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Enhanced level of toxic methylmercury in the aquatic environment caused by hydroelectric dams


Exploiting Canadian hydroelectric resources is a key component of North American plans for meeting future energy demands by using carbon neutral energy resources. Unfortunately, flooding of soils lead to enhanced releases of CO2, methane (CH4), and methylmercury (MeHg) for decades produced by microbial production under the associated changes in geochemical conditions. Impact of CO2 and CH4 release reduce the positive balance of the otherwise carbon neutral energy resource globally. Yet, MeHg is a strong neurotoxin that bioaccumulates in aquatic organisms and biomagnifies along the food-chain and thereby adversely affects the local environment and humans who rely on local food resources. Interestingly, all 22 Canadian hydroelectric facilities being considered for near-term development are located within 100 km of indigenous communities. Previous studies have investigated how reservoir characteristics influence MeHg levels in water and fish within and downstream of the reservoir,  following the flooding and the years after. However a prospective analysis of health risks for humans relying on food from local ecosystems under the influence of hydroelectric power expansion is lacking.

Rapids at the Churchill river in Canada
Figure: This image is credited to American Chemical Society

The new study:
A group of researchers from the U.S. now modeled peak MeHg enrichment relative to measured baseline conditions for a facility in Labrador, Canada (Muskrat Falls) by considering (a) potential MeHg enrichment in the flooded reservoir, (b) MeHg accumulation in the downstream environment (an estuary known as Lake Melville), (c) MeHg biomagnification in country foods, and (d) shifts in MeHg exposures for Inuit individuals. The researchers combined direct measurements and modeling of future environmental concentrations with data collected from local residents and from other flooded regions.

The probabilistic model predicts that the flooding at Muskrat Falls likely will increase MeHg 10-fold in the impounded river and 2.6-fold in the river water downstream of the reservoir. Due to bioaccumulation and biomagnification, MeHg concentrations in fish, birds and seals living in this ecosystem likely will increase up to 10-fold. Inuit populations using these species as a source of food, will be exposed to these enhanced MeHg levels that may exceed U.S. EPA’s reference dose for over half of the young children and women of childbearing age. The model predicts equal or even greater aqueous MeHg concentrations relative to Muskrat Falls for 11 sites across Canada. The researchers therefore emphasized the need for mitigation measures prior to flooding.

The original studies

Ryan S.D. Calder, Amina T. Schartup, Miling Li, Amelia P. Valberg, Prentiss H. Balcom, Elsie M. Sunderland, Future Impacts of Hydroelectric Power Development on Methylmercury Exposures of Canadian Indigenous Communities, Environ. Sci. Technol., 50/23 (2016) 13115-13122. DOI: 10.1021/acs.est.6b04447

Related studies (newest first)

B. Meng, X. Feng, G. Qiu, Z. Li, H. Yao, L. Shang, H. Yan, The impacts of organic matter on the distribution and methylation of mercury in a hydroelectric reservoir in Wujiang River, Southwest China, Environ. Toxicol. Chem., 35/1 (2016) 191-199. DOI: 10.1002/etc.3181

James J. Willacker, Collin A. Eagles-Smith, Michelle A. Lutz, Michael T. Tate, Jesse M. Lepak, Joshua T. Ackerman, Reservoirs and water management influence fish mercury concentrations in the western United States and Canada, Sci. Total Environ., 568 (2016) 739–748. DOI: 10.1016/j.scitotenv.2016.03.050

K.R. Rolfhus, J.P. Hurley, R.A. Bodaly, G. Perrine, Production and retention of methylmercury in inundated boreal forest soils. Environ. Sci. Technol., 49/6 (2015) 3482-3489. DOI: 10.1021/es505398z

Z. Dong, R.C. Jim, E.L. Hatley, A.S. Backus, J.P. Shine, J.D. Spengler, L.A.  Schaider, A longitudinal study of mercury exposure associated with consumption of freshwater fish from a reservoir in rural south central USA. Environ. Res., 136 (2015) 155-62. DOI: 10.1016/j.envres.2014.09.029

D. Kasper, B.R. Forsberg, J.O.H. Amaral, R.P. Leitao, S.S. Py-Daniel, W.R. Bastos, O. Malm, Reservoir Stratification Affects Methylmercury Levels in River Water, Plankton, and Fish Downstream from Balbina Hydroelectric Dam, Amazonas, Brazil. Environ. Sci. Technol., 48/2 (2014) 1032-1040. DOI: 10.1021/es4042644

John E. Gray, Mark E. Hines, Harland L. Goldstein, Richard L. Reynolds, Mercury deposition and methylmercury formation in Narraguinnep Reservoir, southwestern Colorado, USA, Appl. Geochem., 50 (2014) 82–90. DOI: 10.1016/j.apgeochem.2014.09.001

M. Anderson, Duration and extent of elevated mercury levels in downstream fish following reservoir creation, River Syst., 19/3 (2011) 167-176. DOI: 10.1127/1868-5749/2011/019-0023

John E. Gray, Mark E. Hines, Biogeochemical mercury methylation influenced by reservoir eutrophication, Salmon Falls Creek Reservoir, Idaho, USA, Chem. Geol., 258 (2009) 157–167. DOI: 10.1016/j.chemgeo.2008.09.023

A. Robin Stewart, Michael K. Saiki, James S. Kuwabara, Charles N. Alpers, Mark Marvin-DiPasquale, David P. Krabbenhoft, Influence of plankton mercury dynamics and trophic pathways on mercury concentrations of top predator fish of a mining-impacted reservoir, Can. J. Fish. Aquat. Sci., 65 (2008) 2351–2366. DOI: 10.1139/F08-140

Sabine Castelle, Jörg Schäfer, Gerard Blanc, Stephane Audry, Henri Etcheber, Jean-Pierre Lissalde, 50-year record and solid state speciation of mercury in natural and contaminated reservoir sediment, Appl. Geochem., 22 (2007) 1359–1370. DOI: 10.1016/j.apgeochem.2007.03.025

M. Mailman, L. Stepnuk, N. Cicek, R.A. Bodaly, Strategies to lower methyl mercury concentrations in hydroelectric reservoirs and lakes: A review. Sci. Total Environ., 368/1 (2006) 224-235. DOI: 10.1016/j.scitotenv.2005.09.041

B.D. Hall, V.L. St. Louis, K.R. Rolfhus, R.A. Bodaly, K.G. Beaty, M.J. Paterson, K.A.P. Cherewyk, Impacts of reservoir creation on the biogeochemical cycling of methyl mercury and total mercury in boreal upland forests. Ecosystems, 8/3 (2005) 248-266. DOI: 10.1007/s10021-003-0094-3

V.L. St. Louis, J.W. Rudd, C.A. Kelly, R. Bodaly, M.J. Paterson, K.G. Beaty, R.H. Hesslein, A. Heyes, A.R. Majewski, The Rise and fall of mercury methylation in an experimental reservoir. Environ. Sci. Technol., 38/5 (2004) 1348-1358. DOI: 10.1021/es034424f

R. Schetagne, R. Verdon, Post-impoundment evolution of fish mercury levels at the La Grande Complex, Queìbec, Canada (from 1978 to 1996). In: Mercury in the Biogeochemical Cycle; M. Lucotte, et al., Eds.; Springer, 1999; pp 235.258.

A. Mucci, S. Montgomery, M. Lucotte, Y. Plourde, P. Pichet, H.V. Tra,  Mercury remobilization from flooded soils in a hydroelectric reservoir of northern Quebec, La Grande-2: results of a soil resuspension experiment. Can. J. Fish. Aquat. Sci., 52/11 (1995) 2507-2517. DOI: 10.1139/f95-841

S.M. Allen-Gil, D.J. Gilroy, L.R. Curtis, An Ecoregion Approach to Mercury Bioaccumulation by Fish in Reservoirs, Arch. Environ. Contain. Toxicol. 28 (1995) 61-68. DOI: 10.1007/BF00213970

D. Brouard, J.-F. Doyon, R. Schetagne, Amplification of Mercury Concentrations in Lake Whitefish (Coregonus clupeaformis) Downstream from the La Grande 2 Reservoir, James Bay, Quebec. In: Mercury Pollution Integration and Synthesis; C.J. Watras, J.W. Huckabee,  Eds.; CRC Press, 1994, 369-380.

R. Verdon, D. Brouard, C. Demers, R. Lalumiere, M. Laperle, R. Schetagne, Mercury evolution (1978-1988) in fishes of the La Grande hydroelectric complex, Quebec, Canada. Water, Air, Soil Pollut., 56 (1991) 405-417. DOI: 10.1007/BF00342287

T.A. Johnston, R. Bodaly, J. Mathias, Predicting fish mercury levels from physical characteristics of boreal reservoirs, Can. J. Fish. Aquat. Sci., 48/8 (1991) 1468-1475. DOI: 10.1139/f91-174

A. Ray Abernathy, Peter M. Cumbie, Mercury accumulation by largemouth bass (Micropterus salmoides) in recently impounded reservoirs, Bull.  Environ. l Contam. Toxicol., 17/5 (1977) 595–602. DOI: 10.1007/BF01685984

Related EVISA Resources

Link database: Toxicity of Organic mercury compounds
Brief summary: Speciation and Toxicity
Link database: Human exposure to methylmercury via the diet

Related EVISA News

October 9, 2016: Tracking down the source of human exposure to mercury by analyzing human hair
December 13, 2013: Most Canadians having dental amalgam in their mouth are exposed to mercury at levels surpassing the reference exposure level (REL)
November 20, 2013: EPA Study: Mercury Levels in Women of Childbearing Age Drop 34 Percent
October 12, 2013: Minamata Convention is adopted
March 22, 2013: Mercury isotope fractionation provides new tool to trace the source of human exposure
January 21, 2013: UNEP mercury treaty exempts vaccines for children
January 14, 2013: Mercury Levels in Humans and Fish Around the World Regularly Exceed Health Advisory Levels
December 24, 2012: Mercury in food – EFSA updates advice on risks for public health

December 9, 2012: Mercury in fish more dangerous than previously believed; Scientists urge for effective treaty ahead of UN talks
June 17, 2012: Factors Affecting Methylmercury Accumulation in the Food Chain
August 21, 2009: USGS Study Reveals Mercury Contamination in Fish Nationwide
February 11, 2009: Mercury in Fish is a Global Health Concern
October 30, 2008: Precautionary approach to methylmercury needed
March 11, 2007: Methylmercury contamination of fish warrants worldwide public warning
February 9, 2006: Study show high levels of mercury in women related to fish consumption
January 12, 2005: Number of fish meals is a good predictor for the mercury found in hair of environmental journalists
April 27, 2004: FDA/EPA recommends pregnant women to restrict their fish consumption because of methylmercury content

last time modified: November 7, 2018


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