In a controlled experiment, the researchers followed mercury as it moved from the water, was taken up by algae, and eventually found its way into small animals called Daphnia, which eat the algae. Daphnia, a type of zooplankton, is in turn a food source for many species of fish.
While not toxic to the Daphnia or the fish at the levels found normally in nature, methylmercury biomagnification presents a serious health hazard for humans and other animals that eat the fish. Under biomagnification, there is a systematic increase in the concentration of elements, found in tissue of organisms, as they move up the food chain.
The study finds that when there is a lot of algae present, methylmercury is dispersed widely throughout the single-celled algae. As a result, Daphnia that eat the algae arent exposed to high levels of mercury. However, in systems with less algae, the mercury is more concentrated on each plant cell, so the Daphnia eat more mercury with each meal.
"Now we understand more fully the connection between mercury in the water and mercury in fish," said Paul Pickhardt, senior author on the paper, and a graduate student at Dartmouth. "We suspected there was an algal link, but few laboratories had the technology to make such precise measurements before. With our trace-metal techniques, weve achieved mercury detection levels that are 50 times more sensitive than any other method."