Environ. Sci. Technol. 1997, 31, 3523-3529
Concentrations, Accumulations, and Inventories of Toxaphene in Sediments of the Great Lakes ROGER F. PEARSON,† D E B O R A H L . S W A C K H A M E R , * ,† S T E V E N J . E I S E N R E I C H , ‡,§ A N D DAVID T. LONG| Environmental and Occupational Health, School of Public Health, Box 807 Mayo Building, University of Minnesota, Minneapolis, Minnesota 55455, Gray Freshwater Biological Institute, University of Minnesota, Navarre, Minnesota 55392, and Department of Geological Sciences, Michigan State University, East Lansing, Michigan 48824
Sediment cores were analyzed for toxaphene from three of the Great Lakes (Superior, Michigan, and Ontario) and from two small control lakes near Lake Superior that receive inputs of toxaphene from only the atmosphere. The two cores from northern Lake Michigan had higher surface concentrations (33 ( 12 ng/g) than the southern Lake Michigan core and the remainder of the Great Lakes cores, which were similar (15 ( 4 ng/g), and similar to the surface concentration in one of the control lakes (9 ng/g). Evidence consistent with the slow degradation of toxaphene (t1/2 g 50 yr) in some of the sediment cores was found. The similar concentrations among all the Great Lakes cores and the control lake core provide strong evidence that the dominant source of toxaphene to the Great Lakes is atmospheric input. The higher concentrations in the northern Lake Michigan cores indicate that northern Lake Michigan may be receiving about 30-50% of its current inputs from non-atmospheric sources. Lake Ontario and Lake Superior may have had a non-atmospheric source in the past.
Introduction The contamination of the Great Lakes by toxic organic contaminants has long been recognized, but efforts to stop inputs or reduce contamination levels have been met with limited success (1). Despite domestic bans of some chemicals, inputs from the atmosphere have continued due to continued use in other countries and volatilization and transport from existing stocks in the environment (2, 3). Determining the magnitude of atmospheric inputs of toxic chemicals and their contribution relative to non-atmospheric inputs is of major importance so that appropriate and cost-effective decisions can be made about the management, regulation, and remediation of the Great Lakes. Technical toxaphene is a broad spectrum pesticide comprised of a complex mixture of chlorinated bornenes and bornanes having from four to ten chlorines. It is produced by the chlorination of camphene in terpentine oil and has been reported to contain over 670 different components (4). * To whom correspondence should be addressed. Phone: (612)626-0435; fax: (612)626-0650; e-mail:
[email protected]. † School of Public Health, University of Minnesota. ‡ Gray Freshwater Biological Institute, University of Minnesota. § Present address: Department of Environmental Sciences, Cook College, Rutgers University, New Brunswick, NJ 08903-0231. | Michigan State University.
S0013-936X(97)00278-2 CCC: $14.00
1997 American Chemical Society
It would be more appropriate to refer to these mixtures as polychlorinated camphenes, polychlorinated terpenes, or chlorobornanes and chlorobornenes. However, none of these names has taken hold in the literature (5), and we refer to the mixture as toxaphene as it continues to be the recognized, if incorrect, nomenclature for this family of compounds. First manufactured for commercial use in the mid-1940s, it was used as a piscicide for removing rough fish from inland lakes in the upper Midwest and Canada in the 1950s (6-8). Following the ban of DDT in 1972, it became the replacement chemical of choice for cotton crops and to a lesser extent corn, soybean, and peanut crops. The majority of its use in the United States was in the southern states from Florida to Texas (9). It was one of the most widely used chlorinated pesticides in the history of U.S. agriculture (10). However, concerns about its toxicity and persistence led to its restriction in the United States in 1982. Despite this, toxaphene in fish in Lake Superior contribute to the need for consumption advisories for several sport fish species (11). Past and present sources to the Great Lakes have not been clearly delineated; but, it is thought that toxaphene had limited application in the Great Lakes drainage basin (12). The available atmospheric measurements indicate a gradient of decreasing air concentrations from the southern United States to the Arctic, a strong seasonal trend in air concentrations, and possibly declining air concentrations over the last decade (2, 13, 14). However, the few data that exist on air concentrations over the Great Lakes indicate that there is no significant gradient across the basin (15). Atmospheric inputs via gas absorption are believed to be the major source of toxaphene to the Great Lakes (16). In the absence of a complete historical record of air and water concentrations of toxaphene in the Great Lakes, the sediment record can be used to test this assumption. Hydrophobic chemicals associate with particles in the water column. They are removed to the bottom of lakes by the settling of particles to which they are sorbed, and their accumulation is recorded over time in the sediments. Thus, the sediment record can be used to assess these types of chemicals’ accumulation over time and, by inference, their changes in inputs over time (17-21). The purpose of this study was to investigate the history of toxaphene concentrations and accumulation in a series of dated sediment cores from three of the Great Lakes (Superior, Michigan, and Ontario) and from control inland lakes that can receive these compounds only via the atmosphere. Cores were selected that would allow us to evaluate the effects of highly industrialized and populated subregions of the Great Lakes basin on accumulation patterns of toxaphene (e.g., Lake Superior vs Lake Ontario; northern Lake Michigan vs southern Lake Michigan). The sediment records across the Great Lakes can be compared, and these records can be compared to the control lakes to assess the relative contribution of atmospheric vs non-atmospheric sources of toxaphene to the Great Lakes. Thus, we can use the sediment cores to test the working hypothesis that atmospheric inputs are the major source of toxaphene to the Great Lakes.
Experimental Methods Sample Collection. A detailed description of the coring methodology and the sites cored (Figure 1) have been presented previously (20-22). All cores from the Great Lakes were collected by box corer; the two control lakes were cored by a scuba diver. Three cores were evaluated in Lake Superior: two of the cores were taken at the same coordinates in different years. One core was obtained in 1991 from the NOAA3 site and was dated (LS-NOAA3-E). This core was extracted and analyzed for PCBs and other pesticides by Dr.
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FIGURE 1. Locations of the sediment cores, site-specific mass sedimentation rates of the cores, and site-specific focusing factors of the cores. S. J. Eisenreich’s laboratory (23), and the resulting extracts were analyzed in our laboratory for toxaphene. A second core from these coordinates was collected 3 yr later (LSNOAA3-S), extracted, and analyzed for toxaphene. We applied the sedimentation rate from the first core to this core to obtain accumulation rates. The third Lake Superior core (LSBasswood) was from a near-shore depositional zone near the Apostle Islands. The three sites in Lake Michigan included one in the southern basin (LM-18) and two in the northern basin (LM-47s, LM-68k). Two cores were analyzed for toxaphene at the LM-68k site: one extracted by this laboratory for toxaphene (LM-68k-S), and one extracted for PCBs and other pesticides in Dr. Eisenreich’s laboratory (LM-68k-E) (24). These cores were replicate subcores from the same box core. Dating information was obtained from a third subcore of the same box core. Three cores were taken from Lake Ontario: one in the western depositional zone (LO-19), one in the central depositional zone (LO-40a), and one in the eastern depositional zone (LO-E30). The two control lake cores were both taken in the area of the Bayfield Peninsula of Lake Superior and included an inland lake (Siskiwit) and a lake on Outer Island of the Apostle Islands of Lake Superior.
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Extraction and Interference Removal. Sediments were analyzed for toxaphene by extracting 10-50 g wet sediment mixed with anhydrous sodium sulfate by Soxhlet extraction for 24 h in a 50:50 (v:v) mixture of acetone and hexane. Interferences were removed from the crude extracts by normal phase silica and alumina chromatography as described in a prior publication (20). For the two cores that were analyzed by Dr. Eisenreich’s laboratory (23, 24), the PCB and pesticide fractions from the Florasil cleanup were combined and analyzed for toxaphene in our laboratory using GC/ECNIMS. A study of the recovery of toxaphene spikes processed through the Florasil interference removal protocol used in Dr. Eisenreich’s laboratory (the PCB and pesticide fractions subsequently combined and analyzed by GC/ECNIMS) gave comparable results to recovery studies using this laboratory’s procedures. Analysis. Prior to instrumental analysis, PCB congener 204 (2,2′,3,4,4′,5,6,6′-octachlorobiphenyl) was added as an internal standard to each extract to be used in the final quantitation. The extracts were analyzed by gas chromatographic (Hewlett Packard 5890A)/mass spectrometry (Hewlett Packard 5988A) with the mass spectrometer operated in the
TABLE 1. Inter-Lake Summary of Toxaphene Data for Control Lakes and Great Lakesa date of core collection
onset date
date of max accum
Siskiwit Outer Island
1991 1991
