The state of mineral nutrition as well as accumulation and translocation of selected heavy metals As, Cr, Hg, and Pb were evaluated in poplar clones Robusta (Populus x euramericana) and I-214 (Populus x euramericana). These clones are characterized by fast growth and biomass production of relatively high quality. Soil water quantity and its dynamics is one of the most important factors for growth of poplar clones, in relation to their high transpiration and nutrient transport. The research was conducted in two locations in eastern and three in western Slovakia. The poplars were grown on alluvial plains continuously influenced by ground waters from surrounding rivers. Differences in As, Cr, and Pb concentrations were recorded among the locations only, whereas between these single-clones no differences were confirmed. Different accumulation patterns were found for some elements (Ca, K, Si) in poplars compared to those of softwood (spruce) and hardwood (beech) species. The mineral elements (Ca, K, Mg, Na, Si) were accumulated in above-ground parts as follows: stem > “small-wood”/bark > wood. Cr was the most represented risk element in biomass, while Hg reached the highest concentrations and in contrast to essential elements was accumulated predominantly in wood. A potential source of Hg was soil/water environment.