Lettuce seedlings (Lactuca sativa L.) were grown in pot experiments on metalliferous soils sampled close to mining and smelting sites in the Province of Styria (Austria), in order to investigate effects of mineral fertilizer (NPK and PK). Additionally, soil samples were collected and extracted by modified electro-ultrafiltration (EUF) in five fractions after using diethylenetriaminepentaacetic acid (DTPA) to obtain the potentially available metals and to describe the release mechanisms with kinetic models. The NPK and PK fertilizer application decreased the Pb content in plants below the maximum threshold set up for human nutrition, but Cd increased slightly. Bioconcentration factors (BCF) for Cd were higher than for Pb and, according to the translocation factor (TSF), leaves contained more Cd but less Pb than corresponding roots. The largest heavy metal amounts of the metalliferous soils were released in the first two fractions of the EUF method. Closest fits in terms of the coefficient of determination (R2) and recalculated results were obtained from the 2nd order polynomial model (y = a + bt + ct2). In contrast to Cd, a statistically significant (P ≤ 0.05) relationship between release rate b of the 2nd order polynomial model and the metal concentration in plants was achieved for Ni in both leaves and roots and for Pb only in leaves.