Persistence of heavy metals in river sediments

The objectives of this work is the assessment of the heavy metals accumulation and equilibrium phenomena in river sediment, in relation to the state of water quality and the assessment of metals lability, analyzing whether and how easily heavy metals are available to generic biota. The Diffuse Gradient in Thin film technique was used to assess the Effective Concentration (CE). The coefficient of solid-liquid distribution of the metals labile pool (Kdl) was calculated to include it in risk analysis inside a more realistic frame. The Esino River was chosen as case study. The results confirmed the necessity to determine experimentally Kd: its values, avalaible in literature, resulted incorrect up with some orders of magnitude. Metals speciation, environmental conditions, type and texture of the sediment, water features, organic fraction, pH and salinity can influence the outcome. The results showed that the two main parameters from which Kd depends are Chemical Oxigen Demand and Specific Surface Area. The concentration CE, which takes into account both the contribution of the water and the labile fraction in the sediment, is the real key parameter. Its order of magnitude is clear: from 8 to 100 times the concentration in the pore water.