Dust and Human Health - Mineral Dust: A Key Player in the Earth System - page 385

present in PM are all of anthropogenic origin (Schlesinger 2007 ), neglecting to note
the observed natural variation of metals with known toxicities and different states
of solubility present in soils and dusts. Examples of geogenic or geoanthropogenic
dusts containing high levels of metal (loid) toxicants include hexavalent chromium-
rich dusts derived from ultramafic rocks in Oman that are deposited to the east in
the United Arab Emirates (Wood et al. 2010 ) and dusts from Owens dry lakebed
in California, USA, that are enriched in arsenic, barium, antimony, lithium, and
tungsten (Reheis et al. 2009 ).
Garrison et al. ( 2006 ) found that dusts from Mali, Africa, and downwind sites in
the Caribbean contained metals, pesticides, polycyclic aromatic hydrocarbons, and
polychlorinated biphenyls from various anthropogenic or geoanthropogenic sources
and over 300 taxa of microorganisms. Additional studies of the collected dusts
demonstrated that while total ppm concentrations for several metals (As, Cr, Cu,
Fe, Mn, and V) decreased slightly at downwind sites, lung fluid bioaccessibility
(solubility in a physiologically based simulated lung fluid) tended to increase
(Morman et al. 2009 ; Garrison et al. 2010 ;Mormanetal. 2014 ). As ferrous
iron release from respirable PM (e.g., asbestos, coal fly ash, iron sulfides, iron-
rich volcanic ash) has been implicated as a contributor to oxidative stress and
toxicity in the lungs (e.g., Aust et al. 2011 ; Horwell et al. 2007 ), these results
raise the possibility that intercontinental dusts may pose risks for chronic, low-
level oxidative stress related to bioaccessible iron (see also Chap. 4 ) . Gyan et al.
( 2005 ) speculated that the increased rates of asthma exacerbation they observed
were caused by potential allergens and irritants in Saharan dust including plant-
derived constituents such as pollens and the high iron content in the form of
surface-complexed iron. More research is needed to elucidate how particle surface
chemistry, occurring during atmospheric transport in chemically and physically
extreme conditions (e.g., exposed to high levels of solar radiation, multiple freeze-
thaw cycles, and relatively acidic conditions), alters the bioaccessibility of metals
transported with dusts (see also Chap. 4 ) .

15.4.2 Microorganisms in Dust

Dusts also serve as a vehicle to carry biological components such as bacteria,
endotoxins, and fungi via atmospheric pathways (Griffin 2007 ; Kellogg and Griffin
2006 ;Prosperoetal. 2005 ). Some microorganisms (pathogens) are acknowledged
as precursors of disease (e.g., meningitis) and their ability to be transported by dust,
wind, or vector has been established. Others, such as endotoxins, may contribute to
asthma-related symptoms and inflammation (Kirkhorn and Garry 2000 ). Although
dust events have occurred for millennia, there is concern that desertification and
the frequency and volume of dusts produced will increase with climate change
(Kuehn 2006 ). Evidence exists that the quantity (Mahowald et al. 2010 ;Prospero
and Lamb 2003 ; Prospero and Nees 1986 ) and composition (Garrison et al. 2003 )
of dust emissions from some primary sources have changed. The implications for