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2970. Persistence of nitrosamines in the environment
The chemical environment
75
2968. Another index of foreign compound metabolism
andhouseholdapplications.More recentstudieshave indicated that acute exposureto high levels of this Notten, W. R. F. & Henderson,P.Th. (1975).The solventmay affect cardiovascularfunction (ibid 1975, influence of n-hexanetreatment on the glucuronic 13, 675)and haveraisedthe questionof whether MC acid pathway and activity of somedrug-metabolizing accumulatingin the &issues as a result of repeated enzymesin guinea-pig.Biochem.Pharmac.24, 127. exposureto lower concentrationsmight have similar effects.The paper cited above is concernedwith the Stimulation of the activity of microsomal-enzyme fate of MC in man following prolonged low-level systemsin the liver by foreign compoundsis often exposureunder industrialconditions. accompaniedby synthesisof D-glucaricacid, with inThe study was carried out in Japan on 196 male termediateformation of D-glUCUrOniC acid in the liver workers,agedbetween23 and 53 years,employedin cell. It follows that enhancedurinary D-glucaricacid four similarprinting plants ownedby one company. excretion may be a usefulindicator of adaptive accel- The men had beenexposedto MC at averageconeration of hepatic xenobiotic metabolism,which in centrationsof 4, 25, 28 or 53 ppm for 8 hr/day, 5.5 turn reflectsthe intake of foreign compounds.To in- days/wk for at least 5 yr. Routine medicalexaminvestigate these concepts, the authors cited above ations,tests for senseof vibration and clinical tests, examinedthe effect of n-hexaneon drug metabolism which included peripheral haemograms,determinaand the glucuronicacid systemin the liver. Prolonged tion of the specificgravity of the blood and urine inhalationexposureto high concentrationsof this sol- analysesfor urobilinogenand protein, were carried vent can causemuscleweaknessand sensorylossin out. No dose-relatedadverseeffects attributable to man (Cired in F.C.7: 1973.11, 157),although there MC were found in any of the workers. The urine is no evidencethat any metabolic stepscontribute content of total trichloro compounds(TTC) was to this toxic effect. found to increaselinearly with the level of MC expoIntraperitonealinjection of guinea-pigswith n-hex- sure. ane (in sesameoil) at a rate of 3 or 60 mg/kg/day Individual urine samples werecollectedfrom seven for 8 days enhancedthe in L&O glucuronyl conjuga- workers during the period between termination of tion of p-nitrophenol,an induction which wasaccom- exposurein the afternoon and resumptionof work paniedby an enhancedmicrosomal-proteincontent. the next morning. From the decreasein the urinary In contrast, in vitro rates of aniline p-hydroxylation TTC, the biologicalhalf-life of MC wasestimatedto and aminopyrineN-demethylationwere,respectively, be 8.7 hr. slightly decreasedand unchanged after n-hexane In a worker exposedto concentrationsof 100-2400 treatment.Treatmentwith 60 mg n-hexane/kg/dayin- ppm MC on Monday-Friday and a lower concentcreasedurinary excretion of D-ghCUrOniC acid within ration (20-33%of the weekday values)on Saturday, 24 hr of the first doseand of D-ghCariC acid after a steady increasein the level of urinary metabolites about 5 days.With the lower doseof n-hexane,given wasnoted towardsthe end of the week.This increase for 35 days,the time lag for increasedD-glucaricacid was attributable primarily to trichloroethanol, the excretionwasabout 21 days.Thesechangeswerepar- level of trichloroaceticacid showingno significantinalleled by induction of the microsomal enzyme, crease.Significant amountsof metabolite continued UDPglucuronosyltransferase. to be excretedfor over 24 hr after exposure.The inThe authors concludethat n-hexanemay causea creasedlevel of metabolitesexcretedtowards the end direct stimulationof glucuronideformation and that, of the week, together with the estimatedbiological during subacuteor more prolonged administration, half-life for MC of 8.7 hr, is in line with previous the hydrocarbon may be consideredas a specificin- indications of storage of MC in the tissuesafter ducer of the glucuronidation system.It has not yet repeatedexposureto the vapour. been established,however, at which step in the The authors considerthat the MC data currently sequenceof enzymic reactionsthe stimulation is in- available support the German thresholdlimit value itiated. of 200 ppm as an acceptable,if tentative, limit for industrialexposureto the solvent vapour. Fe current thresholdlimit value for methylchloroform in the UK and USA is 350 ppm.] 2%9. Industrial exposure to sub-threshold levels of methylchloroform
Seki, Y., Urashima,Y., Aikawa, H., Matsumura, H., Ichikawa, Y., Hiratsuka, F., Yoshioka, Y., Shimbo, S. & Ikeda, M. (1975).Trichloro-compoundsin the urine of humansexposedto methyl chloroform at sub-thresholdlevels.Int. Arch. Arbeitsmed. 34, 39.
Tate, R. L., III & Alexander, M. (1975).Stability of nitrosaminesin samplesof lake water, soil, and sewage.J. natn. Cancer Inst. 54, 327.
Although methylchloroform (l,l,l-trichloroethane; MC) is known to have someneurologicaleffectsin man, limited exposureto concentrationsup to 500 ppm hasbeenfound to have no particularly adverse effect on psychophysiologicalfunctions (Cited in F.C.7: 1972,10, 273).In fact, MC hasgenerallybeen regardedas a relatively safemember of the group of chlorinated solventsof importance in industrial
Previousstudieson nitrosamineshaveconcentrated on their presenceand formation in foods or their metabolismand toxicity in man and laboratory animals.The authorsof the above paper,however,have investigatedthe equally important topic of the stability of nitrosaminesin samplesof natural ecosystems. Dimethyl-, diethyl- and di-n-propylnitrosamines were incubated at 30°C with Williamson silt loam
2970. Persistence of nitrosamines
in the environment
The chemical environment
76
(pH 6.8), littoral water (pH 8.2) from Cayuga Lake, New York, or raw municipal sewage at pH 6.0 or 7.2. Nitrosamine concentrations were estimated colorimetrically and by gas-liquid chromatography. When incubated with soil, the nitrosamines (initial concentrations 13-22 ppm nitroso-nitrogen) were not metabolized for several days, but subsequently the nitroso-nitrogen slowly disappeared, so that after 70 days (when the rate of breakdown had slowed almost to zero) only about 50% of the added nitrosamine remained. When nitrosamines were incubated with samples of lake water, no loss or breakdown occurred over 3 months. However, slow degradation of nitrosamines did occur in sewage, the average weekly loss over a 42-day period being 8.9 ppm at pH 7.2. Sterilization of the sewage by autoclaving had little effect on the rate of breakdown at pH 6.0 and only slightly reduced the rate at pH 7.2, suggesting only a minor involvement of micro-organisms. Attempts to select for bacteria capable of metabolizing nitrosamines proved unsuccessful. The results suggest, therefore, that nitrosamines are likely to be relatively persistent in the environment, especially in lakes and rivers. 2971. Succinonihile
metabolism
in the mouse
Curry, S. H. (1975).Cumulative excretion of succinonitrile in mice.Biochem. Pharmac. 24, 351. The excretion kinetics of succinonitrile and its metaboliteshave been studied in mice given single or multiple ip injections of the “C-labelled compound in dosesof 25 mg/kg. Urine and faeceswere collectedat intervalsup to 72 hr after the singledose and 24-hr urineswere collectedafter administration of the radioactivedosesin the multiple-dosestudies. After injection of a singledoseof [‘4C]succinonitrile, nearly 80%of the radioactivity appearedin the urine within 72 hr and 6.5% wasfound in the faeces within 24 hr. Excretion wasrapid initially, with 60% of the doseappearingin urine and faecesin the first 24 hr, but later it wasrelatively slow.The proportion of radioactivity excretedas unmetabolizedsuccinonitrile washigh in the fust 6 hr and maximal between 0 and 2 hr. Excretion of cyanide(asthiocyanate)and of unidentifiedmaterialsolublein amyl alcohol fluctuated somewhatbut washigh between2 and 48 hr, after which excretion of other water-solublemetabolites wasmost prominent. After dosingof the rats with three daily dosesof unlabelledsuccinonitrilefollowed by a final doseof labelledmaterial, the activity excreted in the urine within 24 hr (52%)was similar to that after a single succinonitriledose(56%).In a further study, in which all four daily doseswere labelled,about 50”/, of the total body content of radioactivity was excreted in each 24-hr period, indicating someaccumulationof metabolitesrather than of succinonitrile,since the proportion of the latter fell steadily as dosing progressed.Mild accumulationof cyanide occurred,but there wasno evidenceof any enzymeinduction. One probablemetabolitewascyanoaceticacid, but neither this suggestion nor the identity of any other metabolites hasyet beenconfirmed.
2972. The burning question of plastics again
Blandford,T. B., Seamon,P. J., Hughes,R., Pattison, M. & Wilderspin,M. P. (1975).A caseof polytetrafluoroethylenepoisoningin cockatielsaccompaniedby polymer fume fever in the owner. Vet. Rec. 96, 175. Petajan,J. H., Voorhees,K. J., Packham,S. C., Baldwin, R. C., Einhorn, I. N., Grunnet, M. L., Dinger, B. G. & Birky, M. M. (1975).Extreme toxicity from combustionproducts of a fire-retardedpolyurethane foam. Science, N. Y 187, 742. For someyears, the high temperaturesgenerated in polytetrafluoroethylene(PTFE) non-stickliningsof domestic utensils when they boil dry have been known to releasefever-inducingtoxic pyrolysis products (Cited in F.C.T. 1969,7, 368). The temperature at which pyrolysis occursdeterminesthe toxicity for different animal species,birds being particularly susceptible(ibid 1974,12, 794). The first paper cited above describesthe curious caseof five cockatiels (Nymphicu~ hollandicus) and their owner.The birds werekept in a loungeadjoining the kitchen where a PTFE milk-pan containing water boileddry over an electric stove,and they died within 30 min of exposureto the fumes.The owner and hiswife continuedto sit in the lounge,but within a further 30 min the man becamebreathless,and 20 min later he wasshivering,dizzy and nauseatedand complainingof tightnessof the chest.After a sleep of 8 hr he woke with a headache,which disappeared during the morning, and a tightnessof the chest which lastedfor the rest of the day. Apart from a possiblememorydefectregardingthe accident,he recoveredfully. His wife wasunaffectedthroughout. No leaksof natural gasor build-up of carbon monoxide on the day of the occurrencecould be traced. Postmortemexaminationof the cockatielsshowedsevere lung congestion and oedema, with serous and fibrinousexudationinto the tertiary bronchioles,and intrabronchiolaroozing of blood into the lung parenchyma.Their livers showedseverecongestionof the sinusoidsand portal veins.The incident confirmsthe high susceptibilityof parakeetsto PTFE pyrolysis products. In the faceof current disquietconcerningthe toxic substancesproduced by pyrolysis of polyurethane foams,the secondpaper cited above indicatesthat the main toxic hazard stemsfrom a fire-retarding agent and not from the material itself. Rats were exposedfor 20 min to smokefrom the non-flaming combustionof Douglasfir or from heated samples of rigid polyurethanefoam which was either treated with the fire-retardant, O,O-diethyl-N,N-bis-(2-hydroxyethyl)aminomethyl phosphonate, or was untreated.lnhalation of wood smokecausedsevererespiratory distressand pulmonary oedemaindicative of carbon monoxide intoxication. Inhalation of fumes from untreatedpolyurethanefoam also showedreae tions characteristicof mild to moderateelevation of carboxyhaemoglobin(28-33%), without respiratory distressor post-mortemevidenceof respiratory-tract irritation. Fumesfrom the fire-retardedfoam induced repeatedseizures,however, leadingto major motor seizures(statusepilepticus)within about 1 hr. Behav-
75
2968. Another index of foreign compound metabolism
andhouseholdapplications.More recentstudieshave indicated that acute exposureto high levels of this Notten, W. R. F. & Henderson,P.Th. (1975).The solventmay affect cardiovascularfunction (ibid 1975, influence of n-hexanetreatment on the glucuronic 13, 675)and haveraisedthe questionof whether MC acid pathway and activity of somedrug-metabolizing accumulatingin the &issues as a result of repeated enzymesin guinea-pig.Biochem.Pharmac.24, 127. exposureto lower concentrationsmight have similar effects.The paper cited above is concernedwith the Stimulation of the activity of microsomal-enzyme fate of MC in man following prolonged low-level systemsin the liver by foreign compoundsis often exposureunder industrialconditions. accompaniedby synthesisof D-glucaricacid, with inThe study was carried out in Japan on 196 male termediateformation of D-glUCUrOniC acid in the liver workers,agedbetween23 and 53 years,employedin cell. It follows that enhancedurinary D-glucaricacid four similarprinting plants ownedby one company. excretion may be a usefulindicator of adaptive accel- The men had beenexposedto MC at averageconeration of hepatic xenobiotic metabolism,which in centrationsof 4, 25, 28 or 53 ppm for 8 hr/day, 5.5 turn reflectsthe intake of foreign compounds.To in- days/wk for at least 5 yr. Routine medicalexaminvestigate these concepts, the authors cited above ations,tests for senseof vibration and clinical tests, examinedthe effect of n-hexaneon drug metabolism which included peripheral haemograms,determinaand the glucuronicacid systemin the liver. Prolonged tion of the specificgravity of the blood and urine inhalationexposureto high concentrationsof this sol- analysesfor urobilinogenand protein, were carried vent can causemuscleweaknessand sensorylossin out. No dose-relatedadverseeffects attributable to man (Cired in F.C.7: 1973.11, 157),although there MC were found in any of the workers. The urine is no evidencethat any metabolic stepscontribute content of total trichloro compounds(TTC) was to this toxic effect. found to increaselinearly with the level of MC expoIntraperitonealinjection of guinea-pigswith n-hex- sure. ane (in sesameoil) at a rate of 3 or 60 mg/kg/day Individual urine samples werecollectedfrom seven for 8 days enhancedthe in L&O glucuronyl conjuga- workers during the period between termination of tion of p-nitrophenol,an induction which wasaccom- exposurein the afternoon and resumptionof work paniedby an enhancedmicrosomal-proteincontent. the next morning. From the decreasein the urinary In contrast, in vitro rates of aniline p-hydroxylation TTC, the biologicalhalf-life of MC wasestimatedto and aminopyrineN-demethylationwere,respectively, be 8.7 hr. slightly decreasedand unchanged after n-hexane In a worker exposedto concentrationsof 100-2400 treatment.Treatmentwith 60 mg n-hexane/kg/dayin- ppm MC on Monday-Friday and a lower concentcreasedurinary excretion of D-ghCUrOniC acid within ration (20-33%of the weekday values)on Saturday, 24 hr of the first doseand of D-ghCariC acid after a steady increasein the level of urinary metabolites about 5 days.With the lower doseof n-hexane,given wasnoted towardsthe end of the week.This increase for 35 days,the time lag for increasedD-glucaricacid was attributable primarily to trichloroethanol, the excretionwasabout 21 days.Thesechangeswerepar- level of trichloroaceticacid showingno significantinalleled by induction of the microsomal enzyme, crease.Significant amountsof metabolite continued UDPglucuronosyltransferase. to be excretedfor over 24 hr after exposure.The inThe authors concludethat n-hexanemay causea creasedlevel of metabolitesexcretedtowards the end direct stimulationof glucuronideformation and that, of the week, together with the estimatedbiological during subacuteor more prolonged administration, half-life for MC of 8.7 hr, is in line with previous the hydrocarbon may be consideredas a specificin- indications of storage of MC in the tissuesafter ducer of the glucuronidation system.It has not yet repeatedexposureto the vapour. been established,however, at which step in the The authors considerthat the MC data currently sequenceof enzymic reactionsthe stimulation is in- available support the German thresholdlimit value itiated. of 200 ppm as an acceptable,if tentative, limit for industrialexposureto the solvent vapour. Fe current thresholdlimit value for methylchloroform in the UK and USA is 350 ppm.] 2%9. Industrial exposure to sub-threshold levels of methylchloroform
Seki, Y., Urashima,Y., Aikawa, H., Matsumura, H., Ichikawa, Y., Hiratsuka, F., Yoshioka, Y., Shimbo, S. & Ikeda, M. (1975).Trichloro-compoundsin the urine of humansexposedto methyl chloroform at sub-thresholdlevels.Int. Arch. Arbeitsmed. 34, 39.
Tate, R. L., III & Alexander, M. (1975).Stability of nitrosaminesin samplesof lake water, soil, and sewage.J. natn. Cancer Inst. 54, 327.
Although methylchloroform (l,l,l-trichloroethane; MC) is known to have someneurologicaleffectsin man, limited exposureto concentrationsup to 500 ppm hasbeenfound to have no particularly adverse effect on psychophysiologicalfunctions (Cited in F.C.7: 1972,10, 273).In fact, MC hasgenerallybeen regardedas a relatively safemember of the group of chlorinated solventsof importance in industrial
Previousstudieson nitrosamineshaveconcentrated on their presenceand formation in foods or their metabolismand toxicity in man and laboratory animals.The authorsof the above paper,however,have investigatedthe equally important topic of the stability of nitrosaminesin samplesof natural ecosystems. Dimethyl-, diethyl- and di-n-propylnitrosamines were incubated at 30°C with Williamson silt loam
2970. Persistence of nitrosamines
in the environment
The chemical environment
76
(pH 6.8), littoral water (pH 8.2) from Cayuga Lake, New York, or raw municipal sewage at pH 6.0 or 7.2. Nitrosamine concentrations were estimated colorimetrically and by gas-liquid chromatography. When incubated with soil, the nitrosamines (initial concentrations 13-22 ppm nitroso-nitrogen) were not metabolized for several days, but subsequently the nitroso-nitrogen slowly disappeared, so that after 70 days (when the rate of breakdown had slowed almost to zero) only about 50% of the added nitrosamine remained. When nitrosamines were incubated with samples of lake water, no loss or breakdown occurred over 3 months. However, slow degradation of nitrosamines did occur in sewage, the average weekly loss over a 42-day period being 8.9 ppm at pH 7.2. Sterilization of the sewage by autoclaving had little effect on the rate of breakdown at pH 6.0 and only slightly reduced the rate at pH 7.2, suggesting only a minor involvement of micro-organisms. Attempts to select for bacteria capable of metabolizing nitrosamines proved unsuccessful. The results suggest, therefore, that nitrosamines are likely to be relatively persistent in the environment, especially in lakes and rivers. 2971. Succinonihile
metabolism
in the mouse
Curry, S. H. (1975).Cumulative excretion of succinonitrile in mice.Biochem. Pharmac. 24, 351. The excretion kinetics of succinonitrile and its metaboliteshave been studied in mice given single or multiple ip injections of the “C-labelled compound in dosesof 25 mg/kg. Urine and faeceswere collectedat intervalsup to 72 hr after the singledose and 24-hr urineswere collectedafter administration of the radioactivedosesin the multiple-dosestudies. After injection of a singledoseof [‘4C]succinonitrile, nearly 80%of the radioactivity appearedin the urine within 72 hr and 6.5% wasfound in the faeces within 24 hr. Excretion wasrapid initially, with 60% of the doseappearingin urine and faecesin the first 24 hr, but later it wasrelatively slow.The proportion of radioactivity excretedas unmetabolizedsuccinonitrile washigh in the fust 6 hr and maximal between 0 and 2 hr. Excretion of cyanide(asthiocyanate)and of unidentifiedmaterialsolublein amyl alcohol fluctuated somewhatbut washigh between2 and 48 hr, after which excretion of other water-solublemetabolites wasmost prominent. After dosingof the rats with three daily dosesof unlabelledsuccinonitrilefollowed by a final doseof labelledmaterial, the activity excreted in the urine within 24 hr (52%)was similar to that after a single succinonitriledose(56%).In a further study, in which all four daily doseswere labelled,about 50”/, of the total body content of radioactivity was excreted in each 24-hr period, indicating someaccumulationof metabolitesrather than of succinonitrile,since the proportion of the latter fell steadily as dosing progressed.Mild accumulationof cyanide occurred,but there wasno evidenceof any enzymeinduction. One probablemetabolitewascyanoaceticacid, but neither this suggestion nor the identity of any other metabolites hasyet beenconfirmed.
2972. The burning question of plastics again
Blandford,T. B., Seamon,P. J., Hughes,R., Pattison, M. & Wilderspin,M. P. (1975).A caseof polytetrafluoroethylenepoisoningin cockatielsaccompaniedby polymer fume fever in the owner. Vet. Rec. 96, 175. Petajan,J. H., Voorhees,K. J., Packham,S. C., Baldwin, R. C., Einhorn, I. N., Grunnet, M. L., Dinger, B. G. & Birky, M. M. (1975).Extreme toxicity from combustionproducts of a fire-retardedpolyurethane foam. Science, N. Y 187, 742. For someyears, the high temperaturesgenerated in polytetrafluoroethylene(PTFE) non-stickliningsof domestic utensils when they boil dry have been known to releasefever-inducingtoxic pyrolysis products (Cited in F.C.T. 1969,7, 368). The temperature at which pyrolysis occursdeterminesthe toxicity for different animal species,birds being particularly susceptible(ibid 1974,12, 794). The first paper cited above describesthe curious caseof five cockatiels (Nymphicu~ hollandicus) and their owner.The birds werekept in a loungeadjoining the kitchen where a PTFE milk-pan containing water boileddry over an electric stove,and they died within 30 min of exposureto the fumes.The owner and hiswife continuedto sit in the lounge,but within a further 30 min the man becamebreathless,and 20 min later he wasshivering,dizzy and nauseatedand complainingof tightnessof the chest.After a sleep of 8 hr he woke with a headache,which disappeared during the morning, and a tightnessof the chest which lastedfor the rest of the day. Apart from a possiblememorydefectregardingthe accident,he recoveredfully. His wife wasunaffectedthroughout. No leaksof natural gasor build-up of carbon monoxide on the day of the occurrencecould be traced. Postmortemexaminationof the cockatielsshowedsevere lung congestion and oedema, with serous and fibrinousexudationinto the tertiary bronchioles,and intrabronchiolaroozing of blood into the lung parenchyma.Their livers showedseverecongestionof the sinusoidsand portal veins.The incident confirmsthe high susceptibilityof parakeetsto PTFE pyrolysis products. In the faceof current disquietconcerningthe toxic substancesproduced by pyrolysis of polyurethane foams,the secondpaper cited above indicatesthat the main toxic hazard stemsfrom a fire-retarding agent and not from the material itself. Rats were exposedfor 20 min to smokefrom the non-flaming combustionof Douglasfir or from heated samples of rigid polyurethanefoam which was either treated with the fire-retardant, O,O-diethyl-N,N-bis-(2-hydroxyethyl)aminomethyl phosphonate, or was untreated.lnhalation of wood smokecausedsevererespiratory distressand pulmonary oedemaindicative of carbon monoxide intoxication. Inhalation of fumes from untreatedpolyurethanefoam also showedreae tions characteristicof mild to moderateelevation of carboxyhaemoglobin(28-33%), without respiratory distressor post-mortemevidenceof respiratory-tract irritation. Fumesfrom the fire-retardedfoam induced repeatedseizures,however, leadingto major motor seizures(statusepilepticus)within about 1 hr. Behav-