Small perch contain more mercury than expected!

Ann Arbor, MI — Some yellow perch from the St. Lawrence River at Cornwall, Ontario, Canada contain paradoxically high concentrations of mercury.

Mercury levels in perch at one site were much higher than at another only 2 km (1.2 miles) downstream, even though mercury concentrations in sediments were higher at the downstream site.

The results have important implications for human health, because mercury is toxic to humans, and the Cornwall waterfront is a popular spot for fishing. As fish grow, they accumulate more mercury, which persists in their muscle tissue. At the contaminated site, about 60% of the perch 14-16 cm (5.5 to 6.2 inches) in length exceeded the concentration considered safe for consumption by pregnant women or children.

The cause may be high rates of methane bubbling from wood fiber buried beneath the sediments, a legacy of 100 years of pulp and paper production. Each 'burp' of methane re-suspends contaminated sediments into the river, making more mercury available to fish.

This hot spot of mercury in perch remained undetected, despite an Ontario program of annual monitoring to determine if fish are safe to eat.

As Queen's University Professor Peter Hodson explained, "Monitoring is done on a regional scale, assuming that one sample of fish taken at one time and place each year accurately reflects the risk of eating fish over a broad area. However, we found that large changes in fish mercury concentrations can occur over small distances."

Hodsen adds, "Risk also changed with season, because in May, fish with low mercury concentrations visited the site briefly to spawn. To understand the true risk, sampling must be done more frequently and at more sites."

Original Publication Information

Results of this study, "Spatial and Seasonal Patterns of Mercury Concentrations in Fish from the St. Lawrence River at Cornwall, Ontario: Implications for Monitoring," are reported by Adrienne R. Fowlie, Peter V. Hodson and M. Brian C. Hickey in the latest issue (Volume 34, No. 1, pp. 72-85) of the Journal of Great Lakes Research, published by the International Association for Great Lakes Research, 2008.

Contacts

For more information about the study, contact Peter Hodson, School of Environmental Studies, Queen's University, Kingston, ON K7L 3N6, Canada; peter.hodson@queensu.ca, (613) 533-6129.

For information about the Journal of Great Lakes Research, contact Marlene Evans, Editor, National Water Research Institute, 11 Innovation Boulevard, Saskatoon, SK, S7N 3H5, Canada; editor@iaglr.org; (608) 692-1076.

Links

Since 1967, IAGLR has served as the focal point for compiling and disseminating multidisciplinary knowledge on North America's Laurentian Great Lakes and other large lakes of the world and their watersheds. In part, IAGLR communicates this knowledge through publication of the Journal of Great Lakes Research, available to members in print and electronic form. A searchable archive of the journal is available online and includes the abstracts of articles from the journal's inception in 1975 through the most recent issue. In addition, complete articles are available to members who have signed up for an electronic subscription.