Environ. Sci. Technol. 2000, 34, 1851-1855
Rates at Which Toxaphene Concentrations Decrease in Lake Trout from the Great Lakes SUSAN T. GLASSMEYER,† DAVID S. DE VAULT,‡ AND R O N A L D A . H I T E S * ,† School of Public and Environmental Affairs and Department of Chemistry, Indiana University, Bloomington, Indiana 47405, and United States Fish and Wildlife Service, Ecological Services, 1 Federal Drive, Fort Snelling, Minnesota 55111
FIGURE 1. Great Lakes lake trout sampling sites.
Toxaphene is a complex mixture of at least 600 hexa- to decachlorinated bornanes and bornenes, which was used as an insecticide in the United States from the late 1950s to the mid-1980s. A previous study in our laboratory showed that the levels of toxaphene in lake trout collected in 1982 and 1992 from Lake Superior had remained about the same but that the concentrations in lake trout from the other Great Lakes had decreased during this same time period. These observations in Lake Superior trout were counter-intuitive given that toxaphene had been banned in 1982. We have reinvestigated this issue using more samples from both Lake Superior and northern Lake Michigan and using an improved analytical method. The level of toxaphene was constant in all of the trout samples from Lake Superior during the period 1977-1992, while the level decreased by a factor of 1.4-5 in trout from the other Great Lakes. These results suggest that the toxaphene concentrations in very large and very cold lakes (such as Lake Superior) decrease much more slowly than they do in relatively small and warm lakes (such as Lake Ontario).
Introduction Toxaphene was first introduced in the United States in the late 1940s by the Hercules Chemical Company for use as an insecticide on cotton (1, 2). Toxaphene’s use gradually increased to include other crops (1, 3, 4), but its use escalated dramatically after DDT was banned in 1972 (5). Toxaphene was produced by the chlorination of camphene, a process resulting in a complex mixture of chlorinated bornanes and bornenes (1). Over 32 000 toxaphene congeners are theoretically possible (6), and approximately 600 of them have been found, but not identified, in commercial toxaphene (7). Toxaphene has been found in fish and marine mammals since the mid-1960s. Toxaphene is present in biota from areas as remote as the Arctic and in species at the highest trophic levels. Concern over toxaphene’s ability to bioaccumulate prompted the U.S. Environmental Protection Agency to cancel its registration in 1982 (8), although existing stocks were used until 1986. Canada canceled toxaphene’s registration in 1983 (9). One area of particular concern to both the United States and Canada has been the Laurentian Great Lakes, an important ecological system forming part of the border * Corresponding author e-mail:
[email protected]. † Indiana University. ‡ United States Fish and Wildlife Service. 10.1021/es990924q CCC: $19.00 Published on Web 03/10/2000
2000 American Chemical Society
between these two countries. Given the ban on toxaphene’s use in 1982-1986, one would expect that its concentration in fish from the Great Lakes would have decreased since that time. In fact, the rate of decrease seems to be somewhat variable. Recent work in our laboratory has shown that the levels of toxaphene in lake trout (Salvelinus namaycush) and rainbow smelt (Osmerus mordax) from Lake Superior did not decrease from 1982 to 1992, but the levels in lake trout, walleye pike (Stizostedion vitreum vitreum), and smelt from the other Great Lakes decreased by about a factor of 5 (on average) during this time (10). Unfortunately, these observations were based on only one average toxaphene concentration per lake per time period and on mixed fish species. We resolved, therefore, to repeat these studies with more replication so that we could relate these rates for toxaphene’s loss from fish to the conditions of the lakes. Thus, in this paper, we will focus only on one species, lake trout, collected at six locations in four of the five Great Lakes.
Experimental Section Sample Collection and Preparation. The lake trout samples were obtained from the U.S. EPA and the U.S. National Biological Survey (NBS) though the Great Lakes Fish Contaminants Monitoring Program. Samples were collected by gill netting in September and October from three locations: near the Apostle Islands in Lake Superior (1977, 1984, 1988, and 1992); off-shore from Charlevoix, MI; and off-shore from Sturgeon Bay, WI (1985 and 1993). Both of the latter sites are in Lake Michigan. The sample collection locations are shown in Figure 1, which also shows the collection locations for some of the lake trout samples we had analyzed previously. After being collected, the fish were weighed, measured for total length, placed in plastic bags (known to be free of contaminants), and shipped to the NBS Great Lakes Science Center (GLSC) in Ann Arbor, MI. At the GLSC, the fish were composited (5 whole fish per sample), homogenized, and stored frozen at
