Dust and Human Health - Mineral Dust: A Key Player in the Earth System - page 386

public health in response to these changes are unclear, but rates of asthma especially
in children are increasing (Braman 2006 ).
Although the production and transportation of dusts is covered elsewhere
(see Chaps. 2 , 3 , 4 , 5 , 6 and 7 ) , it is interesting to note that speculation about far-
traveled dusts from primary sources, such as the Sahel, is not new. In the early
1800s, aeolian dusts were collected over the Atlantic Ocean and archived as part
of the Ehrenberg collection housed in the Museum of Natural History (Gorbushina
et al. 2007 ). Some of the archived samples were recently analyzed (Gorbushina et al.
2007 ) and found to contain numerous viable microorganisms.
Aerobiology is a rapidly developing research area focused on atmospheric
transportation of microorganisms that has broad applications for human and ecosys-
tem health (Kellogg and Griffin 2006 ). Scientists are currently examining the
transportation, survival, and identification of microbes in conjunction with far-
traveled dusts. Misconceptions that may have previously hampered research include
the belief that desert soils are incapable of harboring a diverse microbial community
and that microorganisms could not survive the conditions encountered during
intercontinental transport (freezing, temperatures, desiccation, lack of nutrients,
and UV radiation) (Kellogg and Griffin 2006 ). Several studies now document a
correlation between dust events and increased concentrations of culturable bacteria
and fungi (Wu et al. 2004 ;Prosperoetal. 2005 ;Griffin 2007 ; Smith et al. 2012 ).
How these microbial hitchhikers will affect human health is unclear. Favet et al.
( 2013 ) analyzed samples from various locations in the Republic of Chad, including
the Bodélé depression, and dusts transported to Cape Verde and found only a few
pathogenic strains though the samples contained a wide variety of microbes.
Examples of disease caused by vectors transported with regional dusts include
meningitis, discussed in Sect. 5.2 , and Valley Fever. Caused by inhalation of spores
of the soil fungus Coccidioides immitis , cases of Valley Fever have more than
doubled in some areas of the southwestern United States in the last two decades
(CDC 2012 ). Climatic factors such as drought conditions are thought to be involved
in the recent escalation of reported cases (Galgiani 1993 ; Bultman et al. 2005 ).
Outbreaks often follow dust storms and were observed after the North Ridge,
California earthquake triggered landslides in the area (Kirkland and Fierer 1996 ;
Schneider et al. 1997 ).

15.4.3 Mechanisms of Action

Proposed biological mechanisms responsible for the observed health effects of
PM exposures include oxidative stress and systemic inflammation (Mills et al.
2007 ). Although the inflammatory response to PM exposure plays a significant role
in both respiratory and cardiovascular diseases, the exact physiological pathways
have not been identified (Schwarze et al. 2006 ). Several studies have identified
the role of fine PM (<2.5) in the production of inflammation (Adamson et al.
1999 ; Schaumann et al. 2004 ), though some studies suggest that coarser particles