In this excellent article released yesterday by the American Veterinary Medical Association (AVMA),
Melamine and Cynauric Acid Interaction May Play a Part in Illness and Death from Recalled Pet Food, recent research shows that it may be  the combination of melamine and cyanuric acid that are causing the health problems related to the contaminated pet foods.

The investigation into contaminated pet food has focused on melamine contamination of ingredients imported from China, such as wheat gluten, rice protein concentrate and corn gluten (imported into South Africa). It is now believed that cyanuric acid, as well as melamine, has been found in urine samples from animals that died.
Analysis of the crystals in the kidneys of affected animals have revealed that they are approximately 70 percent cyanuric acid and 30 percent melamine, and are extremely insoluble. Furthermore, tests mixing melamine and cyanuric acid in samples of cat urine resulted in almost immediate formation of crystals that were identical to crystals found in the kidneys of affected animals. Two other melamine- related substances--ammelide and ammeline--may also play roles and are under investigation.

So, what are melamine and cyanuric acid?  What are the health and safety data available on these two chemicals? The following information provided below  has  been taken from the National Library of Medicine, Toxnet, Hazardous Data Bank, unless otherwise sourced.

MELAMINE: Full record here

Characteristics:
CAS #: 108-78-1
Molecular Formula: C3-H6-N6
Molecular Weight: 126.13
Some physical properties: Colorless crystals, slightly soluble in water.

History:
The German scientist Justus von Liebig first synthesized a compound in the 1830s and called it melamine. Commercial interest and synthesis of the compound started in 1937. Nowadays melamine is an important starting material for the production of synthetic thermosetting products worldwide. Melamine is often used as a brand name.
http://www.dsm.com/en_US/html/dmm/faq_page.htm source

Uses:
Melamine is produced as a reactive intermediate for the manufacturing of melamine-formaldehyde (MF) and melamine-urea-formaldehyde (MUF) resins. The predominant uses of melamine resins are for decorative coatings for surfaces and in adhesives for water resistant wood paneling. These are typically found in kitchen countertops, furniture, flooring and wall panels. Melamine is also used to produce kitchen implements and dinnerware, coatings for metal componenets, additives for papers and textiles, flame retardant additives for foams used in furniture and mattresses, and as a component in many other chemical compounds.

Human Health Effects:

From Manufacturer MSDS

Routes of Entry: Inhalation. Ingestion.
Toxicity to Animals:
Acute oral toxicity (LD50): 3161 mg/kg [Rat].
Acute dermal toxicity (LD50): >1000 mg/kg [Rabbit].
Chronic Effects on Humans:
CARCINOGENIC EFFECTS: Classified 3 (Equivocal evidence.) by NTP. 3 (Not classifiable for human.) by IARC.
MUTAGENIC EFFECTS: Mutagenic for bacteria and/or yeast.
Other Toxic Effects on Humans: Hazardous in case of skin contact (irritant), of ingestion, of inhalation (lung irritant).
Special Remarks on Toxicity to Animals: Not available.
Special Remarks on Chronic Effects on Humans:
May cause adverse reproductive effects (fertility, fetotoxicity), and may affect genetic material based on animal data. May also be tumorigenic (carcinogenic) based on animal data.
Special Remarks on other Toxic Effects on Humans:
Acute Potential Health Effects:
Skin: May cause skin irritation.
Eyes: May cause eye irritation
Inhalation: May cause irritation of the respiratory tract and affect respiration. May affect behavior and sense organs, liver and blood.
Ingestion: May cause irritation of the digestive tract with nausea, vomiting and diarrhea. May affect the urinary system.

Workplace Environmental Exposure Level (WEEL): 8-hr Time-weighted Average (TWA) 10 mg/cu m, inhalable; 5 mg/cu m, respirable.

Metabolism/Metabolites: Crystalluria is a metabolite found in excretion after ingestion

Absorption, Distribution & Excretion: Following single oral doses in rats and dogs, 50-60% of administered melamine was recovered in dogs in six hours and up to 85% was recovered in 24 hours. After administration of a single dose of 250g/kg to rats, 50% was recovered within six hours in the urine.

Doses of 2.4g/kg caused diuresis and elimination of crystals of Dimelamine monophosphate in the urine.

CYANURIC ACID: Full record here

Characteristics:
CAS #: 108-80-5
Molecular Formula: C3-H3-N3-O3
Molecular Weight: 129.08
Some physical properties:  Cyanuric acid is in the Chlorinated Isocyanurate family of chemicals. It is an odorless water soluble crystalline powder of anhydrous crystals from concentrated hydrochloric acid or sulfuric acid

History:

The chlorinated isocyanurates first were registered in the United States in 1958 for use as disinfectants, sanitizers, algicides and fungicides. In 1980, EPA issued a Data Call-In requiring additional toxicity data to assess the potential for kidney damage from exposure to these compounds. The Agency issued a Registration Standard for the chlorinated isocyanurates in
May 1988 which evaluated the kidney toxicity data and required additional information to support the indoor and aquatic non-food uses. Currently, technical and end use products are registered containing chlorinated isocyanurates as active ingredients.  Source
http://www.epa.gov/REDs/factsheets/0569fact.pdf

Uses:

Cyanuric acid was used as an ingredient in herbicides and in anti-microbial disinfectants. Its use in herbicides has been cancelled, as discussed above. It is still used, however, as a disinfectant chemical in swimming pools to lower the rate of photochemical reduction of chlorine, hypochlorous acid and the hypochlorite ion.

Cyanuric acid is also used in the production of Melamine, sponge rubber, cyanic acid gas, and as an intermediate chemical in the production of chlorinated bleaches and whitening agents.

Human Health Effects:

Workplace Environmental Exposure Level (WEEL): 8-hr Time-weighted Average (TWA) 10 mg/cu m, total; 5 mg/cu m, respirable.

LD50 Rat oral 5 g/kg

Pesticides, such as cyanuric acid, can be absorbed into the body by three routes: dermal, inhalation, and ingestion(1).  

Non-Human toxicity studies showed the kinds of symptoms that have been reported in cats and dogs exposed to the tainted pet foods. Here are some excerpts:

* When rats & rabbits were given single oral doses of 10g/kg no symptoms resulted. When given 4 oral doses of 20g/kg their appetites decreased.

 * Carcinogenic effects: Inadequate controls cloud the picture. 150-300 mg/kg cyanuric acid was fed to rats, cysterian sarcomas were observed between 19-25 months. Fibroadenoma of mammary glands were noted in 2 females. In mice fed 280-310 mg/kg, myeloid leucosis observed in 2/14 mice that had survived 23 months.

• Renal Effect observed in female and male rates fed 8% Monosodium cyanurate for 20 weeks in diet. 14 males and 4 females died during 20 weeks. Autopsy--histological changes in kidney related to diuretic effect of cyanuric acid.

• Three dogs fed 8% Monosodium cyanurate for 2 years. Two dogs dies at 16 months and 21 months. Autopsy - Kidney fibrosis, focal dilation and epithelial proliferation of Bellini's ducts. Third dog sacrificed after two years showed the same renal changes plus atrophy of the thyroid with lymphocytic infiltration. A diet containing 0.8% of Monosodium cyanurate, however, given to 3 dogs for 6 months caused no evident adverse effects.

• Microscopic examination after dosing reveals atrophy of the gastric mucosa, indicating a pronounced irritating effect. Feeding studies in rats and mice suggest lower tumorigenic potential. Studies of subcutaneous application in mice at an application rate of 550 to 620 mg/kg show no tumor induction. Dermal application of two drops of 20% cyanuric acid in benzene 3 times/wk to mice is reported in which two animals developed liver tumors after 22 mo. Studies of the teratogenic and reproductive effects of the cmpd in mice and rats examined show no dominant lethal response nor any significant difference in reproductive parameters between the experimental and control groups.
  

SUMMARY:

Much of the safety studies conducted on Melamine were concerned with the dermal effects since that was the most likely route of exposure. More studies need to be done on ingestion. From the studies conducted on Cyanuric acid the correlation to the reported effects from ingestion of contaminated pet foods seems very relevant. The recent article from the American Veterinary Medical Association indicates the same. I hope they will initiate new studies.

Clearly we need to know the long term health effects of these chemicals, but I think from the results of my search today indicate that they have no place in either our pets or our own food supply. This is a food safety disaster in the making in the long term. All foods being imported from China need to be ceased immediately and testing of already imported foods must be conducted or that food should be destroyed.