Determination of heavy metal content and pollution indices in the agricultural soils using laser ablation inductively coupled plasma mass spectrometry

In this study, we determined the concentrations of heavy metals in the agricultural soils of Kafr El-Zayat city using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The LA-ICP-MS performance was firstly evaluated by analyzing appropriate reference materials and comparing the concentration values found to those of the reference values. LA-ICP-MS was then applied to examine the content of 21 elements (Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Rb, Sr, Mo, Sn, Ba, Pb, Th, and U) in 16 collected agricultural soil samples from Egypt. The soil quality was assessed by calculating the contamination factor (CF), enrichment factor (EF), and the geo-accumulation index (I_geo) of the measured heavy metals. The average concentrations of V, Cr, Co, Ni, and Cu were higher than the average worldwide background concentrations and exceeded the Canadian soil quality guidelines with values of 162.8, 113.3, 42.2, 88.1, and 70.6 μg/g, respectively. Multivariate analysis was applied to investigate the correlation and sources of heavy metals in agricultural soils. Cluster analysis indicated the clustering of heavy metals into three groups: Cr and Mo; Fe and Mn; and V, Ni, Co, Cu, Zn, and Pb. The results of principal component analysis (PCA) agreed with those of the cluster analysis and yielded three components that explained 81.13% of the total variance. The contamination factor (CF) of soils from all sampling sites showed moderate contamination.

Particle backtracking improves breeding subpopulation discrimination and natal-source identification in mixed populations

We provide a novel method to improve the use of natural tagging approaches for subpopulation discrimination and source-origin identification in aquatic and terrestrial animals with a passive dispersive phase. Our method integrates observed site-referenced biological information on individuals in mixed populations with a particle-tracking model to retrace likely dispersal histories prior to capture (i.e., particle backtracking). To illustrate and test our approach, we focus on western Lake Erie's yellow perch (Perca flavescens) population during 2006-2007, using microsatellite DNA and otolith microchemistry from larvae and juveniles as natural tags. Particle backtracking showed that not all larvae collected near a presumed hatching location may have originated there, owing to passive drift during the larval stage that was influenced by strong river- and wind-driven water circulation. Re-assigning larvae to their most probable hatching site (based on probabilistic dispersal trajectories from the particle backtracking model) improved the use of genetics and otolith microchemistry to discriminate among local breeding subpopulations. This enhancement, in turn, altered (and likely improved) the estimated contributions of each breeding subpopulation to the mixed population of juvenile recruits. Our findings indicate that particle backtracking can complement existing tools used to identify the origin of individuals in mixed populations, especially in flow-dominated systems.

Simultaneous release of Fe and As during the reductive dissolution of Pb-As jarosite by Shewanella putrefaciens CN32

Jarosites are produced during metallurgical processing, on oxidized sulfide deposits, and in acid mine drainage environments. Despite the environmental relevance of jarosites, few studies have examined their biogeochemical stability. This study demonstrates the simultaneous reduction of structural Fe(III) and aqueous As(V) during the dissolution of synthetic Pb-As jarosite (PbFe(3)(SO(4),AsO(4))(2)(OH)(6)) by Shewanella putrefaciens using batch experiments under anaerobic circumneutral conditions. Fe(III) reduction occurred immediately in inoculated samples while As(V) reduction was observed after 72 h. XANES spectra showed As(III) (14.7%) in the solid phase at 168 h coincident with decreased aqueous As(V). At 336 h, XANES spectra and aqueous speciation analysis demonstrated 20.2% and 3.0% of total As was present as As(III) in the solid and aqueous phase, respectively. In contrast, 12.4% of total Fe was present as aqueous Fe(II) and was below the detection limits of XANES in the solid phase. TEM-EDS analysis at 336 h showed secondary precipitates enriched in Fe and O with minor amounts of As and Pb. Based on experimental data and thermodynamic modeling, we suggest that structural Fe(III) reduction was thermodynamically driven while aqueous As(V) reduction was triggered by detoxification induced to offset the high As(V) (328 μM) concentrations released during dissolution.

Reductive dissolution of Tl(I)-jarosite by Shewanella putrefaciens: providing new insights into Tl biogeochemistry

Thallium (Tl) is emerging as a metal of concern in countries such as China due to its release during the natural weathering of Tl-bearing ore deposits and mining activities. Despite the high toxicity of Tl, few studies have examined the reductive dissolution of Tl mineral phases by microbial populations. In this study we examined the dissolution of synthetic Tl(I)-jarosite, (H(3)O)(0.29)Tl(0.71)Fe(2.74)(SO(4))(2)(OH)(5.22)(H(2)O)(0.78), by Shewanella putrefaciens CN32 using batch experiments under anaerobic circumneutral conditions. Fe(II) concentrations were measured over time and showed Fe(II) production (4.6 mM) in inoculated samples by 893 h not seen in mineral and dead cell controls. Release of aqueous Tl was enhanced in inoculated samples whereby maximum concentrations in inoculated and cell-free samples reached 3.2 and 2.1 mM, respectively, by termination of the experiment. Complementary batch Tl/S. putrefaciens sorption experiments were conducted under experimentally relevant pH (5 and 6.3) at a Tl concentration of 35 μM and did not show significant Tl accumulation by either live or dead cells. Therefore, in contrast to many metals such as Pb and Cd, S. putrefaciens does not represent a sink for Tl in the environment and Tl is readily released from Tl-jarosite during both abiotic and biotic dissolution.

Intracellular precipitation of Pb by Shewanella putrefaciens CN32 during the reductive dissolution of Pb-jarosite

Jarosites (MFe(3)(SO(4))(2)(OH)(6)) are precipitated in the Zn industry to remove impurities during the extraction process and contain metals such as Pb and Ag. Jarosite wastes are often confined to capped tailings ponds, thereby creating potential for anaerobic reductive dissolution by microbial populations. This study demonstrates the reductive dissolution of synthetic Pb-jarosite (PbFe(6)(SO(4))(4)(OH)(12)) by a subsurface dissimilatory Fe reducing bacterium (Shewanella putrefaciens CN32) using batch experiments under anaerobic circumneutral conditions. Solution chemistry, pH, Eh, and cell viability were monitored over time and illustrated the reduction of released structural Fe(III) from the Pb-jarosite to Fe(II). Inoculated samples containing Pb-jarosite also demonstrated decreased cellular viability coinciding with increased Pb concentrations. SEM images showed progressive nucleation of electron dense nanoparticles on the surface of bacteria, identified by TEM/EDS as intracellular crystalline precipitates enriched in Pb and P. The intracellular precipitation of Pb by S. putrefaciens CN32 observed in this study provides potential new insight into the biogeochemical cycling of Pb in reducing environments.

Chemical analysis of endolymph and the growing otolith: fractionation of metals in freshwater fish species

The fractionation of metals from water to otolith is an area of research that has received relatively limited attention, especially in freshwater systems. The objectives of the present research were to study the metal partitioning between otolith and endolymph of two freshwater species: Lake trout (Salvelinus namaycush), and burbot (Lota lota). We also included the chemical analyses of water and blood from fish of the same species collected in the same area but during different years. These results provide insight regarding the partition of metals between water and fish. This is one of the first studies to provide a range of trace metal concentrations for endolymph and the growing otolith (both aragonite and vaterite) and to directly measure otolith-endolymph partition coefficients for freshwater fish. The trace elements (Mg, Sr, and Ba) most often used as otolith elemental tracers were the ones with the lowest uptake from water to blood. We found that endolymph and whole blood had similar metal concentrations, with Mg and Fe being the only elements enriched in whole blood. Results showed few significant differences in trace metal content between wild lake trout and burbot endolymph (except for K, Mg, and Ba), but significant differences existed between their aragonitic otoliths. These results suggest two different crystallization processes in these species or the presence of different proteins (and/or organic matrices) that would selectively influence elemental incorporation in the otoliths.

Mouthpart deformities and community composition of Chironomidae (Diptera) larvae downstream of metal mines in New Brunswick, Canada

The effect of metal enrichment on chironomid communities was examined in streams receiving mine drainage from metal mining operations in New Brunswick, Canada. At five sites receiving mine drainage, metal concentrations were significantly (p < 0.05) elevated in water (Zn), periphyton (Cd, Co, Cu, and Zn), and chironomid tissue (Cu, Cd, and Zn) relative to five paired reference locations. Metal concentrations in chironomid larvae were significantly correlated with concentrations in both water and periphyton. Chironomid communities were severely affected at sites receiving mine drainage as demonstrated by reduced genera richness and altered community composition. Sites receiving mine drainage exhibited an increased abundance of metal-tolerant Orthocladiinae and a reduced abundance of metal-sensitive Tanytarsini relative to reference sites. The incidence of mentum deformities was significantly elevated at sites receiving mine drainage (1.43 +/- 0.24%), with the mean percentage approaching a doubling of that observed at reference sites (0.79 +/- 0.22%). Trace metal concentrations at mine-associated streams in New Brunswick significantly affected the benthic community and have the potential to alter the structure and function of these aquatic ecosystems.