Page 3: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Formaldehyde
Formaldehyde enters drinking water via industrial effluent, leaching from polyacetal compression fittings in plastic potable water linesFootnote 4,Footnote 8 and ozonation of humic substances and other organic material.Footnote 9,Footnote 10 Formaldehyde production in the treatment of surface water appears to be proportional to the total organic carbon content of the raw water,Footnote 10 although Huck et al.Footnote 11 did not observe a quantitative relationship between formaldehyde levels and raw water non-volatile organic carbon concentration. In water lines, an interior protective coating generally separates the water from the polyacetal resin. If a break occurs in the coating, however, the water may come in direct contact with the resins, resulting in a continuous release of formaldehyde into the water via hydrolysis of the resin surfaces. The resultant concentrations of formaldehyde vary depending on the residence time of water in the pipes; levels may approximate 20 µg/L in occupied dwellings with normal water usage or reach 100 µg/L in unoccupied dwellings or after a few days of no water usage.Footnote 8 In 16 of 34 U.S. water treatment plants, formaldehyde was detected in the influents at levels ranging from 1.2 to 13 µg/L (median 2.8 µg/L).Footnote 12 The median value for all 34 of the plants was <1.0 µg/L.Footnote 12For three plants using ozone, formaldehyde levels in influent ranged from <1.0 to 3.2 µg/L, while concentrations as high as 31 µg/L were detected in the ozonated drinking water.Footnote 12In Edmonton, formaldehyde levels in raw water for the 10-month period from March 1989 to January 1990 averaged 1.2 µg/L and peaked at 9 µg/L. Test ozonation increased the mean formaldehyde level from 1.2 µg/L to 2.2 or 3.2 µg/L, depending on the ozone dosage.Footnote 11Formaldehyde may be present in foods naturally or as a result of contamination.Footnote 1,Footnote 13 Concentrations of formaldehyde ranging from 3 to 26 mg/kg have been reported in a variety of food materials. Some food additives, such as hexamethylenetetramine, have been reported to decompose gradually to formaldehyde in the presence of proteins or under acidic conditions.1Daily intake of formaldehyde from food is difficult to evaluate; however, the World Health Organization (WHO) estimated it to be in the range of 1.5-14 mg/d (mean 7.75 mg/d) for an average adult.Footnote 5 Owen et al.Footnote 8 estimated it to be 11 mg/d based on a North American diet.
The general population is exposed to formaldehyde mainly by inhalation. It has been estimated that an individual smoking 20 cigarettes per day would receive from 0.38 to 1.0 mg/d by this route.Footnote 5,Footnote 6 Formaldehyde is released into the air from resin glues and plastic materials, and low air levels (parts per billion) may result from the photo-oxidation of fossil fuel-derived hydrocarbons. In one study in Atlanta, Georgia, the ambient levels of formaldehyde at four locations between July and August 1992 were reported to average between 2.7 and 3.0 ppb, with a peak level of 8.3 ppb.Footnote 14In the early 1980s, average Canadian formaldehyde levels in homes ranged from 0.014 to 0.042 mg/m3, whereas the average level in homes with urea-formaldehyde foam insulation was 0.066 mg/m3.Footnote 15,Footnote 16 The overall daily inhalation exposure for an average adult has been approximated as 0.3-2.1 mg (average 1 mg), with exposures as high as 5 mg/d.Footnote 5 Assuming a contribution of approximately 9.4 mg/d from food,Footnote 5,Footnote 81 mg/d from inhalationFootnote 5 and 0.15 mg/d from water (worst-case scenario: 100 µg/L),Footnote 8 an adult would receive 10.55 mg of formaldehyde per day. Less than 2% of this total intake would, therefore, come from drinking water.
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