Chapter 4 -Environmental Monitoring of Mercury
To understand what happens to mercury emissions in the environment and how much of it people and other living things are exposed to, it is necessary to monitor the presence of the various forms of mercury in the overall environment and/or in specific environmental compartments such as air, water or fish. This chapter summarizes what has been learned from such studies in MA. It describes monitoring of mercury levels near the SEMASS MSWC facility; mercury sampling at hazardous waste disposal sites, particularly the Nyanza site in Ashland; monitoring of groundwater levels at six Massachusetts landfills; and the results of extensive fish monitoring studies in MA. The studies indicate that freshwater fish may be a significant potential source of exposure to mercury.
The SEMASS MSWC is a municipal solid waste to energy incinerator in Rochester, Massachusetts. As discussed in the previous section on MSWC mercury emissions, this facility is estimated to have emitted approximately 220 pounds of mercury to the air per year over the 1991-1994 period; this was the third lowest emission rate of the eight facilities for which stack test data are available.
An environmental monitoring program was conducted at this facility to provide baseline information prior to a proposed expansion of the plant and to investigate whether its emissions were detectably impacting the levels of mercury and other contaminants in the area surrounding the plant (SEMASS, 1993). At the time that this multimedia environmental monitoring program was conducted SEMASS had been operation for several years .
The approach to sampling was based on identification of the areas of likely maximum (downwind) and minimum (upwind) particulate deposition from the incinerator's smokestack. These areas were determined with the aid of an air dispersion modeling program.
Soil metals, including mercury, were sampled at locations 500 to 16,000 meters along transects radiating out from the stack to help validate the results of the modeling. In addition, within the high and low deposition areas, air, soils, water, aquatic sediments, terrestrial vegetation, fish, and cow's milk were sampled for mercury, a variety of other metals, dioxins, and furans. The ambient air monitoring program included total suspended particulate monitors for metals and polyurethane foam samplers for dioxins and furans at the designated high and low deposition sites. Each sample was collected over a 48 hour period.
Mercury concentrations were below detection limits in all air samples. Detection limits ranged from 0.3 to 2.8 ng/m3, depending on the volume of air pumped through the samplers. There was therefore no detectable effect of incinerator emissions on particulate mercury air concentrations at the sampling sites around the incinerator.
Soil mercury concentrations at all stations were either at or (most frequently) below detection limits of 0.1 mg/kg. There was no detectable spatial pattern in the mercury concentrations of surficial soils around the incinerator. Mercury concentrations in all water, aquatic sediment, vegetation and milk samples were at or below respective detection limits of 0.001 mg/L, 0.10 mg/kg, 0.01 mg/kg, and 0.001 mg/L. The mercury concentrations of pickerel muscle were not significantly different between fish from the lakes at the low and high impact areas. The mean mercury concentration in all these fish was 0.36 mg/kg wet weight with a standard deviation of 0.09. Conclusions on potential impacts on fish are somewhat limited in this study because only one species was tested and the data was not normalized on the basis of fish size.
Within the limits of its sensitivity, this study suggests that mercury emissions from the SEMASS MSWC have not, to date, detectably changed mercury concentrations in various environmental media surrounding the facility.
Under federal and state hazardous waste cleanup programs, sites that are determined to be the most damaging to the environment and public health are typically managed under the Federal Superfund program. Federal Superfund sites are investigated and remediated primarily by the USEPA. The MADEP Waste Site Cleanup Program participates with the USEPA on the work towards remediating these sites and, in addition, enforces regulations (MGL Chapter 21E) that control the investigation and cleanup of other potential and known waste sites in Massachusetts.
Due to the use of mercury in a number of industrial and manufacturing processes and products, mercury compounds have been found to be a contaminant at many hazardous material sites across the country. However, significant mercury contamination at Massachusetts hazardous waste sites appears to be restricted to a relatively few areas.
Of the approximately 6000 potential or known hazardous waste locations identified under the Massachusetts state waste site cleanup program, only a handful have mercury as a significant contaminant. The Nyanza Federal Superfund Site, discussed in more detail below, is the most significant site contaminated with mercury in Massachusetts. Other MA hazardous waste sites which are contaminated with mercury include a waste site in Amesbury, Massachusetts where the mercury is alleged to have resulted from operations at the former Merrimac Hat Factory which operated from 1856 to 1955. Two other sites being investigated for mercury contamination under the Department's revised waste site cleanup program regulations are the James River Corporation (Bolivar Street, Canton) and Bacon Felt Company on Old Colony Avenue, Taunton.
Additionally, Factory Pond, a small waterbody located in Hanover and Rockland is being investigated by the MADEP Bureau of Waste Site Cleanup (BWSC) due to mercury contamination of fish. In 1994 MADEP found high levels of mercury in fish from this waterbody. The testing was conducted as part of MADEP's fish monitoring program. The mercury levels detected in fish from this pond were some of the highest ever found in the history of the program. Since that time the BWSC has investigated the area and has learned that, from 1907 to 1973, an industrial park in Hanover was the site of a fireworks manufacturer, a World War II munitions plant, and a chemical research company. Sediment sampling of a stream in this watershed detected mercury at levels of 198 to 840 mg/kg in areas close to the munitions factory. Other sediment samples contained less than 1 mg/kg of this metal, suggesting that this factory may have been a primary source of the contamination. Additional site assessments and fish testing are being conducted on this watershed to better determine the extent and source of the mercury contamination.
In general, current hazardous waste sites that contain mercury constitute a minor overall source of new mercury contamination of the environment. However, in some instances possible exposures to mercury derived from such sites may pose unacceptable health risks to individuals living nearby. At these locations, work is underway to reduce and eliminate environmental levels that could result in a significant risk to human health and the environment. The Nyanza Superfund Site
In Massachusetts, the Nyanza Superfund Site is the largest identified site with mercury contamination. At Nyanza, Mercury has spread from the local source of release into the surrounding environment, adversely affecting an extensive area including several waterbodies. This is the major hazardous waste site with mercury contamination in Massachusetts. The Nyanza Chemical Waste Disposal Site covers approximately 35 acres in Ashland, Massachusetts, about 1000 feet south of the Sudbury River. From 1917 to 1978, this site was occupied by a number of different companies which were engaged in the manufacture of textile dyes and related products, the last of which was Nyanza, Inc.
Industrial processes employed by a number of the dye companies over the 60 year history of the site produced a variety of solid and liquid wastes. A major contaminant in these wastes was mercury which was used as a catalyst in dye manufacturing processes. Large quantities of industrial solid wastes and chemical sludges were disposed of on-site. Liquid wastes and process wastewaters were also partially treated and discharged directly into a wetland and two brooks known as Trolley Brook and Chemical Brook. Mercury eventually made its way into the Sudbury River and the Framingham Reservoirs by way of the brooks. It is estimated that the Nyanza Chemical Corporation was responsible for discharging up to 24,000 pounds of mercury into the brooks, resulting in contamination of the brook, sediments, topsoil and groundwater. In 1970, the Nyanza discharge was connected into the municipal sewer system so direct mercury discharges into the Sudbury River stopped.
In 1982, Nyanza was included as a site to be remediated under the federal Superfund Program. Since that time, the USEPA and MADEP have been working closely to investigate and remediate the site. As part of the site investigation, fish were taken from the Sudbury River and from Reservoirs #1 and #2 in Framingham in 1985 by the Division of Water Pollution Control of MADEP (then DEQE) and the Division of Fisheries and Wildlife. Average mercury levels in the fish from Reservoirs #1 and #2 were 1.2 ppm and 1.4 ppm, respectively. Mercury levels from fish taken at the sites along the river averaged somewhat below the federal action level of 1 ppm with some individual fish contaminated at higher levels. Based on these results the MADPH issued an advisory against eating fish caught along the entire length of the Sudbury River from Ashland to its confluence with the Assabet River in Concord where the Concord River begins, approximately 25 miles downstream of the Nyanza site.
In order to alert the public of the fish consumption advisory MADEP posted warning signs at 35 locations along the Sudbury River between Ashland and Concord. Posting of the Framingham Reservoirs is the responsibility of the Metropolitan District Commission (MDC), which posts these locations at least once a year.
Additional fish testing work in the Sudbury River was conducted by MADEP in 1987. Upon review of the mercury levels found in the sampled fish, the MADPH extended the fish consumption advisory to the Concord River. The extent to which the mercury contamination found in these fish is from the Nyanza site and/or from other sources is not known at this time.
A number of efforts have been undertaken to deal with the Nyanza site mercury contamination including groundwater and wetland remediation. Additionally, a number of research studies are currently underway that will provide additional technical information needed for remediating the Sudbury River. These include:
Developing Hydrologic data in Support of the Sediment Transport Model, by the Army Corps of Engineers.
Mercury Species Cycling and Transport below a Superfund Site on the Sudbury River, by the U.S. Geological Survey.
Assessment of the Bioavailability of Sediment-Associated Mercury in the Sudbury River, by US Fish and Wildlife Service.
Stratigraphy of Mercury in Depositional Sediments in the Sudbury River, by US Fish and Wildlife Service.
An Evaluation of Mercury-Contaminated Sediments from the Sudbury River using Freshwater Mussels: Bioaccumulation and Growth, by the National Oceanic & Atmospheric Administration.
The results of these studies will help to better define the human and ecological risks posed by mercury contamination of the Sudbury River and will provide information needed for the design and implementation of additional efforts to reduce these risks. Nonetheless it is anticipated that fish consumption advisories will need to remain in place for portions of the Sudbury River for an extended period of time. This is because the mercury already released into the River will persist there for an extended period of time; practical methods to quickly remove the dispersed mercury from the watershed do not presently exist.
At the end of their useful lives, common consumer and commercial products containing mercury are either recycled or discarded. If they are discarded, they either end up in an incinerator or a landfill. As long as the discarded mercury is securely contained within the confines of the landfill little immediate environmental risk exists. Migration out of the landfill is, however, a concern, especially for older facilities that generally do not have state-of-the-art containment and monitoring technologies installed. The issue is the potential for mercury, as well as other contaminants to enter groundwater, surface water runoff, or the air from the landfill. Potential chemical alterations of mercury in landfills that might lead to the production of methyl mercury are also of concern.
At this point there is not enough data to evaluate whether landfills are significant sources of anthropogenic mercury releases to the environment. Certainly, it is possible that landfills release mercury into the environment via groundwater and gasification. Compared to information on mercury emissions from solid waste combustion facilities, however, there is much less data on the fate of mercury in landfills.
Mercury may get into the air from a landfill if such items as batteries and lighting items are crushed, exposing the mercury to the air, and not quickly covered with daily fill. Following burial, vaporized elemental and organic mercury may still slowly diffuse through the daily cover or may contaminate "landfill gasses" (predominantly methane) that are usually vented or captured for energy production.
There have been only a few studies on this topic. Minnesota's 1993 Mercury-Containing Lamp Management Report cites studies in Sweden and Florida which did in fact detect mercury in landfill gas samples. The Minnesota report concluded, "these data suggest that mercury does evaporate from landfills." The USEPA used data from a Swiss landfill study (Fed. Reg. 59:(143), p38288, 1994) to estimate that only 0.0001 percent of all mercury loaded into municipal solid waste landfills escapes as a gas.
It is also possible, given certain conditions, for mercury in a landfill to contaminate a well or an aquifer. The literature shows, however, that this is unlikely if a landfill is properly designed (with a liner and leachate collection system) and operated according to federal standards. In order for mercury to contaminate groundwater, the following events would have to occur: first, the landfill would have to be unlined or the liner compromised; secondly, the mercury in the disposed products would have to be exposed to water entering the landfill; third, the pH of the landfill's moisture would need to be within a certain range to successfully leach mercury. According to several studies (Little, 1993; Minnesota, 1991), this scenario is possible, but for properly constructed and maintained landfills, unlikely. Of course, unlined landfills have a much greater likelihood of contaminating groundwater than lined landfills.
Should mercury enter a modern landfill's leachate, it would be captured by the leachate collection system. Depending on the level of treatment of this liquid, some mercury may remain in the final discharge. Treated leachate effluent is often discharged to a sewer system. Within the sewage treatment system mercury may be retained in sewage sludge which is either landfilled, incinerated or land-applied as a soil amendment. Mercury not retained in the sludge may be released into the air following volatilization or discharged to a river or bay from the wastewater treatment facility. Thus, mercury originally disposed of into a landfill may end up making its way into the overall environment via multiple pathways. This scenario highlights the true value of pollution prevention efforts in that they prevent this shuffling of contaminants from one medium to another. Landfills in Massachusetts
MSW landfills in Massachusetts accept household and commercial waste containing such items as batteries, fluorescent lights, thermometers and other sources of mercury. Massachusetts' landfill siting and design regulations are based on strict Federal standards and thus require landfills to be lined, operated with a leachate collection system and a groundwater monitoring program that includes routine sampling of water drawn from monitoring wells.
GROUNDWATER MONITORING AT LANDFILLS
It is important to note, however, that Massachusetts still has a number of unlined landfills which are either currently operating or have not been properly closed (capped). A properly capped landfill significantly decreases leachate generation and thus is an important method of groundwater protection. Unlined and/or uncapped landfills increase the probability that contaminants such as mercury will be mobilized from the site into groundwater. Mercury Monitoring Data for Six Massachusetts Landfills
A review of groundwater monitoring data submitted by six large MA landfills (MADEP, Division of Solid Waste Management, 1994), which accept a wide variety of waste, suggests that, while some mercury is being leached from these facilities, the levels have not to date presented a significant threat to drinking water supplies. MADEP reviewed these records in response to a USEPA request for information on mercury releases from non-hazardous waste landfills. In addition to the summary presented below, further information about this study can be found in Appendix C .
Data were analyzed from the following six solid waste landfills: Randolph; Plainville; BFI Fall River; Peabody NESWC; GCR Landfill Peabody; Greenfield Municipal Landfill. These landfills were selected based upon the broad spectrum of waste accepted at each facility, and the amount of data available at MADEP's Boston office at this time. Out of 592 individual leachate, groundwater, and surface water samples analyzed, there were seven exceedences of the Maximum Contaminant Level (MCL), or drinking water standard, for mercury (2 parts per billion or 0.002 mg/L). Five of the exceedences were detected at one landfill (Plainville) in the liquid recovered from the leachate collection system. The other two exceedences were both detected at one other landfill (Peabody); one was from a sample taken from a groundwater diversion manhole and the other was from a sample taken from a private well. However, this well is located cross-gradient from the landfill and it is unlikely that the mercury in the well was derived from the landfill.
Based on the limited data reviewed for these facilities, mercury is capable of being leached from municipal solid waste (see Appendix B). However the groundwater data shows no indication that mercury has moved beyond site boundries at the landfills examined. MADEP is currently analyzing data from other landfills across the Commonwealth to gather a more comprehensive picture of mercury's impact to groundwater via landfills.
Because the ambient water quality criteria for mercury (0.012 ppb for chronic exposure to aquatic life and 0.15 pbb to protect against potential human health effects attributable to fish contamination) are below the detection limits of most of the tests noted above, potential adverse effects on environmental receptors (e.g. fish and other aquatic life etc.) could not be assessed. Also, potential impacts on people who might consume fish contaminated with mercury escaping from specific landfills cannot be ruled out. In addition to requiring more sensitive chemical analysis, evaluating this issue would require determinations of the current volumes of contaminated groundwater discharging to surface waters from these landfills as well as estimates of past discharges. These factors have not been assessed at this time.
The potential mobilization of metallic mercury and methyl mercury via volatilization from landfills was also not assessed in this study. Based on results from other studies as noted above, releases via this pathway are possible but are, however, likely to be small.
By 1984 a coordinated program to analyze freshwater fish (the Toxics in Fish program) had been instituted by the Division of Water Pollution Control and the Division of Fish and Wildlife. This effort coincided with the construction of municipal and industrial water pollution control facilities that significantly reduced pollutant loadings to Massachusetts rivers and coastal waters. Fish from rivers in the process of recovering from severe environmental degradation were among the first to be sampled. For comparison, fish from lakes with no source of contamination were also analyzed.
Mercury in some of the fish from the "clean lakes" was considerably higher than fish from "polluted rivers". Levels from the clean lakes ranged from none detected to above 2 parts per million, though only a few fish in hundreds sampled had levels above 1 ppm. The rivers, by comparison, showed levels from 0.01 to 0.19 ppm. Variability in mercury loadings, sediment flushing, and species composition are likely to be involved in these differences.
More than 10 years of testing for toxics in freshwater fish has produced findings that show high mercury levels are as likely to be found in fish from lakes and ponds of otherwise high water quality than from rivers known to contain other contaminants in their water and sediments. This may result from the greater populations of anaerobic bacteria capable of methylating mercury in the still waters of lakes, combined with potential atmospheric, non-point sources of mercury.
The Toxics in Fish program presently has three major components. One consists of testing fish from specific waterbodies in response to public requests. This testing is a continuing, annual activity, conducted under the supervision of an Interagency Committee for Freshwater Fish Toxics Monitoring and Assessment composed of members of the Office of Research and Standards, the Office of Watershed Management, and the Wall Experiment Station from MADEP, MADPH and the MA Division of Fisheries and Wildlife. This component of the sampling tends to target those locations where known or suspected mercury pollution exists.
The second component of the Toxics in Fish program consists of sampling fish from locations within specific watersheds. The MADEP Office of Watershed Management is conducting a study of Massachusetts river basins of which chemical residues in fish is a significant part. The publication, The Role of Fish Tissue Monitoring in Evaluating and Managing Toxic Substances: A Summary of Massachusetts' Program (Isaac, Maietta & Johnson, 1992) describes the evolution of the fish testing program. This document also describes steps taken by various state agencies to protect health and assess the ecological effects of toxics in fish, including mercury. An extensive database of test results of freshwater fish is available through the Office of Watershed Management, MADEP, Grafton, Massachusetts. The report, Blackstone River Fish Toxics Monitoring (Maietta, 1993), provides data contrasting mercury accumulation in the same species of fish living in rivers heavily influenced by industrial pollution and those from unpolluted lakes.
Data from these two components of the MA fish monitoring program are summarized in Appendix E, Table 1. Over the period of 1982-1993, 28 species of freshwater fish were tested for mercury and other toxic compounds. For the 1,973 fish sampled over this period the overall mean mercury concentration was 0.35 ppm (median 0.22 ppm). Species specific summary data is presented in Appendix E, Table 1. Smallmouth bass, largemouth bass, black crappie and chain pickerel all had mean mercury concentrations that exceeded 0.5 ppm.
The third component of the Toxics in Fish program, begun in 1994, consists of research to investigate regional differences in fish mercury content, the relationship between fish mercury, water and sediment quality, and the range of variation in mercury content in Massachusetts freshwater fish. This project focuses on fish from ponds and lakes that are believed to have not been affected by point sources of mercury pollution. As a result, it should provide insight on "background" levels of mercury in fish and the relative contribution of non-point sources of mercury to these levels.
Three groups within MADEP designed this research project: the Office of Research and Standards, the Office of Watershed Management, and the Wall Experiment Station. Twenty-four lakes in three distinct ecological sub-regions, consisting of the Bristol/Narragansett Lowlands, the Worcester/Monadnock Plateau and the Green Mountain/Berkshires were selected for the study. Criteria for lake selections included the absence of human activities that could affect the waterbody. Thus lakes near farms, towns or settlements, golf courses, and industrial activity were rejected. Lakes of differing trophic status, or degrees of nutrient enrichment, were included. Three species of fish (nine individuals per species) were collected for analysis from each lake.
Preliminary data from this study are presented in Table 4-1 and Figure 4-1. The average concentrations of mercury in brown bullheads (Ictalurus nebulosus), largemouth bass (Micropterus salmoides) and yellow perch (Perca flavescens) are approximately 0.14 mg/kg, 0.40 mg/kg, and 0.31 mg/kg, respectively. It is important to note that these results are based on preliminary analysis of the data and have not been normalized on the basis of fish sizes; many of the fish sampled in this study were smaller than those generally consumed by recreational fisherpeople. Keeping these caveats in mind, the average mercury levels all fall below the MADPH trigger of concern for potential adverse health effects of 0.5 mg/kg. The frequency histograms (Figure 4-1), however, indicate that for all three species, and especially for the bass, many specimens exceeded the 0.5 mg/kg trigger. Thus, potentially unsafe levels of mercury exist in some fish from Massachusetts waterbodies not currently affected by specific point sources of mercury. Additional analysis of this data is underway, in an attempt to identify possible historical inputs of mercury, geographical variation in mercury concentrations and related questions.
|VARIABLE||BROWN BULLHEAD||LARGEMOUTH BASS||YELLOW PERCH|
|Geometric Mean of Concentration||0.114||0.054||0.239|
Because of the popularity of "put-and-take" recreational fishing it is important to note that freshwater fish which are part of the Massachusetts Division of Fisheries and Wildlife fish stocking program do not contain elevated amounts of mercury when stocked. Hatchery-raised fish grow fast as a result of a controlled, nutritious, pelletized diet and generally do not survive for long periods after stocking. This is especially true for most stocked trout. The rapid growth induced by a hatchery diet is reported to decrease fish longevity; most hatchery fish are also caught readily following stocking and are generally less able to compete with wild fish (Keller, personal communication).
In addition to state-sponsored research and monitoring activities, the private sector monitors and assesses contaminants in fish in response to state and federal environmental requirements. An example of such a study, which was described in more detail above, is the Environmental Baseline Monitoring Program prepared for the SEMASS MSWC in Rochester, Massachusetts by SAIC Engineering, Inc. Baseline conditions in the vicinity of the SEMASS facility were documented in air, water, soil, sediment, fish, vegetation and milk, to establish whether a proposed enlargement of operations would adversely affect environmental conditions. As previously noted, no significant differences were found between mercury levels from fish from "high impact" lakes that were predicted to be more affected by mercury air deposition from the facility, and "low impact" lakes that were less affected.
While potential human health risks are of most concern, mercury levels in Massachusetts freshwater fish are also a potential threat to fish-eating bird populations. The borderline amount of mercury in birds thought to produce clinical effects is 10 parts per million. Studies of loons conducted by scientists at Tufts Veterinary School show tissue mercury concentrations of loons averaging 28 parts per million (the lowest concentration in the study was 12 parts per million, the highest was 256 parts per million). Mercury can cause reproductive depression, immuno-suppression and behavioral changes in birds. Behavioral changes that have been observed in loons include deteriorating food-pecking ability, lack of balance and orientation, and an increase in aggressive encounters (Pokras, personal communication). Comparison with Public Health Standards
Freshwater fish represent a potential exposure route to mercury for humans and ecological communities. The environmental chemistry of mercury, which leads to its presence in freshwater bodies and sediments and its metabolism to methyl mercury, results in the potential for significant bioaccumulation of this metal in fish and subsequent exposures to humans and other fish eating predators; methyl mercury is often found at concentrations that are from 10,000-100,000-fold higher than in the waters in which the fish live (WHO, 1989). In contrast, mercury vapor at ambient levels in the atmosphere and mercury dissolved in freshwater bodies, including reservoirs, are generally not present at concentrations that pose a significant risk to human health.
The MADPH uses two guidelines to evaluate the acceptability of freshwater fish for human consumption. If fish are tested for mercury and are found to contain average levels of more than 0.5 ppm mercury, certain health advice is issued to the local public concerning the health effects of eating fish from that waterbody. The advice or "fish consumption advisory" depends on how high the mercury level is in the sample tested. A list of the waterbodies for which MADPH has issued fish consumption advisories is presented in Appendix E. An example of a MADPH consumption advisory and a summary of the criteria used by MADPH for issuing fish consumption advisories are also presented in Appendix E. In summary, if mercury levels exceed an average of 0.5 parts per million for a species of fish, sensitive populations (e.g. pregnant women, women who intend to become pregnant, nursing mothers and children under 12) are advised not to eat that species of fish from the lake. Others are advised to limit consumption to two meals per month. If mercury exceeds 1 part per million, the public is advised to refrain from eating any fish of that species from the waterbody.
The studies underway in Massachusetts and other states suggest that mercury in freshwater fish is a cause for concern in Massachusetts waters. Although many lakes, ponds and streams support fish populations whose mercury content is low enough that it is not a health problem, some fish in certain freshwater lakes and ponds contain high enough levels of mercury to justify the issuance of fish advisories for those lakes by MADPH. Levels of mercury found in fish samples from the 1994 research project, from 24 "clean" lakes and ponds in the state, ranged from none detected to 1.2 parts per million. The average mercury content in this sample of 550 fish was 0.28 parts per million, within levels deemed to be acceptable (0.5 ppm) by MADPH and many other state public health departments. None-the-less, many of the individual fish sampled contained mercury above 0.5 ppm. Additionally, although the overall mean concentration of mercury from the Fish Toxics monitoring program over 1982-1993 was less than the 0.5 ppm MADPH trigger level (see Appendix E) four species exhibited concentrations in excess of this value.
Preliminary results from the 1994 Toxics in Fish research program also demonstrate that mercury concentration tends to be species-specific. Bass, which are predators, are apt to be high in mercury. Mercury levels high enough to be a health concern are usually only found in large fish. After all of the data from the study are analyzed, it may be possible to document if variables such as lake type and geographic location can account for differences in mercury concentrations in fish in MA.
In addition to the fish consumption advisories for mercury that are presently in effect for specific waterbodies in Massachusetts, in September, 1994, MADPH also issued a statewide fish consumption advisory warning pregnant women that freshwater fish may contain unhealthful levels of mercury. This statewide advisory was established to protect the developing fetus, because of its susceptibility to the toxic effects of mercury. As discussed in the health effects section of this report, methyl mercury can cross the placenta and may even reach a higher concentration in the fetus than the mother. The small size of the unborn child and the processes of development of the brain and other organs add to mercury sensitivity at this stage.
Releasing larger sized fish including bass and pickerel rather than consuming them minimizes the risk associated with high mercury levels in sport fish. Large predatory fish, whether marine (like shark and swordfish) or freshwater (like largemouth bass, smallmouth bass and chain pickerel) are highest in mercury content. Comparison with Data from Other States
Maine has a robust database of fish mercury levels, having sampled 117 randomly selected lakes for predatory fish species (Staffords and Haines, 1994). The mean mercury in yellow perch was essentially equal in Maine (0.25 ppm) and Massachusetts (0.27 ppm). Mean mercury levels in largemouth bass in the Maine sample (0.57 ppm) were higher than Massachusetts largemouth bass (0.33 ppm). The difference may not be representative of real differences in fish mercury, however. It could be a result of larger fish in the Maine study. Since the Maine study analyzed composite samples of fish, the size of the individuals could not be factored into the pattern of distribution of mercury contamination.
Mercury in largemouth bass from California mountain lakes has been reported to range from 0.19 to 0.92 ppm, prompting the state Department of Health Services to recommend avoidance of fish from mountain lakes by pregnant women and children under 6 years of age (Stratton, et. al., 1987).
Montana reports low levels of mercury (e.g., 0.14 ppm for yellow perch). However, certain large predatory species can attain high levels (e.g., cutthroat trout=3 ppm in Silver Creek) (Phillips, G. & L. Bahls, 1994). California and Montana contain areas with mercury bearing ores.
The average values of mercury in species of freshwater fish reported by the National Study of Chemical Residues in Fish (USEPA 1992) are provided in Table 4-2. Three hundred and seventy four sites were tested in the USEPA study of chemical residues in fish. Mercury was detected at 92% of them. Measured concentrations ranged up to 1.77 parts per million. Two percent of the sites had mean mercury concentrations higher than 1 part per million. Most of the higher concentrations were in the Northeast. Interestingly, the site with the highest concentration was a site designated as background. Table 4-2
Average Values of Mercury in Freshwater Fish Species
MERCURY PRESENCE SPECIES (ppm) (% of sample) Bottom Feeders Carp 0.11 98% White sucker 0.11 95% Channel catfish 0.09 94% Redhorse sucker 0.27 93% Spotted sucker 0.12 90% Predators Largemouth bass 0.46 98% Smallmouth bass 0.34 100% Walleye 0.51 100% Brown trout 0.14 88% White bass 0.35 100% Northern pike 0.34 100% Flathead catfish 0.27 100% White crappie 0.22 71%
Flounder, pollock and soft-shell clams were among the earliest of Massachusetts marine fish and shellfish to be tested for contaminants, including mercury, by state environmental agencies. The MA fish testing program began in 1982 with studies of these species from Boston Harbor. Mercury levels averaged 0.04 ppm in pollock and 0.19 ppm in flounder. The maximum level in soft-shell clams was 0.19 ppm. The Division of Marine Fisheries continues to monitor these and other species. Recent test results of metal concentrations in winter flounder, American lobster and bivalve mollusks from Boston Harbor, Salem Harbor and coastal Massachusetts have been published (Schwartz et al., 1993, 1995). The latest results show that mercury was lowest in bivalve mollusks (average= 0.035 ppm). American lobster was highest in mercury (between 0.15-0.25 ppm in Boston Harbor). Winter flounder contained low levels (average = 0.14 ppm). Bivalves are filter feeders, lobster are detritus feeders and winter flounder are bottom feeders, characteristics that do not lend themselves to high levels of trophic transfer of mercury to their tissues.
Although these species exhibit low levels of mercury contamination, higher levels of mercury would be expected in larger, predatory marine fish. Species in which large individuals tend to be high in mercury concentrations include sharks, striped bass, tuna, bluefish, grouper, red snapper, swordfish and tilefish. Due to concerns over mercury, the USFDA recommends that pregnant women and those who may become pregnant, limit their consumption of shark and swordfish to one meal a month or less. Most of the commercial catch sold on the market is not tested for mercury or other contaminants. An exception is fish from foreign fishing fleets, from which limited samples of fish are tested. This is an area where additional sampling and analysis may be warranted.
Mercury's impacts can vary substantially depending on the nature and amount of the release. The local impacts can range from non-detectable, as in the case of the SEMASS facility, to widespread and serious, as at the Nyanza hazardous waste site. Fortunately, the Nyanza site is the only known example of such widespread local impacts in MA, and it resulted from uncontrolled hazardous waste disposal practices that are prohibited at present due to State and Federal hazardous waste management regulations.
Data to date suggest that mercury air emissions from municipal waste combustors with appropriate air pollution controls, as required by Massachusetts regulations, as well as groundwater impacts from lined and properly-operated landfills, are unlikely to cause significant changes in mercury levels in their local environments. However, more widespread effects due the integrated releases of mercury from multiple current and past sources over extended periods of time are indicated. In particular, some freshwater bodies appear to have been adversely impacted by such cumulative inputs. Consumption of fish from such waterbodies a potentially significant route of exposure to mercury.