Abstract
A recent problem is mercury pollution of river and fish, and the allowable level of mercury in waste water has been fixed at below 5 ppb. Environmental mercury contamination through dental procedures, especially through waste water from dental offices, was studied and the following results were obtained.
1) High levels of mercury were contained in saliva vacuumed from the oral cavity during amalgam filling, but mercury levels were decreased by using a net bag for removal of amalgam scrapings.
2) Mercury was detected in all waste water from dental practice, such as saliva vacuumed from the oral cavity, water gargled after amalgam filling, waste water from the dental unit, and the final waste water from dental offices. As the amount of flowing waste water increases, mercury levels in waste water decrease. But the amount of mercury discharged from dental practice through waste water was not small.
3) Mercury levels in final waste water from dental offices were at an average of 11.3 ppb. The final waste water of almost all dental offices exceeded the allowablelevel (5 ppb).
4) Mercury levels in soil around dental offices, and even in soil of houses next to dental offices, was higher than control houses. Then it was shown mercury contamination in dental practice was caused not only through waste water but also through the atomosphere.
5) Very high levels of mercury was contained in soil soaked in waste water from dental offices and in sludge from drain-pipes of dental offices. It was shown that soil and sludge absorb and concentrate mercury in waste water.
6) There is almost no risk that mercury metal discharged from dental offices will be converted to more poisonous methylmercury by the action of microorganisms in soil and sludge.
A large amount mercury metal is discharged from dental offices, and it is absorbed, accumulated, and concentrated to very high levels in soil and sludge. Therefore we should strive to find a practical method of extracting mercury from dental waste water.
