Introduction

All of us are familiar with images of smog and haze surrounding cities and major highways. The intent of this document is to help the average citizen better understand the health effects of poorly soluble particles (PSP) (one of the components of air pollution).

People are generally exposed to PSP by inhaling them. The physical properties of PSP determine where in the lungs and other airways PSP are deposited and exert their effects. To start out, it will be helpful to understand what we mean by PSP.

Background

Many industrial processes produce dust-like particles and disperse them into the air. First, airborne particles are categorized by their solubility, that is, how well they dissolve in water. Grains of table salt are a good example of soluble particles because they completely dissolve in water. So a soluble particle is only a particle until it comes into contact with water, such as the moisture lining the body's airways after inhalation. Once a soluble particle has dissolved in the airways, its health effects are mainly dependent on what chemicals made up the particle. Poorly soluble particles do not dissolve well in water. Sand particles are a good example of PSP because they do not dissolve in water but remain visible, individual particles.

Second, airborne PSP can be organized based on their size. Size determines how deep into the lung particles are inhaled. Particle size is measured as the diameter. Particles of toxicological significance are usually in the micrometer (µm) (millionth of a meter) range. Any particles under 500 µm are considered inhalable. Particles over 10 µm and under 0.01 µm are generally filtered out in the nose and don't make it any deeper into the airways. PSP between 10 and 5 µm generally deposit in non-respiratory airways where they are trapped in mucus and pushed up to the throat where they can be swallowed. The more dangerous PSP are those between 5 and 0.01 µm. These are called "fine particles" (below 1 µm particles are considered "ultrafine"). These fine and ultrafine particles can be deposited deep within the respiratory part of the lung (tiny sac-like organs called alveoli). Once a PSP reaches the alveolus, it can be cleared by special cells of the immune system called macrophages. Some of these PSP may even cross the membranes lining the alveoli and enter the blood stream to affect other organs in the body.

Diesel Exhaust Particles are a good example of PSP. These diesel exhaust particles were trapped from air on a Teflon filter and are viewed here by electron microscopy. This is a good example of PSP that can be inhaled deeply into the lung.

Health Effects of PSP

Some of the health effects of PSP are dependent on the chemical composition of the particle. For example, metal particles may increase the risk of neurodegenerative diseases (including a condition like Parkinson's), while grain dust may cause asthma or chronic obstructive pulmonary disease (COPD). The toxicity of some PSP is determined by other chemicals that are absorbed onto their surface. For example, when sand blasting is used to remove old paint from metal, fine sand particles are dispersed into the air. These particles may have paint absorbed onto their surface. This paint may contain the heavy metal lead. In this case, the sand particle can serve as a vehicle to deliver lead deep into the lung.

Even when no toxic chemicals are associated with a PSP, these particles can still cause damage. When immune cells try to clear PSP from the lung, they release toxic chemicals designed to kill organisms like viruses and bacteria. In the presence of PSP, these immune cells may release too much of these chemicals and begin to damage the healthy lung tissue around them. This can lead to chronic inflammation. Over time, this inflammation could increase the risk of lung cancer. In fact, animal studies have shown that a wide variety of PSP can increase the risk of lung cancer in rats. A number of particles found in the workplace, including asbestos, and silica, are associated with increased risk for lung cancer with sufficiently heavy exposures.

PSP clearance from alveolus in the lung. Immune cells, called macrophages, can engulf inhaled PSP and carry them out of the alveolus. Macrophages that have engulfed a PSP may also begin to release toxic chemicals that could damage healthy tissues of the lung. If this condition becomes chronic, it may lead to increased risk of cancer.

Exposure Monitoring

The State of New York Department of Environmental Conservation monitors the state's fine particles (i.e. 2.5 µm or less). They trap particles on Teflon filters. These samples can then be examined by electron microscopy, polarized light microscopy, and x-ray mapping to determine the composition of these particles. Then PSP levels in the air can be mapped out by county to determine those areas of the state with higher-than-normal PSP levels. Using the concentration of these particles in the air and the amount of air that the average person inhales over a chosen time period, the average daily dose of PSP for people in the different areas of the state can be determined.

Regulation

The National Ambient Air Quality Standard (NAAQS) for PSP less than 2.5 µm in diameter is 15 micrograms/cubic meter for an annual average. For a 24-hour average 65 micrograms/cubic meter is acceptable. This standard was set based on levels of exposure that did not lead to adverse health outcomes in animal and human studies.

Precaution

If you work in an environment that includes lots of dust, such as sandblasting, welding, or work in a granary, your employer must meet Occupational Health and Safety Administration (OSHA) standards for specific substances regulated by [OSHA|occupational health and safety administration (osha). You can also contact [OSHA|occupational health and safety administration (osha) directly on their website (http://www.osha.gov/) or by contacting your local OSHA regional office (website has contact info for regional offices). If you are concerned about the outdoor air in your neighborhood, contact the Office of Air and Radiation (OAR) at the Environmental Protection Agency (EPA) (http://www.epa.gov/oar/ or by phone 866-411-4372). Your State may also have an office of air quality in their Department of Ecology or Department of Health.

External Links

• Environmental Protection Agency
  
  
• Occupational Health and Safety Administration