SAHARAN DUST, PM10, BIOACTIVE AND BIOTOXIC METALS, AND HUMAN HEALTH IN A DUSTIER WORLD

Particulates in the atmosphere can reach exceptionally high concentrations in Mali (>11,000 µm m^-3), exceeding World Health Organization limits. Both natural processes (eroded mineral dust – Saharan dust) and human activities (petroleum and biomass combustion, etc.) produce airborne particulates. The most direct, proven threat to human health from air pollution is the concentration of fine particles in the air. Particles less than 10 µm in diameter (PM₁₀) can be inhaled and those less than 2.5 µm (PM_2.5) can reach the deepest regions of the lungs where gas exchange occurs. A growing body of literature shows a strong association between PM₁₀ and PM_2.5 concentrations and mortality from and hospital emergency admissions for heart attack and stroke. There is considerable evidence that PM_2.5 and PM₁₀ fractions cause and/or exacerbate cardiovascular disease. The mechanism has not been proven but inflammation through biochemical (cytokine) cascades is considered likely. In addition, transition metals such as iron, present in high concentrations in Saharan dust, are known to initiate oxygen radical formation which in turn can initiate inflammation. Some climate models predict increased periods of drought in a warmer world, with increased dust production in the Sahara/Sahel, the largest dust exporter in the world. In order to assess current air quality conditions in the dust source region, PM_2.5, PM₁₀, total suspended particulates, and the concentrations of 30 metals and metalloids in the PM₁₀ fraction were quantified over one year in Bamako, Mali. PM_2.5 and PM₁₀ concentrations exceeded U.S. Environmental Protection Agency (USEPA) and European Union (EU) limits for much of the year. Daily human inhalation of biotoxic and bioactive metals (e.g., As, Cu, Fe, U) in the respirable fraction of particulates (PM₁₀) was estimated and compared with USEPA and EU regulatory limits.