In a forensic examination, a prime task is to discern the primary cause of illness or death. In some instances, a gunshot wound for example, the cause may be readily apparent; in other cases, such as those involving contaminated food or water, there may be no visual signs of the cause of death . Knowledge of the nature of the contamination is essential for the forensic examiner.
Water is known as the universal solvent. This means that a great many compounds will dissolve in water. Still others that do not dissolve can become suspended in water, or, if immiscible (incapable of mixing, i.e., gasoline and alcohol), can partition in the immediate vicinity of water.
Many of these compounds can be nutrients for a variety of microbiological life forms. Other microbes may be more dormant in the water, but still capable of growing when exposed to a more nutrient-rich environment. In the latter case, the water becomes the conduit between the organism's natural habitat and humans.
Water contamination is a concern, since the organisms present can cause disease. Typically, these pathogenic organisms are normally residents of the intestinal tract of warm-blooded animals, including humans. Examples include Salmonella, Shigella and Vibrio. In addition, certain types of the intestinal bacterium Escherichia coli can cause infections. A particularly noxious form of E. coli designated O157:H7 can be devastating. O157:H7 contamination of the municipal water supply of Walkerton, Ontario, Canada, in the summer of 2000 sickened over 2,000 people and killed seven others. The intestinal tract also contains viruses (i.e., rotavirus, enterovirus, and coxsackievirus) that can contaminate water and cause disease.
A number of protozoan microorganisms can contaminate water. The two most prominent are members of the genera Giardia and Cryptosporidium. These microorganisms normally live in the intestinal tract of animals such as beaver and deer. The increasing contamination of water by these protozoans reflects the increasing encroachment of urban areas on wilderness.
Municipal drinking water is usually treated to minimize the risk of the contamination of the water with the above microbes. The benefits of water treatment have been reaped for millennia. Thousands of years ago, it was known that the storage of drinking water in metal jugs preserved the water's quality due to the antibacterial effects of the metal ions (although this property was not known until centuries later). Similarly, the protection of water quality by the boiling of the water, which kills the noxious microorganism, has long been known. "Boil water orders" are still routinely issued in municipalities when the water quality is suspect.
Water that is obtained from wells is often protected from contamination by the natural filtering action of the soil and rocky underlayers that the water percolates down through. However, if a well cover or internal casing is broken, then the well water can be directly contaminated.
Surface water supplies are especially prone to contamination, from run-off and the deposition of feces in the water from birds and animals. Surface water that is used as the drinking water supply for an individual or a community should be rigorously treated to ensure that microorganisms, debris, and chemicals have been removed prior to use of the water.
One popular treatment is chlorination. Addition of antibacterial disinfectant compounds, particularly chlorine or derivatives of chlorine, to water has been practiced for over a century. Other treatments that kill bacteria include the use of a gas called ozone and shining ultraviolet light through the water to disrupt the bacterial genetic material. The refinement of filters now allows even viruses to be excluded from filter-treated water.
The killing of the protozoan microorganisms has proved to be challenging, as both Giardia and Cryptosporidium form dormant and chemically resistant structures called cysts during their life cycles. The cyst forms are resistant to chlorine and can pass through the filters typically used in water treatment plants. Contamination of the water supply of Milwaukee, Wisconsin, with Cryptosporidium in 1993 sickened over 400,000 people and killed at least 47 people.
Water contamination can also involve inorganic compounds . Gasoline, oil, pesticides, and other noxious chemicals can also contaminate water. These can be especially insidious, since, unlike microorganisms, they can persist in the water for a long time.
Until relatively recently, water contamination was an accidental occurrence. However, particularly since the domestic terrorist attacks of September, 11, 2001, the vulnerability of water supplies to deliberate sabotage has been recognized.
Pathogenic microorganisms or the toxic by-products of the organisms can be added to water. Drinking the contaminated water can be fatal. While this form of bioterrorism is unlikely in a municipal water supply, because the quantities of microorganisms and toxins that would be needed, contamination of an individual well is entirely possible.
Descriptions of symptoms including diarrhea, vomiting, headache, or muscle ache can alert a forensic investigator to the possibility of a contamination event.
see also Bioterrorism; Escherichia coli ; Pathogens.