treat pesticide poisoning than for any other single class of acute poisons, the number of antidotes is small for non-insecticidal pesticides and these cases must be treated symptomatically. The current acute toxicity protocols do not currently provide the kind of clinical information that is needed in such cases. 

A rather unusual case of pesticide exposure repoted to the New Zealand Poisons Information Centre concerned a helicopter pilot who was involved in the aerial application of a carbamate insecticide onto crops. Foolishly, he mixed the dry powder formulation under the still rotating blades of his helicopter, which caused the powder to disperse into... 

Thirty-seven tobacco workers from Brazil exposed to OP insecticides were clinically evaluated after a 3-momh application season, and some (25/37) were. subsequently evaluated 3 months after the cessation of pesticide use (Salvi et ai, 2003). At the time of the first evaluation, all subjects had been exposed to OP pesticides within 24 hr. None (0/37) had a history of acute intoxication within the past year. Significant extrapyramidal signs and symptoms were present in 12 patients. Although extrapyramidal signs improved during the no-exposure period, 10 patients still exhibited some motor difficulties after removal from pesticide exposure. 

It is estimated that 18% of all new Wilms tumours, affecting the kidneys of Brazilian children, are attributable to pesticide exposure of their parents. Consistently elevated risks were seen among children whose fatlier or mother carried out farm work which involved the frequent use of pesticides. As elsewhere, many pesticides are used in Brazil and researchers estimated that 73 insecticides, 42 fungicides and 59 herbicides are in use. Atrazine and dichlorvos are particularly widely used and both are rated as possibly carcinogenic by the International Agency for Research in Cancer. 

Comparisons of farmers with long-term exposure to pesticides in rice production with farmers with no history of exposure showed that the magnitude of chronic health effects and health costs are directly related to pesticide exposure and that the net benefits of insecticide use aie negative. 

Some veterans were exposed to these pesticides by intentional application, but because many exposures were accidental, it has been difficult to assess pesticide exposure accurately and therefore a topical dose in exposed veterans. Permethrin was intentionally impregnated into the soldier s uniform fabric at a concentration of 0.125 mg/cm to help control insect infestation while in the dessert. This pyrethroid insecticide consists of four different isomers (Figure 9.1), with the cis isomer more toxic than the trans isomer. Permethrin is a large moleeule (MW = 391.3) and has a log octanol-water partition coefficient of 6.5, which suggests that it could readily partition from the uniform into the lipophilic stratum comeum layer of the soldier s skin. With a transfer rate of 0.49% per day of permethrin from the fabric to skin, the daily dose was estimated to be 6.8 x 10" mg/kg/day (National Research Council... 

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