Melamine
Melamine is a trimer of cyanoamide (H2NCN). The industrial use of melamine is basically as a polymer: (after mixing with other chemicals)
(1) Thermoset plastic - melamine resin is very durable. The only problem with it though is that it heats up in microwave, thus it cannot be used in a microwave.
(2) Melamine foam - it can be used as a soundproof/insulation, as well as an abrasive cleaning agent (quite well known by now in Hong Kong and perhaps Japan as 激落君)
On the other hand, since melamine contain more than 60% nitrogen by weight, it has been considered for use as a (rather unsuccessful) nitrogen source in the feed for livestocks[1]. In the melamine-tainted milk incident, it was used to increase the apparent nitrogen content of the milk because some assays measure protein content in milk by measuring the nitrogen content.
The acute toxicity of melamine is very low. the LD50 (lethal dose-50, i.e. the dosage of the medication to kill 50% of a population, usually of laboratory animals, e.g. mice, rats) is around the same as salt, at >3000mg/kg. Chronic toxicity is another problem - melamine by itself requires consumption of large amount of pure melamine without good water intake. This is almost impossible for adults.
Melamine has been implicated in several incidents, including one involving pet food in the past. Together with the 2008 melamine tainted milk incident, it was noted that melamine primarily cause complications due to two mechanisms:
(1) the hydrolysis product of melamine (co-contaminants due to the use of low quality of melamine) inhibits a liver enzyme called uric acid oxidase which decomposes uric acid - this leads to a high blood, and thus urine level of uric acid and cause kidney problems.
(2) melamine is also excreted unchanged in the kidneys, causing stone formation.
Again - the addition of melamine is one act of pure fraud. It is definitely not something acceptable in any society. but then as talked the day before, the dose defines the poison. In the Sanlu milk that caused this whole scandal, the dose detected was up to 2,500mg/kg (=part per million, and later up to >6197mg/kg), which is very high - and this dose is only causing the disease in infants because they almost do not drink anything else - the lack of water intake increases the precipitation.
The story in Hong Kong
According to the Centre for Food Safety, melamine-tainted food that has been seen in Hong Kong had concentration up to 68ppm (in chocolate bars).This level, together with the target population, is unlikely to cause any damage even in the worst case scenario (child eating it as the only food - in which case the parents should be prosecuted for child abuse I think).
And then we see a boycott of milk products from China, as well as all other diary products in Hong Kong because of a detection of concentration averaging around 3 part per million.
And then we saw the hospital authority opening special clinics for those children who "supposingly" had taken melamine-tainted milk. To be honest, if anything, if we have a look at the balance between:
(1) Loss of work hours of parents and study hours for children
(2) Risk of contracting disease from clinic attendence
(3) Delay of other patients in same / different department (e.g. ultrasound appointment)
(4) Pressure of work to our paediatric colleagues
vs
(1) The remote risk of having renal disorders from locally bought milk powder/other products
I think most of us could judge.If the child had Sanlu, Mengniu or Yili infant milk powder from China I think it is very acceptable for doctors to consider a streamlined investigation protocol for them. For others, I think the readers can now decide.
[1] The use of non-protein nitrogen sources in animals has been a practice in farming for quite some time - compounds such as ammonia, urea and biuret can be feed to the ruminants and would eventually be incorporated into protein for the animal because of bacterial action in the ruminant stomach.
No comments:
Post a Comment