Dichlorobenzidine Research Articles

Fate of 3,3′‐dichlorobenzidine in soil: Persistence and binding

AbstractThe fate of the carcinogen 3,3′‐dichlorobenzidine (DCB) in soil was evaluated with regard to persistence and binding. A Brookston clay loam soil was amended with 4 or 40 ppm 14C‐DCB and incubated under aerobic conditions for 32 weeks or under anaerobic conditions for 1 year. Mineralization occurred very slowly in aerobic soil and did not occur in anaerobic soil. Total 14C radioactivity in soil remained essentially constant during the incubations, demonstrating that volatile losses of DCB or DCB decomposition products did not occur in our incubation system. DCB was shown to bind strongly to soil. After 32 weeks of incubation, approximately 90% of the applied radioactivity remained in soil after extraction with ethyl acetate and methanol. The loss of solvent‐extractable DCB occurred mostly in the first several weeks of incubation and was accompanied by an increase in alkali‐extractable DCB. These data strongly suggest the formation of covalent linkages between DCB and soil humic components as the primary fate of DCB in the Brookston soil. The significance of humus‐bound DCB residues as potential sources of future contamination is essentially unknown.

FATE OF 3,3′-DICHLOROBENZIDINE IN SOIL: PERSISTENCE AND BINDING

The fate of the carcinogen 3,3′-dichlorobenzidine (DCB) in soil was evaluated with regard to persistence and binding. A Brookston clay loam soil was amended with 4 or 40 ppm 14C-DCB and incubated under aerobic conditions for 32 weeks or under anaerobic conditions for 1 year. Mineralization occurred very slowly in aerobic soil and did not occur in anaerobic soil. Total 14C radioactivity in soil remained essentially constant during the incubations, demonstrating that volatile losses of DCB or DCB decomposition products did not occur in our incubation system. DCB was shown to bind strongly to soil. After 32 weeks of incubation, approximately 90% of the applied radioactivity remained in soil after extraction with ethyl acetate and methanol. The loss of solvent-extractable DCB occurred mostly in the first several weeks of incubation and was accompanied by an increase in alkali-extractable DCB. These data strongly suggest the formation of covalent linkages between DCB and soil humic components as the primary fate of DCB in the Brookston soil. The significance of humus-bound DCB residues as potential sources of future contamination is essentially unknown.

Urine monitoring of textile workers exposed to dichlorobenzidine-derived pigments.

Urine samples from 36 workers exposed to dichlorobenzidine (DCB)-derived pigments and 12 controls were screened for aromatic amines by a nonspecific colorimetric method and then further analyzed by GC/MS specifically for DCB and monoacetyldichlorobenzidine. Of the samples screened for aromatic amines, six (17%) of the exposed population and one (7%) of the control population registered positive (1.0 part per billion [ppb] or greater). One of the positive samples (5.6 ppb) reflected medication, and the remainder (1.1 to 1.8 ppb) were due to high urinary background. The specific analyses were negative (less than 0.2 ppb) for DCB or monoacetyldichlorobenzidine in all samples.

Disposition of 3,3′-dichlorobenzidine in the rat

The disposition of the carcinogen 3,3′-dichlorobenzidine (DCB) was studied in the male rat following oral administration. [ 14C]DCB was well absorbed by the rat with the maximum plasma radioactivity levels being found within 8 hr after dosing. The radioactivity was well distributed in the tissues 24 hr after administration with the highest levels found in the liver, followed by kidney, lung, and spleen. Repeated administration (six doses) of [ 14C]DCB to animals did not result in a substantial accumulation of 14C in the tissues. The elimination of radioactivity from the plasma, liver, kidney, and lung was biphasic showing an initial rapid decline (half-lives 1.68, 5.78, 7.14, and 3.85 hr, respectively) followed by a slower disappearance phase (half-lives 33.0, 77.0, 138.6, and 43.3 hr, respectively). Approximately half of the total 14C in the liver and kidney was covalently bound to cellular macromolecules 72 hr after dosing. [ 14C]DCB-derived radioactivity was extensively excreted by rats, mainly via the feces. Approximately 23–33% of the administered dose was recovered in the urine and 58–72% in the feces of rats within 96 hr. More than 65% of the administered 14C was eliminated in the bile of bile duct-cannulated rats within 24 hr after dosing. The radioactivity excreted in the urine and bile was primarily in the form of free (urine 71.2%, bile 25.5%) and conjugated (urine 19.6%, bile 57.9%) metabolites of DCB. Thus DCB is readily absorbed following oral administration, and then metabolized and excreted mainly via the feces.

A sensitive colorimetric determination of 3,3′-dichlorobenzidine in urine

Potential employee exposure to 3,3′-dichlorobenzidine (DCB) in textile operations may arise from residual amounts of DCB in certain pigments or by metabolic breakdown of these pigments. The sensitivity of an existing colorimetric method for measurement of DCB in urine was extended into the low ppb range. The method involves extraction of DCB from urine and its reaction with Chloramine-T. The detection of DCB by this method is linear over the range of 1–20 ppb. The linear regression calibration curve for a group of 44 control urines-containing 1–20 ppb of DCB had a relative standard deviation of 4.6%. The mean extraction recovery over this concentration range was 68%. Spectrophotometric scanning of the solution containing the color reaction product from urine concentrations as low as 1–2 ppb yielded spectra with distinguishable characteristic maxima. Such spectra potentially minimize the false-positive detection of DCB.

Removal and decontamination of residual 3,3′-dichlorobenzidine

One of the current methods used to decontaminate 3,3′-Dichlorobenzidine (DCB) in the pigment industry involves the use of a sodium hypochlorite bleach solution. Analyses performed in the laboratory and on actual workplace conditions have revealed that this practice is only partially effective. A subsequent investigation has shown that an aqueous solution of 5% tetrapotassium pyrophosphate and 10% sodium ethyl hexyl sulfate when blended in a jet sprayer did an effective job of removing DCB from the work area (90-99% reduction). Once removed from the worksite and collected in a central location, it was then determined that the diazotization reaction (the addition of sulfuric acid, ice, and sodium nitrite) can chemically react to eliminate any detectable DCB from the washings.

Carcinogenicity studies on different diarylide yellow pigments in mice and rats

Carcinogenicity studies on three purified diarylide pigments and one contaminated with 3,3′-dichlorobenzidine (DCB) were conducted in mice and rats at concentrations of 0.1, 0.3 and 0.9% in the feed. The studies were terminated after 104 weeks of treatment. Both mice and rats tolerated the different pigments up to a dietary level of 0.9%, receiving an equivalent of 715 and 230 g/kg/year, respectively. No adverse effects were exerted on growth, food intake, health condition, survival, or the histological appearance of a wide range of tissues, even when DCB was added to the pigment at a concentration of 20 ppm. In mice and rats of both sexes there was no indication of a significant correlation between treatment and tumour incidence. Based on the results, it is likely that diarylide yellow pigments were not absorbed after oral ingestion and it is unlikely that they underwent a metabolic splitting to DCB or 3,3′-dimethylbenzidine (DMB) either in mice or in rats. This fact was confirmed by an additional study in rabbits after single oral treatment at a dose level of 50 mg/kg.