Environmental assessment of natural radionuclides and heavy metals in waters discharged from a lignite-fired power plant

Gross alpha, gross beta and 226Ra activities as well as the concentration of trace metals (V, Cr, Mn, Ni, Cu, Zn, Mo and Pb) in the discharge waters of the major lignite-fired power plant in Greece were measured during the period October 2004 to May 2006. Gross alpha activity of particulate matter in the discharge waters was 0.75 ± 0.40 Bq g−1 (0.3–1.2 Bq g−1) while the beta activity was 1.54 ± 0.50 Bq g−1 (1.2–1.7 Bq g−1). The ranges of water gross alpha, beta and 226Ra activities were 0.062–0.268 Bq L−1, 0.064–0.268 Bq L−1 and 0.021–0.062 Bq L−1, respectively. The mean concentration of 226Ra in the discharge waters was at least one order of magnitude higher than in natural water bodies. Soil samples were collected from fields irrigated with discharge waters and 29.2 ± 2.2 Bq kg−1 of 238U, 1.2 ± 0.2 Bq kg−1 of 235U, 26.8 ± 0.8 Bq kg−1 of 226Ra, 36.8 ± 1.5 Bq kg−1 of 232Th and 492.6 ± 25.8 Bq kg−1 of 40K were determined. The concentration values of dissolved metals in the discharge waters were higher than those usually observed in water streams near coal-fired power plants or rivers due to metal leaching from lignite or/and by-products. However, the leaching at high pH’s as those observed in the discharged waters does not raise the concentration of the studied metals to values higher than the criteria maximum concentrations and criterion continuous concentration (CCC) values of the US EPA water quality criteria. Statistical analysis was further applied to reveal the correlations between the different water components. Hierarchical cluster analysis revealed four different clusters: the first cluster was primarily composed of radioactivity and physicochemical parameters; the second cluster consisted of Cu, Ni and Zn, the third of Mn, Fe, Mo and Pb and the fourth of V and Cr. This clustering agrees with the associations suggested for elements in most coals or with the Goldschmidt classification.