Effects of cyclic changes in pH and salinity on metals release from sediments

Abstract

The effects of dynamic changes in pH and salinity on metal speciation and release are investigated with sediments posed in a simulated estuarine environment. The release of Zn, Cd, Mn, and Fe was studied using sediment from the Anacostia River (Washington, DC, USA) spiked with freshly precipitated amorphous cadmium sulfide to increase Cd content. The sediment was exposed to salt water (high pH, ionic strength) and freshwater (neutral pH, minimal ionic strength) continuously and alternately (to mimic tidal changes) in small microcosms over 100 d. At the conclusion of the experiments, the vertical profiles of acid volatile sulfide (AVS) and simultaneously extracted metals (SEM) as well as porewater metals and anion concentrations were characterized. Acid volatile sulfide oxidation at the sediment surface led to a commensurate increase in dissolved metal species and metal release that was strongly dependent on the changes in the overlying water characteristics. Total Cd release was substantially higher during exposure to salt water, although, as a result of complexation, predicted dissolved Cd(2+) concentration in the overlying water was higher during exposure to freshwater. Total Zn release was little changed during exposure to salt water and freshwater, although the predicted dissolved Zn(2+) concentration was much higher during freshwater exposures. No significant iron was released because of the rapid oxidation of ferrous iron (Fe(2+)) in aerobic surficial sediments and overlying water. The present study suggests that cyclic changes in pH and salinity in the overlying water can dramatically influence metal release from estuarine sediments.

Mobility of heavy metals after spiking in relation to sediment and metal properties: leaching column study

“…This sediment was saline and sodic in general and was polluted with organic and inorganic contaminant before spiking. Saline waters can affect metal release and availability by anionic complexation or competitive sorption of cations (Atkinson et al 2007;Hong et al 2011). In high ionic strength solutions, the sodium cation might play a role in metal extraction through ion exchange (Li et al 2011).…”

Labile copper and zinc fractions under different salinity conditions in a shipyard area in the patos lagoon estuary, south of Brazil

“…This suggests the liberation of labile Zn, since the availability of metals in sediment is affected by changes in pH and salinity. 13 During this period, the winds were more persistent and varied from NE to N.…”

“…In total, 6 deployments were carried out, two in each seasonal period. Following a conceptual model of the distribution and behavior of dissolved metals vs. salinity in the Patos Lagoon estuary, the range of salinity was classified as low (0-6), intermediate (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25) or high (above 25). 22 In each deployment period, four devices were attached to a rope fixed on a pier at 0.5 m depth about 10 m from the margin area of the estuary.…”

“…In such cases, the analysis of suspended particulate matter (SPM) can be used to investigate changes related to the water and sediments, which may transport and redistribute large amounts of pollutants. 13 The pH and salinity variations in water can also influence the degree to which labile metal fractions are released from estuarine sediments. Moreover, the chemical composition of SPM in an estuary is affected by physical and biogeochemical processes in transitional waters.…”

“…Moreover, the chemical composition of SPM in an estuary is affected by physical and biogeochemical processes in transitional waters. 13 Dissolved organic matter (DOM) in water may also regulate bioavailability of trace metals in water. 14 The characteristics of estuaries contribute to the heterogeneous processes of dissolved phases of elements and SPM, which are fundamental to the geochemical cycles of metals.…”