MEMORANDUM

TO: DOCKET FOR TOXICS MACT

FROM: CHRISTINE DAIVS, RISK AND BENEFITS GROUP

SUBJECT: ECOSYSTEM EFFECTS FOR PROPOSED RULE

DATE: 3/31/2011

Due to space limitations, we were unable to include the full text for the ecosystem effects of 

mercury deposition in the preamble for the RIA and the Appropriate and Necessary Finding for the 

Toxics MACT proposed rule. We provide this memo to the docket as documentation of the ecosystem 

effects to support the information in the communication materials. 

5.3 IMPACT OF MERCURY ON ECOSYSTEMS AND WILDLIFE

5.3.1 INTRODUCTION

Deposition of mercury to waterbodies can also have an impact on ecosystems and wildlife. Mercury 

contamination is present in all environmental media with aquatic systems experiencing the greatest exposures 

due to bioaccumulation. Bioaccumulation refers to the net uptake of a contaminant from all possible 

pathways and includes the accumulation that may occur by direct exposure to contaminated media as well as 

uptake from food.

Atmospheric mercury enters freshwater ecosystems by direct deposition and through runoff from 

terrestrial watersheds. Once mercury deposits, it may be converted to organic methylmercury mediated 

primarily by sulfate-reducing bacteria. Methylation is enhanced in anaerobic and acidic environments, greatly 

increasing mercury toxicity and potential to bioaccumulate in aquatic foodwebs. A number of key 

biogeochemical controls influence the production of methylmercury in aquatic ecosystems. These include 

sulfur, pH, organic matter, iron, mercury “aging”, and bacteria type and activity (Munthe et al.2007).

Wet and dry deposition of oxidized mercury is a dominant pathway for bringing mercury to 

terrestrial surfaces. In forest ecosystems, elemental mercury may also be absorbed by plants stomatally, 

incorporated by foliar tissues and released in litterfall (Ericksen et al., 2003). Mercury in throughfall, direct 

deposition in precipitation, and uptake of dissolved mercury by roots (Rea et al., 2002) are also important in

mercury accumulation in terrestrial ecosystems. 

Soils have significant capacity to store large quantities of atmospherically deposited mercury where it 

can leach into groundwater and surface waters. The risk of mercury exposure extends to insectivorous 

terrestrial species such as songbirds, bats, spiders, and amphibians that receive mercury deposition or from 
aquatic systems near the forest areas they inhabit (Bergeron et al. 2010a, b; Cristol et al. 2008; Rimmer et al. 

2005; Wada et al. 2009 & 2010).

Numerous studies have generated field data on the levels of mercury in a variety of wild species. 

Many of the data from these environmental studies are anecdotal in nature rather than representative or 

statistically designed studies. The body of work examining the effects of these exposures is growing but still 

incomplete given the complexities of the natural world. A large portion of the adverse effect research 

conducted to date has been carried out in the laboratory setting rather than in the wild; thus, conclusions 

about overarching ecosystem health and population effects are difficult to make at this time. In the sections 

that follow numerous effects have been identified at differing exposure levels. 

5.3.2 EFFECTS ON FISH

A review of the literature on effects of mercury on fish (Crump and Trudeau, 2009) reports results 

for numerous species including trout, bass (large and smallmouth), northern pike, carp, walleye, salmon and 

others from laboratory and field studies. The effects studied are reproductive and include deficits in sperm 

and egg formation, histopathological changes in testes and ovaries, and disruption of reproductive hormone 

synthesis. These studies were conducted in areas from New York to Washington and while many were 

conducted by adding MeHg to water or diet many were conducted at current environmental levels. While we 

cannot determine at this time whether these reproductive deficits are affecting fish populations across the 

United States it should be noted that it is possible that over time reproductive deficits could have an effect on 

populations. Lower fish populations would conceivably impact the ecosystem services like recreational fishing 

derived from having healthy aquatic ecosystems quite apart from the effects of consumption advisories due to

the human health effects of mercury.

The Integrated Science Assessment for Oxides of Nitrogen and Sulfur – Ecological Criteria (Final 

Report, 2008) presents information regarding the possible complementary effects of sulfur and mercury 

deposition. The ISA has concluded that there is a causal relationship between sulfur deposition and increased 

mercury methylation in wetlands and aquatic environments. This suggests that lowering the rate of sulfur 

deposition would also reduce mercury methylation thus alleviating the effects of aquatic acidification as well 

as the effects of mercury on fish.

5.3.3 EFFECTS ON BIRDS

In addition to effects on fish, mercury also affects avian species. In previous reports (EPA 1997 and 

CAMR 2005) much of the focus has been on large piscivorous species, in particular the common loon. The 

loon is most visible to the public during the summer breeding season on northern lakes and they have 

become an important symbol of wilderness in these areas (McIntyre and Barr 1997). A multitude of loon 

watch, preservation, and protection groups have formed over the past few decades and have been 

instrumental in promoting conservation, education, monitoring, and research of breeding loons (McIntyre 
and Evers 2000, Evers 2006). Significant adverse effects on breeding loons from mercury have been found to 

occur, including behavioral (reduced nest-sitting), physiological (flight feather asymmetry), and reproductive 

(chicks fledged/territorial pair) effects (Evers 2008, Burgess 2008) and reduced survival (Mitro, et al 2008). 

Additionally Evers et al. (2008) report that they believe that results from their study integrating the effects on 

the endpoints listed above and evidence from other studies the weight of evidence indicates that populationlevel effects negatively impacting population viability occur in parts of Maine and New Hampshire, and 

potentially in broad areas of the loon’s range. 

Recently attention has turned to other piscivorous species such as the white ibis and great snowy 

egret. While considered to be fish-eating generally these wading birds have a diverse diet including crayfish, 

crabs, snails, insects and frogs. These species are experiencing a range of adverse effects due to exposure to 

mercury. The white ibis has been observed to have decreased foraging efficiency (Adams and Frederick 

2008). Additionally ibises have been shown to exhibit decreased reproductive success and altered pair 

behavior at chronic exposure to levels of dietary MeHg commonly encountered by wild birds (Frederick and 

Jayasena 2010). These effects include significantly more unproductive nests, male/male pairing, reduced 

courtship behavior (head bobbing and pair bowing) and lower nestling production by exposed males. In this 

study a worst-case scenario suggested by the results could involve up to a 50% reduction in fledglings due to 

MeHg in diet. These estimates may be conservative if male/male pairing in the wild resulted in a shortage of 

partners for females and the effect of homosexual breeding were magnified. In egrets mercury has been 

implicated in the decline of the species in south Florida (Sepulveda, et al. 1999) and Hoffman (2010) has 

shown that egrets experience liver and possibly kidney effects. While ibises and egrets are most abundant in 

coastal areas and these studies were conducted in south Florida and Nevada, the ranges of ibises and egrets 

extend to a large portion of the United States. Ibis territory can range inland to Oklahoma, Arkansas and 

Tennessee. Egret range covers virtually the entire United States except the mountain west. Insectivorous birds 

have also been shown to suffer adverse effects due to current levels of mercury exposure. These songbirds 

such as Bicknell’s thrush, tree swallows and the great tit have shown reduced reproduction, survival, and 

changes in singing behavior. Exposed tree swallows produced fewer fledglings (Brasso 2008), lower survival 

(Hallinger 2010) and had compromised immune competence (Hawley 2009). The great tit has exhibited 

reduced singing behavior and smaller song repertoire in an area of high contamination in the vicinity of a 

metallurgic smelter in Flanders (Gorissen 2005). While these effects were small and would likely have little 

effect on population viability in such a short-lived species.

5.3.4 EFFECTS ON MAMMALS
In mammals adverse effects have been observed in mink and river otter collected in the wild in the 

northeast where atmospheric deposition from municipal waste incinerators and electric utilities are the largest 

sources (USEPA 1999), both fish eating species. For otter from Maine and Vermont maximum 

concentrations on Hg in fur nearly equal or exceed a concentration associated with mortality. Concentrations

in liver for mink in Massachusetts/Connecticut and the levels in fur from mink in Maine exceed 

concentrations associated with acute mortality (Yates 2005). Adverse sub-lethal effects may be associated with 

lower Hg concentrations and consequently be more widespread than potential acute effects. These effects 

may include increased activity, poorer maze performance, abnormal startle reflex, and impaired escape and 

avoidance behavior (Scheuhammer et al. 2007). Conclusions

The studies cited here provide a glimpse of the scope of mercury effects on wildlife particularly 

reproductive and survival effects at current exposure levels. These effects range across species from fish to 

mammals and spatially across a wide area of the United States. The literature is far from complete however. 

Much more research is required to establish a link between the ecological effects on wildlife and the effect on 

ecosystem services (services that the environment provides to people) for example recreational fishing, bird 

watching and wildlife viewing. EPA is not, however, currently able to quantify or monetize the benefits of 

reducing mercury exposures affecting provision of ecosystem services.

5.3.5 REFERENCES

Adams, Evan M., and Frederick, Peter C. Effects of methylmercury and spatial complexity on foraging 

behavior and foraging efficiency in juvenile white ibises (Eudocimus albus). Environmental 

Toxicology and Chemistry. Vol 27, No. 8, 2008. 

Bergeron, CM., Bodinof, CM., Unrine, JM., Hopkins, WA. (2010a) Mercury accumulation along a 

contamination gradient and nondestructive indices of bioaccumulation in amphibians. 

Environmental Toxicology and Chemistry 29(4), 980-988.

Bergeron, CM., Bodinof, CM., Unrine, JM., Hopkins, WA. (2010b) Bioaccumulation and maternal transfer of 

mercury and selenium in amphibians. Environmental Toxicology and Chemistry 29(4), 989-997. 

Brasso, Rebecka L., and Cristol, Daniel A. Effects of mercury exposure in the reproductive success of tree 

swallows (Tachycineta bicolor). Ecotoxicology. 17:133-141, 2008.

Burgess, Neil M., and Meyer, Michael W. Methylmercury exposure associated with reduced productivity in 

common loons. Ecotoxicology. 17:83-91, 2008.

Cristol D. A., Brasso R. L., Condon A. M., Fovargue R. E., Friedman S. L., Hallinger K. K., Monroe A. P., 

White A. E. (2008) The movement of aquatic mercury through terrestrial food webs. Science 320, 

335–335.

Crump, Kate L., and Trudeau, Vance L. Mercury-induced reproductive impairment in fish. Environmental 

Toxicology and Chemistry. Vol. 28, No. 5, 2009.
Ericksen, J. A., Gustin, M. S., Schorran, D. E., Johnson, D. W., Lindberg, S. E., & Coleman, J. S. (2003). 

Accumulation of atmospheric mercury in forest foliage. Atmospheric Environment, 37(12), 1613-

1622.

Evers, D.C., 2006. Status assessment and conservation plan for the common loon (Gavia immer) in North 

America. U.S. Fish and Wildlife Service, Hadley, MA, USA.

Evers, David C., Savoy, Lucas J., DeSorbo, Christopher R., Yates, David E., Hanson, William, Taylor, Kate 

M., Siegel, Lori S., Cooley, John H. Jr., Bank, Michael S., Major, Andrew, Munney, Kenneth, Mower, 

Barry F., Vogel, Harry S., Schoch, Nina, Pokras, Mark, Goodale, Morgan W., Fair, Jeff. Adverse 

effects from environmental mercury loads on breeding common loons. Ecotoxicology. 17:69-81, 

2008.

Frederick, Peter, and Jayasena, Nilmini. Altered pairing behavior and reproductive success in white ibises 

exposed to environmentally relevant concentrations of methylmercury. Proceedings of The Royal 

Society B. doi: 10-1098, 2010.

Gorissen, Leen, Snoeijs, Tinne, Van Duyse, Els, and Eens, Marcel. Heavy metal pollution affects dawn 

singing behavior in a small passerine bird. Oecologia. 145: 540-509, 2005.

Hallinger, Kelly K., Cornell, Kerri L., Brasso, Rebecka L., and Cristol, Daniel A. Mercury exposure and 

survival in free-living tree swallows (Tachycineta bicolor). Ecotoxicology. Doi: 10.1007/s10646-010-

0554-4, 2010.

Hawley, Dana M., Hallinger, Kelly K., Cristol, Daniel A. Compromised immune competence in free-living 

tree swallows exposed to mercury. Ecotoxicology. 18:499-503, 2009.

Hoffman, David J., Henny, Charles J., Hill, Elwood F., Grover, Robert A., Kaiser, James L., Stebbins, 

Katherine R. Mercury and drought along the lower Carson River, Nevada: III. Effects on blood and 

organ biochemistry and histopathology of snowy egrets and black-crowned night-herons on 

Lahontan Reservoir, 2002-2006. Journal of Toxicology and Environmental Health, Part A. 72: 20, 

1223-1241, 2009.

McIntyre, J.W., Barr, J.F. 1997Common Loon (Gavia immer) in: Pool A, Gill F (eds) The Birds of North 

America. Academy of Natural Sciences, Philadelphia, PA, 313

McIntrye, J.W., and Evers, D.C.,(eds)2000. Loons: old history and new finding. Proceedings of a Symposium 

from the 1997 meeting, American Ornithologists’ Union. North American Loon Fund, 15 August 

1997, Holderness, NH, USA.

Mitro, Matthew G., Evers, David C., Meyer, Michael W., and Piper, Walter H. Common loon survival rates 

and mercury in New England and Wisconsin. Journal of Wildlife Management. 72(3): 665-673, 2008.

Munthe, J., Bodaly, R. A., Branfireun, B. A., Driscoll, C. T., Gilmour, C. C., Harris, R., et al. (2007). Recovery 

of Mercury-Contaminated Fisheries. Environmental Science & Technology, 36(1), 33-44.

Rea, A. W., Lindberg, S. E., Scherbatskoy, T., & Keeler, G. J. (2002). Mercury Accumulation in Foliage over 

Time in Two Northern Mixed-Hardwood Forests. Water, Air, & Soil Pollution, 133(1), 49-67.

Rimmer, C. C., McFarland, K. P., Evers, D. C., Miller, E. K., Aubry, Y., Busby, D., et al. (2005). Mercury 

Concentrations in Bicknell’s Thrush and Other Insectivorous Passerines in Montane Forests of 

Northeastern North America. Ecotoxicology, 14(1), 223-240.
Scheuhammer, Anton M., Meyer Michael W., Sandheinrich, Mark B., and Murray, Michael W. Effects of 

environmental methylmercury on the health of wild birds, mammals, and fish. Ambio. Vol.36, No.1, 

2007. 

Sepulveda, Maria S., Frederick, Peter C., Spalding, Marilyn G., and Williams, Gary E. Jr. Mercury 

contamination in free-ranging great egret nestlings (Ardea albus) from southern Florida, USA. 

Environmental Toxicology and Chemistry. Vol. 18, No.5, 1999.

U.S EPA (Environmental Protection Agency). 2008. Integrated Science Assessment (ISA) for Oxides of 

Nitrogen and Sulfur – Ecological Criteria (Final Report). EPA/600/R-08/082F. U.S. Environmental 

Protection Agency, National Center for Environmental Assessment- RTP Division, Office of 

Research and Development, Research Triangle Park, N.C. Available at 

http://cfpub.epa.gov/ncea/cfm/recorddisplay.cfm?deid+201485.

U.S. Environmental Protection Agency (EPA). 1997. Mercury Study Report to Congress. Volume V: Health 

Effects of Mercury and Mercury Compounds. EPA-452/R-97-007. U.S. EPA Office of Air Quality 

Planning and Standards, and Office of Research and Development.

U.S. Environmental Protection Agency (U.S. EPA). 2005. Regulatory Impact Analysis of the Final Clean Air 

Mercury Rule. Office of Air Quality Planning and Standards, Research Triangle Park, NC., March; 

EPA report no. EPA-452/R-05-003. Available on the Internet at 

<http://www.epa.gov/ttn/ecas/regdata/RIAs/mercury_ria_final.pdf

U.S. Environmental Protection Agency (U.S. EPA).1999. 1999 National Emission Inventory Documentation 

and Data—Final Version 3.0; Hazardous Air Pollutants Inventory—FinalNEI Version 3; HAPS 

Summary Files. (12 December 2006;www.epa.gov/ttn/chief/net/1999inventory.html)Wada, H. and Cristol, 

D.A. and McNabb, F.M.A. and Hopkins, W.A. (2009) Suppressed adrenocortical responses and 

thyroid hormone levels in birds near a mercury-contaminated river. Environmental Science & 

Technology 43(15), 6031-6038.

Wada., H., Yates, DE., Evers, DC., Taylor, RJ., Hopkins, WA. (2010) Tissue mercury concentrations and 

adrenocortical responses of female big brown bats (Eptesicus fuscus) near a contaminated river. 

Ecotoxicology. 19(7), 1277-1284.

Yates, David E., Mayack, David T., Munney, Kenneth, Evers David C., Major, Andrew, Kaur, Taranjit, and 

Taylor, Robert J. Mercury levels in mink (Mustela vison) and river otter (Lonra canadensis) from 

northeastern North America. Ecotoxicology. 14, 263-274, 2005.