Mercury concentrations in historic autopsies from Grassy Narrows First Nation

The Asubpeeschoseewagong Anishinabek (Grassy Narrows First Nation) have been engaged in a decades-long struggle to improve their health and environment after an industrial discharge of between 9000 and 11,000 kg of mercury (Hg) into their river system. Hg concentrations in freshwater fish, central to their cultural identity, livelihood and diet, were among the highest ever reported. Between 1972 and 1992, a Canadian government program measured Hg concentrations in routine autopsies from this community. In 2017, Grassy Narrows obtained their community's autopsy reports. The present study examined the distribution of total mercury (T-Hg) and inorganic mercury (I-Hg) in brain, organ, blood, and hair samples from 21 historic autopsy reports, spanning 1976 to 1986. T-Hg median in blood and hair were 6 ppb (range = 2.5-100) and 2.47 ppm (0.41-49.8), respectively. Hg was present in all brain regions (T-Hg median = 53 ppb, 13-299), with highest concentrations in the cerebellum (63 ppb, 16-365) and basal ganglia (58 ppb, 10-420). I-Hg constituted approximately 25 % of T-Hg in all brain regions. In organ samples, T-Hg was higher [renal medulla (290 ppb, 28-4400), renal cortex (1240 ppb, 100-6000), liver (300 ppb, 64-2400)], with greater proportion of I-Hg (82 %, 74 %, 63 %, respectively). Significant correlations were observed between T-Hg in hair and most brain regions (ρ = 0.70-0.77), blood (ρ = 0.56), and renal cortex (ρ = 0.61). While Hg accumulation in the cerebellum has been documented, the basal ganglia has seldom been an object of interest in the Hg scientific literature. The presence of Hg in the brain and other organs complement current studies on the long-term health consequences of Hg in this community. The findings further suggest the need for a closer examination of the role of basal ganglia in Hg-related disorders.