There have been many scientific studies looking at the levels of toxic mercury (Hg) in fish. After all, fish can end up directly on our plate. However, far fewer studies have examined Hg levels in aquatic insects. This is a significant oversight because aquatic insects are an important source of Hg to fish and even terrestrial wildlife.
Researchers at Texas Christian University in Fort Worth, Texas have found that the presence of fish dramatically alter the amount of insects in small grassland ponds and the level of Hg contamination within insect communities. In ponds where fish were present, there was less Hg in the insect community than in ponds where fish were absent.
"We have found that in ponds without fish there is a large pool of Hg in the aquatic insect community, but when fish are present, Hg is transferred from the insect community into the fish," said Matt Chumchal, assistant professor of biology at Texas Christian University. The TCU Scientists studied 10 ponds at the LBJ National Grassland in north Texas -- five with fish and five without fish.
The observed difference in the size of the pool of Hg in insect communities from ponds with and without fish has significant implications, because small ponds, like those at the LBJ Grasslands, may represent an important source of Hg to aquatic and terrestrial consumers. Waterfowl such as ducks consume insects in aquatic habitats, whereas terrestrial consumers, such as birds and bats, could be exposed to Hg by consuming adult emergent insects.
Hg is a growing concern because concentrations are now elevated above baseline levels in many aquatic ecosystems due to widespread emissions. Hg is released into the atmosphere from a variety of anthropogenic sources where it can remain for years before being deposited. As a result even remote habitats are at risk from Hg pollution.
"There are more than 2.6 million small man-made ponds in the United States and many of them are fishless." said Ray Drenner, a professor of biology at Texas Christian University and coauthor on the paper. "Our study suggests that these small ponds contain Hg-contaminated insects with the potential to expose birds and bats to this dangerous pollutant."
This research appeared in the April 2012 edition of Environmental Toxicology and Chemistry.
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