Exposure to N-nitroso compounds in a population of high liver cancer regions in Thailand: Volatile nitrosamine (VNA) levels in Thai food

The recent case-control studies in Thailand indicate that a high incidence of liver cancer in Thailand has not been associated with common risk factor s such as hepatitis B infection, aflatoxin intake and alcohol consumption. While the infestation by the liver fluke Opisthorchis viverrini (OV) accoun ted for the high risk in north-east Thailand, there a cis no such exposure: in the other regions of the country what: the incidence of liver cancer is also high. Case-control studies suggest that exposure to exogenous and pos sibly endogenous nitrosamines in food or tobacco in betel nut and cigarette s mag; play a role in the development of hepatocellular carcinoma (HCC), wh ile OV infestation and chemical interaction of nitrosamines may also be aet iological factors in the development of cholangiocarcinoma (CCA) Over 1800 samples of Fresh and preserved food were systematically collected and teste d between 1988 and 1996. All the food items identified by anthropological s tudies to be consumed frequently in four major regions of Thailand were ana lysed for volatile nitrosamines using gas chromatography combined with a th ermal energy analyser. Relatively high levels of N-nitrosodimethylamine (ND PA). N-nitrosopiperidine (NPIP) and N-nitrosopyrrolidine (NPYR) a-srs detec ted in fermented fish ("Pla-salid"). NDMA was also detected at levels rangi ng from trace amounts to 66.5 mu g/kg in several salted and dried fish ("La rb-pla" and "Pla-siu"). NDMA and NPYR were frequently detected in several v egetables, particularly fermented beans ("Tau-chiau") at levels ranging bet ween 1 and 95.1 mu g/kg and 0 146 mu g/kg, respectively. The possible role of nitrosamines in Thai food in the aetiology of liver cancer (HCC, CCA) is discussed. 1999 Elsevier Science Ltd. All rights reserved.