Mining, industrial activities and metal smelting results in contamination of soil and water and can reach concentrations that are dangerous to the environment. Heavy metals are often persistent in nature so they accumulate in soils and plants.
The toxicity of transition metals is due to the way in which they disturb the oxidation/reduction balance in cells by a variety of mechanisms.
Heavy metals interfere with activities of plants including photosynthesis, gaseous exchange and nutrient absorption. This can damage plant growth and crop yield.