developed countries. With respect to pollution in the United States, a study done in 1992 showed that batteries "accounted for 86 percent of discarded mercury and dental amalgam a mere 0.56 percent". Mercury is an environmental contaminant and the WHO, OSHA, and NIOSH have established specific occupational exposure limits. Mercury imposes health risks upon the surrounding population. In economics, this pollution is considered an external cost not factored into the private costs of using mercury-based products. Environmental risks from amalgam can be mitigated by amalgam separators and the ISO has issued standards regarding the proper handling and disposal of amalgam waste. Mercury is a naturally occurring element that is present throughout the environment and the vast majority of the pollution (about 99%) comes from large-scale human industrial activity (such as coal-fired electricity generation, hydroelectric dams, and mining, which increase both airborne and waterborne mercury levels). Eventually, the airborne mercury finds its way into lakes, rivers, and oceans, where it is consumed by aquatic life. Amalgam separators may dramatically decrease the release of mercury into the public sewer system, but they are not mandatory in some jurisdictions. When mercury from these sources enters bodies of water, especially acidic bodies of water, it can be converted into the more toxic methylmercury. Cremation of bodies containing amalgam restorations results in near-complete emission of the mercury into the atmosphere, as the temperature in cremation is far greater than the boiling point of mercury. In countries with high cremation rates (such as the UK), mercury has become a great concern. Proposals to remedy the situation have ranged from removing amalgam-containing teeth prior to cremation to installing activated carbon adsorption or other post-combustion mercury capture technology in the flue gas stream. According to the United Nations Environment Programme, it is estimated that globally about 3.6 tonnes of mercury vapor was emitted into the air through cremation in 2010, or about 1% of total global emissions. Mercury emissions from cremation are growing in the US, both because cremation rates are increasing and because the number of teeth in the deceased are increasing due to better dental care. Since amalgam restorations are very durable and relatively inexpensive, many of the older deceased have amalgam restorations. According to work done in Great Britain, mercury emissions from cremation are expected to increase until at least 2020. Organizational statements American Dental Association (ADA) The American Dental Association (ADA) has asserted that