210Pb: a predictive biomarker of retrospective cigarette smoke exposure.

Although cigarette smoking continues to occur worldwide, there are few methods available to assess a person's retrospective exposure to mainstream smoke. The tobacco of cigarettes contains trace quantities of radioactive 210Pb and 210Po, which are volatilized and inhaled when a cigarette is smoked. It was hypothesized that urinary 210Pb and 210Po activity concentrations could be used as biomarkers of exposure to mainstream tobacco smoke. Human subjects (n = 250) were recruited from Beijing, China, and reported their smoking habits. Each subject provided a 24-hour urine sample, which was assayed for its 210Pb and 210Po activity concentrations. Although the urinary 210Po activity from smoking was very low compared with background levels, the urinary 210Pb activity correlated with the number of cigarettes smoked per day (CPD; rho = 0.38, P < 0.001) and the urinary cotinine concentration (rho = 0.52, P < 0.001). In a linear regression model, a 1-unit increase in CPD was associated with an increase of 0.13 mBq in urinary 210Pb activity. In a logistic regression model, a 1-unit increase in urinary 210Pb activity was associated with an estimated 25% increase in the odds of being a smoker. These data were modeled using the respiratory, gastrointestinal, and biokinetic models of the International Commission on Radiological Protection. When the final model was applied for a long-term smoker (20 CPD) that suddenly quits, the predicted urinary activity decreased to 50% of the steady-state activity in about 90 days. Based on this half-time estimate and the regression results, urinary 210Pb can be used to assess the probability of having smoked in the past months.