A cross-sectional study of pulmonary function in carbon black workers in the United States

Nanotoxicology: The Need for a Human Touch?

With the ever-expanding number of manufactured nanomaterials (MNMs) under development there is a vital need for nanotoxicology studies that test the potential for MNMs to cause harm to health. An extensive body of work in cell cultures and animal models is vital to understanding the physicochemical characteristics of MNMs and the biological mechanisms that underlie any detrimental actions to cells and organs. In human subjects, exposure monitoring is combined with measurement of selected health parameters in small panel studies, especially in occupational settings. However, the availability of further in vivo human data would greatly assist the risk assessment of MNMs. Here, the potential for controlled inhalation exposures of MNMs in human subjects is discussed. Controlled exposures to carbon, gold, aluminum, and zinc nanoparticles in humans have already set a precedence to demonstrate the feasibility of this approach. These studies have provided considerable insight into the potential (or not) of nanoparticles to induce inflammation, alter lung function, affect the vasculature, reach the systemic circulation, and accumulate in other organs. The need for further controlled exposures of MNMs in human volunteers - to establish no-effect limits, biological mechanisms, and provide vital data for the risk assessment of MNMs - is advocated.

Ultrafine CB-induced small airway obstruction in CB-exposed workers and mice

The potential threat of superfine carbon black (CB) particles to human health has received attention, but there are few human toxicological data available. The purpose of this study was to investigate the relationships between serum CC16 and SP-A with small airway related pulmonary functions in CB workers. Ninety-nine male CB packers and 115 non-CB-exposed healthy male workers were recruited. Serum CC16 and/or SP-A and pulmonary function tests were evaluated, and the relationship between them were also analyzed. To further assess pulmonary damage induced by CB particles in target organs, an animal inhalation exposure study was conducted. Male C57BL/6 mice were exposed to 15 and 30 mg/m³ CB for 6 h per day for 28 days. Levels of CC16 and SP-A were evaluated by ELISA and immunohistochemical staining (IHC). The results showed a 20% decreased in median CC16 and a 15% increase in median SP-A among CB-exposed workers. FEV1%, FEV/FVC, MMEF%, FEF25%, and FEF75% were also decreased in CB-exposed workers (P < 0.05). A significant positive correlation was observed between serum CC16 concentration and FEV1/FVC, although a negative correlation was found between serum SP-A concentration and FEV1/FVC. Serum CC16 was significantly reduced by 72% in mice with high CB-exposure, and serum SPA was 1.65x and 1.17x higher than CB-unexposed control mice in low and high CB-exposed mice, respectively. Lung CC16 and serum CC16 levels were positively correlated in mice (P = 0.024). Long-term exposure to ultrafine CB particles is associated with a decrease in CC16 and an increase in SP-A in the peripheral blood of CB-exposed workers. In conclusion, superfine CB particles have the potential to cause small airway obstruction.

Reduced pulmonary function and increased pro-inflammatory cytokines in nanoscale carbon black-exposed workers

BACKGROUND

Although major concerns exist regarding the potential consequences of human exposures to nanoscale carbon black (CB) particles, limited human toxicological data is currently available. The purpose of this study was to evaluate if nanoscale CB particles could be responsible, at least partially, for the altered lung function and inflammation observed in CB workers exposed to nanoscale CB particles.

METHODS

Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Brunauer-Emmett-Teller were used to characterize CB. Eighty-one CB-exposed male workers and 104 non-exposed male workers were recruited. The pulmonary function test was performed and pro-inflammatory cytokines were evaluated. To further assess the deposition and pulmonary damage induced by CB nanoparticles, male BALB/c mice were exposed to CB for 6 hours per day for 7 or 14 days. The deposition of CB and the pathological changes of the lung tissue in mice were evaluated by paraffin sections and TEM. The cytokines levels in serum and lung tissue of mice were evaluated by ELISA and immunohistochemical staining (IHC).

RESULTS

SEM and TEM images showed that the CB particles were 30 to 50 nm in size. In the CB workplace, the concentration of CB was 14.90 mg/m³. Among these CB particles, 50.77% were less than 0.523 micrometer, and 99.55% were less than 2.5 micrometer in aerodynamic diameter. The reduction of lung function parameters including FEV1%, FEV/FVC, MMF%, and PEF% in CB workers was observed, and the IL-1β, IL-6, IL-8, MIP-1beta, and TNF- alpha had 2.86-, 6.85-, 1.49-, 3.35-, and 4.87-folds increase in serum of CB workers, respectively. In mice exposed to the aerosol CB, particles were deposited in the lung. The alveolar wall thickened and a large amount of inflammatory cells were observed in lung tissues after CB exposure. IL-6 and IL-8 levels were increased in both serum and lung homogenate.

CONCLUSIONS

The data strongly suggests that nanoscale CB particles could be responsible for the lung function reduction and pro-inflammatory cytokines secretion in CB workers. These results, therefore, provide the first evidence of a link between human exposure to CB and long-term pulmonary effects.

Symptoms of respiratory disease and lung functional impairment associated with occupational inhalation exposure to carbon black dust

PURPOSE

The aim of this study was to ascertain whether symptoms of respiratory disorders and lung functional impairments are associated with occupational inhalation exposure to carbon black (CB) in a group of rubber workers.

METHODS

The study population consisted of 72 male workers with a past history of and current exposure to CB and 69, randomly selected, healthy unexposed male office workers that served as the referent group. Subjects were interviewed and given standardized respiratory symptom questionnaires to answer. Furthermore, pulmonary function tests (PFTs) were performed before and after the work shift for exposed subjects and once during the work shift for referent subjects. Furthermore, to assess the extent to which workers were exposed to CB, using standard methods, inhalable and respirable dust fractions of CB were measured in different dusty worksites.

RESULTS

The levels of exposure to inhalable and respirable CB dust were estimated to be 6.2 ± 1.7 and 2.3 ± 0.29 mg/m(3) respectively (mean ± SD). Respiratory symptom questionnaires revealed that regular cough, phlegm, wheezing and shortness of breath were significantly (p<0.05) more prevalent among exposed workers. Furthermore, significant decreases in some preshift and postshift parameters of pulmonary function of exposed workers with a spirometric pattern consistent with restrictive ventilatory disorder were found.

CONCLUSION

The findings of this study provide circumstantial evidence to support the notion that exposure to CB exceeding its current TLV is associated with a significant increase in the prevalence of respiratory symptoms along with both acute, partially reversible and chronic irreversible significant decreases in some parameters of pulmonary function.

Carbon black should not be classified as a human carcinogen based on rodent bioassay data

Numerous epidemiology studies have failed to adequately demonstrate an increased risk of lung cancer due to occupational exposure to carbon black (CB). CB is not carcinogenic to mice (oral, skin or inhalation), hamsters (inhalation or intratracheal), guinea pigs (inhalation), rabbits (skin or inhalation), primates (skin or inhalation) or rats (oral). Only studies conducted by inhalation and intratracheal administration in rats have shown significant increases in benign and malignant lung tumors and lesions described as benign cystic keratinizing squamous-cell (KSC) tumors. CB-induced lung tumor formation, including KSC lesions, occurs only in rats. An expert panel reviewing KSC lesions (induced in rats by TiO2 or p-aramid) concluded that KSC lesions are not seen in humans. Lung tumors in humans are primarily located in the bronchial airways, whereas in the rat they occur in the parenchyma and are alveolar in origin. This species-specific response (tumor formation and KSC lesions) by the rat to CB, not seen in any other laboratory species and which has not been reported in humans, strongly suggests that the results of the rat inhalation bioassay should not be considered directly relevant when assessing human risk. Therefore, CB should not be classified as carcinogenic to humans based on the rodent bioassay data.

Effects on the lung function of exposure to carbon black dusts. Results of a study carried out on 677 members of staff of the DEGUSSA factory in Kalscheuren/Germany

Spirometry, full-bodyplethysmography, and inhalation challenge tests are the most frequently used methods for lung function testing. In all, 677 examinations were performed among exposed employees at the Degussa carbon black plant in Kalscheuren/Germany using the above mentioned methods, in order to detect whether there is a measurable impact of carbon black fine dust on pulmonary function, or a higher prevalence of obstructive air-way diseases among the study candidates, and whether fine dust exposure is related to the prevalence of bronchial hyperresposiveness. Within the smokers' group carbon black dust exposure reveals a (minimal) impact upon the lung function of the study subjects. However, the impact of fine dust exposure within that group is less significant than the influence of smoking on pulmonary function. Nevertheless, smokers are displaying significant more frequently signs of obstructive airway diseases compared with nonsmokers. In the smokers' group we found 7.3% of study subjects with signs of obstructive airway diseases compared with 3.9% in the group of nonsmokers. No significant impact of fine dust exposure on lung function could be detected within former- and nonsmokers. The overall percentage of 5.1% is not higher than that of subjects with bronchial hyperresponsiveness in other comparable studies.

Effects on respiratory morbidity of occupational exposure to carbon black: a review

Carbon black is a substance of world importance, both in terms of tonnage production and its special ability to strengthen rubber. Its carbonaceous nature and respirable size give rise to concern regarding its effect on respiratory morbidity for those involved in its manufacture and use. A number of studies have used chest radiographs, spirometry and respiratory symptoms as means of assessing the various populations, but almost all of the studies have either methodological shortcomings or fail to report the necessary detail. However, exposure-related effects are evident in those populations studied in terms of small opacities, reduction in forced expiratory volume in 1 s and forced mid-expiratory flow, and symptoms of chronic bronchitis.