John Wiley & Sons, Ltd.

Development of a total dissolved solids (TDS) chronic effects benchmark for a northern Canadian lake

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Courtesy of John Wiley & Sons, Ltd.

Laboratory chronic toxicity tests with plankton, benthos, and fish early life stages were conducted with total dissolved solids (TDS) at an ionic composition specific to Snap Lake (NWT, Canada), which receives treated effluent from the Snap Lake Diamond Mine. Snap Lake TDS composition has remained consistent from 2007 to 2014 and is expected to remain unchanged through life of mine: chloride (45‐47%), calcium (20‐21%), sodium (10‐11%), sulfate (9%); carbonate (5‐7%), nitrate (4%), magnesium (2‐3%), and minor contributions from potassium and fluoride. TDS concentrations that resulted in negligible effects (i.e., 10 or 20% effect concentrations) to taxa representative of resident biota ranged from >1,100 to >2,200 mg/L with the exception of a 21% effect concentration of 990 mg/L for one of two early life stage fish dry fertilization tests (wet fertilization results were >1,480 mg/L). A conservative, site‐specific, chronic effects benchmark for Snap Lake TDS of 1,000 mg/L was derived, below the lowest negligible effect concentration for the most sensitive resident taxon tested, the cladoceran, D. magna (>1,100 mg/L). Cladocerans typically only comprise a few percent of the zooplankton community and biomass in Snap Lake; other plankton effect concentrations ranged from >1,330 to >1,510 mg/L. Chironomids, representative of the lake benthos, were not affected by >1,380 mg/L TDS. Early life stage tests with three fish species resulted in 10 to 20% effect concentrations ranging from >1,410 to >2,200 mg/L. The testing undertaken is generally applicable to northern freshwaters and the concept can readily be adapted to other freshwaters either for TDS where ionic composition does not change or for major ionic components where TDS composition does change. This article is protected by copyright. All rights reserved

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