Metal Concentrations In Pore Water Research Articles

Plant testing with hemp and miscanthus to assess phytomanagement options including biostimulants and mycorrhizae on a metal-contaminated soil to provide biomass for sustainable biofuel production

The need of biofuels from biomass, including sustainable aviation fuel, without using agricultural land dedicated to food crops, is in constant demand. Strategies to intensify biomass production using mycorrhizal fungi, biostimulants and their combinations could be solutions for improving the cultivation of lignocellulosic plants but still lack well-established validation on metal-contaminated soils. This study aimed to assess the yield of Miscanthus x giganteus J.M. Greef & Deuter and Cannabis sativa L. grown on a metal-contaminated agricultural soil (11 mg Cd, 536 mg Pb and 955 mg Zn kg−1) amended with biostimulants and/or arbuscular mycorrhizal fungi, and the shoot Cd, Pb and Zn uptake. A pot trial was carried out with soil collected from a field near a former Pb/Zn smelter in France and six treatments: control (C), protein hydrolysate (a mixture of peptides and amino acids, PH), humic/fulvic acids (HFA), arbuscular mycorrhizae fungi (AMF), PH combined with AMF (PHxAMF), and HFA combined with AMF (HFAxAMF). Metal concentrations in the soil pore water (SPW), pH and electrical conductivity were measured over time. Miscanthus and hemp shoots were harvested on day 90. Both PH and PHxAMF treatments increased SPW Cd, Pb, and Zn concentrations (e.g. by 26, 1.9, and 22.9 times for miscanthus and 9.7, 4.7, and 19.3 times for hemp in the PH and PHxAMF treatments as compared to the control one, respectively). This led to phytotoxicity and reduced shoot yield for miscanthus. Conversely, HFA and HFAxAMF treatments decreased SPW Cd and Zn concentrations, increasing shoot yields for hemp and miscanthus. Shoot Cd, Pb, and Zn uptakes peaked for PH and PHxAMF hemp plants (in μg plant-1, Cd: 310–334, Pb: 34–38, and Zn: 232–309 for PHxAMF and PH, respectively), while lowest values occurred for PH miscanthus plants mainly due to low shoot yield. Overall, this study suggested that humic/fulvic acids can be an effective biostimulant for increasing shoot biomass production in a metal-contaminated soil. These results warrant further investigations of the HFAxAMF in field trials.

Experimental evaluation of vertical metal retardation in stormwater management practices as influenced by cycles of baseline and high salinity

The application of NaCl as a deicer increases salinity of stormwater runoff, which may impact the speciation and mobility of various contaminants, including metals. Salt can remain in the fill media of stormwater management practices for an extended period after application, creating annual cycles of baseline and high salinity. This study evaluated the impacts of NaCl concentration and application cycles on metal retardation in fill media via 1-D continuous flow bench-scale columns. The high salinity scenario of 0.1 M NaCl decreased retardation factors of metals when compared to baseline salinity scenario of 0.01 M NaCl. Application of cycling baseline and high NaCl caused substantial fluctuations in the effluent metal concentration. The metals that were adsorbed during the baseline salinity periods were desorbed during the high salinity periods, leading to elevated concentrations of metals in porewater and effluent. Flushing with water removed only Na from the fill media top layers, while applying cysteine, as an environmentally friendly chelator, was demonstrated to be a promising approach to mobilizing accumulated metals from top layers to deeper layers. The results suggest that incorporating seasonal changes in environmental variables such as salinity enhances accuracy of contaminant transport modeling in fill media.

From sediments to soils: changes in pore water metal bioavailability

The use of sediments as soils is an area of interest for Beneficial Use of dredged sediments. In this study the impact of the transition from sediments to soils is researched by looking at the seasonal and long year (10 year) change in pore water metal chemistry of sediments which are considered clean (class A) according to the Dutch soil directive. This study is based on a combination of geohydrological, geochemical and ecotoxicological risk models and validated against measured pore water concentrations for metals over an dry/wet period. The pore water metal concentrations are compared against standards and expressed as at Risk Characterization Ratio’s (RCR) values. The RCR values are high (> 1) during the first 3 years after the application of sediments as soil, especially at the end of the summer. The multi substances Potentially Affected Fraction (ms-PAF) shows a similar trend as the RCR values, although it takes 5 years before the combined calculated potential ecotoxicity is below the legal 40% threshold level. Translated to land use, it is advised to restrict land use for farming on soils where these clean (class A) sediments are applied for a five-year transition period.Article HighlightsBeneficial Use of sediments should take into account the different conditions when used as soils.Use of sediments as soils lead to a predicable seasonal and multiple year trend in metal concentrations in pore water.The predicted results in metal pore water concentrations are translated into an advice for temporal land use.

Refining our understanding of metal bioavailability in sediments using information from porewater: Application of a multimetal biotic ligand model as an extension of the equilibrium partitioning sediment benchmarks.

The equilibrium partitioning sediment benchmarks (ESBs) derived by the US Environmental Protection Agency (USEPA) in 2005 provide a mechanistic framework for understanding metal bioavailability in sediments by considering equilibrium partitioning (EqP) theory, which predicts that metal bioavailability in sediments is determined largely by partitioning to sediment particles. Factors that favor the partitioning of metals to sediment particles, such as the presence of acid volatile sulfide (AVS) and sediment organic matter, reduce metal bioavailability to benthic organisms. Because ESBs link metal bioavailability to partitioning to particles, they also predict that measuring metals in porewater can lead to a more accurate assessment of bioavailability and toxicity to benthic organisms. At the time of their development, sediment ESBs based on the analysis of porewater metal concentrations were limited to comparison with hardness-dependent metals criteria for the calculation of interstitial water benchmark units (IWBUs). However, the multimetal biotic ligand model (mBLM) provides a more comprehensive assessment of porewater metal concentrations, because it considers factors in addition to hardness, such as pH and dissolved organic carbon, and allows for interactions between metals. To evaluate the utility of the various sediment and porewater ESBs, four Hyalella azteca bioassay studies were identified that included sediment and porewater measurements of metals and porewater bioavailability parameters. Evaluations of excess simultaneously extracted metals, IWBUs, and mBLM toxic units (TUs) were compared among the bioassay studies. For porewater, IWBUs and mBLM TUs were calculated using porewater metal concentrations from samples collected using centrifugation and peepers. The percentage of correct predictions of toxicity was calculated for each benchmark comparison. The mBLM-based assessment using peeper data provided the most accurate predictions for the greatest number of samples among the evaluation methods considered. This evaluation demonstrates the value of porewater-based evaluations in conjunction with sediment chemistry in understanding toxicity observed in bioassay studies. Integr Environ Assess Manag 2022;18:1335-1347. © 2021 SETAC.

Sink or source? Insights into the behavior of copper and zinc in the sediment porewater of a constructed wetland by peepers

The H-02 free water surface constructed wetland has been applied to remove heavy metals, mainly copper (Cu) and zinc (Zn), from wastewater on the Savannah River Site (Aiken, SC, USA). More and more studies focus on the metal behavior between the sediment and the overlying water, which directly reflects the stability of metals after sedimentation in constructed wetlands. This study focused on the biogeochemical pathways in metal bioavailability and remobilization in the sediment after metals were removed from the overlying water. The dialysis sampling device (peeper) was used to collect porewater samples from eight depths in the sediment for the measurement of Cu, Zn, dissolved organic carbon (DOC), and major anions (sulfate and chloride). Surface water samples were also collected for the measurement of Cu, Zn, DOC, and anions. Different temporal trends were observed for dissolved Cu between the surface and bottom waters, but not for dissolved Zn. There were no obvious changes in porewater metal concentrations with increasing depths in the sediment. Sediment served as a sink for Cu as only 3% of porewater samples showed higher labile Cu concentrations than the surface water during the entire year, and these samples were collected below the sediment-water interface. However, sediment served as a source for Zn in summer and winter as 32% of porewater samples showed higher labile Zn concentrations than the surface water, and these samples were collected at all sediment depths. We think the seasonal changes in the behaviors of Cu and Zn are primarily controlled by the sulfur dynamics and the metal removal processes in the constructed wetland, as well as the different complexing chemistry between Cu and Zn. Also, our study supports that peeper is a powerful tool for studying the biogeochemistry of metals in the sediment.

A comprehensive exploration on distribution, risk assessment, and source quantification of heavy metals in the multi-media environment from Shaying River Basin, China

Comprehensively understand the distribution of pollutants in the multi-media environment at basin scale is of major importance to the ecological risk assessment and pollution control. In this study, multi-media contamination characteristics of eight heavy metals in the water, soil, and sediment from the Shaying River Basin of China have been analyzed to probe their ecological risks and potential sources. Results revealed that heavy metal concentrations in pore water were higher than those in surface water. While the mean concentrations of most heavy metals increased follow the order of bankside soil (BS)<water-level-fluctuating zone soil (WLFZS)<sediment. The WLFZ was an important transition zone between the BS and sediment for pollutant exchange. The mean heavy metal concentrations in surface water were all below their corresponding water quality standards except Hg. Whereas the mean concentrations of Cr, Ni, Zn, Cd, and Hg in BS, WLFZS, and sediment exceeded their corresponding background values. The assessment results of pollution and risks indicated that Hg and Cd posed the highest potential risks in each medium. Furthermore, according to the factor analysis and PMF model, six potential sources were identified, in which agricultural, fuel combustion, and industrial sources were the dominant anthropogenic sources, accounting for 23.84%, 17.43%, and 14.25% of the total contribution.

Collection and use of porewater data from sediment bioassay studies for understanding exposure to bioavailable metals.

The US Environmental Protection Agency Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks (ESBs) for the Protection of Benthic Organisms: Metal Mixtures (Cadmium, Copper, Lead, Nickel, Silver and Zinc) equilibrium partitioning approach causally link metal concentrations and toxicological effects; they apply to sediment and porewater (i.e., interstitial water). The evaluation of bioavailable metal concentrations in porewater, using tools such as the biotic ligand model, provides an advancement that complements sediment-based evaluations. However, porewater characterization is less commonly performed in sediment bioassays than sediment chemistry characterization due to the difficulty and expense of porewater collection as well as concerns about interpretation of porewater data. This study discusses the advantages and disadvantages of different porewater extraction methods for analysis of metals and bioavailability parameters during laboratory sediment bioassays, with a focus on peepers and centrifugation. The purpose is to provide recommendations to generate bioassay porewater data of sufficient quality for use in risk-based decision-making, such as for regulated cleanup actions. Comparisons of paired data from previous bioassay studies indicate that metal porewater concentrations collected via centrifugation tend to be higher than those collected via peepers. However, centrifugation disrupts the redox status of the sediment; also, metal concentrations can vary markedly based on centrifugation conditions. Data to compare the concentrations of peeper- and centrifugation-collected bioavailability parameters (e.g., major ions, pH) are much more limited, but indicate smaller differences than those observed for metal concentrations. While peepers can be sampled without altering the redox status of the porewater, the small volume of porewater peepers collected is enough for metal concentration analysis, but insufficient for analysis of all metal bioavailability parameters. Given the benefits of metal collection via peepers, it is optimal to use centrifugation and peepers in tandem for bioassay porewater collection to improve bioavailability predictions. Environ Assess Manag 2022;18:1321-1334. © 2021 SETAC.

Effect of biochar amendment on mobility and plant uptake of Zn, Pb and Cd in contaminated soil

This study aimed to assess the effect of rice straw biochar application as a soil amendment on the mobility, availability, speciation and plant uptake of Zn, Pb and Cd in contaminated soil. A pot experiment with maize (Zea mays L.) was conducted using different rates 0, 1, 2, and 5% (w/w) of rice straw biochar. The soil pore water properties; pH, EC, and DOC concentration, the dissolved metal concentrations in soil pore water as well as plant metals uptake were determined at the end of the experiment. The BCR sequential extraction procedure was adopted to determine the effect of biochar on speciation and partitioning of the studied metals.Results showed that the application of biochar is significantly increased the plant shoots biomass by 94.5% with 5% biochar rates compared to untreated soil. Similarly, the soil pore water properties pH, EC, and DOC concentration were also increased with biochar addition compared to untreated soil. The dissolved metal concentrations were decreased in soil pore water with the increasing of biochar rates by 92%, 81.5%, and 90% for Zn, Pb and Cd, respectively at 5% biochar rate. In the same trend, the plant metals uptake reduced significantly with the increasing of biochar dose. Compared to untreated soil, the BCR sequential extraction showed that the biochar addition induced the transformation of the exchangeable metal fractions to oxidizable and residual fractions. These results confirmed the ability of rice straw biochar to immobilize the studied metals and therefore reducing their bioavailability and their uptake by plant.

Enrichment of Trace Metals (V, Cu, Co, Ni, and Mo) in Arctic Sediments—From Siberian Arctic Shelves to the Basin

AbstractWith 50% of the Arctic Ocean is consisted of continental shelves, extensive shelf‐basin exchange processes exist here and plays a key role in regulating the biogeochemical recycling process of trace metals in the Arctic region. In this study, short sediment cores were collected along three transects from Siberian‐Chukchi shelves to adjacent slope/basin areas. An increasing trend was found for the bulk concentrations of several metals (V, Cu, Co, Ni, and Mo) from shelf to slope/basin cores with increasing water depth. Sequential extraction experiments indicated that the Fe/Mn oxide fractions increased significantly from shelf (9%–21%) to basin cores (24%–76%) for Cu, Co, Ni, and V, while the organic/sulfide phase remained significant (∼40%) for Mo. In addition, the observed dissolved metal concentrations in porewater indicated the remobilization of Fe, Mn, and Mo from shelf sediment, while V was always removed from water to the sediment, both on the shelf or in the slope/basin. Overall, in combination with the statistical analysis, we proposed that metals are transported from shelves to the central Arctic and are scavenged mainly by Mn oxides from the water column, which results in the enrichment of metals in slope/basin sediment. With the climate change, such transport and accumulation mechanism may be intensified over time, slowly leading the Arctic sediment to be a more and more important sink for those metals.

Trace Metal Dynamics in a Tropical Mangrove Tidal Creek: Influence of Porewater Seepage (Can Gio, Vietnam)

Mangrove soils are considered as sinks for trace metals, protecting coastal waters from pollutions. However, the cycling of trace metals in mangroves is complex due to various biogeochemical processes across the intertidal zone, notably the dissolution of bearing phases resulting in high trace metal concentrations in porewaters. Previous studies demonstrated a decrease of trace metal stocks in mangrove soils seaward, possibly due to the export of dissolved metals through tidal pumping. Can Gio mangrove is the largest one in Vietnam, developing downstream Ho Chi Minh City (Viet Nam’s biggest industrial city). The objectives of the present study were to characterize the dynamics of trace metals in a tidal creek of the Can Gio mangrove that does not receive any upstream inputs and to identify the role of porewater seepage on their dynamics. To reach our goals, surface water and suspended particulate matters were collected every 2 hours during two different tidal cycles (spring and neap tides) and at the two different seasons, dry and wet. Mangroves porewaters were also collected. In addition to particulate and dissolved trace metals, physico-chemical parameters and a groundwater tracer (Radon-222Rn) were measured. The results showed that trace metal concentrations at flood tides, both in the dissolved and the particulate phases, were in the same range that those measured in the Can Gio Estuary. Then during ebb tides, we evidenced high inputs of dissolved Fe, Mn, Co, and Ni from mangrove soils. However, the dynamics of these inputs differed depending on the element considered. Mn was exported from the tidal creek in its dissolved form. However concerning Fe, and to a lesser extent Co and Ni, we suggest that, when delivered to the creek from the soils under dissolved forms, these trace metals precipitated because of different physicochemical characteristics between mangrove soils and tidal creek, notably higher dissolved oxygen concentrations and higher pH. Consequently, these elements were exported to the estuary in particulate forms. We suggest that budget studies of trace metals in mangroves should be developed like the ones concerning carbon to efficiently determine their role as a barrier for pollutants between land and sea.

Assisted phytoremediation of a former mine soil using biochar and iron sulphate: Effects on As soil immobilization and accumulation in three Salicaceae species

Metal(loid) accumulation in soils, is of increasing concern because of the potential human health risks. Therefore, metal(loid) contaminated sites need rehabilitation. It is becoming increasingly popular to use phytoremediation methods for the reclamation of sites containing metal(loid)s. However, plant establishment and growth on contaminated soils can be difficult due to high metal(loid) concentrations and poor fertility conditions. Consequently, amendments, like biochar and iron sulphate, must be applied. Biochar, obtained from plant biomass or animal wastes pyrolyzed under minimal oxygen supply, showed beneficial effects on soil properties and plant growth. Iron sulphate can effectively immobilize anions, thus mitigating metal(loid) toxicity and hence promoting plant development. This study aimed to assess the effect of two different modalities of biochar amendment application (top third of the tube and all tube height) combined with iron sulphate addition on the physico-chemical properties of a mining polluted soil and the growth and metal(loid) uptake of three Salicaceae species. A 1.5 year mesocosm experiment under field condition was conducted using a former tin mine contaminated by arsenic, amended with biochar and iron sulphate and vegetated with three Salicaceae species. Results showed that the combination of biochar and iron sulphate improved soil characteristics by increasing pH and electrical conductivity and reducing soil pore water metal(loid) concentrations. Between the two biochar application methods, the addition of biochar on the all tube height showed better results. But for such contaminated soil, biochar, in combination with iron sulphate, had no positive effect on plant growth, for all species tested and especially when incorporating on the top third of the tube. Finally, S. purpurea presented high root metal(loid) concentrations associated to the better growth compared to P. euramericana and S. viminalis, making it a better candidate for phytostabilization of the studied soil.

A laboratory assay of in situ stabilization of toxic metals in contaminated boreal forest soil using organic and inorganic amendments

Metal-contaminated soils present a great threat to natural ecosystems and human health. Remediation studies focusing on metal-polluted soils with high organic matter (OM &gt; 20%) are limited. This study evaluated the effectiveness of biochar, compost, diammonium phosphate (DAP), and iron oxides (Fe-O), in immobilizing metals from an OM-rich boreal forest soil contaminated with arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn). A laboratory incubation study was conducted with soil amended with biochar (5% w w−1), compost (5% w w−1), DAP (0.2% w w−1), or Fe-O (0.2% w w−1), and a control (without amendment) for 6 months at field capacity moisture content. Metal concentrations were determined in pore water collected at 0, 2, 4, and 6 months after incubation. Soil was extracted sequentially for metals after the incubation period. Metal concentrations in pore water were significantly reduced by different amendments as follows: As by biochar and Fe-O, Cd by biochar, compost, and DAP, Cu by biochar, Pb by compost and DAP, and Zn by biochar and compost. Sequential extractions revealed biochar and (or) compost transferred Cd, Cu, Pb, and Zn from the labile pool to the non-labile pool confirming their effectiveness as amendments for remediation of metal-contaminated OM-rich boreal forest soil.

Concentrations of porewater heavy metals, their benthic fluxes and the potential ecological risks in Daya Bay, South China

Heavy metal (Cr, Mn, Fe, Ni, Cu, Zn, Cd, Pb) concentrations in surface sediment porewater and their benthic fluxes were investigated in Daya Bay, South China, to study their accumulation and transfer at the sediment-water interface, as well as the impact of human activities on heavy metals. Heavy metals in porewater displayed different patterns in three partitions (top, center and inlet), which was mainly attributed to the difference in the biogeochemical conditions, hydrodynamic force inner the bay and the human activities along the bay. Ecological risk assessment results showed that heavy metals in porewater dramatically exceeded the background values. The average release of heavy metals from sediment were (6.1 ± 3.3) × 104–(2.7 ± 1.6) × 108 g a−1 in the bay, so they had potential risks to the water environment, and sediment should be paid more attention to as the endogenesis of contamination.

Fate of cobalt and nickel in mackinawite during diagenetic pyrite formation

AbstractAs iron sulfide mineral phases are important sedimentary sinks for naturally occurring or contaminant metals, it is important to know the fate of metals during the diagenetic transformation of primary sulfide minerals into more stable phases, such as pyrite (FeS2). Furthermore, the trace metal content of pyrite has been proposed as a marine paleoredox proxy. Given the diverse low-temperature diagenetic formation pathways for pyrite, this use of pyrite requires validation. We, therefore, studied nickel (Ni) and cobalt (Co) incorporation into freshly precipitated mackinawite (FeSm), and after experimental diagenesis to pyrite (FeS2) using S0 as an oxidant at 65 °C. Metal incorporation was quantified on bulk digests using ICP-OES or ICP-AES. Bulk mineralogy was characterized with micro-X-ray diffraction (micro-XRD), documenting the transformation of mackinawite to pyrite. Epoxy grain mounts were made anoxically of mackinawite and pyrite grains. We used synchrotron-based micro-X-ray fluorescence (μXRF) to map the distribution of Co and Ni, as well as to collect multiple energy maps throughout the sulfur (S) K-edge. Iron (Fe) and S K-edge micro-X-ray absorption near edge spectroscopy (μXANES) was used to identify the oxidation state and mineralogy within the experimentally synthesized and diagenetically transformed minerals, and map end-member solid phases within the grain mounts using the multiple energy maps. Metal-free FeSm transformed to pyrite, with residual FeSm detectable. Co- and Ni-containing FeSm also transformed to pyrite, but with multiple techniques detecting FeSm as well as S0, implying less complete transformation to pyrite as compared to metal-free FeSm. These results indicate that Co and Ni may inhibit transformation for FeSm to pyrite, or slow it down. Cobalt concentrations in the solid diminished by 30% during pyrite transformation, indicating that pyrite Co may be a conservative tracer of seawater or porewater Co concentrations. Nickel concentrations increased several-fold after pyrite formation, suggesting that pyrite may have scavenged Ni from the dissolution of primary FeSm grains. Nickel in pyrites thus may not be a reliable proxy for seawater or porewater metal concentrations.

Development of a two‐layer transport model in layered muddy–permeable marsh sediments using 224Ra–228Th disequilibria

AbstractUnderground seepage and the sediment–water interface are important pathways for transporting concentrated pore water solutes through permeable sediments. In this study, we utilized radium‐224/thorium‐228 disequilibria to examine solute transport throughout shallow sediments (depth &lt; 30 cm) of a tidal marshland, North Inlet, South Carolina, over a seasonal cycle. Distinct 224Ra–228Th disequilibria patterns indicate that significant pore water exchange occurred both directly across the sediment–water interface and at depth as underground seepage. Temporal variations in phosphorus (P), iron (Fe), and manganese (Mn) pore water concentrations also support this two‐layer transport model. Solute transport across the interface was influenced by seasonal bioirrigation, with highest exchange rates occurring in the late spring. Interfacial flux of dissolved Fe ranged over two orders of magnitude, from 0.5 mmol m−2 d−1 to 134 mmol m−2 d−1, and fluxes of soluble reactive phosphate (SRP) and dissolved Mn varied from 0.01 mmol m−2 d−1 to 0.72 mmol m−2 d−1 and from 0.04 mmol m−2 d−1 to 2.7 mmol m−2 d−1, respectively. Seepage occurs year‐round, with fluid exchange rates related to the distance from the tidal creek. SRP transport via seepage ranged from 0.98 mmol m−2 d−1 to 5.0 mmol m−2 d−1, one order of magnitude higher than across the sediment–water interface. Reduction/oxidation reactions at depth diminished trace metal concentrations in deep pore water, and lowered the transport efficiency of Fe and Mn along seepage paths. Although an appreciable fraction of exported solutes likely returns to marsh sediments during tidal circulation, our results indicate that organic‐rich sediments provide a potentially large source of nutrients and trace elements to the coastal ecosystem.

Biochar from sewage sludge and pruning trees reduced porewater Cd, Pb and Zn concentrations in acidic, but not basic, mine soils under hydric conditions

This study aimed to assess the effectiveness of biochar from sewage sludge -BSS- and from pruning trees -BPT- (addition dose of 6% d.w.) to immobilise metals in acidic (pH ∼ 4.7) and basic (pH ∼ 7.4) mine soils under variable flooding conditions, and to determine biochar influence on plant (Sarcocornia fruticosa -Sf-) growth and metal uptake. BSS had lower pH (∼8.2 vs. ∼ 9.8), CaCO3 (∼71 vs. ∼ 85 g kg−1), total organic carbon (∼354 vs. ∼ 656 g kg−1) and higher water soluble organic carbon (WSOC ∼ 0.15 vs ∼ 0.06 mg kg−1) than BPT. PVC columns (15 × 30 cm) were prepared with the following treatments (n = 4): 1) no Biochar-no Sf; 2) no Biochar-Sf; 3) BSS-no Sf; 4) BSS-Sf; 5) BPT-no Sf; 6) BPT-Sf. Changes in water table level (WL) were simulated for 303 days with tap water (upper 0–15 cm alternating flooding-drying conditions, lower 15–30 cm always underwater). The pH, redox potential (Eh), temperature and porewater WSOC, Zn, Cd and Pb concentrations were regularly measured, and plants were removed at the end and length, fresh weight and metal concentrations in tissues measured. In the basic soil, there were no consistent evidences that BSS and BPT were effective decreasing porewater metal concentrations and reducing metal uptake in plants. Sf contributed to mobilise Zn, and in less extent Cd, in the upper soil layer, regardless of the type of biochar, and this effect increased with aging. In the acidic soil, BSS and BPT were effective increasing the pH and decreasing porewater metals. BSS increased its efficiency with aging, which can be mainly attributable to the more reduced conditions that induced (lower Eh values) due to its higher WSOC content. Biochar was effective hindering metal mobilisation by Sf and reducing plant's metal uptake (e.g. reduction in roots: ∼7 fold for Zn, ∼19-fold for Cd and ∼ 2-fold for Pb). BSS was more effective promoting Sf growth (fresh weight) than BPT. Therefore, in relation with the use of biochar from sewage sludge and from pruning trees as soil amendments under flooding-non flooding conditions, we can conclude that it can be a useful option in acidic mine soils for decreasing water soluble metals and improving plant growth. However, in basic mine soils, we have no evidences to support the advantages of using these two types of biochar as amendments. Hence, the use of biochar in metal-polluted wetlands has environmental implications that must be planned for each specific case in order to optimize the positive aspects (wetland as sinks of pollutants) and reduce the drawbacks (wetland as source of pollutants).

Relation between different metal pollution criteria in sediments and its contribution on assessing toxicity

Several tools have been developed and applied to evaluate the metal pollution status of sediments and predict their potential ecological risk assessment. To date, a comprehensive relationship between the information given by these sediment tools for predicting metal bioavailability and the effective toxicity observed is lacking. In this work, the possible inter-correlations between the data outcoming from using several qualitative evaluation tools of the sediment contamination (contamination factor, CF, the enrichment factor, EF, or the geoaccumulation index, Igeo), metal speciation on sediments (evaluated by the modified BCR sequential extraction procedure) and free metal concentrations in pore waters were studied. It was also our aim to evaluate if these assessment tools could be used for predicting the pore waters toxicity data as toxicity proxy. Principal component analysis and cluster analysis revealed that two quality indices used (CF and EF) were highly correlatable with the more labile fractions from BCR sediment speciation. However, neither of these parameters did correlate with the toxicity of pore waters measured by the chronic toxicity (72 h) in Pseudokirchneriella subcapitata. In contrast, the toxic effects of the given total metal load in sediments were better evaluated by using an additive metal approach using pore water free metal concentrations.

Effects of compost and technosol amendments on metal concentrations in a mine soil planted with Brassica juncea L.

Mining activities often cause important impacts on soil and water quality. The main objective of this study was to evaluate the effect of amendments (compost and technosol made from waste) on metal concentrations in a mine soil planted with Brassica juncea. A greenhouse experiment with cylinder pots was carried out during 11months. The mine soil was collected from the settling pond of the depleted copper mine of Touro (Galicia, Northwest Spain). A series of characteristics were analysed including soil pseudototal metal concentrations, soil CaCl2-extractable (phytoavailable) metal concentrations and metal concentrations in soil pore water. The results showed that at depth 0-15cm SCP (mine soil + compost, grown with B. juncea) had a significantly lower CaCl2-extractable Cu, Pb, Ni and Zn concentration than STP (mine soil + technosol, grown with B. juncea) over the time (P < 0.05). At depths 15, 30 and 45cm, STP and SCP had lower Cu pore water concentration than S over the time. The highest translocation factor (TF) values for all metals (Cu, Pb, Ni and Zn) were observed at time 1 (3months) in the settling pond soils treated with technosol and B. juncea L. The conclusions of this experiment revealed that SCP compared to STP caused a higher reduction on Cu, Pb, Ni and Zn phytoavailable concentrations in the first depths.

Dietary intake risks of trace metal(loid)s via maize–animal–human pathway and derivation of bioavailability-based soil criteria in Hezhang county, China

Historically metal-polluted agricultural soils are an important source of human exposure to toxic metals such as arsenic (As), cadmium (Cd), and lead (Pb) through food chains, especially in remote rural areas like Hezhang county, China. This paper aimed to investigate the processes by which a staple food crop, maize (Zea mays L.), became contaminated, identify the dominant exposure pathway and dietary intake risks, identify soils that were unsafe for growing maize, and share findings with farmers and decision-makers. A greenhouse experiment was performed using 20 historically metal-polluted soils with different soil types, properties, and contamination levels. Metal(loid) concentrations in maize grains, soil porewater (in situ), and DTPA (0.005 M) extracts of rooting-zone soils were measured to investigate the factors that influence the availability and the uptake of metal(loid)s. An investigation was performed to identify the main exposure pathway. Regression models describing metal(loid)s transfer from soils to maize grains were inversely used to derive bioavailability-based soil criteria. Soil results indicated that 28% of total Cd and 17% of total Pb in soils were potentially plant-available whereas the labile fractions in soil porewater were negligible due to high soil pH (> 7.5). For As in soils, approximately 2% was the non-specifically adsorbed fraction. Grain metal(loid)s (i.e., As, Cd, and Pb) levels were satisfactorily predicted using porewater concentrations and key properties such as pH and dissolved organic carbon contents (adj. R2 0.814 - 0.887). The bioaccumulation of As in maize was very limited. However, the level of Cd in 73% and Pb in 25% of grain samples exceeded Chinese food quality standard, thereby threatening food safety. Metal(loid)s transfer through maize → animal → human pathway would result in a substantial dietary intake of metals, e.g., 79.7 μg Pb day−1 and 217.9 μg Cd day−1. A more implementable soil criterion for DTPA-extractable Cd (0.6 mg kg−1) was derived allowing identification of soils that were unsafe for growing maize. Hezhang residents experience dietary intake risks of Pb and Cd. Excessive Cd and Pb in maize are the result of soil pollution. Soil with DTPA-extractable Cd concentration < 0.6 mg kg−1 can ensure a zero exceedance of Cd and other trace metals as well in maize. Findings are of importance to farmers and policy-makers to lower the risks of exceedance of Cd and Pb in food crops by soil management.

The porewater nutrient and heavy metal characteristics in sediment cores and their benthic fluxes in Daya Bay, South China

Nutrient and heavy metal (Fe, Mn, Ni, Cu, Pb, Zn, Cr, Cd and As) concentrations in porewater in sediment cores and their diffusive benthic fluxes were investigated in Daya Bay, South China, to study the accumulation and transfer of nutrients/metals at the sediment-water interface, and to discuss the impact of human activities on nutrients/metals. Nutrients and heavy metals displayed different profiles in porewater, which was mainly attributed to the distinct biogeochemical conditions in sediments. Total mean fluxes of nutrients (except NO3 and NO2) and metals in study area were positive, indicating nutrients and metals diffused from the sediment to overlying water, and sediment was generally the source of nutrients/metals. Human activities and the weak hydrodynamic force made nutrients/metals accumulate in sediment, so the sediment should be paid more attention to as the endogenesis of contamination in Daya Bay waters.