[Drinking water types, microcystins and colorectal cancer]

To assess the relationship between microcystins (a blue-green algal toxin) in drinking water and colorectal cancer.

Eight townships were randomly selected as study sites in Haining city of Zhejiang province, China. Four hundred and eight colon and rectum carcinoma cases diagnosed from 1977 to 1996 were identified from cancer registry in the study sites. A retrospective survey on types of drinking water of all 408 cases was conducted. Population data and drinking water sources data were provided by local household registration and local health institution, respectively. Water samples from different sources (well, tap-water, river and pond) were collected and microcystins concentrations were measured by an indirect competitive ELISA method.

The incidence rates of colorectal cancer were significantly higher among people drinking river or pond water than those who drank well water or tap-water in both males and females. And comparing with other sources to well water, the relative risks (RR) were much higher for people using river water (7.94) and pond water (7.70). The positive detection rates (> 50 pg/ml) of microcystin in well, tap-water, river and pond water were 0.00%, 0.00%, 36.23% and 17.14% respectively. The highest concentrations of microcystins were 1 083.43 pg/ml (river) and 1 937.94 pg/ml (pond) in the positive samples. Microcystins concentrations in river and pond were significantly higher than the concentrations in well and tap water (P < 0.01). The Spearman rank correlation analysis showed that in the study sites, the microcystins concentrations of river and pond water were positively correlated with the incidence of colorectal cancer (r = 0.881, P < 0.01).

Drinking surface water (river or pond) is one of the risk factors for colorectal cancer. Microcystins may be associated with incidence of colorectal cancer. It is suggested that further study should be carried out to clarify the relationship between colorectal cancer and microcystin in drinking water.