Academic journal article Journal of Environmental Health

Assessing Health Risk in Drinking Water from Naturally Occurring Microbes

Academic journal article Journal of Environmental Health

Assessing Health Risk in Drinking Water from Naturally Occurring Microbes

Article excerpt

In April, 1994, in this journal, a comprehensive review of California bottled water by Allen and Darby was published (1). That paper compared and contrasted bottled water with tap water. This review was written to expand and clarify one critical aspect of that paper: the author's thesis that bottled water deteriorates microbiologically during storage and that microbiological changes occurring in the bottle can have adverse health effects. It is necessary to closely examine the nature of bacteria present in bottled water and the dynamics they experience after bottling in order to make appropriate health risk assessment and generate enforceable regulations which will best protect public health.

Allen and Darby (1) presented four basic components to support their contention that water quality is decreased during storage: (i) heterotrophic plate count bacteria (HPC) increase markedly in numbers; (ii) the HPC concentration in the bottle exceeds 500/mL, which represents a health risk; (iii) the immunocompromised are endangered by HPC; and (iv) the lack of residual disinfectant in bottled water compared to tap water contributes to its deterioration.

Heterotrophic plate count bacteria do indeed increase in numbers in a sealed vessel after bottling (2). No drinking water is sterile (3, 4). Both tap water and bottled water have some HPC content regardless of treatment method or residual disinfection concentrations. No treatment process used in mass production of drinking water yields a sterile product - it produces a safe product. Even tap water with high residual chlorine levels have HPC present (5, 6). Once water enters the bottle the small number of HPC present do what they do in nature - they utilize available nutrients and multiply (7, 8, 9,10,11). Because their natural habitat is water, they can utilize the environmental carbon and nitrogen to multiply (8,12, 13). They do so at an extremely low ionic strength and low water temperature. When one species of HPC completely utilizes its particular environmental nitrogen and carbon sources, it dies and is replaced by another species (13). The dead HPC deteriorate returning available carbon and nitrogen, in a different form, to the water. Thus, individual species increase and decrease in numbers over a long period of time. Accordingly, the microbiological "landscape" of bottled water varies widely both in numbers of HPC/mL and species\present over time. Accordingly, sampling a particular bottle will only produce a snapshot of the HPC content at that one point in time. Eventually, all the nutrients are utilized and the HPC counts become very low, or even undetectable. For example, water stored for the army more than thirty years ago has been found to be sterile (14). It is in part because of these natural cycles that it is not rational to write regulations based on any particular concentration of bacteria in the bottle at any specific point in time after the bottle is filled, nor does an expiration date have meaning.

The conditions under which the environmental HPC multiply are much different from the physical/chemical conditions found in humans. Humans are considerably warmer, saltier, and have much higher concentrations of sugar and protein (2,15). The great majority of naturally occurring HPC that multiply in bottled water will not do so under ambient conditions within the human body (16).

Allen and Darby stated that "changes in the bacteriological quality indicated by heterotrophic plate counts were strongly dependent on the initial water quality...." It should be noted, however, that the concentrations of HPC reached in the bottle, and the cycles of multiplication and decrease, are independent of the initial concentrations of HPC entering the bottle. The small number of HPC initially present at the time of bottling will eventually reach concentrations above [10.sup.4]/mL (10). Even though the specific species might differ, an analogous situation occurs in tap water. …

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