CALFED MERCURY PROJECT

Transcription

1 CALFED MERCURY PROJECT Subtask 3A: Field assessment of avian mercury/selenium exposure in San Francisco Bay, Suisun Bay and the Sacramento -San Joaquin Delta. Primary Research Team: Dr. Steven Schwarzbach, Terry Adelsbach U.S. Fish and Wildlife Service Environmental Contaminants Division Sacramento Field Office 2800 Cottage Way Sacramento, California Summary of task objectives: 1. Assess mercury and selenium concentrations in ly collected bird eggs of a range of species in different geographic regions of the bay and delta to determine if concentrations exceed established Lowest Observed Adverse Effect Concentrations (LOAECs) for the avian egg (Currently the LOAEC in bird eggs for Hg is 0.5 ppm fresh wet weight. Species specific LOAECs may ultimately be modified by subtask 3b.) 2. Assess mercury and selenium concentrations in fail-to-hatch bird eggs of endangered species nesting within the estuary to determine if concentrations exceed established Low effect concentrations in the avian egg. 3. Determine the proportion of methylmercury in bird eggs in a subset of those eggs analyzed for total mercury for each species assessed. 4. Evaluate the species and geographic patterns of mercury concentrations and determine if they track findings for mercury in other biota, water or sediment. 5. Evaluate correlations of selenium and mercury and methylmercury in bird eggs of a range of species in different geographic regions of the bay and delta. Summary of hypotheses and methods: We hypothesize that some bird species inhabiting the bay/delta will have mercury concentrations in eggs elevated above the LOAEC of 0.5 ppm. Further we hypothesize that nearly all of the mercury in bird eggs, of all 16 species assessed, will be methylmercury. We expect to find that mercury concentrations will vary with degree of piscivory and will be greatest in birds nesting in the south bay. We tested these hypotheses by the collection of eggs from a variety of species from multiple locations in different regions of the bay/delta. We also collected fail-to hatch eggs from endangered species where egg collections were not permissible.

2 Discussion of progress to date/results: To date 175 avian eggs were collected in the 2000 field season, representing 16 bird species and approximately 160 eggs have been collected in the 2001 field season representing five species. The 2000 field season collections ranged from the south bay to Suisun Bay. The 2001 field collections were focused on the delta and represent 21 different locations within the delta with eggs collected from the north, central, south, east and west Delta. Species represented in the 2001 field season include Great Blue Heron (67), Double Crested Cormorant (22) and Great Egret (49) as well as some Snowy Egrets and Black-crowned Night Herons. Mercury, methylmercury and selenium results are available for the 2000 field season and are discussed below. Analytical chemistry results for the 2001 field season are not yet available. At this time due to limited remaining funds only mercury will be analyzed in delta eggs, although samples will be archived and possibly analyzed at a later date for selenium. Results have thus far been obtained for total mercury in all of the 2000 field season eggs and methylmercury in a sub-set of 40 eggs in 13 species to evaluate the relative percentage of methylmercury among different species. Only fresh eggs were utilized for the methylmercury analysis due to potential for demethylation in fail to hatch eggs with dead and decomposing embryos. Mean concentrations of mercury are summarized for each species by region in table 1. Table one should be regarded as preliminary and subject to change given the reanalysis which is planned for the coming year. Five of 16 species had mercury concentrations above the 0.5 ppm (ww) threshold. With regard to egg mercury concentrations we found the following pattern among species: Caspian Terns (south bay) > Clapper Rails (south Central Bay) > Forsters Terns > DC Cormorants > snowy plovers (south bay)> black necked stilts > Great egrets and Great blue herons > snowy egrets and black-crowned night herons. Western gulls and California gulls were relatively uncontaminated. Species foraging on aquatic invertebrates in wetlands (stilts, rails, plovers) were surprisingly high in mercury compared to their more piscivorous counterparts (snowy egrets and black crowned night herons. Mallards and Bitterns from a freshwater wetland upstream of the delta near Davis California were relatively uncontaminated with mercury but slightly elevated in selenium. Cormorant results from the 2000 field season indicated there may be a hot spot for mercury in Suisun Bay. Double Crested Cormorants in Suisun Bay had nearly double the mercury found in cormorants nesting on the bay bridge. Caspian Tern results confirm the south bay is a mercury hot spot as well. Caspian Terns in the south bay were the most contaminated eggs sampled (1.36 ppm ww.) and had a third more mercury than their counterparts in the north bay. Methylmercury results for forty eggs from 13 species were received in These results indicated close agreement in most eggs between total mercury measurements and methylmercury. but with a few eggs not in agreement at all and a few others indicating quite low percentages of methylmercury. The slope of the regression between methyl and total mercury in the first analysis was Because our purpose was to reliably determine the percentage of methylmercury in eggs we decided to rerun 10 of the forty eggs for both total and

3 methylmercury. Upon re-analysis of the 10 eggs, results of methylmercury and total mercury in the sum of all eggs were in much better agreement (R 2 =.98, p = 0) and the slope was 1.04 (figure 1.). Average percentage of methylmercury was 96%. Given the uncertainties that occur when putting two analytical methods together (total mercury and methylmercury) we may not be likely to get a better estimate than 96% using total and methylmercury analysis as the means to evaluate the relative amount of inorganic and organic mercury. It is likely that at least some amount of mercury in the yolk of eggs, however small, is indeed inorganic mercury. A superior approach to fine tune the final small percentage of mercury which is not methyl in eggs would be to do inorganic rather than total mercury, however, that is not an option for now. Interestingly there appear to be some species in our analysis that may have mercury as a lower percentage of the total. These include the eggs of great blue heron, great egret and American bittern, which were closer to 80-85% methylmercury (figure 2). These results are complicated by small sample sizes and the combined error margin of the two measurements. Consequently we intend to do further work and rerun all 40 eggs for mercury and methylmercury. A possible explanation for lower percentage of methylmercury in the large terns and herons is perhaps the dietary similarity in these species, that is to say a not exclusively a piscivorous diet, which could include a higher proportion of inorganic mercury. Alternatively an enhanced demethylation ability in these species could result in some greater amount of inorganic mercury, perhaps bound to selenium. Preliminary results of Heinz and Hoffman in task 3A may be indicating greater sensitivity in egrets (Pers. Comm. Gary Heinz, 17 July 2001). If egrets turn out to be the most sensitive species to methylmercury in the egg, then it will become of greater import from a risk assessment point of view to answer more definitively the question of how much mercury in the egret egg is indeed methyl. A sub-set of 98 avian eggs from the 2000 field season were also analyzed for selenium. The average concentration of selenium in these eggs was 2.7 mg/kg (dry weight). This average is well below the lowest avian egg toxicological threshold of 6 mg/kg. Concentrations in these 98 eggs ranged from 0.86 mg/kg to 7.76 mg/kg. The highest selenium concentrations were seen in great egrets and snowy egrets from West Marin Island and also black-crowned night herons nesting at Alcatraz. Except for one great egret egg from West Marin Island all egg concentrations were all below 6 ppm. Selenium and mercury were statistically correlated but there was a great deal of variability in the correlation (r2 =.17, p = 0) (see figure 3). This result indicates a high confidence in the overall trend of a relationship between selenium and mercury in avian eggs but not much confidence in predicting the results for individual egg. We plan further statistical evaluations by species to assess whether this relationship sorts out better by species. Conclusions: Among factors affecting mercury concentration, species appears to be more important than location in determining the degree of mercury contamination in the 16 species of avian eggs sampled. Among ly collected eggs the greatest mercury concentrations were found in Caspian Terns followed by Forsters Terns then Double crested Cormorants from Suisun Bay. Within species comparisons of Caspian Terns indicated the south bay was a hot spot for mercury. Comparisons between double crested Cormorants indicated Suisun Bay was a hot spot as compared with the Central Bay. Mercury is elevated high enough throughout the ecosystem to put a third of the bird species sampled at risk of embryo mortality - if established egg thresholds in mallards and pheasants can be applied other species. Species at risk in Suisun/ San Francisco Bay include Caspian Terns, Forster s Terns, Double-crested Cormorants, California Clapper Rails, and snowy plovers. The latter two species are federally protected as endangered species. Degree of piscivory was not the sole determinant of mercury concentrations in eggs. Benthic foragers like plovers, stilts and rails also accumulated significant amounts of mercury in the egg. We have confirmed that methylmercury comprises most of the mercury in avian eggs. Selenium concentrations in eggs from the 2000 field season were generally not elevated, with the exception of a few of the egret eggs. Selenium concentrations in eggs from the interior of the delta have not been examined. Potential for future research/recommended changes in existing research program: Work in FY 2002 will focus on chemical analysis of eggs collected in 2001 as well as re-analysis for methylmercury in some 2000 season eggs, as well as statistical analysis of data. We expect to develop a good picture of mercury exposure in piscivorous birds at interior delta locations with the samples collected this year. Analysis of the 2001 eggs for selenium would be highly desirable for other CalFed objectives related to understanding selenium, if it could be somehow funded. We hope in the coming year to get the results of task 2B to assess mercury concentrations in prey items near a sub-set of the bird colonies sampled so that we may make some assessment of bioacummulation factors from prey to egg in delta species. Questions for the Scientific Review Committee to consider: The 2001 field season collected a geographically comprehensive set of eggs from the interior and upstream and downstream margins of the Delta. Should selenium be assessed in these eggs? How important is it to do further work on methylmercury in avian eggs? Should field studies of reproductive success as it relates to mercury be attempted in addition to the monitoring of exposure and conducting laboratory tests?

4 Section B: Figures and Tables Table 3.A.1. Mean Mercury Concentrations (ppm wet weight) in Avian Eggs in San Francisco and Suisun Bays, Year 2000 Results. Means in excess of 0.5 ppm are bolded. Species Suisun Bay North Bay Central Bay South Bay Caspian Tern Forsters Tern D-C Cormorant Brandt s Cormorant Least Tern fail-to-hatch Clapper Rail fail-to-hatch Snowy Plover fail-to-hatch Great Egrets Great Blue Heron Snowy Egret Black -Crowned Night Heron Black-Necked Stilt California Gull Western Gull American Bittern (Davis) Mallard (Davis) 0.66 (3) 0.22 (14) 0.42 (1).14 (2).05 (2) (6) (11) (6) 1.04 (6) (6).19 (15).42 (2).07 (3) (15) 0.55 (3) 0.45 (1).13 (8).07 (4).34 (11).12 (2)

5 18 THG_DRY vs. MHG_DRY (Casewise MD deletion) MHG_DRY = * THG_DRY Correlation: r = MHG_DRY THG_DRY Regression 95% confid. figure 1.

6 140 Percent Methyl Mercury in Avian Eggs by species %METHYL DC Corm G Egret W Gull Avocet Stilt GB Heron Bittern Brandt's S egret Forsters Caspian BC Heron Mallard SPECIES ±1.96*Std. Dev. ±1.00*Std. Dev. Mean figure 2.

7 9 Correlation of mercury and selenium in avian eggs SE_DW = * HG_DRY Correlation: r = , p = SE_DW HG_DRY Regression 95% confid.

8 figure 3.