Nitrobenzene in Drinking-water
Draft of the background document for development of
WHO Guidelines for Drinking-water Quality
Nitrobenzene in Drinking-water
Background document for development of WHO Guidelines for Drinking-water Quality
World Health Organization 2009
The illustration of the cover page is extracted from Rescue Mission: Planet Earth,
Peace Child International 1994; used by permission.
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Table of contents
1. GENERAL DESCRIPTION
1.1 Identity......
1.2 Physicochemical properties......
1.3 Major uses and sources in drinking water......
1.4 Environmental fate......
2. HUMAN EXPOSURE
3. TOXICOLOGICAL SUMMARY
3.1 Kinetics and metabolism
3.2 Acute toxicity......
3.3 Short-term exposure toxicity......
3.4 Long-term exposure toxicity and carcinogenicity......
3.5 Reproductive/Developmental toxicity......
3.6 Genotoxicity......
3.7 Effects on humans......
4. PRACTICAL ASPECTS
4.1 Analytical methods and analytical achievability......
4.2 Treatment and control methods and technical achievability
5. CONCLUSION......
6. REFERENCES
NITROBENZENE IN DRINKING WATER
1. GENERAL DESCRIPTION
1.1 Identity
CAS No.: / 98-95-3Molecular formula: / C6H5NO2
IUPAC name: nitrobenzene.
1.2 Physicochemical properties
Nitrobenzene is a colourless to pale yellow oily liquid that presents a fire hazard. Its odour resembles that of bitter almonds or "shoe polish. Its chemical and physical properties are shown below.
Property / ValueSpecific gravity / 1.2037 at 20 ºC
1.205 at 28 ºC
Melting point / 5.7 ºC
Boiling point / 211 ºC
Vapour pressure / 20 Pa (0.15 mmHg) at 20 ºC
38 Pa (0.284 mmHg) at 25 ºC
47 Pa (0.35 mmHg) at 30 ºC
Water solubility / 1900 mg/L at 20 ºC
2090 mg/L at 25 ºC
Log octanol-water partition coefficient
(log Kow) / 1.85 (1.6–2.0)
Its odour resembles that of bitter almonds or "shoe polish," with reported odour thresholds of 0.092 mg/m3 (0.018ppm) (Amoore & Hautala, 1983) and 0.03 mg/m3 (0.005 ppm) (Manufacturing Chemists Association, 1968). Its odour threshold in water has been reported as 0.11 mg/litre (Amoore & Hautala, 1983) and 0.03 mg/litre (US EPA, 1980).
1.3 Major uses and sources in drinking water
Nitrobenzene is used primarily in the production of aniline, but it is also used as a solventand as an ingredient of metal polishes and soaps. It is also used in the synthesis of other organic compounds, including acetaminophen. It was reported that most of the production of aniline and other substituted nitrobenzenes from nitrobenzene goes into the manufacture of various plastic monomers and polymers (50%) and rubber chemicals (27%).
Past minor uses of nitrobenzene included as a flavouring agent, as a solvent in marking inks and in metal, furniture, floor and shoe polishes, as a perfume, including in perfumed soaps, as a dye intermediate, as a deodorant and disinfectant, in leather dressing, for refining lubricating oils, and as a flavouring agent. It is not known whether it is still used in some countries as a solvent in some consumer products.
1.4 Environmental fate
The physical properties of nitrobenzene suggest that transfer from water to air will be significant, although not rapid.Actual data on the evaporation of nitrobenzene from water bodies appear to be somewhat conflicting, with a computer model predicting a volatilization half-life of 12–68 days. The shortest estimate cited in the literature was 1 day; in another study of experimental microcosms, simulating land application of wastewater, nitrobenzene was reported not volatilized but totally degraded.Due to its moderate water solubility and relatively low vapour pressure, it might be expected that nitrobenzene would be washed out of the atmosphere by rain to some extent; however, in field experiments, it appeared that washout by rainfall and dryfall of particulates was negligible. Because of its vapour density, removal processes from the atmosphere may include vapour settling.
Nitrobenzene can undergo degradation by both photolysis and microbial biodegradation.Photodegradation of nitrobenzene in air and water is slow. In water bodies, direct photolysis appears to be the degradation pathway that proceeds most rapidly (half-life: 2.5–6 days).Degradation studies suggest that nitrobenzene is degraded in sewage treatment plants by aerobic processes, with slower degradation under anaerobic conditions. Degradation was generally found to be increased with acclimation of the microbial population and other easily degradable substrates. Adaptation of the microflora and additional substrates also seems to be a limiting factor in the decomposition of nitrobenzene in soil. The measured bioconcentration factors for nitrobenzene in a number of organisms indicate minimal potential for bioaccumulation, and nitrobenzene is not biomagnified through the food chain.
2. HUMAN EXPOSURE
Concentrations of nitrobenzene in environmental samples such as surface water, groundwater and air are generally low. In surface water, nitrobenzene levels are around 0.1–1 μg/Lin most caseswhile they vary depending on location and season. Based on limited data, it appears that there may be greater potential for contamination of groundwater than surface water; several sites measured in the USA in the late 1980s had levels of 210–250 and 1400 μg/L.
The general population can be exposed to variable concentrations of nitrobenzene in air and possibly drinking water. Nitrobenzene has been reported in studies conducted in the 1970s and 1980s on drinking water in the USA and United Kingdom, albeit in only a small proportion of samples, but was not detected in 30 Canadian samples (1982 report).There is also potential exposure from consumer products, but accurate information is lacking. Based on air studies and on estimates of release during manufacture, only populations in the vicinity of manufacturing activities and petroleum refining plants are likely to have any significant exposure to nitrobenzene; however, people living in and around abandoned hazardous waste sites may also have potential for higher exposure, due to possible groundwater and soil contamination and uptake of nitrobenzene by plants.
Occurrence
(The following is taken from Environmental Health Criteria 230 Nitrobenzene, IPCS 2003. No other substantive data were found.)
Surface water
Nitrobenzene was not detected in any surface water samples collected near 862 hazardous waste sites in the USA, according to the Contract Laboratory Program Statistical Database (CLPSD, 1988). Nitrobenzene was not detected (detection limit 4 µg/litre) in thePotomac River, USA (Hall et al., 1987). Detailed surveys of Japanese surface waters were undertaken in 1977 and 1991. In the 1977 survey, nitrobenzene was detected in 22 of 115 samples at a level of 0.13–3.8 µg/litre (detection limit 0.1– 30 µg/litre). In the 1991 survey, nitrobenzene was detected in 1 of 153 surface water samples at a level of 0.17 µg/litre (detection limit 0.15 µg/litre). The samples were taken from both industrialized and rural areas (Kubota, 1979; Environment Agency Japan, 1992).
Staples et al. (1985) reported that of the 836 determinations of nitrobenzene in ambient surface water contained in the US STORET database, nitrobenzene was detected in 0.4% of the samples, with a median level of <10 µg/litre. In a year-long survey of water from two reservoirs near Calgary, Canada, nitrobenzene was not detected in any of the samples taken (detection limit 0.1 µg/litre) (Hargesheimer & Lewis, 1987).
In reviewing available data, generally low levels (around 0.1–1 µg/litre) of nitrobenzene have been measured in surface waters. One of the highest levels reported was 67 µg/litre in the river Danube in ex-Yugoslavia (Hain et al., 1990). Many of the rivers sampled for nitrobenzene are known to suffer from industrial pollution and so may not represent the general situation. After a temporary failure in an industrial wastewater treatment plant at BASF Aktiengesellschaft in May 1984, a peak nitrobenzene concentration of 25 µg/litre was measured in the river Rhine, Germany (BUA, 1994).
Groundwater
Nitrobenzene was detected in groundwater at 3 of 862 hazardous waste sites in the USA at a geometric mean concentration of 1400 µg/litre, according to the Contract Laboratory Program Statistical Database (CLPSD, 1988). Nitrobenzene was not detected (<1.13 µg/litre) in groundwater at an explosives manufacturing site in the USA. The aquifer at the site was known to be contaminated with explosives residues (Dennis et al., 1990; Wujcik et al., 1992).
Nitrobenzene was detected at a level of 210–250 µg/litre in groundwater from Gibbstown, USA (Rosen et al., 1992). No nitrobenzene was detected (minimum detection limit 0.67 µg/litre) in three groundwater sources of domestic water in the Mexico City region (Downs et al., 1999).
Drinking water
Nitrobenzene was detected in 1 of 14 samples of treated water in the United Kingdom. The positive sample was water derived from an upland reservoir (Fielding et al., 1981). In a survey of 30 Canadian potable water treatment facilities, nitrobenzene was not detected in either raw or treated water (detection limit 5 µg/litre) (Otson et al., 1982). Kopfler et al. (1977) listed nitrobenzene as one of the chemicals found in finished tap water in the USA, but did not report its concentrations or locations. According to the BUA (1994), the nitrobenzene content in potable water following passage through the soil was 0.1 µg/litre (mean), with a maximum value of 0.7 µg/litre in 50 samples taken from the river Lek at Hagestein, Netherlands, in 1986.
3. TOXICOLOGICAL SUMMARY[1]
3.1 Kinetics and metabolism
Although no studies have been performed regarding the extent of uptake of nitrobenzene by humans after oral exposure, oral absorption would appear to be rapid and extensive, based on the very large number of clinical reports of poisonings(IPCS 2003). Some of these reportsshowed that metabolites identified in the urine werep-aminophenol and p-nitrophenol (Von Oettingen, 1941; Ikeda & Kita, 1964; Myślak et al., 1971).In one volunteer given oral nitrobenzene, the half-lives of elimination for p-nitrophenol were estimated to be about 5 h (initial phase) and >20 h (late phase) (Piotrowski, 1967). For inhalation exposure, Salmowa et al. (1963) reported that the retention of nitrobenzene in the lungs averaged 80% (73–87%) in seven men breathing 5–30 mg nitrobenzene/m3 for 6 hr, and10–20% of the inhaled dose of nitrobenzenewas excreted as p-nitrophenol into the urine. The elimination of p-nitrophenol in urine had estimated half-lives of about 5 and 70 h.
In rats and rabbits,the major part of orally administered nitrobenzene(about 80% of the dose) was metabolized and eliminatedwithin 8 days at the most (Rickert et al. 1983; Freitag et al., 1982; Albrecht & Neumann, 1985; Parke, 1956). The major route of excretion was urine. In mice, oral doses appeared to be less well absorbed than in these animals; about 35 % was excreted in urine within 3 days (compared with 57–63% in rats). In rats and mice, urinary metabolites werefree and conjugated forms of p-hydroxyacetanilide, p- and m-nitrophenol and, in mice only, p-aminophenol (Rickert et al., 1983). For inhalation exposure, no quantitative estimation of absorption was made, but p-nitrophenol and p-aminophenol were detected in the urine of rats exposed to nitrobenzene vapour in the 24-h and 48-h collection periods (Ikeda & Kita, 1964). Metabolic studies using caecal contents of rats showed that nitrobenzene was sequentially reduced to nitrosobenzene, hydroxylaminobenzene, ultimately, aniline; this anaerobic metabolism occurred 150 times faster than reduction by the hepatic microsomal fraction (Levin & Dent, 1982). Nitrobenzene activation in rats to methaemoglobin-forming metabolites appears to be mediated to a significant degree by intestinal microflora (Reddy et al., 1976; Goldstein et al., 1984).
3.2 Acute toxicity
Oral LD50 in rats was reported to be 600–640 mg/kg (Smyth et al., 1969;Sziza & Magos 1959); around this dose, methaemoglobinaemia and histopathological changes in the brain as well as clinical signs of toxicity such as lethargy and ataxia were noted (Morgan et al., 1985;Sziza & Magos 1959).At lower doses, histopathological changes were found in the liver (at >110 mg/kg) and testes (at >300 mg/kg) (Bond et al., 1981). The minimal fatal dose of 750–1000 mg/kg in dogs was also stated by the oral route (Von Oettingen, 1941).In an inhalation study, Sprague-Dawley rats were exposed to an atmosphere saturated with nitrobenzene vapour. None of the 12 rats died during 3 h of exposure or within the post-exposure period of 14 days, but 3 of 12 rats died after 7 h exposure (BASF, 1977). For dermal exposure, it was reported that the LD50s were approximately 2,100 mg/kg in rats(Sziza & Magos 1959) and 760 mg/kg in rabbits (Harton & Rawl, 1976), and the minimal fatal dermal dose was about 480 mg/kg in mice(Shimkin 1939).
3.3 Short-term exposure toxicity
3.3.1Oral administration
A 28-day repeated-dose gavage study was performed in Fischer-344 rats at doses of 0, 5, 25 and 125 mg/kg/day (Shimo et al., 1994). An additional two groups of animals exposed to 0 or 125 mg/kg were kept for a 2-week recovery period. In the 125 mg/kg group,1/6 deaths of females on day 27, decreased movement, pale skin, gait abnormalities, and decreases in body weights, body weight gains and food consumption were seen. Haematological examination revealed decreases in red blood cells (RBC), haemoglobin (Hb) and haematocrit (Ht), and increased white blood cells(WBC) in 25 and 125 mg/kg groups. In blood biochemical examination, increases in total cholesterol were seen at 5 mg/kg and more, and increases in albumin at 25 mg/kg and more. In the 125 mg/kg group, increases in total protein, A/G ratio, ALT andALP were also observed. At necropsy, increases inthe relative weight of the liver at 5 mg/kg and more, of the spleen at 25 mg/kg and more and of the brain and kidneys at 125 mg/kg, and decreases in the relative weights of the testesand thymus at 125 mg/kg were found. Histopathological changes secondary to haemolytic anaemia were observed in the cerebellum, liver, kidneys,spleen and bone marrow. Congestion, increased brown pigmentation in red pulp and increased extramedullary haematopoiesis in the spleen and increased haematopoiesis of the bone marrow were detected even at the lowest doses of 5 mg/kg. In addition, spongiotic change of the cerebellum, epithelial degeneration and atrophy of the seminiferous tubules in the testes, and reduction of spermatozoa in the epididymides were observed at 125 mg/kg. Most of the above findings disappeared or tended to decrease during the recovery period, but brown pigmentation in the liver and kidneys and reduction of spermatozoa in the epididymishardly recovered.LOAEL was established to be 5 mg/kg/day.
In a range-finding US National Toxicology Program (NTP) study, nitrobenzene was administered to B6C3F1 mice and Fischer-344 rats by gavage at doses in the range 37.5–600 mg/kg/day for 14 days (NTP, 1983a).All rats and mice at 600 mg/kg and all rats at 300 mg/kg died or were sacrificed in a moribund condition prior to the end of treatment. Treated animals were inactive, ataxic, prostrate, cyanotic and dyspnoeic. Significant depression of weight gain was seen in mice at 37.5 mg/kg and in mice at 75 mg/kg. Haematologically, reticulocyte (Ret) counts were increased in mice at 75 mg/kg, whereas methaemoglobin (M-Hb) levels were increased in mice in all dose groups except 75 mg/kg males and 37.5 mg/kg females. Treated rats showed increases in M-Hb and in Ret counts.Histologically, mice and rats showed changes in the brain, liver, lung, kidney and spleen. NOAEL/LOAEL could not be established because detailed data were not available.
In an NTP study, nitrobenzene was administered by gavage to B6C3F1 mice at 0, 18.75, 37.5, 75, 150 or 300 mg/kg/day and to Fischer-344 rats at 0, 9.375, 18.75, 37.5, 75 or 150 mg/kg/day for 13 weeks (NTP, 1983a). In mice, three high-dose males died or were sacrificed moribund in weeks 4 and 5. Clinical signs included ataxia, lethargy, dyspnoea, convulsions, irritability and rapid head-bobbing movements. Haematological examination revealed increases in M-Hb and Retat 18.75 mg/kg and more, with decreases in Hb at 75 mg/kg and more and inHt and RBC at 150 mg/kg and more. Male mice exhibited leukopenia at 18.75 and 150 mg/kg and leukocytosis at 300 mg/kg. Similarly, lymphopenia was seen in all treated males except at 300 mg/kg, at which lymphocytosis was seen. High-dose females exhibited neutrophilia and lymphocytosis. Liver weight in treated mice was increased at 150 mg/kg and more in males and at 18.75 mg/kg and more in females.On histopathology, liver and spleen haematopoiesis and splenic haemosiderin accumulation at 75 mg/kg and more, and lymphoid depletion at 150 mg/kg and more were observed.In adrenal glands,fatty change was found in the X-zone in high-dose female mice. Testicular atrophy was observed at 18.75 mg/kg, 37.5 mg/kg, 150 mg/kg and 300 mg/kg. One high-dose male had acute necrosis in the area of the vestibular nucleus in the brain. In rats, seven males and one female died, and two males and two females were sacrificed moribund during weeks 6–13 in the high-dose group. Clinical signs included ataxia, left head tilt, lethargy, trembling, circling and dyspnoea, as well as cyanosis of the extremities at 75 mg/kg and more.In haematological examination, there were dose-related increases in M-Hb, Ret, polychromasia and anisocytosis, along with decreases in Hb, Ht and RBC. In the surviving high-dose animals, there was marked leukocytosis, with lymphocytosis and neutrophilia. Histopathological changes such as pigmentation and/or increased hematopoiesis, which were considered to be secondary to haemolytic anaemia, were observed in the spleen, liver, kidneys and bone marrow.In the spleen, thickening and fibrosis of the splenic capsule were noted at 9.375 mg/kg and more with occasional mast cells, haemosiderin-filled macrophages and fragmented necrotic cells, and hypertrophied and/or hyperplastic mesothelial cells.Brain lesions, characterized by demyelination, loss of neurons, varying degrees of gliosis, haemorrhage, and occasional neutrophil infiltration were also found at 150 mg/kg. In addition, the testes were mildly to markedly atrophic at 75 mg/kg and more, with varying degrees of hypospermatogenesis and multinucleated giant cell formation.LOAEL was established to be 18.75 mg/kg/day for mice and 9.375 mg/kg/day for rats (IPCS 2003).
In accordance with the OECD ReproTox protocol, nitrobenzene was given by gavage to Sprague-Dawley rats at 0, 20, 60 or 100 mg/kg/day throughout premating, mating, gestation and lactation(Mitsumori et al., 1994).Male rats were examined for haematology, blood biochemistry, macroscopic findings, organ weights and histopathology at the completion of the 41–42 day dosing period.At 100 mg/kg, animals exhibited clinical signs of toxicity, such as piloerection, salivation, emaciation, torticollis, circling movement and abnormal gait with deaths of 2/10 males and 9/10 females. Torticollis and abnormal gait were also observed in 1/10 females at 60 mg/kg, and one female each from the 20 and 60 mg/kg groups died. Depression of body weight gain was found in both sexes of the 100 mg/kg group and in females of the 60 mg/kg group.Haematological examination revealeddecreases in RBC, Hb and Ht, and increases in M-Hb at 20 mg/kg and more with elevation in erythroblasts and Retat 60 mg/kg and more. Increased WBC was also noted at 100 mg/kg.On blood biochemical examination, a dose-related increase in total bilirubin was evident. Increasedalbumin and total protein at 60 mg/kg and more, and in A/G ratio and total cholesterol at 100 mg/kg were also found. At necropsy, increasedliver and spleen weights at 20 mg/kg and more and kidney weights at 60 mg/kg and more, and decreases in the testis and epididymideweights at 60 mg/kg and more were noted. Histopathologically, centrilobular swelling of hepatocytes wasobservedin the liver at 20 mg/kg and more. At the same doses, atrophy of the seminiferous tubules was found in the testes with Leydig cell hyperplasia at 60 mg/kg and more. In the epididymides, decreased numbers of cells with round nuclei per seminiferous tubule and loss of intraluminal sperm were detected. Neuronal necrosis and gliosis were observed in certain nuclei in the cerebellar medulla and pons at 60 mg/kg and more. In addition, various changes secondary to haemolytic anaemia were observed in the liver, spleen, bone marrow and kidneysat 20 mg/kg and more. LOAEL was established to be 20 mg/kg/day.