Pollution assessment and spatial variation of soil heavy metals in Lixia River Region of Eastern China

Purpose

The effect of soil heavy metals on crops and human health is an important research topic in some fields (Agriculture, Ecology et al.). In this paper, the objective is to understand the pollution status and spatial variability of soil heavy metals in this study area. These results can help decision-makers apportion possible soil heavy metal sources and formulate pollution control policies, effective soil remediation, and management strategies.

Materials and methods

A total of 212 topsoil samples (0–20 cm) were collected and analyzed for eight heavy metals (Cd, Hg, As, Cu, Pb, Cr, Zn, and Ni) from agricultural areas of Yingbao County in Lixia River Region of Eastern China, by using four indices (pollution index (PI), Nemerow pollution index (PI_N), index of geo-accumulation (I _geo), E _i /risk index (RI)) and cluster analysis to assess pollution level and ecological risk level of soil heavy metals and combining with geostatistics to analyze the concentration change of heavy metals in soils. GS+ software was used to analyze the spatial variation of soil heavy metals, and the semi-variogram model is the main tool to calculate the spatial variability and provide the input parameters for the spatial interpolation of kriging. Arcgis software was used to draw the spatial distribution of soil heavy metals.

Results and discussion

The result indicated that the eight heavy metals in soils of this area had moderate variations, with CVs ranging from 23.51 to 64.37 %. Single pollution index and Nemerow pollution index showed that about 2.7 and 1.36 % of soil sampling sites were moderately polluted by Cd and Zn, respectively. The pollution level of soil heavy metals decreased in the order of Cd?>?Zn?>?Pb?>?As?>?Cu?>?Cr?>?Ni?>?Hg. The I _geo values of heavy metals in this area decreased in the order of Zn?>?Cd?>?As?>?Pb?>?Cu?>?Cr?>?Hg?>?Ni. According to the E _i index, except Cd that was in the moderate ecological risk status, other heavy metals in soils were in the light ecological risk status, and the level of potential ecological risk (RI) of soil sampling sites of the whole area was light.

Conclusions

The results of four indices and the analysis of spatial variation indicated that the contents of Cd and Zn were contributed mainly by anthropogenic activities and located in the south-east of this study area. However, the contents of Hg, As, Cu, Pb, Cr, and Ni in soils were primarily influenced by soil parent materials.

     

Heavy metal content and toxicity of mine and quarry soils

Purpose

Soils formed in metallic mines and serpentinite quarries, among other unfavourable features, have high levels of heavy metals. They can release into the environment causing surface and subsurface water contamination, uptake by plants, their accumulation in the food chain and adverse effects on living organisms. In this work, we studied the magnitude of the soils’ toxic effects not only on spontaneous plants but also on two species with phytoremediation potential.

Materials and methods

Several soils from two different exploitations were selected: a lead and zinc mine and a serpentinite quarry. Soils were characterized, and the pseudo-total and extractable contents of Co, Cr and Ni in soils from a serpentinite quarry were determined. The Cd, Pb and Zn pseudo-total and extractable contents were determined in soils developed in the Pb/Zn abandoned mine. Using a biotest, the chronic toxicity of the soil samples on higher plants was determined. Festuca ovina L., Cytisus scoparius (L.) Link., Sinapis alba L. and Brassica juncea L. were selected, the first two because they are spontaneous plants in the study areas and the last two because they have heavy metal phytoremediation potential.

Results and discussion

Pseudo-total contents of Co, Cr and Ni in the serpentinite quarry soils and of Zn, Pb and Cd in the Zn/Pb mine soils exceed generic reference levels. CaCl₂ is the reactant that extracts the highest proportion of Co, Cr and Ni in the quarry soils and EDTA the largest proportion of Pb Zn and Cd content in the mine soils. The germination index values based on seed germination and root elongation bioassays revealed increasing plant sensitivity to the mine soils in the following order: B. juncea?<?S. alba?<?F. ovina?<?C. scoparius. The wide range of GI values indicates that the response of test plants to soil heavy metals depended on their concentrations and soil characteristics, especially pH and organic matter content.

Conclusions

The pollution index indicates severe Cd, Pb and Zn contamination in the mine soils, as well as high Cr and Ni and moderate Co contamination in the serpentinite quarry soils. The performed biotests were suitable for identifying toxic soils and showed that the studied soils are toxic to the spontaneous plants, more to C. scoparius than to F. ovina. They also indicate that the mine soils are more toxic than the quarry soils for both species.

     

Effect of aerotechnogenic emissions on the content of heavy metals in herbaceous plants of the Lower Don region

The effect of soil properties and distance from the source of technogenic emission on the input of Pb, Zn, Cd, Cu, Mn, Cr, and Ni into daisy family plants (Asteraceae) has been studied. It has been found that the high level of anthropogenic load related to the atmospheric emissions from the Novocherkassk power plant (NPP) favors the accumulation of heavy metals (HMs) in herbaceous plants. Contamination with Pb, Cd, Cr, and Ni is revealed in plants growing near the NPP. The main factors affecting the distribution of HMs in the above- and underground organs of plants include individual physiological features of plant species controlling the barrier functions of different plant organs. Ambrosia artemisiifolia L., Artemisia austriaca Pall. ex. Wild. Jack., and Tanacetum vulgare L. are accumulators of HMs. The resistance of herbaceous plants to pollution has been determined from the acropetal coefficient and actual biogeochemical mobility of HMs. Ambrosia artemisiifolia L. is most resistant to contamination with Mn; Achillea nobilis L. is most resistant to Pb, Ni, and Cd; Cichorium intybus L. is most resistant to Zn and Cu.     

Bioavailability of Cd and Zn in soils treated with biochars derived from tobacco stalk and dead pigs

Purpose

Previous studies show that application of biochar can reduce the bioavailability of heavy metals in soil. A plant growth experiment was carried out to evaluate the effect of tobacco stalk- and dead pig-derived biochars on the extractability and redistribution of cadmium (Cd) and zinc (Zn) in contaminated soil, and the impact on tobacco (Nicotiana tabacum L.) plant growth.

Materials and methods

The top 20 cm of a soil contaminated with Cd and Zn was used in this study. Biochars derived from tobacco stalk and dead pig were applied to the soil at four application rates (0, 1, 2.5, and 5 %), and tobacco plants were grown. After 80-days growth, the pH, electrical conductivity (EC), CaCl₂-extractable heavy metals and fractions of heavy metals in soil samples, as well as the plant biomass and the concentrations of heavy metals in the plant were determined.

Results and discussion

The plant growth experiment demonstrated that tobacco stalk biochar and dead pig biochar significantly (P?<?0.05) increased the pH, but had no significant effect on the electrical conductivity (EC) of the soil. The CaCl₂-extractable Cd and Zn content decreased as the application rates increased. The concentration of extractable Cd and Zn decreased by 64.2 and 94.9 %, respectively, for the tobacco stalk biochar treatment, and 45.8 and 61.8 %, respectively, for the dead pig biochar treatment at 5 % application rate. After biochar addition, the exchangeable Cd was mainly transformed to fractions bound to carbonates and Fe-Mn oxides, while the Zn was immobilized mainly in the fraction bound to Fe-Mn oxides. Tobacco stalk biochar increased the tobacco plant biomass by 30.3 and 36.2 % for shoot and root, respectively at the 5 % application rate. Dead pig biochar increased the tobacco plant biomass by 43.5 and 40.9 % for shoot and root, respectively, at the 2.5 % application rate. Both biochars significantly (P?<?0.05) decreased the Cd and Zn accumulation by tobacco plant.

Conclusions

As a soil amendment, tobacco stalk biochar was more effective at removing Cd, whereas dead pig biochar was more effective at removing Zn, and a higher application rate was more effective than a lower application rate. Overall, biochar derived from tobacco stalk was more effective, than dead pig biochar, at remediating soil contaminated with Cd and Zn, as well as promoting tobacco growth.

     

Effect of the Simultaneous Action of Zinc and Chromium on <Emphasis Type="Italic">Arthrobacter</Emphasis> spp.

Bacteria are regarded as the most effective in the detoxification of heavy metals, being environmental compatible. Metalloresistant bacteria are usually found in nature in highly contaminated environment where they interact with a combination of several toxic metals. For the present research, Arthrobacter oxydans and Arthrobacter globiformis have been isolated from the soil samples of the most polluted regions of Georgia, rich with manganese and iron, and contain co-produced toxic metals such as Cr, V, Zn, Ni, Pb, and Mo. We have studied the effects of the metals with different valence/charge on the metalloresistant Arthrobacter spp., the divalent cation—Zn(II) and the hexavalent anion—Cr(VI). The permanent presence of a nontoxic concentration of zinc alone or zinc together with the subtoxic concentration of chromium at the growth of A. oxydans and A. globiformis as batch culture causes the activation of the zinc primary uptake system transporters from the ZIP family (Zrt1). Chromium does not affect the process. The studied Arthrobacter spp. differ by the character of the activation of the antioxidant defense system. Chromium and zinc concomitant action causes the strongest oxidative stress in the case of A. globiformis that is demonstrated by the increased activity of superoxide dismutase (SOD) and catalase. In the case of A. oxydans, the zinc separate action, and the joint action of zinc and chromium decreases the activity of SOD and catalase. The antioxidant system is active in A. globiformis at the prolonged action of metals (96 h), whereas the cells of A. oxyidans activate the other defense mechanisms to survive.     

Rhizosphere effects of <Emphasis Type="Italic">Populus euramericana</Emphasis> Dorskamp on the mobility of Zn,Pb and Cd in contaminated technosols

Purpose

This study aimed at investigating the rhizosphere effects of Populus euramericana Dorskamp on the mobility of Zn, Pb and Cd in contaminated technosols from a former smelting site.

Materials and methods

A rhizobox experiment was conducted with poplars, where the plant stem cuttings were grown in contaminated technosols for 2 months under glasshouse conditions. After plant growth, rhizosphere and bulk soil pore water (SPW) were sampled together. SPW properties such as pH, dissolved organic carbon (DOC) and total dissolved concentrations of Zn, Pb and Cd were determined. The concentrations of Zn, Pb and Cd in plant organs were also determined.

Results and discussion

Rhizosphere SPW pH increased for all studied soils by 0.3 to 0.6 units compared to bulk soils. A significant increase was also observed for DOC concentrations regardless of the soil type or total metal concentrations, which might be attributed to the plant root activity. For all studied soils, the rhizosphere SPW metal concentrations decreased significantly after plant growth compared to bulk soils which might be attributed to the increase in pH and effects of root exudates. Zn, Pb and Cd accumulated in plant organs and the higher metal concentrations were found in plant roots compared to plant shoots.

Conclusions

The restricted transfer of the studied metals to the plant shoots confirms the potential role of this species in the immobilization of these metals. Thus, P. euramericana Dorskamp can be used for phytostabilization of technosols.

     

Leachability of cadmium, lead, and zinc in a long-term spontaneously revegetated slag heap: implications for phytostabilization

Purpose

For abandoned slag heaps, the spontaneous establishment of a vegetation cover is usually considered beneficial as it represents a means of phytostabilization. However, for slag containing heavy metals, such a vegetation cover has a potential long-term effect on the fate of the metals. The objective of this study was to investigate how the long-term spontaneous revegetation of a slag heap can affect the fractionation and the leachability of Cd, Zn, and Pb.

Materials and methods

Soils from two plots covered by either Armeria maritima or Agrostis tenuis and a bare plot soil were sampled from a slag heap from a zinc smelting plant and characterized. The Community Bureau of Reference (BCR) sequential extraction scheme was adopted to determine the metal pools. The leachability of Cd, Pb, and Zn was assessed by means of a leaching column experiment.

Results and discussion

Long-term presence of a plant cover increased the proportion of Zn in the most mobile fraction and Pb in the fraction bound to organic matter. Cd distribution was relatively unaffected. Overall, the metal leachability was enhanced in the revegetated soils, notably due to higher organic anion release. However, responses of metal behavior to revegetation depended on the established plant species. The highest leachability of Cd was found in the soil covered by Agrostis tenuis, while the highest leachability of both Zn and Pb was observed in the soil below Armeria maritima.

Conclusions

Any remediation strategy for metal-rich waste dumps by phytostabilization should take into careful consideration the potential long-term mobilization effect of plant establishment on heavy metals. We conclude that, when using pioneer plants for phytostabilization purposes, preference should be given to pseudo-metallophyte over hyperaccumulator species.     

Land contamination by toxic elements in abandoned mine areas in Italy

Purpose

The present paper concerns the distribution and mobility of heavy metals (Cu, Pb, Zn and Fe) in the soils of some abandoned mine sites in Italy and their transfer to wild flora.

Materials and methods

Soils and plants were sampled from mixed sulphide mine dumps in different parts of Italy, and the concentrations of heavy metals were determined.

Results and discussion

The phytoremediation ability of Salix species (Salix eleagnos, Salix purpurea and Salix caprea), Taraxacum officinale and P?lantago major for heavy metals and, in particular, zinc was estimated. The results showed that soils affected by mining activities presented total Zn, Cu, Pb and Fe concentrations above the internationally recommended permissible limits. A highly significant correlation occurred between metal concentrations in soils.

Conclusions

The obtained results confirmed the environmental effects of mine waste; exploring wild flora ability to absorb metals, besides metal exploitation, proved a useful tool for planning possible remediation projects.

     

Effects of biochar on Cd and Pb mobility and microbial community composition in a calcareous soil planted with tobacco

An experiment was conducted with tobacco (Nicotiana tabacum L.) grown in a Cd- and Pb-contaminated calcareous soil amended with 0.0, 1.0, 2.5, and 5.0% (w/w) tobacco stalk biochar (BC). The BC amendment significantly increased organic matter, total C, N, P, and K contents of soil, and the C/N ratio. Bioavailable metal concentrations (DTPA extraction) decreased by increasing BC application rate. The 5.0% BC amendment significantly decreased the DTPA-extractable Cd and Pb by 10.4 and 13.6%, respectively. Correspondingly, the bioaccumulation and translocation factors of Cd and Pb also decreased by increasing the BC addition rates and this indicated that BC inhibited the uptake and transfer of both Cd and Pb by tobacco plants. Moreover, high-throughput sequencing revealed that BC increased Chao1 richness, Shannon’s diversity and Simpson’s diversity of bacterial communities of soil. The relative abundance and genera composition of Adhaeribacter, Rhodoplanes, Pseudoxanthomonas, and Candidatus Xiphinematobacter increased under BC treatments, while those of Kaistobacter, Lacibacter, and Pirellula decreased. Overall, BC increased soil nutrients (C, N, P, and K contents), enhanced bacterial diversity indexes and richness, and changed the bacterial community composition, which may all have contributed to reduce the mobility and bioavailability of both Cd and Pb in a calcareous soil.     

Assessment of heavy metal tolerance in two plant species growing in experimental disturbed polluted urban soil

Purpose

Urban soil, which is strongly influenced by anthropogenic activities, receives a major proportion of trace metal wastes. The aim of this work was to determine heavy metal concentration in (a) soil, to know the degree of the soil pollution; (b) roots and leaves of two plant species, Brassica juncea as an accumulator plant and Solanum lycopersicum as a crop plant; and (c) drainage water, to evaluate the heavy metal mobility.

Materials and methods

The study area is located in Sants, a neighborhood in Barcelona (Catalonia, Spain). Thirty kilograms of two representative soil depths (0–15 and 15–40 cm) was sampled and subsequently mixed. The two studied species were cultivated for 3 weeks in greenhouse conditions, and all pots were irrigated with water weekly to field capacity with a nutrient solution (pH = 6.5). If not otherwise stated, given results are means ± standard deviation of four replicated pots each with a composite sample of 12 individual plants per treatment. X-ray fluorescence (FRX) and diethylenetriaminepentaacetic acid soil extraction (DTPA) were used for total and available metal soil contents, respectively. Weekly cumulative drainage water of each pot was collected in polyethylene bottles and stored at 4 °C until analysis.

Results and discussion

The main pollutants are Cu, Pb, and Zn with topsoil total concentrations of approximately 1355, 2230, and 6239 mg kg^?1, respectively. The same soil elements for available fractions were slightly elevated (9.6, 5.8, and 6.7% of total concentration). The concentrations of Cu, Pb, and Zn in the plants’ leaves are greater in B. juncea than in S. lycopersicum. Furthermore, they are greater in the roots than in leaves. The Pb concentrations in a crop plant exceeded the 0.10 mg kg^?1 limit established for vegetables devoted for food in the European legislation. Unusually elevated concentrations of Pb (over 10 μg L^?1) were detected in the drainage water. These values exceeded the acceptable toxic concentrations in waters, according to the Spanish legislation.

Conclusions

The urban soil studied was highly contaminated by Cu, Pb, and Zn, and this pollution is more evident in the topsoil. A great part of these heavy metals was bioavailable for plants. Thus, the two plants (S. lycopersicum and B. juncea) had an ability to transport heavy metals from the roots to the shoots, especially for Zn. Great contents of heavy metals in the drainage water after the irrigation of plants were observed.

     

Combined bioremediation of soil co-contaminated with cadmium and endosulfan by <Emphasis Type="Italic">Pleurotus eryngii</Emphasis> and <Emphasis Type="Italic">Coprinus comatus</Emphasis>

Purpose

The subjects of this study were to investigate the remediating potential of the co-cultivation of Pleurotus eryngii and Coprinus comatus on soil that is co-contaminated with heavy metal (cadmium (Cd)) and organic pollutant (endosulfan), and the effects of the co-cultivated mushrooms on soil biochemical indicators, such as laccase enzyme activity and bacterial counts.

Materials and methods

A pot experiment was conducted to investigate the combined bioremediation effects on co-contaminated soil. After the mature fruiting bodies were harvested from each pot, the biomass of mushrooms was recorded. In addition, bacterial counts and laccase enzyme activity in soil were determined. The content of Cd in mushrooms and soil was detected by the flame atomic absorption spectrometry (FAAS), and the variations of Cd fractions in soil were determined following the modified BCR sequential extraction procedure. Besides, the residual endosulfan in soil was detected by gas chromatography-mass spectrometry (GC-MS).

Results and discussion

The results indicated that co-cultivation of P. eryngii and C. comatus exerted the best remediation effect on the co-contaminated soil. The biomass of mushroom in the co-cultivated group (T group) was 1.57–13.20 and 19.75–56.64% higher than the group individually cultivated with P. eryngii (P group) or C. comatus (C group), respectively. The concentrations of Cd in the fruiting bodies of mushrooms were 1.83–3.06, 1.04–2.28, and 0.67–2.60 mg/kg in T, P, and C groups, respectively. Besides, the removal rates of endosulfan in all treatments exceeded 87%. The best bioremediation effect in T group might be caused by the mutual promotion of these two kinds of mushrooms.

Conclusions

The biomass of mushroom, laccase activity, bacterial counts, and Cd content in mushrooms were significantly enhanced, and the dissipation effect of endosulfan was slightly higher in the co-cultivated group than in the individually cultivated groups. In this study, the effect of co-cultivated macro fungi P. eryngii and C. comatus on the remediation of Cd and endosulfan co-contaminated soil was firstly reported, and the results are important for a better understanding of the co-remediation for co-contaminated soil.

     

Effect of <Emphasis Type="Italic">Silene vulgaris</Emphasis> and Heavy Metal Pollution on Soil Microbial Diversity in Long-Term Contaminated Soil

In this study, we analysed the impact of heavy metals and plant rhizodeposition on the structure of indigenous microbial communities in rhizosphere and bulk soil that had been exposed to heavy metals for more than 150 years. Samples of the rhizosphere of Silene vulgaris and non-rhizosphere soils 250 and 450 m from the source of emission that had different metal concentrations were collected for analyses. The results showed that soils were collected 250 m from the smelter had a higher number of Cd-resistant CFU compared with the samples that were collected from 450 m, but no significant differences were observed in the number of total and oligotrophic CFU or the equivalent cell numbers between rhizosphere and non-rhizosphere soils that were taken 250 and 450 m from the emitter. Unweighted pair group method with arithmetic mean (UPGMA) cluster analysis of the denaturing gradient gel electrophoresis (DGGE) profiles, as well as a cluster analysis that was generated on the phospholipid fatty acid (PLFA) profiles, showed that the bacterial community structure of rhizosphere soils depended more on the plant than on the distance and metal concentrations. The sequencing of the 16S rDNA fragments that were excised from the DGGE gel revealed representatives of the phyla Bacteroidetes, Acidobacteria, Gemmatimonadetes, Actinobacteria and Betaproteobacteria in the analysed soil with a predominance of the first three groups. The obtained results demonstrated that the presence of S. vulgaris did not affect the number of CFUs, except for those of Cd-resistant bacteria. However, the presence of S. vulgaris altered the soil bacterial community structure, regardless of the sampling site, which supported the thesis that plants have a higher impact on soil microbial community than metal contamination.     

Assessing the influence of technosol and biochar amendments combined with <Emphasis Type="Italic">Brassica juncea</Emphasis> L. on the fractionation of Cu,Ni, Pb and Zn in a polluted mine soil

Purpose

Soil metal pollution is a widespread problem around the world and remediation of these soils is difficult. The objective of this study was to investigate the effect of two different strategies on the chemical fractions of metals in a soil of a depleted copper mine: (1) amending with a mixture of a technosol made of wastes and biochar and (2) amending combined with planting vegetation (Brassica juncea).

Materials and methods

A 3-month greenhouse experiment was carried out to evaluate the effects of organic amendments and vegetation on the metal fractionation of Cu, Ni, Pb and Zn in a mine soil of the depleted copper mine at Touro (Spain). We compared the influence of organic amendments alone (technosol?+?biochar) and combined with mustard plants (Brassica juncea L.).

Results and discussion

The results showed that amending with a technosol made of wastes promoted plant growth (from 0.7 to 2.9 g of biomass produced) and reduced the CaCl₂-extractable metal concentration in soil, reduced the mobility factor of Cu from 18.3 to 1.6, Ni from 47.5 to 2.3 and Pb from 17.9 to 2.1, and also reduced the concentration of metals in the mobile soil fractions. It was not possible to grow up Brassica juncea plants in the untreated settling pond soil due to the extremely degraded conditions of that soil. However, the application of the used technosol increased the Pb and Zn pseudototal concentrations in the amended soils.

Conclusions

We conclude that the combination of amending with wastes and planting B. juncea provides little additional benefit for remediating a metal-polluted soil compared with incorporation of wastes alone.

     

Concentrations of potentially toxic elements and soil environmental quality evaluation of a typical Prosecco vineyard of the Veneto region (NE Italy)

Purpose

The aim of this work was to assess the concentrations of potentially toxic elements and to evaluate the soil quality of a typical Prosecco Denomination of Controlled and Guaranteed Origin vineyard of the Veneto region, NE Italy.

Materials and methods

Soil samples and leaves of Taraxacum officinale and Vitis vinifera were collected during spring–summer 2014. Element determination (Al, Cd, Cr, Cu, Fe, Mg, Mn, Ni, P, Pb, V, and Zn) were performed with ICP-OES after microwave digestion of samples. Soil quality was assessed via the biological soil quality (BSQ-ar) index. Lipid peroxidation test was performed to evaluate the vegetation oxidative stress, based on malondialdehyde (MDA) content via spectrophotometer.

Results and discussion

High concentrations of Al, Mg, and P were identified in soil, while high contents of Al, Cu, Fe, and Zn were found in V. vinifera leaves. The high concentrations in soil are probably due to agricultural activities, whereas those in leaves are probably due to atmospheric deposition and repeated use of foliar sprays in viticulture. The bioconcentration factor showed an effective transport of Cu, P, and Zn, from soil to leaf. The BSQ-ar values registered were similar to those obtained in preserved soils; hence, the biological class (VI) of these soils is high. The MDA content in T. officinale and V. vinifera leaves was below the reference value for T. officinale (2.9?±?0.2 μM), suggesting that the metal content did not stress the vegetation in the investigated site.

Conclusions

The MDA value for V. vinifera (1.1?±?0.7 μM) could be adopted as another control value for soil quality, which in our case is of “good quality.” Moreover, our results suggest that high concentrations of elements detected in the analyzed samples do not influence negatively the quality of soil, but a better agronomic management could improve soil quality in the studied area.

     

Application of Response Surface Methodology and Machine Learning Combined with Data Simulation to Metal Determination of Freshwater Sediment

A comparative study between conventional methods (EPA 3050B and ISO 11466.3) of metal extraction and a simple low-cost method, using aqua regia, was carried out in this work. Six elements (Mn, Cu, Zn, Pb, Ni, and Cd) were determined by flame atomic absorption spectrometry (FAAS) in a certified sample of sediment (CNS 392). Central composite design (CCD) and response surface methodology (RSM), as well as machine learning, were used to find the optimal conditions for metal extraction. The influence of the parameters—volume of nitric acid in aqua regia (v), time of extraction (t), and temperature (T)—on Mn, Cu, Zn, and Pb recoveries was investigated. The best condition for the recovery of all the metals was v = 2.5 mL of HNO₃, t = 2 h, and T = 90 °C. In comparison with the conventional methods, the aqua regia method was found to present better recovery values and lower standard deviations for all the metals studied.     

Transfer of Cd, Pb, and Zn to water spinach from a polluted soil amended with lime and organic materials

Purpose

The transfer of heavy metals from soil to crops comprises several steps, including soil-to-root and subsequent root-to-shoot tranfer. The purpose of this study was to investigate the different steps of soil-to-crop transfer of Cd, Pb, and Zn.

Materials and methods

This study was carried out with a greenhouse pot experiment using a soil polluted with Cd, Pb, and Zn which was amended with rice straw, pig manure, sheep dung, or peat, with and without lime. Water spinach (Ipomoea aquatica) was used as the test crop and was grown after a season of rice cultivation.

Results and discussion

The results showed that all the amendments promoted the root-to-shoot transfer of Cd, Pb, and Zn. The soil-to-root transfer factors (TFs) of Pb and Zn tended to increase with increasing available Pb and Zn in the soils, while no clear relationship between the TF of Cd and available soil Cd was observed. The root-to-shoot TF of Cd, Pb, and Zn tended to decrease with increasing available amounts in the soils and were negatively correlated with the concentrations of the metals in the roots (r _Cd?=?0.820, r _Pb?=?0.789, r _Zn?=?0.769).

Conclusions

The soil-to-root transfer of Cd, Pb, and Zn was significantly different from the root-to-shoot transfer. The soil-to-root transfer was mainly influenced by the amount of available metal in soil, whereas the root-to-shoot transfer was mainly controlled by the concentrations of the metals in the root.     

Heavy metal distribution in different soil aggregate size classes from restored brackish marsh,oil exploitation zone,and tidal mud flat of the Yellow River Delta

Purpose

Heavy metal distribution in soils is affected by soil aggregate fractionation. This study aimed to demons trate the aggregate-associated heavy metal concentrations and fractionations in “sandy,” “normal,” and “mud” soils from the restored brackish tidal marsh, oil exploitation zone, and tidal mudflat of the Yellow River Delta (YRD), China.

Materials and methods

Soil samples were sieved into the aggregates of >2, 0.25–2, 0.053–0.25, and <0.053 mm to determine the concentrations of exchangeable (F1), carbonate-bound (F2), reducible (F3), organic-bound (F4), and residual fraction (F5) of Cd, Cr, Cu, Ni, Pb, and Zn.

Results and discussion

The 0.25–2 mm aggregates presented the highest concentrations but the lowest mass loadings (4.23–12.18 %) for most metal fractions due to low percentages of 0.25–2 mm aggregates (1.85–3.12 %) in soils. Aggregates <0.053 mm took majority mass loadings of metals in sandy and normal soils (62.04–86.95 %). Most soil aggregates had residual Cr, Cu, Ni, Zn, and reducible Cd, Pb dominated in the total Cd, Cr, Cu, Ni, Pb, and Zn concentrations. Sandy soil contained relatively high F4, especially of Cu (F4) in 0.25–2 mm aggregates (10.22 mg kg^?1), which may relate to significantly high organic carbon contents (23.92 g kg^?1, P?<?0.05). Normal soil had the highest total concentrations of metals, especially of Cu, Ni, and Pb, which was attributed to the high F3 and F5 in the <0.053 mm aggregates. Although mud soil showed low total concentrations of heavy metals, the relatively high concentrations of bioavailable Cd and Cu resulted from the relatively high Cd (F2) and Cu (F2) in the >2 mm aggregates indicated contribution of carbonates to soil aggregation and metal adsorption in tidal mud flat.

Conclusions

Soil type and aggregate distribution were important factors controlling heavy metal concentration and fractionation in YRD wetland soil. Compared with mud soil, normal soil contained increased concentrations of F5 and F3 of metals in the 0.053–0.25 mm aggregate, and sandy soil contained increased concentrations of bioavailable and total Cr, Ni, and Zn with great contribution of mass loadings in the <0.053 mm aggregate. The results of this study suggested that oil exploitation and wetland restoration activities may influence the retention characteristics of heavy metals in tidal soils through variation of soil type and aggregate fractions.

     

Response of CaCl<Subscript>2</Subscript>-extractable heavy metals,polychlorinated biphenyls,and microbial communities to biochar amendment in naturally contaminated soils

Purpose

Biochar can be used to reduce the bioavailability and leachability of heavy metals, as well as organic pollutants in soils through adsorption and other physicochemical reactions. The objective of the study was to determine the response of microbial communities to biochar amendment and its influence on heavy metal mobility and PCBs (PCB52, 44, 101, 149, 118, 153, 138, 180, 170, and 194) concentration in application of biochar as soil amendment.

Materials and methods

A pot (macrocosm) incubation experiment was carried out with different biochar amendment (0, 3, and 6 % w/w) for 112 days. The CaCl₂-extractable concentration of metals, microbial activities, and bacterial community were evaluated during the incubation period.

Results and discussion

The concentrations of 0.01 M CaCl₂-extractable metals decreased (p?>?0.05) by 12.7 and 20.5 % for Cu, 5.0 and 15.6 % for Zn, 0.2 and 0.5 % for Pb, and 1.1 and 8.9 % for Cd, in the presence of 3 and 6 % of biochar, respectively, following 1 day of incubation. Meanwhile, the total PCB concentrations decreased from 1.23 mg kg^?1 at 1 day to 0.24 mg kg^?1 at 112 days after 6 % biochar addition, representing a more than 60 % decrease relative to untreated soil. It was also found out that biochar addition increased the biological activities of catalase, phosphatase, and urease activity as compared with the controls at the same time point. Importantly, the Shannon diversity index of bacteria in control soils was 3.41, whereas it was 3.69 and 3.88 in soils treated with 3 and 6 % biochar soil. In particular, an increase in the number of populations with the putative ability to absorb PCB was noted in the biochar-amended soils.

Conclusions

The application of biochar to contaminated soils decreased the concentrations of heavy metals and PCBs. Application of biochar stimulated Proteobacteria and Bacteroides, which may function to absorb soil PCB and alleviate their toxicity.

     

Distributions of Heavy Metals and Benzo[<Emphasis Type="Italic">a</Emphasis>]pyrene in Oligotrophic Peat Soils and Peat Gleyzems of Northeastern Sakhalin

The contents and profile distributions of Cr, Ni, Cu, Zn, Cd, Hg, Pb, and benzo[a]pyrene in oligotrophic peat soils, oligotrophic peat gley soils (Dystric Fibric Histosols), humus-impregnated peat gleyzems (Dystric Histic Gleysols), and mucky gleyzems (Dystric Gleysols) have been analyzed with consideration for their degree of oligotrophicity and anthropogenic loads. Horizons with the accumulation (O, Tpyr, TT) and removal (Ghi,e) of heavy metals have been revealed. The increase in the content of heavy metals and benzo[a]pyrene in the upper layer of oligotrophic peat soils under technogenic fallouts in the impact zone of flare and motor transport has been considered. Statistical parameters of the spatial variation of parameters in organic and gley horizons have been calculated. The variation coefficients of pollutant elements (Pb and Zn) in the surface horizons of soils increase to 100–125%. Positive correlations revealed between the content of some heavy metals in litter indicate their bioaccumulation and possible joint input with aerotechnogenic fallouts. No correlations are found between the contents of benzo[a]pyrene and heavy metals, but a reliable negative correlation with the ash content is noted in the peat horizon.     

Effects of red mud addition on cadmium accumulation in cole (<Emphasis Type="Italic">Brassica campestris</Emphasis> L.) under high fertilization conditions

Purpose

Applications of mineral and organic fertilizer increased soil cadmium (Cd) and could enhance Cd concentrations in edible crops, respectively. Although red mud (RMD) effectively decreased metal bioavailability in soil, the influence of RMD addition on vegetable growth and metal accumulation under high fertilization conditions has rarely been addressed. The aim of this study was to investigate the effects of raw RMD addition on cole growth, quality, and nutrition and Cd accumulation under high fertilization conditions.

Materials and methods

Pot experiments with cole (Brassica campestris L.) were carried out in a greenhouse. Three treatments, CK (with no mineral fertilizer and RMD addition), CT (more than 2.5 times conventional level of mineral fertilizer applied without any RMD), and RM (more than 2.5 times conventional level of mineral fertilizer applied with RMD added at 0.4 % w/w), were established. After 40 days, the cole plants and soils of every replicate of all treatments were sampled. The Cd, biomass, vitamin C (VC), and total nitrogen and phosphorus of the cole plant samples and the Cd, pH, nitrate, and phosphorus of the soil samples were determined.

Results and discussion

In contrast to the CT treatment, RM treatment did not significantly influence the biomass and nitrate concentration of the aboveground cole. However, it significantly reduced the Cd content in cole shoots and its bioaccumulation factors by 30.0 and 28.5 %, respectively. The reduction of bioavailable Cd in soil by RMD sorption and the competition with calcium released from RMD led to low Cd assimilation by root. Finally, less Cd was transported to aboveground plant parts in the RM treatment compared with the CT treatment. RMD addition markedly enhanced the total nitrogen in cole shoots by >16.0 %, and the VC by 20.9 %. The promotion of bacterial abundance and soil enzyme activity by RMD addition and calcium release from RMD generated substantial plant available nitrogen.

Conclusions

With large rate of mineral fertilizer application to the soil, RMD (0.4 %, w/w) addition did not significantly influence the biomass, nitrate, and VC of aboveground cole; however, it significantly reduced the Cd and markedly enhanced the total nitrogen in cole shoots. This study provides valuable information for the safe application of RMD in vegetable production.