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(P293) Incorporation of arsenic bioavailability in ecological risk assessment.
Ollson, Christopher*,1, Hough, Christopher2, Koch, Iris1, Reimer, Kenneth1, 1 Royal Military College of Canada, Kingston, On, Canada2 Department of National Defence, Ottawa, On, Canada
ABSTRACT- A field-based ecological risk assessment was conducted in Yellowknife, NWT. The study consisted of characterizing arsenic in soil/tailings, plants and deer mice (Peromyscus maniculatus) from two arsenic contaminated mine sites. The average arsenic concentration in soils at trapping locations was 1630±1200 ppm. When soils were subjected to a gastric fluid extraction (GFE) only 2.5±2.0% of the arsenic was determined to be bioavailable. The predominant species extracted was As(V). Deer mice edible plants were collected from the trapping locations and had a mean arsenic concentration of 25±21 ppm. The predominant arsenic species detected in plants (methanol/water extraction) were arsenate As (V), arsenite As(III) and DMA. Only 33±20% of the total arsenic in plants was bioavailable using GFE. As(V) and As(III) were the dominant species with DMA also being detected in some samples. Arsenic concentrations ranged between non-detectable to 72 ppm (median 2.7) in deer mice tissues, with concentrations decreasing in the following order: stomach contents>skin (fur)>carcass>liver>kidney. As (III) and DMA were the predominant forms of arsenic in the tissues, with lesser amounts of arsenate and MMA also detected. This suggests that there is significant biotransformation of arsenic occurring in deer mice, from the ingestion of predominantly As (V) and conversion to As (III) and DMA. Using average total arsenic concentrations in soil, water and plants in traditional risk assessment calculations yielded an estimated daily intake (EDI) of 37 mg arsenic/kg body weight/day for mice. However, incorporation of an exposure time of six months (accounting for hibernation), the 2.5 % arsenic soil and 33% arsenic plant bioavailability factors results in a 15 fold decrease in the EDI (2.3 mg/kg body weight/day). This translates to a deer mouse hazard quotient of 2.0 when bioavailability is factored in. Therefore, ecological risk models that use total arsenic concentrations overestimate risk posed to small mammals.
Key words: arsenic, ecological risk assessment, bioavailability, speciation
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