ESTIMATING THE POTENTIAL FOR REES TO IMPACT AQUATIC ORGANISMS.
James McGeer1, Alex Loveridge1, O. Vukov1, Che Lu1, J. Ford1, H. Leonard1, A. Carvajal2 and D Scott
Smith2
1
Dept of Biology; 2 Dept. of Chemistry and Biochemistry
Wilfrid Laurier University, Waterloo, ON.
ABSTRACT
The toxicological understanding of rare earth elements (REEs) in the aquatic environment is very limited.
This can result in excessively conservative approaches when establishing discharge objectives and water
quality guidelines/criteria. There currently are no water quality guidelines or criteria for REEs. The
overall objectives of this research are to contribute towards the understanding of the potential impacts of
REEs in aquatic environments and to determine the influence of water chemistry on toxicological
responses. In this particular project the toxicity modifying influences of cationic competition (Ca, Mg and
Na) and dissolved organic matter (DOM) on the toxicity of Ce, Sm, Dy and Tm to fish (e.g. rainbow trout)
and sensitive invertebrates (e.g. Hyalella azteca and Daphnia pulex) was assessed with the goal of
developing toxicity prediction models. Standard methods (Environment Canada) were used for culture and
testing which was done in intermediate hardness waters (60 mg/L CaCO 3, pH 7.2, Ca 0.5 mM, Mg 0.15
mM). The protective effect of cationic competition was tested with Ca (0.1 to 2.0 mM), Mg (0.03 to 0.5
mM) and Na (0.1 to 2.0 mM) and in general Ca and sometimes Na mitigated the impact of REEs but Mg
generally did not. As well, DOM reduced toxicity of all the elements tested. The pH of test solutions had
a significant influence on toxicity with low pH resulting reduced Dy toxicity. Geochemical equilibrium
modeling approaches such as the biotic ligand model were applied to simultaneously estimate toxicity
under different water chemistry conditions. This research was funded by NSERC and Environment
Canada via the Strategic Grants Program.
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(B)
(A)
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LC50 Dy3+ (nM)
LC50 Dy3+ (nM)
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Ca2+
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Na+
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(µM)
Figure 1 – Effect of Ca2+ (left) and Na+ (right) concentration on the acute toxicity of Dy3+ to the aquatic
invertebrate Hyalella azteca. Symbols show the 96 h LC50 value (the Dy3+ concentration that induced
70
5000
50%
Dy3+ concentrations were estimated from
(C) lethality over 96 h) with 95% confidence intervals. (D)
measured
60 dissolved Dy concentrations using the Windermere Humic Aqueous Model (WHAM ver 7.02).
4000
50
LC50 Dy3+ (nM)
LC50 Dy3+ (nM)
KEYWORDS
REEs, aquatic,
toxicity,
water
quality,
biotic
ligand
model 3000
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Mg2+
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(µM)
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H+
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(µM)
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