This metal is considered by some researchers as the most toxic among the heavy metals. Anthropogenic sources of lead are the processes of mining, coal burning, the production of batteries (for automobiles). Lead is also present in fertilizers and pesticides used in agriculture. Thus, lead is a very important environmental contaminant, being present in water, vegetable foods (edible sheets, cereals, tubers, grains, fruits) grown close to industrialized regions and in fish and shellfish. Its toxic effects on humans include memory loss, headaches, mental confusion, distorted perception, muscle and joint pain, gastrointestinal disturbance, allergies, vision problems and chronic fatigue, among others.