Exposure to o-toluidine, aniline, and nitrobenzene in a rubber chemical manufacturing plant: a retrospective exposure assessment update

Research progress in human biological monitoring of aromatic hydrocarbon with emphasis on the analytical technology of biomarkers

Aromatic hydrocarbons are unsaturated compounds containing carbon and hydrogen that form single aromatic ring, or double, triple, or multiple fused rings. This review focuses on the research progress of aromatic hydrocarbons represented by polycyclic aromatic hydrocarbons (including halogenated polycyclic aromatic hydrocarbons), benzene and its derivatives including toluene, ethylbenzene, xylenes (o-, m- and p-), styrene, nitrobenzene, and aniline. Due to the toxicity, widespread coexistence, and persistence of aromatic hydrocarbons in the environment, accurate assessment of exposure to aromatic hydrocarbons is essential to protect human health. The effects of aromatic hydrocarbons on human health are mainly derived from three aspects: different routes of exposure, the duration and relative toxicity of aromatic hydrocarbons, and the concentration of aromatic hydrocarbons which should be below the biological exposure limit. Therefore, this review discusses the primary exposure routes, toxic effects on humans, and key populations, in particular. This review briefly summarizes the different biomarker indicators of main aromatic hydrocarbons in urine, since most aromatic hydrocarbon metabolites are excreted via urine, which is more feasible, convenient, and non-invasive. In this review, the pretreatment and analytical techniques are compiled systematically for the qualitative and quantitative assessments of aromatic hydrocarbons metabolites such as gas chromatography and high-performance liquid chromatography with multiple detectors. This review aims to identify and monitor the co-exposure of aromatic hydrocarbons that provides a basis for the formulation of corresponding health risk control measures and guide the adjustment of the exposure dose of pollutants to the population.

Occurrence of primary aromatic amines and nicotine in sediments collected from the United States

Despite extensive use of primary aromatic amines (AAs) in consumer products, little is known about their occurrence in the environment. In this study, we investigated the occurrence of 14 AAs and nicotine in 75 sediment samples collected from seven estuarine and freshwater ecosystems in the Unites States. Additionally, risk quotients (RQs) were calculated to assess potential risks of these chemicals to aquatic organisms. Of the 14 AAs analyzed, seven of them were found in sediments. The sum concentrations of seven AAs in sediments were in the range of 10.2 to 1810 ng/g, dry wt (mean: 388 ng/g). Aniline was the most abundant compound, accounting for, on average, 53 % of the total concentrations. Nicotine was found in sediments at a concentration range of <LOQ to 1340 ng/g, dry wt (mean: 119 ng/g). Among the seven sampling locations studied, AAs and nicotine concentrations were the highest in sediment from Altavista wastewater lagoon in Virginia (AV, mean: 1700 ng/g) followed in descending order by Chicago Sanitary and Ship Canal (CSSC, mean: 807 ng/g), Indiana Harbor and Ship Canal (IHSC, mean: 698 ng/g) and New Bedford Harbor (NBH, mean: 482 ng/g). Sediments from the upper Mississippi River (MISS, mean: 63.4 ng/g) and Tittabawassee River (TBR, mean: 52.3 ng/g) contained the lowest concentrations. The RQ values for AAs in sediment ranged from 0 to 733 and that for nicotine ranged from 0 to 2060. Among AAs, the highest RQ value was found for 4-chloroaniline. Nicotine exhibited notable RQ values, which suggested risk from this chemical to aquatic organisms. This is the first study to report the occurrence of AAs in sediments and our results suggest the need for further investigations on the sources and ecological impacts of these chemicals in aquatic ecosystems.

Bioaccessibility of Organic Compounds Associated with Tire Particles Using a Fish In Vitro Digestive Model: Solubilization Kinetics and Effects of Food Coingestion

Tire and road wear particles (TRWP) account for an important part of the polymer particles released into the environment. There are scientific knowledge gaps as to the potential bioaccessibility of chemicals associated with TRWP to aquatic organisms. This study investigated the solubilization and bioaccessibility of seven of the most widely used tire-associated organic chemicals and four of their degradation products from cryogenically milled tire tread (CMTT) into fish digestive fluids using an in vitro digestion model based on Oncorhynchus mykiss. Our results showed that 0.06-44.1% of the selected compounds were rapidly solubilized into simulated gastric and intestinal fluids within a typical gut transit time for fish (3 h in gastric and 24 h in intestinal fluids). The environmentally realistic scenario of coingestion of CMTT and fish prey was explored using ground Gammarus pulex. Coingestion caused compound-specific changes in solubilization, either increasing or decreasing the compounds' bioaccessibility in simulated gut fluids compared to CMTT alone. Our results emphasize that tire-associated compounds become accessible in a digestive milieu and should be studied further with respect to their bioaccumulation and toxicological effects upon passage of intestinal epithelial cells.

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.

Profiles of primary aromatic amines, nicotine, and cotinine in indoor dust and associated human exposure in China

Despite the widespread use of primary aromatic amines (AAs) in consumer products, little is known about their prevalence in house dust. In this study, we investigated the occurrence of 35 AAs and two tobacco chemical markers (nicotine and its breakdown product cotinine) in 119 samples of house dust collected from five provinces in China. Ten of the 35 AAs and [nicotine and cotinine] were found in >80% and 100% of the samples, respectively, at concentration ranges of 29.1-19,200 (median: 700 ng/g) and 23.2-22,400 (4600) ng/g, respectively. Aniline was the predominant AA found in all dust samples (median: 257 ng/g). Dust samples from Henan and Shanxi provinces contained higher summed concentrations of the 10 AAs than those from Sichuan and Shandong, although the concentrations did not vary significantly among the five provinces (p > 0.05). A significant (p = 0.048), positive correlation (r = 0.882) existed between concentrations of nicotine and cotinine in dust samples. Similarly, concentrations of AAs were significantly correlated with those of nicotine in dust samples. Dyestuffs, rubber products, polyurethane foam and tobacco smoke are the major sources of AAs in the indoor environment. The estimated daily intakes (EDI) through dust ingestion ranged from 0.349 (adults) to 6.62 ng/kg-bw/day (toddlers) for AAs and from 1.27 to 51.1 ng/kg-bw/day for nicotine which are well below the current tolerable daily intakes.

Risk assessment for o-toluidine and bladder cancer incidence

BACKGROUND

Elevated bladder cancer incidence has been reported in a cohort of 1875 workers manufacturing chemicals used in the rubber industry and employed any time during 1946-2006. o-Toluidine (OT), an aromatic amine, was the prime suspect agent. Using the available environmental data and process characterization, previous investigators assigned ranks to volatile chemical air concentrations across time in departments and jobs, reflecting probabilities of exposure and use of personal protective equipment for airborne and dermal exposures. Aniline, another aromatic amine, was present at comparable concentrations and is known to be an animal carcinogen but produced lower levels in post-shift urine and of hemoglobin adducts than OT in a group of workers.

METHODS

A quantitative risk assessment was performed based on this same population. In this study, cumulative OT exposures were estimated (a) based on previously assigned ranks of exposure intensity and reported actual exposures in jobs with the highest assigned rank, and (b) directly from the historical environmental sampling for OT. Models of bladder cancer incidence were evaluated taking into account possible healthy worker survivor effects.

RESULTS

Under various assumptions regarding workforce turnover, the excess lifetime risk of bladder cancer from OT exposure at 1 ppb was estimated to be in the range 1-7 per thousand.

CONCLUSIONS

The current ACGIH TLV and OSHA standards for OT are 2 and 5 ppm, respectively, 1000-fold higher than the exposure estimated here for 1-7 per thousand excess lifetime risk.

Retrospective Exposure Assessment Methods Used in Occupational Human Health Risk Assessment: A Systematic Review

As part of the assessment and management of chemical risk and occupational hygiene, retrospective exposure assessment (REA) to chemical agents can be defined as the estimate of exposure associated with a person's work history. The fundamental problem underlying the reconstruction of the exposure is that of transforming this type of information in quantitative terms to obtain an accurate estimate. REA can follow various approaches, some of which are technically complicated and both time and resource consuming. The aim of this systematic review is to present the techniques mainly used for occupational REA. In order to carry out this evaluation, a systematic review of the scientific literature was conducted. Forty-four studies were identified (published from 2010 to date) and analyzed. In exposure reconstruction studies, quantitative approaches should be preferable, especially when estimates will be used in the context of health impact assessment or epidemiology, although it is important to stress how, ideally, the experimental data available for the considered scenario should be used whenever possible as the main starting information base for further processing. To date, there is no single approach capable of providing an accurate estimate of exposure for each reasonably foreseeable condition and situation and the best approach generally depends on the level of information available for the specific case. The use of a combination of different reconstruction techniques can, therefore, represent a powerful tool for weighting and integrating data obtained through qualitative and quantitative approaches, in order to obtain the best possible estimate.

Evaluation of 2-methoxy-4-nitroaniline (MNA) in hypersensitivity, 14-day subacute, reproductive, and genotoxicity studies

2-Methoxy-4-nitroaniline (MNA), an intermediate in the synthesis of azo dyes used in textiles and paints, is structurally similar to carcinogenic anilines. Human exposure occurs primarily in the occupational setting through handling of dye dust, and through use and disposal of MNA-containing products. MNA has been reported to induce contact hypersensitivity in a human, myocardial necrosis in rats, and bacterial mutagenicity. This study assessed the subacute toxicity, genotoxicity, contact hypersensitivity, and reproductive toxicity of MNA in rodents in an effort to more fully characterize its toxicological profile. B6C3F1/N mice were exposed to 0, 650, 1250, 2500, 5000, or 10,000 ppm MNA by dosed feed for 14-days to evaluate subacute toxicity and histopathological endpoints. In female mice, decreased body weight (13.5 %) and absolute kidney weight (14.8 %), compared to control, were observed at 10,000 ppm MNA; increased relative liver weight (10-12 %), compared to control, occurred at 5,000-10,000 ppm MNA. In male mice, absolute (15 %) and relative liver weights (9-13 %) were increased at 2,500-5,000 ppm and 1250-10,000 ppm MNA, compared to control, respectively. In both sexes of mice, minimal elevations of hemosiderin pigmentation (a breakdown product of erythrocytes), relative to control, were observed in the liver (10,000 ppm); minimal to moderate elevations of hemosiderin pigmentation (5,000-10,000 ppm) and minimal increases in hematopoietic cell proliferation occurred in the spleen (≥ 1250 ppm). In a reproductive toxicity study, timed-mated female Harlan Sprague Dawley rats were exposed to 0-10,000 ppm MNA by dosed feed from gestation day 6 through postnatal day (PND) 21. Decreases in mean litter weights were observed at 5000 ppm MNA, compared to control, beginning at PND1. To evaluate potential contact hypersensitivity, MNA (2.5-50 %, in dimethylformamide) was applied to the dorsa of both ears of female Balb/c mice once daily for three days. The increase observed in lymph node cell proliferation (10-50 % increase in thymidine uptake compared to control) did not reproducibly achieve the Sensitization Index (SI) 3 level, and there was no ear swelling evident following sensitization with 10-50 % MNA and challenge with 25 % MNA in the mouse ear swelling test. In bacterial mutagenicity assays, MNA (250-1000 μg/plate) induced significant increases, compared to control, in mutant colonies with and without metabolic activation enzymes in Salmonella typhimurium strains TA100 and TA98. These data indicate that MNA is genotoxic, and may induce erythrocyte damage and reactive phagocytosis by macrophages in the liver and spleen.

A Review of Environmental Occurrence, Fate, Exposure, and Toxicity of Benzothiazoles

Benzothiazole and its derivatives (BTs) are high production volume chemicals that have been used for several decades in a large number of industrial and consumer products, including vulcanization accelerators, corrosion inhibitors, fungicides, herbicides, algicides, and ultraviolet (UV) light stabilizers. Several benzothiazole derivatives are used commercially, and widespread use of these chemicals has led to ubiquitous occurrence in diverse environmental compartments. BTs have been reported to be dermal sensitizers, respiratory tract irritants, endocrine disruptors, carcinogens, and genotoxicants. This article reviews occurrence and fate of a select group of BTs in the environment, as well as human exposure and toxicity. BTs have frequently been found in various environmental matrices at concentrations ranging from sub-ng/L (surface water) to several tens of μg/g (indoor dust). The use of BTs in a number of consumer products, especially in rubber products, has resulted in widespread human exposure. BTs undergo chemical, biological, and photolytic degradation in the environment, creating several transformation products. Of these, 2-thiocyanomethylthio-benzothiazole (2-SCNMeS-BTH) has been shown to be the most toxic. Epidemiological studies have shown excess risks of cancers, including bladder cancer, lung cancer, and leukemia, among rubber factory workers, particularly those exposed to 2-mercapto-benzothiazole (2-SH-BTH). Human exposure to BTs continues to be a concern.

Hemoglobin Adducts and Urinary Metabolites of Arylamines and Nitroarenes

Arylamines and nitroarenes are intermediates in the production of pharmaceuticals, dyes, pesticides, and plastics and are important environmental and occupational pollutants. N-Hydroxyarylamines are the toxic common intermediates of arylamines and nitroarenes. N-Hydroxyarylamines and their derivatives can form adducts with hemoglobin (Hb-adducts), albumin, DNA, and tissue proteins in a dose-dependent manner. Most of the arylamine Hb-adducts are labile and undergo hydrolysis in vitro, by mild acid or base, to form the arylamines. According to current knowledge of arylamine adduct-formation, the hydrolyzable fraction is derived from the reaction products of the arylnitroso derivatives that yield arylsulfinamide adducts with cysteine. Hb-adducts are markers for the bioavailability of N-hydroxyarylamines. Hb-adducts of arylamines and nitroarenes have been used for many biomonitoring studies for over 30 years. Hb-adducts reflect the exposure history of the last four months. Biomonitoring of urinary metabolites is a less invasive process than biomonitoring blood protein adducts, and urinary metabolites have served as short-lived biomarkers of exposure to these hazardous chemicals. However, in case of intermittent exposure, urinary metabolites may not be detected, and subjects may be misclassified as nonexposed. Arylamines and nitroarenes and/or their metabolites have been measured in urine, especially to monitor the exposure of workers. This review summarizes the results of human biomonitoring studies involving urinary metabolites and Hb-adducts of arylamines and nitroarenes. In addition, studies about the relationship between Hb-adducts and diseases are summarized.

Development of suspect and non-target screening methods for detection of organic contaminants in highway runoff and fish tissue with high-resolution time-of-flight mass spectrometry

Untreated urban stormwater runoff contributes to poor water quality in receiving waters. The ability to identify toxicants and other bioactive molecules responsible for observed adverse effects in a complex mixture of contaminants is critical to effective protection of ecosystem and human health, yet this is a challenging analytical task. The objective of this study was to develop analytical methods using liquid chromatography coupled to high-resolution quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) to detect organic contaminants in highway runoff and in runoff-exposed fish (adult coho salmon, Oncorhynchus kisutch). Processing of paired water and tissue samples facilitated contaminant prioritization and aided investigation of chemical bioavailability and uptake processes. Simple, minimal processing effort solid phase extraction (SPE) and elution procedures were optimized for water samples, and selective pressurized liquid extraction (SPLE) procedures were optimized for fish tissues. Extraction methods were compared by detection of non-target features and target compounds (e.g., quantity and peak area), while minimizing matrix interferences. Suspect screening techniques utilized in-house and commercial databases to prioritize high-risk detections for subsequent MS/MS characterization and identification efforts. Presumptive annotations were also screened with an in-house linear regression (log K_owvs. retention time) to exclude isobaric compounds. Examples of confirmed identifications (via reference standard comparison) in highway runoff include ethoprophos, prometon, DEET, caffeine, cotinine, 4(or 5)-methyl-1H-methylbenzotriazole, and acetanilide. Acetanilide was also detected in runoff-exposed fish gill and liver samples. Further characterization of highway runoff and fish tissues (14 and 19 compounds, respectively with tentative identification by MS/MS data) suggests that many novel or poorly characterized organic contaminants exist in urban stormwater runoff and exposed biota.

Coronary artery disease and cancer mortality in a cohort of workers exposed to vinyl chloride, carbon disulfide, rotating shift work, and o-toluidine at a chemical manufacturing plant

BACKGROUND

We updated through 2007 the mortality experience of 1,874 workers employed at a New York State chemical manufacturing plant between 1946 and 2006.

METHODS

Reassessed exposures to vinyl chloride, carbon disulfide, and shift work and categories of o-toluidine exposure were based on year, department and job title. Standardized mortality ratios (SMR) compared mortality to that of the US population. Internal comparisons used directly standardized rate ratios.

RESULTS

Hepatobiliary cancer mortality was elevated among workers ever exposed to vinyl chloride (SMR = 3.80, 95% confidence interval 1.89-6.80); directly standardized rates increased with increasing vinyl chloride exposure duration. No increase in non-Hodgkin lymphoma mortality was observed with vinyl chloride and shift work exposures. Internal comparisons showed increased coronary artery disease mortality among long-term workers exposed to carbon disulfide and shift work for 4 years or more.

CONCLUSIONS

Excess coronary artery disease mortality confirms earlier results; further investigation is needed to understand risk factors.

Bladder cancer incidence among workers exposed to o-toluidine, aniline and nitrobenzene at a rubber chemical manufacturing plant

BACKGROUND

An earlier investigation found increased bladder cancer incidence among workers at a rubber chemical manufacturing plant that used o-toluidine, aniline and nitrobenzene. The cohort was expanded to include additional workers (n=1875) and updated through 2007 to assess bladder cancer with improved exposure characterisation.

METHODS

Work histories were updated and exposure categories and ranks were developed for o-toluidine, aniline and nitrobenzene combined. Incident cancers were identified by linkage to six state cancer registries. Residency in time-dependent cancer registry catchment areas was determined. SIR and standardised rate ratios for bladder cancer were calculated by exposure category and cumulative rank quartiles for different lag periods. Cox regression was used to model bladder cancer incidence with estimated cumulative rank, adjusting for confounders. Indirect methods were used to control for smoking.

RESULTS

Excess bladder cancer was observed compared to the New York State population (SIR=2.87, 95% CI 2.02 to 3.96), with higher elevations among workers definitely exposed (moderate/high) (SIR=3.90, 95% CI 2.57 to 5.68), and in the highest cumulative rank quartile (SIR=6.13, 95% CI 2.80 to 11.6, 10-year lag). Bladder cancer rates increased significantly with estimated cumulative rank (10-year lag). Smoking only accounted for an estimated 8% elevation in bladder cancer incidence.

CONCLUSIONS

Bladder cancer incidence remains elevated in this cohort and significantly associated with estimated cumulative exposure. Results are consistent with earlier findings in this and other cohorts. Despite other concurrent chemical exposures, we consider o-toluidine most likely responsible for the bladder cancer incidence elevation and recommend a re-examination of occupational exposure limits.