Waste incinerators that are not equipped with efficient flue-gas cleaning systems are known to be one of the most significant sources. Wood-burning stoves and the burning of leaded automotive fuel also add to loadings in the atmosphere. Dioxins and furans also enter the environment as trace byproducts of industrial processes, including processes used in metallurgical industries. Pulp and paper mills using elemental chlorine in their bleaching process often release water contaminated with dioxins. HCB is also emitted to the atmosphere by waste incineration and metallurgical processes.
Many substances used as flame retardants have chemical properties that are similar to PCBs.
Polybrominated diphenyl ethers can leach out of electrical equipment, building materials, car interiors, and textiles treated with flame retardant to contaminate the environment. Knowledge of the toxicity of brominated flame retardants is very limited. Although most industrialized countries have eliminated or restricted the use of first-generation pesticides over the last two decades, much of the developing world still uses them for public health and pest control purposes. Of primary concern are DDT, toxaphene, chlordane, mirex, aldrin, dieldrin, and hexachlorocyclohexanes. 3.4 Metals Metals occur naturally in the environment as part of the earth's crust.