DETECTION OF MICROCYSTINS, A BLUE-GREEN-ALGAL HEPATOTOXIN, IN DRINKING-WATER SAMPLED IN HAIMEN AND FUSUI, ENDEMIC AREAS OF PRIMARY LIVER-CANCER IN CHINA, BY HIGHLY SENSITIVE IMMUNOASSAY

An epidemiological survey for the causes of a high incidence of primar y liver cancer (PLC) in Haimen city, Jian-Su province and Fusui county , Guangxi province in China, found a close correlation between the inc idence of PLC and the drinking of pond and ditch water. With an aim to clarify whether microcystins (MC), a hepatotoxic peptide produced by water bloom algae, contaminate the drinking water in the endemic areas of PLC in China, a highly sensitive enzyme-linked immunosorbent assay with a detection limit of 50 pg/ml, was introduced to monitor the MC. Three trials to survey the drinking water were carried out in 1993-19 94. Samples, 1135 in total, were collected from different sources such as: ponds, ditches, rivers, shallow wells and deep wells in Haimen ci ty. The first survey in September 1993 found that three out of 14 ditc h water specimens were positive for MC, with a range of 90-460 pg/ml. Several toxic algae such as Oscillatoria agardhii were present in some of the ditches. In the second trial, samples were collected from five ponds/ditches, two rivers, two shallow wells and two deep wells month ly for the whole year of 1994. These data showed that MC was highest i n June to September, with a range of 62-296 pg/ml. A third trial on th e 989 different water samples collected from the different types of wa ter sources in July 1994 revealed that 17% of the pond/ditch water, 32 % of the river water, and 4% of the shallow-well water were positive f or MC, with averages of 101, 160 and 68 pg/ml respectively. No MC was detected in deep well water. A similar survey on 26 drinking water sam ples in Fusui, Guangxi province, demonstrated a high contamination fre quency of MC in the water of ponds/ditches and rivers but no MC in sha llow and deep wells. These data support a hypothesis that the blue-gre en algal toxin MC in the drinking water of ponds/ditches and rivers, o r both, is one of the risk factors for the high incidence of PLC in Ch ina. Based on previous findings on the epidemiology of PLC and the pre sent results from the mass screening of MC in the drinking water, an a dvisory level of MC in drinking water was proposed to below 0.01 mu g/ l. The combined effect of a potent hepatocarcinogen AFB(1) and an inte rmittent intake of MC in drinking water in the summer season was discu ssed as an etiology of PLC.