Effects of Platinum Nanoparticles on Rice Seedlings (Oryza sativa L.): Size-dependent Accumulation, Transformation, and Ionomic Influence.

Platinum nanoparticles (PtNPs) are increasing in the environment largely due to their wide use and application in automobile and medical industries. The mechanism of uptake behavior of different-sized PtNPs and their association with PtNPs-induced phytotoxicity to plants remains unclear. The present study investigated PtNP uptake mechanisms and phytotoxicity simultaneously to further understand the accumulation and transformation dynamics. The uptake mechanisms were investigated by comparing the uptake and toxicological effects of three different-sized PtNPs (25, 50, and 70 nm) on rice seedlings across an experimental concentration gradient (0.25, 0.5, and 1 mg/L) during germination. The quantitative and qualitative results indicated that 70 nm-sized PtNPs were more efficiently transferred in rice roots. The increase in the PtNP concentration restricted the particle uptake. Particle aggregation was common in plant cells and tended to dissolve on root surfaces. Notably, the dissolution of small particles was simultaneous with the growth of larger particles after PtNPs entered the rice tissues. Ionomic results revealed that PtNP accumulation induced element homeostasis in the shoot ionome. We observed a significant positive correlation between the PtNP concentration and Fe and B accumulation in rice shoots. Compared to particle size, the exposure concentration of PtNPs had a stronger effect on the shoot ionomic response. Our study provides better understanding of the correlation of ionomic change and NP quantitative accumulation induced by PtNPs in rice seedlings.

A state-of-the-art review on cadmium uptake, toxicity, and tolerance in rice: From physiological response to remediation process.

Cadmium (Cd), a major contaminant of concern, has been extensively reviewed and debated for its anthropogenic global shifts. Cadmium levels in rice grains raise wide food safety concerns. The aim of this review is therefore to capture the dynamics of Cd in paddy soil, translocation pathways of Cd from soil to consumption rice, and assess its bio-accessibility in human consumption. In crop plants, Cd reduces absorption of nutrients and water, triggers oxidative stress, and inhibits plant metabolism. Understanding the mechanisms and behaviour of Cd in paddy soil and rice allows to explain, predict and intervene in Cd transferability from soil to grains and human exposure. Factors affecting Cd movement in soil, and further to rice grain, are elucidated. Recently, physiological and molecular understanding of Cd transport in rice plants have been advanced. Morphological-biochemical characteristics and Cd transporters of plants in such a movement were also highlighted. Ecologically viable remediation approaches, including low input cost agronomic methods, phytoremediation and microbial bioremediation methods, are emerging.

Sedimentation of metals in Sundarban mangrove ecosystem: Dominant drivers and environmental risks.

Metal contamination from upstream river water is a threat to coastal and estuarine ecosystem. The present study was undertaken to unveil sedimentation processes and patterns of heavy metal deposition along the salinity gradient of a tropical estuary and its mangrove ecosystem. Sediment columns from three representative sites of differential salinity, anthropogenic interference, and sediment deposition pattern were sampled and analyzed for grain size distribution and metal concentrations as a function of depth. Sediments were dominantly of silty-medium sand texture. A suite of fluvial and alluvial processes, and marine depositional forcing control the sediment deposition and associated heavy metal loading in this estuary. The depth profile revealed a gradual increase in heavy metal accumulation in recent top layer sediments and smaller fractions (silt + clay), irrespective of tidal regimes. Alluvial processes and long tidal retention favor accumulation of heavy metals. Enrichment factor (0.52-15), geo-accumulation index (1.4-5.8), and average pollution load index (PLI = 2.0) indicated moderate to higher heavy metal contamination status of this estuary. This study showed that alluvial processes acted as dominant drivers for the accumulation of metals in sediments, which prevailed over the influence of marine processes. Longer tidal retention of the water column favored more accumulation of heavy metals. Metal accumulation in the sediments entails a potential risk of bioaccumulation and biomagnification through the food web, and may increasingly impact estuarine ecology, economy, and ultimately human health.

Application of biochars and solid fraction of digestate to decrease soil solution Cd, Pb and Zn concentrations in contaminated sandy soils.

Biochar prepared from waste biomass was evaluated as a soil amendment to immobilize metals in two contaminated soils. A 60-day incubation experiment was set up on a French technosol which was heavily contaminated with Pb due to former mining activities. Grass biochar, cow manure biochar (CMB) and two lightwood biochars differing in particle size distribution (LWB1 and LWB2) were amended to the soil at a rate of 2% (by mass). Rhizon soil moisture samplers were employed to assess the Pb concentrations in the soil solution at regular times. After 30 days of incubation, soil solution concentrations in the CMB-amended soil decreased by more than 99% compared to the control. CMB was also applied to a moderately contaminated Flemish soil and resulted in lowered soil solution Cd and Zn concentrations. While the application of 4% CMB resulted in 90% and 80% reductions in soil solution concentrations of Cd and Zn, respectively, the solid fraction of digestate (as a reference) reduced the soil pore water concentrations by only 63% for Cd and 73% for Zn, compared to the concentrations in the control. These results emphasize the potential of biochar to immobilize metals in soil and water systems, thus reducing their phytotoxicity.

Distribution characteristics of Cd in different types of leaves of Festuca arundinacea intercropped with Cicer arietinum L.: A new strategy to remove pollutants by harvesting senescent and dead leaves.

Although cost-effective, phytoremediation is too expensive when considering the large-scale pollution. Relative to harvesting the whole plant, it is more practicable to remove and dispose of senescent and dead leaves after phytoremediation. The phytoremediation efficiency of Festuca arundinacea for Cd was evaluated in this study, because over about 7% of the land area in China was contaminated with Cd. The accumulation, redistribution, and extraction of Cd were evaluated in different leaves of F. arundinacea intercropped with N-fixing species at different densities (Cicer arietinum L). The results showed that coordinate and malposed intercropping systems increased the dry weight of the senescent and dead leaves of F. arundinacea by 30-41% and 103-168% compared to the monoculture system, respectively. More Cd was redistributed to the senescent and dead leaves of F. arundinacea under both intercropping systems. Occupying only 22-30% of the total leaf biomass, senescent and dead leaves accumulated 74-88% of leaf Cd under different cultivation conditions. Relative to the monoculture system, intercropping decreased the amount of time needed to reduce soil Cd by 44-53%. The biomass production and Cd accumulation of F. arundinacea were higher in the malposed intercropping system, and it had higher remediation efficiency than the coordinate intercropping system. This study demonstrated that intercropping, especially malposed intercropping of F. arundinacea and C. arietinum L., is a practicable technology for leaf harvesting phytoremediation.

Watering regime influences Cd concentrations in cultivated spinach.

In washed spinach, a maximum Cd concentration of 0.20 mg/kg fresh weight (FW) is allowed according to European regulations. Producers experience that this concentration can sometimes be exceeded even on soils with baseline Cd concentrations. There is a growing need to quantify the factors determining Cd uptake in the crop in order to anticipate the risk of exceedance when selecting a field for cultivation. Interseasonal variation in precipitation may be one of the factors influencing Cd uptake by crops. A pot experiment was set up where spinach plants were subject to different watering regimes. Treatment with more limited water supply during periods of high demand resulted in significantly higher accumulated Cd concentrations (0.25-0.31 versus 0.17-0.23 mg/kg FW). Concentrations at or above the maximum allowed limit were of concern, considering that the soil used in the experiment originated from a typical field in an agricultural region without any specific contamination. Probabilities to exceed maximum concentrations in the different watering regimes were estimated using Monte Carlo simulation. Results suggested that the watering regimes significantly determine the effective risk of exceeding the maximum concentrations. Their effects may be of high practical importance in the field.

Bioaccessibility of selenium from cooked rice as determined in a simulator of the human intestinal tract (SHIME).

BACKGROUND: As an essential but also potentially toxic element, both overexposure and underexposure to selenium (Se) can significantly affect public health. Rice is a common source of Se, especially in Asia. Not all Se may be released from the rice and become available for absorption into the bloodstream upon digestion in the gastrointestinal tract. Therefore, the bioaccessibility of Se in cooked white (polished) rice was assessed in vitro using the static gastrointestinal simulator SHIME (Simulator of the Human Intestinal Microbial Ecosystem). RESULTS: The common cooking procedure in China prior to consumption [i.e. boiling at low rice:water ratios (1:3) until all of the water is absorbed into the rice] did not change total Se levels in the rice. Gastrointestinal digestion of the cooked rice matrix revealed a Se bioaccessibility of 67-76% of total Se. Subsequent microbial activity in the colon reduced the accessibility of Se in the cooked rice to 51-62%. CONCLUSION: Not all Se present in cooked white rice should be considered as being bioavailable in the small intestine. A minor part is transferred with the remaining food matrix to the colon, where it is available for the microbial metabolism. © 2017 Society of Chemical Industry.

Metal contamination in sediments of dam reservoirs: A multi-facetted generic risk assessment.

The quality of bottom sediments is a key factor for many functions of dam reservoirs, which include water supply, flood control and recreation. The aim of the study was to combine different pollution indices in a critical generic risk assessment of metal contamination of bottom sediments. Both geochemical and ecological indices reflected that sediment contamination was dominated by Zn, Pb and Cd. The ecological risk indices suggested a high riks for all three metals, whereas human health risks were high for Pb and Cd. An occasional local contamination of sediments with Cr and Ni was revealed, although at levels not expected to cause concerns about potential ecological or health risk. Sediments from the Rybnik reservoir for Cu only revealed a high potential ecological risk. EF turned to be as being the most useful, whereas TRI (∑TRI) was the most important ecological index. All multi-element indices suggested similar trends, indicating that Zn, Pb and Cd taken altogether had the greatest impact on the level of sediment contamination and posed the greatest potential ecological and health risks to organisms. The use of sequential BCR extraction and ecotoxicity analyses allowed for a multi-facetted generic risk assessment of metals in sediments of dam reservoirs.

Machine learning based prediction and experimental validation of arsenite and arsenate sorption on biochars.

Arsenic (As) contamination in water is a significant environmental concern with profound implications for human health. Accurate prediction of the adsorption capacity of arsenite [As(III)] and arsenate [As(V)] on biochar is vital for the reclamation and recycling of polluted water resources. However, comprehending the intricate mechanisms that govern arsenic accumulation on biochar remains a formidable challenge. Data from the literature on As adsorption to biochar was compiled and fed into machine learning (ML) based modelling algorithms, including AdaBoost, LGBoost, and XGBoost, in order to build models to predict the adsorption efficiency of As(III) and As(V) to biochar, based on the compositional and structural properties. The XGBoost model showed superior accuracy and performance for prediction of As adsorption efficiency (for As(III): coefficient of determination (R2) = 0.93 and root mean square error (RMSE) = 1.29; for As(V), R2 = 0.99, RMSE = 0.62). The initial concentrations of As(III) and As(V) as well as the dosage of the adsorbent were the most significant factors influencing adsorption, explaining 48 % and 66 % of the variability for As(III) and As(V), respectively. The structural properties and composition of the biochar explained 12 % and 40 %, respectively, of the variability of As(III) adsorption, and 13 % and 21 % of that of As(V). The XGBoost models were validated using experimental data. R2 values were 0.9 and 0.84, and RMSE values 6.5 and 8.90 for As(III) and As(V), respectively. The ML approach can be a valuable tool for improving the treatment of inorganic As in aqueous environments as it can help estimate the optimal adsorption conditions of As in biochar-amended water, and serve as an early warning for As-contaminated water.

Chromium (III) removal by perennial emerging macrophytes in floating treatment wetlands.

Floating treatment wetlands (FTWs) are a sustainable solution to treat polluted water, but their role in chromium (Cr(III)) removal under neutral pH conditions remains poorly understood. This study evaluated the potential of FTWs planted with two perennial emergent macrophytes, Phragmites australis and Iris pseudacorus, to remove Cr(III) and nutrients (N and PO4-P) from water containing 7.5 mg/L TN, 1.8 mg/L PO4-P, and Cr(III) (500, 1000, and 2000 µg/L). Within 1 h of exposure, up to 96-99% of Cr was removed from the solution, indicating rapid precipitation. After 50 days, Phragmites bound 9-19% of added Cr, while Iris bound 5-22%. Both species accumulated Cr primarily in the roots (BCF > 1). Biomass production and growth development were inhibited in Cr treatments, but microscopic examination of plant roots revealed no histological changes at 500 and 1000 µg/L Cr, suggesting high resistance of the tested species. At 2000 µg/L Cr, both species exhibited disruptions in the arrangement of vessel elements in the stele and increased aerenchyma spaces in Phragmites. At the end of the experiment, 70-86% of TN and 54-90% of PO4-P were removed.

Health risk-benefit assessment of the commercial red mangrove crab: Implications for a cultural delicacy.

Mangrove forests, provide vital food resources and are an endangered ecosystem worldwide due to pollution and habitat destruction. A risk-benefit assessment (RBA) was performed on the red mangrove crab (Ucides occidentalis) from the threatened Guayas mangroves in Ecuador. It was aimed to assess the combined potential adverse and beneficial health impact associated with crab consumption and define a recommended safe intake (SI) to improve the diet of the Ecuadoran population while ensuring safe food intake. Target hazard quotients (THQs), benefit quotients (Qs), and benefit-risk quotients (BRQs) were calculated based on the concentrations of the analyzed contaminants (121 pesticide residues, 11 metal(loid)s, antimicrobial drugs from 3 classes) and nutrients (fatty acids, amino acids, and essential nutrients). Except for inorganic arsenic (iAs), the THQ was below 100 for all investigated contaminants, suggesting that the average crab consumer is exposed to levels that do not impose negative non-carcinogenic or carcinogenic health effects in the long and/or short term. Concentrations of iAs (average AsIII: 25.64 and AsV: 6.28 µg/kg fw) were of the highest concern because of the potential to cause negative health effects on long-term consumption. Despite the thriving aquaculture in the Guayas estuary, concentrations of residues of the antimicrobial drugs oxytetracycline (OTC), florfenicol, and nitrofurans still were low. Based on the fact that different risk reference values exist, related to different safety levels, four SI values (0.002, 0.04, 4, and 18 crabs/day) were obtained. The strictest intake values indicate a concern for current consumption habits. In conclusion, the red mangrove crab contains various important nutrients and can be part of a balanced diet for the Ecuadorian population when consumed in limited portions. The present study emphasizes the importance of safeguarding the quality of the environment as a prerequisite for procuring nutritious and safe food.

Potential of visible and near infrared spectroscopy coupled with machine learning for predicting soil metal concentrations at the regional scale.

Chemical analytical methods for metal analysis in soils are laborious, time-consuming and costly. This paper aims to evaluate the potential of short-range (SR) and full-range (FR) visible and infrared spectroscopy (vis-NIR) combined with linear and nonlinear calibration methods to estimate concentrations of nickel (Ni), cobalt (Co), cadmium (Cd), lead (Pb) and copper (Cu) in soils. A total of 435 soil samples were collected over agricultural sites, forest (7 %), pasture (5 %) and fallow land across a region in the northern part of Belgium. Generally, better predictions were obtained when using partial least squares regression (PLSR) and nonlinear calibration method [i.e., random forest (RF)] for processing of the spectral data, than when using support vector machine (SVM). FR generally outperformed SR and provided the best prediction results for Ni (R2p = 0.76), Co (R2p = 0.77), Cd (R2p = 0.64) and Pb (R2p = 0.65), when using PLSR and RF. SVM produced the best prediction result only for Pb (R2p = 0.57) using the SR spectra. The metals Ni, Co, Cd and Pb can be predicted successfully (good accuracy) from the FR vis-NIR spectra using PLSR for Co, and RF for Ni, Cd, Pb and Cu. Compared to the FR spectrophotometer, improvement in accuracy was obtained for Cd and Co, using the SR spectra when combined with PLSR and RF, respectively. It is concluded that the SR spectrometer can be used successfully for the prediction of Co with RF (R2p = 0.70), while it best predicted Cd with PLSR with an R2p value of 0.67, which is of value for regional survey.

Cu phytoextraction and biomass utilization as essential trace element feed supplements for livestock.

Copper (Cu), as an essential element, is added to animal feed to stimulate growth and prevent disease. The forage crop alfalfa (Medicago sativa L.) produced during Cu phytoextraction may be considered a biofortified crop to substitute the Cu feed additives for livestock production, beneficially alleviating Cu contamination in soils and reducing its input into agriculture systems. To assess this, alfalfa was grown in three similar soils with different Cu levels, i.e., 11, 439 and 779 mg kg-1 for uncontaminated soil (A), moderately Cu-contaminated soil (B) and highly Cu-contaminated soil (C), respectively. EDDS (Ethylenediamine-N,N'-disuccinic acid) was applied to the soils seven days before the first cutting at four rates (0, 0.5, 2 and 5 mmol kg-1) to enhance bioavailable Cu uptake. Alfalfa grew well in soils A and B but not in the highly Cu-contaminated soil. After applying EDDS, a significant biomass reduction of the first cutting shoot was only observed with 5 mmol kg-1 EDDS in the highly Cu-contaminated soil, with a 45% (P < 0.05) decrease when compared to the control. Alfalfa grown in the three soils gradually wilted after the first cutting with 5 mmol kg-1 EDDS, and Cu concentrations in the first cutting shoot were augmented strongly, by 250% (P < 0.05), 3500% (P < 0.05) and 6700% (P < 0.05) compared to the controls, respectively. Cu concentrations in alfalfa shoots were found to be higher in this study than in some fodder plants and further augmented in soils with higher Cu levels and with EDDS application. These findings suggest that alfalfa grown on clean soils or soils with up to 450 mg Cu kg-1 (with appropriate EDDS dosages) has the potential to be considered as a partial Cu supplementation for livestock. This research laid the foundation for the integration between Cu-phytoextraction and Cu-biofortification for livestock.

The beneficial and hazardous effects of selenium on the health of the soil-plant-human system: An overview.

Selenium (Se), which can be both hazardous and beneficial to plants, animals and humans, plays a pivotal role in regulating soil-plant-human ecosystem functions. The biogeochemical behavior of Se and its environmental impact on the soil-plant-human system has received broad attention in the last decades. This review provides a comprehensive understanding of Se biogeochemistry in the soil-plant-human system. The speciation, transformation, bioavailability as well as the beneficial and hazardous effects of Se in the soil-plant-human system are summarized. Several important aspects in Se in the soil-plant-human system are detailed mentioned, including (1) strategies for biofortification in Se-deficient areas and phytoremediation of soil Se in seleniferous areas; (2) factors affecting Se uptake and transport by plants; (3) metabolic pathways of Se in the human body; (4) the interactions between Se and other trace elements in plant and animals, in particular, the detoxification of heavy metals by Se. Important research hotspots of Se biogeochemistry are outlined, including (1) the coupling of soil microbial activity and the Se biogeochemical cycle; (2) the molecular mechanism of Se metabolic in plants and animals; and (3) the application of Se isotopes as a biogeochemical tracer in research. This review provides up-to-date knowledge and guidelines on Se biogeochemistry research.

Mechanisms of cerium-induced stress in plants: A meta-analysis.

A comprehensive evaluation of the effects of cerium on plants is lacking even though cerium is extensively applied to the environment. Here, the effects of cerium on plants were meta-analyzed using a newly developed database consisting of approximately 8500 entries of published data. Cerium affects plants by acting as oxidative stressor causing hormesis, with positive effects at low concentrations and adverse effects at high doses. Production of reactive oxygen species and its linked induction of antioxidant enzymes (e.g. catalase and superoxide dismutase) and non-enzymatic antioxidants (e.g. glutathione) are major mechanisms driving plant response mechanisms. Cerium also affects redox signaling, as indicated by altered GSH/GSSG redox pair, and electrolyte leakage, Ca2+, K+, and K+/Na+, indicating an important role of K+ and Na+ homeostasis in cerium-induced stress and altered mineral (ion) balance. The responses of the plants to cerium are further extended to photosynthesis rate (A), stomatal conductance (gs), photosynthetic efficiency of PSII, electron transport rate, and quantum yield of PSII. However, photosynthesis response is regulated not only by physiological controls (e.g. gs), but also by biochemical controls, such as via changed Hill reaction and RuBisCO carboxylation. Cerium concentrations <0.1-25 mg L-1 commonly enhance chlorophyll a and b, gs, A, and plant biomass, whereas concentrations >50 mg L-1 suppress such fitness-critical traits at trait-specific concentrations. There was no evidence that cerium enhances yields. Observations were lacking for yield response to low concentrations of cerium, whereas concentrations >50 mg Kg-1 suppress yields, in line with the response of chlorophyll a and b. Cerium affects the uptake and tissue concentrations of several micro- and macro-nutrients, including heavy metals. This study enlightens the understanding of some mechanisms underlying plant responses to cerium and provides critical information that can pave the way to reducing the cerium load in the environment and its associated ecological and human health risks.

Distribution and mobilization of pollutants in the sediment of a constructed floating wetland used for treatment of combined sewer overflow events.

Sediments in combined sewer overflow treatment systems may exhibit elevated pollutant concentrations. Concentrations measured in the sediment of a floating treatment wetland ranged from 0.17 to 1.6 (cadmium), 28 to 142 (copper), 10 to 33 (chromium), 50 to 141 (manganese), 5 to 20 (nickel), 50 to 203 (lead), and 185 to 804 (zinc) mg/kg dry matter and 7.4 to 17 (iron), 2 to 8 (total nitrogen), and 1.3 to 4.4 (total phosphorus) g/kg dry matter. During overflow events, the entering water volumes can disturb the sediments. A greenhouse experiment was set up to evaluate the possible mobilization of pollutants through disturbation. The disturbation did not result in an increased mobilization of cadmium, copper, chromium, nickel, lead, zinc, nitrogen, phosphorus, and organic carbon towards the pore and surface water. Calcium concentrations in the surface water increased for all sediments, as a result of release from the exchangeable sediment pool and dissolution of carbonates. Geochemical speciation modeling indicated that, in the pore water, the free ion form was the most abundant for calcium, iron, manganese, cadmium, and nickel, with its fraction increasing with time.

Modification of ordered mesoporous carbon for removal of environmental contaminants from aqueous phase: A review.

Contamination of water bodies by potentially toxic elements and organic pollutants has aroused extensive concerns worldwide. Thus it is significant to develop effective adsorbents for removing these contaminants. As a new member of carbonaceous material families (activated carbon, biochar, and graphene), ordered mesoporous carbon (OMC) with larger specific surface area, ordered pore structure, and higher pore volume are being evaluated for their use in contaminant removal. In this paper, modification techniques of OMC were systematically reviewed for the first time. These include nonmetallic doping modification (nitrogen, sulfur, and boron) and the impregnation of nano-metals and metal oxides (iron, copper, cobalt, nickel, magnesium, and rare earth element). Reaction conditions (solution pH, reaction temperature, sorbent dosage, and contact time) are of critical importance for the removal performance of contaminants onto OMC. In addition, the pristine and modified OMC have been investigated for the removal of a range of contaminants, including cationic/anionic toxic elements and organic contaminants (synthetic dye, phenol, and others), and involving different and specific mechanisms of interaction with contaminants. The future research directions of the application of pristine and modified OMC were proposed. Overall, this review can provide sights into the modification techniques of OMC for removal of environmental contaminants.

Zn phytoextraction and recycling of alfalfa biomass as potential Zn-biofortified feed crop.

Zn is an essential micronutrient for living organisms and, in that capacity, it is added to animal feed in intensive livestock production to promote growth and eliminate diseases. Alfalfa (Medicago sativa L.) may have the potential to compensate and substitute the need for chemical Zn additives in feeds as a Zn-biofortified feed crop when grown on Zn-enriched soils. Thus, this possibility was investigated with a greenhouse experiment using three soils with Zn concentrations (mg kg-1) of 189 (soil A), 265 (soil B) and 1496 (soil C). Ethylenediamine-N,N'-disuccinate acid (EDDS) and Nitrilotriacetic acid (NTA) at different rates (0 as control, 0.5, 2 and 5 mmol kg-1) were applied as soil additives to enhance the phytoextraction efficiency of alfalfa. The results showed that Zn was highly transferable in alfalfa tissues in the three soils even without additives. EDDS was more effective than NTA in enhancing Zn phytoextraction by alfalfa. The maximum Zn accumulation in the third cutting shoots was obtained with the EDDS concentration of 5 mmol kg-1 in soil A and of 2 mmol kg-1 in soil B, with a 462% and 162% increase compared with controls, respectively. However, the higher EDDS concentration resulted in a significant reduction in biomass production. In soil C, all EDDS concentrations resulted in similar Zn accumulations in the third shoot. To improve the phytoextraction efficacy of Zn while minimizing its phytotoxicity on alfalfa, the rate of 2 mmol kg-1 EDDS proved to be optimal for soil B, and 0.5 mmol kg-1 EDDS for soils A and C. Findings suggest that phytoextraction of Zn-enriched soil can be combined with Zn biofortification, thus allowing to recycle Zn into biomass that can, to an extent, substitute Zn feed additives. This study provided a primary data set for the combination of Zn-biofortification and Zn-phytoextraction.

Speciation, transportation, and pathways of cadmium in soil-rice systems: A review on the environmental implications and remediation approaches for food safety.

Cadmium (Cd) contamination in paddy fields is a serious health concern because of its high toxicity and widespread pollution. Recently, much progress has been made in elucidating the mechanisms involved in Cd uptake, transport, and transformation from paddy soils to rice grains, aiming to mitigate the associated health risk; however, these topics have not been critically reviewed to date. Here, we summarized and reviewed the (1) geochemical distribution and speciation of Cd in soil-rice systems, (2) mobilization, uptake, and transport of Cd from soil to rice grains and the associated health risks, (3) pathways and transformation mechanisms of Cd from soil to rice grains, (4) transporters involved in reducing Cd uptake, transport, and accumulation in rice plants, (5) factors governing Cd bioavailability in paddy, and (6) comparison of remediation approaches for mitigating the environmental and health risks of Cd contamination in paddy fields. Briefly, this review presents the state of the art about the fate of Cd in paddy fields and its transport from soil to grains, contributing to a better understanding of the environmental hazards of Cd in rice ecosystems. Challenges and perspectives for controlling Cd risks in rice are thus raised. The summarized findings in this review may help to develop innovative and applicable methods for controlling Cd accumulation in rice grains and sustainably manage Cd-contaminated paddy fields.

Leaching behavior of Cd, Zn and nutrients (K, P, S) from a contaminated soil as affected by amendment with biochar.

In Campine region in Flanders (Belgium) there are contaminated sites with Cd and Zn due to atmospheric deposition from industry. Flanders is also known for its large surpluses of nitrogen and phosphorous coming from intense livestock production. To solve both issues, the potential of biochar to sorb metals and nutrients was investigated. Experiments were conducted to examine whether biochar could reduce the leaching of nutrients (K, P and S) and metals (Cd and Zn) into the soil solution. Most biochars caused an increase in pH of approximately 1 unit which is often the main driver of the metal immobilization. Nutrient concentrations in the leachate of soil amended with oak-based biochar were lower compared to the blank soil. For the other amendments, however, the results were higher due to the nutrients leached from the applied products. The result of this experiment emphasize the potential of biochar to immobilize nutrients and metals in soil water systems, thus keeping the nutrients longer available for the plant and reducing the metal toxicity. However, the amount of metals immobilized was lower than expected. Further research is required to determine whether biochar from livestock products could act as a slow release fertilizer.