December 6, 2008
The World Health Organization convened a meeting of toxicology experts in Ottawa (Canada) this past week to figure out a Tolerable Daily Intake (TDI) of melamine. The expert panel arrived at a consensus of 0.2 milligrams of melamine daily per kilogram of body weight (one kilogram equals 2.2 pounds).
This is a significant reduction from the previous working numbers of 0.5 mg/Kg (in Europe), and 0.63 mg/Kg on which the US Food and Drug Administration based its Interim Risk Assessment. The WHO announcement did not provide any details explaining the basis for the change.
An obvious question is whether this reduced TDI will alter the interim limit guidelines that have been applied around the world for melamine in food. At present, those guidelines stipulate a maximum of 2.5 ppm (i.e., 2.5 mg/Kg) of melamine in most foods and feeds. Foods intended to be the main source of nutrition for infants and toddlers (age cut-off of 36 months) must meet a stricter melamine limit of 1.0 ppm.
It's easiest to answer the question by working through an example – a 3-year old child weighing 15 Kg (33 pounds).
According to the new recommendations, this child can safely consume 3 milligrams of melamine daily (0.2 mg/Kg body weight, multiplied by 15 Kg). Assuming that all food contains the permitted limit of 2.5 ppm of melamine, the child would need to eat or drink 1.2 Kg – more than 2.6 pounds – of food and beverage every day in order to consume 3 milligrams of melamine.
Using the same arithmetic, an adult weighing 70 Kg (154 pounds) would have to consume 5.6 Kg (more than 12 pounds) of food and beverage daily to reach his or her TDI of 14 milligrams of melamine.
There are other considerations, of course. Not everyone will respond to melamine the same way. Individuals whose kidney functions already are impaired may be more susceptible to low doses of melamine. Infants and young children may be far more susceptible than adults. And no one knows to what extent the presence of other related compounds (such as cyanuric acid) may alter the health equation. For the moment, though, the current guidelines are likely to remain in force.
The WHO report states clearly that the TDI of 0.2 ppm is a Tolerable – not a safe – level for melamine. In principle, melamine should not be present in food. In practice, food can become contaminated by trace amounts of melamine from products used in food plant sanitation, from the metabolism of certain pesticides by crops, and by migration from food contact surfaces, such as melamine-based dish ware.
Until society finds a way to eliminate all possible sources of melamine contamination of our food supply, it would appear that we shall have to tolerate the possibility that we are ingesting melamine along with our meals.