Abstract
Biofilms can be used as a biomonitoring tool to determine metal bioavailability in streams affected by mining and other anthropogenic activities. Surface water and biofilm were sampled over two years from rivers located in the vicinity of a mine located in a Nordic ecosystem (Nunavik, Quebec). Biofilm metal content (Cd, Cu, and Ni) as well as a variety of physicochemical properties were determined to examine relationships between metal accumulation and water quality. Among the three metals of interest, copper and nickel had the highest levels of accumulation and cadmium had the lowest. When considering the exposure levels, nickel was the most abundant metal in our sampling sites. Both exposure and accumulation levels were consistent over time. Biofilm metal content was highly correlated to the ambient free metal ion concentration for sites of circumneutral pHs for all three metals. When the surface water pH was below 6, biofilm metal content was much lower than at other sites with similar aqueous metal concentrations of exposure. This apparent protective effect of decreasing pH can be explained by proton competition with dissolved metals for uptake binding sites at the surface of the organisms within the biofilm as described by the Biotic Ligand Model principles. The relationships obtained for Cd and Cu were overlapping those observed in previous publications, indicating strong similarities in metal accumulation processes in biofilms over very large geographical areas. Although more data are needed for Ni, our results show that biofilms represent a promising metal biomonitoring tool.
Highlights
The demand for base metals has been sharply increasing worldwide since industrialization [1].Anthropogenic activities involving metals, such as mining, have led to a growing mobilization of elements on a global scale [2]
Sunda and Guillard [3] showed that copper uptake by marine phytoplankton was not related to the total copper concentration, but rather to the free cupric ion activity
Despite the simplicity of the BLM principles, the exact impact of water composition on metal bioavailability requires a fairly large amount of data. This includes data on water chemistry, the thermodynamics of metal-ligand complexes, metal binding to transport sites of the target organism, and the impacts of each pertinent, potentially competing ion that could provide a protective effect against metal uptake and toxicity
Summary
The demand for base metals has been sharply increasing worldwide since industrialization [1]. Despite the simplicity of the BLM principles, the exact impact of water composition on metal bioavailability requires a fairly large amount of data This includes data on water chemistry (e.g., ionic composition, organic carbon concentrations), the thermodynamics of metal-ligand complexes, metal binding to transport sites of the target organism, and the impacts of each pertinent, potentially competing ion that could provide a protective effect against metal uptake and toxicity. From an ecologic perspective, biofilms are known to play a key role in aquatic systems, as they are involved in nutrient cycling (e.g., organic matter decomposition) They are at the base of the food chain and accumulated metals can be transferred to grazers [27,28,29]. We fully characterized the water chemistry to identify any potential parameters required to develop a predictive tool for metal bioavailability using stream biofilms
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