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Melamine

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This article is about the chemical substance called melamine. The term "melamine" is also used to describe melamine resin, a plastic material.

Template:Distinguish2

Template:Chembox new 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.[1] It was also reported that cyromazine is converted to melamine in plants.[2][3]

Synthesis

Melamine was first synthesized by Liebig in 1834. In early production, first calcium cyanamide is converted into dicyandiamide, then heated above its melting temperature to produce melamine. However, today most industrial manufacturers use urea in the following reaction to produce melamine

6 (NH2)2CO → C3H6N6 + 6 NH3 + 3 CO2

It can be understood as two steps. First, urea decomposes into cyanic acid in an endothermic reaction (NH2)2CO → HCNO + NH3. Then cyanic acid polymerizes to form melamine and carbon dioxide: 6 HCNO → C3H6N6 + 3 CO2. The second reaction is exothermic and the overall process is endothermic.

The above reaction can be carried out by either of two methods:catalyzed gas-phase production or high pressure liquid-phase production. In one method, molten urea is introduced onto a fluidized bed with catalyst for reaction. Hot ammonia gas is also present to fluidize the bed and inhibit deammonization. The effluent then is cooled. Ammonia and carbon dioxide in the off-gas are separated from the melamine-containing slurry. The slurry is further concentrated and crystallized to yield melamine.[4] Major manufacturers and licensors such as DSM, BASF and Eurotecnica have developed some proprietary methods.

The off-gas contains large amounts of ammonia. Therefore melamine production is often integrated into urea production which uses ammonia as feedstock.

Crystallization and washing of melamine generates a considerable amount of waste water, which is a pollutant if discharged directly into the environment. The waste water may be concentrated into a solid (1.5-5% of the weight) for easier disposal. The solid may contain approximately 70% melamine, 23% oxytriazines (ammeline, ammelide and cyanuric acid), 0.7% polycondensates (melem, melam and melon).[5]

Uses

Melamine is used combined with formaldehyde to produce melamine resin, a very durable thermosetting plastic, and melamine foam, a polymeric cleaning product. The end products include countertops, dry erase boards, fabrics, glues, housewares and flame retardants. Melamine is one of the major components in Pigment Yellow 150, a colorant in inks and plastics.

Melamine is also used to make fertilizers.

Melamine derivatives of arsenical drugs are potentially important in the treatment of African trypanosomiasis[6]

Melamine use as non-protein nitrogen (NPN) for cattle was described in a 1958 patent.[7] In 1978, however, a study concluded that melamine "may not be an acceptable nonprotein N source for ruminants" because its hydrolysis in cattle is slower and less complete than other nitrogen sources such as cottonseed meal and urea.[8]

Melamine is sometimes unethically added to food products in order to increase the apparent protein content. Standard tests such as the Kjeldahl and Dumas tests estimate protein levels by measuring the nitrogen content, so they can be misled by adding nitrogen-rich compounds such as melamine. [9]

Regulation

The Food Safety and Inspection Service (FSIS) of the United States Department of Agriculture (USDA) provides a test method for analyzing cyromazine and melamine in animal tissues in its Chemistry Laboratory Guidebook which "contains test methods used by FSIS Laboratories to support the Agency's inspection program, ensuring that meat, poultry, and egg products are safe, wholesome and accurately labeled."[10][11] In 1999, in a proposed rule published in the Federal Register regarding cyromazine residue, the United States Environmental Protection Agency (EPA) proposed "remov[ing] melamine, a metabolite of cyromazine from the tolerance expression since it is no longer considered a residue of concern."[12] Melamine, classified a controlled substance in China[citation needed], has been illegally used in the high profile 2008 baby milk scandal case which led to the death of at least 4 infants[13].

Toxicity

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.[14] In a 1945 study, large doses of melamine were given orally to rats, rabbits and dogs with "no significant toxic effects" observed.[15]

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[16]) could be more toxic than either melamine or cyanuric acid alone.[17] 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.[18]

Chronic toxicity

Ingestion of melamine may lead to reproductive damage, or bladder or kidney stones, which can lead to bladder cancer.[14][19][20][21][22]

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.[23]

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.”[24][25][26]

2007 pet food recalls

Further information: 2007 pet food recalls

In 2007 a pet food recall was initiated by Menu Foods and other pet food manufacturers who had found their products had been contaminated and caused serious illnesses or deaths in some of the animals that had eaten them.[27][28][29] On 30 March 2007, the US Food and Drug Administration reported finding white granular melamine in the pet food, in samples of white granular wheat gluten imported from a single source in China, Xuzhou Anying Biologic Technology[30] as well as in crystalline form in the kidneys and in urine of affected animals.[31] Further vegetable protein imported from China was later implicated. See Chinese protein export contamination.

The practice of adding "melamine scrap" to animal feed is reported to be widespread in China in order to give the appearance of increased protein content in animal feed.[32]

Official US statements

On 27 April the U.S. Food and Drug Administration subjected all vegetable proteins imported from China, intended for human or animal consumption, to detention without physical examination, including wheat gluten, rice gluten, rice protein, rice protein concentrate, corn gluten, corn gluten meal, corn byproducts, soy protein, soy gluten, soy meal, and mung bean protein.[33]

On 28 April, the U.S. Department of Agriculture (USDA) and the FDA, in a joint press release acknowledged that pork from hogs fed melamine-contaminated feed had entered the human food supply, stating: "Based on information currently available, FDA and USDA believe the likelihood of illness after eating pork from swine fed the contaminated product would be very low."[34]

On 30 April, the USDA and the FDA updated their 28 April food safety position to include poultry, reflecting contaminated feed being fed to chickens in Indiana.[35]

On 7 May, the USDA and the FDA issued a joint press release reflecting the combined judgment of five federal agencies with regard to the risk to humans in consuming meat from animals fed feed contaminated with tainted pet food scraps, concluding: "There is very low risk to human health" in such cases involving pork and poultry. The risk assessment was conducted by scientists from FDA, the Food Safety and Inspection Service (FSIS) of USDA, CDC, the United States Environmental Protection Agency (EPA), and U.S. Customs and Border Protection: "In the most extreme risk assessment scenario, when scientists assumed that all the solid food a person consumes in an entire day was contaminated with melamine at the levels observed in animals fed contaminated feed, the potential exposure was about 2,500 times lower than the dose considered safe"[36] using criteria established prior to current research focusing on the apparent increased toxicity related to the interaction of melamine and cyanuric acid in vivo,[37] for which there is no established safe dosage. FDA and USDA are in the process of identifying a group of experts to convene a scientific advisory board that would be charged with reviewing the risk assessment and contributing to future scientific analysis related to the risk of melamine and its compounds to humans and animals.[36]

Risks to human health from this mode of entering the human food supply have been said to be low according to a number of FDA, CDC and university toxicologists, though it was acknowledged that how melamine had harmed cats and dogs remains something of a mystery.[38]

On 10 May, on further inquiry into the risk to animal and human health of ingesting melamine and cyanuric acid in combination, Dr. David Acheson, Assistant Commissioner for Food Protection with the FDA said: "I'm not aware of any published studies on that. I have seen some preliminary data that would indicate that they are additive. When you put the two together, they are additive rather than synergistic.... The risk assessors also estimated that even if synergism were to occur, it would be unlikely to result in more than a tenfold increase in overall toxicity, and that still gives you a very large margin of safety." No data supporting additivity was produced at this time. No basis for estimating a tenfold increase in risk in the case of synergism was offered.[39]

On 15 May USDA announced that meat from pigs that ate melamine-tainted food has been cleared for human consumption. About 56,000 pigs have been affected in several states. However, no tests have been carried out on the effects of cyanuric acid in pork as well as possible affects of interaction with melamine in the body. While the statement also said that there is no evidence of bioaccumulation of melamine alone, no mention was made whether bioaccumulation might be affected by the interaction of melamine and cyanuric acid in vivo.[40]

On 25 May, in a US FDA/CSFAN (Food & Drug Administration/ Center for Food Safety and Applied Nutrition) Interim Melamine and Analogues Safety/Risk Assessment, FDA stated: "While it is entirely possible that the analogues are more or less potent than the parent compound, melamine, we have no information that assesses the relative potency of the three analogues as compared to melamine; therefore, for the purpose of this interim assessment, we have made an assumption of equal potency. It has been hypothesized that melamine may interact synergistically with its three analogues, but no studies have been conducted that specifically test this hypothesis. Very preliminary work suggests that if it does occur, the formation of lattice crystals, particularly between melamine and cyanuric acid, takes place at very high dose levels and is a threshold and concentration dependent phenomenon that would not be relevant to low levels of exposure. Although still under investigation, it now appears that the combination of melamine and cyanuric acid has been linked to the acute renal failure in cats and dogs that have eaten the suspect pet foods...."[41]

On 30 May the FDA issued a press release stating that two US-based animal feed manufacturers had been adulterating livestock feed and fish/shrimp feed with melamine.[42][43]

In addition to now testing a wide variety of imported food products and ingredients for melamine contamination, FDA has also "asked the Centers for Disease Control and Prevention (CDC) to use its surveillance network to monitor for signs of human illness, such as increased renal failure, that could indicate contamination of the human food supply."[44]

Official EC statements

On 7 June (updated 4 July), the European Food Safety Authority (EFSA), in EFSA's Provisional Statement on a Request from the European Commission Related to Melamine and Structurally Related Compounds such as Cyanuric acid in Protein-rich Ingredients Used for Food and Feed, concluded: "EFSA provisionally recommends to apply a TDI of 0.5 mg/kg b.w. for the total of melamine and its analogues .... A source of uncertainty is the combined toxicity of melamine and cyanuric acid and their possible synergistic effects in relation to the recently observed toxicity linked to the acute renal failure and death of pet animals (cats and dogs) in the U.S. This mechanism is currently under investigation."[45]

On 21 June The Health & Consumer Protection Directorate-General of the European Commission (EC) in reporting the Summary Minutes of the Meeting of the Standing Committee on the Food Chain and Animal Health (7 June & 8) directed that "in case food producing animals have been fed with feed contaminated with melamine and related compounds, there is for the purpose of protecting human health, taking into account the conclusions of the EFSA statement, no need to take restrictive measures as regards the animals which have been fed with contaminated feed and as regards food of animal origin originating from animals fed with contaminated feed."[46]

2007 Ohio recalls

Melamine has also been purposely added as a binder to fish and livestock feed manufactured in the United States and traced to suppliers in Ohio and Colorado.[43]

2008 Sanlu milk powder recalls

Further information: 2008 baby milk scandal

In September 2008 Sanlu recalled all powdered milk in the north-west China's Gansu province where melamine was reported to have been used in 22 brands of infant formula, making more than 6,200 infants ill. Melamine has also been found in products produced by Yili Industrial Group Co, and Mengniu Dairy Co.[47]

As of 18 September 2008 there had been four confirmed infant deaths from the contamination of powdered milk with melamine with a number of survivors diagnosed with acute kidney failure.[48]

Melamine may have been added to fool government quality tests after water was added to fraudulently increase the milk's volume. The adulterant melamine was added to the milk to allow the company to dilute the milk with water and circumvent government regulations, since melamine will cause a false increase in the measurement of protein by increasing the nitrogen levels in the milk. In 2004, at least 13 babies died of malnutrition and nearly 200 fell ill after they were fed with a fake milk powder made in East China's Anhui Province. [49] [50]

Officials estimate that about 20 percent of the dairy companies tested in China sell products tainted with melamine.[51]

Sunday Sep 21, 2008 [52] China's food safety crisis widened yesterday after melamine was found in liquid milk, prompting stores to pull milk from their shelves and adding to evidence chemicals are routinely put in watered-down milk.

The chief financial officer of one of the companies, Mengniu, has apologised for the tainted milk. But he insisted only a small portion of the company's inventory had been contaminated and said the tainted milk came from small-scale dairy farmers.

"Large-scale milk farms are very disciplined. They won't take the risk to do something like that," Yao Tongshan told reporters in Hong Kong.

The crisis was thought to have been confined to milk powder used to make baby formula that has been blamed in the deaths of four infants.

But tests found melamine in liquid milk taken from China's two largest dairy producers, Mengniu Dairy Group and Yili Industrial Group, as well as Shanghai-based Bright Dairy.

Testing methods for melamine and cyanuric acid

The Food Safety and Inspection Service (FSIS) of the United States Department of Agriculture (USDA) provides a test method for analyzing cyromazine and melamine in animal tissues in its Chemistry Laboratory Guidebook which "contains test methods used by FSIS Laboratories to support the Agency's inspection program, ensuring that meat, poultry, and egg products are safe, wholesome and accurately labeled."[10][11]

On 24 April, Stephen Sundlof, director of the FDA's Center for Veterinary Medicine, told reporters: "We have found cyanuric acid. It is somewhat related to melamine. Another compound that is very high in nitrogen and we are testing for that compound as well."[citation needed]

On 7 May, the FDA sent a letter to food manufacturers, to remind them "of their legal responsibility to ensure that all ingredients used in their products are safe for human consumption."[53] The FDA has made available to food manufacturers a procedure providing a general guide for the sample preparation and analysis of wheat gluten and pet food matrices for melamine using gas chromatography/mass spectrometry, the same methodology used by the FERN laboratories.[54]

On 15 May, the process for testing meat from swine was validated by USDA's Food Safety and Inspection Service (FSIS).[40]

On 9 November 2007, FDA presented a method of HPLC Determination of Melamine, Ammeline, Ammelide, and Cyanuric Acid Contamination in Wheat Gluten and Rice Protein Concentrate.[55]

Reported widespread use in Chinese feed and food

Recent production of melamine in China

Between the late 1990s and early 2000s, both consumption and production of melamine grew considerably in China. In the United States Geological Survey 2004 Minerals Survey Yearbook, in a report on worldwide nitrogen production, the author stated that "China continued to plan and construct new ammonia and urea plants using coal gasification technology."[56]

By early 2006, melamine production in China is reported to be in "serious surplus".[57] In April 2007, DSM's melamine industry update painted a grave global picture.[58] Between 2002 and 2007, while the global melamine price remained stable, a steep increase in the price of urea (feedstock for melamine) has reduced the profitability of melamine manufacturing. Currently, China is the world's largest exporter of melamine, while its domestic consumption still grows by 10% per year. However, reduced profit has already caused other joint melamine ventures to be postponed there.

Media reports of melamine adulteration in China

Main article: Chinese protein export contamination

On 30 April 2007, The New York Times reported that the addition of "melamine scrap" into fish and livestock feed to give the false appearance of a higher level of protein was an "open secret" in many parts of China, reporting that this melamine scrap was being produced by at least one plant processing coal into melamine.[32] This production has been described as also producing "melamine scrap" which is not "pure melamine but impure melamine scrap that is sold more cheaply as the waste product after melamine is produced by chemical and fertilizer factories here.”[59] Shandong Mingshui Great Chemical Group, the company reported by the New York Times as producing melamine from coal, produces and sells both urea and melamine but does not list melamine resin as a product.[60]

As per melamine synthesis, the off-gas in production contains large amounts of ammonia. Therefore melamine production is often integrated into urea production which uses ammonia as feedstock. Crystallization and washing of melamine generates a considerable amount of waste water, which is a pollutant if discharged directly into the environment. The waste water may be concentrated into a solid (1.5-5% of the weight) for easier disposal. The solid may contain approximately 70% melamine, 23% oxytriazines (ammeline, ammelide and cyanuric acid), 0.7% polycondensates (melem, melan and melon).[61]

On 3 May the New York Times reported that, despite the widely reported ban on melamine use in vegetable proteins in China, at least some chemical manufacturers continue to report selling it for use in animal feed and in products for human consumption. Said Li Xiuping, a manager at Henan Xinxiang Huaxing Chemical in Henan Province: "Our chemical products are mostly used for additives, not for animal feed. Melamine is mainly used in the chemical industry, but it can also be used in making cakes."[62]

On 12 September 2008, Xinhua News Agency widely reported adulteration of baby food formula with melamine. The substance caused kidney stones as large as 1 cm in diameter in many babies. The adulterated baby formula was manufactured by Sanlu Group, a leading Chinese dairy producer. Sanlu ordered a recall of more than 10,000 tonnes of the potentially contaminated formula produced before 6 August 2008.

The Chinese Ministry of Health confirmed two infant deaths in the northwestern Gansu Province. In that same province, 59 babies have been hospitalized. Similar numbers have been reported all across China, in Shaanxi Province and Ningxia Hui Autonomous Region in the northwest, Shandong, Jiangsu and Anhui provinces in the east and in the central provinces of Hubei and Hunan. In fact, an official report of China showed a number of Chinese milk vendors adulterate melamine to improve the nitrogen content.

The United States Food and Drug Administration has issued a warning regarding the sale of Chinese-made baby formula, which is illegal in the United States. The Chinese Ministry of Health is conducting an investigation.

On 15 September 2008, China’s Ministry of Health announced that 1,253 babies in China became sick after drinking melamine-contaminated baby formula, with 340 hospitalized and 53 in a serious condition. A 5-month-old boy and 8-month-old girl from Gansu Province died on 1 May and 22 July respectively.[63]

.[64]On September 19 2008 By TINI TRAN - Associated Press Writer - China's tainted milk crisis widened Friday after tests found the industrial chemical melamine in liquid milk produced by three of the country's leading dairy companies, the quality watchdog said. Singapore suspended the sale and import of all Chinese milk and dairy products because several tested items were contaminated. Tainted baby formula has been blamed for killing four infants and sickening 6,200 in China since the scandal broke last week. Some 1,300 babies, mostly newborns, are currently in hospitals and 158 of them are suffering from acute kidney failure. Thousands of parents across the country were bringing their children to hospitals for health checks.

Detection of melamine in food

Until the 2007 pet food recalls, melamine had not routinely been monitored in food, except in the context of plastic safety or insecticide residue. This could be due to the previously assumed low toxicity of melamine, and the relatively expensive methods of detection.

Because melamine resin is often used in food packaging and tableware, melamine at ppm level (1 part per million) in food and beverage has been reported due to migration from melamine-containing resins.[65] Small amounts of melamine have also been reported in foodstuff as a metabolite product of cyromazine, an insecticide used on animals and crops.[66] Romer Labs now offers a rapid Melamine test kit (AgraQuant Melamine ELISA test kit).

See also

References

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