Is mercury in the body from fillings or fish?

But a new study that measured mercury isotopes in the hair and urine from 12 Michigan dentists found that their urine contained a mix of mercury from two sources: the consumption of fish containing organic mercury and inorganic mercury vapor from the dentists’ own amalgam fillings.
“These results challenge the common assumption that mercury in urine is entirely derived from inhaled mercury vapor,” says Laura Sherman, a postdoctoral research fellow in the department of earth and environmental sciences at University of Michigan and lead author of a paper in Environmental Science & Technology.
“These data suggest that in populations that eat fish but lack occupational exposure to mercury vapor, mercury concentrations in urine may overestimate exposure to mercury vapor from dental amalgams.
Mercury is a naturally occurring element, but more than 2,000 tons are emitted into the atmosphere each year from human-generated sources such as coal-fired power plants, small-scale gold-mining operations, metals and cement production, incineration, and caustic soda production.
This mercury is deposited onto land and into water, where micro-organisms convert some of it to methylmercury, a highly toxic organic form that builds up in fish and the animals that eat them, including humans. Effects on humans include damage to the central nervous system, heart, and immune system. The developing brains of fetuses and young children are especially vulnerable.
http://www.futurity.org/health-medicine/is-mercury-in-the-body-from-fillings-or-fish/