1. Exposure Data

For hundreds of years, chimneys have been swept with long steel brushes inserted manually into the chimney from the top and from the bottom. Chimney sweeps are exposed to soot, with concurrent exposure to sulfur dioxide and arsenic (Bagchi & Zimmerman, 1980).

Soot is black particulate matter that is formed as a by-product of combustion or pyrolysis of organic (carbon-containing) materials, such as coal, wood, fuel oil, waste oil, paper, plastics and household refuse. The chemical composition and properties of soots are highly variable and depend on the type of starting material and the conditions of combustion. Soots vary considerably with respect to their relative content of carbon, their particle type, size and shape, and the types of organic and inorganic compounds adsorbed onto the particles. In general, soots have a total carbon content of up to 60%, a high content of inorganic material, and a soluble organic fraction. The latter is extractable with organic solvents and consists largely of PAHs and their derivatives. Inorganic constituents may include oxides, salts, metals, sulfur and nitrogen compounds, water, and other adsorbed liquids and gases (IARC, 1985; Watson & Valberg, 2001).

Table 1.1 summarizes several recent studies that investigated exposure of chimney sweeps to PAHs. Knecht et al. (1989) assessed exposures in the breathing zone of chimney sweeps during so-called ‘dirty’ or ‘black work’ on 11 working days. Samples were taken per ‘job category’, based on the type of fuel fired: oil fuel, oil/solid or solid fuels. Twenty PAHs were quantified in a total of 115 samples. Higher concentrations were seen in soots that originated from burning of solid fuels. A bio-monitoring study carried out in Germany (n = 93) and Poland (n = 7) in 1995 reported 1-hydroxypyrene concentrations in the urine ranging from below the detection limit (0.1 μg/L) up to 12.8 μg/L (Letzel et al., 1999). Urinary concentrations in the samples from Poland were on average five times higher, most probably due to the fact that coal and wood are used more often as fuels in Poland. The concentrations in urine samples from workers in Germany were relatively low. The use of personal protective devices among this group of 100 chimney sweeps was not mentioned. In an Italian study, Pavanello et al. (2000) analysed the urine of 27 chimney sweeps: the 1-hydroxypyrene concentrations were in the same wide range as those reported for the chimney sweeps in Germany and Poland (Letzel et al., 1999).

Table 1.1

Concentrations of PAHs in the ambient air and in urine of chimney sweeps.

Increased concentrations of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans were found in blood lipids of 227 chimney sweeps from Bavaria (Wrbitzky et al., 2001).

2. Cancer in Humans

In IARC Monograph Volume 92 (IARC, 2010), epidemiological studies of cancer in humans were considered to provide sufficient evidence for the carcinogenicity of occupational exposure as a chimney sweep. The evidence partly came from a large series of reports on cases of scrotal skin cancer in this occupational group. Soot was first noted as a cause of scrotal cancer in humans by Pott (1775). Many case reports of scrotal and other skin cancers among chimney sweeps appeared subsequently in several different countries (e.g. Earle, 1808; Butlin, 1892; Henry & Irvine, 1936; Henry, 1937, 1946, 1947). A total of 1487 cases of scrotal cancer were reported to the Registrar General for England and Wales from 1911–1935 (Henry, 1937). Of these, 6.9% had occurred in chimney sweeps; the estimated proportion of chimney sweeps in England and Wales in 1921 and 1931 was about 0.06% of all adult males, indicating a large excess of scrotal cancer among workers in this profession.

Evanoff et al. (1993) conducted large cohort study of Swedish chimney sweeps and found an excess of cancer of the lung, bladder, oesophagus and haematolymphatic organs; a study from Finland corroborated these findings (Pukkala, 1995). These studies did not include individual adjustments for tobacco smoking, but in the Swedish study an adjustment was made for smoking at the group level, whereas in the Finnish study adjustment was for social class. Both analyses indicated that confounding from tobacco smoking did not explain the findings regarding lung cancer. In two Danish cohort studies an excess of total cancer was found, but the studies were too small to evaluate individual cancer sites (Hansen et al., 1982; Hansen, 1983; see Table 2.1, available at http://monographs.iarc.fr/ENG/Monographs/vol100F/100F-16-Table2.1.pdf).

Pukkala et al. (2009) reported on a record-linkage study from the Nordic countries encompassing 15 million people aged 30–64 identified from the censuses in 1960, 1970, 1980/81, and 1990, and followed for cancer in the national cancer registries until 2005. A total of 5498 male chimney sweeps from Denmark, Finland, Norway and Sweden were identified in the cohort. Statistically significant excesses of cancers of the lung, oesophagus, pharynx, bladder, and colon were found. There was no excess of non-melanoma skin cancer. There was not a large heterogeneity in risk between countries, and no adjustment for smoking was made.

The above-mentioned study by Pukkala et al. (2009) – which included information from the earlier study (Pukkala, 1995) – adds to the previous evidence of an excess of cancer of the lung, bladder and oesophagus among chimney sweeps. Despite the classical risk for scrotal cancer in chimney sweeps, studies of this occupational group under modern working conditions show no such excesses.

Overall, considering a consistently observed increased lung-cancer risk in several studies, and on the basis of a large cohort study that demonstrated an internal dose–response after group-level adjustment for smoking, there is evidence from human epidemiological studies that lung cancer is causally associated with occupational exposure during work as a chimney sweep. No internal dose–response was observed for bladder cancer in the large Swedish study, and the evidence for an excess bladder cancer among chimney sweeps must be considered as limited. The incidence of oesophageal cancer is highly correlated with smoking and alcohol consumption, and in the absence of control for these two factors, the evidence of an association with occupational exposure as a chimney sweep is inadequate. From historical case reports there is sufficient evidence of an increased risk for (scrotal) skin cancer among chimney sweeps.

3. Cancer in Experimental Animals

Coal soot was tested in two experiments in mice by whole-body exposure, but these studies were inadequate for evaluation. Coal-soot extracts applied to the skin of mice produced skin tumours in two studies (IARC, 1985).

In limited studies, subcutaneous implants of wood soot in female rats produced a few local sarcomas. Similar implants in the scrotal sac of rats did not produce tumours. One study of wood-soot extract applied to the skin of mice was uninformative (IARC, 1985).

One study of an extract of fuel-oil soot applied to the skin of mice was uninformative. Extracts of soot from the combustion of oil shale produced skin tumours in mice after dermal application and lung tumours in rats after intratracheal instillation (IARC, 1985).

Extracts of soot from the combustion of heating oil produced from shale oil produced skin tumours in mice in two skin-application experiments (IARC, 1985).

4. Other Relevant Data

5. Evaluation

There is sufficient evidence in humans for the carcinogenicity of soot as found in occupational exposure of chimney sweeps. Soot, as found in occupational exposure of chimney sweeps, causes cancer of the skin (observed in the scrotum), and of the lung.

Also, a positive association has been observed between exposure to soot as found in occupational exposure of chimney sweeps and cancer of the bladder.

There is inadequate evidence in experimental animals for the carcinogenicity of soot.

There is sufficient evidence in experimental animals for the carcinogenicity of soot extracts.

Extracts of soots contain carcinogenic polycyclic aromatic hydrocarbons and are genotoxic. Based on a small number of genotoxicity studies in humans there is moderate evidence for a genotoxic mechanism for occupational exposures as a chimney sweep.

Soot as found in occupational exposure of chimney sweeps is carcinogenic to humans (Group 1).

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