Use of metanil yellow and other toxic industrial dyes as food colors in India.

Synthetic colors permitted to be used in India in food products is limited to eight odd synthetic dyes listed in the 'Food Safety and Standards Rules, 2011'.

S. No.	Colour	Common name	Colour Index	Chemical Class
1.	Red	Ponceau 4R	16255	Azo
		Carmoisine	17420	Azo
		Erythrosine	45430	Xanthene
2.	Yellow	Tartrazine	19140	Pyrazolone
		Sunset Yellow FCF	15985	Azo
3.	Blue	Indigo Carmine	73015	Indigoid
		Brilliant Blue FCF	42090	Triarylmethane
4.	Green	Fast Green FCF	42053	Triarylmethane

Even for these permitted dyes, the use is again confined by the law to a limited list  of non-staple food products in order to ensure that the total intake by a population over a period of time from various sources stays within a safe limit. Among the food products thus listed in rule 29 are ice-creams, frozen dessert, flavored milk, yoghurt, biscuits, peas, strawberries, cherries, custard powders, ice-candy etc. The regulation also imposes a maximum permissible limit of 100 mg of the dye per kg of the product as a general limit and a 200mg/kg for certain products.

Even though the legislators thus took every possible safeguard to protect against the probable chronic toxicity of synthetic dyes, the food market in India on the other side presents an absolutely different reality. In fact, more than half a dozen industrial dyes, never permitted by the law for use in food, are used in India in products including staple food. According to a study conducted by the 'Food, Drugs and Chemical Toxicology Group', of the CSIR, and the 'Indian Institute of Toxicology Research', Lucknow (ref 2), the most common non-permitted dyes used in India are rhodamine B, orange II, metanil yellow, malachite green, quinoline yellow and auramine. All of these are synthetic industrial dyes manufactured mostly for the paper, leather and textile industries.

The study by CSIR (ref 2) found the use of these non-permitted dyes in 16% of the products they tested from all over India, while it was  28.7% in eastern India. In the remaining 84% which used permitted colors, as much as 58% exceeded the maximum allowable limit of 100 mg/kg of the product. The study found Rhodamine-B, a tracer dye, in 30% of the tested samples making it the most commonly used illegal color in India. Levels of the dye in the samples ranged from 36.9 to 542mg/kg. The other non-permitted dyes viz; orange II, metanil yellow and malachite green, were found in ranges: 23.8 to 456mg/kg, 36.8 to 256mg/kg and 57.4 to 231mg/kg respectively.

Metanil Yellow powder 

Metanil Yellow, also known as Acid Yellow 36 (empirical formula: C18H14N3O3SNa) is a synthetic industrial dye. It is a mono-azo acid, shipped usually in powder form, yellow or reddish brown in color depending on the pH. Metanil yellow is used in dyeing paper, leather, textiles, silk, nylon, wool, cosmetics, and wash fast inks. Its is also used as an analytic reagent, pH indicator, and in staining biological specimens - cytoplasmic and connective tissue. In India, even though not permitted by law, metanil yellow is a principal food coloring agent used extensively in products like whole turmeric, turmeric powder, ladoo, jalebi, fried banana chips, fruit squashes, soft drinks, fruit jams, pulses etc.

Oral consumption of metanil yellow is not known to cause any acute symptoms, neither is it fatal. Research data available on the acute toxicity of metanil yellow in limited to evidences of hepatic activity (ref 6). Upon oral consumption of azo compounds, the azo linkage gets reduced in the digestive tract by liver microsomes, cytosolic enzymes and colonic bacteria leaving the constituent aromatic amines. Metanil yellow thus gets reduced into 'p-Aminodiphenylamine' and 'Metanillic acid'. Of these, metanillic acid, even though toxic, is poorly absorbed, hence excreted (ref 7).

Among the data on the chronic toxicity of metanil yellow is a report on a study conducted by NIMHANS, Bangalore. The report says (ref 1): "The effects of long-term consumption of metanil yellow on the developing and adult brain were studied using Wistar rats. ........ In the treated rats the amine levels in the hypothalamus, striatum and brain stem were significantly affected, and the changes were not generally reversible even after withdrawal of metanil yellow in developing rats. The striatum showed an early reduction of AChE activity, whereas the hippocampus showed a delayed but persistent effect of reduced AChE activity. Treated rats also took more sessions to learn the operant conditioning behaviour. These effects on these major neurotransmitter systems and on learning, indicate that chronic consumption of metanil yellow can predispose both the developing and the adult central nervous system (CNS) of the rat to neurotoxicity."

25 kg HDPE shipping drums labelled for Metanil Yellow

Metanil Yellow packaged in plastic bag by Bright Chemicals, a Chineese manufacturer

Among the data available on the  carcinogenicity of metanil yellow and malachite green is an article published by CSIR researchers Monisha Sundarrajan, S. Prabhudesai, S. C.  Krishnamurthy, and K.V.K. Rao. The work attempts to study the possible mechanisms by which metanil yellow and malachite green enhances tumor development in N-nitrosodiethylamine induced carcinogenesis in Wistar rats. The study "tested the effects of metanil yellow and malachite green on DNA synthesis and PCNA expression in preneoplastic hepatic lesions during N-nitrosodiethylamine (DEN) induced hepatocarcinogenesis in male Wistar (WR) rats. .......The effects of metanil yellow  and malachite green were monitored on the basis of cell proliferation markers - DNA synthesis and PCNA expression both by immunohistochemical and immunoblotting. ...... Following DEN administration, metanil yellow, malachite green and PH showed stimulation of DNA synthesis and increased PCNA expression when compared with either the corresponding controls or only DEN treated animals. In the present study, enhancing effect of metanil yellow, malachite green and PB on the cell proliferation markers during DEN-induced hepatic preneoplasia in rats was observed."

References:

1. "Effects of chronic consumption of metanil yellow by developing and adult rats on brain regional levels of noradrenaline, dopamine and serotonin, on acetylcholine esterase activity and on operant conditioning" by Nagaraja T. N, & Desiraju T. Department of Neurophysiology, National Institute of Mental Health and Neuro Sciences, Bangalore, India. http://www.ncbi.nlm.nih.gov/m/pubmed/8095244/
2. "All India Survey for Analyses of Colors in Sweets and Savories: Exposure Risk in Indian Population", Sumita Dixit, Subhash K. Khanna and Mukul Das. Food, Drugs and Chemical Toxicology Group, CSIR - Indian Inst. of Toxicology Research, Lucknow 226001, U.P., India. First published online: 6 MAR 2013. Referred in: http://www.rsc.org/chemistryworld/2013/04/toxic-food-dye-colour-india-sweets Article: http://onlinelibrary.wiley.com/doi/10.1111/1750-3841.12068/abstract
3. Research Article: "Bees’ Honey Attenuation of Metanil-Yellow-Induced Hepatotoxicity in Rats", Abdulrahman L. Al-Malki (Department of Biochemistry, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia) and Ahmed Amir Radwan Sayed (Chemistry Department, Faculty of Science, Minia University, Egypt), published in Evidence-Based Complementary and Alternative Medicine, Volume 2013. http://www.hindawi.com/journals/ecam/2013/614580/
4. The law governing and regulating food colors in India now is the 'Food Safety and Standards Act, 2006', which replaced the former 'The Prevention of Food Adulteration Act, 1954'. And the framework of rules and regulations now in force, built and named after the act, are the 'Food Safety and Standards Rules, 2011' and the 'Food Safety and Standards Regulations, 2011' which replaced 'The Prevention of Food Adulteration Rules, 1955'. The governmental agency responsible for implementing these rules is the 'Food Safety and Standards Authority of India (FSSAI)'.
5. "Effect of metanil yellow and malachite green on DNA synthesis in N-nitrosodiethylamine induced preneoplastic rat livers", Monisha Sundarrajan, S. Prabhudesai, S. C.  Krishnamurthy, K.V.K.Rao, 'Indian Journal of Experimental Biology', Vol 39, September 2001, Published by  NISCAIR-CSIR, India. http://nopr.niscair.res.in/handle/123456789/23998
6. "Effect of Oral and Parenteral Administration of Metanil Yellow on Some Hepatic and Intestinal Biochemical Parameters", Shanta Ramchandani, Mukul Das, Anjulika Joshi, and Subhash K. Khanna, 'Journal of Applied Toxicology', Volume 17, Issue 1, pages 85–91, January 1997. http://onlinelibrary.wiley.com/doi/10.1002/(SICI)1099-1263(199701)17:1%3C85::AID-JAT394%3E3.0.CO;2-K/abstract
7. "Metabolism of AZO Dyes: Implication for Detoxification and Activation", Walter G. Levine, 'Drug Metabolism Reviews', Vol 23, Issue: 3-4, Pages: 253-309, 1991. http://www.ncbi.nlm.nih.gov/m/pubmed/1935573/