Of the heavy metals, mercury is a major concern due to its toxicity and high volatility. It is subject to the European Waste Incineration Directive, which puts limits on emissions to air, so the flue gas is treated post-combustion. The resulting toxic fly ash must be handled as hazardous waste.
Acute exposure to mercury vapour can lead to irritation of the lungs, coughing, chest pain and shortness of breath, and central nervous system (CNS) effects such as tremors and mood changes. Chronic exposure also leads to CNS effects such as increased excitability, excessive shyness and irritability.
Cadmium emissions from an incinerator the size of the Exeter plant are approximately equivalent to one-eightieth of the emissions from a medium sized UK coal-fired power station.
Acute inhalation exposure to cadmium can lead to irritation of the lungs. Chronic exposure can cause a build-up of cadmium in the kidneys that can lead to kidney disease.
Although zinc poses no documented health risks, if its physical state is altered during use then health risks can be created. Inhalation of metallic oxide fumes can lead to metal fume fever.
Non-ferrous and/or ferrous metals are recovered (separated from Municipal Solid Waste or Incinerator Bottom Ash) and recycled from most incinerators in the UK.