Total mercury was measured in 259 total diet food composites from two Canadian cities. Levels were generally low, with 46% of the composites having concentrations below the limit of detection, which ranged from 0.026 to 0.506 ng g(-1). The fish category contained the highest mercury concentrations, which averaged 67 ng g(-1) and ranged from 24 to 148 ng g(-1). All composites were below the Canadian guideline for total mercury in fish of 0.5 ppm. Dietary intakes of mercury averaged 0.022 microg kg(-1) body weight/day (microg kg(-1) day(-1)), and ranged from 0.012 microg kg(-1) day(-1) for females over 65 years old to 0.062 microg kg(-1) day(-1) for 0-1-month-old infants. For fish consumers, fish contributed to more than half of the ingested mercury. All intakes were well below Joint FAO/WHO Expert Committee on Food Additives Provisional Tolerable Weekly Intakes, expressed on a daily basis, of 0.71 microg kg(-1) day(-1) total mercury and 0.47 microg kg(-1) day(-1) methyl mercury, and also below a recent Health Canada recommended maximum methyl mercury intake of 0.2 microg kg(-1) day(-1) for children and women of child-bearing age.

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A cold vapor atomic absorption spectrometric method was developed for the subnanogram-per-gram determination of total Hg in a wide variety of foods. Foods were weighed into 50 mL polypropylene centrifuge tubes and dried without charring at 55°C in a circulating oven. Samples were then digested at 58°C with HNO3, HCl, and H2O2. After matrix modification with solutions of 2% Mg(NO3)2, 0.01% Triton X-100, and Cu(II) at 10 μg/mL, samples were analyzed by using a CeTAC Technologies M-6000A dedicated Hg analyzer. Based on a 2 g sample weight, the detection limit of the method over 12 batches averaged 0.30 ng/g wet weight and ranged from 0.03 to 0.6 ng/g. Recoveries of Hg added to 17 different foods, analyzed in a routine manner, averaged 97%, and individual recoveries ranged from 77 to 107%. Accuracy was confirmed by analysis of 7 biological reference materials from the National Research Council of Canada and the National Institute of Standards and Technology. Stabilization of low concentrations of Hg in solutions containing no sample was required to prevent loss of Hg from blanks. In a comparison of NaCl, potassium dichromate, and Au(III), chloride was much more effective for stabilization than the other two, and HCl was used for subsequent stabilization.