Cadmium food chain

Some metals used as metallic coatings are considered nontoxic, such as aluminum, magnesium, iron, tin, indium, molybdenum, tungsten, titanium, tantalum, niobium, bismuth, and the precious metals such as gold, platinum, rhodium, and palladium. However, some of the most important poUutants are metallic contaminants of these metals. Metals that can be bioconcentrated to harmful levels, especially in predators at the top of the food chain, such as mercury, cadmium, and lead are especially problematic. Other metals such as silver, copper, nickel, zinc, and chromium in the hexavalent oxidation state are highly toxic to aquatic Hfe (37,57—60). 

There are concerns that land application of sludge will result in an increase of pathogenic bacteria, viruses, parasites, chemicals and metals in drinking water reservoirs, aquifers, and the food chain. This raises additional concerns of cumulative effects of metals in cropped soils. Research shows that if metals such as zinc, copper, lead, nickel, mercury, and cadmium are allowed to build up in soils due to many applications of sludges over the years, they could be released at... 

Standards imposed to the industrial waste streams charged in heavy metals are more and more drastic in accordance with the updated knowledges of the toxicity of mercury, cadmium, lead, chromium... when they enter the human food chain after accumulating in plants and animals (Forster Wittmann, 1983). Nowadays, the use of biosorbents (Volesky, 1990) is more and more considered to complete conventional (physical and chemical) methods of removal that have shown their limits and/or are prohibitively expensive for metal concentrations typically below 100 mg.l-i. 

The release of heavy metals into the environment presents a serious threat. Over recent decades, the annual worldwide release of heavy metals reached 22,000 T for cadmium, 939,000 T for copper, 783,000 T for lead, and 1,350,000 T for zinc.3 Because of their high solubility in the aquatic environments, heavy metals can be absorbed by living organisms and enter the food chain.6 Exposure to high levels of these metals has been linked to cytotoxic, mutagenic, and carcinogenic effects on... 

EFSA - European Food Safety Authority (2009) Scientific Opinion of the Panel on Contaminants in the Food Chain on a request from the European Commission on cadmium in food. EFSA J 980(2009) 1-139... 

Cadmium biomagnifies in terrestrial food chains and tends to accumulate in liver and kidneys of older apex organisms (Scheuhammer 1987). This process was documented in the chain of soil to vegetation to invertebrates to upper trophic level consumers, including roe deer (Capreolus capreolus), bam owls (Tyto alba), weasels (Mystela nivalis), and kestrels (Falco tinnunculus Gorree... 

Ferard, J.F., J.M. Jouany, R. Truhaut, and P. Vasseur. 1983. Accumulation of cadmium in a freshwater food chain experimental model. Ecotoxicol. Environ. Safety 7 43-52. 

Gorree, M., W.L.M. Tamis, T.P. Traas, and M.A. Elbers. 1995. BIOMAG a model for biomagnification in terrestrial food chains. The case of cadmium in the Kempen, the Netherlands. Science Total Environ. 168 215-223. 

Like many technological innovations, nickel-cadmium batteries carry risks as well as benefits. After being discharged repeatedly, they eventually wear out. In theory, worn-out nicad batteries should be recycled. In practice, however, many end up in garbage dumps. Over time, discarded nicad batteries release toxic cadmium. The toxicity of this substance makes it hazardous to the environment, as cadmium can enter the food chain. Long-term exposure to low levels of cadmium can have serious medical effects on humans, such as high blood pressure and heart disease. 

Metals frequently occurring in the state s waste streams include cadmium, chromium, lead, arsenic, zinc, copper, barium, nickel, antimony, beryllium, mercury, vanadium, cobalt, silver, and selenium. These metals are toxic to humans and other organisms, are persistent in the environment, and can bioaccumulate in food chains. They are typically used by businesses in many industrial categories, as shown in Table 2.1-1. 

On the basis of chemical profile, Wood (38) predicted that arsenic, selenium, and tellurium will be methylated in the environment, and lead, cadmium, and zinc will not. Elemental concentration in the aquatic food chain has been reported for As (39), Hg (40), Cd (41), Pb (42), and Cu (43). The biological half-life of methylmercury in fish, for example, is one to two years (44). Pillay et al. (40) implicated heavy coal burning in the mercurial contamination of plankton and fish populations of Lake Erie. Other metals, notably cadmium, have been shown to be incorporated into the grazing grasses surrounding a coal burning source (27). Trace element contamination, therefore, can enter the food chain at various points. Disposal of solid wastes in the form of ash and slag is yet another environmental consideration (45). 

Statutory legislation to control the levels of such substances in food has been introduced in the UK and elsewhere. In more recent years, other potentially toxic elements have come into focus. Lead, cadmium and mercury have been the subject of much monitoring of the food chain and other metals, in particular aluminium, are continuing to attract attention. Nitrate and nitrite in food from food additive use is regulated across the European Union, but its presence in food crops has raised concerns. 

An impact on wildlife of acid precipitation in forests may cause the accumulation of heavy metals like lead and cadmium in mushrooms and mosses, which constitute a part of the food chain and thus may be dangerous for both wildlife and man. 

E. Hahn, K. Hahn, M. Stoeppler, Bird feathers as bioindicators in areas of the German Environmental Specimen Bank - bioaccumulation of mercury in food chains and exogenous deposition of atmospheric pollution with lead and cadmium, Sci. Total Environ., 139/140 (1993), 259-270. 

Heavy metals absorbed by crops from contaminated soils are also passed up the food chain. Cadmium, zinc, and lead are absorbed by wheat and rice plants. I19l Cultivated ryegrass absorbs cadmium from polluted soilJ21 Ryegrass is a crop fed to cattle, which absorb the cadmium and pass it up the food chain to humans. 

Brams, E., Anthony, W., and Witherspoon, L. (1989). Biological monitoring of an agricultural food chain soil cadmium and lead in ruminant tissues. J. Environ. Qual. 18, 317. 

Fox MR, S. 1987. Assessment of cadmium, lead and vanadium status of large animals as related to the human food chain. J Anim Sci 65 1744-1752. 

Some epidemiological studies report data from populations exposed to selenium in the food chain in areas with high selenium levels in soil. It is likely that selenite, selenate, and the selenium found in food and in dietary supplements comprise the majority of selenium compounds to which oral, off-site selenium exposures will occur at or near hazardous waste sites. Aside from the variation in effective dose, the health effects from exposure to selenate, selenite, and dietary selenium are not expected to differ greatly. However, oral exposures to many other compounds of selenium could occur (primarily through soil or edible plant ingestion) if those compounds were deposited at the site, or if local environmental conditions greatly favor transformation to those forms. Heavy metal selenides, aluminum selenide, tungsten diselenides, and cadmium selenide are used in industry and may end up in waste sites. 

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