Do Cancer Clusters Relate to Water Pollution in Tributaries of the Huai River Basin

Background: Globally environmental pollution is an important cancer risk factor. The study of cancer clusters in a tributary of Huai River Basin (HRB) provides a unique opportunity to examine the association between water pollution and cancer clusters. Methods: We selected QS County of the HRB as a representative region as it has emerged as a high-cancer-risk area from a low-cancer-risk area in the past four decades, thus creating an ideal ‘self-control study’. Spatial pattern analysis for geographic clusters of cancer mortality was performed and we excluded the low-cancer-risk areas to recalculate cancer mortality. We then integrated pollutant-fingerprint-tree analysis, hydrography modeling, and mathematical simulation to confirm the relationship between water pollution and cancer clusters. Findings: Standardized mortality rates for cancers of the esophagus, stomach and liver in the QS County significantly shifted from 42.01/100,000 in 1973-1975 to 93.17/100,000 in 2015. Cancer mortality in polluted areas was 1.7-fold higher than that in areas without irrigation canals. After excluding villages in the three high cancer mortality (HCM) clusters, the average cancer mortality of the remaining villages was 57.67/100,000, comparable to the national average. We attribute the HCM in villages in the region to local water pollution (F = 36.82, P < 0.001; r = 0.856). The three independent HCM clusters demonstrated similarity in pollutant fingerprints and were linked by irrigation canals. Modeling analysis indicated that even one irrigation canal is enough to contaminate groundwater leading to pollutant transfer. Interpretation: Irrigation canals affect the trans-regional redistribution of cancer clusters, which triggers the trans-regional transportation of cancer risk, and the migration of water pollution leads to the convergence of cancer occurrence among distant populations. Our novel method provides a tool for the study of environmental pollution on cancer occurrence and offers a foundation for developing cancer intervention strategies. Funding: This project was supported by the Chinese National Natural Science Foundation (81325017, 30972438, 81202165 & 81930094), The Key Project of National High-tech R&D Program of China - 863 Program (2013AA065204), National Key R&D Program of China (No.2017YFC1600200), National Key Technology R&D Program in the 12th Five Year Plan (2012BAJ25B05 & 2013BAI12B03), National Key Technology R&D Program in the 11th Five Year Plan (No. 2006BAI19B02), Shanghai Municipal Health Bureau Leading Academic Discipline Project (No. 08GWD14), and ‘Dawn’ Program of Shanghai Education Commission (No. 07SG01). Declaration of Interests: The authors declare that they have no conflict of interest.