Describe The Mechanisms Of Particle Deposition Biology Essay

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Chemical classification can be identified using three ways; namely chemical properties, usage and physical form. This physical form known as particulate matter can be recognized using their physical properties such as dust, mist, fumes, gases and vapour. This chapter will look at some particulate matter that can pose health hazard. The occupational disease and condition associated with inhalation of these particulate matters will be discussed with relation between particle size and distribution. Finally the several national regulation and guides that are related to particulate matter will be highlighted.

4.1 DEFINITION

Particulate matter is a small discrete mass of solid or liquid matter that remains individually dispersed in gas or liquid emissions usually considered to be an atmospheric pollutant. In the field of industrial hygiene, particulate matter (PM) is traditionally defined as small that is less than 100 micrometers in diameter pieces of solid materials, liquid droplets, or microbiological organisms.

Particulate matter typically encountered in the occupational environment can be divided into a number of types, based primarily on how the particulate matter was created, its shape, and its composition. Table 4.1 lists the broader classifications and some sub classifications of particulate matter.

Table 4.1: General Types of Particulate Matter (PM)

[Source: Barbara A. Plog and Patricia J. Quinlan (2001) Fundamentals of Industrial Hygiene, National Safety Council: pg 171]

Type of PM

Sub-Type

Defining Characteristic

Examples/Sources

Dusts

General

Produced by mechanical action on larger Lead dust while scraping paint

pieces of the material (e.g., grinding,

cutting, tearing)

Quartz dust when jack hammering

Fibers

Dust classified because of its shape as long thin tendrils

Asbestos, Ceramic fibers, Fiberglass

Biological

Typically organic dusts created by disturbance of plant or animal materials

Wood dust

Cotton dust

Animal dander

Radioactive

Radiotoxicity is often more significant than chemical toxicity

Radon progeny

Radioactive waste

Uranium

Mists

General

Droplets of liquid. Always defined in the context of an aerosol. Created by mechanical action breaking liquid into small particles

Droplets from bubbling dip tanks

Paint overspray

Fog

Droplets of liquid caused by recondensation of vapour

Boiling acids in chemical digestion

Fume

All

Formed by the evaporation and rapid condensation of metal vapour into very small particles

Welding

Arc or torch cutting

Foundry work

Biological

agents

All

These include living and non-living agents that may be allergenic, toxigenic or infectious

Bacteria (and related organisms)

Viruses

Fungal spores

Prions

Smokes

All

Smokes are the products of incomplete combustion of organic materials. Created by vaporization of organic material with subsequent condensation. Sometimes used interchangeably with "fumes"

Diesel exhaust

Coke or coal powered furnaces

Human tissue during laser surgery

Second-hand cigarette smoke

4.2 PARTICLE SIZE

Particulate matter comes in very wide range of size. The size is measure in Aerodynamic Equivalent Diameter which is a diameter of hypothetical sphere of unit density having the same terminal settling velocity of particle in still air. These sizes are relates to inhalation risk and ability of particle to penetrate the respiratory tract. Figure 4.1 shows the size range of various particles which are naturally occurring and man-made particles and the particle size fraction.

Figure 4.1: Size range of various particulate matters

Particulate matter is regard as a hazard when suspended in air, forming an aerosol, which can then be inhaled. Only particles less than approximately 100 micrometers in diameter have the potential to remain suspended in the air for any length of time to form a hazardous aerosol.

As shown in Figure 4.1, particulate matter are group into three (depend on its size fraction) that is inhalable, thoracic and respirable. The inhalable fraction refers to substances that are hazardous wherever they are deposited in respiratory tract: the nose and throat, the airways, or the deep lung. While the thoracic fraction is used to indicate materials that are hazardous when deposited in the bronchi (airways) or in the gas-exchange (alveolar) region and the respirable fraction is used for materials that are hazardous when deposited in the gas exchange region of the lungs, the alveoli.(refer to Figure 4.2).

Figure 4.2: The human respiratory tract

C:\Program Files\Microsoft Office\MEDIA\CAGCAT10\j0090070.wmfSelfCheck

SELF CHECK 4.1

Define the particulate matter

Name five (5) type of particulate matter.

Name the three fraction of particulate matter in term of penetration into the respiratory tract.

4.3 PARTICLE SIZE DISTRIBUTION

Employees can be exposing to large masses of particles suspended in air, commonly called a particle cloud. Particle clouds have a variety of characteristics that often must be understood to fully evaluate and control the hazard they may present.

Particle clouds may be fairly monodisperse or polydisperse. Monodisperse particle clouds are consist of particles that full within a very narrow size range. Polydisperse particle clouds are containing a wide range of particle size. The examples of monodisperse particles are fresh welding fume and fog from condensed boiling acid. Both of these types of particulate matter result from vaporization and recondensation, which has a tendency to form uniformly sized particles. Fresh welding fume is typically very small, on the order of 0.01 μm in diameter. The fog caused by acid digestion, often called "fume" by chemists, tends to be formed of larger particles, several micrometers in diameter.

Polydisperse particle clouds always occur from the majority of occupational aerosol-generating activity. The activity such sand blasting usually produce some of large particles (>100 μm) unbroken, however also form very small fines. The size distribution of particles is very broad. It happens for many demolition activities, such as concrete breaking, and many construction activities. For a given agent, the distribution of particle sizes can range over several orders of magnitude.

Particle clouds can have a single peak when size is plotted against count is called unimodal or they can have multiple peaks which namely as multimodal. This can be happen with a single agent in a number of ways or may occur from the mixing of several different forms of aerosol clouds. For example, in the case of welding fume, although fresh fume tends to be composed of very small, spherical particles, as the fume "ages" it has a strong predilection to agglomerate or "flocculate" into irregularly shaped, extended, and enlarged groups of small spheres. A person working near the process may be exposed to larger agglomerates and fine primary fume, a distribution with two peaks.

On the other hand, bimodal or trimodal distributions of particle sizes may occur when several operations are occurring in the same area of a workplace. In a foundry, a pouring location that generates very fine fumes may be located close to a polishing operation that creates mid-sized metal particles and also to a needle gunning operation that forms very large particles. Thus the chemical composition may be the same, but when evaluated with a size-selective instrument, three distinct modes or peaks are detected. More commonly, chemically heterogeneous multimodal particle clouds are found, such as in a machine shop, where large particles of cutting fluid are mixed with mid-sized particles of metal from grinding operations, and with very small particles of organic smoke from an electronic discharge machining operation. Idealized examples of particle cloud distributions are shown in Figure 4.3.

Figure 4.3: Ideal monodisperse, polydisperse, unimodal, and multimodal particulate matter clouds (log-normal plots).

The particle size may also vary over quite a wide range. It is not unusual for the particles of a suspension produced in a grinding operation, for example, to vary by a factor of 100 from the smallest to the largest size. To describe such situations we normally break the range up into a number of classes and try to find out how many particles are in each size range. This range is called the particle size distribution (PSD), and it can be represented in the form of a table or a histogram (refer to Figure 4.4).

Figure 4.4: A typical particle size distribution in the form of a histogram

4.3.1 Measuring the Particle Size Distribution

There are two methods to measure a particle size distribution.

Separate out the different sizes and then count (or otherwise estimate) how many particles are in each size range as shown in Figure 4.4 could be obtained by counting the particles of different sizes in a microscope (or electron microscope) image.

Estimating the particle size distribution without first separating out the different size fractions.

The first method is the preferred one when we have plenty of time because it can, in principle, yield the most reliable results. There are, however, many situations in which it is much better to have a reasonable estimate of the PSD, especially if it can be obtained quickly.

The most obvious such situation is in a flowing process stream where the particle size might be a crucial factor in determining the success of a chemical engineering process. Such situations are common in the ceramics industry, in the food processing, cosmetics manufacture and pharmaceutical industries and even in computer chip manufacture. Scientists and engineers have applied great ingenuity to the development of such particle sizing methods in recent years and there are now a number of ways of obtaining reliable estimates of PSDs in real time. It is important to recognize, however, that such methods will not normally all yield the same results when applied to a particular system.

That does not mean necessarily that one is more accurate than the rest. Indeed, the only time one can expect different methods to yield exactly the same result is when all of the particles are spherical and of the same size. Different methods measure different aspects of the distribution and sometimes, by combining results from two or more methods, one can obtain information that is not otherwise available from the individual methods.

4.3.2 Plotting the Particle Size Distribution

When the particle size distribution is very broad it is difficult to represent it accurately on the normal scale. It is often advantageous in that case to plot the frequency against the logarithm of the size rather than the size itself. A comparison between the two is shown in Figures 4.5 and Figure 4.6.

Figure 4.5: Typical PSD plotted with respect to the radius (microns)

Notice how asymmetric the plot is in Figure 4.5 and how the conversion to the log plots (Figure 4.6) makes for a much more symmetric frequency distribution. The symmetric plot is in this case the normal error curve or the Gaussian distribution function and is the basis of all standard statistical formulae.

Figure 4.6: The same PSD as Figure 4.5 with respect to log (radius (in microns))

Figure 4.6 show that particle size distribution is a log normal distribution. It is so close to the normal distribution curve when plotted in this way, it can be very easily represented. In fact if one specifies the median size (which in this case corresponds to the maximum frequency) and the spread of the distribution, the entire curve is fully specified. This is the way that most particle size distributions are represented. Almost any real distribution can be approximated in this way, unless it is one that has two or more maxima. Such multi-modal distributions are usually thought of as being the sum of two or more normal (or log-normal) distributions.

In some industrial situations it is important to be able to distinguish the presence of a bimodal distribution (where, for example, the presence of a population of larger particles might interfere with the main process). The particle size methods that first separate the different sizes and then measure them are intrinsically better able to detect the presence of a bimodal distribution. It is, however, sometimes possible to detect such situations, in a rapid real time (online) measurement, but only if the peaks in the size distribution are sufficiently separated from one another.

ACTIVITY 4.1

(a) Explain the characteristics of fume and smoke.

(b) Explain the two methods to measure a particle size distribution.

4.4 Particles and disease

Throughout evolutionary history humans have been exposed to dusty air. The bronchial lining of mucus and its movement out of lungs is the anatomical response to this environmental problem. However, this system can be saturated or toxic particles may be inhaled in the workplace. Pneumoconiosis is a general term used to describe the harm done by inhalation of solids as the result of occupational exposure. Common symptoms include dyspnea (shortness of breath), chest pains, fatigue on exertion and cyanosis (shortage of oxygen). Accompanying damage to the lung circulatory system can cause strain to the right side of the heart which is responsible for pumping blood to the lungs. Chemicals transfer from particles in the lungs into the blood stream, travel to other organs and causing damage.

Various problems result from particulate entering the lungs. Below is a brief explanation between particle associate with the disease.

4.4.1 Silica

Silica exposure occurs when dust that contains crystalline silica particles is inhaled. Silica, or silicon dioxide, is a naturally occurring mineral that is composed of one silicon atom and two oxygen atoms. When silica molecules line up and create a repeating pattern they form a crystal (crystalline silica). Different crystal patterns are given different names; the most common is quartz. Silica is a major component of sand and granite.

The following is a list of construction materials that contain crystalline silica:

Brick

Blasting abrasives

Concrete

Cement mortar

Granite

Sandstone

Slate

Mineral deposits

Rock and stone

Sand

Topsoil

Asphalt

Silicosis, an occupational lung disease, is a respiratory disease caused by inhalation of silica dust. When crystalline silica (a component of silica dust) is inhaled, it causes inflammation of the lung tissue. This inflammation leads to scar tissue formation on the lungs, also known as nodules, which obstruct the flow of oxygen into the lungs and into the bloodstream.

The earliest symptoms of silicosis may include: Shortness of breath, coughing, wheezing, fatigue, chest pain, loss of appetite, fever, and occasional bluish skin at ear lobes or lips

As the lung disease progress, more severe symptoms such as pulmonary and cardiac impairment will occur. In some cases, pulmonary function will be impaired to the point where the patient will need to be supplied with oxygen.

Occupations that put workers at an increased risk of silica exposure include:

Construction

Demolition

Mining

Sandblasting

Stone masonry

Abrasives manufacturing

Glass manufacturing

Pottery

Railroad track setting, laying, and repair

Painting

Plumbing

4.4.2 Asbestos

Asbestos is the common name for any variety of silicate materials that are fibrous in structure and are more resistant to acid and fire than other materials. It has two forms, serpentine and amphibole, and is made of impure magnesium silicate. Asbestos is used for thermal insulation, fire proofing, electrical insulation, building materials, brake linings and has been used in numerous industries.

Asbestosis is caused by inhalation of asbestos fibres (Figure 4.7). Asbestosis is a breathing disorder caused by inhaling high levels of asbestos fibres. Accumulation of these fibres in the lungs can lead to scarring which is known as fibrosis, of lung tissue and diminished breathing capacity. Human might not beware that have asbestosis because it usually does not appear until years after exposure. But once known, the condition often worsens and can lead to death and disability.

220px-Anthophyllite_asbestos_SEM.jpg

Figure 4.6: Asbestos fibres

Asbestosis common signs and symptoms include; shortness of breath, initially only with exertion but eventually even while resting, decreased tolerance for physical activity, coughing, and chest pain. Although these are similar to signs and symptoms of a condition such as asthma, in asbestosis the effects of the disease are insidious, occurring over months and years.

4.4.3 Metals

Inhalation of metal fumes or dust produced from grinding, machining, sawing and sanding. Metal oxides, which are metal atoms combined with oxygen atoms are another form of potentially can also be inhaled which commonly known as iron oxide or rust. Inhaled metals differ in their site of effect. Table 4.2 shows the site of effect for some metals.

Table 4.2: The sites of effect for some metal

Metal

Common Name of Disease

Organs or System Affected

Aluminum

Aluminosis

Nervous system, respiratory tract

Beryllium

Berrylliosis

Respiratory tract, skin

Cadmium

-

Kidneys, nervous system, gastrointestinal tract, respiratory tract, bones, heart

Chromium

-

Kidneys, nervous system, liver, respiratory tract, skin, teeth

Copper

-

Gastrointestinal tract, hematopoietic system

Iron

Siderotic lung disease: silver finisher's lung, hematite miner's lung, arc welder's lung

Nervous system, liver, gastrointestinal tract, respiratory tract, hematopoietic system

Lead

-

Kidneys, nervous system, gastrointestinal tract, hematopoietic system, skin, reproductive system

Mercury

-

Kidneys, nervous system, gastrointestinal tract, respiratory tract

Nickel

-

Nervous system, respiratory tract, skin

Thallium

-

Kidneys, nervous system, liver, gastrointestinal tract, respiratory tract

Tin

Stannosis

Nervous system, gastrointestinal tract

4.4.4 Organic Particles

Inhalation of some organic particles can lead to lung impairments that reactive airway disease and allergic alveolitis. The reactive airway diseases are characterized by sensation tightening of the chest, wheezing, and shortness of breath. The symptoms occur a few hours after exposure begin, but disappear after work. The other reactive airway disease is called byssinosis. It is a disease associated with exposure to natural fibre such as cotton, linen, hemp, and flax.

While allergic alveolitis occur when foreign particle such as spores from fungi, molds elicit an allergic response to the lung. The symptoms are coughing, increase production of mucus, fever, fatigue, and muscle aches. Table 4.3 shows some example of organic agents and their associate disease.

Table 4.3: Example of organic agents and their associate disease

Causative Agent

Associate Disease

Actinomyces spores

Farmer's lung; may develop into non febrile form, characterized by gradual lung impairment with potential for severe damage if untreated

Protein in bird dropping

Histoplasmosis; bird fancier's lung/ pigeon handler's lung

Redwood sawdust

Sequoiosis; allergic response to protein in redwood saw dust-a similar response has been seen among persons exposed to cedar sawdust

Moldy sprouted barley

Malt worker's lung

Wheat flour protein

Wheat weevil disease

Cork dust

Suberosis

Maple bark

Maple bark disease

[Source: Nims DK (1999). Basics of Industrial Hygiene. John Wiley & Sons, Inc.: pg 90]

ACTIVITY 4.2

Match the particles and its common disease

Silica

â-

â-

Asbestosis

Tin

â-

â-

Aluminosis

Beryllium

â-

â-

Stannosis

Alluminum

â-

â-

Berylliosis

Asbestos

â-

â-

Silicosis

.

4.5 mECHANISMS OF PARTICLE

DEPOSITION

Every day billions of particles are inhaled with the ambient air in a workplace. Many of these particles are deposited in the respiratory tract depending on the size, density, shape, charge, and surface properties of the particles and the breathing pattern of the individual. These inhaled particles can cause a variety of pulmonary illnesses and diseases such as asthma, bronchitis and chronic obstructive pulmonary diseases (COPD). There are five primary mechanisms of particle deposition; inertial impaction, interception, sedimentation, electrostatic attraction and diffussion.

Inertial impaction- When particles are suspended in air, they have a tendency to travel along their original path. When there is a bend in the airway system, for example, many particles do not turn with the air but rather impact or stick to a surface in the particles' original path. The likelihood of impaction depends on the air velocity and the particle mass.

Figure 4.7: Inertial impaction

Interception- A particle is intercepted or deposited when it travels so close to a surface of the airway passages that an edge of the particle touches the surface. This method of deposition is most important for fibres such as asbestos. The fibre length determines where the particle will be intercepted. For example: fibres with a diameter of 1 micrometre (µm) and a length of 200 µm would be deposited in the bronchial tree

Figure 4.8: Interception

Sedimentation-is the settling out of particles in the smaller airways of the bronchioles and alveoli, where the air flow is low and airway dimensions are small. The rate of sedimentation is dependent on the terminal settling velocity of the particles, so sedimentation plays a greater role in the deposition of particles with larger aerodynamic diameters. Hygroscopic particles may grow in size as they pass through the warm, humid air passages, thus increasing the probability of deposition by sedimentation.

Figure 4.9: Sedimentation

Electrostatic attraction- Most of airborne particles carry some net charge. Charged collection surfaces will tend to attract and hold oppositely charged particles.

Diffussion- is the primary mechanism of deposition for particles less than 0.5 microns in diameter and is governed by geometric rather than aerodynamic size. Diffusion is the net transport of particles from a region of high concentration to a region of lower concentration due to Brownian motion. Brownian motion is the random wiggling motion of a particle due to the constant bombardment of air molecules. Diffusional deposition occurs mostly when the particles have just entered the nasopharynx, and is also most likely to occur in the smaller airways of the pulmonary (alveolar) region, where air flow is low.

Figure4.10: Diffussion

SELF CHECK 4.2SelfCheck

Differentiate between monodisperse or polydisperse.

What are the five primary mechanisms of particle deposition?

4.6 national regulation and guide

Malaysia as an industrial country is not exempt from the particulate matter issue. The use of various chemical agents in industries makes it crucial to develop a regulation and guideline to guarantee the employees are protected.

The Occupational Safety and Health (Use and Standards of Exposure of Chemicals Hazardous to Health) Regulations 2000 is the sixth set of regulations make under the Occupational Safety and Health Act 1994 (ACT 514). The purpose of the Regulations is to provide a legal framework for the employer to control chemicals (including particulate matter) which are hazardous to health with respect to their use and to set workplace exposure standards so as to protect the health of employees and other persons at the place of work.

The Regulations clearly stipulate the responsibility of the employer (including the self-employed person), in respect of his employees and any other persons, so far as is practicable to protect their safety and health from being affected by chemicals hazardous to health. These chemical hazardous to health is referring to Schedule I and II in Occupational safety and health act and regulation, any of the properties categorized in part B of Schedule I of the CPL Regulation, possesses comes within the definition of "pesticide" under the Pesticides Act 1974 and First Schedule of the Environment Quality (Schedule Wastes) Regulations, 1989.

The duties of the employer stipulated under these regulations are:

Identification of chemicals hazardous to health

Complying with the permissible exposure limits.

Conducting chemical health risk assessment.

Taking action to control hazardous exposure.

Labelling and relabelling chemicals hazardous to health.

Provide information, instruction and training.

Monitoring employee exposure at the place of work.

Conducting health surveillance.

Posting of warning signs

Record keeping

Other than regulation, there are also guidelines under Occupational Safety and Health (Use and Standard of Exposure of Chemicals Hazardous to Health) such as Guidelines to Control chemical hazardous to Health that elaborate on and explain the requirements of Regulation 14 to Regulation 19 which stipulates the duty of employer to take action to control chemicals hazardous to health, through progressive application of control measures in the order of elimination, substitution, isolation, process modification, engineering control, safework procedure and personal protective equipment which can reduce the exposure level of employees to the lowest practicable level. The Guidelines also recommend, some method of control that have been used widely by the industries world wide. Meanwhile Guidelies on Monitoring of Airborne Contaminant for Chemical Hazardous to Health is to supplement the requirement of regulation 26 specifying a method of monitoring and analysis.

SELF CHECK 4.3SelfCheck

List the duties of the employer regarding particulate matter that stipulated under Occupational Safety and Health (Use and Standards of Exposure of Chemicals Hazardous to Health) Regulations 2000

DISCUSSION

You are a new employer of Small Medium Enterprise in wood industry. You are aware that the employees are exposed to particulate matter such as wood dust, toxic chemicals, flammable or explosive aerosols and vapors. As a new employer, discuss what are the step can be taken to protect the safety and health of employees and other persons at the workplace and adhere to Occupational Safety and Health Act.

ACTIVITY 3.1

SELF CHECK 3.2

ACTIVITY 3.2

Summary

Particulate matter is a small discrete mass of solid or liquid matter that remains individually dispersed in gas or liquid emissions in the form dust, mist, fumes, biological agent and smoke.

There are three particle size fractions, classify as inhalable, thoracic and respirable.

Employee are expose to particle cloud in form monodisperse and polidisperse

Particle clouds can have a single peak when size is plotted against count is called unimodal or they can have multiple peaks which namely as multimodal.

Pneumoconiosis is a general term used to describe the harm done by inhalation of solids as the result of occupational exposure

Asbestosis is caused by inhalation of asbestos fibres.

Silicosis is an occupational lung disease, is a respiratory disease caused by inhalation of silica dust.

There are five primary mechanisms of particle deposition; inertial impaction, interception, sedimentation, electrostatic attraction and diffusion.

The Occupational Safety and Health (Use and Standards of Exposure of Chemicals Hazardous to Health) Regulations 2000 is present a legal framework for the employer to control chemicals (including particulate matter) which are hazardous to health with respect to their use and to set workplace exposure standards so as to protect the health of employees and other persons at the place of work.

Key Terms

Inhalable

Thoracic

Respirable

Monodisperse

Polidisperse

Use and Standards of Exposure of Chemicals Hazardous to Health

Inertial impaction

Interception

Sedimentation

Diffusion

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