POTENTIAL ETIOLOGICAL AGENTS OF BLACKFOOT DISEASE CAUSED BY DRINKING GROUNDWATER IN TAIWAN: AN OVERVIEW

The blackfoot disease (BFD), which was endemic peripheral vascular disease in southwestern Taiwan before the 1990s, has known to be caused by drinking arsenic-contaminated groundwater. Although arsenic has been regarded as the most important determinant BFD, several compounds are found in the high arsenic well water, including ergotamine, organic chloride, and fluorescent humic substances. In addition, trace elements such as molybdenum, mercury, copper, and cadmium, were reported to be higher in the serum and/or urine of BFD patients and in the groundwater. The etiological agent of the BFD is rather complicate and remains unclear up to present. Intriguingly, the symptoms for the patients that drank groundwater from the artesian well water in the southwestern coast of Taiwan (Chia-Nan plain) were significantly different from those in the northeastern coast of Taiwan (Ilan plain) due to the differences in the constituents and biochemical structures of potential etiological agents. The symptoms for the patients in the Chia-Nan plain was characterized particularly by BFD, skin diseases (e.g., hyperkeratosis, skin cancer, etc.) and internal cancers (e.g., lung, bladder, prostate, etc.) that were caused by arsenic and lesser amounts of fluorescent humic substances in the groundwater, while those in the Ilan plain was characterized particularly by skin diseases and internal cancers but not BFD that were caused by arsenic and considerable amounts of fluorescent humic substances in the groundwater. The humic substances having a benzene rings could possess polymers of many ions (COOH group, C=O group, and OH group) presenting chelating ability, thereby easily combining with arsenic and other metal groups (e.g., iron, manganese, strontium, lead, zinc, nickel, etc.), fatty acids, phthalate esters, some unknowns, and free radicals to form an organometallic complex. The health effects in the Chia-Nan and Ilan plains were serious with water from artesian wells that tapped groundwater under reducing conditions, and they were absent with water from shallow wells that tapped groundwater under phreatic conditions. In general, in the blackfoot disease-endemic area in Taiwan, artesian wells contained higher arsenic and fluorescent humic substances relative to shallow wells.