Lability, solubility and speciation of Cd, Pb and Zn in alluvial soils of the River Trent catchment UK

Abstract

5Alluvial soils can store a wide range of metal contaminants originating from point and diffuse sources. The biological health of these soils is important as they act as an interface between terrestrial and aquatic environments, therefore playing an important role in maintaining the quality of surface waters. The aim of this work was to examine the lability, solubility and bioavailability of Pb, Zn and Cd in the top (0-15 cm) and sub soil (35-50 cm) of metal contaminated alluvial soils from the Trent catchment, U.K. Samples 10 (n=46) were collected from within 10m of the river bank. Sources of contamination include historical mining, industry, sewage treatment works and energy production. Enrichment factors based on total metal concentrations showed that contamination in soils declined with distance from the mining areas before rising again as a result of general urbanisation and identified point sources (e.g. river dredging activities). Pore waters were extracted and isotopic dilution and single extraction assays were undertaken on the soils 15 to assess the lability and solubility of the metals. Multi-element isotopic dilution assays were used to determine the labile pool or E-value of these metals in the soil. E-value concentrations were found to range between 0.5-14 mg/kg, 11-350 mg/kg and 25-594 mg/kg for Cd, Pb and Zn, respectively. Comparison of the E-value assay with the EU standard extraction assay for trace element availability (0.05M EDTA) showed that EDTA extractions generally over-estimated the E-value for Zn and Pb,with 20 the difference being greater as contamination levels increased. Bioavailability of the metals was assessed by speciating the pore waters [M Sol ] using WHAM 7 to obtain estimates of free ion activities (M 2+ ). Values of (M 2+ ) were compared to published 'median critical limits' for soils that estimate levels of protection for 95% of biological species. For each of the three metals, (M 2+ ) was found to exceed these critical limits at some sites. Solubility of the metals are reported using K d values expressed using both the 25 total and E-value as the solid phase. Finally we examine the use of different metal pools (total, E-value, EDTA-extractable) and different measures of Fe oxide pools (total, free total, free amorphous), in predicting [M Sol ] concentrations and (M 2+ ) using WHAM 7 in assemblage modelling mode. Overall best simultaneous model predictions for the three metals were obtained using the E-values. Larger overestimates of [M Sol ] and (M 2+ ) were produced using the EDTA and total metal pools whereas a better 30 fitting in the prediction was obtained when models used either the total or the free total FeOx pools. IntroductionAlluvial soils act as archives for fluvially dispersed metal contaminants from numerous sources [1][2][3][4][5] . These soils are often used in intensive agricultural systems. Several studies in the UK 35 have previously noted the potential for metal transfer into cattle, when grazing grass grown on contaminated alluvial soils [6][7] . In a...

Measurement of isotopically‐exchangeable Zn in Zn‐deficient paddy soil

“…The labile pool of Zn was ≈11 mg kg −1 for all data ( n = 24) for both soil types (Table ), which is similar to that in other non‐polluted agricultural soils (Ayoub et al ., ; Sinaj et al ., ; Nazif et al ., ). Only 9 and 14% of the total Zn in the Bay and Tiaong soils, respectively, is labile, which is similar to the values for polluted and unpolluted soil (10–33%) in the literature (Young et al ., ; Degryse et al ., ; Gabler et al ., ; Izquierdo et al ., ).…”

“…non‐silicate‐bound soil phases). Figure shows our data together with those from other soils used for rice cultivation in the Philippines (Izquierdo & Kirk, 2013, unpublished results) and uncontaminated alluvial soil from the UK (Izquierdo et al ., ) with small concentrations of available Zn. Although our dataset is limited, it seems that extraction with 0.05 m EDTA could provide a simple non‐isotopic estimate of the geochemically active Zn in soil where it is poorly available across a range of redox potentials.…”

“…For comparison, results for other lowland paddy soils from the P hilippines (Izquierdo & Kirk, 2013, unpublished results) and relatively uncontaminated alluvial soil from the UK (Izquierdo et al. , ) are plotted.…”

Potentially toxic elements in the riparian soils of the Sava River

“…loads from diffuse industrial and agricultural sources (runoff) and reduce in-stream pollution during flooding (Karr and Gorman 1975), while riparian soil acts as an important sink for pollutants, especially heavy metals from river water or upland, through adsorption and sedimentation (Zhang et al 2010;Izquierdo et al 2013). These soils are under intense pressure from various anthropogenic sources of pollutants, which could contribute significantly to multiple stress conditions (Navarro-Ortega et al 2015;Wang et al 2015).…”

Spatial and Temporal Stability of Major and Trace Element Leaching in Urban Stormwater Sediments

“…To assess the risk of contamination of the subsoil and groundwater, the mobility of elements trapped in these sediments must be investigated [11] [12].…”