Pesticides persistent

Chemical, cultural, and mechanical weed control practices have been relatively successful ia reducing yield losses from weeds (448). However, herbicide-resistant weed populations, soil erosion, pesticide persistence ia the environment, and other problems associated with technologies used (ca 1993) to control weeds have raised concerns for the long-term efficacy and sustainability of herbicide-dependent crop production practices (449). These concerns, coupled with ever-increasing demands for food and fiber, contribute to the need for innovative weed management strategies (450). 

Willis GH, McDowell LL. 1987. Pesticide persistence on foliage. Rev Environ Contam Toxicol 100 23-73. 

Vrochinskii, K. K. (1981). Pesticide persistence in water. Chemistry in Agriculture, 10, 43-45. 

Why is this important It is important because it has a direct impact on the meaning of USDA certified organic foods. In order to receive a USDA certification as an organic food, the food producer must not have used pesticides for the previous three years. However, as evidenced by the food data collected by the FDA, banned pesticides persist in the soil to this very day. Furthermore, the vast majority (i.e., about 95 percent) of the food sold in the United States is grown and produced in the United States. This means that those foods found to contain banned pesticides had to come from farms in the United States. 

The length of time pesticides persist in the forest floor and soil bears strongly on the probability they will be lost by volatilization (28-31). The phenoxy herbicides are commonly applied to forests as the low-volatile esters. These esters are readily hydrolyzed to their respective acids in soil or on the forest floor. For example, Smith (32) reported that no traces of 2,4,5-T and 2,4-D esters were observed in any of four moist soils after 48 and 72 hours, respectively, and most of them were hydrolyzed in less than 24 hours. The vapor pressures of the acids are much lower than the esters and this hydrolysis, along with subsequent degradation of the acids, results in a very low potential for volatilization of these materials from soil. 

As Figure 4 shows, pesticide persistence or disappearance relationships on and in crops will be affected by the type of toxicant involved, its dosage and formulation, as well as the number of applications. The crops foliage development and growth characteristics and the type of insect to be controlled will be contributory factors in pesticide persistence. Of prime importance will be the local weather conditions to which the chemical will be subjected over a long period of time. 

Beulke S., Dubus I. G., Brown C. D., and Gottesbiiren B. (2000) Simulation of pesticide persistence in the field on the basis of laboratory data—A review. J. Environ. Qual. 29, 1371-1379. 

All manner of pollutants are considered under the discipline of terrestrial ecotoxicology including pesticides, persistent organic pollutants, other organic substances, and metals and metalloids (e.g., selenium and arsenic). Naturally occurring toxins such as those produced by poisonous plants, snakes, or invertebrates generally are not included unless people intentionally apply them for pest control. For example, the pyrethroid pesticides are derived from the naturally occurring pyrethrin toxin that is found in chrysanthemum. 

Soil-water content ( ) and temperature (T) are the two major soil environmental factors that control pesticide degradation rates. Walker ( 34 ) and Walker and Barnes ( 35 ) have proposed a model for pesticide persistence in soils. In their model the 0-depgndence of described by a power function [two =... 

During the 30 years following the discovery of microbial adaptation for pesticide degradation, there were intermittent reports of the same phenomenon affecting the persistence of other pesticides. However, due to the fact that virtually none of these reports concerned situations where reduced pesticide persistence affected pest control efficacy, microbial adaptation for pesticide degradation was largely relegated to the status of academic curiosity. In fact,... 

In an effort to determine the criteria that should be used to invoke cases of enhanced degradation, an experimental approach for Its study was developed that focused on laboratory investigations with field-collected soils. It was obvious that Insecticide control failures were common occurrences and certainly not all due to enhanced degradation, as Investigations of faulty application methods and unusual environmental conditions have shown (18). The ideal approach to the study of enhanced degradation would Involve controlled field research in which pesticide persistence and control efficacy were both measured at many locations over a number of years. However, the tremendous cost In time and effort and confounding of results by environmental variables make a controlled laboratory approach desirable. The limitation of laboratory efforts focused exclusively on the soil-lnsecticlde Interaction is that they cannot fully address the additional insect-insecticide and Insect-crop interactions present in the field. This means that caution must be excercised when proof of enhanced degradation is discovered In the laboratory, for this does not necessarily mean that Insect control and crop yield will be adversely affected under field conditions. 

Note The microbial inhibitors listed above have been used in the field or laboratory to inhibit the enhanced biodegradation of certain pesticides and extend pesticide persistence. No attempt has been made to separate them based on their mode of action. 

Mobility index that relates pesticide persistence (half-life) and sorption (A oc) in soil. It is used to rate pesticides for their potential to move towards groundwater. 

The presence of organic substances and clay particles increases pesticide persistence in the soil. This is a result of an increased adsorption of these substances on humus and clay particles. As a result of this, pesticides become a suitable substrate for the activity of soil microorganisms. The rate of their evaporation and washing out is decreased. 

Dumped pesticides persist in Tanzania Pesticides News 37, September 1997... 

The separation or complexation of humic substances and/or heavy metals is successful in favorable cases, e.g., by the addition of bovine serum albumin (BSA) in a trinitrotoluene enzyme-linked immunosorbent assay (ELISA) [18]. In the. screening of soil samples for pesticides, persistent centrifugation at 17 000 rpm, and simple dilution with bidi.stilled water in the ratio 1 10 was sufficient [19]. 

This chapter is divided into seven main sections. The first of these sections is focused on technological contaminants, namely heterocyclic amines, acrylamide, furan, chloropropanok and their fatty acid esters, polycycKc aromatic hydrocarbons, monocyclic aromatic hydrocarbons, nitroso compounds, and ethyl carbamate. Other sections deal with microbial toxins (mycotoxins and bacterial toxins), persistent organohalogen contaminants (such as polychlorinated biphenyls, dibenzodioxins and dibenzofurans), chlorinated ahphatic hydrocarbons, pesticides (persistent chlorinated hydrocarbons and modem pesticides), veterinary medicines and contaminants from packaging materials. Presented for each of these contaminants are structures, properties, occurrence and the main sources of dietary intake, mechanisms of formation, possibilities of food contamination, prevention and mitigation and health and toxicological evaluations. 

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