Two higher plants (Platanus occidentalis and Pinus sylvestris) were used as bioindicators for assessment of contamination by Pb and Cd in an urban and industrialized area. Both toxic metals in plant tissue were determined by transverse-heated electrothermal atomic absorption spectrometry-longitudinal Zeeman background correction combined with automated ultrasonic slurry sampling. Twenty sampling points were established to observe a relationship between metal concentration in plant and traffic density. Screening optimization of variables influencing slurry preparations (sonication time, sonication power, and surfactant concentration) followed a fractional factorial design at 2 levels. No significant effects were observed in the interval of variables studied. Limits of detection of Pb and Cd in the plants were 0.28 and 0.025 microg/g (dry weight), respectively. Metal concentrations in the plants were in the range of 5-51 and 0.05-0.7 microg/g for Pb and Cd, respectively. Factor analysis to data of metal concentration in both plants, extractable metal content in soil, distance to traffic, and traffic density, showed a significant association between features such as concentration of Pb and Cd in leaves of P. occidentalis and traffic density, which accounted for the largest variance. Other features such as extractable metal contents in soil accounted for lesser variance, meaning that soils in the area investigated were less suitable than plants for monitoring metal pollution caused by vehicular traffic.