Bioavailability Of Cr Research Articles

Chemical transformation and bioavailability of chromium in the contaminated soil amended with bioamendments

The biotoxicity of chromium (Cr) present in the soil is determined by the transformation and bioavailability of chemical species. A better understanding of these factors aids in developing appropriate remediation strategies for Cr contaminated soils. The present work studied the transformation of Cr in soil and the effect of bioamendments by conducting a laboratory closed incubation experiment of 60 days (duration). The physical properties of the contaminated soil were enhanced by the addition of bioamendments such as farmyard manure, composted poultry manure, pressmud compost, and biochar with two moisture conditions. The biochar reduced the bioavailable fractions of Cr due to the high surface area. Therefore, it facilitates a higher adsorption rate, whereas poultry manure and pressmud compost increased the bioavailability of Cr. The pH ranged from 7.04 to 8.25 throughout the experiment in both the condition. Comparing the other fractions, higher concentration was recorded in the residual fractions of 89.85 to 124.77 mg Kg−1 in the field capacity condition and 93.85 to 114.29 mg Kg−1 in alternate wetting and drying conditions. FTIR analyses of bio-amendments demonstrated similar variations in physicochemical characteristics wherein higher concentration was observed in biochar (3700–3200 cm −1 ). A significant reduction of bioavailable fractions of chromium was observed in biochar (80%) amended soil, followed by farmyard manure (70%). The lowest reduction was observed in the pressmud amended soils (55%). Biochar amended soil significantly reduced the fractions of Cr and increased the organic carbon; thus, it demonstrating the impacts of bioamendments on the mobilization or immobilization of Cr in the contaminated soil, and this can be effectively used in the bioremediation of Cr contaminated soil.

A remediation approach to chromium-contaminated water and soil using engineered biochar derived from peanut shell.

Hexavalent chromium (Cr[VI]) is one of the major environmental concerns due to its excessive discharge through effluents from the leather tanning industry. Peanut production leads to the generation of residual shells as waste calling for sustainable disposal. In this study, we employed an innovative approach of applying peanut-shell-derived pristine and engineered biochar for the remediation of Cr-contaminated wastewater and soil. The peanut shell waste was converted to biochar, which was further engineered with cetyltrimethylammonium bromide (CTAB, a commonly used cationic surfactant). The biochars were then used for the adsorption and immobilization of Cr(VI) in water and soil, respectively. The adsorption experiments demonstrated high Cr(VI) removal efficiency for the engineered biochar (79.35%) compared with the pristine biochar (37.47%). The Langmuir model best described the Cr(VI) adsorption onto the biochars (R2>0.97), indicating monolayer adsorption. Meanwhile, the adsorption kinetics indicated that chemisorption was the dominant mechanism of interaction between the Cr(VI) and the biochars, as indicated by the best fitting to the pseudo-second-order model (R2>0.98). Adsorption through the fixed-bed column also presented higher Cr(VI) adsorption onto the engineered biochar (qeq=22.93mgg-1) than onto the pristine biochar (qeq=18.54mgg-1). In addition, the desorption rate was higher for the pristine biochar column (13.83mgg-1) than the engineered biochar column (10.45mgg-1), indicating that Cr(VI) was more strongly adsorbed onto the engineered biochar. A higher immobilization of Cr(VI) was observed in the soil with the engineered biochar than with the pristine biochar, as was confirmed by the significant decreases in the Cr(VI) bioavailability (92%), leachability (100%), and bioaccessibility (97%) compared with the control (soil without biochar). The CTAB-engineered biochar could thus potentially be used as an efficient adsorbent for the removal and the immobilization of Cr(VI) in water and soil, respectively.

Chromium Immobilization by Polysulfide Supported Nzvi@Biochar in Contaminated Soil: Cr Bioavailability and Immobilization Mechanism

Chromium Immobilization by Polysulfide Supported Nzvi@Biochar in Contaminated Soil: Cr Bioavailability and Immobilization Mechanism

Long-term and high-bioavailable potentially toxic elements (PTEs) strongly influence the microbiota in electroplating sites

Multiple potentially toxic elements (PTEs) wastes are produced in the process of electroplating, which pollute the surrounding soils. However, the priority pollutants and critical risk factors in electroplating sites are still unclear. Hence, a typical demolished electroplating site (operation for 31 years) in the Yangtze River Delta was investigated. Results showed that the soil was severely polluted by Cr(VI) (1711.3 mg kg−1), Ni (6754.0 mg kg−1) and Pb (2784.4 mg kg−1). The spatial distribution of soil PTEs performed by ArcGIS illustrated that the soil pollution varied with plating workshops. Hard Cr electroplating workshops (HCE), decorative Cr electroplating workshops (DCE) and sludge storage station (SS) were the hot spots in the site. Besides, the toxicity characteristic leaching procedure (TCLP) - extractable Cr and Ni contents in different workshops were significantly related (P < 0.05) to their bioavailable fractions (exchangeable fraction (F1) + bound to carbonate fraction (F2)), which pose potential risk to humans. Although the soil total Pb concentration was high, its mobility was very low (<0.007%). Moreover, the soil microbial community dynamics under the stress of long term and high contents of PTEs were further revealed. The soil microbiota was significantly disturbed by long term and high concentration of PTEs. A bit of bacteria (Caulobacter) and fungi (Cladosporium and Monocillium) showed tolerance potential to multiple metals. Furthermore, the canonical correspondence analysis (CCA) showed that the bioavailable fractions (F1 + F2) of Cr and Ni were the most critical environmental variables affecting microbiota. Therefore, remediation strategies are required urgently to reduce the bioavailability of soil Cr and Ni. The results of this study provide an overview of the pollution distribution and microbial dynamics of a typical plating site, laying a foundation for ecological remediation of electroplating sites in Yangtze River Delta of China.

Se changed the component of organic chemicals and Cr bioavailability in pak choi rhizosphere soil.

Rhizosphere organic chemicals response and its role on Cr/Se adsorption are of great importance to understand Cr/Se bioavailability in Cr-contaminated soil with the application of Se. In the current work, the processes were carried out using rhizobox experiment (Brassica campestris L. ssp. chinensis Makino). The results showed that in soil contaminated by 200 mg kg-1 Cr(III), Se(IV) complexed with Cr(III) and carboxylic acid (cis-9,10-Epoxystearic acid, hexadecanedioic acid) reduced Cr(VI) to Cr(III), thus increasing of Cr adsorption, furtherly decreasing Cr bioavailability. While in soil contaminated by 120 mg kg-1 Cr(VI), Se(VI) competed for adsorption sites with Cr(VI) and salicylic acid activated insoluble Cr(III), thus decreasing Cr adsorption, finally increasing Cr bioavailability. Moreover, with Cr contamination, Se bioavailability in soil was enhanced by the secretion of carboxylic acid, which can reduce Se to lower valent state and compete the adsorption sites and complex with Se oxyanion. These results yielded a better understanding of rhizosphere dynamics regulating by Se application in Cr-contaminated soil. Moreover, the current study supplemented the theoretical basis for beneficial elements application as an environment-friendly resource to facilitate cleaner production in heavy metal contaminated soil.

Bioaccumulation of trace metals in the ocypodid burrowing crab, Paratylodiplax blephariskios, in Richards Bay Harbour, South Africa

Bioaccumulation of metals in an endemic ocypodid burrowing mud crab, Paratylodiplax blephariskios, was investigated in contaminated mudflats of the subtropical Richards Bay Harbour (RBH), South Africa. Following sampling of water, sediment and mud crabs from three sites (Bhizolo, Mzingazi and Richards Bay Coal Terminal) in RBH during 2016/2017, tissue and sediment samples were oven dried for 48 hours, weighed and digested in an advanced microwave digester. Samples were then analyzed in triplicate for Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn using inductively coupled plasma optical emission spectrometry (ICP-OES). Highest tissue concentrations of Co, Cu, Mn, Ni, Pb and Zn were recorded at Bhizolo. High Biota Sediment Accumulation Factor (BSAF) values for Cd, Cu, Mn, Ni and Zn at all sites confirmed that crabs bioaccumulated these metals. The high Cr concentration in sediment (Bhizolo: 104 ± 18.2 µg g−1; Richards Bay Coal Terminal (RBCT): 104 ± 29.2 µg g−1; Mzingazi: 94.1 ± 38.7 µg g−1) was not reflected in the biota-sediment accumulation factor (BSAF) value, suggesting low bioavailability of Cr. High BSAF values for Cd, Cu, Mn, Ni and Zn suggest that the threshold of regulation in P. blephariskios was exceeded, resulting in net bioaccumulation.

Spatial distribution, contamination assessment and potential ecological risk of some trace metals in the surface sediments of the Gulf of Tunis, North Tunisia

To evaluate the trace metals contamination status in the Gulf of Tunis, forty one sediment samples were analyzed using different approaches. According to certain contamination and ecological risk indices (Contamination Factor, Geoaccumulation index and Ecological risk index), Hg has the highest contamination level while pollution by Ni, Pb, Cd and Cr was absent. The highest concentrations of trace metals were found in sediments collected from the offshore and coastal areas located opposite the main exchange points with the gulf particularly, the Mejerda and Meliane Rivers, the Khalij Channel, Ghar El Melh and El Malah lagoons, Tunis Lake and Sebkhat Ariana. However, further ecological indices (Potential ecological risk index, Toxic unit and Mean effect-range median quotient) and comparison with sediment quality guidelines suggest that in addition to Mercury, Cr, Pb and Ni concentrations are detrimental to biota in both the offshore and areas near to the exchange points with the gulf. Moreover, in these areas the results from sequential extraction and individual contamination factor calculation pointed to the mobility and bioavailability of Cr, Pb and Ni.

Arbuscular mycorrhizal fungi modulate the chromium distribution and bioavailability in semi-aquatic habitats

• Arbuscular mycorrhizal fungi (AMF) improve the wetland plant tolerance to Cr stress. • Cr transformation from roots to shoots decrease in AMF inoculated semi-aquatic habitats. • AMF can reduce Cr bioavailability and Cr (VI) concentrations in substrates. • AMF beneficial for the reduction of Cr content in water under fluctuating water depth. Arbuscular mycorrhizal fungi (AMF) can improve plant tolerance to heavy metal stress in the terrestrial system. However, the detoxification ability of AMF to heavy metals in aquatic systems remains poorly understood. This study investigated the effects of AMF on chromium (Cr) distribution and bioavailability in semi-aquatic habitats under different water depths. Results showed that AMF increased the Cr accumulation in the roots of Iris pseudacorus by 10.0–20.0%. Conversely, Cr concentrations in the shoots of AMF inoculated I. pseudacorus were 21.7–68.4% lower than those in the non-inoculated controls. Besides, Cr concentrations and mass contents in water were decreased by 34.1–35.3% and 15.4–23.3% under the low Cr stress (5 mg kg −1 ) with AMF inoculation compare to the non-inoculated treatments, respectively. Moreover, Cr (VI) concentrations in substrates under the Cr contents of 5 mg kg −1 were 27.0–44.0% lower than those under the non-inoculated controls. Meanwhile, AMF reduced the Cr bioavailability in substrates under the fluctuating water depth (water depth of 6–3 cm), with an acid-soluble state of Cr decreased by 4.1–5.6%. Furthermore, AMF also enhanced the biomass, nutrient contents (TC, TN, Ca, Mg, Fe, and Mn) in the I. pseudacorus under the fluctuating water depth. Therefore, it provides a possibility that AMF can be used to remove heavy metals from polluted wastewater by semi-aquatic habitats under fluctuating water depth (e.g. tidal flow constructed wetlands).

Effect of wheat straw derived biochar on the bioavailability of Pb, Cd and Cr using maize as test crop

A pot experiment was conducted in the greenhouse to assess the effect of wheat straw derived biochar on the bioavailability of Pb, Cd and Cr using maize as test crop. Surface (0–20 cm) soil collected from the research farm of The University of Agriculture Peshawar was amended with 0, 2, 4 and 6% biochar respectively. Ten kg soil was placed in pots and all pots were spiked with Pb, Cd and Cr at concentrations 0, 5, 10 and 50 mg kg−1 of each element. The experiment was conducted in a completely randomized design, replicated three times. Maize seeds were sown in pots in wetter conditions. Soil and plant samples were taken at harvest time. Results show that soil Pb, Cd and Cr reduced from 15.5, 5.38 and 5.85 mg kg−1 in control to 1.34, 0.69 and 0.75 mg kg−1 respectively with application of 6% biochar when values were averaged over the contamination levels. Similarly, Pb, Cd and Cr accumulation in plant were reduced by the application of biochar as compared to control. As compared to control, there was a significant improvement in the plant growth with biochar at elevated levels of Pb, Cd and Cr in soil. Overall, the application of wheat straw biochar might be effective in immobilization of metal in the soil and reducing its uptake to plant. However, investigation of the residual effect of biochar is required for sustainable use of biochar for remediation of contaminated soil.

Effect of the reduction–mineralization synergistic mechanism of Bacillus on the remediation of hexavalent chromium

Through the synergistic effect of reduction and mineralization by Bacillus strain T124, hexavalent chromium (Cr(VI)) is reduced to a state with lower toxicity, where stable mineralization occurs, and this results in the reduction of the migration and bioavailability of Cr(VI) in the environment. In this study, a chromium (Cr)–resistant mineralization strain, Bacillus thuringiensis T124, was selected from the soil around an electroplating company, and the mechanism underlying the reduction–mineralization of Cr by this strain was studied. The reduction process mainly occurred on the cell wall membrane. The reducing enzymes were found in each component of the strain; however, a majority of them were internal. The strain could tolerate and reduce the toxicity of Cr toward itself. On fitting the data to enzyme kinetics, the K m was found to be 2925.03 μmol·L −1 , V m was 7.48 mg·(h·L) −1 , and urease activity was 66.4 U·mL −1 . The final mineralization of Cr(VI) by the strain yielded CaCO 3 and Ca 10 Cr 6 O 24 (CO 3 ). The proposed mechanism is that Cr(VI) is reduced by biological reductase, which reduces the toxicity of Cr and indirectly increases urease activity of the strain. Urease can decompose the substrate to form a CaCO 3 precipitate with Ca(II). Cr replaces a part of the lattice of CaCO 3 to mineralize Cr, thereby forming a Ca Cr coprecipitate. These minerals occupy a part of the binding site of the strain. The reduction–mineralization synergistic mechanism thus plays an important role in the immobilization of Cr(VI) on the cell wall of the strain. • Bacillus strain T124 reductase can reduce Cr(VI) to Cr(III), reducing the toxicity of Cr. • The Cr ion was captured during the formation of CaCO 3 and fixed in the lattice. • Cr(VI) can be fixed as Ca 10 Cr 6 O 24 (CO 3 ), with a good crystal form and stable structure. • The reduction-mineralization system has a synergistic effect, which can better repair Cr (VI).

Microscopic understanding about adsorption and transport of different Cr(VI) species at mineral interfaces

Cr(VI) ranks as one of the most toxic heavy metals and herein, microscopic mechanisms for adsorption and transport of different Cr(VI) oxyanions (Cr2O72- and CrO42-) at kaolinite interfaces are addressed by dispersion-corrected periodic density functional theory calculations. Cr(VI) oxyanions adsorb favorably at both tetrahedral and octahedral surfaces, and K+ ions serve as bridge for Cr(VI) oxyanions and tetrahedral surfaces while Cr(VI) oxyanions serve as bridge for K+ ions and octahedral surfaces. Adsorption structures are altered significantly by pH variation, and stability trends at different pH ranges are deciphered by the dominant interaction force with clay surfaces: Electrostatic interaction with K+ ions at tetrahedral surfaces whereas combined action of electrostatic and H-bonding interactions with Cr(VI) oxyanions at octahedral surfaces. Electron transfers are strongly pH-dependent, and clay surfaces serve as electron reservoirs. CrO42- rather than Cr2O72- is dominant at clay interfaces, and HCrO4- can co-exist under acidic conditions. Cr2O72- transformation to CrO42- is kinetically blocked at pH ≈ PZC while preferred at pH < PZC. Cr(VI) removal and reclamation should proceed at pH > 7.0 and pH < PZC, respectively. Results greatly promote the understanding about Cr(VI) bioavailability and fate in surficial environments and are also useful for Cr(VI) removal and reclamation.

Sulphur nutrition and iron plaque formation on roots of rice seedlings and their consequences for immobilisation and uptake of chromium in solution culture

The contribution of sulphur (S)-induced responses to chromium (Cr) tolerance of rice plants is not yet fully elucidated. It is hypothesised that S nutrition mitigates the accumulation and toxicity of Cr through enhanced formation of iron plaque (IP) and S-containing chelators. This study aimed to investigate the responses of iron (Fe) and Cr availability and transfer in the hydroponic rice system to added S levels. We explored the influence of S nutrition on Cr accumulation in rice under a combination of Cr (VI) (+Cr, –Cr) and S (0, 1.75, 3.5, 7 mM) treatments. S additions at rates of 1.75 and 3.5 mM gave the least decline in root and shoot growth of rice seedlings under Cr stress. Fe concentration in shoots was consistent with the level of Cr uptake. The subcellular distribution of Cr in roots and shoots differed with varying S supply levels. Our results also revealed that S treatment at a moderate level (3.5 mM) was more effective in suppressing the bioavailability of Cr in rice shoots than were the other levels. S-induced reduction in shoot Cr concentration, particularly from 1.75 to 3.5 mM, was likely attributed to the enhanced biosynthesis of glutathione (GSH) and phytochelatins (PCs) in roots than the enhanced physical resistance of IP induced by S. The poor barrier capacity of IP to Cr absorption in rice plants primarily ascribed to the level of applied Cr concentration and partly to the competition between Cr and S at the absorbing sites.

Influence of culinary treatment on the concentration and on the bioavailability of cadmium, chromium, copper, and lead in seafood

BackgroundSeafood present important advantages for human nutrition, but it can also accumulate high levels of toxic and potentially toxic elements. Culinary treatments could influence seafood chemical element content and element bioavailability. In this study, the influence of culinary treatments on the total concentration and on the bioavailability of Cd, Cr, Cu and Pb in shark, shrimp, squid, oyster, and scallop was assessed. MethodsBoiling, frying, and sautéing with or without seasonings (salt, lemon juice and garlic) were evaluated. Total concentration and bioavailability of Cd, Cr, Cu and Pb in seafood after all these culinary treatments were compared with those in uncooked samples. Analytes were determined by triple-quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS). An alternative to express the results avoiding underestimated or overestimated values was proposed. ResultsThe analytes concentration in seafood without culinary treatment varied from 0.0030 μg g−1 (shrimp) to 0.338 μg g−1 (oyster) for Cd; 0.010 μg g−1 (squid) to 0.036 μg g−1 (oyster) for Cr; 0.088 μg g−1 (scallop) to 8.63 μg g−1 (oyster) for Cu, and < 0.005 μg g−1 (shrimp, squid and oyster) to 0.020 μg g−1 (shark) for Pb. Only Cd (in scallop) was influenced by culinary treatments (reduction from 37 to 53 % after boiling, frying, and sautéing). Bioavailability percentage varied from 11% (oyster) for Cd; 18% (oyster) to 41% (shark) for Cr; 6% (shark) for Cu, and 8% (oyster) for Pb. Bioavailability percentage was not influenced by culinary treatments. ConclusionCadmium concentration was reduced in scallop after some culinary treatments (reduction o 37-53% after boiling, frying, and sautéing), but bioavailability percentage was not influenced. The employed analytical method was adequate for the purpose, presenting import results for food safety assessment about the influence of culinary treatments on metals concentration and bioavailability in seafood.

The Effect of Composting on the Multiple Heavy Metals in the River Sediment Investigated by Multivariate Analysis

This study investigated the passivation of multiple heavy metals (Cd, Cr, Cu, Zn, and Pb) in river sediments by composting with rice straw. The correlation between the selected environmental factors and the distribution of heavy metal fractions was assessed by multivariate analysis. The results suggested that the composting could reduce the bioavailability of Cu, Cd, Cr, and Pb. The influences of composting on the passivation of these five heavy metals are different. The greatest passivation of heavy metals is for Cd, which its bioavailability decreased 17.72%. The bioavailability of Cu, Pb, and Cr also partly decreased. However, there was almost no effect on the bioavailability of Zn. The results of multivariate analysis revealed that the predominant parameters affecting the variation of the bioavailability of different heavy metals were different in a complex composting system with multiple heavy metal pollution. While the variation partitioning analysis indicated that water-soluble carbon (WSC) was the statistically main factor affecting the bioavailability of Cd, Cr, Cu, Zn, and Pb. It provides a theoretical reference for optimizing the co-composting process in remediation of different heavy metal contamination in sediments.

Sorption and desorption behaviour of chromium in soils of Punjab

The present study was carried out to understand soil chromium (Cr) sorption/desorption phenomena, and hence Cr bioavailability in surface soils collected from Jalandhar, Ludhiana and Mandi Gobindgarh in Punjab. Chromium sorption isotherms were derived by sorption of Cr from solutions containing a range of concentrations equivalent to 50, 100, 300 600 and 900 μg Cr g−1 soil in the presence of a background electrolyte, 0.01 M Ca(NO3)2. Chromium desorption isotherms were derived from the Cr desorbed (μg g1 soil) after each of five desorption periods, carried out by sequentially equilibrating same soil samples used for Cr sorption study in Cr-free 0.01 M Ca(NO3)2. It was observed that with the increase in rate of Cr application, amount of Cr sorbed by the soils also increased; however, the per cent Cr sorbed decreased. The Cr sorption data of the three selected soil samples were best described by Freundlich (R2 = 0.986 to 0.994) followed by Langmuir (R2 = 0.959 to 0.995), and Dubinin-Radushkevich (D-R) adsorption isotherms (R2 = 0.926 to 0.973). The constants measuring adsorption capacity, derived from all the three adsorption isotherms, indicated that the soil from Mandi Gobindgarh has higher Cr sorption capacity than the other two soils. Desorption of Cr as well as per cent Cr desorbed from the selected soils increased with the increase in added Cr concentration. The Cr desorption data of the soils were very well described by Langmuir desorption isotherm (R2 = 0.96 to 0.99). Desorption maxima derived was also observed to be higher in case of Mandi Gobingarh soil which implies that this soil has maximum desorption capacity. The differences in amounts of Cr sorbed and desorbed by experimental soils may be due to variation in soil parameters such as organic carbon and cation exchange capacity.

Structural and physiological effects of chromium uptake in the seagrass Halophila stipulacea

This work aims to provide insight on the effects of chromium (Cr) uptake in seagrasses at environmentally relevant exposure concentrations; information on this issue can further increase the utility of marine angiosperms as indicators of trace metal contamination. Cr uptake kinetics, effects on physiological and structural cell traits, and the uptake-effects relationship in Halophila stipulacea leaves incubated in 0.01–10 mg L−1 (0.2–200 μM) of Cr (VI) were examined. An initial uptake was followed by a decrease at 0.01–0.5 mg L−1 (0.2–10 μM); at higher exposures, the fit of uptake data to a Michaelis-Menten-type equation was significant (p < 0.001). The mean tissue concentration over the exposure period, and the highest tissue concentration attained both increased as exposure concentration (Cw) increased from 0.05 to 10 mg L−1 (1 to 200 μM); uptake rate generally increased with Cw. Cytotoxic effects occurred even at 0.01 mg L−1 (0.2 μM). Actin filaments (AFs) and endoplasmic reticulum (ER) were impacted in a dose- and time- dependent pattern, while microtubule integrity was not markedly affected even at the highest exposure. AF disruption in differentiating cells initiated at 0.01 mg L−1 (0.2 μM), while ER disorganization did so at 0.1 mg L−1 (2 μM); regression equations described the relationships of Cw vs. time required for effect onset, and of Cw vs. AF disturbance progress. Elevated levels of hydrogen peroxide (H2O2) were detected on the 2d. In addition, a significant reduction in epidermal cell viability appeared at 5–10 or 10 mg L−1 (100–200 or 200 μM), depending on the leaf age. The lowest tissue concentration associated with effect onset was 31.05 μg g−1 dry wt (2d, 5 mg L−1); at lower exposures, higher tissue concentrations did not coincide with impact, implying that the uptake rate rather than the tissue concentration relates to the effect onset. The above suggest that (a) Cr (VI) may pose a high risk to seagrass meadows, (b) H. stipulacea can act as a bioindicator of ambient Cr (VI) bioavailability, mainly at elevated exposure concentrations, (c) AF and ER disturbances in seagrass leaf cells could be considered as sensitive biomarkers of Cr (VI)-induced stress, (d) regression equations describing the relationships Cw vs. time required for effect onset and Cw vs. effect progress increase the utility of AF and ER impairment as biomarkers, and (e) the time frame of the exposure should be considered in the interpretation of tissue residues. Our findings improve the utility of seagrasses as indicators of trace metal contamination and could be utilized in the overall effort for seagrass meadows conservation.

Physico-chemical properties of sediments governing the bioavailability of heavy metals in urban waterways

Bioavailability is a critical facet of metal toxicity. Although past studies have investigated the individual role of sediment physico-chemical properties in relation to the bioavailability of heavy metals, their collective effects are little-known. Further, limited knowledge exists on the contribution of nutrients to metal bioavailability. In this study, the influence of physico-chemical properties of sediments, including total organic carbon (TOC), total phosphorus (TP), total nitrogen (TN), cation exchange capacity (CEC), specific surface area (SSA), and mineralogical composition to metal bioavailability is reported. The weak-acid extraction method was used to measure Cd, Cr, Cu, Ni, Pb and Zn as the potentially bioavailable fraction in sediments in an urban creek. The results confirmed that Cu has strong selectivity for organic matter (r = 0.814, p < 0.01). Cr bioavailability was influenced by either sediment mineralogy, nutrients, CEC or SSA. Zn, Ni and Pb showed strong affinity to mineral oxides, though their preferred binding positions were with nutrients, particularly organic matter (r = 0.794, 0.809, and 0.753, p < 0.01, respectively). The adsorption of Cd was strongly influenced by the competition with other metals and its bioavailability was weakly influenced by ion exchange (CEC: r = 0.424, p < 0.01). The study results indicate that nitrogen and phosphorus compounds can elevate metal bioavailability due to complexation reactions. Generally, the estuarine area was more favourable for the adsorption of weakly-bound metals. This is concerning as estuaries generate high biogeochemical activity and are economically important.

Potential mechanisms involving the immobilization of Cd, As and Cr during swine manure composting

This study aims to investigate the relationship between key physicochemical parameters related to composting process and bioavailability of Cd, As and Cr during swine manure composting through regulating different initial carbon to nitrogen (C/N) ratios (15:1, 20:1, 25:1) and bulking agent types (straw, green waste). Results showed that higher initial C/N ratio of 20:1 or 25:1 and straw as bulking agent were optimal to reduce the bioavailability of Cd, As and Cr (62.4%, 20.6% and 32.2% reduction, respectively). Redundancy analysis implied that the bioavailability of Cd was significantly associated with total phosphorus and total nitrogen, deducing the formation of phosphate precipitation and biosorption might participated in the reaction process, while that of As and Cr were mainly influenced by organic matter (OM), cation exchange capacity (CEC) and OM, CEC, electric conductivity, respectively. A total of 48.5%, 64.6% and 62.2% of Cd, As and Cr redistribution information could be explained by the above parameters. Further correlation analysis revealed that bioavailable As and Cr were negatively correlated with humic acid to fulvic acid ratio. In summary, this study confirms that the mechanisms of phosphate precipitation, biosorption and humification played critical role in reducing Cd, As and Cr bioavailability during swine manure composting.

Heavy metals speciation study revealing merits of anaerobic co-disposal of municipal solid waste with discrete paper mill sludges: An experimental investigation in simulated landfill bioreactors

Speciation of heavy metals (Cu, Cr, Pb, Ni, Cd and Zn) during anaerobic co-disposal of two distinct paper mill sludges viz. effluent treatment plant sludge and de-inking plant sludge with municipal solid waste in anaerobic landfill bioreactor was investigated. Effects of moisture content, volatile solids and pH on fractionation of heavy metals over the course of landfilling were also analyzed. Study revealed enhancement in bioavailability of Cu, Cr, Ni and Cd on sole disposal municipal solid waste in bioreactor landfill over 300 days. However, co-disposal of effluent treatment plant sludge with municipal solid waste showed reduction in bioavailability of every analyzed heavy metals with maximum increment in stable residual forms of Cu, Cr, Pb, Ni and Zn by 3.70 %, 0.73 %, 3.08 %, 1.17 % and 3.45 % (dry weight), respectively. De-inking sludge co-disposal was also found effective for reducing bioavailability of Cu, Cd and Zn while bioavailability of Cr, Ni and Pb was unaltered. Strong correlations between increase in residual forms of heavy metals and volatile solid reduction obtained for both co-disposed bioreactors.

Impact of soaking, germination, fermentation, and thermal processing on the bioaccessibility of trace minerals from food grains

The effects of soaking, germination, fermentation, and thermal processing on the bioaccessible copper (Cu), manganese (Mn), and chromium (Cr) from selected food grains as well as from some chiefly consumed food products—idli, dosa, and dhokla were investigated. Soaking of the legumes (chickpea and green gram) and cereal–pulse combinations (rice + black gram) used for idli and dosa preparation, improved the bioaccessible Cr; however, the bioaccessible Cu and Mn were reduced. Germination improved the Cu and Cr bioaccessibility. Fermentation enhanced only the Cr bioaccessibility in idli and dosa batter. Also, cooking enhanced only the bioaccessible Cu in idli and dosa. The beneficial effects of these processing methods were more visible in Cr bioaccessibility, followed by Cu. The present study can be helpful in understanding the effects of household methods on the bioaccessibility of less understood minerals (Cu, Mn, and Cr), and thus, in developing dietary strategies. Practical applications Copper (Cu), manganese (Mn), and chromium (Cr) are the essential trace minerals required by humans for normal physiological functions. Cereals and pulses are the primary sources of these minerals. However, the bioavailabilities of these minerals from plant foods are compromised due to the presence of several antinutrients such as phytates, polyphenols, oxalates, etc. Household methods such as soaking, germination, fermentation, and thermal processing are known to affect the bioavailability of minerals both positively and negatively. However, the information on the effect of these food processing methods on Cu, Mn, and Cr is poorly documented. In this study, we reported the beneficial effect of germination and thermal processing on bioaccessible Cu, and, soaking, germination, and fermentation on bioaccessible Cr from food grains. Thus, we can recommend using these household methods to access the plant foods with higher bioavailability of essential trace minerals, Cu and Cr.