A team led by Karl J. Rockne and James L. Drummond of the University of Illinois, Chicago, has investigated how much mercury and methylmercury, a bioaccumlative neurotoxin, is released from dentists' offices (Environ. Sci. Technol., DOI: 10.1021/es7027058). Mercury from dental waste accounts for 13–78% of Hg in publicly treated wastewater and primarily comes from amalgams used for fillings. Some dental clinics use traps to collect particulate waste, but in prior work the researchers found that dental drills grind the amalgam into very fine particles that may form stable suspensions in water, allowing mercury to escape the traps. In the new study, they let dental wastewater samples settle for 24 hours and then sampled the supernatant to estimate how much mercury would sidestep standard traps. They found a wide range of total mercury concentrations, from 0.02 to 5,000 μM, as well as methylmercury concentrations ranging from 2 to 270 nM. The researchers also tested for sulfate-reducing bacteria that are known to methylate mercury. They found a strong correlation between the bacteria and methylmercury levels, indicating that the bacteria may play a significant role in producing methylmercury in dentists' wastewater.