Dietary mercury exposure and effects of foods containing phytochemicals on mercury bioavailability
Mercury and fatty acids in canned tuna (n=240), salmon (n=16), mackerel (n=16), and fish sandwich (n=30) from six retail restaurant chains were measured. The average mercury levels were 188, 45, 55, and 52 ppb, respectively and did not exceed the FDA Action Level of 1000 ppb. "White/albacore tuna in water" contained the highest amount of EPA/DHA (x¯ =902 mg/100 g wet tissue) among the canned tuna but mercury levels were four times higher than those in "light tuna in water" (x¯ =54 ppb). EPA/DHA amounts were higher in salmon and mackerel which contain less mercury than canned tuna product. Average total EPA plus DHA level was between 91 and 620 mg per sandwich. The effect of foods on bioaccessibility and uptake of methylmercury from fish tissue was investigated using in vitro digestion with a TC7 clone of Caco-2 cells. All test mixtures (fish along with food) were subjected to a simulated gastric and small intestinal digestion. Aqueous fraction was separated and subsequently mixed with basal medium for cell treatment. Mercury bioaccessibility, the amount of mercury in aqueous fraction, significantly reduced in green tea (31--2000 mg), black tea (31--2000 mg), soy protein (50--1000 mg), and sodium copper chlorophyllin (0.1--25 mg) in a dose dependent manner (p<0.05), whereas grapefruit juice (0.5--10 mL) did not significantly decrease mercury bioaccessibility. Compared to a control, mercury bioaccessibility with wheat bran (0.05--1 g), oat bran (0.05--1 g), and psyllium decreased by 84%, 75%, and 31%, respectively. Cellular mercury uptake was significantly lower in both green and black tea when compared to control (p<0.05). Soy protein decreased mercury uptake in a dose-dependent manner after addition of 100 mg of soy protein to fish tissue, while grapefruit had no effect on final intracellular mercury levels. Sodium copper chlorophyllin reduced cellular mercury uptake from 0.352 to 0.052 μg mercury/mg protein. Mercury uptake from wheat bran and oat bran was reduced by 0.145 and 0.263 μg mercury/mg protein, respectively. Psyllium did not have a significant effect on mercury uptake. This study suggested that foods rich in phytochemicals/dietary fiber can inhibit methylmercury bioavailability.
Santerre, Purdue University.
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