Page 6: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Colour
Limits for colour in potable water have traditionally been based on aesthetic considerations. It has been noted, however, that provision of a supply of visibly coloured water may lead consumers to seek colourless, but possibly unsafe, alternative sources of drinking water.Footnote 65 Other health-related criteria include the previously discussed relationships between colour and trihalomethane production, removal of turbidity and interference with chlorine residuals.
Many beneficial human health effects have also been attributed over the years to the consumption of coloured water and to the use of humic preparations in the treatment of disease.Footnote 66 These beneficial uses include the treatment of rheumatic feverFootnote 67; the healing of skin defectsFootnote 68; the stimulation of wound healingFootnote 69; and the prevention of swelling in battle wounds. Humic substances in water and sediments are also intimately involved with hydrotherapy and balneotherapy, which are respected and widely practised elements of European medicine.Footnote 70
Few toxicological studies of organic colouring agents have been undertaken. The median lethal dose for intracardial application of humic acid in the rat was found to be 1127 ± 200 mg/kg bw; the lethal reaction was ascribed to the possible reaction of humic acids with serum proteins.Footnote 71 Male rats were supplied with drinking water containing 10, 100 and 1000 mg/L of a low ash preparation of soil fulvic acid for periods of up to 90 days; no significant changes in body weight, food and water intake, organ/body weight ratios or tissue histology were observed.Footnote 72 The same fulvic acid was also given daily to rats by gavage at a dosage of 1000 mg/kg for 14 days. No mortality occurred at this dose level, although the rate of weight gain was less than that in control animals, and slight changes were noted in some of the kidney enzyme concentrations.Footnote 72 In the most relevant study to date, humic material at two dose levels was fed to rats in their drinking water for periods of 19 to 35 weeks; the authors concluded that a safety factor of approximately 100 would apply to the human consumption of drinking water containing 2.5 mg of "humic acid" per litre.Footnote 66
Very little study has been devoted to the comparative toxicities of trace metals and their humate complexes with reference to human health.Footnote 73 It has been shown that the acute mammalian toxicities of iron, lead, barium, silver, copper and zinc are substantially enhanced on intravenous injection as their humate complexes, but that orally ingested lead humate is at least 60% less toxic than lead acetate.Footnote 74 Large increases, from 50 to 100%, were found in the amounts of ionic material -- calcium, magnesium, iron, manganese, zinc and sulphate -- permeating the intestine in the presence of humic acid.Footnote 75 Unfortunately, the substances studied did not include toxic trace metals. No information has been published to date on the bioavailability to mammals of the humate complexes of toxic organic substances.
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