Objectives Risk associated with dioxin-like chemicals (DLCs) can be estimated using cancer slope factor (SF) derived from epidemiology data, and lifetime average daily dose (LADD). However, for shorter term exposure, such analysis has not been done. We propose a method to estimate cancer risk using internal exposure dose.

Method In 1979, approximately 2000 people in central Taiwan accidentally consumed rice oil contaminated by dioxin-like chemicals polychlorinated biphenyls (PCBs)- and dibenzofurans (PCDFs). Blood samples were collected between 1994 and 2003. Serum toxic equivalency (TEQ) was back-extrapolated to the time at the beginning of the exposure by using half-life of 8.7 years. The LADD of the background population was estimated by serum level, and the excess cancer risk of the background population was estimated by multiplying LADD by the cancer SF. Thereafter, the LADD and excess cancer risk of the Yucheng population was estimated correspondingly by the ratio of serum TEQ area under curve (AUC) between the exposed and the background population.

Results The average serum concentration of 245 exposed people in 1994–2003 and the estimated serum concentration in 1979 were 424 (SD=334) and 1602 (SD=1135) pg-TEQ/g-lipid, respectively. The estimated LADD of DLCs in background population was 2.18 pg-TEQ/kg-body weight/day, and the lifetime excess cancer risk caused by background exposure to DLCs is 3.4*10–4. The average value of exposed people’s serum TEQ AUC and the risk (i.e., 5.7*10–3) are16.8 times higher than those of the background population.

Conclusions Based on this method, individual risk can be estimated when serum concentration of DLCs are available.