ABSTRACT

1. Effects of Dust Flux on Human Health Carlie Bulen ES473 Environmental Geology ABSTRACT One field of study in medical geology examines the effects of atmospheric dust on human health. These effects can have significant health consequences, but are not widely recognized in the literature. Dust inhalation and lung accumulation is known to cause long term chronic health conditions. Sources in the atmosphere include wind deflation, burning of vegetation, volcanic eruptions, and anthropogenic disturbance. Classic locations associated with dust-related lung complications include the great dry lands of the northern hemisphere, the U.S. Great Basin, and southern hemisphere arid regions of Australia, South America and southern Africa. These locations are notoriously associated with high rates of silicosis and asbestosis, and attendant lung disease. Factors that influence the severity of these conditions include duration of exposure, the size of particles inhaled, and the toxicity of minerals comprising the particles. One detrimental element found in dust particles that is linked to a significant number of these conditions is silica. Although dust-related lung disease is a significant problem in underdeveloped countries and desert regions, few public health actions are being implemented to mitigate harmful effects of dust inhalation. This paper presents an overview of the geological influences on global dust flux and case examples of chronic health effects associated with excessive inhalation. • Health Connection • How up taken- Inhaled coarse mineral particles are commonly lodged in the upper respiratory tract and are rejected by expectoration, but they may constitute a health risk if the mineralogy is toxic. Inhalation of the finer mineral dust eventually leads to deposition in the pulmonary alveoli where chronic lung disease is initiated. Some types of inhaled particulates are degraded by macrophages, but many are highly resistant to this process and persist in the lungs. The fraction of dust that penetrates more deeply into the finer lung passages may cause silicosis, asbestosis, and other lung conditions. • What effects on the body- factors include size, shape, chemical and mineral composition of dust particles, length of exposure, and certain lung functions. • Lung Conditions- Pneumoconiosis, silicosis, fibrosis, asbestosis. Figure 3. Long-term dust storm frequency, showing a distribution of major sources closely similar to other data sources. Sources occur in all continents except Europe and Antarctica. Figure 4. Before and during a Mongolian dust pall over Beijing, April 2003. • Introduction • Loess and Dust-Loess is windblown silt. Characteristic properties of loess include high porosity and collapsibility on wetting. Dust aerosols include gases, liquids and solid particles suspended in the atmosphere for varying lengths of time. Solid aerosols include particles injected into the atmosphere such as mineral dust and sea salt, and those that form within the atmosphere, such as sulfates. Other contributors to dust hazards are smoke plumes from natural and man-made fires, and biomass burning, producing black carbon. • Mineral components- Loess mineralogy consists of angular, blade-shaped, quartz grains, with minor feldspars, micas and carbonates. • Where found- High Asia, China, U.S. Great Basin, North Africa, Middle East, Australia, South Africa, and South America. Figure 2. Some essential links in the direct and indirect pathways from dust sources to human inhalation and ingestion. Figure 4. Lungs with Silicosis vs. normal lungs. • Case Examples • A radiographic study of 54 Bedouin people in the Negev Desert strongly suggested that the incidence of fibrosis is age related, with progression more notable in women (13 out of 22) than in men (only 4 out of 32), perhaps related to greater exposure in and around the family tents. • In Ladakh dust storms are frequent, mineral dust found on the wooden beam rooftop of Ladakhi houses is all finer than 15 µm, more than 25% by weight being finer than 1 µm. The silica content >60%. Study of necropsy lung tissue samples from villagers revealed heavy dust deposition with abundant hard 1-3mm nodules and a lymph node largely replaced by hyaline collegenous nodules, a classis feature of silicosis. • Mineral dust finer than 3 µm found in lung tissue form one Chinese postmortem subject made up about 75% by weight of the total dust burden in the lungs. Summary Dust and loess accumulation can have very deleterious effects on human health when inhaled. The mineral compound, duration of exposure, and particle size and shape can influence these effects and cause such lung complications as silicosis, asbestosis, pneumoconiosis, and fibrosis. The World’s dry lands are a major source of dust and are associated with many cases of these and other lung complications and diseases. Figure 1. Sketch showing the two modes of aeolian dust transport and deposition, based on a transect from the Chinese dry lands to the Loess Plateau and the North Pacific Ocean. • Geological Process • Why dust amount is higher in certain areas of the world: • 1-High Asia- one of the world’s most efficient producers of loess due to the combination of the highest known uplift rates, rapid river incision, unstable slopes, glaciations and widespread rock breakup by crystal growth during freezing, and by hydration of salts. • 2-North Africa and China- dried out former lake beds, deserts. In parts of North China loess formation exceeds 300m in thickness. References Cited Derbyshire, E., Natural Dust and Pneumoconiosis in High Asia, p. 15-18. Derbyshire, E., 2005, Natural Aerosolic and Mineral Dusts and Human Health: Elsevier Inc., p. 459-480. Derbyshire, E., 2007, Natural Minerogenic Dust and Human Health: Royal Swedish Academy of Sciences, p. 73-77.