Cadmium (Cd) is a silvery-white, soft, ductile chemical metal with atomic number 48 and belonging to the group 12 element in d block and period 5. It was discovered by German chemist F.Strohmeyer in 1817 as a constituent of smithsonite (ZnCO3) from zinc ore.
Food is the primary source of cadmium exposure among general population as a consequence of the bio-concentration of cadmium from soil. The high mobility in soils make cadmium accumulation in plants poses a serious threat to animal and human health.
Cadmium is a common contaminant found in most human foodstuffs due to the high transfer factor properties of plants. The bioconcentration of cadmium from soil to the foodstuffs makes diet a primary source of cadmium exposure among non-smoking, non-occupationally exposed populations. Certain foods such as shellfish, kidney, liver, mushrooms and root crops contain especially high levels of cadmium.
The tobacco plant naturally accumulates relatively high concentrations of cadmium in its leaves. Thus, smoking tobacco is an important source of exposure, and the daily intake may exceed that from food in the case of heavy smokers.
Chronic cadmium exposure has been reported to be associated with chronic kidney disease, osteoporosis, diabetes, cardiovascular disease and cancer. Cadmium is toxic to the kidney, while exposure to high levels of tin from, e.g. canned food in incorrectly manufactured tins can cause gastrointestinal irritation and upsets.
Cadmium accumulates primarily in the kidneys, and its biological half-life in humans is 10–35 years. This accumulation may lead to renal tubular dysfunction, which results in increased excretion of low molecular weight proteins in the urine.
According to the current knowledge kidney damage (renal tubular damage) is probably the critical health effect. Other effects of cadmium expo-sure are disturbances of calcium metabolism, hypercalciuria and formation of stones in the kidney.
Several epidemiological studies suggest that cadmium exposure may potentiate the effects diabetes on the kidney.
It has also been associated with lung damage (including induction of lung tumors) and skeletal changes in occupationally exposed populations. Cadmium is relatively poorly absorbed into the body, but once absorbed is slowly excreted, like other metals, and accumulates in the kidney causing renal damage.
Because of the sufficient evidences in humans for the carcinogenicity of cadmium and its compounds, International Agency for Research on Cancer re-evaluated and classified cadmium and its compounds as carcinogens to humans. Cadmium and cadmium compounds cause cancer of the lung and are positively associated with kidney and prostate cancer.
Drinking-water contains very low concentrations of cadmium, usually in the range 0.01–1 μg/liter. The lowest concentrations are found in milk (around 1 μg/kg). The concentration of cadmium is in the range 1-50 μg/kg in meat, fish and fruit and 10-300 μg/kg in staple foods such as wheat, rice and potatoes.
The highest cadmium levels (100-1000 μg/kg) are found in the internal organs (kidney and liver) of mammals and in certain species of mussels, scallops and oysters. When grown on a cadmium-polluted soil, some crops, such as rice, can accumulate considerable amounts of cadmium (more than 1000 μg/kg).
Public health and food safety: Exposure to cadmium
