Heavy metals persist for a long time after being introduced into soils. Taking cadmium as an example, it does not decompose, but relocates to lower soil layers, or transfers into waterways. It can be taken up by plants, the extent of which is influenced by the total volume of heavy metal containing material applied, the concentration of heavy metal in the material, prevailing climate conditions, soil properties (e.g. PH levels) and plant properties.
From here dietary intake become relevant. The higher the consumption of crops grown in cadmium, or other heavy metals, containing soils and the higher the transfer rate, the higher the risk to health via accumulation and toxicity. That said, it is not always the crops with the highest contamination that one needs to worry about. The European Food Safety Authority (EFSA) has found that while some foods can contain higher concentrations of cadmium, it is ultimately the foods that are consumed in large quantities that present the greatest risk. Some more prominent examples include potatoes, cereals (mainly wheat) and vegetables.
As is the case in soils, once ingested, cadmium is expelled slowly from the human body. So after long-term exposure, it may accumulate, particularly in the kidney, resulting in toxicity. Kidney and bone disease are the most sensitive toxicological effects of excessive cadmium intake.
Other heavy metals such as lead, arsenic and mercuty affect the skin, bones, nervous system functionality and can contribute to the development of cancer.