One or more of these pollutants were released into Maine’s environment by more than 100 firms during a one-year period, according to a report released this week.

Heavy Metals: While metals like mercury, nickel, lead, chromium, cadmium and antimony occur naturally in the Earth’s crust and even human bodies, unnaturally high concentrations can be carcinogenic and individual metals have been linked to birth defects, memory problems, miscarriages and asthma.

Arsenic: Like metals, arsenic is a naturally occurring substance. It has been used commercially in the past as a pesticide and a wood preservative. In high concentrations, arsenic can increase the risk of cancers and cause reproductive problems.

Dioxins: Created when chlorine interacts with other chemicals, some 75 different dioxins can be inadvertently emitted into the air by waste incineration (particularly of plastics), paper bleaching operations and manufacturing. Exposure has been linked to liver damage and several cancers.

Napthalene: Known more commonly as tar camphor, napthalene is created naturally as a byproduct when fuels are burned. Its best-known use is in mothballs, but it is also burned as a fuel. It is known to damage red blood cells and is believed to be carcinogenic.

Brominated Flame Retardants: These manmade chemicals are added to plastics and even clothing to make them inflammable. The health effects are unknown, but BFRs have recently been found in human breast milk, and are known to cause cancer in animals.

Trichlorobenzene: This chemical compound has been used as an industrial solvent, in pesticides, and as a wood preservative. Exposure is known to cause liver and kidney damage, as well as affect the nervous system.

Perflourinated Chemicals: These manmade chemicals are ubiquitous, used in such commercial brands as Teflon, Gore-Tex and Scotchguard. PFCs have been found in human tissue worldwide, and several are known carcinogens in animals.

Polycyclic Aromatic Compounds: PACs include more than 100 chemical compounds that are formed when garbage, wood or fossil fuels are incompletely burned. Laboratory tests suggest that PACs can be carcinogenic.