Biological monitoring of o-toluidine in urine pretreated by an enzymatic deconjugation method

Health Risk Assessment of Ortho-Toluidine Utilising Human Biomonitoring Data of Workers and the General Population

The aim of this work was to demonstrate how human biomonitoring (HBM) data can be used to assess cancer risks for workers and the general population. Ortho-toluidine, OT (CAS 95-53-4) is an aniline derivative which is an animal and human carcinogen and may cause methemoglobinemia. OT is used as a curing agent in epoxy resins and as intermediate in producing herbicides, dyes, and rubber chemicals. A risk assessment was performed for OT by using existing HBM studies. The urinary mass-balance methodology and generic exposure reconstruction PBPK modelling were both used for the estimation of the external intake levels corresponding to observed urinary levels. The external exposures were subsequently compared to cancer risk levels obtained from the evaluation by the Scientific Committee on Occupational Exposure Limits (SCOEL). It was estimated that workers exposed to OT have a cancer risk of 60 to 90:106 in the worst-case scenario (0.9 mg/L in urine). The exposure levels and cancer risk of OT in the general population were orders of magnitude lower when compared to workers. The difference between the output of urinary mass-balance method and the general PBPK model was approximately 30%. The external exposure levels calculated based on HBM data were below the binding occupational exposure level (0.5 mg/m3) set under the EU Carcinogens and Mutagens Directive.

Risk of bladder cancer in male Japanese workers exposed to ortho-toluidine and other aromatic amines

PURPOSE

Nine bladder cancer (BCa) cases were reported among aromatic amine-exposed male workers at a factory manufacturing organic dye/pigment intermediates in Japan. We aimed to evaluate the characteristics of aromatic amine-exposed workers by cross-sectional observation, and the risk of BCa by assessing the standardized incidence ratio (SIR).

METHODS

In the cross-sectional study, our subjects were: 9 BCa patients, 36 aromatic amine-exposed non-patients, and 79 non-exposed workers from 3 factories. We evaluated the subjects' medical history, urinalysis, qualitative determination of nuclear matrix protein 22, and urinary cytology. For SIR assessment, 98 aromatic amine-exposed workers from 1 factory were included, and the Japanese general male population was used as a referent population. Since no direct aromatic amine-exposure data were available, we calculated surrogate exposure levels using information on job sites, exposure potency, and duration.

RESULTS

Coexistent aromatic amines were ortho-toluidine (OT), aniline, para-toluidine, ortho-anisidine, 2,4-xylidine, and ortho-chloroaniline. The prevalence rates of cystitis and bladder lesion-related symptoms in both BCa patients and aromatic amine-exposed non-patient workers were significantly higher than those of non-exposed workers. Overall, the SIR for BCa in OT-exposed workers was 56.8 (95% CI 27.7-104.3) and apparent dose-response relationships were revealed between the SIR and the surrogate exposure level in the 0-10-year lagged analyses. Overall, SIRs in other aromatic amine-exposed workers were also significantly high but no or unclear dose-response relationships were observed.

CONCLUSIONS

We conclude that OT may be responsible for the increased risk of BCa. Regular monitoring of bladder lesion-related symptoms is essential for the early identification of BCa.

Biological monitoring of o-toluidine in urine pretreated by an enzymatic deconjugation method

OBJECTIVES

To establish an enzymatic deconjugation method to separately quantify urinary o-toluidine (OT), its six metabolites, another six chemicals present in an OT-processing plant, and one metabolite of p-toluidine, and to propose optimal urinary biological monitoring items of OT exposure.

METHODS

Thirty-six urine samples of an OT-processing plant's workers were obtained and pretreated by an enzymatic deconjugation method employing β-glucuronidase/arylsulfatase for 3 hours at 37°C and measured by liquid chromatograph-mass spectrometry (LC-MS). An alkaline hydrolytic pretreatment and 1-chlorobutane extraction procedure was also examined as a widely used urinary OT measurement method.

RESULTS

The 14 chemicals were separated by LC-MS condition set by us and 13 chemicals other than 2-chloroaniline showed satisfiable linearity and limits of determination. Standard substances of six OT metabolites decomposed after the alkaline heating. In the 36 urine samples, OT, N-(4-hydroxy-2-methylphenyl) acetamide (NHM), and 4-amino-m-cresol (ACR) accounted for approx. 90% of the total OT and OT metabolites, but inter-individual variation of the three substance excretion seemed to be wide. Time course of urinary excretion revealed that concentration of the three substances was higher 24 hours after the work shift's end rather than just after the work shift.

CONCLUSIONS

OT and its six metabolites can each be determined with LC-MS. The alkaline method is not so optimal for exact biological monitoring. Rather, the sum of urinary OT, NHM, and ACR measured by the enzymatic method is a better index, and "end of the workweek" is a good urine-sampling time for the biological monitoring of OT exposure.