DDT, one of the most effective insecticides used in agriculture, passes from the soil to plants, then to herbivores, carnivores, and finally to superpredators. While biomass diminishes as we go up the food chain, the quantity of DDT is transmitted with very little loss. Its concentration therefore increases at each nutritional level, and organisms at the top of the chain (such as humans) have the highest proportion. DDT, which upsets the endocrine system and can cause cancer, is now banned in many countries.