Soil particles, pesticide residues

In conclusion, soil composition (pesticide residue) played an important role in controlling fabric/soll Interactions. Captan, an aqueous suspension of particles, was more difficult to remove In 100% cotton denim. This was attributed to particle size and the clay-llke nature of the materials comprising the pesticide formulation. 

Toxic contamination of water by pesticides can result from leaching through the soil profile into ground water, by surface runoff, by erosion of eontaminated soil particles, or direetly by pestieide applieation close to surface waters. For a comprehensive evaluation of the risk of pestieide residues to the environment, the OECD (1997) recommends a risk as well as a state approach within the framework of environmental indicators. 

In general most of the pesticide residues are immobilized on soil particles, although in some cases, such as alachlor, atra-zine, benomyl, diphenamid, EPTC, naptalam and propachlor, significant amounts were found in the liquid phase. This presence in the liquid phase, which is primarily aqueous, can cause environmental problems if the liquid contents are lost due to leakage. 

Insecticides tend to persist longer in soils of high organic matter. In fact, in muck soils (50% or more organic matter), residues have been found bound to soil particles to such an extent that the same amount of toxicant is less effective in muck soil as compared with a sandy type. It has been noted that pesticides are absorbed into crops most readily from sandy soils and least from muck soils. Moisture enhances the release of volatile pesticides from soil particles and also influences the breakdown of other toxicants. Microbial attack has been found to oxidize aldrin to dieldrin, and parathion in the presence of yeast is reduced to the nontoxic aminoparathion in soil. As might be expected, increased soil temperatures can dramatically increase the rate of pesticide loss owing to volatilization and increased breakdown. Cover crops, such as alfalfa, can decrease pesticide volatility from soil whereas cultivation... 

Noncompetitive assays can only be apphed for high-molecular-mass analytes with more than one antigenic determinant (i.e. Ag) or low-molecular-mass analytes (haptens) bound to a solid phase, exposing the antigenic determinant. They work with an Ab excess. Noncompetitive lAs have been employed for the detection of soil-bound pesticides. In this case the soil particles, to which the pesticide residues have bound, form the sohd phase, and the residues can be detected by a labeled Ab specific to the analyte. 

Chemicals may attach to soil, vegetation, or other surfaces once they are in the environment. Some portions of chemicals are not recovered by conventional extraction procedures because these bound or unextractable chemical residues are tightly bound to the soil or other sohd particles. It is very difficult to differentiate between bound residues of a parent compound and its transformation products. Concerns about bound pesticide residues in soil have been investigated since the late 1960s [33]. The exact mechanism of soil-binding and the ultimate fate of bound residues and their biological significance are not well understood for most chemicals. 

Rapid water runoff and nutrient losses occur when crop biomass residues are harvested for fuel and rainfall easily erodes soils. Water quickly runs off unprotected soil because raindrops free small soil particles thaL in turn, clog holes in the soil and reduce water infiltration. This water runoff transports soil organic matter, nutrients, sediments, and pesticides to rivers and lakes where it harms natural aquatic species. For example, conventional corn production lost an average of about 20 t/ha/yr of soil compared with only about 5 t/ha/yr with ridge- and no-till. 

Solubility in water is one of the key characteristics of pesticides that determines their distribution and the stability of the individual components in the environment and in plants. Retention (sorption) of particularly soluble polar pesticides to soil particles is relatively small, but they can penetrate into undergroimd water resources. Polar pesticides are not very stable in the environment and are biodegradable they can be easily hydrolysed and oxidised. Their limited stability is then the cause of a relatively rapid decrease of their residual amounts in contaminated agricultural products during thermal processing. On the other hand, the loss of polar... 

The dissociation constant indicates the ability of pesticide residues to dissociate under normal environmental conditions (pH values are in the range of 5 8). In general, the degree of ionisation determines the solubilisation processes, evaporation from aqueous media and the extent of photolysis. Dissociation is obviously influenced by the sorption of pesticides to sediments and soil particles, and by their bioaccumulation. 

The octanal water partition coefficient Kqq normaUsed to the organic carbon content indicates the sorption ability of pesticides to soil or sediment particles. Pesticides with high values ofXoc are often very persistent in the environment, since the bound (adsorbed or absorbed) residue is immobilised and can only leach, evaporate or be biodegraded with difficulty. 

Exposure to toxicants from terrestrial sources is very common because of the intimate association between animals and plants that live on the land with soil. Modem agricultural practices call for the application of large quantities of herbicides and other pesticides to plants and soil residues of these substances may readily enter living organisms. Soil is the repository of a variety of air pollutants, especially airborne particles that settle onto soil. Improper disposal of industrial wastes and toxic substances washed from or blown off of hazardous waste sites has contributed to exposure of soil. 

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