Food chain effects, cadmium

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... 

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... 

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. 

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. 

Mathews T, Fisher NS (2008) Evaluating the trophic transfer of cadmium, polonium, and methyl-mercury in an estuarine food chain. Environ Toxicol Chem 27 1093-1101 McAlpine D, Araki S (1959) Minamata disease late effects of an unusual neurological disorder caused by contaminated fish. AM A Arch Neurol 1 522-530 McGeer J, Brix KV, Skeaff JM, Deforest DK, Brigham SI, Adams WJ, Green AS (2003) The inverse relationship between bioconcentration factor and exposiure concentration for metals implications for hazard assessment of metals in the aquatic environment. Environ Toxicol Chem 22 1017-1037... 

Clearly, effects which have to be studied are the extent to which the enhanced levels in the contaminated soils now characteristic of urban areas, lead to increased trace-element levels in plants grown for human or animal consumption, the extent to which increased trace-element uptake can lead to phytotoxic effects and the possibility of toxic effects on livestock and human beings. The possible consequences of the permanent presence of enhanced levels of elements such as cadmium and mercury in food chains are so far-reaching and unpredictable that there is everything to be said for preventing the development of such a situation. 

---