Residential Proximity to Metal-Emitting Industries and Toenail Metal Concentration in the US Gulf States

The US Gulf region is heavily reliant on metal-emitting petrochemical and manufacturing industries. We sought to characterize associations between residential proximity to metal-emitting sites and toenail metal concentration in men from four US states along the Gulf of Mexico with particular attention to potential differential exposure burden by race. We measured toenail concentrations of arsenic, chromium, lead, manganese, mercury, and selenium using inductively coupled plasma mass spectrometry in 413 non-smoking men from the Gulf Long-term Follow-Up Study (2011-2013). Point sources of industrial metal emissions were identified using the US EPA's National Emissions Inventory (NEI) database and mapped to geocoded participant residential addresses. For each metal, we examined relationships between toenail metal concentrations and linear distance to the nearest metal emitting site, inverse distance weighted number of emissions sites, and inverse distance weighted volume of air metal emissions within 30 km radial buffers of participant residences using multivariable linear regression. Results were stratified by self-reported race. Compared to self-identified White participants, Black participants lived closer to NEI sites but had 23-70% lower toenail concentrations of arsenic, chromium, mercury, manganese, and selenium adjusting for personal/behavioral factors. Toenail lead concentration was positively associated with residential proximity to leademitting NEI sites though the relationship was significantly attenuated after adjustment for neighborhood-level socioeconomic factors such as poverty level and age of housing stock. Residential proximity to lead-emitting NEI sites in the Gulf region is associated with a higher body burden of lead as measured in the toenail. This relationship may be driven in part by nonNEI factors related to residence in industry-adjacent neighborhoods. Further research into dietary/occupational exposures is needed to explain the unexpected racial disparities in metal body burden in this population.