Direct pesticide applications

At present, there are generally two basic situations involving water supply contamination by pesticides chronic contamination, which is usually at levels of less than 1 p.p.b., and short term and higher level contamination. The chronic contamination results from the more or less continuous bleed-off of pesticide residues from land and continuous or periodic discharges from industrial wastes. The second or high level contamination may involve accidents, massive runoff from land following heavy rains, or direct pesticide applications to water to control unwanted fish, insects, or aquatic plants. 

Holmstedt (1959) and Brown and Muir (1971) have reviewed perocular absorption of pesticides. More recently, Sinow and Wei (1973) have shown that the quartemary herbicide paraquat can be lethal to rabbits if applied directly to the surface of the eyes. Parathion, in particular, is exceedingly toxic when administered via the eye, a concern that must be kept in mind for the protection of pesticide applicators. 

While all nations of the world possess the sovereign right to establish their own acceptable levels for pesticide residues in foods, many lack the resources to develop their own regulatory programs and instead rely upon a set of international standards developed by the Codex Alimentarius Commission, frequently referred to as Codex. The Codex international standards are termed maximum residue limits (MRLs) and, like U.S. tolerances, are established primarily as enforcement tools for determining whether pesticide applications are made according to established directions. While many countries have adopted Codex MRLs, others, such as the U.S. and several Asian countries, rely on their own standards. Thus, there is no uniformity among the world with respect to allowable levels of pesticides on foods. A pesticide-commodity... 

There are no data on intermediate-duration inhalation or dermal exposures in either humans or animals. Data on intermediate inhalation and dermal exposures would be useful since the inhalation of vapors or direct contact with residual heptachlor from residential pesticide application or at NPL sites may be potential routes of exposure for the general population. 

In the past (prior to 1974), exposure of humans to heptachlor and heptachlor epoxide was directly related to the application of heptachlor as an insecticide. However, because of the persistence and bioaccumulation of heptachlor and heptachlor epoxide, exposure of the general population can occur through ingestion of contaminated food (especially cow s or maternal human milk), inhalation of vapors from contaminated soil and water, or direct contact with residual heptachlor from pesticide application. People whose homes have been treated may continue to be exposed to these chemicals in the air over long periods. Occupational exposure can occur in the manufacture of the chemical or from use of heptachlor to control fire ants. The most likely routes of exposure at hazardous waste sites are unknown. Heptachlor has been found infrequently in soil and groundwater at hazardous waste sites. Children who eat contaminated soil or people who obtain tap water from wells located near hazardous waste sites might be exposed to heptachlor. Also, since both compounds can volatilize from soil, people living near hazardous waste sites may be exposed to the compounds in the air. 

Diazinon is released into water directly from point source discharges, from drift during pesticide applications, and from nonpoint source runoff from agricultural and urban areas. Since diazinon is not a Priority Pollutant under the Clean Water Act, it has not been evaluated extensively in water quality... 

In other cases, products may be restricted for sale only to (or at the request of) those who are trained to use them properly. Thus consumers can purchase some medicines only when the medicines are prescribed by a physician. Some agricultural chemicals are classified as restricted pesticides because of the hazards they pose. These products can be sold and used only under the direction of a certified pesticide applicator, a person who is certified as trained and knowledgeable about hazardous pesticides. 

It is correct to note that the specific tolerance levels requested by the manufacturer are determined solely on the basis of agricultural practices and not upon potential human health considerations. As such, tolerances represent enforcement tools to determine whether pesticide applications were made in accordance with the law but should not be considered as safety standards. In the case where a pesticide is used properly, the resulting residue level should be below the tolerance level. Residues detected in excess of the established tolerance are likely encountered only in cases where applications are not made in accordance with the legal directions. Results obtained from federal and state monitoring programs demonstrate that the incidence of residues detected in excess of tolerances is very low and suggest that most pesticide applications are made legally. 

Pesticide application to a drinking-water storage tank leads directly to contamination of drinking-water... 

The literature contains ample evidence that the atmosphere may become contaminated locally as the direct result of pesticide application, especially by air-spraying operations. Such occurrences have been documented, for example, by West (12) and Kraybill (7). Tabor (10) has shown that the air over both rural and urban communities contains pesticides, which reflect their use in local agricultural applications and in communities conducting mosquito-control operations. In this study,... 

Pesticide residues in humans, animals, and fish in areas remote from pesticide application can, in many cases, be attributed to an intermediate such as the food chain. Thus, migratory fish and birds can easily accumulate pesticide residues from foods directly contaminated by pesticide application. In those instances where the food chain cannot serve as a reasonable explanation, then, clearly, the atmosphere, including dust and rainfall, offers an alternative solution to pesticides translocation. 

Wind—Wind speed and direction can greatly alter the effectiveness of a pesticide application. Excessive wind can blow the pesticide off target and resnlt in inadeqnate control. Even moderate winds can greatly alter the coverage of ULV and mist blower applications. Sometimes the applicator can compensate for minor winds by applying the pesticides at an angle where the winds blow the chemical towards the area to be protected. 

Airblast/mistblower applications, unless performed while in an enclosed cab, are likely to expose the pesticide applicator to large quantities of drifting "mist," often to the point of being completely drenched in the pesticide fallout. Such exposure cannot be avoided, even if the application is performed in conditions of little or no wind and care is taken to remain out of the direct path of the air blast. 

A formulation can contain more than one active ingredient to increase the efficacy range per application. This reduces labor time, because fewer sprajdngs are necessary than with separate spra3dngs of single pesticide formulations. A similar result is achieved when several products are mixed directly before application (tank mixes). However, the products of the different formulations must be compatible. For instance, oil- and water-based products cannot be mixed and would lead to phase separation. Chemical incompatibility can occur as result of reaction of acids with bases or hydrolysis of pH sensitive compounds. 

Landers, A.J. (1993) Direct injection sprayers - a method of reducing environmental pollution. Proceedings, ANPP — BCPC Second International Symposium on Pesticide Application Techniques, Strasbourg, pp. 305-312. 

Chloride and bromide are the tracers of choice. Tracers must be applied at the time of pesticide application, so that the movement of the tracer can be directly correlated to the movement of pesticide. However, in a more detailed study, Tennyson and Settergren (38) found that bromide moved more rapidly in soil-water than would be expected from the laboratory determined soil hydraulic conductivity (K). Radioactive materials, organic dyes, gases, and fluorocarbons are not recommended for use as tracers. The fluorocarbons have been used successfully, though they have not been used extensively to date (39) After the application of pesticide and tracer, the procedures previously outlined should be followed for monitoring soil and ground water. 

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