Translocated pesticides

Plant uptake is one of several routes by which an organic contaminant can enter man s food chain. The amount of uptake depends on plant species, concentration, depth of placement, soil type, temperature, moisture, and many other parameters. Translocation of the absorbed material into various plant parts will determine the degree of man s exposure—i.e., whether the material moves to an edible portion of the plant. Past experience with nonpolar chlorinated pesticides suggested optimal uptake conditions are achieved when the chemical is placed in a soil with low adsorptive capacity e.g., a sand), evenly distributed throughout the soil profile, and with oil producing plants. Plant experiments were conducted with one set of parameters that would be optimal for uptake and translocation. The uptake of two dioxins and one phenol (2,4-dichlorophenol (DCP)) from one soil was measured in soybean and oats (7). The application rates were DCP = 0.07 ppm, DCDD 0.10 ppm, and TCDD = 0.06 ppm. The specific activity of the com-... 

Bernstein, D. N., T. T. Drew, and M. Kuschner (1980). The translocation and fate of sized man-made mineral fibers following exposure by intratracheal instillation in rats, pp. 343-390. In Levin, A., ed. Proceedings of the National Workshop on Substitutes for Asbestos. EPA Doc. No. 560/3-80-001. Office of Pesticides and Toxic Substances, Washington, DC. 

Similiarly variable is the systemic activity of these compounds, that is the translocation in the vascular system of the plant. In this respect, cymoxanil with its very localized distribution, and fosetyl with its fast and strong translocation both acropetally and basipetally, are the extremes (Table IV). From this point of view, fosetyl is the most remarkable structure it is the only commercial pesticide showing effective acropetal and basipetal translocation at normal use rates. 

Hinman, M.L., Klaine, S.J. (1992) Uptake and translocation of selected organic pesticides by the rooted aquatic plant Hydrilla verticillata royale. Environ. Sci. Technol. 26, 609-613. 

Martin, H., Worthing, C.R., Eds. (1977) Pesticide Manual. 5th Edition, British Crop Protection Council, Thornton, United Kingdom. Martin, R.A., Edgington, L.V. (1981) Comparative systemic translocation of several xenobiotics and sucrose. Pest. Biochem. Physiol. 16(2), 87-96. 

Arsenic is a constituent of most plants. As can be phytotoxic and the toxicity of arsenite is greater than that of arsenate (Peterson et al., 1981). It is suggested that As uptake is passive (Streit and Stumm, 1993), and that it is translocated to most parts of the plant, most being found in roots and old leaves. Natural As levels in plants seldom exceed 1 mg kg 1, but the leaf content may be higher if arsenic pesticides have been used. As accumulates in Pseudotsuga mensiesii, up to 2000 — 5000 mg kg-1 have been reported in the plant ash (Hewitt and Smith, 1975). 

Herbicides, or weed killers, may be classified as pesticide chemicals. They can kill plants on contact, or they can be translocated (i.e absorbed by one part of the plant and carried to other parts where they exert their primary toxic effect). Most commonly used herbicides have a low toxicity and have caused few adverse effects in users. Some herbicides pose more serious problems to the central nervous system (CNS) and can cause depression. The skin absorption of herbicides also may cause skin irritation, dermatitis, and photosensitization in addition to peripheral motor neuropathies. 

There are other advantages, too. With lower levels of insecticide, wildlife are not apt to be affected and environmental problems associated with pesticide use, e.g., groundwater contamination and pesticide translocation, will definitely be diminished or eliminated. 

To appraise the extent of environmental contamination is a problem in organic pesticide analysis. Analytical methods for such diverse samples as air and human tissue have been developed and are yielding important information. The fate and persistence of pesticides constitutes another complex problem. It includes consideration of environmental and biological effects upon pesticides, how they move in rivers, and how they are translocated from one environmental medium to another. Finally, there is the question of damage control. Can we reduce the introduction of pesticides into air and water If not, can we effectively remove these poisons from the parts we consume ... 

There is increasing evidence that pesticides have contaminated extensive areas of the world not directly treated with pesticides. In many instances, the translocation can be attributed to food or water as the transmission vehicle. Another medium of dispersal of pesticides is the atmosphere. Analyses of rainwater and dust have revealed the presence of chloro-organic substances in all samples examined. Identification of specific pesticides has demonstrated that at least some of the chloro-organic compounds are pesticidal in origin. An analysis of dust, whose distant origin was documented by meteorological evidence, proved that pesticide-laden dust can be transported over great distances via the atmosphere and can be deposited over land surfaces remote from the point of application. 

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. 

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