Lead has been used extensively for thousands of years. Once introduced into the environment, like any other heavy metal, lead accumulates in soil and sediments. High lead concentrations in river and lake sediments can be harmful to aquatic organisms. At present, uncontaminated water sediments in the northern and central parts of Poland contain below 9 mg of lead per kg. The lakes located within the following lake districts: Greater Poland, Pomeranian and Masurian, provided 409 samples of surface sediments from deep spots (the profundal zone). All the samples were tested for the content of Pb and other selected macroelements. The content of Ca, Mg, Fe, K, Mn, Na, P, Pb and S was determined by ICP-OES and the total organic carbon (TOC) was evaluated by the coulometric titration method. The observed range of lead concentration was from below 3 to 222 mg kg-1. The average content was 37 mg kg-1, the geometric mean 30 mg kg-1, and the median 33 mg kg-1. In the majority of  samples, the lead concentration was higher than the geochemical background. Only in 5.77% of the samples, the lead content was lower than 10 mg kg-1. The lead concentration in the sediments was relatively well correlated with the total organic carbon (r=0.59), aluminium (r=0.45) and sulphur (r=0.47), moderately correlated with iron (r=0.26) and potassium (r=0.28), very weakly correlated with phosphorus (r=0.12) and negatively correlated with the calcium concentration (r=-0.28). No correlation was observed for manganese (r=-0.05), magnesium (r=0.07) and sodium (r=-0.07).  Factor analysis revealed the presence of two factors that together accounted for nearly 45% of variation. The first factor included aluminium, potassium and magnesium, and the second one - sulphur and organic carbon. The lead share was low in the first factor (0.343), but very high in the second factor (0.757). Based on the results of the factor analysis, it can be assumed that lead in the organic matter-rich sediments of the profundal zone is deposited mainly in the form of sulphides. Lead concentration varied among the sediments obtained from various lake districts; it was lower in the lakes located within the Pomeranian Lake District than in those from Greater Poland and Masurian Lakes.

19.3.2014