Page 3: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Chromium
Occurrence
Of the common trivalent chromium salts, the chloride, nitrate, and sulphate are readily soluble in water; the hydroxide and carbonate are quite insoluble. Of the common hexavalent chromium salts, only sodium, potassium, and ammonium chromates and the corresponding dichromates are soluble. Most of the chromium in soils is present in the form of highly insoluble chromites. Weathering, oxidation, and bacterial action convert these chromites into soluble forms, and in this way chromium mineral deposits contribute slightly to the chromium content of natural waters. Chromium can also be present in natural waters as a contaminant from the discharge of industrial wastes or water from cooling systems in which chromates are used as corrosion inhibitors.
Total dissolved chromium is the parameter most often determined in trace element analyses of surface and ground waters. It is generally assumed that the trivalent form is not likely to be present in waters of pH 5 or above because of the low solubility of the hydrated oxide.Footnote 3 In preliminary studies, both trivalent and hexavalent forms have been shown to exist in surface waters. Analysis of samples from the Upper Susquehanna River Basin in New York State revealed the predominance of chromium(III) in uncontaminated waters and an increase in the mean chromium(VI) content of the river downstream from a sewage outfall.Footnote 4 Chromium(III) added to natural lake waters is converted very slowly to chromium(VI).Footnote 5 In chlorinated drinking water, chromium is usually present in the hexavalent state.
Chromium is generally present at low concentrations in Canadian surface waters. Concentrations in the Great Lakes averaged approximately 0.001 mg/L (range 0.0002 to 0.019 mg/L),Footnote 6,Footnote 7 and concentrations in Canadian rivers were between 0.002 and 0.023 mg/L.Footnote 7 Data from NAQUADAT stations during the period 1980 to 1985 showed that, for the Central region of Canada, total chromium concentrations in raw water ranged from the detection limit of 0.002 mg/L to 0.044 mg/L; for the Atlantic region, the concentrations ranged from the same detection limit to 0.024 mg/L.Footnote 8 Concentrations of chromium in Canadian waters have been stated to be usually less than 0.025 mg/L.Footnote 1
A survey of Canadian drinking water supplies suggested that the maximum concentrations of chromium in raw water and in treated and distributed waters were 0.014 and 0.009 mg/L, respectively. The median concentration of chromium in three types of water was 0.002 mg/L.Footnote 9 Chromium concentrations above 0.001 mg/L were detected in only 11 percent of samples taken at consumers' taps from 969 U.S. water systems; the average concentration of chromium in these samples was 0.0023 mg/L.Footnote 10
There is insufficient information to indicate mean concentrations of chromium in the air of Canadian communities. The concentrations of chromium in air samples from five remote areas in Canada ranged from 0.00000032 to 0.000025 mg/m3.Footnote 11 In the United States, chromium concentrations in urban air ranged from less than 0.00001 mg/m3 to 0.00005 mg/m3.Footnote 12
Foods vary considerably in chromium content. Milk and dairy products (mean, 0.06 mg/kg), meat (0.07 mg/kg), cereal (0.17 mg/kg), potatoes (0.05 mg/kg), fruits (0.06 mg/kg), and sugars (0.34 mg/kg) are the main dietary sources of this element.Footnote 13 Concentrations of chromium ranging from 0.13 to 0.85 mg/kg have been recorded in a variety of seafoods commercially available in Canada.Footnote 14 Carbonated beverages and fruit juices generally contain less than 0.01 mg/L.Footnote 15 Chromium concentrations in imported and domestic wines available in Canada were between 0.02 and 0.06 mg/L.Footnote 16 Chromium occurs in food mainly in the trivalent form, although as much as 63 percent of the total chromium in some foods is present in the hexavalent form.Footnote 17 In cooked food, levels of chromium may be slightly higher because of the contribution from stainless steel utensils.