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(P294) Arsenic toxicity testing: the importance of chemical speciation and dissolved oxygen condition.
Irving, Elaine*,1, Liber, Karsten1, Xie, Q.2, Kerrich, Robert2, Culp, Joseph3, Lowell, Rick3, 1 Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada2 Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, Canada3 National Water Research Institute, Saskatoon, Saskatchewan, Canada
ABSTRACT- In the aquatic environment arsenic (As) predominantly exists as two inorganic species, As(III), As(V), which may differ in toxicity. Arsenic toxicity tests are often conducted under the assumption that speciation remains stable throughout the test. Yet As(III) can be oxidized to As(V), and As(V) reduced to As(III), depending on abiotic and biotic conditions. In addition to speciation, low dissolved oxygen (DO) condition may also be a confounding factor in toxicity testing. This study addressed these concerns using the test organism Hyalella azteca. A series of 10-d As(III) and As(V) tests were conducted under high (6.5 mg/L) and low (3.5 mg/L) DO conditions. H. azteca were moved to new exposure vessels every 48 h to limit As speciation changes, which were monitored using combined HPLC-ICP-MS. Additional vessels were added during the As(III) exposure under low DO conditions, where H. azteca were also exposed to the same solution for 10 d. Speciation, physicochemical variables and bacteria numbers were monitored in all vessels. As(III) speciation at 0.1 and 1 mg/L remained stable after 48 h, but 0.1 mg/L As(III) oxidized to As(V) after 3 d, while 1 mg/L As(III) still remained stable. 1 mg/L As(III) later oxidized to As(V), which was detected after 6 d. Physiochemical variables remained constant, but bacteria increased in these exposure solutions. Overall, As(III) appeared to be more toxic than As(V), but the difference in toxicity was not as pronounced as previously determined for Chironomus tentans. As(III) oxidized to As(V) in a dose dependant manner, likely due to bacteria present in the vessels, which has important implications for As toxicity assessment.
Key words: arsenic speciation , dissolved oxygen , toxicity, Hyalella azteca
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