Arsenic is a well-known lung carcinogen in humans. In 2006, IARC upgraded inorganic lead as a possible human carcinogen (2A). The aim of this thesis has been to evaluate the lung cancer mortality and incidence in long-term exposed primary lead smelter workers and also to estimate present exposures to arsenic and lead in relation to those occurring in the past. The basic cohort (N=3832 workers; hired before 1967 and followed up from 1950-1981; SMR comparisons with general and local reference populations) showed an excess of deaths for total mortality, malignant neoplasms (e.g. lung and stomach cancer), ischaemic heart diseases, and cerebrovascular diseases compared to the general population. In a subcohort of lead workers (N=437; regular blood lead sampling since 1950) only the raised SMR for lung cancer (162) was sustained. In a follow-up study of the basic cohort (N=3979), a subcohort of lead exposed workers (N=1992) was formed. The expected mortality in 1955-1987 and cancer incidence in 1958-1987 were calculated relative to county rates. A cumulative blood lead index (CBLI) was used for dose-response analyses. The lung cancer incidence was raised in the total cohort (SIR 2.8; 95 % CI 2.1 3.8). A higher lung cancer risk was observed in workers hired before 1950 (SIR 3.6; 95 % CI 2.6-5.0). The increased lung cancer risks were further elevated in the subcohort of lead exposed workers, especially in the highest exposed subgroup (SIR 5.1; 95 % 2.0-10.5; latency period of 15 y). No excesses of other malignancies were observed. The increased relative risks for lung cancer may have been caused by interactions between inorganic lead and other substances at the smelter, e.g. arsenic. To further analyze the effects from inorganic lead, two subcohorts of workers at the lead departments were formed from the original cohort (N=3979), one of 710 workers and the other of 383 workers. The lung cancer incidence was raised in both subcohorts (Lead subcohort 1; SIR 2.4; 95 % CI 1.2-4.5; Lead subcohort 2; SIR 3.6; 95 % CI 1.2-8.3). Among the 10 workers that had developed lung cancer in lead subcohort 1 all but one had a considerable exposure also to arsenic. Thus, a possible interaction effect between lead and arsenic may explain the increased lung cancer risks. To further elucidate the impact from lead and arsenic a case control study was undertaken. In the basic cohort (N=3979), 46 male workers had contracted respiratory malignancies. They were compared with 141 agematched male referents from the primary smelter by conditional logistic regression analysis using smoking habits, cumulative blood lead and air arsenic exposure as predictor variables. The lung cancer cases showed a significantly higher smoking rate than referents (Odds ratio, OR = 4.0; 95 % CI 1.6-10.1; p=0.003). When restricted to smokers, the cumulative arsenic air exposure index, but not the lead exposure indices, were significantly higher among the cases (OR=1.07; 95 % CI 1.02-1.11; p = 0.005). Accordingly, cumulative arsenic exposure and smoking were identified as significant risk factors for the development of lung cancer in the final analyses, while lead exposure was not a significant risk factor. However, inorganic lead still may play a minor role in the multifactorial genesis of lung cancer. These studies describe risks from exposures occurring from time periods before 1950 up to 1981. Because of the long latency period for lung cancer, exposures after 1970 probably have had limited impact on the reported results. Compared to the levels in the early 1970´s present exposures to arsenic are lower by a factor of ten or more and risks probably correspondingly lower.

Arsenic is a universal environmental toxicant associated mostly with skin related diseases in people exposed to low doses over a long term. Low dose arsenic trioxide (ATO) with long exposure will lead to chronic exposure. Experiments were performed to provide new knowledge on the incompletely understood mechanisms of action of chronic low dose inorganic arsenic in keratinocytes. Cytotoxicity patterns of ATO on long-term cultures of HaCaT cells on collagen IV was studied over a time course of 14 days. DNA damage was also assessed. The percentages of viable cells after exposure were measured on Day 2, Day 5, Day 8, and Day 14. Statistical and visual analytics approaches were used for data analysis. In the result, a biphasic toxicity response was observed at a 5 μg/ml dose with cell viability peaking on Day 8 in both chronic and acute exposures. Furthermore, a low dose of 1 μg/ml ATO enhanced HaCaT keratinocyte proliferation but also caused DNA damage. Global gene expression study using microarray technique demonstrated differential expressions of genes in HaCaT cell exposed to 0.5 μg/ml dose of ATO up to 22 passages. Four of the up-regulated and 1 down-regulated genes were selected and confirmed with qRT-PCR technique. These include; Aldo-Keto Reductase family 1, member C3 (AKR1C3), Insulin Growth Factor-Like family member 1 (IGFL1), Interleukin 1 Receptor, type 2 (IL1R2) and Tumour Necrosis Factor [ligand] Super-Family, member 18 (TNFSF18), and down-regulated Regulator of G-protein Signalling 2 (RGS2). The decline in growth inhibiting gene (RGS2) and increase in AKR1C3 may be the contributory path to chronic inflammation leading to metaplasia. This pathway is proposed to be a mechanism leading to carcinogenesis in skin keratinocytes. The observed over expression of IGFL1 may be a means of triggering carcinogenesis in HaCaT keratinocytes. In conclusion, it was established that at very low doses, arsenic is genotoxic and induces aberrations in gene expression though it may appear to enhance cell proliferation. The expression of two genes encoding membrane proteins IL1R2 and TNFSF18 may serve as possible biomarkers of skin keratinocytes intoxication due to arsenic exposure. This research provides insights into previously unknown gene markers that may explain the mechanisms of arsenic-induced dermal disorders including skin cancer / Environmental Sciences / D. Phil. (Environmental science)

Arsenic is a universal environmental toxicant associated mostly with skin related diseases in people exposed to low doses over a long term. Low dose arsenic trioxide (ATO) with long exposure will lead to chronic exposure. Experiments were performed to provide new knowledge on the incompletely understood mechanisms of action of chronic low dose inorganic arsenic in keratinocytes. Cytotoxicity patterns of ATO on long-term cultures of HaCaT cells on collagen IV was studied over a time course of 14 days. DNA damage was also assessed. The percentages of viable cells after exposure were measured on Day 2, Day 5, Day 8, and Day 14. Statistical and visual analytics approaches were used for data analysis. In the result, a biphasic toxicity response was observed at a 5 μg/ml dose with cell viability peaking on Day 8 in both chronic and acute exposures. Furthermore, a low dose of 1 μg/ml ATO enhanced HaCaT keratinocyte proliferation but also caused DNA damage. Global gene expression study using microarray technique demonstrated differential expressions of genes in HaCaT cell exposed to 0.5 μg/ml dose of ATO up to 22 passages. Four of the up-regulated and 1 down-regulated genes were selected and confirmed with qRT-PCR technique. These include; Aldo-Keto Reductase family 1, member C3 (AKR1C3), Insulin Growth Factor-Like family member 1 (IGFL1), Interleukin 1 Receptor, type 2 (IL1R2) and Tumour Necrosis Factor [ligand] Super-Family, member 18 (TNFSF18), and down-regulated Regulator of G-protein Signalling 2 (RGS2). The decline in growth inhibiting gene (RGS2) and increase in AKR1C3 may be the contributory path to chronic inflammation leading to metaplasia. This pathway is proposed to be a mechanism leading to carcinogenesis in skin keratinocytes. The observed over expression of IGFL1 may be a means of triggering carcinogenesis in HaCaT keratinocytes. In conclusion, it was established that at very low doses, arsenic is genotoxic and induces aberrations in gene expression though it may appear to enhance cell proliferation. The expression of two genes encoding membrane proteins IL1R2 and TNFSF18 may serve as possible biomarkers of skin keratinocytes intoxication due to arsenic exposure. This research provides insights into previously unknown gene markers that may explain the mechanisms of arsenic-induced dermal disorders including skin cancer / Environmental Sciences / D. Phil. (Environmental science)