BEIJING — Over the past few years, trips back to my home village, Huaihua Di, on the Lanxi River in Hunan Province, have been clouded by news of deaths — deaths of people I knew well. Some were still young, only in their 30s or 40s. When I returned to the village early last year, two people had just died, and a few others were dying. My father conducted an informal survey last year of deaths in our village, which has about 1,000 people, to learn why they died and the ages of the deceased. After visiting every household over the course of two weeks, he and two village elders came up with these numbers: Over 10 years, there were 86 cases of cancer. Of these, 65 resulted in death; the rest are terminally ill. Most of their cancers are of the digestive system. In addition, there were 261 cases of snail fever, a parasitic disease, that led to two deaths. The Lanxi is lined with factories, from mineral processing plants to cement and chemical manufacturers. For years, industrial and...