Tanya Suvendrini Lena’s research while affiliated with Women's College Hospital and other places

Background The watershed in Asubpeeschoseewagong Netum Anishinabek (Grassy Narrows First Nation) territory has been contaminated by mercury (Hg) since 1962, resulting in very high Hg concentrations in fish, central to the community’s culture, traditions, economy and diet. Biomarkers of Hg exposure (umbilical cord blood and hair/blood samples), monitored between 1970 and 1997, decreased over time. A recent Grassy Narrows Community Health Assessment (GN-CHA) survey included current symptoms of nervous system dysfunction. The present study aimed to cluster self-reported symptoms and examine their associations with past Hg exposure. Methods The GN-CHA included 391 adults. Symptom clustering used a two-step segmentation approach. Umbilical cord Hg and/or yearly measurements of equivalent hair Hg were available for 242 participants. Structural Equation Models (SEM) displayed the associations between Hg exposure and clusters, with Hg exposure modelled as a latent variable or in separate variables (prenatal, childhood and having had hair Hg ≥ 5 μg/g at least once over the sampling period). Longitudinal Mixed Effects Models (LMEM) served to examine past hair Hg with respect to clusters. Results A total of 37 symptoms bonded into 6 clusters, representing Extrapyramidal impairment, Sensory impairment, Cranial nerve disturbances, Gross motor impairment, Neuro-cognitive deficits and Affect/Mood disorders. Median Hg concentrations were 5 μg/L (1–78.5) and 1.1 μg/g (0.2–16) for umbilical cord and childhood hair, respectively. More than one-third (36.6%) had hair Hg ≥ 5 μg/g at least once. In SEM, latent Hg was directly associated with Extrapyramidal and Sensory impairment, Cranial nerve disturbances and Affect/Mood disorders. Direct associations were observed for prenatal exposure with Affect/Mood disorders, for childhood exposure with Extrapyramidal impairment and Cranial nerve disturbances, and for hair Hg ≥ 5 μg/g with Extrapyramidal and Sensory impairment. For all clusters, a further association between past Hg exposure and symptom clusters was mediated by diagnosed nervous system disorders. LMEM showed higher past hair Hg among those with higher scores for all clusters, except Affect/Mood disorders. Conclusion Our findings provide evidence that in this First Nation community, past Hg exposure from fish consumption was associated with later-life clusters of coexisting symptoms of nervous system dysfunction.

Background: The watershed in Asubpeeschoseewagong Netum Anishinabek (Grassy Narrows First Nation) territory has been contaminated by mercury (Hg) since 1962, resulting in very high Hg concentrations in fish, central to the community’s culture, traditions, economy and diet. Biomarkers of Hg (umbilical cord blood and hair/blood samples), monitored between 1970 and 1997, decreased over time. A recent Grassy Narrows Community Health Assessment (GN-CHA) survey included current symptoms of nervous system dysfunction. The present study aimed to cluster self-reported symptoms and examine their relation to past Hg exposure. Methods: The GN-CHA included 391 Registered adult Band members. Symptom clustering used a two-step segmentation approach. Umbilical cord Hg and yearly measurements of hair Hg were available for 242 participants. Longitudinal Mixed Effects Models (LMEM) served to examine past hair Hg with respect to clusters. Structural Equation Models (SEM) displayed direct and indirect pathways between Hg exposure and clusters, with Hg exposure modelled as a latent variable or in separate time periods (prenatal, childhood and having had hair Hg ≥ 5µg/g at least once). Results: A total of 37 symptoms bonded into 6 clusters, representing Extrapyramidal impairment, Sensory impairment, Cranial nerve disturbances, Gross motor impairment, Neuro-cognitive deficits and Affect/Mood disorders. Median Hg concentrations were 5µg/L (1-78.5) and 1.1µg/g (0.2-16) for umbilical cord and childhood hair, respectively. More than one-third (36.6%) had hair Hg ≥ 5 µg/g at least once. LMEM shows higher long-term hair Hg among those with higher scores for most clusters. In SEM, latent Hg is directly and indirectly associated with all clusters. The contribution of prenatal exposure is mediated by childhood exposure, except for Affect/Mood disorders, where the association is direct. Hair Hg ≥ 5 µg/g is directly related to Extrapyramidal and Sensory impairment. Conclusion: Our findings provide evidence that in this First Nation community, past Hg exposure from fish consumption was associated with later-life clusters of coexisting symptoms of nervous system dysfunction. Given the complexity of the interrelations between the various determinants of chronic health problems in this and other First Nation communities, LMEM and SEM methods provide the opportunity to trace direct and/or indirect effect routes of potential “causal impact”.