Metal contamination in residential snow and indoor dust near the Horne Smelter: a citizen-science study in Rouyn-Noranda, Quebec.

The Horne Smelter (Rouyn-Noranda, Quebec) is the only copper smelter in Canada and a major source of atmospheric emissions of toxic metals, including lead (Pb), arsenic (As), and cadmium (Cd). Biomonitoring studies have reported elevated exposure in nearby residents, yet limited data are available on the immediate residential environment. As part of a citizen-led initiative, residents collected indoor dust and snow to characterize indoor and outdoor residential metal contamination. Samples were collected from 23 residences and adjacent grounds located 540 to 2,080 m from the smelter. Cu, Pb, Cd, As, Zn, and Cr concentrations were measured, and their relationships with smelter location (distance and wind direction) and selected residential characteristics were examined. Metal concentrations in snow and indoor dust generally decreased with increasing distance from the smelter. Accounting for both distance and wind direction, smelter location explained 73% (Cu, Cr), 58% (Cd, Pb), 56% (As), and 44% (Zn) of the variability in snow metal concentrations (p < 0.01). For indoor dust, distance explained 36% (Cu), 33% (Cd), 29% (Pb), and 15% (As) of the variability (p < 0.01 for all except As, p < 0.10). Copper, used as a tracer of smelter activity, was strongly associated with other metals in both matrices (R2 > 70% in snow). Few associations were observed between indoor dust metal concentrations and residential characteristics after adjustment for distance. These findings highlight the smelter's dominant influence on residential metal contamination. This participatory study demonstrates the value of citizen science for site-specific environmental monitoring and for generating locally relevant evidence in communities affected by industrial emissions.