Dust particles respirable

Crystalline silica, or quartz, is an abundant mineral found in sand, rock, and soil. Respirable silica dust (particles <5pm) is a known occupational hazard of the dusty trades (e.g., pottery or china manufacturing, work involving sandblasting or abrasive grinding, some construction trades). High level exposure to respirable silica can result in the chronic, progressive lung disease silicosis, characterized by inflammation and fibrosis. 

It is postulated that chemotactic agents leach from respirable cotton dust particles in the small bronchioles. AECD recruit PMNs to the lung in the following sequence connective tissue beneath the basal lamina, between airway cells, and, finally, into the lumen. Chest tightness is also correlated with leucocyte recruitment (41). Although it has been proposed that extracellular lysosomal enzymes from PMNs cause the symptoms of byssinosis by initiating release of histamine and/or other chemical mediators (25), it has not been shown that cotton dust actually liberates hist j. jjfg m j y... 

Dichlorobenzidine is not a volatile chemical. In the air, it may exist as dust particles or boimd to particulate matter. The absorption of 3,3 -dichlorobenzidine from such respirable particles into the body depends, in part, on the size of the particle. Large particles tend to deposit in the upper airways and are subsequently cleared by ciliary action with little absorption across limg tissues. However, the ciliary action transports the particles to the epiglottis where they are often swallowed, leading to gastrointestinal absorption. Smaller particles can penetrate more deeply into the respiratoiy tree, where 3,3 -dichloro-benzidine absorption may be significant. 

Dust Airborne solid particles (an aerosol) that range in size from 0.1 to 50pm and larger in diameter. A person with normal eyesight can see dust particles as small as 50 pm in diameter. Smaller airborne particles cannot be seen unless strong light is reflected from the particles. Dust of respirable size (below 10 pm) cannot be seen without the aid of a microscope. 

Toxicants to which subjects are exposed in the environment or occupationally, particularly through inhalation, may be in several different physical forms. Gases are substances such as carbon monoxide in air that are normally in the gaseous state under ambient conditions of temperature and pressure. Vapors are gas-phase materials that can evaporate or sublime from liquids or solids. Benzene or naphthalene can exist in the vapor form. Dusts are respirable solid particles produced by grinding bulk solids, whereas fumes are solid particles from the condensation of vapors, often metals or metal oxides. Mists are liquid droplets. 

Acute high-level silica exposures may be associated with natural and other disasters, such as earthquakes, volcanic eruptions, and building collapse. High-level exposure to respirable silica dust (particles <5 pm) can cause chronic inflammation and fibrosis in the lungs and other organs. Silica exposure in humans has also been associated with increased production of autoantibodies, serum immunoglobulins, and immune complexes. 

Inhalation is actually a less Important route of entry than assumed by CDC, if other data are considered. For example, the EPA has estimated that the average concentration of total suspended particulates (TSP) In Missouri Is about one-half the level assumed by CDC, or about 0.070 mg/m (32.33). Secondly, only a fraction (about 30%) of the total amount of airborne dust Is respirable (less than 10 pm aerodynamic diameter) (32). The percentage of TSP which Is respirable has been estimated by EPA to be no more than 50% (2). Also, the assumption that all of the airborne particles are derived from dioxin-contaminated soil Is overly conservative. Actually, about 50% of the Inhaleable particles are respirable and the remainder are between 10 and 50 pm. Further, about 83% of the non-respirable particles are from crustal material (e.g., soil) and only 47% of the respirable particles are from soil (32). Larger studies conducted by the U.S. EPA have suggested that the portion of Inhaleable dust due to soil can often be much less (34). 

Toxicohgy Dust may irritate respiratory system, eyes, and skin respirable dust particles may contain a small amt. of silica ACGIH TLV 3 mg/ m (respirable dust)... 

Do not wear your respirator into atmospheres containing contaminants for which your respirator is not designed to protect against. For example, a respirator designed to filter dust particles will not protect you against gases, vapors, or very small solid particles of fumes or smoke. 

Respirable dust Dust particles 5 pm or less in size. 

Dust particles have very irregular shapes. For example, a fibre is a particle with a length of at least three times its width. A respirable fibre has a diameter of approximately 3 ijim or less, depending on its density. 

Qualitative monitoring techniques include smoke tubes and the dust observation lamp. Smoke tubes generate a white smoke which may be used to indicate the direction of flow of air - this is particularly useful when the air speed is very low or when testing the effectiveness of ventilation ducting. A dust observation lamp enables dust particles which are normally invisible to the human eye to be observed in the light beam. This dust is usually in the respirable range and, although the lamp does not enable any measurements of the dust to be made, it will illustrate the operation of a ventilation system and the presence of such dust. 

Mycotoxins are complex organic compounds, with molecular weights in the range of 450-500. They are nonvolatile at ambient temperatures, but become respirable when attached to airborne dust particles [47]. At least 350 different fungi are known to produce more than 400 individual toxins belonging to at least 20 different myco-toxin classes. 

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