Infants may be more sensitive than adults to exposures because, for example, infant formula is the sole source of nutrition, exposure continues for up to 12 months, and renal function may be more immature compared to adults. This raises a high degree of uncertainty with regard to the determination of safety/risk. Given these conditions, FDA has applied an additional 10-fold safety factor, yielding a combined safety factor of 1000-fold, to compensate for these uncertainties. This results in a TDI/10 of 0.063 mg melamine/kg-bw/d.
The next step is to convert from a dose of 0.063 mg/kg bw/d to total melamine consumed per day.
0.063 mg/kg-bw/d x 3 kg/infant = 0.189 mg melamine/infant/day. To estimate the level of melamine that does not raise public health concerns, FDA used a worst case exposure scenario in which all of an infant’s total daily dietary intake (typically 0.15 kg powdered infant formula) is contaminated with melamine. The previously determined (see above) total amount of melamine/infant/day:
0.189 mg/infant/day divided by 0.15 kg of food = the food contamination level that would provide this amount of melamine to a 3 kg infant per day. Thus, 0.189 mg melamine divided by 0.15 kg of food = 1.26 mg melamine/kg food. Therefore, if 100% of the diet were contaminated at a level of 1.26 ppm of melamine, an infant’s daily intake would equal 0.063 mg/kg bw/d. This value of 1.26 ppm is rounded down to 1.0 ppm melamine to provide an additional margin of safety.
The safety/risk assessment assumes the analogues to have equal effect. Thus, levels of melamine or one of its analogues alone below 1.0 ppm in infant formula do not raise public health concerns.
FDA is continuing to sponsor and conduct animal studies to assess the potential toxicity from co-ingestion of melamine and cyanuric acid. As this ongoing research is completed, FDA will ｕｐｄａｔｅ its interim safety/risk assessment for melamine and its analogues, as appropriate.
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