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Geochemistry and toxicity of aluminum in the saguenay river, québec, Canada, in relation to discharges from an aluminum smelter

The transformation of bauxite to alumina, the first step in the production of metallic aluminum (Al), generates Al‐rich effluents. One installation is located near Jonquière (QC, Canada), with the effluents being discharged into the Saguenay River. We undertook an integrated geochemical and ecotoxicological study to determine if these Al discharges affected the receiving water. In the spring, summer, and autumn of 1997, samples of river water were collected from stations upstream and downstream of the effluent outfalls and from a regional reference site. Samples were analyzed for Al (e.g., particulate and dissolved Al, total monomeric and organic monomeric Al, dissolved polymeric Al) and for parameters known to affect Al speciation (pH, SO4, fluoride, dissolved organic carbon). Parallel samples were used for ambient toxicity tests with fathead minnow and Ceriodaphnia dubia. Concentrations of total Al (231‐596 μg/L) and dissolved Al (112‐344 μg/L) at downstream stations were 1.1 to 3.7 times higher than those at the station immediately upstream. Average levels of total and dissolved Al exceeded the Québec provincial criterion of 87 (μ acid‐recoverable Al/L, even at sites upstream of the plant. Inorganic monomeric Al at downstream stations ranged from 22 to 88 (μ/L. With the exception of a single elevated value observed at one downstream site, inorganic monomeric Al levels were> 75 μg/L. Other studies in soft neutral‐pH waters have shown that no toxic effects occur at this concentration of inorganic monomeric Al. None of the river water samples from stations 300 m downstream from the outfalls caused significant toxicity to C. dubia or fathead minnows. We suggest that expressing guidelines as monomeric inorganic Al would offer a more useful basis for comparison with ambient Al concentrations.