Comparative study of arsenic toxicosis and ocular pathology in wild muskrats (Ondatra zibethicus) and red squirrels (Tamiasciurus hudsonicus) breeding in arsenic contaminated areas of Yellowknife, Northwest Territories (Canada).

The Giant Mine is an abandoned gold mine in Yellowknife, Northwest Territories, Canada. Throughout its operation from 1948 to 2004, the Giant Mine released heavy amounts of arsenic trioxide into the environment, thus contaminating the soil and surface water within and around the vicinity of the mine site. Chronic arsenic (As) poisoning negatively impacts wildlife health and can induce multi-organ damages including neurodegeneration and visual dysfunction depending on concentration and duration of exposure. The aim of the current study was to comparatively assess retina layer changes and prevalence of ocular lesions in wild rodent populations (i.e. muskrats and red squirrels) breeding in arsenic endemic areas of Yellowknife, near the vicinity of the abandoned Giant mine site (∼2 km radius), at an intermediate location (approximately 20 km from the mine area) as well as a reference location (spanning 52-105 km from the city of Yellowknife, Canada). Eye globes were removed from euthanized muskrats and squirrels from the three sampling locations with increasing distance from the Giant mine area. Optical Coherence Tomography (OCT) was used to attempt a pan-retinal layer assessment, and histologic examination was utilized for assessment and confirmation of ocular lesions. The retinal layers were measured and statistically compared between the groups based on sampling locations to enhance the scope of histologic evaluations. The preliminary results revealed that thicknesses of ganglion cell layer (GCL), retina nerve fibre layer (NFL), and inner retina layer (IR) were statistically reduced in the muskrats from arsenic endemic area, particularly near the vicinity of the Giant mine compared to the control group. Generalized ocular pathology was histologically confirmed in all the muskrats from the arsenic endemic areas with the manifestation of moderate to severe lymphocytic plasmacytic uveitis (LPU), keratitis and subcapsular cataracts. Inner retinal degeneration was also observed in all the muskrats from the arsenic endemic areas, while muskrats from the control group were predominantly normal. Three muskrats from the control group were noted to have a mild LPU and keratitis. Significant histopathologic changes were not detected in the squirrel eyes from the three groups except for incidental mild cornea scars from all the locations. In general, these preliminary findings confirm the presence of ocular lesions and retina abnormalities in wild muskrats in the Yellowknife area and provide the first evidence of visual dysfunction and impairment in wildlife inhabiting arsenic endemic areas of Canada.