RESULTS
Results of analysis for total metals concentration in surface water at each sample site were below the minimum limit of detection (LOD) of 0.0002 ppm for mercury, and 0.005 ppm for Selenium. Therefore, results of each sample analysis are reported as not detectable (ND) in Table 2.
For all sample sites, surface water temperatures ranged from 6.5° C to 11.0° C, (mean= 8.5° C). pH ranged from 6.85 to 8.08, (median= 7.68). Turbidity ranged from 0.31 NTU to 1.23 NTU (mean= 0.77 NTU). Conductivity ranged from 62 umhos/cm to 260 umhos/cm (mean= 141.4 umhos/cm). Hardness ranged from 27 ppm CaCO3 to 152 ppm CaCO3 (mean= 73.4 ppm). Water quality data is presented in Table 1.
Results of fish body size, age at capture, and metal concentrations of the muscle tissues collected are presented in Table 2. Fork length (FL) of fish captured ranged from 301 mm to 1010 mm (mean= 625). A length frequency of fish captured is presented in Table 3. All fish captured were sampled. Age of fish based on vertebrae aging ranged from 2 years to 19 years of age (mean= 6.8 years). Weight of fish ranged from 250 grams to 7000 grams (mean= 2130 grams). Twenty-five (25) males and twenty-three (23) females were captured resulting in a male to female ratio of 1.1:1.
All muscle tissue samples analyzed were above the LOD of 0.005 ppm for total mercury, but below the LOD of 0.400 ppm for total selenium. Total mercury in muscle tissue ranged from 0.091 ppm wet weight to 0.832 ppm wet weight (mean= 0.438 ppm). Columbia Analytical Services (CAS) analytical report is presented in Appendix A. CAS reported the metals concentrations in both wet weight (as received) and dry weight. The dry weight values can be converted to wet weight by using equation 1:
% Freeze Dried Solids
ppm Wet Weight 100 x ppm Dry Weight
Equation 1.
For all sample sites combined, concentrations of total mercury in muscle tissue show a strong positive correlation when plotted against the total length of the fish (Figure 2). The Pearson correlation coefficient is r=0.816.
Fish from the Camp Creek sample site, the creek where upstream gold placer mining had occurred, had a Pearson correlation coefficient of r=0.873 when mercury in fish tissue was plotted against the fork length of the fish. The remaining three drainages sampled, where no documented mining has taken place, resulted in the following Pearson correlation coefficients: North Creek/American Creek r=0.918, Bonanza Creek r=0.617, and Yukon Creek r=0.707.
For all sample sites combined, plotting the age of fish against the total mercury concentrations in fish tissues results in a strong positive correlation. The Pearson correlation coefficient is r=0.737. Total mercury plotted vs. age of fish is presented in Figure 3.
DISCUSSION
Results from all water quality parameters sampled were within the Alaska Water Quality Standards 18 AAC 70. The low turbidity levels for Camp Creek and Bishop Creek suggest little or no physical water quality degradation, suspension, or resuspension of sediments, at least downstream to the sample sites was occurring. This may be directly related to the fact that no placer or lode mining activities were taking place during the sample period.
The absence of mercury and selenium being detected in surface waters is not necessarily surprising. Similar research has shown that while total mercury and selenium are below detection limits in surface waters, these same metals were above detection limits in fish muscle tissue (Speyer, 1980). The USFWS has data for two sites sampled within this study and also show mercury to be below detection limits in surface waters while fish tissues contained detectable amounts. The two sites sampled by USFWS in the study area were Bishop Creek and Camp Creek (Snyder-Conn et. al, 1992b).
All fish sampled, regardless of sample site, had mercury concentrations above method detection limits. This is consistent with preliminary results from a recent USFWS draft technical report for thirty-one (31) northern pike sampled at ten (10) sites within three national wildlife refuges in the area. For the Kaiyuh Flats total mercury wet weight muscle tissue concentrations reported for twelve (12) northern pike (assuming 25% freeze dried solids) ranged from 0.205 ppm to 0.563 ppm (mean= 0.403 ppm). Kidney and liver tissue also were analyzed for each specimen (Mueller et al. 1995).
Each individual sample site within this project has a strong positive correlation when Hg is plotted vs. fork length of fish and age of fish. These strong positive correlations are indicative of bioaccumulation (uptake via gills and skin) and biomagnification (food chain transfer) of mercury within the aquatic system. No specific sample site within the Kaiyuh Flats appeared to have fish with a significantly higher amount of mercury when correlated to fish size and fish age. Rather, mercury concentrations in fish muscle tissue appear to be ubiquitous.
The possibility of mercury accumulation as a result of off-refuge movements by northern pike was initially considered. During 1994 and 1995 the USFWS Fishery Resource Office, Fairbanks, AK and the ADF&G, Sportfish Division, Fairbanks, AK monitored northern pike movements in the Kaiyuh Flats using radio telemetry techniques. No off-refuge movements of northern pike were observed (Lubinski, USFWS, pers. comm.). It is unlikely that any off-refuge movements by northern pike are a contributing factor to on-refuge fish tissue mercury concentrations. Although, additional information on prey (whitefish) movements would assist in determining contributions to the mercury body burden of on-refuge northern pike.
Erosion of natural mercury deposits may be a source of mercury to the Kaiyuh Flats, but it appears that there are no documented cinnabar (HgS) deposits that could weather and drain into the Kaiyuh Flats catchment basin (Cruz and Cobb, 1984). Therefore, atmospheric deposition of mercury should be considered as a possible source of mercury to the Kaiyuh Flats.
Selenium concentrations in pike tissue were all below the LOD of 0.400 ppm wet weight. These results suggest that selenium may be present in insufficient quantities within the aquatic and biotic systems to potentially counteract the adverse effects of methylmercury. However, Mueller et al. (1995) reports selenium to be above detection limits of 0.500 ppm (reported as dry weight) in muscle, tissue, liver tissue, and whole body samples of all pike captured within the Kaiyuh Flats. After conversion to wet weight, the mean concentration for selenium in muscle tissue is 0.254 ppm wet weight, and the mean concentrations of mercury and selenium appear to be in a 1.6:1 ratio. The reason for this discrepancy is not known at this time, but could be a function of the relatively high method reporting limit of 0.400 ppm as reported by CAS. One researcher offered that the majority of selenium present in the specimens collected may have been concentrated in the liver and still provided an antagonistic effect on the mercury present in muscle tissue (P. Weber-Scannell, ADF&G, pers. comm. 1996).
Comparing the mercury concentrations in fish tissue from this project to guidelines used by the Minnesota Department of Health (Schubat 1990), the concentrations are considered to be low to moderate. However, all results of northern pike sampled for total mercury concentrations fell below the 1.0 ppm Food and Drug Administration (FDA) action level for consumption advisories.
Using the least squares method to calculate a straight line for mercury plotted against fork length results in the linear equation Y= -0.1662 + 0.00097 X. Mean length-at-age data from 925 northern pike captured from the Kaiyuh Flats during a USFWS/ADF&G 1994 radio telemetry project resulted in a fork length modal peak (n=161) at 642 mm and a maximum fork length of 1160 mm (Taube 1995). Substituting 642 mm and 1160 mm for X in the linear equation and solving for Y, results in calculated mercury concentrations of 0.457 ppm and 0.959 ppm, respectively. Therefore, based on the linear equation derived from this project, the largest specimen from a sample size of 1004 northern pike [48 fish from this project, 31 from Mueller, et al. (1995), and 925 from the USFWS/ADF&G 1994 project] does not exceed the 1.0 ppm FDA action level.
Fish Consumption and Risk Assessment
Several states have issued fish consumption advisories concerning specific species with elevated concentrations of mercury. At this time the State of Alaska has no advisories for fish consumption in marine or fresh waters. FDA action levels are essential on a national and inter-state basis, but may not be appropriate for local and site-specific situations where more definitive information is available.
An example of using results from this project in a fish consumption advisory model would be as follows: If the average size of fish that are harvested is 625 mm (È 25 inches), the calculated concentration of mercury in muscle tissue (based on the linear equation of Y= -.1662 + 0.00097 X) would be 0.440 ppm. Using this 0.440 ppm value in a model (Equation 2) proposed by Dourson and Clark (1990), the recommended amount of fish muscle tissue to be consumed over a year-long period without any adverse health effects would be approximately 17.4 kilograms (38.3 lbs). This advised amount of consumption is calculated for an adult male whose body weight is 70 kg (I 54 lbs.).
RfD (mg of chemical/kg bw/day) X 70 (kg bw)
Fish intake (kg of fish/day)= fish concentration (mg of chemical/kg of fish)
Equation 2. Where reference dose (RfD) for mercury is 3 E-4 and (bw) is body weight.
Schubat (1991) recommends that sensitive individuals (pregnant women, nursing mothers, and children under six (6) years of age) consume only 25% of this amount, therefore reducing the recommended amount of consumption to approximately 4.4 kg. (9.6 lbs.) per year. Table 3 presents various fish sizes, calculated mercury concentrations, and recommended consumption amounts based on Shubat (1991) and Dourson and Clark (1990).
It should be noted that the Minnesota Department of Public Health has classified fish consumers as either long term (chronic), 3-12 months/year, and short term (acute), 3 months/year or less. Long term more consistent exposure poses more of a concern because as the period of exposure increases the adverse effect concentration (ppm) decreases. Nearly all of the RfDs are based on long-term daily exposure, therefore, incorporating a more conservative approach into fish advisory models. Based on models proposed by Shubat (1991), it would be safe to chronically consume 2.8 meals/month of fish containing 1.0 ppm. In this case 1 meal would be considered 0.5 lbs.
The reader should be aware of the considerable debate and dissatisfaction among scientists, health care professionals, regulators, and ordinary citizens regarding human health risk assessment associated with mercury in the environment (Graham 1995). The fish consumption models described above use reference doses (RfD) within their respective equations. A RfD is an estimate of daily exposure of the human population to mercury that would not result in an appreciable risk of deleterious effects during a lifetime. However, new approaches are being explored using a "benchmark" approach to more accurately estimate RfDs. The "benchmark" approach utilizes all data points in a set rather than relying on individual data points for RfD estimation.
Depending on an individual's fish consumption habits, level of consumption, and body weight, the recommended consumption levels will vary. Due to the lack of published data on actual consumption rates for the residents of the villages of Kaltag, Nulato, and Koyukuk, estimates of consumption rates are variable and are based on personal communication.
Area residents continue to use the Kaiyuh Flats area for numerous subsistence activities. Northern pike are generally harvested using hook and line techniques. Pike are eaten on site and/or brought back to the villages for human consumption as well as dog food. Northern pike are prepared for consumption in various ways, including: head off and boiled, fried guts (cleaned intestines), livers, kidneys, and gonads, and boiled and made into "ice cream." "Ice cream" is a combination of boiled pike muscle tissue, moose fat, and berries. The mixture is frozen and usually eaten within two weeks. Although some area residents regularly harvest and consume northern pike, there are still concerns of elevated mercury concentrations in the fish. As a result, there is a general feeling that the larger fish should not be eaten. Additionally, it is difficult to quantify the amount of fish harvested and consumed on a yearly basis (G. Yaska and C. Peter, pers. comm. 1995).
Subsistence harvests of northern pike by Galena area residents during 1985 and 1986 have been reported by the ADF&G as 5.2 pounds of edible fish per capita (Marcotte 1990). This report does not describe the area of harvest, therefore, an unquantified amount of the northern pike may have been harvested from the Yukon River mainstem.
Possible comparisons may be made between the villages of Kaltag and Nulato to other villages in interior Alaska that are located in similar basin settings. The villages of Huslia and Minto are each situated in lake/river regions and residents fish for pike in open water and through the ice. Values for edible pounds of pike harvested per capita for Huslia was 28.8 pounds in 1983, and 76.7 pounds for Minto in 1984 as reported by the ADF&G (Walker et al. 1988). These reported values represent the edible pounds of pike harvested. The need for further research on actual pounds of fish consumed on a per capita basis must be stressed.
RECOMMENDATIONS
1) It is the recommendation of TCC's Wildlife & Parks Program that results from this project be used by the State of Alaska Department of Health and Social Services, Division of Public Health, to determine whether guidelines are needed concerning consumption rates of northern pike harvested within the study area. Concern remains regarding recommended consumption of fish by sensitive individuals (pregnant women, nursing mothers, and children under six (6) years of age).
2) Additional information should be gathered regarding actual amounts of fish consumed per capita by Kaiyuh Flats area residents.
3) Due to potential hard rock mining activities proposed for the Kaiyuh Mountains, periodic heavy metals information should be gathered from sediment, water, and fish tissue within the Kaiyuh Flats area.