Fish: to eat or not to eat? Everyone has heard that consuming fish while pregnant can be harmful to the baby, as fish contain levels of mercury that can be unsafe for a developing child.
Why fish in particular, though? What causes them to store up mercury to the point that consumption is harmful?
“As an analytical chemist, I measure things, mostly related to the environment,” said James Cizdziel, associate professor of biology at the University of Mississippi. “I measure concentrations of different analytes, like arsenic in food or mercury in fish or water.”
Mercury levels in water have become a global environmental issue. This is the result of increasing reliance, both domestically and internationally, on burning coal, a process that releases mercury into the air. But this airborne mercury has not yet taken its most dangerous form.
Cizdziel’s research concerns the methylmercury content of water in five lakes around Lafayette County, the largest of which is Sardis Lake. Water samples are taken periodically from the lakes to study fluctuations in the methylmercury levels, Cizdziel said. Methylmercury is a neurotoxin present in water habitats and fish populations, and is particularly harmful to the brains of developing children.
“Mercury is a very interesting element because it has really complex cycling, meaning it can be released into the atmosphere through natural sources, like volcanic emissions or forest fires,” Cizdziel said. “But there’s also anthropogenic sources in the atmosphere, the major one being combustion of fossil fuels, particularly coal. Although coal has a very minute, low level of mercury, we burn enough of it so that mercury is released into the air.”
The South provides the best conditions for the formation of methylmercury, and southern lakes tend to have high concentrations than northern ones, Cizdziel said. The warm climate, longer summers, and numerous wetlands are favorable for beginning the methylation process, which converts mercury to methylmercury. Because mercury, once released into the air, is more water-soluble and has a relatively long half-life, rainwater pushes it from the atmosphere and into water sources, Cizdziel said.
Bacteria in the water soak up the mercury and convert it to methylmercury, which follows the aquatic food chain to fish that by the time they are caught for human consumption, have ingested large amounts of methylmercury. The problem, Cizdziel says, is that it is hard to determine if the levels are safe without extensive testing. As there are fishermen who depend on the lakes for food, it is important to periodically measure local water supplies.
“Methylmercury is spread throughout an ecosystem through the food chain,” Brian Spurlock, senior biology and chemistry major, said. “It travels from bacteria to invertebrates to fish and eventually to humans, becoming more concentrated at every level.”
Cizdziel said he plans to build upon this research and begin studying mercury in other areas, such as how mercury is spread throughout the food web by mosquitos.
For the time being, though, Oxford’s mercury levels are right in the middle when compared with national averages.
“I wouldn’t say our levels, compared to the national average, are particularly high,” Cizdziel said. “At the same time, I wouldn’t say they are particularly low.”
At this time, the levels are not dangerous, Cizdziel said. Although mercury levels are something people should be conscious of, there is no reason yet to swear off seafood.
“Mercury consumption is more of a long term concern than an immediate one,” Jonathon Wilson, senior biology major, said. “Eating fish a few times a week is fine, but extend that over a long period and you can start to see health problems.”
Maybe this is one list Oxonians should be glad they did not rank first on.
