Environ. Sci. Technol. 1996, 30, 220-224
Historical Input and Degradation of Toxaphene in Lake Ontario Sediment MICHAEL J. HOWDESHELL AND RONALD A. HITES* School of Public and Environmental Affairs and Department of Chemistry, Indiana University, Bloomington, Indiana 47405
The historical input of toxaphene to Lake Ontario has been determined. We analyzed total toxaphene concentrations in eight Lake Ontario sediment cores by electron capture gas chromatographic mass spectrometry and found that toxaphene maximizes in 1973 ( 6 yr with a horizon date of 1945 ( 6 yr. The maximum toxaphene flux to Lake Ontario sediment was 22 ( 8 µg/m2 yr in about 1973, and the total toxaphene load in the lake is 10 ( 3 t. By comparing the toxaphene burdens for the cores, we conclude that toxaphene is deposited to Lake Ontario sediment from both the Niagara River and from the atmosphere. We also found that toxaphene is slowly dechlorinated after deposition in Lake Ontario sediment.
Introduction Toxaphene is a semivolatile, hydrophobic insecticide consisting of hundreds (perhaps even thousands) of norbornanes and norbornenes with 6-10 chlorines; it is produced by the reaction of camphene and chlorine (1).
Other relatively minor uses included killing scabies on cattle and rough fish control (7, 8). Toxaphene inputs to the environment have been studied by several authors. Based on an atmospheric deposition model, Voldner and Schroeder estimated that toxaphene use maximized in 1972 at about 25 × 106 kg/yr (7). Bidleman et al. compiled data from multiple sources on toxaphene production and use and estimated that the maximum use occurred in 1972-1974 at rates around 27 × 106 kg/yr (8). Rapaport and Eisenreich found the highest deposition of toxaphene to peat bogs in North America occurred between 1975 and 1978 (2). Wania and Mackay have modeled toxaphene emissions into the atmosphere and found them to maximize in about 1975. They also predicted that temperate climatic zone lake sediment concentrations would maximize around 1978 (9). These four studies suggest that toxaphene inputs into the environment should have maximized between 1972 and 1978. We have tested these predictions for Lake Ontario by analyzing eight representative sediment cores. Lake Ontario, located last in the Great Lake’s chain, is the 14th largest lake in the world, but it is the smallest of the Great Lakes with an area of about 19 000 km2. More than 7 million people live in its drainage basin and use Lake Ontario as a major water source for many recreational, residential, agricultural, and industrial purposes (10). The lake has had problems with a variety of organic pollutants including polychlorinated biphenyls (PCBs), dioxins, DDT, and mirex (11-13). Toxaphene is also a problem in Lake Ontario. For example, in 1982 the toxaphene concentration in Lake Ontario trout was about 24 µg/g lipid, and in smelt, it was about 11 µg/g lipid (14). With the data from this study, we have addressed several questions: What is the history and extent of the input of toxaphene to Lake Ontario? Does this agree with the models (2, 7-9)? Is the input from atmospheric sources, from nonatmospheric sources, or from a combination of the two? Is the toxaphene transformed after deposition?
Experimental Section
Over 180 companies have produced toxaphene since the Hercules Chemical Company first introduced it in 1947 (2). It has been called by a variety of names including camphechlor, polychlorinated camphene, Allotox, Melipax, Toxadust, and Hercules 3956 (3). The United States Environmental Protection Agency (EPA) banned toxaphene in November 1982; however, toxaphene in stock at that time was allowed to be used until 1986 for specific purposes as outlined by the EPA (4). The United States, China, India, Brazil, Finland, and Sweden have completely banned toxaphene; Argentina, Spain, Norway, and Mexico allow restricted use (5). Toxaphene was the most heavily used insecticide between 1966 and the mid-1970s (6). It was primarily used in the southern United States as a broad spectrum insecticide on cotton. In the late 1970s, use shifted to other crops including wheat, corn, soybean, rice, and pineapples. * Corresponding author e-mail address:
[email protected].
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Sampling. Lake Ontario sediment cores were collected in July 1993 aboard the C.S.S. Limnos. The eight sampling sites are shown in Figure 1, and the exact locations of these sites are listed in Table 1. The sites were selected to give two representative cores from each of the four main sedimentation basins (the bottom areas in the lake where sediment collects, shown as shaded areas in Figure 1). Cores were collected with a 1-m3 sediment box corer, subsamples were taken with 10 cm diameter polycarbonate tubes, and the samples were hydraulically extruded and sectioned at 1-cm intervals for the first 12 cm and at 2-cm intervals after that. The subsections were frozen on ship, returned to our laboratory, stored at -18 °C, and thawed for analysis. Sample Preparation and Extraction. A known amount of wet sediment (about 10 g) was centrifuged to remove interstitial water, mixed with about 80 g of clean Na2SO4, placed in a glass Soxhlet extractor thimble, and spiked with a known amount of 37Cl6-trans-nonachlor (EPA Repository; Research Triangle Park, NC) as the internal standard. The sample was then Soxhlet extracted for 24 h with 2-propanol and for another 24 h with dichloromethane. The extracts
0013-936X/96/0930-0220$12.00/0
1995 American Chemical Society
FIGURE 1. Approximate sampling locations in Lake Ontario showing site numbers and sedimentation basin names. Shaded areas indicate sedimentation basins; there is no appreciable sediment accumulation in the unshaded areas of the lake. TABLE 1
Lake Ontario Sampling Locations station No.
latitude north
longitude west
20 600 601 602 603 607 608 609
43°20′18′′ 43°38′00′′ 43°41′30′′ 43°44′30′′ 43°38′30′′ 44°09′00′′ 44°02′15′′ 43°43′30′′
79°11′44′′ 78°43′03′′ 78°10′30′′ 77°55′24′′ 77°19′30′′ 76°36′30′′ 76°51′30′′ 76°45′00′′
were combined, rotary evaporated, exchanged into hexane, and reduced to a final volume of about 5 mL. The combined extract was chromatographed on a column containing 20 g of 1% water deactivated silica gel with 2 g of activated copper placed at the bottom to remove elemental sulfur. The column was topped with 1 g of anhydrous Na2SO4 to remove water. The sample was charged to the column and eluted with 50 mL of hexane, 50 mL of 80% dichloromethane in hexane, and 50 mL of 100% dichloromethane. The 80% and 100% dichloromethane fractions contained the toxaphene and internal standard; they were combined for analysis. This fractionation scheme is different from our previous method that used PCB congener 204 as the internal standard (15). In that method, PCB congener 204 eluted in the hexane fraction, which was subsequently combined for analysis. This hexane fraction also contained many other PCB congeners that caused some analytical interferences (15). Sediment Dating. For each core, the sedimentation rate and the sediment focusing factor were determined using the well-known 137Cs technique (16-18). For each core section, a known amount of dried, finely crushed sediment was transferred into weighing bottles, all of which were of equal geometry and wall thickness. The 137Cs amount was determined by counting disintegrations with a lithiumdrifted germanium detector connected to a multichannel analyzer to separate and quantify the 662 keV γ-ray emitted by 137Cs. This isotope was quantitated by comparison to a standard, and corrections were made for solid angle and transmittance through the sample. The data were then compared to the theoretical 137Cs inventory (0.30 Bq/cm2) in the Great Lakes to determine a focusing factor (19). This factor was determined by dividing the theoretical 137Cs inventory by the measured 137Cs inventory in the core. The resulting values, which ranged from 0.62 to 1.67, indicate
whether sediment is being transported to (focusing factors less than 1) or transported from (focusing factors greater than 1) a given sediment collection site in the lake. The use of these correction factors is a well-developed method of removing some of the heterogeneity associated with uneven sediment deposition throughout a lake (17, 18). Quantitation. Toxaphene was quantitated using gas chromatographic mass spectrometry operating in the negative ionization electron capture mode. The instrument was a Hewlett Packard 5989A system equipped with a 30 m × 250 µm DB-5 fused-silica capillary column, which had a 0.25-µm film thickness (J&W Scientific; Folsom, CA). The ion source was held at 125 °C, and the transfer line was held at 285 °C. Helium was used as the carrier gas at a velocity of 40 cm/s. Methane was the chemical ionization reagent gas, which was used to generate low-energy elections; the ion source pressure was 0.43 Torr. Samples of 1 µL were introduced by splitless injection with a vent time of 0.9 min. The column temperature was held at 40 °C for 1 min, increased to 100 °C at 30 °C/min, then to 200 °C at 10 °C/min, then to 230 °C at 1.5 °C/min, and finally to 280 °C at 10 °C/min where it was held for 5 min. Response factors for total toxaphene were determined by comparison of the relative response factors (rrf) of a toxaphene standard (Ultra Scientific; North Kingstown, RI) to that of the 37Cl6-trans-nonachlor internal standard. Typical rrf values ranged from 0.7 to 0.9. The quantitation, confirmation, and correction ions (m/z) for toxaphene have been reported by Swackhamer et al. (15). The ions used for 37Cl6-trans-nonachlor were m/z 454, 452, and 444, respectively (the latter corrects for any trans-nonachlor present in the sediment). Quality Control. All solvents were of glass-distilled grade, and all glassware was acid washed and heated at 450 °C overnight. The copper, Na2SO4, and silica gel were cleaned for 24 h by Soxhlet extraction with dichloromethane and subsequently heated at 160 °C overnight. Procedural blanks were run with each batch of five samples; they were taken through all phases of extraction, isolation, and analysis. The blanks did not show toxaphene congeners in any sample set.
Results and Discussion Transport. Total toxaphene concentration profiles for the eight Lake Ontario sediment cores are plotted in Figure 2. Total burdens (BTOT) for each core were calculated by n
BTOT ) φ
∑F Y
(1)
i i
i)1
where Fi is the flux for a given section (in µg/m2 yr), Yi is the number of years represented by that section, and φ is the unitless focusing (or defocusing) factor for the core. The fluxes were calculated by multiplying the concentration of each section by the in situ density of that section and by the overall sedimentation rate for that core. Table 2 summarizes the core location, focusing factor, maximum flux of each core (µg/m2 yr) adjusted by the 137Cs focusing factor, the total burden (µg/m2) adjusted by the focusing factor, and the maximum and horizon years for toxaphene in each core. We found the average maximum flux to be 22 ( 8 µg/m2 yr. The average burden for Lake Ontario is 500 ( 180 µg/m2, and the individual core burdens range from 240 to 840 µg/m2. The highest burden is at site 20 in
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FIGURE 2. Toxaphene concentration profiles in Lake Ontario cores with core identification, basin, and total burden (adjusted for sediment focusing) listed on the plot. See Figure 1 for core locations. TABLE 2
TABLE 3
Lake Ontario Core Locations, Sediment Focusing Factors, Maximum Fluxes and Burdens, and Maximum and Horizon Years for Toxaphene
Summary of Toxaphene Deposition to Lake Ontario
core
basin
20 600 601 602 603 609 607 608
Niagara Niagara Mississauga Mississauga Rochester Rochester Kingston Kingston
av SD
adjusted adjusted focusing max flux burden max horizon factor (µg/m2 yr) (µg/m2) year year 1.19 1.08 1.67 0.93 0.62 0.78 0.95 0.78
32 10 14 28 22 22 17 28
840 240 660 400 500 520 410 430
1968 1968 1969 1982 1972 1970 1981 1971
1938 1952 1945 1955 1945 1940 1943 1944
22 8
500 180
1973 6
1945 6
the Niagara Basin. This site is at the mouth of the Niagara River, and it collects material transported into Lake Ontario from Lake Erie. All other basin burdens are within about 30% of the average burden for the lake. Using the average Lake Ontario burden value and the Lake Ontario surface area of 18 960 km2, we estimate that about 10 ( 3 t of toxaphene is buried in Lake Ontario’s sediment. Table 3 summarizes our measurements and literature estimates of the year in which the environmental input of toxaphene maximized and the flux associated with each estimate (when available). As discussed above, other authors have suggested that the maximum toxaphene input to the Great Lakes would have occurred between 1972 and 1978 (2, 7-9). The horizon should be about 1947, the year when toxaphene was first produced (2, 4). These maximum and horizon values are in agreement with our data for the Lake Ontario cores, which show a maximum year of 1973 ( 6 and a horizon year of 1945 ( 6 (see Table 2). Table 3 also shows that the predicted maximum fluxes range from 4 to 15 µg/m2 yr (2, 9). Our measured maximum average flux value of 22 ( 8 µg/m2 yr is about twice these estimates; however, given the errors associated with both the mea-
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ref
max year
8
1975
2 9
1975-1978 1978
this 1973 ( 6 yr study
flux measurement (µg/m2 yr) source
4 15a 22 ( 8
deposition area total toxaphene input Alfred, ON temperate zone
peat bogs modeled sediment sediment Lake Ontario cores
a Calculated from the modeled concentration reported by Wania and Mackay (9) in Lake Ontario using an average in situ density of 0.5 g/cm3 and an average sedimentation rate of 1 cm/yr.
surements and with the estimates, we suggest that this difference is not significant. Chlorination level profiles for toxaphene were obtained by ratioing the total concentration at one chlorination level to the total toxaphene concentration. This calculation assumes that all toxaphene congeners within each chlorination level have equivalent GC/MS response factors, and that if they do not, those with a greater response are off-set by those with a lesser response. Figure 3 shows two sets of data: one represents the average distribution for the eight surface sediment samples, and the other represents the toxaphene standard (measured eight times). The centroids for the standard and the surface sediment toxaphene distributions are 7.5 ( 0.9 and 7.2 ( 0.8 (one standard deviation), respectively. It is clear that there is no difference between the toxaphene distributions in the surface sediment and in the standard. How did toxaphene get into Lake Ontario? Based on the elevated burden at site 20 just off the mouth of the Niagara River, which is the main riverine source of sediment and water to Lake Ontario (20), it seems likely that this river is the source of some of the toxaphene in the lake. However, atmospheric deposition is also important. If toxaphene were coming only from the Niagara River, then the burdens in the Kingston Basin would be less than 20% of the burdens in the other cores (21, 22). This is not the case.
TABLE 4
Individual Lake Ontario Sediment Core Degradation Values; see Figure 5 for Composited Data core 20 600 601 602a 603 609 607 608 av rsd (%)
FIGURE 3. Chlorination profiles for technical toxaphene and toxaphene in Lake Ontario surface sediments. Error bars represent 1 SD.
a
basin
intercept
slope (yr-1)
n
r
significance level (%)
N N M M R R K K
0.694 0.494 0.578 1.86 0.694 0.553 0.733 0.524
0.016 0.016 0.012
