title: Bioaccumulation and trophic transfer of mercury and selenium in african sub-tropical fluvial reservoirs food webs (Burkina Faso).
abstract: The bioaccumulation and biomagnification of mercury (Hg) and selenium (Se) were investigated in sub-tropical freshwater food webs from Burkina Faso, West Africa, a region where very few ecosystem studies on contaminants have been performed. During the 2010 rainy season, samples of water, sediment, fish, zooplankton, and mollusks were collected from three water reservoirs and analysed for total Hg (THg), methylmercury (MeHg), and total Se (TSe). Ratios of δ13C and δ15N were measured to determine food web structures and patterns of contaminant accumulation and transfer to fish. Food chain lengths (FCLs) were calculated using mean δ15N of all primary consumer taxa collected as the site-specific baseline. We report relatively low concentrations of THg and TSe in most fish. We also found in all studied reservoirs short food chain lengths, ranging from 3.3 to 3.7, with most fish relying on a mixture of pelagic and littoral sources for their diet. Mercury was biomagnified in fish food webs with an enrichment factor ranging from 2.9 to 6.5 for THg and from 2.9 to 6.6 for MeHg. However, there was no evidence of selenium biomagnification in these food webs. An inverse relationship was observed between adjusted δ15N and log-transformed Se:Hg ratios, indicating that Se has a lesser protective effect in top predators, which are also the most contaminated animals with respect to MeHg. Trophic position, carbon source, and fish total length were the factors best explaining Hg concentration in fish. In a broader comparison of our study sites with literature data for other African lakes, the THg biomagnification rate was positively correlated with FCL. We conclude that these reservoir systems from tropical Western Africa have low Hg biomagnification associated with short food chains. This finding may partly explain low concentrations of Hg commonly reported in fish from this area.
authors: Groupe de recherche interuniversitaire en limnologie, Département de sciences biologiques, Université de Montréal, Montréal, Québec, Canada.
authors: Ousséni
authors: O
authors: Ouédraogo
authors: Environment Canada, National Wildlife Research Centre, Carleton University, Ottawa, Ontario, Canada.
authors: John
authors: J
authors: Chételat
authors: Groupe de recherche interuniversitaire en limnologie, Département de sciences biologiques, Université de Montréal, Montréal, Québec, Canada.
authors: Marc
authors: M
authors: Amyot
mesh_terms: D000818:Animals; D002050:Burkina Faso; D017753:Ecosystem; D004784:Environmental Monitoring; D005399:Fishes; D020387:Food Chain; D005618:Fresh Water / Q000032:analysis* / Q000737:chemistry*; D005843:Geography; D008628:Mercury / Q000032:analysis*; D012307:Risk Factors; D012643:Selenium / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*; D015048:Zooplankton
chemical_list: D014874:Water Pollutants, Chemical; D008628:Mercury; D012643:Selenium