Virginia H. Garrison, U.S. Geological Survey, 600 Fourth Street South, St. Petersburg, FL 33701
Hundreds of millions of tons of African dust are transported annually from the Sahara and Sahel to the Caribbean and Americas in the west, and to Europe and Asia in the north and east. A similar dust system originating in Asia carries dust from the Gobi and Takli Makan deserts across China, Korea, Japan, and the northern Pacific to the Hawaiian Islands, and periodically continues eastward to Europe. These global atmospheric systems have been moving fine soil particles across oceans for hundreds of thousands of years. The quantity of dust transported varies interannually as a result of global climate, local meteorology, geomorphology of source areas, and more recently, human activities, with a documented increase in the amount of dust transported to the Caribbean over the past 40 years. We suggest that the composition of dust air masses has changed as a result of human activities in the source regions and the areas over which the dust travels: burning of biomass and waste; widespread use of pesticides, plastics, other synthetic organics, and pharmaceuticals; and increased industrialization. A series of pilot projects was initiated to test our hypothesis that African dust air masses carry viable microorganisms, trace metals, and persistent organic pollutants (POPs) thousands of kilometers to the Americas and the Caribbean, and that these contaminants and eroded mineral soils may adversely affect downwind ecosystems and human health. POPs, trace metals, and hundreds of types of viable microorganisms, including known pathogens, have been identified in air samples from the Sahel (Republic of Mali) and from dust events in the Caribbean (U.S. Virgin Islands and Trinidad). Air samples from source regions (Mali) have been shown to contain orders of magnitude more viable microorganisms per volume than air samples from dust events in the Caribbean; air samples from dust events in the Caribbean contain 3-4 times the concentration of cultureable microbes than from non-dust conditions. Trace-metal concentrations were found to be similar to average crustal composition, with slight enrichment of lead in Mali. Preliminary findings indicate a greater number of POPs, most of them in higher concentrations in Mali than in Caribbean air samples during dust events. Many of the identified POPs are known to act as toxins, carcinogens, immune-system suppressors, and/or endocrine disruptors in humans and other organisms. Preliminary ecotoxicology tests indicate African dust collected in the Caribbean is highly toxic to the sensitive life stages of some marine organisms. Identification of toxic components is underway, as are toxicity tests on additional coral reef species. Possible causal links between African dust and pediatric asthma emergency-room admissions in Trinidad are currently being investigated. Concentrations of aerosols smaller than 10 Ám (PM10) and 2.5 Ám (PM2.5), particle-surface composition (particularly PAHs and metals), POPs, microorganisms, and pollens are of interest. Findings from these exploratory studies will guide subsequent research on the effects of the African dust-associated contaminants on coral reef organisms and human health in the Caribbean. We welcome collaborations with soil scientists and scientists from other disciplines to expand our understanding of erosion processes in the source region, surface physical properties and chemical composition of transported soil particles, and the changes that occur on and to particles during long-distance transport.
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