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Calcium
1987
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Table of Contents
- General
- Occurrence
- Canadian Exposure
- Analysis
- Treatment Technology
- Health Considerations
- Other Considerations
- Conclusion
- References
There is no evidence of adverse health effects specifically attributable to calcium in drinking water. Insufficient data are available to set a specific value for an aesthetic objective for calcium in drinking water. A guideline for calcium has therefore not been specified.
General
Calcium is the fifth most abundant natural element. It enters the freshwater system through the weathering of rocks, especially limestone, and from the soil through seepage, leaching and runoff.(Footnote 1) The average concentration of calcium in soil is about 1.37 ' 104 mg/kg.(Footnote 2) The leaching of calcium from soil has been found to increase significantly with the acidity of rainwater.(Footnote 3)
Calcium oxide (lime) is used extensively in mortar, stucco and plaster in the building industry. It is used in pulp and paper production, sugar refining, petroleum refining and tanning.(Footnote 4) Lime is also widely used as a wastewater treatment chemical. In 1985, the total consumption of lime in Canada was estimated to be 1 842 800 tonnes.(Footnote 5)
Occurrence
The concentration of calcium in water depends on the residence time of the water in calcium-rich geological formations.
Measurements of water samples collected from 71 municipalities across Canada showed that the mean calcium concentrations were 21.8 (1.3 to 77.3), 18.2 (1.6 to 55.8) and 21.4 (£1.1 to 112.8) mg/L for raw, treated and distributed water, respectively. Raw water supplies that received lime treatment showed significant increases in the amount of calcium in the treated water (e.g., for Ottawa, the calcium concentration increased from 8.6 mg/L in raw water to 16.3 mg/L in treated water).(Footnote 6)
Surface water generally contains lower concentrations of calcium than groundwater.(Footnote 7) A 1977 survey of Canadian surface waters reported low calcium concentrations in Newfoundland, Quebec, British Columbia and the Northwest Territories.(Footnote 8) The highest concentration, 365 mg/L, was recorded in Prince Edward Island, and the lowest, 0.3 mg/L, in Newfoundland. Data collected from 24 stations in Saskatchewan in 1980 and 1981 showed that the concentration of calcium in surface waters ranged from 2 to 141 mg/L,(Footnote 9) whereas the average concentrations from sampling stations in all provinces ranged from 1 to 336 mg/L.
The concentration of calcium in the Great Lakes ranges from 13 to 40 mg/L(Footnote 10,Footnote 11); industrial effluent loadings of calcium in these lakes during 1973 to 1975 were 14 800 tonnes/year for Lake Superior and 6200 tonnes/year for Lake Huron.(Footnote 10) The environmental concentration of calcium in Canadian surface waters during 1980 to 1985 ranged from <0.002 mg/L to a high of 1370 mg/L, the high being recorded in Bench Mark Creek in Alberta.(Footnote 9)
Atmospheric calcium is derived mainly from industrial activities.(Footnote 12) A major source of atmospheric calcium is the burning of fossil fuels, which contain calcium at concentrations of approximately 10 000 mg/kg.(Footnote 13) Atmospheric loading of calcium in the Great Lakes basin is estimated to be greater than 100 000 tonnes.(Footnote 10,Footnote 14) Reported concentrations of calcium (in particulates) in air over Edmonton in 1978 to 1979 showed a marked seasonal variation, peaking in the summer. For the three one-month periods (November, March/April and July/August) during which air concentrations were measured, the mean concentrations were 1.6, 2.2 and 2.6 µg/m3, respectively. Low enrichment factors support the conclusion that a substantial portion of the calcium was of natural origin.(Footnote 15) Calcium concentrations measured over Windsor, Ontario, averaged 0.078 mg/m3 during a day of abundant particulate pollution and 0.009 mg/m3 when pollution was less abundant.(Footnote 16) Calcium concentrations in rainwater in a rural area near Toronto ranged from 0.1 to 0.4 mg/L.(Footnote 17)
The concentrations of calcium in certain foods are as follows: 12 800 mg/kg in dried skimmed milk, 8000 mg/kg in cheese, 100 mg/kg in meat, 250 to 1200 mg/kg in fish, 30 to 2220 mg/kg in fruit and vegetables and 0 to 150 mg/kg in fats.(Footnote 18,Footnote 19)
Canadian Exposure
It has been estimated that the daily intake of calcium from the average Canadian diet is 1000 mg,(Footnote 20) although some women consume less than 800 mg/day.(Footnote 21,Footnote 22) Drinking water in Canada usually contains between 1.1 and 112.8 mg/L calcium.(Footnote 6) These values are used in Table 1 to estimate the contribution of drinking water to the total calcium intake.
| Type of water | Water (mg/day)  |
RNI (mg/day) |
Total | Percent from water |
|---|---|---|---|---|
|
||||
| Soft water (1.1 mg/L Ca2+) | 1.65 |
800 |
801.7 |
0.2 |
| Hard water (112.8 mg/L Ca2+) | 169.2 |
800 |
969.2 |
17.5 |
Analysis
Air-acetylene flame atomic absorption spectrometry (AAS) and inductively coupled plasma (ICP) emission spectrometry are accurate methods for determining calcium in water. Two other methods, titration with permanganate and titration with ethylene-diaminetetraacetic acid (EDTA) or its salts provide good results for control and routine applications at higher concentrations. The EDTA titration procedure is preferable to the permanganate method because of its simplicity and rapidity.(Footnote 25)
The detection limit of the AAS method on direct aspiration is 3 µg/L, and the optimum concentration ranges from 0.2 to 20 mg/L. The recovery of added calcium in a spiked sample is between 85 and 115 percent. The detection limit of the ICP method is 10 µg/L at a 317.93 nm wavelength.(Footnote 25)
Treatment Technology
Calcium is one of the principal cations associated with hardness in drinking water. The hardness of water can range from less than 75 mg/L as CaCO3 (considered a soft water) to more than 300 mg/L as CaCO3 (considered a very hard water).(Footnote 26)
Calcium can be efficiently removed from source water by softening the water either by ion exchange or by chemical precipitation. Because of the variation in consumer acceptance of hardness in drinking water, the finished water hardness produced by different utility softening plants will range from 50 to 150 mg/L as CaCO3.(Footnote 26)
Health Considerations
Absorption, Distribution and Excretion
Calcium is primarily absorbed in the proximal portion of the small intestine by a vitamin D-enhanced active transport process. The amount of calcium absorbed from the diet depends on the concentrations of a number of dietary components, as well as on non-dietary factors, such as pH of the intestine. Absorption ranges widely, from 12 to 67 percent, and is the chief means of controlling body calcium concentrations.
The total body burden of calcium in an adult male is about 1010 g, of which >99 percent is associated with the skeleton and only 0.1 percent with the extracellular fluids. The extracellular concentrations are regulated by parathyroid hormone and calcitonin, which, respectively, increase and decrease the calcium concentrations. A calcium buffer is provided by the bones, where 0.5 to 1.0 percent of the total bone mass, consisting of calcium phosphate compounds, is rapidly available.
About 180 mg calcium are excreted daily in the urine, compared to 740 mg in the faeces and 30 to 150 mg in sweat. Both faecal and urinary calcium vary with intake.(Footnote 27)
Adverse Effects
Because of the efficient homeostatic mechanisms that control calcium metabolism, adverse effects are observed only following the intake of extremely large quantities of calcium. High dietary calcium levels may adversely affect the bioavailability of other minerals in the diet. Calcium, in association with phosphate, may reduce iron absorption.(Footnote 28) Magnesium balance is reportedly affected by dietary calcium,(Footnote 29,Footnote 30) although there is some evidence to the contrary.(Footnote 31) There is evidence that the relationship between dietary calcium and magnesium may vary with age and sex.(Footnote 32) Zinc absorption is affected by dietary calcium in animals(Footnote 33) but apparently not in humans.(Footnote 34,Footnote 35) Foods that are high in both calcium and phosphorus, however, may inhibit zinc absorption.(Footnote 36) Both chromium(Footnote 37) and manganese(Footnote 38) absorption appear to be inhibited by high dietary calcium concentrations. The presence of calcium in drinking water could reduce the availability of copper as a result of the less aggressive leaching of copper in the delivery system.(Footnote 39)
Beneficial Effects
Calcium blocks the absorption of heavy metals, and it has been found, for example, that a low-calcium diet increases the susceptibility of rats to lead poisoning.
Adequate calcium in the diet of humans under the age of 30 is thought to retard the development of osteoporosis through an increase in bone mass. For post-menopausal women and men over 60 years of age, it has been suggested,(Footnote 40) but is not universally accepted,(Footnote 41) that increased dietary calcium could slow down the process of bone resorption. A greater incidence of eclampsia during pregnancy is reported in populations on a low-calcium diet.(Footnote 42) Calcium supplements have been shown to lower the blood pressure of pregnant women.(Footnote 43)
A diet rich in calcium may prevent colon cancer in humans(Footnote 44) and may, in fact, reverse early signs of colorectal cancer.(Footnote 45) Colorectal cancer occurs more frequently than anticipated in people drinking soft, low-calcium water.(>46)
Dietary calcium has also been proposed as an anti-hypertensive agent. This is supported by evidence from large-scale epidemiological studies,(Footnote 42,Footnote 47) dietary surveys,(Footnote 48,Footnote 49) intervention dietary studies(Footnote 50-52) and experimental physiological studies.(Footnote 53-55)
Supplemental dietary calcium reduced plasma cholesterol in young goats.(Footnote 56) However, when both calcium and vitamin D were supplemented in these studies, there was a significantly greater incidence of aortic calcification, which is also considered to be a sign of atherosclerotic lesions. Hard drinking water could, therefore, be an important supplementary calcium source, as its beneficial effects would not be offset by increased vitamin D intake, as would occur upon intake of dairy products supplemented with vitamin D.
There are several proposed biological mechanisms involving calcium that could account for some of the statistical relationships provided by epidemiological studies(Footnote 57,Footnote 58) between hard drinking water and a lower incidence of cardiovascular disease (see "Hardness" review in the Supplementary Documentation).
Other Considerations
As a contributor to hardness, calcium can have detrimental effects on drinking water quality. These effects are mainly aesthetic and are discussed in the "Hardness" review in the Supplementary Documentation.
Conclusion
1. There is no evidence of adverse health effects specifically attributable to calcium in drinking water.
2. Undesirable effects due to the presence of calcium in drinking water may result from its contribution to hardness. These effects have been dealt with in the "Hardness" review in the Supplementary Documentation.
3. A separate maximum acceptable concentration for calcium has, therefore, not been specified.
References
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