Arsenic is a naturally occurring semi-metal element found in combination with other elements in the Earth’s crust. Due to natural geologic processes, as well as human activities, arsenic can be found in soil and water. In the arid Southwest, water and soils can be impacted by wind-borne distribution of dust from arsenic-laden mine tailings (over 300,000 acres).
Arsenic has long been known as a poison. Whether arsenic has an effect on health depends on the route, dose (how much), and duration (how long) of exposure. Exposure to arsenic via inhalation can occur as an occupational hazard, or due to proximity to dust, such as from mine tailings. Arsenic exposure can also occur through ingestion in water or food, and children can be affected by hand-to-mouth ingestion of arsenic in dirt. Worldwide, drinking water is the most prevalent route of arsenic exposure.
Short-term (acute) exposure to high levels of arsenic can produce a variety of toxic effects, including death, but is relatively rare. More problematic is the long-term (chronic) exposure to arsenic that occurs in many parts of the world. Epidemiological (population-level) studies have shown that even low-level exposure to arsenic over time is associated with various complex illnesses, including cancer. Thus, chronic, low-level arsenic exposures of are growing concern to public health.
UA SRP investigators are studying how early-life exposure to low-level arsenic affects lung development and disease.
Mine tailings are large piles of crushed rock that are left over after valuable metals have been separated from the ore that contained them. The composition of the tailings depends on the composition of the ore and the extraction process used. The majority of the material is crushed rock that has been ground into fine particles that can range from fine silt to coarse sand. The tailings may contain trace quantities of the metals of interest. The extraction process may also concentrate unwanted minerals in the tailings, or leave behind chemical additives.
In arid and semi-arid areas of the world, including regions of the western United States and the northern region of Mexico, mine tailings and their associated contaminants are prone to water erosion and wind dispersion. The impact of acid rock drainage on surface-water and groundwater contamination is considered to be a primary environmental concern for many hardrock mining sites in the US.
UA SRP Investigators are investigating the processes that control movement and treatment of mining contaminants in groundwater.
Wind dispersion occurs because the fine tailings particles are easily suspended into the atmosphere by wind and dispersed throughout the environment as dust particles. Spread of metal toxicants in association with tailings particles, through a combination of wind dispersion and water erosion, has been shown to result in measurable elevated levels in wildlife and humans even significant distances from the tailings site. Many mining areas have been economically developed within the last century, and as a result, are now located next to large urban populations. Human exposures to mine tailings dust can occur through inhalation and ingestion. Children are more likely than adults to ingest dust, and are more vulnerable to the effects of toxic contaminants.
Particle size is an important factor influencing the dispersion and transport of dust in the atmosphere and the effects of dust on human health. Particle size affects how long a particle stays suspended in the atmosphere; smaller particles stay airborne longer. Particle size also affects deposition in the human respiratory system. Coarse particles are mainly deposited in the upper respiratory tract (nasal cavity and throat). They are ultimately swallowed and eliminated through the digestive system. In contrast, fine particles penetrate more deeply into the lungs and can be transferred directly to the blood stream. Thus, determining the distribution of toxic metals in dust fractions also has important implications for human exposure and public health.
UA SRP investigators are measuring particle size and association with metal contaminants in wind-blown dust from tailings and other mining operations.
One way to limit dust exposure and clean up metal contamination found in the tailings is to grow a vegetative plant cover. However, mine tailings are often characterized by adverse conditions such as low pH, high metal content, high salt content, lack of mineral nutrients and organic matter, and poor microbial diversity. As a result, these sites do not develop normal soil structure or support the establishment of a plant cover. Additions such as compost, manure, fertilizer, and/or irrigation are often required to allow plants to grow.
UA SRP investigators are determining the conditions required to establish a healthy plant cover, and studying how interactions between plants, metals, and microbes affect revegetation of mine tailings, including stabilizing metals and limiting dust transport.