Air and Water Purity, Forensic Tests

Consumption of contaminated water or breathing in air that contains a noxious compound can be debilitating or lethal. Thus, forensic testing can include the testing of water or air to assess purity or impurity.

Many noxious gases can be transported in the air. For example, people are cautioned against leaving an automobile engine running in an enclosed space. This is because the tasteless, odorless, and colorless carbon monoxide (CO) emitted in the exhaust can cause illness or death, depending upon the concentration of the gas in the air. For example, at a concentration of 200 parts per million (ppm), CO produces a slight headache within hours. A concentration of 800 ppm causes nausea and convulsions (seizures) within 45 minutes of exposure, and can lead to unconsciousness, coma, and ultimately, death.

CO replaces oxygen in the bloodstream, by competing with oxygen molecules for the binding site in the transport compound of the blood called hemoglobin . As a result, the body becomes starved for oxygen.

As with gases, particulate material such as soot and asbestos can also be light enough to drift on currents of air. Microorganisms such as bacteria, viruses, and molds (and the spores produced by some strains) that dislodge from a surface can also drift on air currents.

The presence of these various agents in the air can be accidental. For example, the growth of molds and fungi in a damp wall of a house can lead to the aerial dissemination of spores. Of particular note, the fungus designated Stachybotrys chartarum produces spores that are toxic if inhaled. The fungus was implicated in the illness of 27 infants, nine of whom died, in Cleveland, Ohio, in 1993. All the infants lived in homes that sustained flood damage.

Besides S. chartarum, Aspergillus versicolor and several species of Penicillium are potentially toxic, and also thrive in damp environments.

Noxious agents have also been deliberately introduced into the air. For example, on March 20, 1995, the Japanese cult Aum Shinrikyo released sarin nerve gas in the Tokyo subway system, killing 10 people. And, at various times during the 1990s, the cult attempted to aerially disperse Clostridium botulinum spores.

Another form of spore is produced by the bacterium called Bacillus anthracis; the cause of anthrax . In the fall of 2001, a series of incidents occurred in the United States, in which letters containing a powdery form of anthrax spores were mailed to public figures including Senators Patrick Leahy and Tom Daschle and NBC news-anchor Tom Brokaw. Five people died after inhaling the spores released from tainted letters.

Water has been described as "the universal solvent." A huge number of inorganic compounds can dissolve in water. As well, microorganisms can be maintained in suspension and can survive for varying periods of time. The result if the water is used for drinking, washing food, bathing, and even recreation, can be illness or worse.

A particularly graphic example of the hazard posed by impure water occurred in the Canadian town of Walkerton, Ontario, in the summer of 2000. Contamination of one of the municipality's wells by a disease-causing (pathogenic) bacterium called Escherichia coli O157:H7 sickened over 2,000 people and killed seven. A number of those who recovered have been left with permanent kidney damage. Contamination of water and food by E. coli O157:H7 causes an estimated 73,000 illnesses and over 60 deaths in the United States each year, according to the Centers for Disease Control and Prevention .

Other bacteria including species of Salmonella, Vibrio and Shigella, which, like E. coli, normally dwell in the intestinal tract, can enter water when the water is contaminated by feces, as can intestinal viruses and protozoans. Contamination of drinking water by a protozoan called Cryptosporidium in 1993 produced a diarrhea-like illness in over 400,000 people in Milwaukee, Wisconsin.

Forensic testing of air and water is accomplished using the standard analytical procedures employed in other sectors. With air, for example, a device can be used that draws a defined amount of air through a filter. The size of the holes (pores) in the filter is big enough to allow the air molecules to pass, but restricts the passage of particulate material. Even viruses can be retained, if the filter's pore size is in the nanometer (10^-9 meter) range.

The particles are subsequently recovered from the filters and analyzed. Analysis techniques include spectroscopy , electron microscopy, and the examination of genetic material. The latter can involve the use of a technique called polymerase chain reaction (PCR ), which greatly increases the number of copies of a selected target region of the deoxyribonucleic acid (DNA ). The sequence of nucleotide building blocks that comprise the DNA can then be determined.

Water samples can also be filtered to recover particulates and suspended microorganisms. The above techniques can then be used to examine a sample. As well, particularly for bacteria, assays that rely on the growth of the organisms on an appropriate food source, first developed hundreds of years ago, are still an important means of identifying the bacterial cause of an illness.

The types of forensic air and water analyses that are performed rely on the skill of the forensic examiner. Knowledge of the circumstances surrounding an illness or death, appearance of the scene, and the symptoms or behavior of the victim can provide clues suggestive of the involvement of a particular noxious agent.

see also Aflatoxin; Air plume and chemical analysis; Biosensor technologies; DNA typing systems; Escherichia coli ; Nerve gas; Pathogens; Sarin gas; Toxicological analysis; Water contamination.