Critical Types of Hazardous Dust

Dust are tiny solid particles that are scattered or suspended in the air. The particles are inorganic or organic depending on the source of the dust. There are different types of dust with different chemistries, particle sizes, reactivities and effects on human life, animals and the environment at large. The fingerprint of a dust particle depends on its parent source and the process that generated it. In this article, we will focus on the types of hazardous dust generated from human activities such as processes in mining, quarrying, farming, etc

What are the types of Hazardous Dust?

• Crystalline silica dust 
• Coal dust 
• Asbestos dust 
• Metalliferous dust 

Crystalline silica dust:

Crystalline silica dust is generated from activities such as drilling, blasting, crushing, sieving, and transportation of silica-containing rock materials in the mining, quarrying and tunnelling industry. Quartz is the most common form of crystalline silica in nature. Quartz is present in alpha and beta forms. Alpha quartz is the most common form and is found in many rocks and soils. Silica is the main part of sand, so abrasive manufacturers, glass workers, stone cutters and sandblasters are also exposed to silica. Silica is a chemical compound found in abundance in nature. It is comprised of quartz, a constituent of rock, and makes up 90-95% of sand. High exposure to respirable crystalline silica dust causes silicosis, a lung disease that can lead to serious breathing difficulties, lung cancer and loss of life. There are three types of silicosis, namely – chronic silicosis accelerated silicosis and acute silicosis. Chronic silicosis results from long term exposure to low amounts of silica dust. Accelerated silicosis occurs after exposure to larger amounts of silica over a shorter period. Acute silicosis results from short-term exposure to very large amounts of silica. Silicosis increases the susceptibility to other ailments such as tuberculosis, chronic obstructive pulmonary disease, kidney and autoimmune disease. 

Coal dust:

Coal dust is generated from coal mining activities which are usually on the surface or underground. Coal is mined and stockpiled until it can be loaded into a truck or train car, and then transported to the purchaser. Depending on production rates, it is more of an ongoing situation of adding coal to the stockpile, removing coal for loading and adding more coal. For surface mines, much of the dust problems are not with coal itself, but silica dust from trucks being tracked onto roads and usually affects the nearby communities. Coal is a by-product of decayed matter that has been compressed and cemented over long periods. In its nature, coal exists in four different ranks according to the metamorphic stages. The different types of coal include anthracite, bituminous, sub-bituminous and lignite which are given in order of rank from the lowest to the highest respectively. Australia is known to have bituminous and lignite coal types. Exposure to coal dust can cause a person to develop coal worker’s pneumoconiosis also known as black lung disease. There is an inherent relationship between silica dust and coal dust. Most safety standards that limit exposure to coal dust do not cover silica. That omission creates a window for over-exposure to silica on the premise of just dealing with coal dust. The chemistries of the two are different and it is important to acknowledge that modern equipment pulverizes not only coal but the rock around it, thus exposing miners to silica dust. 

Asbestos dust:

Asbestos dust is generated from asbestos which consists of naturally occurring minerals composed of soft, flexible fibers that are heat resistant. There are three main types of asbestos: amosite – brown asbestos, crocidolite – blue asbestos and chrysotile – white asbestos. Asbestos may be found in large deposits or as contaminates in other minerals such as talc and vermiculite. They are all naturally occurring minerals mainly magnesium silicate. When heated they fluff up to a fibrous material that can be woven into cloth, be mixed with cement to form sheets or used for insulation. It is refractory so will block fire. The downside of asbestos dust fibers is that when inhaled, they settle deeply into the lungs and cause fibrosis known as asbestosis and in time cause cancer, mesothelioma. Fiber sizes play a critical role in the contribution to asbestosis. Amosite is less implicated in the causative analysis owing to its larger fibers relative to smaller fibers of crocidolite which are highly dangerous. Crocidolite fibers are widely used in the shipbuilding industry and in insulation in railway carriages where the workers used to eat their lunch sitting on bales of the stuff. No amount of asbestos is safe, the more the asbestos you are exposed to, the greater the chances of contracting an asbestos-related disease. 

Metalliferous dust:

Metalliferous dust is generated from both surface and underground mining of iron ore, copper, tin, nickel, gold, silver and zinc. Inhalable and respirable dust in metalliferous mining is generated from mining activities such as drilling, extraction, crushing, hauling, stockpiling and processing of minerals. Some metalliferous ores uranium, silver and nickel contain toxic dusts cause chemical reactions within the respiratory systems or allow compounds to be absorbed into the blood stream through the alveolar walls. They are poisonous to body tissue or to specific organs. The toxicity and bioaccessibility of particulate matter depends on size mode, mass concentration, acidity, particle surface chemistry and area, particle chemistry such as metals and carbon and solubility. Metalliferous mine dusts and associated potentially toxic elements released through mining activities have different chemistries which also determines their mechanisms of action in the mine workers exposed to them. Potentially toxic elements associated with minerals in ore deposits include copper, nickel, uranium and zinc. Even though copper and zinc are essential for life their excess exposure can be toxic. Metalliferous mine dust including uranium and transition metals such as copper, nickel and zinc can generate reactive oxygen species in biological tissues via Fenton type reactions. In addition, iron-bearing minerals such as iron oxides are potential contributors to inflammation in the human lung.

Why particle size is important?

The factors influencing the effects of dust as inhaled particles. Among these are some properties of the particles themselves. Particle size is usually the critical factor that determines where in the respiratory tract that particle may be deposited. Chemical composition is important because some substances, when in particle form, can destroy the cilia that the lungs use for the removal of particles. The changes with occur in the lungs vary with the different types of dust. Silica dust in the lungs is marked by an island of scar tissue surrounded by lung tissue. The injured areas are separated from each other by normal tissue; hence the lungs do not completely lose their elasticity. In contrast, the scar tissue produced by asbestos, beryllium and cobalt covers the surfaces of the deep airways. The lungs become stiff and lose their elasticity. Not all inhaled particles produce scar tissue. In summing up, the lungs are constantly exposed to danger from the different types of dusts that is inhalable and respirable. Ending dust at its source is the only form of prevention as there is no cure. 

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REFERENCES 

• Asbestos. Retrieved 22/05/21 https://www.asbestos.com/asbestos/
• Noble et al. 2017. Mineral Dust Emissions at Metalliferous Mine Sites. Environmental Indicators in Metal Mining. https://www.springerprofessional.de/en/mineral-dust-emissions-at-metalliferous-mine-sites/10899610 
• State of New South Wales. 2017. Airborne contaminants – metalliferous mines. Department of Planning & Environment. https://www.resourcesregulator.nsw.gov.au/__data/assets/pdf_file/0003/823422/Airborne-Contaminants-PHMP-Guide.pdf
• What are the different types of coal? https://www.americangeosciences.org/critical-issues/faq/what-are-the-different-types-of-coal Retrieved 22/05/21 
• When is Asbestos Dangerous? Retrieved 22/05/21