Monitoring of occupational exposure to cyclohexanone by diffusive sampling and urinalysis

The present study was initiated in order to identify the best marker of occupational exposure to cyclohexanone among cyclohexanone and its metabolites in urine. To examine if diffusive samplers are applicable to personal monitoring of exposure to cyclohexanone in workroom air, the performance of carbon cloth to adsorb cyclohexanone in air was studied by experimental exposure of the cloth to cyclohexanone at 5, 10, 25 or 50 ppm (i.e. 20, 40, 100 or 200 mg m-3) for up to 8 h. Cyclohexanone in the exposed cloth was extracted with carbon disulphide followed by gas chromatographic (GC) analysis. The cloth adsorbed cyclohexanone in proportion to the concentration (up to 50 ppm) and the duration (up to 8 h), and responded quantitatively to a 15 min exposure at 100 ppm. In a field survey, end-of-shift urine samples were collected from 24 factory workers occupationally exposed to cyclohexanone (up to 9 ppm) in combination with toluene and other solvents. Urine samples were also collected from 10 subjects with no occupational exposure to solvents. The urine samples were treated with acid or an enzyme preparation for hydrolysis, and extracted with dichloromethane or ethyl acetate. The extracts were analysed by GC for cyclohexanone, cyclohexanol, and trans- and cis-isomers of 1,2- and 1,4-cyclohexanediol. Both cyclohexanol and trans-1,2-cyclohexanediol in urine correlated significantly with time-weighted average intensity of exposure to cyclohexanone. Although trans -1,4-isomer was also excreted, its quantitative relation with cyclohexanone exposure could not be established, because the solvent extraction rate was low and unstable. Excretion of cis-isomers was not confirmed. The two analytes, cyclohexanol and trans-1,2-cyclohexanediol, appeared to be equally valid as exposure markers, but the latter may be superior to the former in the sense that it is sensitive enough to separate the exposed from the non-exposed at 1 ppm or less cyclohexanone exposure.     

Biological monitoring of occupational exposure to 1-bromopropane by means of urinalysis for 1-bromopropane and bromide ion

The purposes of the present study are (1) to develop a sensitive analytical method to measure 1-bromopropane (1-BP) in urine, (2) to examine if 1-BP or bromide ion (Br) in urine is a useful biomarker of exposure to 1-BP, and (3) to identify the lowest 1-BP exposure concentration the method thus established can biomonitor. A factory survey was carried out on Friday, and 33 workers (all men) in cleaning and painting workshops participated; each worker was equipped with a diffusive sampler (carbon cloth KF-1500 as an adsorbent) to monitor 1-BP vapour for an 8-h shift, and offered a urine sample at the end of the shift for measurement of 1-BP and Br in urine. In addition, 10 non-exposed men offered urine samples as controls. The performance of the carbon cloth diffusive sampler was examined to confirm that the sampler is suitable for monitoring time-weighted average 1-BP vapour exposure. A head-space GC technique was employed for analysis of 1-BP in urine, whereas Br in urine was analysed by ECD-GC after derivatization to methyl bromide. The workers were exposed to vapours of seven other solvents (i.e. toluene, xylenes, ethylbenzene, acetone, etc.) in addition to 1-BP vapour; the 1-BP vapour concentration was 1.4 ppm as GM and 28 ppm as the maximum. Multiple regression analysis however showed that 1-BP was the only variable that influenced urinary 1-BP significantly. There was a close correlation between 1-BP in urine and 1-BP in air; the correlation coefficient (r) was >0.9 with a narrow variation range, and the regression line passed very close to the origin so that 2 ppm 1-BP exposure can be readily biomonitored. The correlation of Br in urine with 1-BP in air was also significant, but the r (about 0.7) was smaller than that for 1-BP, and the background Br level was also substantial (about 8 mg l^-1). Thus, it was concluded that 1-BP in end-of-shift urine is a reliable biomarker of occupational exposure to 1-BP vapour, and that Br in urine is less reliable.     

Biological variables as soil quality indicators: Effect of sampling time and ability to classify soils by their suitability

Soil biological variables are considered good soil quality indicators due to their high sensitivity and ability to reflect soil management effects. However, they frequently show high temporal variability. Our objectives were: (a) to analyze temporal stability and seasonal effect on biological variables, (b) to choose between autumn and spring to sample for soil biological variables, and (c) to determine biological variables able to discriminate among selected soil subgroups. Areas with minimal human disturbance were sampled in three soil orders (Mollisol, Vertisol and Alfisol) during two and a half years, each autumn and spring. Microbial biomass C and N (MBC, MBN), basal respiration (Resp), metabolic quotient (qCO₂), potential of N mineralization (PNM-AI), soil organic C (TOC) and total soil N (TON) were measured in three composite soil samples collected from homogeneous areas at 0–15 cm depth. For the studied soils, selected soil biological variables presented different levels depending on the time of sampling, spring or autumn. Hence, the importance of pointing out the time of sampling to report results of these variables in this kind of studies is remarked. In general, biological variables presented higher stability when we sampled soils in autumn compared to spring. Because of this, we used autumn soil samples to determine the best soil biological variables to discriminate among selected subgroups of soils. The separation of soil subgroups by means of discriminant analysis using just TOC and TON was scrutinized, considering that these soil variables are routinely measured in soil test laboratories. Nonetheless they were not able to discriminate properly among soil subgroups because they showed high error rates classifying the samples in the correct subgroups. In contrast, the variables PMN-AI, MBC, and MBN adequately discriminated the five soil subgroups. From the biological variables, PMN-AI and MBC were the best ones to characterize (discriminate) among the five soil subgroups. Particularly, PMN-AI was able to separate soils by their suitability for agricultural purposes.     

Biological monitoring of exposure to n-heptane by gas chromatographic mass spectrometric determination of its metabolites

Urine samples from 10 workers that had been exposed to n-heptane were analysed by the GC/MS technique to verify the concentrations and the relative abundances of its metabolites. The procedure of sample preparation has undergone some modifications with respect to the Perbellini method and the mass spectrometric detection was carried out in selected ions monitoring conditions. The analyses of samples collected during three different workshifts showed that 2 heptanol was not the main metabolite and that the remains of 2 heptanone, valerolactone and 2,5 heptanedione were present at the beginning of the successive work week at 12, 34 and 39 of the average values found at the end of the previous week. Overall, a very slow excretion rate was detected for the last metabolite. The main and significant metabolite at the end of the two workshifts was 2 heptanone which was detected in urine at average values of 413 and 238 μg g^-1 creatinine. This urinary ketone correlated better than other metabolites with respect to the airborne n-heptane at the end of both the workshift and work week. These preliminary data suggest that further studies should be carried out to confirm whether 2 heptanone is really useful as an n-heptane marker in biological monitoring.     

Monitoring of occupational exposure to epichlorohydrin by genetic effects and hemoglobin adducts

The present work is focused on the determination of in vivo doses and studies of genetic effects in workers exposed to epichlorohydrin (ECH). The studied endpoints were hemoglobin (Hb) adducts, frequencies of hprt mutants, micronuclei in cytochalasin B blocked binucleated lymphocytes, sister chromatid exchanges (SCE) and high frequency cells (HFC). Blood samples were collected from office clerks and ECH exposed factory workers at an industrial plant in Germany. The workers were exposed to 0.11–0.23 ppm ECH in the air 45 h per week and to 0.2–2.6 ppm for 3 h per week. Some Swedish non-exposed subjects were also used for Hb adduct measurements. The genetic data, HFC and SCE, showed a significant difference between exposed and unexposed donors. In contrast to earlier studies on SCE, no impact of smoking was observed. Effects on micronuclei were on the borderline of significance, whereas there was no effect for HPRT mutants. The average Hb adduct level was higher in exposed than in non-exposed donors, although the difference was only significant when the exposed group was compared to Swedish controls. Smoking gave significantly increased adduct levels. The absence of significant correlations between individual data for Hb adducts and genetic effects, may be explained by the different periods of time covered by the responses in these endpoints. Whereas Hb adducts reflect the exposure during up to 4 months (i.e. the life span of human erythrocytes), the SCE, and particularly the HFC, seem to accumulate for years in a long-lived fraction of T-lymphocytes without DNA repair. Thus, the adduct data does not reflect the exposure backwards in time unless it can be shown that exposure conditions have remained unchanged. The origin of the background adduct levels in non-smoking control persons is at present not known.     

Urinary 1-hydroxypyrene as a biomarker of exposure to polycyclic aromatic hydrocarbons: biological monitoring strategies and methodology for determining biological exposure indices for various work environments

This article reviews the published studies on urinary 1-hydroxypyrene (1-OHP) as a biomarker of exposure to polycyclic aromatic hydrocarbons (PAHs) in work environments. Sampling and analysis strategies as well as a methodology for determining biological exposure indices (BEIs) of 1-OHP in urine for different work environments are proposed for the biological monitoring of occupational exposure to PAHs. Owing to the kinetics of absorption of pyrene by different exposure routes and excretion of 1-OHP in urine, in general, 1-OHP urinary excretion levels increase during the course of a workday, reaching maximum values 3-9 h after the end of work. When the contribution of dermal exposure is important, post-shift 1-OHP excretion can however be lower than pre-shift levels in the case where a worker has been exposed occupationally to PAHs on the day prior to sampling. In addition, 1-OHP excretion levels in either pre-shift, post-shift or evening samples increase during the course of a work-week, levelling off after three consecutive days of work. Consequently, ideally, for a first characterization of a work environment and for an indication of the major exposure route, considering a 5-day work-week (Monday to Friday), the best sampling strategy would be to collect all micturitions over 24 h starting on Monday morning. Alternatively, collection of pre-shift, post-shift and evening urine samples on the first day of the work-week and at the end of the work-week is recommended. For routine monitoring, pre-shift samples on Monday and post-shift samples on Friday should be collected when pulmonary exposure is the main route of exposure. On the other hand, pre-shift samples on Monday and Friday should be collected when the contribution of skin uptake is important. The difference between beginning and end of work-week excretion will give an indication of the average exposure over the workweek. Pre-shift samples on the first day of the work-week will indicate background values, and, hence, reflect general environment exposure and body burden of pyrene and/or its metabolites. On the other hand, since PAH profile can vary substantially in different work sites, a single BEI cannot apply to all workplaces. A simple equation was therefore developed to establish BEIs for workers exposed to PAHs in different work environments by using a BEI already established for a given work environment and by introducing a correction factor corresponding to the ratio of the airborne concentration of the sum of benzo(a)pyrene (BaP) equivalent to that of pyrene. The sum of BaP equivalent concentrations represents the sum of carcinogenic PAH concentrations expressed as BaP using toxic equivalent factors. Based on a previously estimated BEI of 2.3 μmol 1-OHP mol^-1 creatinine for coke-oven workers, BEIs of 4.4, 8.0 and 9.8 μmol 1-OHP mol^-1 creatinine were respectively calculated for vertical pin Söderberg workers, anode workers and pre-bake workers of aluminium plants and a BEI of 1.2 μmol 1-OHP mol^-1 creatinine was estimated for iron foundry workers. This approach will allow the potential risk of cancer in individuals occupationally exposed to PAHs to be assessed better.     

Biological monitoring of exposure to sevoflurane in operating room personnel by the measurement of hexafluoroisopropanol and fluoride in urine

The objectives of this study were to evaluate the value of urinary hexafluoroisopropanol (HFIP) and fluoride (F^-) measurement for the biological monitoring of operating room personnel exposed to sevoflurane. Fifty members of operating room staffs from eight different hospitals took part in the study. To assess external exposure to sevoflurane, air samples were collected during the whole anaesthesia period by a passive sampling device (3M 3500 organic vapour monitor) attached close to the breathing zone of each subject. Urine was collected before (BA) and at the end of anaesthesia (EA) for the determination of HFIP, fluoride and creatinine. Average airborne concentration of sevoflurane was 19.0 ppm (range: ND-139.9 ppm) with a mean duration of anaesthesia of 221 min (range: 60-435 min). There was a better correlation between external and internal exposure as estimated by EA urinary HFIP (r = 0.78; p <0.0001) compared with EA urinary F^- (r = 0.41; p = 0.0031). Furthermore determination of urinary HFIP seemed more suited than that of F^- for the assessment of sevoflurane exposure because of lower background in BA samples (86 % of BA HFIP values were under the limit of detection). Based on these results, values of 9.6 and 4.3 mg HFIP g^-1 creatinine correspond to airborne concentrations of 50 and 20 ppm of sevoflurane, respectively. Among the confounding parameters investigated (body mass index (BMI), sex, cytochrome P450 polymorphism) only BMI showed statistically significant influence on sevoflurane metabolism at these low levels of exposure. The measurement of HFIP in urine at the end of the surgical procedure constitutes a good index to assess occupational exposure to sevoflurane. Further studies will be necessary to propose an health-based limit value which remains to be determined from the relationship between effects and internal dose as can be assessed by HFIP measurement in urine.     

Development of a urinary biomarker for exposure to the organophosphate propetamphos: data from an oral and dermal human volunteer study

Propetamphos is a member of the vinyl phosphate group of insecticides and is mainly used for sheep dipping. There have been no published metabolic studies on the effect of propetamphos in man to date, although the present authors have published the identification of a metabolite. The present paper presents data from a human volunteer study investigating the toxicokinetics of the organophosphorus pesticide propetamphos following oral and dermal exposure. Five volunteers ingested a propetamphos dose of 10 μg kg^-1 (35nmol kg^-1) body weight. Following a washout of 4 weeks, a 100mg (356 μmol) dermal dose of propetamphos was applied, occluded to 80cm² of the inner forearm, for 8 h to the same five volunteers. In a pilot study (several weeks before the main study), one volunteer also received an occluded dermal dose of 50 mg (178 μmol) propetamphos. Unabsorbed propetamphos on the skin was washed off after 8 h and collected. Blood and urine samples were collected over 30 and 54 h for the oral and dermal exposures respectively. Blood samples were analysed for plasma and erythrocyte cholinesterase. Urine samples were analysed for a urinary metabolite of propetamphos: methylethylphosphoramidothioate (MEPT). Following oral and dermal exposure, peak urinary MEPT levels occurred at 1 and 10-12 h respectively. The apparent urinary elimination half-lives of MEPT had means of 1.7h (oral exposure) and 3.8 h (dermal exposure). Approximately 40% of the oral dose and 1% of the dermal dose were recovered as urinary MEPT or metabolites, which could be hydrolysed to MEPT. Approximately 90% of the dermal dose was recovered from the skin washings. Data from a volunteer showed that a doubling of the dermal dose resulted in approximately double the concentration of total MEPT. Alkaline hydrolysis of urine samples increased the level of MEPT detected after both oral and dermal doses. The increase was greater and statistically significant (p < 0.001, paired t-test) for the dermal dose. This increase in MEPT suggests the presence of other MEPT-containing metabolites or conjugates. The difference in the increase between oral and dermal doses raises the question of a difference in metabolism between the two routes. No individual showed a significant depression compared with their pre-exposure levels of erythrocyte acetyl cholinesterase or plasma cholinesterase activity for either dosing route. However, on a group basis, there was a statistically significant mean depression in plasma cholinesterase activity at 8 and 24 h for oral exposure, with a maximum mean depression of 7% from pre-exposure levels at 8 h. Hydrolysis of urine samples had the effect of reducing the interindividual coefficient of variation (CV) for total excretion of MEPT following both oral (CV reduced from 36 to 8%) and dermal (CV reduced from 40 to 17%) exposure. The ability to detect and follow the elimination of low doses of propetamphos by measurement of 'total' (after hydrolysis) urinary MEPT suggests it is a suitable biomarker of propetamphos exposure. The comparatively short elimination half-lives suggest a strategy for biological monitoring of occupational exposure based on samples collected at the end of the shift.     

Haemoglobin adducts and specific immunoglobulin G in humans as biomarkers of exposure to hexahydrophthalic anhydride

The aim of this study was to determine whether haemoglobin adducts Hb of hexahydrophthalic anhydride HHPA and HHPA specific immunoglobulin G IgG can be used as biomarkers of exposure to HHPA. The exposures of HHPA in 10 workers were determined from the mean urinary hexahydrophthalic acid HHP acid levels range 76-3300 nmol HHP acid mmol-1 creatinine during a period of 4 weeks. Blood was collected at the end of the period and Hb-HHPA adducts were analysed by gas chromatography mass spectrometry. The Hb-HHPA adduct levels ranged from 0.45 to 24.7 pmol g-1 Hb. There was a close correlation between the urinary HHP acid levels and the amount of Hb-HHPA adducts r = 0.87 . One day exposures to HHPA and methylhexahydrophthalic anhydride MHHPA in 142 workers were determined from analysis of urinary HHP acid range 0-3300 nmol HHP acid mmol-1 creatinine and methylhexahydrophthalic acid MHHP acid; range 0-1700 nmol MHHP acid mmol-1 creatinine. HHPA specific IgG were analysed in the 142 workers with an ELISA method. The optical density for HHPA specific IgG varied between 0 and 1.25. There was no statistically significant correlation between the sum of the urinary HHP acid and MHHP acid and the HHPA specific IgG r = 0.12; p = 0.14 . Thus, Hb-HHPA adducts seem to be applicable as biomarkers of exposure to HHPA while the possible role of HHPA specific IgG as an indicator of exposure has to be further evaluated.     

Haemoglobin adducts and specific immunoglobulin G in humans as biomarkers of exposure to hexahydrophthalic anhydride

The aim of this study was to determine whether haemoglobin adducts Hb of hexahydrophthalic anhydride HHPA and HHPA specific immunoglobulin G IgG can be used as biomarkers of exposure to HHPA. The exposures of HHPA in 10 workers were determined from the mean urinary hexahydrophthalic acid HHP acid levels range 76-3300 nmol HHP acid mmol-1 creatinine during a period of 4 weeks. Blood was collected at the end of the period and Hb-HHPA adducts were analysed by gas chromatography mass spectrometry. The Hb-HHPA adduct levels ranged from 0.45 to 24.7 pmol g-1 Hb. There was a close correlation between the urinary HHP acid levels and the amount of Hb-HHPA adducts r = 0.87 . One day exposures to HHPA and methylhexahydrophthalic anhydride MHHPA in 142 workers were determined from analysis of urinary HHP acid range 0-3300 nmol HHP acid mmol-1 creatinine and methylhexahydrophthalic acid MHHP acid; range 0-1700 nmol MHHP acid mmol-1 creatinine . HHPA specific IgG were analysed in the 142 workers with an ELISA method. The optical density for HHPA specific IgG varied between 0 and 1.25. There was no statistically significant correlation between the sum of the urinary HHP acid and MHHP acid and the HHPA specific IgG r = 0.12; p = 0.14 . Thus, Hb-HHPA adducts seem to be applicable as biomarkers of exposure to HHPA while the possible role of HHPA specific IgG as an indicator of exposure has to be further evaluated.     

Monitoring for occupational exposure to 4,4′-methylenebis(2-chloroaniline) by gas chromatographic-mass spectrometric analysis of haemoglobin adducts, blood, plasma and urine

The feasibility of using plasma, blood and haemoglobin adducts for monitoring occupational exposure to the suspected human carcinogen 4,4′-methylenebis(2-chloroaniline) (MOCA) was investigated. A method utilising capillary gas chromatography-negative-ion chemical-ionisation mass spectrometry (GC-MS) for the determination of pentafluoropropionyl (PFP) derivatives of MOCA, released by alkaline hydrolysis from protein adducts and conjugates, was both sensitive and selective. When selected ion monitoring was used, sub-femtomole amounts of PFP-MOCA could be measured. The detection limit for haemoglobin adducts of MOCA was below 10 fmol/g Hb, well below the levels found for occupationally exposed individuals. Capillary GC with electron-capture detection also had the required sensitivity for the determination of MOCA in blood and urine of five individuals who were exposed to MOCA during the manufacture of polyurethane elastomers were determined by the GC-MS method. The MOCA concentrations for the various blood fractions and urine were within the following ranges: haemoglobin adducts, 0.73–43.3 pmol MOCA/g Hb; plasma alkaline hydrolysate, 0.05–22.0 nmol/l; whole blood, 0.13–17.4nmol/l; urine, 4.5–2390 nmol/l. Because the products of MOCA in the blood reflect metabolic activation of MOCA and integrate exposure over a period of weeks, the use of blood samples for monitoring exposure to MOCA offers advantages over the currently used urinary MOCA measurements.     

Monitoring of Biocontrol Agents Based on Trichoderma Strains Following Their Application to Glasshouse Crops by Combining Dilution Plating with UP-PCR Fingerprinting

Universally primed (UP) PCR analysis was used to characterize strains of Trichoderma spp., which constitute the active ingredients of commercial products for biocontrol of phytopathogens. Several UP primers were able to generate distinct and reproducible fingerprints for each strain, allowing them to be differentiated from a collection of other Trichoderma spp. strains. In order to test whether the UP-PCR method in combination with dilution plating could be useful to detect and enumerate propagules of biocontrol strains of Trichoderma spp. when applied on a commercial scale, sampling was carried out in three commercial glasshouse operations. Dilution plating was carried out using a semi-selective medium and a number of the Trichoderma spp. recovered were subjected to UP-PCR analysis with one selected UP primer. The results showed that the method could be used to identify the isolates from the biocontrol products applied in the different glasshouses. Furthermore, it was found that a biocontrol strain also colonized an untreated bench in one of the glasshouses. The combined methods enable verification of the active ingredient concentration, facilitating monitoring establishment and spread of the Trichoderma strains.     

Control of the circadian rhythm of carbon dioxide assimilation in Bryophyllum leaves by exposure to darkness and high carbon dioxide concentrations

The circadian rhythm of CO₂ assimilation in detached leaves of Bryophyllum fedtschenkoi at 15° C in normal air and continuous illumination is inhibited both by exposure to darkness, and to an atmosphere enriched with 5% CO₂. During such exposures substantial fixation of CO₂ takes place, and the malate concentration in the cell sap increases from about 20 mM to a constant value of 40–50 mM after 16 h. On transferring the darkened leaves to light, and those exposed to 5% CO₂ to normal air, a circadian rhythm of CO₂ assimilation begins again. The phase of this rhythm is determined by the time the transfer is made since the first peak occurs about 24 h afterwards. This finding indicates that the circadian oscillator is driven to, and held at, an identical, fixed phase point in its cycle after 16 h exposure to darkness or to 5% CO₂, and it is from this phase point that oscillation begins after the inhibiting condition is removed. This fixed phase point is characterised by the leaves having acquired a high malate content. The rhythm therefore begins with a period of malate decarboxylation which lasts for about 8 h, during which time the malate content of the leaf cells must be reduced to a value that allows phosphoenolpyruvate carboxylase to become active. Inhibition of the rhythm in darkness, and on exposure to 5% CO₂ in continuous illumination, appears to be due to the presence of a high concentration of CO₂ within the leaf inhibiting malic enzyme which leads to the accumulation of high concentrations of malate in the leaf cells. The malate then allosterically inhibits phosphoenolpyruvate carboxylase upon which the rhythm depends. The results give support to the view that malate synthesis and breakdown form an integral part of the circadian oscillator in this tissue.Abbreviations B. Bryophyllum - PEPCase phosphoenolpyruvate carboxylase     

Biological monitoring,by in vivo XRF measurements,of occupational exposure to lead,cadmium, and mercury

In vivo X-ray fluorescence (XRF) techniques were used for biological monitoring of lead, cadmium, and mercury. Lead accumulates in bone, the level of which may thus be used for monitoring of exposure. However, there was no close association between lead levels in bone and exposure time, partly because of differences in exposure patterns and partly, probably, because of variations in the toxicokinetics of lead. There are at least two separate bone lead compartments. The average over-all half-time is probably 5–10 yr. The finger bone level may be an index of the lead status of the total skeleton. In lead workers, the mobilization of bone lead causes an “internal” lead exposure and affects the blood lead level considerably. In cadmium workers, in vivo XRF is a sensitive and risk-free method for assessment of accumulation in kidney cortex, the critical tissue as to toxic effects; workers displayed increased levels. However, there was no clear association with duration and intensity of exposure, cadmium levels in urine, or microglobulinuria. Determinations of kidney cadmium may add important information on the state of accumulation and, thus, risk of kidney damage. Workers exposed to elemental mercury vapor, as well as fishermen exposed to methyl mercury, had mercury levels in bone below the detection limit of the XRF method.     

Monitoring of individual human exposure to aflatoxins (AF) and N-nitrosamines (NNO) by immunoassays

Highly sensitive immunoassays have been used to quantitate aflatoxins (AF) and N-nitrosamines (NNO) in human body fluids and tissues, respectively. This approach was taken in order to quantitate environmental exposure to these agents at an individual level to facilitate the investigation of their role in the etiology of human cancer. In order to analyse AF in human urine, an immunopurification step has been developed by using AF-specific antibody bound to AH-Sepharose 4B gel in a small (4-ml gel volume) affinity column prior to enzyme-linked immunosorbent assay (ELISA). The ELISA can be used to quantitate aflatoxin B1 (AFB1) over the range 0.01 ng/ml to 10 ng/ml and the assay system has been validated by using human urine samples spiked with AFB1 over this concentration range. In addition, 29 urine samples from the Philippines have been analysed and found to contain a range of levels from zero to 4.25 ng/ml AFB1 equivalent with a mean of 0.875 ng/ml. This compared with a mean of 0.066 ng/ml AFB1 equivalent in samples from France. Radioimmunoassay of O6-methyldeoxyguanosine (O6-medG) has been performed on human oesophageal and cardiac stomach mucosal DNA from tissue samples obtained during surgery in Linxian County, People's Republic of China, an area of high risk for both oesophageal and stomach cancer. Using the methodology described and having 1 mg of hydrolyzed DNA allows the detection of approximately 25 fmol O6medG per mg DNA.(ABSTRACT TRUNCATED AT 250 WORDS)