Soil, agriculture lead contamination

Contaminated soil serves as a direct source of radionuclides leading to the contamination of all agricultural products. Contaminated soil used in greenhouses could add significantly to the contamination of vegetables. 

An extensive pesticide properties database was compiled, which includes six physical properties, ie, solubiUty, half-life, soil sorption, vapor pressure, acid pR and base pR for about 240 compounds (4). Because not all of the properties have been measured for all pesticides, some values had to be estimated. By early 1995, the Agricultural Research Service (ARS) had developed a computerized pesticide property database containing 17 physical properties for 330 pesticide compounds. The primary user of these data has been the USDA s Natural Resources Conservation Service (formerly the Soil Conservation Service) for leaching models to advise farmers on any combination of soil and pesticide properties that could potentially lead to substantial groundwater contamination. 

The assessment of plant-available soil contents can frequently be achieved and validated by field experiments for nutritionally essential elements, and, for a few potentially toxic elements such as chromium, nickel and molybdenum, at the moderately elevated concentrations that can occur in agricultural situations. The validation of extraction methods, devised for agricultural and nutritional purposes, is much less easy to achieve when they are applied to heavy metals and other potentially toxic elements, especially at the higher concentrations obtained in industrially contaminated land. This is not surprising in view of the fact that for some heavy metals, for example lead, there is an effective root barrier, in many food crop plants, to their uptake and much of the metal enters plants not from the root but by deposition from the atmosphere on to leaves. In these circumstances little direct correlation would be expected between soil extractable contents and plant contents. For heavy metals and other potentially toxic elements, therefore, extraction methods are mainly of value for the assessment of the mobile and potentially mobile species rather than plant-available species. This assessment of mobile species contents may well, however, indicate the risk of plant availability in changing environmental conditions or changes in land use. 

Due to the wide use of cadmium-based products, cadmium is widely distributed in the environment. The cadmium content in soil and water has been increasing as a result of disposal of cadmium-contaminated waste and the use of cadmium-containing fertilizers (particularly on cereal crops). Commercial sludge, contaminated with cadmium, has been used to fertilize agricultural fields. Cadmium concentrations in urban air are quite low, because of regulation of industrial air emissions. Lead and zinc smelters and waste incineration account for the majority of cadmium present in ambient air. 

These high values of lead in water at the Jua Kali sites is an indicator of contamination of the human beings and aquatic animals who use water from the water bodies for both domestic and agricultural purposes. Lead particles deposited in the soil from flaking lead paint, from incinerators, and from motor vehicles that use leaded gasoline, as well as water runoff and waste disposal from such Jua Kali sites, all contribute to lead to the environment. 

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