Cadmium, contaminant concentration

Cadmium is a widely distributed metal used in manufacturing and is present in a number of consumer products. Dietary exposure to cadmium is possible from shellfish and plants grown on cadmium-contaminated soils. Absorption is increased when associated with low levels of iron or calcium in the diet. Some plants, such as tobacco, can concentrate cadmium from even low levels in the soil. The lung readily absorbs cadmium, thus cigarette smokers have elevated cadmium exposure. Cadmium is also used as a metal alloy, in paint, and in batteries (Ni-Cad, nickel-cadmium). Workplace exposure can occur in welding and battery manufacture. 

It should be noted that in most of these studies, especially in those on the barley leaf discs, the metal concentrations applied are significantly higher than those found in the field. It remains, therefore, to be proven that the cadmium effects described occur at the metal concentrations present in intact plants growing in situ on a cadmium-contaminated substrate. 

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. 

Reprecipitation A drastic but effective way to minimize the effects of adsorption is reprecipitation. In this process, the filtered solid is redissolved and reprecipitated. The first precipitate ordinarily carries down only a fraction of the contaminant present in the original solvent. Thus, the solution containing the redissolved precipitate has a significantly lower contaminant concentration than the original, and even less adsorption occurs during the second precipitation. Reprecipitation adds substantially to the time required for an analysis but is often necessary for such precipitates as the hydrous oxides of iron(III) and aluminum, which have extraordinary tendencies to adsorb the hydroxides of heavy-metal cations such as zinc, cadmium, and manganese. 

The diet is the major route of human exposure to cadmium. Contamination of foods with cadmium results from its presence in soil and water. Concentrations of cadmium in foods range widely, and the highest average concentrations are found in mollusks, kidneys, livers, cereals, cocoa, and leafy vegetables. A daily intake of about 60 [tg would be required to reach a concentration of 50 mg/kg in the renal cortex of persons 50 years of age, assuming an absorption ratio of 5%. About 10% of the absorbed daily dose is rapidly excreted (WHO, 1989, 2001). 

The concentrations of cadmium in surface water in the Czech Republic in 1996 are shown in Table II. According to the cadmium contamination, the most of the... 

A field demonstration of electrokinetic remediation was conducted by the USAEC and the ERDC at the Naval Air Weapons Station (NAWS), Point Mugu, California, in 2000 (USAEC, 2000). Major contaminants in this area were chromium and cadmium, and the system was developed with the aim to reduce the contaminant concentrations below the regulatory action levels for metal concentration and toxicity criteria. The developed system was basically the same as other existing electrokinetic remediation processes. It involved the use of citric acid as an amendment to control the formation of the pH front in the treatment area. The design included a system for the recovery of the electrolyte after separating the metal contaminants. 

It is now conservatively estimated that adverse effects on fish or wildlife are either pronounced or probable when cadmium concentrations exceed S.Op-g/L in freshwater, 4.5p,g/L in saltwater, 100.0 p,g/kg in the diet, or 100.0 p-g Cd/m in air. Cadmium residues in vertebrate kidney or liver that exceed 10.0 mg/kg FW or 2.0 mg/kg whole body FW should be viewed as an evidence of probable cadmium contamination residues of 200.0 mg Cd/kg FW kidney, or more than... 

Guarding against cadmium contamination of biological samples is particularly important when analyzing blood samples because cadmium concentrations in blood samples from nonexposed populations are generally less than 2 pg/l (2 ng/ml), while occupationally-exposed workers can be at medical risk to cadmium toxicity if blood concentrations exceed 5 pg/l (ACGIH 1991 and 1992). This narrow margin between exposed and unexposed... 

Normal levels of cadmium in plants grown in uncontaminated soil are probably less than 1 ppm in dry matter, but John [309] has quoted a level of 668 ppm cadmium in the dry matter of lettuce leaves from plants grown in cadmium-contaminated soil. This level is certainly exceptionally high, but it is clear that in cadmium, we have an element which is both highly toxic and readily taken up by plants to produce quite high concentrations in the plant without the appearance of phytotoxic symptoms, so that an apparently normal crop may be unsafe for human or animal consumption. It is evident from the results of these experiments that even a small addition of cadmium to uncontaminated soil can produce striking increases in the cadmium contents of a number of widely different kinds of crops. Cadmium is therefore an element which can readily enter mammalian food chains at a dangerous level. 

Cadmium is commonly present in sewage sludges, sometimes in quite high concentrations of the order of 100 ppm in the dry matter. Since this material is now being actively promoted as a fertiliser in the interests of disposal, it seems inevitable that there will be increases in the concentration of this metal in food marketed for human consumption as a result of cadmium contamination of agricultural soils. It is already clear that the uptake of cadmium by plants... 

Ritter and co-workers [1] conducted interlaboratory testing of polymers for the determination of cadmium, chromium and lead. They found that even when contaminant concentrations were identical the determination of heavy metals in plastics was strongly dependent on the polymer matrix. 

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