Sorption behavior of three aromatic acids (benzoic acid, 1-naphthoic acid and 9-anthroic acid) on biochar: Cosolvent effect in different liquid phases.

Influence of the cosolvent on the sorption of organic acids on biochar has not been well understood. For this purpose, the sorption (log Km, L kg-1) of three aromatic acids (benzoic acid (BA, pKa = 4.20), 1-naphthoic acid (1-NAPA, pKa = 3.70), and 9-anthroic acid (9-ANTA, pKa = 3.65) was evaluated as a function of methanol volume fraction (fc = 0.0, 0.25, and 0.5), liquid pH (2.5 and 7.0), ionic composition (CaCl2 and KCl) and ionic strength (0.005 M, 0.5 M, and 1 M CaCl2). A giant Miscanthus-derived biochar (ZPC of 2.86) was used as the sorbent. For all solutes, the sorption coefficients (log Km) measured at pH 2.5 (i.e., pH < pKa) tended to decrease with increasing fc, as expected from the cosolvency model, while the result obtained at pH 7.0 was not fully explained by the same model. The log Km of 1-NAPA in the CaCl2 system was always greater than in the KCl system (p < 0.05) and the impact became pronounced at high pH (>pKa) with increasing fc. Increasing the Ca2+ concentration at fc = 0.0 (from 0.005 M to 1 M) enhanced the value by 0.32 log unit of Km. These phenomena indicate a significant role of dissolved Ca2+ in the liquid phase, most likely due to the formation of cation bridges between aromatic carboxylates and the biochar surface (i.e., [R-COO--Ca2+]-{Biochar-}). A decrease in the dielectric constant of the methanol mixture could fortify the formation of this bridge. Regardless of the degree of cosolvency power (σ), as the number of aromatic rings of solutes increases, Km decreases in the order BA > 1-NAPA > 9-ANTA, where fc = 0.0. In conclusion, the sorption potential of biochar can be significantly weakened by increasing pH and fc, and in the absence of a divalent cation.

Mitigating from COVID-19 during Intercollegiate Sports Match.

The coronavirus disease 2019 pandemic has posed a significant threat not only to health outcomes but also to other societal sectors, including the educational system. Apart from youth education, colleges and universities are characterized by the integration of in-depth theoretical and practical knowledge in young adulthood. Our observations in this study suggest that college fairs, sports matches, and extracurricular activities can be safely resumed when population-level immunity has reached herd protection.

Site-specific ecological risk assessment of metal-contaminated soils based on the TRIAD approach.

Ecological risk assessment based on scientific data is crucial for understanding causal relationships between chemical pollution and environmental risks. Simultaneously, a balance is required between socioeconomic factors and scientific evidence. The TRIAD approach, which incorporates three lines of evidence (LoE)-chemical (Chem-LoE), ecotoxicological (Ecotox-LoE), and ecological (Eco-LoE)-was applied in five sites of an abandoned mine for site-specific soil ecological risk assessment (SERA). In combination, the three LoEs showed that two sites had extremely high risks, one site had moderate risk, and the other site had low risk. At all sites, Chem-LoE exhibited high-integrated risk values. In Ecotox-LoE and Eco-LoE, some species were not affected despite high metal concentrations in the soil samples collected from the sites, indicating that the bioavailability of metals differed according to the physiochemical properties of the soil medium. This study is significant as multiple analyses were performed considering ecosystem structure to reduce uncertainty in SERA. The results provide information to support effective decision-making risk management to protect the soil ecosystem. Moreover, these findings will be useful in establishing policies and priorities for soil risk management.

Multigeneration toxicity of Geunsami® (a glyphosate-based herbicide) to Allonychiurus kimi (Lee) (Collembola) from sub-individual to population levels.

Glyphosate-based herbicide (GBH) is the most widely used herbicide worldwide and has long been considered to have significantly low toxicity to non-target soil invertebrates based on short-term toxicity tests (<56 d). However, long-term GBH toxicity assessment is necessary as GBH is repeatedly applied in the same field annually because of the advent of glyphosate-resistant crops. In this study, a multigeneration test was conducted where Allonychiurus kimi (Collembola) was exposed to GBH for three generations (referred to as F0, F1, and F2) to evaluate the long-term toxic effect. The endpoints used were adult survival and juvenile production for the individual level toxicity assessment. Phospholipid profile and population age structure were the endpoints used for sub-individual and population levels, respectively. GBH was observed to have no negative effects on adult survivals of all generations, but juvenile production was found to decrease in a concentration-dependent manner, with EC50s being estimated as 572.5, 274.8, and 59.8 mg a.i. kg-1 in the F0, F1, and F2 generations, respectively. The age structure of A. kimi population produced in the test of all generations was altered by GBH exposure, mainly because of the decrease in the number of young juveniles. Further, differences between the phospholipid profiles of the control and GBH treatments became apparent over generations, with PA 16:0, PA 12:0, and PS 42:0 lipids not being detected at the highest concentration of 741 mg kg-1 in F2. Considering all our findings from sub-individual to population levels, repeated and long-term use of GBH could have significantly higher negative impacts on non-target soil organisms than expected.

Sorption of anthracene (C14H10) and 9-anthroic acid (C15H10O2) onto biochar-amended soils as affected by field aging treatments.

There is a lack of information on how aging affects the sorption of ionizable organic compounds on biochar-amended soils. To that end, this study investigates the sorption of two hydrophobic solutes (anthracene (ANT) and 9-anthroic acid (9-ANCA)) onto biochar-amended (5%, w/w) soils as a function of aging period (0, 6, and 12 months), electrolyte (5 mM CaCl2 and 10 mM KCl), and aqueous pH. The isotherm plot of both solutes was fairly linear (r2 > 0.998) and the linear sorption coefficient (Kd, L kg-1) was obtained from this. In CaCl2 solution at pH 5, the log Kd of ANT tended to decrease (from 3.90 to 3.72) with an increasing aging period, which was attributed to clogged pore surface, whereas the differences in 9-ANCA sorption (from 2.56 to 2.51) were not significant (α = 0.05). The increased ANT sorption at acidic pH (<4) could be attributed to π-π interaction. Aqueous Ca2+ ions played an important role in 9-ANCA sorption by forming a Ca-bridge between anionic solute and negatively charged adsorbent surface, thus accounting for up to 35% of its sorption at alkaline pH (>8). The spectroscopic data and isoelectric point measurement results indicated that the number of oxygen-containing functional groups and the content of elemental oxygen were both higher in aged samples, resulting in a more polar (negatively charged) surface. The formation of surface polar groups and the associated deformation altered the adsorbent nature of the tested biochar, thereby fortifying the hydrophilic retention propensity for ionizable organic solutes.

Chitosan-Grafted Halloysite Nanotubes-Fe3O4 Composite for Laccase-Immobilization and Sulfamethoxazole-Degradation.

A surface-engineered nano-support for enzyme laccase-immobilization was designed by grafting the surface of halloysite nanotubes (HNTs) with Fe3O4 nanoparticles and chitosan. Herein, HNTs were magnetized (HNTs-M) by a cost-effective reduction-precipitation method. The synthesized HNTs-M were grafted with 0.25%, 0.5%, 1%, and 2% chitosan (HNTs-M-chitosan), respectively. Synthesized HNTs-M-chitosan (0.25%), HNTs-M-chitosan (0.5%), HNTs-M-chitosan (1%) and HNTs-M-chitosan (2%) were linked with glutaraldehyde (GTA) for laccase immobilization. Among these formulations, HNTs-M-chitosan (1%) exhibited the highest laccase immobilization with 95.13% activity recovery and 100.12 mg/g of laccase loading. The optimized material was characterized thoroughly by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray powder diffraction (XRD), thermal gravimetric analysis (TGA), and vibrating sample magnetometer (VSM) analysis. The immobilized laccase (HNTs-M-chitosan (1%)-GTA-Laccase) exhibited higher pH, temperature, and storage stabilities. The HNTs-M-chitosan (1%)-GTA-Laccase possesses excellent reusability capabilities. At the end of 10 cycles of the reusability experiment, HNTs-M-chitosan (1%)-GTA-Laccase retained 59.88% of its initial activity. The immobilized laccase was utilized for redox-mediated degradation of sulfamethoxazole (SMX), resulting in 41%, 59%, and 62% degradation of SMX in the presence of 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), guaiacol (GUA), and syringaldehyde (SA), respectively. Repeated SMX degradation (57.10% after the sixth cycle) confirmed the potential of HNTs-M-chitosan (1%)-GTA-Laccase for environmental pollutant degradation. Thus, we successfully designed chitosan-based, rapidly separable super-magnetic nanotubes for efficacious enhancement of laccase biocatalysis, which can be applied as nano-supports for other enzymes.

Comparison of Ammonia Emission Estimation between Passive Sampler and Chamber System in Paddy Soil after Fertilizer Application.

Ammonia (NH3) is an important precursor for particulate secondary aerosol formation. This study was conducted to evaluate the applicability of a passive sampler (PAS) for estimating the NH3 emission from chemical fertilizer application (85 kg-N·ha-1) at field scale and to compare the results with a chamber system for the calculation of NH3 emission flux at lab scale. The application of chemical fertilizer increased the ambient NH3 concentration from 7.11 to 16.87 µg·m-3. Also, the ambient NH3 concentration measured by the PAS was found to be highly influenced by not only the chemical fertilizer application but also the weather (temperature and rainfall). Wind rose diagram data can be useful for understanding the distribution of ambient NH3 concentration. In the case of a chamber with few environmental variables, NH3 was emitted very quickly in the early stages and gradually decreased, whereas it was delayed at intervals of about one week at the site. It was found that daily temperature range, atmospheric disturbance by wind and rainfall, changes in soil moisture, and the presence of a flooded water table were the main influencing factors. The PAS data and the chamber system data were observed to have significant differences in spatial-temporal scale. In order to reduce the gap, it seems to be necessary to further develop a chamber system, in order to improve the precision of field analysis and to strengthen the connection between experimental results.

Effect of HNO3 and H2SO4 on the Paddy Ecosystem: A Mesocosm Study with Exposure at PNEC and HC50 Levels.

Paddy mesocosms comprising of rice (Oryza sativa), snail (Pomacea canaliculata), and worm (Tubifex tubifex) were used to assess the damage caused by two acids (HNO3 and H2SO4) at predicted no-effect concentration (PNEC) and hazardous concentration for 50% of species (HC50) levels. In the fourth week, the fresh weight and shoot height of O. sativa at H2SO4-HC50 were reduced by 83.2% and 30.3%, respectively. Wilted leaves (%) at HC50 were approximately twice that at PNEC. No P. canaliculata and T. tubifex were recovered at HC50. At H2SO4-PNEC, the length and weight of P. canaliculata were reduced by 7.4% and 25.9%, respectively, whereas fewer adult (46.5%) and juvenile (84%) T. tubifex were recovered. In the 20th week, rice growth and productivity were correlated with initial pH (pHi) and nitrogen levels. Poor correlation with chlorophyll at the active tillering stage suggests the disturbance of nutrient uptake by roots. Partial least squares path modeling (PLS-PM) results further supported that the pHi directly affects grain yield and quality, as well as plant growth. The indirect effect via intervening fourth-week-variables was also substantial. Therefore, it is important to measure initial pH upon acid spill to estimate the risk to the paddy ecosystem. Information on the change in soil properties associated with acidity will also aid in predicting the yield and quality of grain to be harvested.

Mechanism of simultaneous removal of aluminum and fluoride from aqueous solution by La/Mg/Si-activated carbon.

La/Mg/Si-activated carbon derived from palm shell has been a suitable material for removal of aluminum and fluoride from aqueous solution. In the study, the mechanism of simultaneous removal of aluminum and fluoride by La/Mg/Si-activated carbon (La/Mg/Si-AC) was investigated to understand its high efficiency. It was found that the removal of aluminum and fluoride by La/Mg/Si-AC was favored at lower pH compared to the point of zero charge of La/Mg/Si-AC and high temperature. Adsorption capacity of Al(OH)4- was about 10 times higher than that of F- due to the strong binding affinity of Al(OH)4- on protonated surface and competition between F- and OH- toward charged adsorption site. Kinetics results showed that the aluminum and fluoride adsorption were explained using the pseudo-second-order kinetic model and intra-particle diffusion model. Adsorption process of Al(OH)4- and F- was driven by the potential rate-limiting step involved in mass transport process occurred on the boundary diffusion layer of porous adsorbent surface. Electrostatic interaction between protonated surface of La/Mg/Si-AC and negatively charged ions (i.e., Al(OH)4- and F-) as well as ion-exchange between hydroxide and ionic metal species were important mechanisms in the process of aluminum and fluoride adsorption. Driving forces for adsorption of individual Al(OH)4- and F- were not entirely different. Identifying the dominant mechanism will be helpful in understanding the adsorption process and developing new adsorbent.

Effect of drying treatment on the leachability of metallic elements from weathered solid mine wastes.

Leaching of toxic metallic elements (Cu, Zn, As, Cd, and Pb) from two solid mine wastes was characterized under different drying treatments. During 14 batch decant-refill leaching steps, samples were intermittently dried four times in 40 °C oven or -20 °C freezer. For all leachates, the pH, pE, Fe2+/Fe3+, and SO42- were analyzed. The parameters of the two-site model (kfast, kslow, and ffast) and labile fractions (F1 + F2) were determined. High levels of toxic metallic elements were determined in waste samples; however, their leaching was limited, as evidenced by the magnitudes of F1 + F2, ffast, and kslow. Leachate solutions were acidic, at pH 3-4, and oxic, at 150 mV < Eh 300 < mV, thus having negligible Fe2+. Leachate concentrations of toxic metallic elements increased (4-58%) after drying at 40 °C and were strongly correlated (r2 = 0.780) with those of sulfate in liquid phase. The mass of element elution was in the order of 40 °C drying > -20 °C drying ≥ continuous wetting. Results indicate that the element leachability is increased through drying events and the leachate concentration is associated with the dissolution reaction of sulfur-bearing minerals. Frequent occurrence of prolonged droughts along with high temperatures over the mine waste disposal site, can enhance the leaching potential of toxic metallic elements.

Screening level ecological risk assessment of abandoned metal mines using chemical and ecotoxicological lines of evidence.

In the present study, a screening level site-specific ecological risk assessment (ERA) was conducted on 10 abandoned metal mines in Korea to determine the ecological risk and prioritize the mines requiring further investigation. A cost-saving approach was adopted by combining both the chemical (ChemLoE) and the ecotoxicological (EcotoxLoE) lines of evidence for the evaluation of integrated risk (IR), rather than applying the full spectrum of Triad, including ecological LoE. The risk values for ChemLoE were derived by calculating the toxic pressure based on the total and 0.01 M CaCl2 extractable metal(loid) concentrations. The risk values for EcotoxLoE were based on the mortality and reproduction of the collembolan species Paronychiurus kimi in the mine soils. A response surface model with a central composite design (CCD) was constructed to standardize the effects of soil physicochemical properties (i.e., organic matter content, clay content, and soil pH) on the reproduction of P. kimi. The predicted number of offspring was used as a reference for the calculation of risk value for reproduction. The ChemLoE and EcotoxLoE values ranged from 0.34 to 1.00 and 0.12 to 0.49, respectively, in the surveyed mines. The contribution of the ChemLoE value to the IR was higher than that of the EcotoxLoE value for all mines. Overall, two of the 10 mines were classified as high-risk soils with high IR values (IR > 0.76), but large deviations were also observed between the LoEs in these mines, suggesting the need for further studies to confirm the potential risks. The future investigations of these mines should focus particularly on providing additional evidence to reduce the degree of uncertainty for risk assessment.

Transfer and biological effects of arsenate from soil through a plant-aphid system to the parasitoid wasp, Aphidius colemani.

The accumulation of metalloid elements during transfer from contaminated soil to higher trophic levels may potentially result in the exposure of parasitic arthropods to toxic concentrations of these elements. This study examined the transfer of arsenate (As(V)) to aphids (Myzus persicae) from pepper plants cultivated in As(V) contaminated soils of two concentrations (2 and 6 mg As(V)/kg dry soil), and the subsequent biological effects on the aphid parasitoid, Aphidius colemani. Results showed that considerable quantities of As(V) were transferred to the plant in a concentration-dependent manner and were partitioned in the plant parts in the order of roots > stems > leaves. The accumulation of As(V) in the aphids increased with the concentrations in the plants; however, the transfer coefficient of As(V) from leaf to aphid was relatively similar and constant (0.07-0.08) at both soil As(V) concentration levels. Increased levels of As(V) significantly affected fecundity and honeydew production in aphids, but survival and developmental time were unaffected. Fecundity (mummification rate) of the parasitoid was not impaired by host As(V) contamination; however, vitality (eclosion rate) was significantly affected. Results are discussed in relation to possible ecological risks posed by the transfer of soil As(V) via the plant-arthropod system to parasitoid arthropods in agroecosystems.

Soil attenuation of the leaching potential of mine-related metallic elements (Zn, As, and Cd) under different leachate solute compositions.

Leachate from abandoned mine is frequently enriched with toxic elements but their off-site movement is not well addressed. In this study, the attenuation potential of mine-related metallic elements (Zn, As, and Cd) through downward soil was investigated using batch equilibrium sorption and seepage column studies under simulated leachate composition (single, binary, and ternary solutes in 5-mM CaSO4). In the batch result, the retention of Cd was suppressed by 40-45% in the presence of Zn while the Zn was less affected by Cd. The retention of As increased by 14-25% in the presence of both cations, with a greater effect from Zn. The phenomena were explained by the combined effects of sorption selectivity, the relative element abundance, and the operating sorption mechanism (nonspecific vs. specific). These effects also influenced the effluent element concentrations in the seepage study, as numerically indicated by a two-site model fit and moment analysis (e.g., the peak arrival time and peak concentration). For 500 PV seepage, element retention by the column (Mretention) was strongly correlated (r2 = 0.907) with the sorption constant (Kd∗) during the sorption-dominant stage, but the same correlation was poor (r2 = 0.346) during the depletion-dominant stage, due to the desorption resistance of As compared to Zn and Cd. Therefore, the attenuation of the leaching potential by surrounding soils and the effect of cosolutes dissolved in the leachate phase must be concurrently understood when assessing the off-site leaching of metallic elements from abandoned mine sites.

Factors influencing As(V) stabilization in the mine soils amended with iron-rich materials.

Chemical stability of As(V) in amended mine-impacted soils was assessed according to functions of incubation period (0, 1, 2, 4, and 6 months), amendment dose (2.5 and 5%), and application timing (0 and 3rd month). Six soils contaminated with 26-209 mg kg-1 of As(V) were collected from two abandoned mine sites and were treated with two alkaline iron-rich materials (mine discharge sludge (MS) and steel-making slag (SS)). Seventeen to 23% of As(V) in soils was labile. After each designated time, As(V) stability was assessed by the labile fractions determined with sequential extraction procedures (F1-F5). Over 6 months, a reduction (26.9-70.4%) of the two labile fractions (F1 and F2) and a quantitative increase (7.4-29.9%) of As(V) in F3 were observed (r 2 = 0.956). Two recalcitrant fractions (F4 and F5) remained unchanged. Temporal change of As(V) stability in a sample was well described by the two-domain model (k fast, k slow, and Ffast). The stabilization (%) correlated well with the fast-stabilizing domain (Ffast), clay content (%), and Fe oxide content (mg kg-1), but correlated poorly with kinetic rate constants (k fast and k slow). Until the 3rd month, the 2.5%-MS amended sample resulted in lower As(V) stabilization (25-40%) compared to the 5% sample (50-60%). However, the second 2.5% MS addition on the 2.5% sample upon the lapse of the 3rd month led to a substantial reduction (up to 38%) of labile As(V) fraction in the following 4th and 6th months. As a result, an additional 15-25% of As(V) stability was obtained when splitting the amendment dose into 3-month intervals. In conclusion, the As(V) stabilization by Fe-rich amendment is time-dependent and its efficacy can be improved by optimizing the amendment dose and its timing.

Sorption of sulfathiazole in the soil treated with giant Miscanthus-derived biochar: effect of biochar pyrolysis temperature, soil pH, and aging period.

Agricultural soil was treated with biochar (5% w/w) produced from two pyrolysis temperatures (400 and 700 °C) of giant Miscanthus (GMC-400 and GMC-700, respectively), and the subsequent sorption of sulfathiazole (STZ) was evaluated as a function of pH (2, 5, and 7) and aging period (0, 3, and 6 months). Because sorption was nonlinear, with 0.51 < N < 0.75, the linearized sorption coefficient (K d*) was used for the comparison across samples. The K d* of GMC-400 treatment (3.96-9.96 L kg-1) was higher than that of GMC-700 treatment (1.27-3.38 L kg-1). In laps of aging period over 6 months, the sorption of GMC-400-treated soil had gradually increased to be 3.3 times higher than that of untreated soil, whereas there was no statistical difference for GMC-700 treatment. Results of FTIR and SEM analyses revealed that the number of O-containing functional groups in the GMC-400 treatment increases and the micropores of GMC-700 are deformed over time. Sorption was also pH-dependent in the order of pH 2 > pH 5 > pH 7. The sorption hysteresis (H) index for the GMC-400 treatment was higher at pH 7 (3.99) than at pH 5(2.53), and both values had increased after 6 months (4.18 and 3.17, respectively). The results of this study clearly demonstrate that the sorption of STZ on GMC-treated soils is greatly enhanced, mainly through the greater micropore surfaces, the abundance of hydrophilic functional groups over time, and π+-π electron donor-acceptor interaction at low pH.

Sorption of ionic and nonionic organic solutes onto giant Miscanthus-derived biochar from methanol-water mixtures.

The sorption of naphthalene (NAP) and 1-naphthoic acid (1-NAPA) onto giant Miscanthus-derived biochar was investigated in methanol volume fractions (fc) of 0-0.6 as a function of ionic composition (5mM CaCl2 and 10mM KCl) and liquid pH (2 and 7). The sorption onto biochar was nonlinear with 0.42≤N≤0.95; thus, a concentration-specific sorption constant (Km) was compared. The Km log linearly decreased with increasing fc, except for 1-NAPA from a CaCl2 mixture at pH7. Isotherm data was fitted with a cosolvency sorption model through which the slope (ασ) of the inverse log linear Km-fc plot and empirical constant (α) were obtained. NAP sorption was well described by the cosolvency model with the α value being 0.41-0.53, indicating a methanol-biochar interaction favoring more sorption than the cosolvency based prediction. In particular, the slope (ασ) of 1-NAPA was lower than that of NAP, indicating less reduction of 1-NAPA sorption (i.e., lower α value) by methanol. In comparison with other sorbents, the α value was approximately intermediate between a humic substance and kaolinite clay. An analysis of FT-IR spectra suggested the transformation of O-containing functional groups by methanol, which will subsequently boost the π-π interaction between an organic solute and biochar. Moreover, Ca2+-induced sorption between anionic 1-NAPA and a negatively charged biochar surface was also fortified in the methanol mixture. The results revealed unexplored cosolvent effects on organic solute sorption onto biochar and identified the hydrophobic and hydrophilic sorption moieties of biochar as affected by the cosolvent.

Soil attenuation of the seepage potential of metallic elements (Cu, Zn, As(V), Cd, and Pb) at abandoned mine sites: A batch equilibrium sorption and seepage column study.

Soil attenuation of off-site leaching potential of metallic elements at the two abandoned mine sites was investigated using batch sorption and layered column studies. In batch study, the leachate concentration-specific sorption (Kd*) by downgradient clean soils was in the order of Pb>Cu>Cd>Zn>As for DY site and Pb>As>Cu>Cd>Zn for BS site. In the layered (mine+clean) soil column, element elution was significantly reduced (e.g., no initial flush, retarded peak arrival, and lower peak concentration) while sulfate elution can be an indicator of the dissolution of sulfur-bearing minerals in mine soils. The greatest reduction was observed for Pb and Cu while the lowest was for Cd (2-19%) and Zn (6-51%), consistent with the batch data. Both the reduced elution at slow seepage and concentration drop after flow interruption support the time-limited propensity. In column segments, the sorptive elements (Cu, Pb, and As) were dominantly found in the inlet while less sorptive ones (Zn and Cd) in the outlet. Both batch and column data suggest that the element leaching with mine leachate movement can be greatly attenuated by the interactions with the surrounding downgradient soil during the seepage process.

Influence of an iron-rich amendment on chemical lability and plant (Raphanus sativus L.) availability of two metallic elements (As and Pb) on mine-impacted agricultural soils.

Variation of the chemical extractability and phytoavailability of two metallic elements (e.g., As and Pb) on amendment-treated soils was investigated. Four mine-impacted agricultural soils contaminated with both As (174-491 mg kg-1) and Pb (116-357 mg kg-1) were amended with an iron-rich sludge at the rate of 5 % (w/w). After a 4-, 8-, and 16-week incubation, the extractability of metallic elements was assessed by sequential extraction procedure (SEP; F1-F5). The control without amendment was also run. In amended soils, the labile element mass (i.e., F1 + F2) promptly decreased (15-48 % of As and 5-10 % of Pb) in 4 weeks, but the decrement was continued over 16 weeks up to 70 and 28 % for As and Pb, respectively. The labile mass decrement was quantitatively corresponded with the increment of F3 (bound to amorphous metal oxides). In plant test assessed by radish (Raphanus sativus) grown on the 16-week soils, up to 57 % of As and 28 % of Pb accumulation was suppressed and 10-43 % of growth (i.e., shoot/root elongation and fresh weight) was improved. For both the control and amended soils, element uptake by plant was well correlated with their labile soil concentrations (r 2 = 0.799 and 0.499 for As and Pb, respectively). The results confirmed that the iron-rich material can effectively suppress element uptake during R. sativus seedling growth, most likely due to the chemical stabilization of metallic elements in growth medium.

Joint toxic action of binary metal mixtures of copper, manganese and nickel to Paronychiurus kimi (Collembola).

The joint toxic effects of binary metal mixtures of copper (Cu), manganese (Mn) and nickel (Ni) on reproduction of Paronhchiurus kimi (Lee) was evaluated using a toxic unit (TU) approach by judging additivity across a range of effect levels (10-90%). For all metal mixtures, the joint toxic effects of metal mixtures on reproduction of P. kimi decreased in a TU-dependent manner. The joint toxic effects of metal mixtures also changed from less than additive to more than additive at an effect level lower than or equal to 50%, while a more than additive toxic effects were apparent at higher effect levels. These results indicate that the joint toxicity of metal mixtures is substantially different from that of individual metals based on additivity. Moreover, the close relationship of toxicity to effect level suggests that it is necessary to encompass a whole range of effect levels rather than a specific effect level when judging mixture toxicity. In conclusion, the less than additive toxicity at low effect levels suggests that the additivity assumption is sufficiently conservative to warrant predicting joint toxicity of metal mixtures, which may give an additional margin of safety when setting soil quality standards for ecological risk assessment.

Removal and co-transport of Zn, As(V), and Cd during leachate seepage through downgradient mine soils: A batch sorption and column study.

The removal of Zn, As(V), and Cd during the leachate seepage process was measured in single, binary, and ternary solute systems by batch sorption and 1-D column flow experiments, followed by a sequential extraction procedure (SEP). In single-solute systems, sorption (Kd(⁎)) occurred in the order of As(V)>Zn≫Cd, and this sequence did not change in the presence of other solutes. In multi-solute systems, the sorption of Zn (~20%) and Cd (~27%) was enhanced by As(V), while Zn and Cd suppressed the sorption of each other. In all cases, As(V) sorption was not affected by the cations, indicating that As(V) is prioritized by sorption sites to a much greater degree than Zn and Cd. Element retention by column soils was strongly correlated (r(2)=0.77) with Kd(⁎). Across column segments, mass retention was in the order of inlet (36-54%)>middle (26-35%)>outlet (20-31%), except for Cd in the Zn-Cd binary system. The result of SEP revealed that most of the retained Cd (98-99%) and Zn (56-71%) was in the labile fraction (e.g., the sum of F1 and F2) while only 9-12% of As(V) was labile and most (>55%) was specifically adsorbed to Fe/Al oxides. Plots of the labile fraction (f(labile)) and the fast sorption fraction (f(fast)) suggested that the kinetics of specific As(V) sorption occur rapidly (f(fast)>f(labile)), whereas labile Zn and Cd sorption occurs slowly (f(labile)>f(fast)), indicating the occurrence of kinetically limited labile sorption sites, probably due to Zn-Cd competition. In conclusion, the element leaching potential of mine leachate can be greatly attenuated during downgradient soil seepage. However, when assessing the soil attenuation process, the impact of sorption competitors and the lability of adsorbed elements should first be considered.