Geochemistry and toxicity of aluminum in the Saguenay River, Quebec, 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 Jonquiere (QC, Canada), with the effluents being discharged i nto the Saguenay River. We undertook an integrated geochemical and ecotoxic ological study to determine if these Al discharges affected the receiving w ater. in the spring, summer, and autumn of 1997, samples of river water wer e collected from stations upstream and downstream of the effluent outfalls and from a regional reference site. Samples were analyzed for Al (e.g., par ticulate and dissolved Al, total monomeric and organic monomeric Al, dissol ved polymeric Al) and for parameters known to affect Al speciation (pH, SO4 , fluoride, dissolved organic carbon). Parallel samples were used for ambie nt toxicity tests with fathead minnow and Ceriodaphnia dubia. Concentration s of total Al (231-596 mu g/L) and dissolved Al (112-344 mu g/L) at downstr eam stations were 1.1 to 3.7 times higher than those at the station immedia tely upstream. Average levels of total and dissolved Al exceeded the Quebec provincial criterion of 87 mu g acid-recoverable Al/L, even at sites upstr eam of the plant. Inorganic monomeric Al at downstream stations ranged from 22 to 88 mu g/L. With the exception of a single elevated value observed at one downstream site, inorganic monomeric Al levels were <75 mu g/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 samp les from stations 300 m downstream from the outfalls caused significant tox icity to C. dubia or fathead minnows. We suggest that expressing guidelines as monomeric inorganic Al would offer a more useful basis for comparison w ith ambient Al concentrations.