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In this study, river bed sediments were submitted to a BCR sequential extraction, together with three bioavailability tests: a weak acid elutriate (HCl), a physiologically based extraction test (PBET) and a toxicity characteristic leaching procedure (TCLP). The most remarkable features of the BCR procedure were: i) Mn and Zn showed the highest proportion of the F1 exchangeable fraction; ii) in addition to Fe, Pb and Zn were the metals with the higher percentages in the F2 reducible fraction; iii) Fe and Cu were the elements with the highest proportion of the F3 oxidizable fraction; iv) the application of Principal Component Analysis to the metals in each of the three fractions did not show clear associations between metals and sediment components considered as metal scavengers, v) considering the sum of the three BCR fractions, the elements showed a decreasing availability of: Fe > Pb > Zn > Cu > Mn > Ni > Cr. The single extractions followed a decreasing extractability order of: HCl > PBET > TCLP and they were far from the extractability deduced from the sum of fractions in the BCR extraction. [Copyright &y& Elsevier]

The Anllóns basin (NW Spain) has been included in the Natura 2000 Network and declared as Site of Community Importance. The main contamination problems of the basin come from a former gold mine and from agricultural activities, which influence the quality of the sediment–water system. Phosphorus (P) enrichment in the bed sediments was evaluated by analyzing P in the pore waters, in the surface bed sediments, and in the vertical sediment profiles, including both total and bioavailable forms. Two granulometric fractions (<2 mm and <63 μm) were evaluated. Pore waters, bed sediments, and vertical profiles showed high percentages of the bioavailable P fraction with respect to the total P content, which evidences the potential risk of pollution which suppose the bed sediments of the Anllóns River. The vertical profiles showed P enrichment in the superficial layers, which could be the consequence of the increased use of fertilizers in the last decades. With regards to the granulometric distributions, the <63 μm showed, in general, higher P concentrations than the <2 mm fraction. However, at the sampling points most heavily contaminated, the concentration of both fractions becomes similar, thus indicating that, at these sites, the coatings formed over sands can retain important P concentrations in the bed sediments. [ABSTRACT FROM AUTHOR]

We have studied the distribution and sorption behavior of phosphate and arsenate in bed sediments of the Anllóns river (NW Spain). As a consequence of the intense gold-mining activity in the past, substantial amounts of arsenic were found in the river sediments. For phosphorus, higher concentrations were found near two sources of P pollution. Sorption isotherms were described by the Freundlich, Langmuir and Tempkin equations. In general, the sediments sorbed more P than As. The equilibrium P concentration (EPC) reveals that sediments act as a scavenger for soluble P; by contrast, equilibrium As concentration (EAC) values were high for the As-rich sediments and correlates well with total arsenic content. Amorphous Fe oxides content, organic matter and fraction of clay plus silt were the main properties of the sediments related with the sorption of arsenate and phosphate. The results obtained provide a first estimate of the sorption behavior and availability of the phosphate and arsenate anions in the sediments of the Anllóns river. [ABSTRACT FROM AUTHOR]