Pollutants from common sources, including some intended to make our lives better, are ending up in our waterways. Recent government efforts are aimed at reducing two of these: contamination from prescription and non-prescription drugs, and mercury from dental fillings.
Last Saturday, the US Drug Enforcement Agency, with support from the USEPA, sponsored “take-back events” for prescription and over-the-counter drugs at 1,700 sites around the country. Many unused drugs are disposed of improperly and end up in surface waters and even drinking water supplies, as explored in this May 2010 Stormwater article.
This week, the EPA is announcing a proposed rule to reduce mercury that enters the environment from dental offices. It’s estimated that 3.7 tons of mercury comes from dental offices annually, when older fillings containing mercury are replaced. A lot of the substance is simply flushed down the drain, eventually ending up in wastewater treatment plants and in surface water systems. Roughly half of the mercury reaching wastewater treatment plants comes from dental waste.
Although there has been some debate, it’s generally accepted that the older fillings don’t pose much hazard while they’re in place; it’s once they’re removed that the problems begin. Once in rivers and lakes, the mercury can enter the food chain when microorganisms convert it to methylmercury, the bioavailable form. Eaten by fish and shellfish and eventually by humans, mercury can cause damage to the brain and nervous system, especially in children.
The proposed rule would require the use of amalgam separators, which can remove about 95% of the mercury that would otherwise reach wastewater treatment plants. The rule is expected to be final by 2012, but until then EPA is encouraging dental offices to voluntarily install amalgam separators—already required by some cities and 12 states.