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Contents lists available at ScienceDirect
Ecotoxicology and Environmental Safety
journal homepage: www.elsevier.com/locate/ecoenv
Association of wheat chaﬀ derived silica fiber and esophageal cancer in T
Changhong Liana, Shuzhe Xiea, Weijun Lib, Jinjiin Rand, Jian Zhangb, Zheshen Hand, Xinxin Zuoc, Linwei Tiand,∗ a Department of Surgical Oncology, Heping Hospital, Changzhi Medical College, Changzhi, China
b School of Earth Sciences, Zhejiang University, Hangzhou, China
c State Key Laboratory for Subtropical Mountain Ecology, College of Geographical Sciences, Fujian Normal University, Fuzhou, China
d School of Public Health, The University of Hong Kong, 7 Sassoon Road, Hong Kong SAR, China
Keywords: Biogenic silica fiber
Taihang mountain area
Phytolith Wheat chaﬀ Silicified prickle
Background: Despite decades of research and intervention programs, the epidemic of esophageal squamous cell carcinoma (ESCC) in the Taihang Mountain area of north China has not seen convincing explanation by any risk factor yet and the incidence has not seen a substantial decrease. Based on recently disclosed association of G-418 and wheat consumption with esophageal cancer, we revisited the hypothesis of biogenic silica in esophageal cancer development.
Methods: From the archives of the Pathology Department of Heping Hospital, Changzhi Medical College, we selected three pairs of formalin-fixed samples, tumor tissues and distant normal tissues, of three patients op-erated for ESCC who had no history of workplace exposure to silica dust. Two pairs of dried tissue samples were used for phytolith (silica body) analysis and another pair for microanalysis with Transmission Electron Microscope (TEM).
Results: One of the phytoliths in ESCC tumor tissue was similar to the prickle hair on the surface of wheat bract. In the mineral particles detected in the tumor tissue the predominant elements were Si, Ca, and P, whereas Si signals were not obvious in the distant normal tissue. Conclusions: The preliminary findings on the detection of phytoliths and the higher than normal Si concentration in ESCC tumor tissue warrants further testing the role of biogenic silica in esophageal cancer.
1.1. Lingering high incidence of esophageal cancer in north China
In the atlas of cancer mortality of 2392 counties in China, published in the 1970s, rates of esophageal cancer varied more than 10-fold and sharp contrasts were found even over short geographic distances (see Fig. S1) (Editorial Committee for the Atlas of Cancer Mortality in the People’s Republic of China, 1979; Li et al., 1981; Yang, 1980). The most studied high-incidence region of China has been the 3 North China provinces of Henan, Hebei, and Shanxi in the Taihang Mountain range, aﬀecting a total of 90 million people. Certain areas in this region have the highest incidence rates of esophageal cancer in the world, exceeding 100 per 100,000 population (Lin et al., 2017). Since ancestry,
esophageal cancer has been a fearful disease in this region. This disease was so dreadful that the “Throat-God” (Hou Wang) in the “Throat-God Temple” (Houwang Miao) was once worshiped by the local residents (Yang, 1980).
Esophageal cancer has two main histological types: esophageal squamous cell carcinoma (ESCC) and esophageal adenocarcinoma (EAC). ESCC is the predominant histological type in China, as well as in the “Central Asian Esophageal Cancer Belt” extending from Iran and Afghanistan to China along the Silk Road (Craddock, 1993; Jabbari et al., 2008) and the African ESCC corridor stretching south from Sudan to the Eastern Cape Province of South Africa (McCormack et al., 2017). Epidemiological studies on the causative factors of ESCC began as early as 1959 in this Taihang Mountain range of China. Despite decades of research and intervention programs, however, the epidemic of ESCC in
Abbreviations: ESCC, esophageal squamous cell carcinoma; TEM, Transmission Electron Microscope; EDS, energy-dispersive X-ray spectrometer
this region has not seen convincing explanation by any risk factor yet (Lin et al., 2017) and the incidence has not seen a substantial decrease (He and Shao, 2011; Qiao et al., 2001). There might be some unknown risk factors not under control and the lingering high incidence of ESCC in north China calls for new etiological hypotheses.
2. Previously explored risk factors of ESCC
2.1. Alcohol and tobacco
Studies in Linxian (currently known as ‘Linzhou’), China and northeastern Iran failed to find association of esophageal cancer with alcohol or tobacco (Craddock, 1993). Surveys in high-incidence areas did not indicate alcohol as an important etiologic factor; the highest proportion of habitual drinkers among esophageal cancer patients was about 50%. Cut tobacco was consumed more often than cigarettes and there were very few women smokers in the rural areas of north China. It was believed that alcohol and tobacco play a negligible part in the development of esophageal cancer in most high-risk areas in China (He et al., 2010; Li et al., 1989; Li and Cheng, 1984). It is likely that other strong risk factors in these high-risk areas accounted for most of the ESCC cases and thus diluted the eﬀect of smoking and drinking.