Field application of hydroxyapatite and humic acid for remediation of metal-contaminated alkaline soil.

The quality of soil is essential for ensuring the safety and quality of agricultural products. However, soils contaminated with toxic metals pose a significant threat to agricultural production and human health. Therefore, remediation of contaminated soils is an urgent task, and humic acid (HA) with hydroxyapatite (HAP) materials was applied for this study in contaminated alkaline soils to remediate Cd, Pb, Cu, and Zn. Physiochemical properties, improved BCR sequential extraction, microbial community composition in soils with superoxide dismutase (SOD), peroxidase (POD), and chlorophyll content in plants were determined. Among the studied treatments, application of HAP-HA (2:1) (T7) had the most significant impact on reducing the active forms of toxic metals from soil such as Cd, Pb, Cu, and Zn decreased by 18.59%, 9.12%, 11.83%, and 3.33%, respectively, but HAP and HA had a minor impact on metal accumulation in Juncao. HAP (T2) had a beneficial impact on reducing the TCleaf/root of Cd, Cu, and Zn, whereas HAP-HA (T5) showed the best performance for reducing Cd and Cu in EFleaf/soil. HAP-HA (T5 and T7) showed higher biomass (57.3%) and chlorophyll (17.9%), whereas HAP (T4) showed better performance in POD (25.8%) than T0 in Juncao. The bacterial diversity in soil was increased after applying amendments of various treatments and enhancing metal remediation. The combined application of HAP and HA effectively reduced active toxic metals in alkaline soil. HAP-HA mixtures notably improved soil health, plant growth, and microbial diversity, advocating for their use in remediating contaminated soils.

Application of humic acid and hydroxyapatite in Cd-contaminated alkaline maize cropland: A field trial.

Soil quality is critical to the quality and safety of agricultural products, and remediation of heavy metal contaminated soils is an urgent task to be implemented. This study applied hydroxyapatite (HAP) and humic acid (HA) as remediation materials to Cd-contaminated alkaline cropland. Data on soil pH, electrical conductivity (EC), cation exchange capacity (CEC), soil organic matter (SOM), diethylenetriamine pentaacetic acid (DTPA) extraction, and improved BCR sequential extraction were obtained for different periods. The joint application of HAP and HA enhanced the soil's buffering capacity. During the experiment, treatment groups CK, H1, H2, H3, and H4 showed changes in pH of 0.29, 0.28, 0.21, 0.24, and 0.32, respectively, and changes in the conductivity of 341.4, 183.0, 133.1, 104.6 and 320.2 µS/cm. Soil organic matter had a positive effect on soil's effective phosphorus content. HAP and HA both reduced the BCFgrain/soil of Cd for the maize, but the impact of HA was more substantial (20.19 % reduction compared to CK). HA increased the yield of maize by 44.20 %. The combination of HA and HAP was recommended.

Determination of interactions of ferrihydrite-humic acid-Pb (II) system.

Ferrihydrite often precipitates with humic acid in natural ways, affecting the fate of lead ions, the stabilization of humic acid, and the aging process of ferrihydrite. A series of 2-line ferrihydrite-humic (Fh-HA) acid with varying C loadings has been prepared, the morphology and surface properties of Fh-HA organo-minerals have been characterized, and the adsorption property of Pb ions onto Fh-HA has been studied. The results indicated that a strong interference of HA to ferrihydrite 2-line Fh dominated mineral phase in all samples, but with increasing C/Fe molar ratios, the crystallinity gradually weakened, particles became smaller, and SSA decreased significantly. The data of Mössbauer spectra confirmed C loadings changed the unit structure of ferrihydrite. Fh-HA performed good adsorption properties to Pb (II): high efficiency and big capacity, especially Fh-HA_2.0. pH had great effect on Pb (II) sorption, the pH change affects not only the amounts of competitive ions in solutions, but also the dissociation and protonation of functional groups on the surface of Fh-HA. Sorption kinetics can be well modeled by a pseudo-second-order model, and the process was controlled by film and intraparticle adsorption simultaneously. The adsorption isotherms can be well described by Freundlich isotherm model. The detailed determination results of Fe 2p, O 1 s, and Pb 4f spectra before and after lead adsorption showed mononuclear bidentate or binuclear bidentate ligands occurring on Fh-HA surface, forming stable inner-sphere complex. By comparison of Mössbauer spectra and TEM images, with aging time, a slower evolution of iron oxide/oxyhydroxide phases in Fh-HA-Pb system happened compared to pure ferrihydrite. Ferrihydrite has transformed to a combination of ferrihydrite, goethite, and hematite phases. In this study, the determination of C-Fe interaction, Pb fate influenced by Fh-HA, and transformation of ferrihydrite would have a great implication to application of Fh-HA precipitates in remediation for surface water or groundwater polluted by heavy metals.

Distributions, compositions, and ecological risk assessment of polycyclic aromatic hydrocarbons and phthalic acid esters in surface sediment of Songhua river, China.

The distribution, composition, and ecological risk of 16 types of polycyclic aromatic hydrocarbons (PAHs) and 6 types of phthalic acid esters (PAEs) in the surface sediment of Songhua river, northeast China, were investigated. The total weight of the PAHs (∑16PAHs) varied from 226.70 to 7086.62 ng/g dry weight (dw), whereas that of the PAEs (∑6PAEs) ranged from 819.44 to 24,035.39 ng/g dw. The dominant PAHs were four-membered ring PAHs, which varied from 18.65% to 78.10% of the total PAHs. The most abundant PAEs was di-2-ethylhexyl phthalate ester (DEHP), which accounted for 65.02-99.07% of the total PAEs, followed by di-n-butyl phthalate ranging from 1.50 to 55.43%. Pyrolytic origin was the dominant PAH source. Approximately 12.70% target PAHs in the Songhua river sediment exhibited moderate ecological risk with 23.49-1404.09 ng/g carcinogenic toxicity equivalent. DEHP in 80.95% of the sediment samples exceeded the effects range low, indicating its potential harmfulness to the aquatic environment.

Effect of humic acid on the stabilization of cadmium in soil by coprecipitating with ferrihydrite.

Coprecipitation of humic acid (HA) with ferrihydrite (Fh) has been proposed to reduce the activity of heavy metals in aqueous solutions. The effect of the amount of HA added to the coprecipitates on the stabilization of Cd in soil is unclear. In this research, five different Fh-HA coprecipitates were synthesized to study the impact of different HA additions on the fractionation of Cd in the soil and the optimal addition ratio of C/Fe. Characterization technique as Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), specific surface area analyzer, and scanning electron microscopy (SEM) was used in order to test and analyze of the microstructure and physicochemical property of the coprecipitates. The results showed that the Fh-HA coprecipitate is mainly combined by the coordination exchange of -OH on the surface of the Fh with the carboxyl group of the HA. Adding HA could stabilize Fh and increase its surface roughness. Changes in the fractionation of the Cd were used to evaluate the stabilization effect of the coprecipitate. Before treatment, Cd in different contaminated soils was existed only a small amount of residual fraction. After the addition of the Fh-HA coprecipitate, the proportion of residual Cd in each contaminated soil increased. When the C/Fe ratio was 1.5, the maximum residual fraction were 62.94%, 55.67%, and 52.99% respectively. Residual Cd could remain relatively stable indicating that the Fh-HA coprecipitate is a promising amendment for repairing Cd-contaminated soil. The addition of HA has strengthened the active role of Fh on stabilizing heavy metals.

[Speciation Characteristics and Bioavailability of Heavy Metals in Oasis Soil Under Pb, Zn Combined Stress].

Pot experiments were conducted on cole (Brassica) grown in oasis soil under combined stress of lead and zinc, to study the effect of heavy metal combined pollution on cole growth as well as the speciation conversion rules and bioavailability. The result showed that the promoting effect on cole growth was shown in the low concentration treatments, especially on stem leaves. With addition of exotic heavy metals, the main speciations of Pb and Zn in the soil transformed from tight-bound to loose-bound forms as compared to the control, and the bioavailability of heavy metals was increased. And, the exchangeable Pb and the carbonate bound form of Zn were the major contributing speciations which were absorbed in different parts of cole. What's more, the capabilities of uptake and translocation of Pb and Zn by cole were stronger at lower stress levels, and the enrichment and migration coefficients decreased with the increasing content of bioavailable fraction of the corresponding element or the coexisting element. In all treatments, the Pb concentration in the stem leaves of cole exceeded the food safety threshold, therefore it is recommended to conduct detection of relevant indicators before planting foliage vegetables in this kind of soil.

Induced effects of advanced oxidation processes.

Hazardous organic wastes from industrial, military, and commercial activities represent one of the greatest challenges to human beings. Advanced oxidation processes (AOPs) are alternatives to the degradation of those organic wastes. However, the knowledge about the exact mechanisms of AOPs is still incomplete. Here we report a phenomenon in the AOPs: induced effects, which is a common property of combustion reaction. Through analysis EDTA oxidation processes by Fenton and UV-Fenton system, the results indicate that, just like combustion, AOPs are typical induction reactions. One most compelling example is that pre-feeding easily oxidizable organic matter can promote the oxidation of refractory organic compound when it was treated by AOPs. Connecting AOPs to combustion, it is possible to achieve some helpful enlightenment from combustion to analyze, predict and understand AOPs. In addition, we assume that maybe other oxidation reactions also have induced effects, such as corrosion, aging and passivation. Muchmore research is necessary to reveal the possibilities of induced effects in those fields.

[Uptake effect of Cd and Pb by rape under single Cd/Pb and Cd-Pb combined stress].

This paper investigated the effects of single Cd/Pb and Cd-Pb combined pollution of desert grey soils from the oasis regions on the uptake and translocation of Cd and Pb by rape (Brassica campestris L.), and analyzed the interaction between Cd and Pb. The results of pot experiment showed that the concentration of Cd or Pb was promoted when the concentration of Cd in soil was less than 7.0 mg x kg(-1) and the concentration of Pb in soil was less than 1 500 mg x kg(-1) in single Cd/Pb and Cd-Pb combined pollution. There was an obvious antagonism between Cd and Pb in Cd-Pb combined pollution. As the concentration of Cd in soil increased in single Cd pollution, the enrichment and translocation ability of Cd in rape was firstly improved and then reduced. As the concentration of Pb in soil increased in single Pb pollution, the enrichment and translocation ability of Pb in rape was reduced continuously. The Cd-Pb combined stress reduced the enrichment capacity of Cd and Pb as well as the migration ability of Pb, but improved the migration ability of Cd. The enrichment and translocation ability of Cd was greater than that of Pb. Models of uptake and translocation of Cd and Pb in rape under single Cd/Pb and Cd-Pb combined stress were both well fitted to quadratic equations.

Bioaccumulation and translocation of cadmium in cole (Brassica campestris L.) and celery (Apium graveolens) grown in the polluted oasis soil, Northwest of China.

A pot experiment was conducted to study the bioaccumulation and translocation of cadmium (Cd) in cole (Brassica campestris L.) and celery (Apium graveolens) grown in the Cd-polluted oasis soil, Northwest of China. The results showed that Cd in the unpolluted oasis soil was mainly bound to carbonate fraction (F2) and Fe-Mn oxide fraction (F3). However, marked change of Cd fractions was observed with increasing soil Cd concentrations, in which the concentration of Cd in Fl (exchangeable fraction), F2 and F3 increased significantly (p < 0.001 for Fl, F2 and F3). The growth of cole and celery could be facilitated by low concentrations of Cd, but inhibited by high concentrations. The correlation analysis between the fraction distribution coefficient of Cd in the soil and Cd concentration accumulated in the two vegetables showed that Cd in F1 in the soil made the greatest contribution on the accumulation of Cd in the two vegetables. The high bio-concentration factor and the translocation factor of Cd in both cole and celery were observed, and Cd had higher accumulation in the edible parts of the two vegetables. Therefore, both cole and celery grown in Cd-polluted oasis soil have higher risk to human health. And the two vegetables are not suitable to be cultivated as vegetables consumed by human in the Cd-polluted oasis soil.

Chemical fractionations and bioavailability of cadmium and zinc to cole (Brassica campestris L.) grown in the multi-metals contaminated oasis soil, northwest of China.

A pot experiment was conducted to study the relationship between distribution of cadmium (Cd) and zinc (Zn) and their availability. to cole (Brassica campestris L.) grown in the multi-metal contaminated oasis soil in northwest of China. The results showed that Cd and Zn in the unpolluted oasis soil was mainly found in the residual fractionation, however, with increasing contents of Cd and Zn in the oasis soil, the distribution of Cd and Zn changed significantly. The growth of cole could be promoted by low Cd and Zn concentration, but significantly restrained by high concentrations. There was antagonistic effect among Cd and Zn in the multi-metals contaminated oasis soil. Stepwise regression analysis between fractionations distribution coefficients of the two meals in the soil and their contents in cole showed that both Cd and Zn in the exchangeable fractionation in the oasis soil made the most contribution on the uptake of Cd and Zn in cole. The bio-concentration factor (BCF) of Cd was greater than Zn in cole, and BCFs of the two metals in leaves were greater than those in roots. The translocation factors of the two metals in cole were greater than 1, and the two metals mainly accumulated in the edible parts in cole. Therefore, cole is not a suitable vegetable for the oasis soil because of the plants notable contamination by heavy metals.

Accumulation and distribution of cadmium and lead in wheat (Triticum aestivum L.) grown in contaminated soils from the oasis, north-west China.

BACKGROUND: Crops grown in soils contaminated by heavy metals are an important avenue for toxic metals entering the human food chain. The objectives of our study were to investigate the accumulation and distribution of cadmium (Cd) and lead (Pb) in wheat plants cultivated in arid soils spiked with different doses of heavy metal, as well as bioavailability of these metals in the contaminated arid soils from the oasis, north-west China. RESULTS: The concentrations of Cd in the roots of wheat plants were about 5, 14 and 8 times higher than those in the shoots, shells and grains, respectively. The concentrations of Pb in the roots were about 23, 76 and 683 times higher than those in the shoots, shells and grains, respectively. Grains contained 11-14% and 0.1-0.2% of Cd and Pb found in roots of wheat plants. The bioconcentration factor (BCF) is the ratio of metal concentration in plant tissues and metal concentration in their rooted soils. The average BCF of Cd and Pb in grains was 0.6270 and 0.0007. Cd and Pb contents in different parts of wheat plants mainly correlated with the bound-to-carbonate metal fractions in contaminated arid soils. CONCLUSION: The preliminary study indicated that Cd and Pb were predominantly accumulated and distributed in wheat roots and shoots, and only a small proportion of these metals can reach the grains. The carbonate fractions mainly contributed to Cd and Pb bioavailability in contaminated arid soils.