Pesticides and herbicides used in the killing of unwanted animals and plants have toxins such as lead, mercury and nitrate, etc ; these chemicals may enter the lakes and rivers through the sewage system or through the dumping of toxics by the large factories or can be collected by rain and will eventually drain into the rivers, lakes and oceans. When animals drink water or eat plants which have been sprayed with toxin chemicals they can lose their lives. Much research has been done and was concluded that more than ten million people in the united states alone drink water which contains pesticide and causes death in children as well as adults when drinking water which contains nitrates. "Many diseases caused by water contamination go un-noticed because the effect takes months or even years to materialize," Elizabeth Humphreys observes. (Humphreys Elizabeth)