allowable legal limits for long-term work place (occupational) safety. Two recent randomized clinical trials in children discovered no statistically significant differences in adverse neuropsychological or renal effects observed over a five-year period in children whose caries were restored using dental amalgam or composite materials. In contrast, one study showed a trend of higher dental treatment need later in children with composite dental fillings, and thus claimed that amalgam fillings are more durable. However, the other study (published in JAMA) cites increased mercury blood levels in children with amalgam fillings. The study states, "during follow-up [blood mercury levels were] 1.0 to 1.5 μg higher in the amalgam group than in the composite group." EPA considers high blood mercury levels to be harmful to the fetus and also states, "exposure at high levels can harm the brain, heart, kidneys, lungs, and immune system of people of all ages." Currently, EPA has set the "safe" mercury exposure level to be at 5.8 μg of mercury per one liter of blood. While mercury fillings themselves do not increase mercury levels above "safe" levels, they have been shown to contribute to such increase. However, such studies were unable to find any negative neurobehavioral effects. Environmental impact Environmental concerns over external costs exist as well. In the United States, dental amalgam is the largest source of mercury received by sewage treatment plants. The mercury contaminates the treatment plant sludge, which is typically disposed of by land application, landfilling or incineration. In the United States, several states, including New Jersey, New York, and Michigan, required the installation of dental amalgam separators prior to 2017. EPA promulgated an effluent guidelines regulation in 2017 which prohibits most dental practices from disposing amalgam waste down the drain. Most dental offices nationwide are now required to use amalgam separators. The WHO reported in 2005 that in the United Kingdom mercury from amalgam accounted for 5% of total mercury emissions. In Canada, dental amalgam was estimated to contribute one-third of the mercury in sewer system waste, but it is believed amalgam separators in dental offices may dramatically decrease this burden on the public sewer system. The 2005 WHO report stated that mercury from amalgam was approximately 1% of total global mercury emissions, and that one-third of the total mercury in most sewage systems was discharged from dental offices. Other studies have shown this to be a gross exaggeration or not reflective of