Contaminant Trends in Whole Fish
 

Contaminant Concentrations in Great Lakes whole fish

Below are descriptions of the most recent contaminant concentrations reported for whole lake trout and walleye from the Great Lakes over time.  It is important, when looking at graphs, to notice the difference in scale, particularly in the contaminant concentration.  For this reason, it is not easy to compare graphs to each other.  It is also important to note that the below graphs are for whole fish, which include skin, bones, and organs.  The concentrations monitored from these fish are meant to protect wildlife health and NOT human health.

Are PCBs in Great Lakes fish?

The most recent PCB concentrations recorded are lowest in Lake Superior and greatest in Lake Michigan.  This observation is consistent with previous analysis of the contaminant concentrations in the Great Lakes ( DeVault et al. 1996).  The significant differences in concentrations in Lakes Superior and Lake Erie between 1999 and 2000 are highly unlikely due to lake-wide differences between years, but rather due to differences between sites and/or populations.  In Lake Superior, the collection location was moved slightly in order to obtain the proper number of fish for the sample.  Because a different fish population (subpopulation) was sampled, it can be assumed that differences in site or in the food base are the reason for the differences in concentration from year to year.  Different subpopulations may have different PCB concentrations if some subpopulations are native and other are from stocks.  The stocked fish would have had different exposures to contaminants in the hatcheries, leading to differences in tissue concentration as fry.  It is also possible that different subpopulations (stocked or not) may have different food bases or foodwebs.  For example, some populations may feed more in the mid waters of the lake while others may feed closer to the bottom of the lake.  These differences in food base would result in different contaminant concentrations in fish tissue, as the contaminant concentration of prey is what controls the concentrations in top predators (Thomann and Connolly 1984; Thomann et al. 1992). 

In Lake Erie, PCB concentrations are greater in the western basin sediments compared to the eastern basin (Marvin et al. 2002), and this gradient may be reflected in the walleye collected from those regions.  While walleye are known to migrate throughout the lake, the collections made in 1999 and 2000 may be more representative of the local environment.  These differences are not seen for other contaminants, which is consistent with the fact that PCBs have several point sources in the Detroit River and western basin thus creating the gradient, while other contaminants do not have the same well-defined gradients.

 Is DDT in Great Lakes fish?

DDT, or total DDT, is made up of three components (DDT, DDD, and DDE).  DDD typically contributes negligible concentration to fish tissue.  DDE is the dominant total DDT contaminant, while DDT typically contributes 10-30% of total DDT.  However, variations in DDT contribution vary.  For example, Lake Superior in 1999 and Lake Ontario in 2000 show higher than expected levels of DDT based on previous monitoring events.  This may reflect real differences in the foodwebs of these sites, or may be due to a laboratory procedure.  This difference is currently being examined by the principal investigator for the GLFMP.  The discussion of differences in ΣDDT concentration between years in Lake Superior (1999 and 2000) is the same as the discussion found above for PCBs.  Concentrations of ΣDDT in lake trout were lowest in Lake Superior which was similar to Lake Huron.  Concentrations were highest in Lake Michigan.  Concentrations in Lake Erie walleye were lower than lake trout. 

Is Chlordane in Great Lakes fish?

Total chlordane is made up of five components (trans nonachlor, cis nonachlor, trans chlordane, trans chlordane, and oxychlordane).  Trans nonachlor is the most prevalent of the chlordane compounds and is shown below.  Concentrations of trans nonachlor were highest in Lake Michigan lake trout to less than half that value in the other lakes’ trout.  Lake Erie walleye were lower in trans nonachlor concentration than were lake trout.  The significant difference in trans nonachlor concentration in Lake Superior between 1999 and 2000 is not likely due to lake-wide differences between years, but rather due to differences between sites and/or populations (see explanation in PCB section). 

Is Dieldrin in Great Lakes fish?

Concentrations of dieldrin in lake trout appear to be declining in all Lakes and are lowest in Lake Superior and highest in Lake Michigan.  Concentrations in Lake Erie walleye were the lowest of all lakes. 

Acknowledgments

DeVault, D.S., Hesselberg, R., Rodgers, P.W., and Feist, T.J., 1996. Contaminant Trends in Lake Trout and Walleye from the Laurentian Great Lakes. J. Great Lakes Res. 22(4): 884-895.

U.S. EPA. 1997. The incidence and severity of sediment contamination in surface waters of the United States. Volume 1: National Sediment Quality Survey. EPA 823-R-97-006. U.S. EPA. Washington D.C. pp. B14-B15.