Walpole Island First Nation (WIFN) is surrounded by water and relies on the St. Clair River for their traditional food, drinking water and economy. WIFN has been subjected to the effects of both waterborne and airborne pollution for decades because of its physical location north-west of Detroit and downriver from Sarnia's Chemical Valley, a huge petrochemical complex in Southwestern Ontario, which is estimated to release 20% of all industrial pollutants in Ontario.
This study measured the various chemical forms of mercury and arsenic in traditional foods (particularly fish), drinking water and environmental samples (St Clair River water and sediments) at Walpole Island. Hair, blood and urine samples were taken from community residents to determine mercury and arsenic body burden. Also, a food frequency questionnaire and a 24-hour dietary recall survey were administered to capture the frequency of consumption of common food items available to the community.
The results showed that the concentration of mercury found in water samples from the St Clair River (raw water entering the WIFN treatment plant and treated water leaving the plant) were below the maximum acceptable concentration (MAC). Arsenic levels in sediments and water were of no concern. Mercury was detected in all sediment samples with the highest concentrations found in samples collected near St. Clair River and Johnson Channel and with the lowest concentrations detected in sediments further away from the St. Clair River.
The concentrations of mercury and arsenic in fish species were generally low. Only one sample of fish species, smallmouth bass, exceeded the Health Canada mercury guideline of 0.5 ppm. All other mercury concentrations in muscle were 0.2 ppm or lower. Human biomonitoring for mercury and arsenic indicated that there was no significant environmental exposure to arsenic and mercury among members of the WIFN.