Interacting Effect of pH, Phosphate and Time on the Release of Arsenic from Polluted River Sediments (Anllóns River, Spain)

Abstract

The interacting effect of pH, phosphate and time on the release of arsenic (As) from As-rich river bed sediments was studied. Arsenic release edges and kinetic release experiments (pH range 3-10), in the absence and presence of phosphate, coupled with sequential extraction procedures, SEM/EDX analyses and geochemical calculations, were carried out to evaluate As remobilisation and to elucidate the mechanisms involved. The results showed that As release underwent pronounced kinetic effects, which were strongly influenced by pH and phosphate. Remobilisation of As after 24 h was low (between *1 and 5%) and varied slightly with pH, whereas alkaline conditions generally promoted As remobilisation after 168 h, with up to 12-21% of total As released. The results showed that depending on the pH and sediment considered, the release of As increased dramatically after *48-72 h, suggesting that different processes are involved at different reaction periods. The addition of phosphate (1 mM) increased both the amount of As released (between 2 and 8 times) and the rate of As release from the sediments within the entire pH range (3-10) and period (168 h) studied. Moreover, in some cases, it also affected the shape of the As release edges and kinetic profiles. The similarities in the release profiles and the positive correlations between As and some sediment components, especially Fe and Al hydroxides, and organic matter-which appears to play a key role at high pHsuggest that As release from the studied sediments may be associated with solid phase dissolution processes under both acid and alkaline pH, whereas desorption plays a key role in the short term and at natural pH conditions, especially in the presence of phosphate, which acts as an As-displacing ligand. Evaluation of As mobility based on short-time leaching experiments may seriously underestimate the mobilisation of As from sediments.

Arsenic Mobility in As-Containing Soils from Geogenic Origin: Fractionation and Leachability

“…The As distribution in the soils of the Anllóns Basin was slightly different from that observed in the bed sediments of 8 Journal of Chemistry this river, where the residual phase predominates (up to 75% of pseudo-total As in some samples), followed by As bound to Fe oxides, representing up to 55% of pseudo-total l As [31,33]. However the results of the fractionation are in agreement with those found in vineyard soils by Nóvoa-Muñoz et al [51], who have observed a predominance of the As fraction associated with crystalline Al and Fe oxides; they also agree with those of Moreno-Jiménez et al [49] who also have found a predominance of As retained by Al and Fe hydrous oxides in soils adjacent to an old mine site and with those of Li et al [25] analysing the speciation of geogenic arsenic in soils.…”

“…Arsenic concentrations in the rocks of the area are usually around 1%, but in mineralized zones with semimassive arsenopyrite they can reach up to 10%. High As concentrations have been found in the bed sediments of the Anllóns River, downstream of the mineralized area, with a maximum of 264 mg kg −1 , which have been attributed to natural geogenic arsenic enrichment, exacerbated by gold mining activities carried out since Roman times [31][32][33]. At some points along the river course, these high As concentrations have been identified as being responsible for ecotoxicity [34,35].…”

“…All experiments were run in triplicate and blanks were run simultaneously. Pseudo-total As content of these specific samples was determined by microwave-assisted acid digestion at 150 ∘ C. To this end, 0.2 g soil was introduced into Teflon6 microwave digestion vessels with 10 mL acid solutions formed by 9 mL HNO 3(conc) and 1 mL HF (conc) [33]. After digestion, extracts were made up to 100 mL with 2.5% H 3 BO 3 solution added to "neutralize" the excess HF and complex fluoride (forming tetrafluoroboric acid) in solution, as described by Wilson et al [42].…”

Distribuição de metais pesados nos sedimentos de fundo dos rios Caceribu e Guaxindiba, afluentes da Baía de Guanabara - Rio de Janeiro, Brasil

“…Rubinos et al (2011) afirmam que metais catiônicos semelhantes ao Cd, Cu, Mn, Ni, Pb e Zn se tornam mais móveis com o decrésci-mo do pH, pois a dissolução dos metais, óxidos/hidróxidos e carbonatos aumentam e a adsorção dos cátions trocáveis na superfície dos sedimentos diminui.…”

Investigation of Combined Pollution between Malathion and a Variety of Pollutants Based on the Fractional Factorial Design (Resolution IV)

“…David et al studied the interacting effects of pH, phosphate, and time on the release of arsenic from As-rich riverbed sediments. Arsenic release edges and kinetic release experiments, in the absence and presence of phosphate, coupled with sequential extraction procedures, SEM/EDX analyses, and geochemical calculations, were carried out to evaluate and to elucidate the mechanisms involved [20]. Guo et al measured the effects of Cr (VI) and As (V) on lindane sorption.…”