Manganese is a natural element that is actually essential to the human diet in small doses, but over exposure can cause problems with the nervous system and muddy up drinking water. The amount of manganese in drinking water continues to increase across the U.S. due to its industrial use.
Mercury can contaminate water supplies when erosion of natural deposits, discharge from factories, or runoff from landfills and croplands occurs. After long-term exposure, mercury can cause kidney damage and can possibly lead to cancer.
Methoxychlor is an endocrine-disrupting insecticide similar to DDT; banned in the U.S. in 2002, it was historically used on farm animals and in animal feed, lumber, gardens and certain crops.
Plastic debris that is smaller than a sesame seed is considered a microplastic. These might be degraded pieces of larger plastic waste, can come from clothing as it goes through a washing machine or a dryer, or tiny microbeads like those found in face wash. These plastics easily pass through large scale water filtration systems (such as those used during municipal water treatment). They are considered a huge potential threat to oceans and aquatic life.