Persistence of heavy metals in river sediments

The objective of this study was to assess heavy metals accumulation and equilibrium phenomena in river sediment, in relation to water quality, and to assess metals lability, analysing 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 solid-liquid distribution coefficient of the metals labile pool (Kdl) was calculated to include it in risk analysis within a more realistic frame. The Esino River was chosen for the case study. The results confirmed the need to determine Kd experimentally; values of Kd taken from the literature resulted in errors of some orders of magnitude. Metals speciation, environmental conditions, the type and texture of the sediment, features of the water, organic fraction, pH and salinity can all influence the outcome. The results showed that the two main parameters on which Kd depends are chemical oxygen demand and specific surface area. CE, which takes into account the contribution of both the water and the labile fraction in the sediment, is a key parameter and may be 5-100xthe concentration in the pore water.