Patai S., Rappoport Z. 1996 The chemistry of functional groups. The chemistry of amino, nitroso, nitro and related groups. Part 2 / 1169 1214

25. Environmental aspects of compounds

1189

Over the last two decades there has been a net decrease in both nitrate and nitrite in cured meats and foods. In cured meat products it is generally accepted that the formaldehyde present in the wood smoke is involved in the formation of N-Nitrosothiazolidine (NTHZ) and N-Nitrosothiazolidine-4 carboxylic acid (NTCA). Bacon represents a unique case as uncooked bacon is generally free of nitrosamines, but high levels of nitrosamines are formed during cooking. The conditions leading to formation of nitrosamines in bacon have been widely studied and the presence of NTCA in raw and fried bacon has been reported93 97. It has been suggested that the thermal process results in transformation of NTCA into NTHZ during the frying process98.

Over 300 NOC have been shown to be carcinogenic to more than one animal species. Table 7 shows some compounds present in the diet, their occurrence and their carcinogenecity99.

F. Endogenous Formation

There is sufficient evidence to indicate that the NOC compounds represent a serious potential health hazard, although the magnitude of this hazard remains to be established. Exposure to nitroso compounds and their precursors is mainly via ingestion. However, in some cases inhalation may become the major route of exposure. Figure 13 illustrates the total exposure of NOC compounds on humans occurring via both exogenous and endogeneous routes100.

Nitric oxide is formed endogenously in the body by many types of cells for the purpose of intercellular communication (brain, cardiovascular system), or as a part of the immune or inflammatory response (macrophages, endothelial cells). The chemistry of nitric oxide formation in the body is very complex both in terms of chemical species and in the number of parallel and consecutive reactions. Damage to DNA in mammalian cells is caused by at least two major pathways: one arising from the reaction of NO with molecular oxygen and the other by reaction of NO with superoxides. The first route gives N2O3, which can either (1) nitrosate secondary amines to form carcinogenic or mutagenic N-nitrosamines or (2) nitrosate primary amines on DNA bases. The latter reaction results in deaminated bases from adenine, cytosine, 5-methylcytosine and guanine. NOC have been shown to produce cancer in humans, particularly when exposure starts early in life and persists over a long period101. Figure 14 shows endogeneous NOC synthesis in the human body102. The NOC production is brought about by bacterial enzymes which catalyse nitrosation from

Total exposure

Exogenous exposure

Endogenous exposure

Life style	Occupational
Tobacco + tobacco smoke	Rubber industry
Food	Leather industry
Cosmetic products	Chemical industry
Household commodities	Mining
Indoor air	Pesticide production
Drugs

FIGURE 13. NOC and total exposure

Uptake of precursors	Formation of precursors
Nitrite	nitrite from nitrate
Nitrous gases NOx
Nitrosatable amino
compounds

TABLE 7. N-Nitroso compounds in the diet, carcinogenicity and occurrence99

Carcinogenicity

(following oral administration)

Major dietary source (mg/kg)

Concentration

N-Nitroso compound

Species

Organotropy

Foodstuff

Range

Mean

N-Nitrosodimethylamine

Rat

Liver, kidney, (lung)

Cured meats

1.0

5.0

4.0

(NDMA)

Mouse

Liver, kidney, lung

Fried bacon

<23

Me

Hamster

Liver, (glandular stomach)

Marine products:

8.6

ON

N

Guinea pig

Liver

Dried fish (Japan)

3.0

39

Rabbit

Liver, lung

Dried fish (Greenland)

8.6

38

Me

43.9

Mink

Liver

Dried shrimps (China)

5.4

132

Broiled squid (China)

<300

Millet flour and grain

products (China)

0.1

1.3

0.5

Dairy and cheese products

1

6

Dried milk products

<7.0

Edible oils and fats

<1.0

Pickled/fermented vegetables

<5.0

Beer

<0.5

0.2

Alcoholic beverages (whisky)

<2.0

1.0

N-Nitrosoethylmethylamine

Rat

Liver, nasal cavity,

Pickled/fermented vegetables

<5.0

(NEMA)

(oesophagus)

(China)

Me

Hamster

Liver, nasal cavity, trachea

ON

N

Et

N-Nitrosodiethylamine

Rat

Liver, kidney,

Cured meats (packed

<2.4

(NDEA)

(oesophagus)

in rubber nettings)

Et

Mouse

Liver, lung, oesophagus,

Salami

ON

N

forestomach

Hamster

Trachea, lung, nasal cavity,

<3.9

0.6

Et

(oesophagus, forestomach,

Millet flour and grain

0.1

0.5

0.22

liver

products (China)

1190

	Rabbit, cat	Liver, oesophagus
	Guinea pig,	Liver	Dried cuttlefish	<4.5					1.4
	dog, monkey
N-Nitrosodibutylamine	Rat	Liver, urinary bladder,	Cured meats (packed	1		56			10.2
(NDBA)		(oesophagus, pharynx)	in rubber nettings)
Bu	Mouse	Forestomach, liver,	Smoked chicken	<5.3
ON N		oesophagus,	Dried fish (Japan)
Bu		urinary bladder, (lung)		<3.1
	Hamster	Respiratory tract, lung,
		urinary bladder
	Guinea pig	Liver, urinary bladder
N-Nitrosopyrrolidine	Rat	Liver, nasal cavity,	Cured meats	1.0				5.0	1.8
(NPYR)		(vagina, testis)	Fried bacon	<130					17
	Mouse	Lung	Pickled vegetables	<96
			Mixed spices	<10
N			Dried chillies	<6.0					3.1
			Broiled squid	2.4				13
NO
N-Nitroso-3-hydroxy-	Rat	Liver	Cured meats	<7.0
pyrrolidine (NHPYR)			Fried bacon	0.4				3.9	2.2
OH
N
NO
N-Nitrosopiperidine	Rat	Liver, oesophagus,	Cured meats	<20
(NPIP)		upper respiratory	Fried bacon	<9.2
		and digestive tracts,
		nasal cavity	Peppered salami	<30					5.8
N	Mouse	Forestomach, liver, lung	Pepper	<300
	Hamster	Liver, upper respiratory	Mixed spices	0.6				3.5
NO		and digestive tracts	Pickled vegetables	<14

(continued overleaf )

1191

TABLE 7. (continued)

			Carcinogenicity
		(following oral administration)			Major dietary source (mg/kg)
									Concentration
N-Nitroso compound		Species	Organotropy		Foodstuff		Range			Mean
N-Nitrosothiazolidine		Rat	Non-carcinogenic		Cured meats	<32
(NTHZ)				Fried bacon		<30				8.9
S				Smoked fish		<6
				Smoked oyster		<109
N
NO
N-Nitroso-2-hydroxymethyl-			No data available	Cured meats		Occasionally
thiazolidine (NHMTHZ)				Smoked ham		<2.8
	S
HOCH2	N
	NO
N-Nitrosomorpholine		Rat	Liver, (kidney, ovary)	Packaging contamination of:
(NMOR)		Mouse	Liver, lung		Fats/margarine	1.7			3.8
O		Hamster	Liver, upper respiratory		Dairy products	<3.2
			tract, colon
N
NO
N-Nitrososarcosine (NSAR)		Rat	Oesophagus	Cured meats		<410
	Me	Mouse	Lung, nasal cavity,	Pickled vegetables		<36
ON N			(small intestine)	Brewing malt		Occasionally

CH2 COOH

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N-Nitrosoproline (NPRO)	Rat	Non-carcinogenic	Cured meats	20				580	140
	Mouse	Non-carcinogenic	Preserved fish	<89
COOH			Broiled squid	<94
			Dried vegetables	<24
N
			Dried chillies	<132
NO			Brewing malt	<113
N-Nitroso-4-hydroxy-			Beer	1		6			1.7
	Rat	Non-carcinogenic	Cured meats	10				560
proline (NHPRO)	Mouse	Non-carcinogenic

HO

	N	COOH
	NO
N-Nitrosothiazolidine-			No data available	Cured meats	<1620
4-carboxylic acid (NTCA)				Fried bacon	<14,000			85
S				Smoked poultry	<1240
				Smoked fish	<1600			67
N	COOH			Smoked oyster	<167
				Smoked cheese	5		24
NO
N-Nitroso-2-methylthia-			No data available	Cured meats	<28
zolidine-4-carboxylic acid				Smoked poultry	<98
(NMTCA)
	S
Me		COOH

N

NO

(continued overleaf )

1193

1194

TABLE 7.		(continued)
				Carcinogenicity
			(following oral administration)			Major dietary source (mg/kg)
										Concentration
N-Nitroso compound			Species	Organotropy		Foodstuff			Range		Mean
N-Nitroso-2-hydroxymethyl-				No data available	Cured meats		<2100
thiazolidine-4-carboxylic					Smoked cheese		<1628
acid (NHMTCA)					Smoked poultry		<462
		S
HOCH2		COOH
		N
		NO
N-Nitrosooxazolidine-4-				No data available	Cured meats		40			70
carboxylic acid (NOCA)
O
N	COOH
NO
N-Nitroso-5-methyloxazo-				No data available	Cured meats		30			120
lidine-4-carboxylic acid
(NMOCA)
O
Me	N	COOH

NO

N-Nitroso-N-	Mice	Forestomach	Moldy millet and	<1.2
(1-methylacetonyl)-		(tested by feeding with	wheat flour
2-methylpropylamine		amine C nitrite)
(NMAMPA)
O
N
NO
N-Nitroso-N-(1-methyl-		No data available	Millet flour and	0.1		1.3	0.2
acetonyl)-3-methylbutyl-			grain products
amine (NMAMBA)			(China)

O

N

NO

Reproduced with permission from Reference 83.

1195

1196	H. K. Chagger and A. Williams
Bacteria		Macrophages	Endothelial cells
(30-90% strains from		(activated by LPS, BCG)	(bradykinin)
human sources)

NO3 , NO2

Arginine

Arginine

Nitric oxide

Nitrosating agent

NOC

FIGURE 14. Proposed scheme of formation of NOC by bacterial activated macrophages and endothelial cells through intermediate nitric oxide

nitrates or nitrites, probably through formation of nitric oxide at natural pH. Activated macrophages use arginine as a source to produce nitric oxide. Once generated, nitric oxide can be oxidized to nitrosating agents that form NOC readily in the presence of amines. A similar reaction is thought to occur also in endothelial cells.

V. AMINES

Several amino compounds are being used extensively in industrial processes. Most of these compounds are manufactured, except hydrazine. Azo dyes are produced by diazotization of aromatic amines and currently there are at least 3000 azo dyes in use. These dyes are used widely in textiles, leather, printing, paper making, drug and food industries. In the past three decades many food, drug and cosmetic colours have been banned from commercial use as food colourants. This section gives a brief account of adverse affects caused by the use of various amino compounds.

A. Hydrazine

The only known natural source of hydrazine is found in tobacco plants and it may also occur as an intermediate in biological nitrogen fixation. Alkaline solutions of hydrazine in water can be subject to autooxidation by dissolved oxygen, leading to increased hardness and high pH. Decomposition of hydrazine and the increase of pH just below 7 have adverse effects on the marine life ecology. Frog spawn showed teratogenic effects, the embryos of fathead minnows showed deformities and the rainbow trout had poor fitting jaws, pronounced mouth gap and absence of body movement. In air, hydrazine can be oxidized by ozone and hydroxyl radicals. Hydrazine can also be co-metabolised to nitrogen gas by the nitrifying bacterium Nitrosomonas. Germination of seeds of brush squash, peanut and

25. Environmental aspects of compounds

1197

corn was inhibited upon exposure to hydrazine and led to wilting and subsequently death of the plant2.

NOC might be generated by aerial oxidation of the hydrazines. Experimental studies on oxidation of 1,1-dimethylhydrazine which is not a mutagen and N-aminopiperidine which is a mutagen indicated that the oxides of both hydrazide samples were mutagenic103.

B. Azo Dyes

These dyes are used extensively and can be divided into four different categories: azo dyes containing a nitro group, azo dyes containing benzeneamines and related chemicals, azo dyes containing a benzidine group and miscellaneous azo dyes. This section will not lay too much emphasis on the subject of azo dyes as several reviews exist on this topic104,105. Some of the dyes are not mutagenic but become mutagenic through intestinal microflora mechanism for mammalian azo reduction and chemical reduction. It is also possible that the carcinogenesis occurs due to formation of aromatic amines, formed by enzymatic cleavage of azo bonds with subsequent N-ring hydroxylation and N-acetylation of aromatic amines. Table 8 gives a list of dyes which were shown to be carcinogenic and mutagenic to animals and humans106. The C sign indicates that metabolic activation was required and the sign shows cases where no activation was required, i.e. which are direct mutagens.

VI. CONTROL AND LEGISLATION

Most of the pollution of nitroso and other nitrogen related compounds occurs mainly through anthropogenic sources, the largest contributor being combustion. Hence, legislation and control is basically oriented around controlling the amount of dry NOx input into the atmosphere. The estimated global NOx arising from anthropogenic sources is of the order 100 ð 106 t/a, and it is increasing every year. By the year 2020 the expected NOx level is calculated to go up by a factor of 15%. In developed countries like Canada, USA, Europe and Japan limits and guidelines have been specified for the NO/NO2 concentration levels. Amongst the developing countries China is one of the biggest NOx contributors; the total emission is around 6.77 Tg nitrogen per year107. The NOx level is in the developing countries are quite high due to lack of legislative and strategic policies. In order to control the increasing levels of NOx these countries need to implement specified levels of NOx concentrations that should be emitted into the atmosphere. To date, several reviews exist on the control technologies of NOx 6, the issue is to reduce the formation of nitroso and nitro compounds which are formed inadvertently in industrial processes or in the atmosphere. In case of the rubber industry, new accelerators are being tested which are relatively safe as they do not form carcinogenic nitrosamines108. Some of the straight-chain accelerators do not produce detectable amounts of environmentally undesirable N-nitrosoamines. The main source of NDMA and other nitrosamines occurs in food and beverages when direct fire is employed. This has been controlled by reducing the nitrate concentration in the foods and by employing ultra-low NOx burners. The formation of nitroso compounds in cosmetic products can be reduced by elimination of secondary amines as cosmetic ingradients, reduction of the levels of secondary amines and nitrite in the raw products, and avoiding contamination of cosmetics and raw materials with oxides of nitrogen. The federal government in the USA is imposing and amending regulations to reduce the discharge of nitroso compounds into the atmosphere. Besides this, smoking contributes to a high level of indoor pollution, hence most offices and work places are being designated as non-smoking zones in order to cut down the nitroso levels.

1198

TABLE 8. Mutagenic azo dyes: chemical structures and requirements for metabolic activation106

Common			Chemical
name			structure
Azo Dyes Containing Nitro Groups
			N2 O
Alizarin Yellow G G		O2 N		O
			N N	OH
			HO
Acid Alizarin Yellow R				O
		O2 N	N N	OH
Red GTL	O2 N	N N	N	C2 H2
				+	−
(C.J. Basic Red 18)				C2 H4 H (CH3 )3 X
		OH	OH	Cl
Orasol Navy Blue 2RB			N N		CO

O2 N

Cl

2

Metabolic activationa

š

š

Azo Dyes Containing Benzeneamines and Related Compounds

NH

Chrysoidin			C
(C.I. Index	11270)	N N	NH2