African dust, coral reefs and human health


OVERVIEW
Hundreds of millions of tons of mineral dust are transported thousands of miles through the atmosphere from the Sahara and Sahel of Africa to the Caribbean and the Americas every year.  We are investigating whether African dust is playing a role in coral reef declines throughout the Caribbean region, and if African dust has a negative effect on human health.  If so, what processes are involved? We are sampling dust in the air (aerosols) in the dust source region (Mali), off the coast of Africa (Cape Verde Islands), and at downwind sites in Tobago (southeastern Caribbean) and St. Croix (US Virgin Islands, northeastern Caribbean) for laboratory toxicity testing, and for identification of chemical and biological contaminants.  Chemical contaminants [pesticides, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs), and metals] and microorganisms have been identified in dust air samples from all sites. Testing the toxicity of dust on marine organisms, microorganisms including pathogens, and humans (human cells and fluids) is the next step.


SUMMARY OF FINDINGS
1. Chemical contaminants: (banned and current use pesticides, PAHs and PCBs) have been identified in air samples from the US Virgin Islands (USVI), Trinidad and Tobago, and the Cape Verde Islands during dust conditions, and from Mali.  Air samples from Mali contained significantly higher concentrations of the same suite of contaminants than USVI, Trinidad, and Cape Verde air samples. The contaminants persist in the environment, bioaccumulate, and are bio-toxins known to affect one or more of the following: endocrine, immune, hepatic, neurological, and reproductive systems.  Some act as carcinogens, mutagens, and/or teratogens.
2. Preliminary identification has been made of >300 species of microorganisms cultured from air samples collected on St. Croix, St. John (USVI) and Trinidad during dust and non-dust conditions.  Fifty isolates have been identified using molecular techniques. Air samples collected during dust events in the USVI and Trinidad contain approximately 2-8 times as many culturable microorganisms per volume as do air samples collected during non-dust conditions. Of those taxa identified to date, 25% are known plant pathogens and 10% are known opportunistic pathogens of humans. 
3. Air in Mali contains orders of magnitude more microorganisms per volume than air sampled in the downwind areas (USVI, Trinidad, and Cape Verde) and more species. Of the hundreds of microorganisms cultured and isolated from Sahara and Sahel (Mali, West Africa) air samples, DNA sequencing has been used to identify 50 species of bacteria (and 3 genera of fungi).  Of the culturable bacteria identified thus far, 10% are known animal pathogens, 5% are plant pathogens, and 27% are opportunistic human pathogens.
4. The pathogenic strain of the fungus known to cause sea fan disease and mortality of sea fans throughout the Caribbean region has been isolated from:
a. air samples collected in the USVI during African dust conditions but not from non-dust periods. 
b. soil from the Sahel (Mali).

CURRENT STUDIES
Air samples collected in 2008 in Mali, Tobago and the US Virgin Islands will be tested for:
a. > 3,000 bacterial taxa, including known human , plant, and animal pathogens, including coral pathogens. 
b. heavy metal content (e.g., Cu, As, Pb, Se, Cd)
c. biomobility and bioavailability of metals in four human fluid models.
d. toxicity to marine organism cell cultures, and marine organisms and gametes.
e. toxicity to human cell cultures.
f. effects on coral pathogens.