The implications for risk assessment of measuring the relative contribution to exposure from occupation, environment and lifestyle: hemoglobin adducts from amino- and nitro-arenes

S-(3-Aminobenzanthron-2-yl)cysteine in the globin of rats as a novel type of adduct and possible biomarker of exposure to 3-nitrobenzanthrone, a potent environmental carcinogen

3-Nitrobenzanthrone (3-NBA), a potent environmental mutagen and carcinogen, is known to be activated in vivo to 3-benzanthronylnitrenium ion which forms both NH and C2-bound adducts with DNA and also reacts with glutathione giving rise to urinary 3-aminobenzanthron-2-ylmercapturic acid. In this study, acid hydrolysate of globin from rats dosed intraperitoneally with 3-NBA was analysed by HPLC/MS to identify a novel type of cysteine adduct, 3-aminobenzanthron-2-ylcysteine (3-ABA-Cys), confirmed using a synthesised standard. The 3-ABA-Cys levels in globin peaked after single 3-NBA doses of 1 and 2 mg/kg on day 2 to attain 0.25 and 0.49 nmol/g globin, respectively, thereafter declining slowly to 70-80% of their maximum values during 15 days. After dosing rats for three consecutive days with 1 mg 3-NBA/kg a significant cumulation of 3-ABA-Cys in globin was observed. 3-ABA-Cys was also found in the plasma hydrolysate. Herein, after dosing with 1 and 2 mg 3-NBA/kg the adduct levels peaked on day 1 at 0.15 and 0.51 nmol/ml plasma, respectively, thereafter declining rapidly to undetectable levels on day 15. In addition, sulphinamide adducts were also found in the exposed rats, measured indirectly as 3-aminobenzanthrone (3-ABA) split off from globin by mild acid hydrolysis. Levels of both types of adducts in the globin samples parallelled very well with 3-ABA/3-ABA-Cys ratio being around 1:8. In conclusion, 3-ABA-Cys is the first example of arylnitrenium-cysteine adduct in globin representing a new promising class of biomarkers to assess cumulative exposures to aromatic amines, nitroaromatics and heteroaromatic amines.

Aromatic Amines in Experimental Cancer Research: Tissue-Specific Effects, an Old Problem and New Solutions

Carcinogenic aromatic amines usually produce tumors in specific target tissue, such as 2-acetylaminofluorene (AAF) producing liver tumors in rats, in contrast to some other structurally related arylamines. A hypothesis is presented that explains the mode of action in this rat liver model. Genotoxic and nongenotoxic effects work together and make AAF a complete rat liver carcinogen. The cytotoxic, promoting effects are particularly important. N-Hydroxy-2-aminofluorene and 2-nitrosofluorene, two metabolites of AAF, are able to uncouple the mitochondrial respiratory chain. They entertain a redox cycle that removes electrons from the respiratory chain and impairs ATP production. The dose-dependent opening of the mitochondrial permeability transition pore signals the viability of the cell. If the pore is opened to a certain extent, the cell is eliminated by apoptosis. As a consequence, oval cells proliferate, and as this process is overloaded, the liver transforms into a cirrhosis-like situation and thus provides the conditions under which initiated liver cells develop tumors. Such an interpretation is based on assumptions that have been debated for a long time. Some of these often forgotten developments are reviewed in support of the hypothesis, which allows a more comprehensive view of the complex in vivo situation at a time when in vitro models prevail.

Toxicological guidelines for monocyclic nitro-, amino- and aminonitroaromatics, nitramines, and nitrate esters in drinking water

In order to secure a safe drinking water supply, the setting of tolerable/acceptable ceilings of drinking water hygiene is required with regard to xenobiotics resulting from several anthropogenic impacts. This is done in practice by using drinking water guidelines or standards as quantitative objectives. The list of the new EU Directive or the German drinking-water standards is limited to those parameters that have the highest relevance for drinking water quality; nitro compounds (NCs) are not regulated. Because other substances contained in water can also represent a hazard for human health, the German Drinking Water Ordinance clarifies that specific actions must be implemented if compounds other than those regulated appear at concentrations that may be a cause for concern regarding human health. NCs serve as intermediates for dyes, pharmaceuticals, and synthetic materials; they themselves are used as solvents, explosives, and pesticides. During their commercial production or from their use, they may be released to the environment and lead to a contamination of aquatic systems and thus also of drinking water resources. In practice, therefore, a need for assessment is frequently given for relevant NCs. For 19 nitro-, amino-, and aminonitroaromatics, nitramines, and nitrate esters health-based drinking water guide values have been derived. For toxicological evaluation and derivation of guideline values for the NCs of interest, the tolerable daily intake approach was used for chemicals exhibiting a threshold for toxic effects. This was done by using established tolerable body doses for humans based on an identified no-observed-adverse-effect level/low-observed-effect-level for the most sensitive indicator for toxicity. In the case of nonthreshold chemical substances, suitable estimates of excess lifetime cancer risk have been applied.

Simultaneous determination of various aromatic amines and metabolites of aromatic nitro compounds in urine for low level exposure using gas chromatography-mass spectrometry

A newly developed method permits the simultaneous quantitative determination of various aromatic amines (or metabolites of aromatic nitro compounds, respectively) in human urine in one analytical run. Applying this method it is possible to determine aniline, toluidines, 4-isopropylaniline, o-anisidine, 3- and 4-chloroaniline, 4-bromoaniline, aminonitrotoluenes, aminodinitrotoluenes, 3,5- and 3,4-dichloroaniline, alpha- and beta-naphtylamine and 4-aminodiphenyl. After separation from the urinary matrix by a simple liquid-liquid extraction at pH 6.2-6.4 the analytes are converted into their pentafluoropropionic acid amides. Separation and quantitative analysis is carried out by capillary gas chromatography and mass-selective detection in the single ion monitoring mode. The limits of detection were within the range from 0.05 microg/l (4-aminobiphenyl, o-anisidine, 3,5-dichloroaniline) to 2 microg/l urine (4-amino-2,6-dinitrotoluene). The relative standard deviation of the within-series imprecision (determined at spiked concentrations of 2.0 microg/l and 10 microg/l) was between 2.9 and 13.6% depending on analyte and concentration. The relative recovery rates were in the range of 70-121%. The analytes that do not contain a nitro function showed better performance regarding the analytical reliability criteria. In order to determine the suitability of this new method for biological monitoring we analysed 20 12-h urine samples of persons without known exposure to aromatic amines, nitroaromatics or precursors in a pilot study. In these samples various aromatic amines could be clearly identified. The general population renally excretes aniline (median: 3.5 microg/l; 95th percentile: 7.9 microg/l), o- (0.12 microg/l; 2.7 microg/l), m- (0.17 microg/l; 2.2 microg/l) and p-toluidine (0.11 microg/l; 0.43 microg/l), and o-anisidine (0.22 microg/l; 0.68 microg/l). Additionally, we found that the persons investigated also excrete 3- (<0.05 microg/l; 0.55 microg/l) and 4-chloroaniline (0.11 microg/l; 0.57 microg/l) as well as 3,5-dichloroaniline (0.18 microg/l; 1.5 microg/l). 3,4-Dichloroaniline was found in some specimens (20%) in concentrations near the limit of detection (<0.05 microg/l; 0.12 microg/l). We did not detect alpha- or beta-naphtylamine, 4-aminobiphenyl or metabolites of explosives in the samples.

Biomonitoring of exposure to aromatic amines: haemoglobin adducts in humans

Haemoglobin (Hb) adducts from aromatic amines (AAs) are well established biomarkers of exposure. Tobacco smoking and occupational exposure are major sources of AA Hb adducts. The origin of background levels in non-smokers and non-occupationally exposed humans are largely unknown. Here we examine the determination of AA Hb adducts, focussing on the analytical strategies for Hb isolation, removal of unbound AAs from Hb solutions, hydrolysis of the Hb bound AAs, extraction, preconcentration, clean-up and derivatisation of the free amines for determination by gas chromatography-mass spectrometry. Finally, a detailed summary of available results on the determination of AA Hb adducts is given.

Biotransformation and partial mineralization of the explosive 2,4,6-trinitrotoluene (TNT) by rhizobia

Three strains, T10, B5, and M8, each belonging to a different species of the family Rhizobiaceae and isolated from atrazine-contaminated soils, were tested for their ability to transform 2,4,6-trinitrotoluene (TNT) (50 microg x mL(-1)) in liquid cultures using glucose as the C-source. All three strains were able to transform TNT to hydroxylaminodinitrotoluenes (2-HADNT, 4-HADNT), aminodinitrotoluenes (2-ADNT, 4-ADNT), and diaminonitrotoluene (2,4-DANT). The transformation was significantly faster in the presence of glutamate. Furthermore, the major metabolites that accumulated in cultures were 2-ADNT with glucose, and 4-ADNT with glutamate plus glucose. Rhizobium trifolii T10 was also tested for its ability to transform high levels of TNT (approximately 350 microg x mL(-1)) in a soil slurry. Almost 60% of the TNT was transformed within 2 days in bioaugmented soil slurries, and up to 90% when cultures were supplemented with glucose and glutamate. However, mineralization was minimal in all cases, less than 2% in 78 days. This is the first report on the degradation of TNT by rhizobial strains, and our findings suggest that rhizobia have the potential to play an important role in the safe decontamination of soils and sites contaminated with TNT if bioaugmentation with rhizobia is shown to have no ecotoxicological consequence.

Endpoints and surrogates for use in population studies in toxicology

Risk characterisation of human exposure to chemicals requires information on the intrinsic toxic (hazardous) properties of the chemical, dose response of effects for the critical endpoints and exposure of the population. Information on hazardous properties, including data on mechanism and toxicokinetics, is necessary to define the critical endpoints and the relevant parameters to assess internal exposure and its relation to external exposure. Consequently the design of population studies to evaluate toxic effects or to monitor exposed cohorts must consider the critical endpoints of toxic effects and exposure. External exposure is determined by chemical analysis of the chemicals in food, water or air. The more relevant internal exposure is assessed by analysis of the chemical or its metabolites in body fluids and, if appropriate, by protein- or DNA-adducts. Effects are monitored by determining the relevant organ-specific parameters. In the case of genotoxic agents, effect biomonitoring parameters, like cytogenetic effects in peripheral blood cells or DNA strand breaks, are applied. Genotyping to detect deficiencies in the expression of enzymes, e.g. those involved in metabolic activation or inactivation, may explain interindividual differences in susceptibility. Overall prospective population studies allow exposure monitoring and risk assessment of human exposure only when such parameters are included.

Health risk of combustion products: toxicological considerations

Combustion of organic material produces an almost uncountable number of products among which are many chemicals known to have toxic properties. A pertinent example is the diesel engine emission. There is concern about the possible health effects and we would like to know what risk is associated with the exposure. If risk is defined as the probability that a certain health effect occurs within a defined time span or as a result of a certain strain (Royal Society Study Group)--and it is important to emphasize the quantitative aspect of this definition--we must admit that we do not know a good answer. The example of diesel exhaust is used to demonstrate the toxicological approach to risk characterization in general and the possible improvement of exposure assessment with nitroarenes as indicators for environmental contaminations in particular.

Polycyclic nitroarenes (nitro-PAHs) as biomarkers of exposure to diesel exhaust

Diesel exhaust contains numerous genotoxic carcinogens. It is essentially unknown to which extent this source contributes to the total load of these chemicals in humans. One possible approach to the problem is to find suitable biomarkers. To this end five polycyclic mononitroarenes (nitro-PAH) were selected and methods developed to determine the sulfinic acid-type hemoglobin adducts they form in vivo. The nitro-PAHs are: 1-nitropyrene, 2-nitrofluorene, 3-nitrofluoranthene, 9-nitrophenanthrene, and 6-nitrochrysene. Hydrolysis of the hemoglobin adducts yields the respective arylamines which were analyzed by gas chromatography/mass spectrometry. The detection limit was 0.01-0.08 pmol/g Hb. Blood samples were analyzed from 29 bus garage workers, occupationally exposed to diesel exhaust, and from 20 urban hospital workers and 14 rural council workers as controls. Hb adducts above the detection limit were found in most blood samples. The most abundant cleavage products were 1-aminopyrene and 2-aminofluorene with levels ranging from 0.01 to 0.68 pmol/g Hb. However, there was no significant difference between the groups for 1-nitropyrene and 2-nitrofluorene supporting the conclusion that both are widespread environmental contaminants resulting in significant background exposures. A significant difference on a group from individuals from urban and rural areas was found only if all five adducts were added, this may indicate an additional exposure from traffic. The new specific nitro-PAH Hb adducts are proposed to be used as biomarkers to trace the sources and to identify above-background exposures.

Biological fate of [14C]-1-nitropyrene in rats following intragastric administration

1-Nitropyrene (1-NP), a weak carcinogen associated with diesel exhaust particles, has previously been detected in workplace atmospheres with in-use diesel engines and in the general environment. In order to gain insight in its biological fate, a single dose of [14C]-1-NP (27.6 microCi, 750 mg/kg body weight, b.w.) was administered intragastrically to rats and the presence of metabolites in blood and tissue homogenates, and radioactivity associated with blood proteins and tissue DNA, were studied. Early peak levels of radioactivity observed in blood and tissue homogenates indicated a rapid absorption of [14C]-1-NP from the gastrointestinal tract. Metabolite patterns observed in plasma, liver and kidney homogenates strongly suggested an important role of the intestinal microflora in the enterohepatic recirculation, but not in nitroreduction of 1-NP prior to absorption from the gastrointestinal tract. This might explain the low levels of radioactivity associated with blood proteins, since 1-nitrosopyrene, a product of nitroreduction of 1-NP, is likely to be involved in protein binding. Levels of radioactivity associated with plasma proteins were approximately four times higher than the levels of radioactivity associated with hemoglobin (401.0 and 84.1 pmol/g protein per micromol 1-NP kg b.w., respectively, at 24 h). Maximal 25% of the associated radioactivity was released following mild alkaline hydrolysis of either hemoglobin or plasma proteins. 1-Aminopyrene was the only released compound after hydrolysis of hemoglobin. In addition to 1-aminopyrene, two more polar unidentified metabolites were detected following hydrolysis of plasma proteins. Association of radioactivity with DNA was highest in the liver at the first moments of observation (7.4 pmol 14C Eq./mg DNA per micromol 1-NP kg b.w.), but decreased rapidly to levels lower than observed for kidney DNA (max. 3.0 pmol 14C Eq./mg DNA per micromol 1-NP kg b.w. at 24 h). In lungs 8-50 times less radioactivity was associated with DNA than observed in the liver and kidneys. The results of this study show, that 1-NP undergoes an extensive and complex biotransformation in vivo, resulting in a variety of metabolites present in blood and tissue homogenates and a diversity of blood protein adducts. Concentrations of plasma metabolites, blood protein adducts and DNA adducts were rather low. In addition, previous studies also showed relatively low concentrations of metabolites present in urine. Therefore, sensitive and selective methods will be needed in order to evaluate the biological fate of 1-NP, associated with diesel exhaust particles, in humans.

Biological monitoring of dinitrotoluene by gas chromatographic-mass spectrometric analysis of 2,4-dinitrobenzoic acid in human urine

The method of analysis described permits the determination of 2,4-dinitrobenzoic acid down to the lower microg l(-1) range in the urine of persons exposed to dinitrotoluene. 2,4-Dinitrobenzoic acid is the main metabolite of 2,4-dinitrotoluene and technical dinitrotoluene. After acidic hydrolysis, which served to release the conjugated part of the 2,4-dinitrobenzoic acid, the analyte was selectively separated from the urine matrix via various extraction steps and then derivatised to the methyl ester. Quantitative analysis was carried out using capillary gas chromatography and mass selective detection. 3,5-Dinitrobenzoic acid was used as an internal standard. The detection limit was 1 microg l(-1) urine. The relative standard deviations of within-series imprecision were between 5 and 6%. The relative recoveries were between 91 and 110% depending on the concentration. The analytical method developed as part of this study was used to investigate a collective consisting of 82 urine samples from persons working in the area of explosives disposal. The concentrations of 2,4-dinitrobenzoic acid determined ranged from the detection limit to 95 microg l(-1) urine. The method allowed the quantification of low-level internal exposure to dinitrotoluene.