Mercury concentrations in small fish from Illinois streams have decreased since the turn of the 20th century, but mercury pollution persists in the environment, even in rural areas far from mercury sources, according to findings from a study conducted by scientists from the Prairie Research Institute, University of Illinois.
Researchers David Gay, coordinator of the National Atmospheric Deposition Program, Illinois State Water Survey, and Jeffrey Levengood, wildlife toxicologist, Illinois Natural History Survey, and their colleagues selected fish common to two rural streams in Illinois. In 2006 and 2007, fish were collected from Panther Creek in Jasper County, considered a “high mercury” site due to mercury levels reported previously, and from Saline Branch Ditch in Champaign County, considered a “low mercury” site.
Findings showed that as predicted, fish from Panther Creek had higher concentrations of mercury than did those from Saline Branch Ditch. Although there were no point sources of mercury upstream in either location, there are more and larger power plants in the vicinity of Panther Creek than Saline Branch.
Although the history of land use, the make-up of soils in the area, and a wider stream corridor at Panther Creek could all contribute to the observed findings, “our results are consistent with the higher wet deposition of mercury in the area and the state’s sport fish consumption advisories for Jasper and neighboring counties, which indicate higher mercury loads in large species of fish in this region,” Levengood said.
To examine mercury concentrations over time, the researchers also tested preserved blackstripe topminnows collected in 1900 and 1961 from Panther Creek. They found a dramatic decrease (64 percent) in mercury levels from the turn of the century to the early 1960s, which is consistent with the changing use of coal during that time period.
The most prevalent anthropogenic sources of mercury historically were domestic heating and industry, although coal was also used to power locomotives and steam shovels, and was even used in medications and beauty products and to make hats. This changed with the discovery of petroleum and advent of coal-fired power plants. In Illinois, most of the coal production and use was, and still is, located in the southern and western portions of the state.
Mercury concentrations in the fish from Panther Creek increased slightly between 1961 and 2006. The researchers surmised that this could be due to landscape changes that have taken place in that timeframe, such as the advent of intensive row crop agriculture and continued conversion of more natural habitats to farmland. Such changes would allow mercury deposited atmospherically for many years to leach into streams at a faster rate.
As a pollutant, mercury can stay in the atmosphere for years, Gay said. Distributed by rain and wind, mercury found in Illinois streams may originate from both local and distant sources.
“If mercury is in a water body, there is no guarantee that it is only from a local source,” Gay said. “The difficulty is in distinguishing among sources.”
Mercury monitoring is important in setting regulatory benchmarks and for measuring the success of environmental controls. The researchers hope to conduct a more intensive study of mercury in small fish from various locations in Illinois.
The results of the study, Mercury in small Illinois fishes: Historical perspectives and current issues, were recently published in the international journal Environmental Monitoring and Assessment (Volume 185(8):6485-6494). David Soucek and Chris Taylor of the Illinois Natural History Survey were co-authors.