Toxicity[edit]
The short-term lethal dose of melamine is on a par with common table salt, with an
LD50 of more than 3 grams per kilogram of bodyweight.
[15] U.S. Food and Drug Administration (FDA) scientists explained that when melamine and
cyanuric acid are absorbed into the bloodstream, they concentrate and interact in the urine-filled
renal tubules, then crystallize and form large numbers of round, yellow crystals, which in turn block and damage the renal cells that line the tubes, causing the kidneys to malfunction.
[16]
The
European Union set a standard for acceptable human consumption (
tolerable daily intake or TDI) of melamine at 0.2 mg per kilogram of body mass,
[17] (previously 0.5 mg/kg), Canada declared a limit of 0.35 mg/kg, and the US FDA's limit was put at 0.063 mg/kg (previously 0.63 mg/kg). The
World Health Organization's food safety director estimated that the amount of melamine a person could stand per day without incurring a bigger health risk, the TDI, was 0.2 mg per kilogram of body mass.
[18]
Toxicity of melamine can be mediated by
intestinal microbiota. In culture,
Klebsiella terrigena, which rarely colonizes mammalian intestines,
[19] was shown to convert melamine to cyanuric acid directly. Rats colonized by
K. terrigena showed greater melamine-induced kidney damage compared to those not colonized.
[20]
Acute toxicity[edit]
Melamine is reported to have an oral
median lethal dose (LD50) of 3248
mg/kg based on rat data. It is also an irritant when inhaled or in contact with the skin or eyes. The reported dermal LD50 is >1000 mg/kg for rabbits. A study by Soviet researchers in the 1980s suggested that
melamine cyanurate, commonly used as a fire retardant,
[21] could be more toxic than either melamine or cyanuric acid alone.
[22] For rats and mice, the reported LD50 for melamine cyanurate was 4.1 g/kg (given inside the stomach) and 3.5 g/kg (via inhalation), compared to 6.0 and 4.3 g/kg for melamine and 7.7 and 3.4 g/kg for cyanuric acid respectively.
A toxicology study in animals conducted after recalls of contaminated pet food concluded that the combination of melamine and cyanuric acid in diet does lead to
acute kidney injury in cats.
[23] A 2008 study produced similar experimental results in rats and characterized the melamine and cyanuric acid in contaminated pet food from the 2007 outbreak.
[24] A 2010 study from
Lanzhou University attributed kidney failure in humans to uric acid stone accumulation after ingestion of melamine resulting in a rapid aggregation of metabolites such as cyanuric acid diamide (
ammeline) and cyanuric acid.
[25] A 2013 study demonstrated that melamine can be metabolized to cyanuric acid by gut bacteria. In particular,
Klebsiella terrigena was determined to be a factor in melamine toxicity. In culture,
K. terrigena was shown to convert melamine to cyanuric acid directly. Cyanuric acid was detected in the kidneys of rats administered melamine alone, and the concentration after Klebsiella colonization was increased.
[20]
Chronic toxicity[edit]
Ingestion of melamine may lead to
reproductive damage, or
bladder or
kidney stones, which can lead to
bladder cancer.
[26][27][28][29]
A study in 1953 reported that dogs fed 3% melamine for a year had the following changes in their urine: (1) reduced
specific gravity, (2)
increased output, (3) melamine
crystalluria, and (4)
protein and
occult blood.
[30]
A survey commissioned by the American Association of Veterinary Laboratory Diagnosticians suggested that crystals formed in the kidneys when melamine combined with cyanuric acid, "don't dissolve easily. They go away slowly, if at all, so there is the potential for chronic toxicity."
[31][32][33]
https://en.wikipedia.org/wiki/Melamine#Toxicity
