Ground Water Resources of British Columbia
Chapter 6 — Ground Water and Human Health
Harold D. Foster
It is extremely difficult to evaluate the human health implications of the various substances found in ground water (National Academy of Sciences, 1977; Reeder, 1979). Data is often incomplete and relationships between health and contaminants are complex and characterized by uncertainty (Rohlich, 1978). Nevertheless, it is clear that ground water can, and does, contain a wide variety of substances that have health implications. In addition, it is also possible that even deficiencies of certain elements may pose serious health threats (Marier, Neri and Anderson, 1979; Foster, 1986).
For convenience, water contaminants can be subdivided into four major classes; physical, microbiological, chemical, and radionuclides. Of these the chemical contaminants are unique in that many are essential in maintaining human health; whilst others are a major threat to it. Included amongst elements that are thought to play an essential role in human nutrition are calcium, chlorine, chromium, cobalt, copper, fluorine, iodine, iron, magnesium, manganese, molybdenum, nickel, phosphorus, potassium, selenium, silicon, sodium, strontium, sulphur, tin, vanadium and zinc (Kirschmann and Dunne, 1984). In contrast, aluminum, cadmium, lead and mercury are definitely toxic, but in widely varying concentrations. Arsenic, however, may be an essential trace element at low concentrations, despite the fact that it is clearly harmful when ingested at higher doses (Frost, 1984). Similarly, boron may be critical in calcium utilization by the body (Nielsen, Hunt, Mullan and Hunt, 1987). The roles played by beryllium and silver are less clear (Rohlich, 1978; Kirschmann and Dunne, 1984). Naturally, the percentage of human intake of any of these substances obtained from drinking water is greatly influenced by both their solubility and the nature of local bedrock geology and soils.
The situation is further complicated because even potentially beneficial elements may give rise to a whole spectrum of negative health effects, depending on the levels ingested in drinking water and foods, or taken in through the lungs or skin. This dose dependency can be represented by a dose-response curve; one group of illnesses being associated with too little of the element and another group with too much. This complexity can be illustrated with reference to fluorine. At ground water concentrations of 1 to 1.5 mg/L fluoride reduces tooth decay. At levels of up to 6 mg/L, it depresses the incidence of osteoporosis, giving some protection against bone loss. However, when water levels rise to more than 8 mg/L, excessive bone formation occurs in the periosteum and ligaments begin to calcify (Cargo and Mallory, 1974; Bernstein, et al., 1966). Similarly, whilst iodine deficiency has been clearly linked to both goitre (the over-development of the thyroid gland) and cretinism (mentally retarded dwarfism) (Matovinovic, 1983), it is possible that in Caucasions excessive amounts may be associated with the skin cancer, melanoma (Foster, 1986).
Many inorganic solutes are present in both surface and ground water due to natural processes, such as the chemical weathering of bedrock and soil leaching. The presence of others may be due to contamination caused by waste disposal, mining, agriculture, or manufacturing. In addition, various forms of water treatment, including chemical coagulation, lime softening, and ion exchange are used to reduce trace metal concentrations in drinking water. In British Columbia, many surface waters do not receive adequate treatment and, in consequence, ground water supplies from protected aquifers are generally considered to be safer. However, the chemicals used in some treatment processes, together with the corrosion of pipes in the distribution system may also add trace metals, such as iron, copper and lead, to the water supply. It is unlikely that ground water provided by major suppliers will reach harmful levels of any of these inorganic solutes; since federal and provincial water standards must be met by source utilized for public consumption. However, private wells may be of concern, especially if the distribution system is being corroded, or if they are in close proximity to sources of ground water contamination. Unfortunately, the testing of water quality by private suppliers is often limited to the more common elements and compounds. In general, however, when compared with surface waters, ground waters tend to be bacteriologically safer, cheaper to treat, less affected by radionuclides from fall out, have a lower turbidity and tend to be less affected by accidental chemical spills.
There is considerable controversy over the significance of the relative absence of certain solutes from many surface and ground water supplies. In particular, disagreement has focused on the health implications of drinking soft, low-pH waters. According to the U.S. National Academy of Sciences (1977) there have been more than 50 studies, in nine countries, that have indicated an inverse relationship between water hardness and mortality from cardiovascular disease. That is, people who drink water that is deficient in magnesium and calcium generally appear more susceptible to this disease (Foster, 1987a). The US National Academy of Sciences has estimated that a nation-wide initiative to add calcium and magnesium to soft water might reduce the annual cardiovascular death rate by 150,000 in the United States. However, this suggestion is very controversial, other authors being unwilling to accept that water hardness influences the death rate from cardiovascular disease (Hammer and Heyden, 1980).
Soft water, deficient in calcium and magnesium, has also been linked to elevated rates of Sudden Infant Death Syndrome (Caddell, 1972), diabetes (Foster, 1987b), cerebrovascular disease (Foster, 1987a) and cancer (Allen-Price, 1960; Foster, 1986). It should be noted that both surface and ground water hardness in British Columbia is very variable, being generally highest in the east of the province and lowest in the west (Swain, 1985). However, ground water in general has a tendency to be harder than surface water supplies because of its greater contact with bedrock.
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