Organic Matter Reactions Involving Herbicides in Soil

Abstract

Documentary evidence is presented in support of the view that organic matter plays a major role in the adsorption of herbicides in soil, and that organic matter content is usually the soil factor most directly related to herbicidal behavior. Major attention is given to the nature and origin of humic and fulvic acids, with special emphasis being given to the types of reactive sites responsible for the binding of pesticide chemicals. The various aspects of humus chemistry are discussed as they relate to investigations on herbicide‐soil organic matter relationships, including the inadequacies of methylation procedures for blocking specific functional groups in connection with bonding mechanism studies. Adsorption mechanisms are suggested and possible chemical transformations brought about by organic substances are outlined.

Sorption, degradation and mobility of microcystins in Chinese agriculture soils: risk assessment for groundwater protection

“…1 and Table 2, the adsorption of MCs in any of the soils decreased in the following order: RR > Dha 7 LR > LR, furthermore, for each MC variant in the three soils, the adsorption in the soils decreased in the following order: soil A > soil C > soil B. In numerous cases, soil organic matter contents have been shown to affect the organic pollutants adsorption in soils (Stevenson, 1972;Worrall et al, 2001;Spark and Swift, 2002), however, in the present study the sorption behavior did not depend on the total organic matter contents (Table 1), but on the content of clay in the soils. That is to say, the soil type and the soil clay content are the main factors influencing the adsorption of MCs in soils.…”

Comparative degradation of organophosphorus insecticides in soil: specificity of enhanced microbial degradation

“…Isofenphas, fonofos, ethoprop, terbufos, and phorate were all more persistent in the higher organic matter Canisteo soils than in the Tama soils. Increased organic matter in soil is often associated with increased adsorption of pesticides (Stevenson, 1972), which can render pesticides less susceptible to microbial degradation (Ogram et al, 1985). In the present study, only chlorpyrifas was less persistent in the Canisteo soils than in the Tama soils, being represented by greater quantities of 3,5,6-trichloropyridinol in the former so&.…”

Changes in valued ?Capacities? of soils and sediments as indicators of nonlinear and time-delayed environmental effects

“…Two examples are diquat and paraquat, each of which has a half-life in soils of at least 10-20 years (de Haan;: As shown in Figure 13 for the case of diquat, such pesticides also contain positive charges and thus may be adsorbed at cation exchange sites. de Haan, 1987, andStevenson, 1972. The most important question regarding these stored toxic materials is the potential in the future for increased mobility, resulting in their leaching into groundwaters or uptake by edible plants. In order to make such an assessment, it may be useful to apply the so-called "bottom-up" approach described by Parry and Carter (1987).…”