What is Melamine?

Melamine is an organic base with the chemical formula C3H6N6, with the IUPAC name 1,3,5-triazine-2,4,6-triamine. It is only slightly soluble in water.
Melamine is a trimer of cyanamide. Like cyanamide, it is 66% nitrogen (by mass) and provides fire retardant properties to resin formulas by releasing nitrogen when burned or charred. Dicyandiamide (or cyanoguanidine), the dimer of cyanamide, is also used as a fire retardant.
Melamine is a metabolite of cyromazine, a pesticide. It is formed in the body of mammals who have ingested cyromazine. It was also reported that cyromazine is converted to melamine in plants.

Acute toxicity
Melamine is reported to have an oral LD50 of >3000 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. In a 1945 study, large doses of melamine were given orally to rats, rabbits and dogs with "no significant toxic effects" observed.
A study by USSR researchers in the 1980s suggested melamine cyanurate (a salt formed between melamine and cyanuric acid, commonly used as a fire retardant) could be more toxic than either melamine or cyanuric acid alone. 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 conducted after recalls of contaminated pet food concluded that the combination of melamine and cyanuric acid in diet does lead to acute renal failure in cats.[19]

Chronic toxicity
Ingestion of melamine may lead to reproductive damage, or bladder or kidney stones, which can lead to bladder cancer.
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.
Wilson Rumbeiha, an associate professor in Michigan State University’s Diagnostic Center for Population and Animal Health, commenting on results from a survey commissioned by the American Association of Veterinary Laboratory Diagnosticians and designed and implemented by MSU toxicologists presented at the AAVLD's October 2007 meeting, said: "Unfortunately, these melamine cyanurate crystals don’t dissolve easily. They go away slowly, if at all, so there is the potential for chronic toxicity