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Arsenic Cancer Risk Confounder in Southwest Taiwan Data Set

Quantitative analysis for the risk of human cancer from the ingestion of inorganic arsenic has been based on the reported cancer mortality experience in the blackfoot disease (BFD)–endemic area of southwest Taiwan. Linear regression analysis shows that arsenic as the sole etiologic factor accounts for only 21% of the variance in the village standardized mortality ratios for bladder and lung cancer. A previous study had reported the influence of confounders (township, BFD prevalence, and artesian well dependency) qualitatively, but they have not been introduced into a quantitative assessment. In this six-township study, only three townships (2, 4, and 6) showed a significant positive dose–response relationship with arsenic exposure. The other three townships (0, 3, and 5) demonstrated significant bladder and lung cancer risks that were independent of arsenic exposure. The data for bladder and lung cancer mortality for townships 2, 4, and 6 fit an inverse linear regression model (p < 0.001) with an estimated threshold at 151 μg/L (95% confidence interval, 42 to 229 μg/L). Such a model is consistent with epidemiologic and toxicologic literature for bladder cancer. Exploration of the southwest Taiwan cancer mortality data set has clarified the dose–response relationship with arsenic exposure by separating out township as a confounding factor.

Cancer of the nose and paranasal sinuses (ICD 160) accounts for -0.04% of all deaths in the Republic of Ireland each year (Central Statistics Office, 1978) and for a similar percentage in the U.K. (OPCS, 1982). The contribution to overall mortality is small, but an interesting body of evidence has accumulated from epidemiological studies which has identified occupational exposures with a high risk of this comparatively rare tumour.
The first report of an association of nasal cancer with a specific occupational exposure was by Bridge (1933) who described 9 cases among workers in a nickel refinery; later Doll et al. (1977) estimated an excess risk of 300-400 fold in those workers up to about 1930. It appears that exposure to impure nickel carbon sulphide was the most likely cause (Doll et al., 1977;Pedersen et al., 1973;Enterline et al., 1982) and since 1930 the process does not appear to be associated with excess risk (Cox et al., 1981). Recent suggestions that chromate (Alderson et al., 1981) and isopropyl alcohol (Alderson & Rattan, 1980) manufacture may increase risk of nasal cancer need confirmation from larger studies.
Observations that air-borne dusts of some organic materials were associated with risk of nasal cancer were first made by Macbeth (1965) who described an excess risk of adenocarcinoma in woodworkers in the furniture industry. This excess was confirmed by Acheson et al., (1967Acheson et al., ( , 1968Acheson et al., ( , 1972 in the U.K. and subsequently in the U.S.A., Denmark, Sweden and Italy (Brinton et al., 1976;Engzell et al., 1978;Olsen & Sambroe, 1978;Cecchi et al., 1980). Further studies indicated that workers engaged in boot and shoe manufacture and shoe repairers were also at increased risk (Acheson et al., 1970, Cecchi et al., 1980. A recent survey of the boot and shoe industry in Northamptonshire (Acheson et al., 1982) suggested that excess nasal cancer occurs in those exposed to dust from leather soles and heels.
A recent leading article in the Lancet (1983) summarised the findings of these and other studies and noted that an excess of nasal cancer has also been found in coalminers, furnacemen in the gas coke and chemical industry and in foundries, and also in dressmakers, tailors, bakers, pastry cooks and paper and printing workers.
In a recent case-control study of head and neck cancer in Ireland (Herity et al., 1981) a presenting sample of 152 male patients with head and neck cancer included 7 with carcinoma of the paranasal sinuses (ICD 160.2, 160.8). A detailed occupational history had been obtained by the author from each of the patients in the study and it was noted that of the 7 patients with a diagnosis of paranasal sinus carcinoma 3 had been employed in the production of peat. The occupations of the other 4 patients were, woodworker, 1 gardener, 1 farm labourer and 1 manager in an electrical firm. Histological classification of the tumours was as follows: 4 undifferentiated (2 peat-workers, 1 gardener, 1 woodworker) 2 squamous (1 manager, 1 farm labourer) and there was no histology available for 1 peat-worker. There were no peat-workers among the remaining 145 male cases. Of the 152 male controls (with diagnoses of non-smoking-related cancers) in the head and neck cancer study, 3 were employed in the peat production industry; 2 were peat workers (diagnoses, I lymphoma, 1 carcinoma of rectum) and one was a personnel manager in the industry (diagnosis, multiple myeloma).
The peat production industry includes the cutting of sod peat by specialised heavy machinery and its drying, collection and distribution for use as fuel; the milling of peat into fine particles to fuel specially designed furnaces at power-stations and for the manufacture of 'briquettes' which are blocks of compressed fine peat used as industrial and domestic fuel; and the production of moss peat of (© The Macmillan Press Ltd., 1984 Received 29 September 1983; accepted 28 November 1983. various grades for use in agriculture and horticulture. It seems likely that the latter two processes, at least, may be associated with the production of air-borne peat dust. The strength of the association of carcinoma of the paranasal sinuses with the occupation of peatproduction in this study is shown in Tables I and  II. Table I shows the relative risk (RR) (calculated by adding 0.5 to each of the observed frequencies) of carcinoma of the paranasal sinuses for peatworkers among a group with head and neck cancer, to be 226.3 (P <0.001). Table II compares the paranasal sinus carcinoma cases (mean age, 64.8 years) with 152 controls from the initial study (mean age, 63.4 years). The RR of paranasal sinus carcinoma for peat-workers is 37.3 (P<0.005). The actual RR could even be higher since the proportion of peat-workers in the community is considerably less than the 2% noted in the control group.
The possibility that inhalation of air-borne peat dust may be associated with the development of paranasal sinus carcinoma is biologically plausible in view of the epidemiological evidence referred to above associating wood, leather and other dusts of natural materials with that tumour. Peat production is an industry restricted to certain welldefined geographical areas but the use of peat products such as moss peat or potting composts in horticulture is ubiquitous and it is important to further investigate this association which occurred as a chance finding in a study of head and neck cancer. Work is at present underway at St. Luke's Hospital, Dublin, to try to further define the occupational risk of this tumour.   Fisher's exact test P <0.005. RR = 37.3.