Sampling station in Bamako, Mali.
Sal Island, Cabo Verde.
Galera Point, Trinidad.
To date, banned and current-use pesticides, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCB congeners) have been identified in dust event air samples collected from the African Sahara/Sahel (Mali), offshore from the African continent (Cape Verde), and from the Caribbean (Trinidad-Tobago and the U.S. Virgin Islands). Air samples from Mali contained significantly higher concentrations of the same suite of contaminants than U.S. Virgin Islands, Trinidad, Tobago, and Cape Verde air samples. Mixtures of multiple persistent organic contaminants and bioactive metals occurred in all dust air mass samples. Dioxins and furans were detected only in air samples from the source region. All of these contaminants are known to persist in the environment, bioaccumulate, and be toxic to organisms, including humans, at low concentrations. All are known to affect one or more of the following: endocrine, immune, hepatic, neurological, and reproductive systems. Some act as carcinogens, mutagens, and/or teratogens. Only a few metals were enriched over mean upper crustal concentrations, primarily lead in Mali. This was likely a reflection of use of petrol containing lead in Mali (until February 2008) and in Trinidad (until 2006).
Bioaccessibility of some metals with known or suspected human/ecosystem health risks generally was greater in the eastern Caribbean following long-range transport than in the dust-source region (Mali). Inhalation and ingestion exposure pathways were explored by extraction of the samples using simulated lung and gastric fluids. Some sample metal concentrations exceeded EPA residential soil screening levels (SSls) and ecological (ECO) SSLs and are under further investigation.
Air samples collected during dust events in the U.S. Virgin Islands and Trinidad contained approximately 2-8 times as many cultureable microorganisms per volume as did air samples collected during non-dust conditions. Air in Mali contained orders of magnitude more cultureable microorganisms per volume than air sampled in the downwind areas (U.S. Virgin Islands, Trinidad, and Cape Verde) and more taxa.
The pathogenic strain of the fungus known to cause sea-fan disease and mortality of sea fans throughout the Caribbean region was isolated from:
- air samples collected in the U.S. Virgin Islands during African dust conditions but not from non-dust periods.
- soil from the Sahel (Mali).
Recent molecular data (PhyloChip) detailing types of bacteria in the dust source-region and the eastern Caribbean sites are currently being analyzed. No known pathogens (other than plant pathogens) were identified from any site (Mali, Tobago and VI).
Inhalable dust particles (PM2.5 and PM10)
Particles less than 100 μm can be inhaled by humans. Only particles smaller than 10 μm (PM10) can be inhaled into the trachea and bronchi. Those less than 2.5 μm (PM2.5) can be inhaled into the alveoli where gas exchange takes place. Epidemiological studies show a strong association of PM2.5 and PM10 concentrations in the air an increase in mortality and emergency room admissions from cardiorespiratory causes.
We are currently completing gravimetric analysis of PM2.5, PM10 and total suspended particulates and metals analysis of the PM10 particle fraction of samples collected in Bamako, Mali. This work will allow us to estimate the amounts of biotoxic and bioactive metals, as well as fine particles that a human could inhale during dust incursions at the sites sampled.