Air and Water Purification, Security Issues
█ BRIAN HOYLE
Both water and air are particularly vulnerable to contamination by some bacteria and protozoa, and by their toxic products. Chemicals can also be dispersed in water and by
air. A recent example occurred in 1995, when the Japanese cult Aum Shinrikyo released sarin gas into the Tokyo subway system. The poisonous gas attack killed 12 people and sickened 5,000.
Technologies exist to kill the microorganisms that might be present (disinfection) or to completely remove the microbes and chemicals from the air or water (purification). These technologies, however, are usually designed to remove naturally occurring or polluting contaminants.
Groundwater or surface water treatment focuses on providing water that is fit to drink. Typically, the water is filtered to remove large debris. Some jurisdictions also pass the water through microfilters that remove objects as small as viruses from the treated water. Most drinking water is treated with chlorine or chlorine-containing compounds to kill any bacteria. Other treatments that are gaining widespread acceptance include the use of ultraviolet light, ozone, and other chemicals such as bromine. Water can also be purified by techniques involving reverse osmosis and steam distillation, although these techniques are not typically used, as they are expensive and purify relatively small volumes of water at one time.
Treatment and monitoring ensure that the water emerging from the treatment plant is safe to drink and that it remains that way all the way to the consumer's tap. However, these measures are not intended to thwart a deliberate act of sabotage. Many of the water treatment and distribution systems in use around the world were built decades ago. Domestic terrorism was virtually unknown at that time, and protective measures were seldom part of the system's design. For example, surface water supplies are often unguarded and exposed (unfenced, etc.).
For large surface water supplies, the volume of water alone makes the possibility of deliberate contamination remote. For example, it has been estimated that the contamination of the Crystal Springs Reservoir that supplies some of the water for San Francisco, California with enough hydrogen cyanide to harm anyone who drinks a glass of water would require over 400,000 metric tons of the poison. Similarly, huge amounts of bacteria or viruses would be required.
Poisoning smaller water sources, particularly after the water has left the treatment plant, is a more realistic possibility. Even if the water has been chlorinated, disease causing microorganisms such as Giardia and Cryptosporidium are resistant to chlorine, as are bacterial toxins.
More than 100,000 communities in the United States obtain their water from a community well, without the benefit of chlorination or other treatment. Deliberate contamination of these systems could put millions of people at risk.
Another security risk with water supplies involves the nature of monitoring the water. As of 2002, most monitoring techniques for living and nonliving contaminants requires up to 24 hours. "Real time" tests are not routinely available. Thus, contamination would not be detected until long after people had consumed the water.
Air is vulnerable to contamination with a variety of bacteria, viruses, and fungi that are light enough to become dispersed in air currents. When inhaled, the microbes can cause infections. Chemicals and toxins can also float in the air, to be inhaled or settle onto exposed skin.
Air purification has long been possible using filters. Bacteria, viruses, and even some inorganic chemicals can be retained on specialized filters. These filters are mainly suitable for laboratories or relatively small, specifically designed ventilation systems. In large indoor environments such as malls or sizeable office buildings, and in the open air, air purification is virtually impossible.
Contamination of the open air poses a similar problem as the contamination of a large volume of water, namely the amount of poisonous agent that is required. For example, estimates are that hundreds of pounds of anthrax spores would be needed to achieve a massive contamination of the population of a large city.
The release of toxic agents into a more limited area such as an office building is more plausible. Some buildings that are deemed to be a security risk, or which are used for research with highly infectious microbes, are equipped with safeguards to prevent the spread of airborne infectious agents or poisons. Air treatment, ventilation filters, alarms, and the ability to isolate contaminated zones are usually part of the designed safeguards.
█ FURTHER READING:
Drell, S. D. The New Terror: Facing the Threat of Biological and Chemical Weapons. Stanford, CA: Hoover Institute Press, 1999.
Henderson, D. A., "The Looming Threat of Bioterrorism." Science no. 283 (1999): 1279–1282.
Kowalski, W. J., W. P. Bahnfleth, and T. S. Whittam. "Filtration of Airborne Microorganisms: Modeling and Prediction." ASHRAE Transactions 105 (1999): 4–17.
O'Toole, T. "Smallpox: An Attack Scenario." Emerging Infectious Diseases 5 (1999): 540–546.