Dry cultivation enhances cadmium solubility in contaminated soils but minimizes cadmium accumulation in a leafy vegetable

Purpose

Water management has a strong influence on Cd solubility in agricultural soils, affecting Cd uptake in crops. In the process, sulfur interaction with other metals such as zinc may play an important role. A pot experiment was carried out to investigate the effects of water management coupled with zinc and sulfate amendment on Cd uptake by the leafy vegetable amaranth with a strong Cd accumulation tendency in its edible parts.

Materials and methods

The soils were amended with Cd, Cd+SO₄ and Cd+SO₄+Zn with no amendment as control. Then, the soils were flooded for 1 month, after which amaranth was grown with soil kept saturated (wet cultivation). In the succeeding planting, soils were tilled to aeration condition under which amaranth was grown again (dry cultivation). Soil and crop samples were collected and analysed for various parameters.

Results and discussion

The readily exchangeable quantities of Cd and Zn in the soil decreased under wet cultivation, increasing again under dry cultivation but to levels lower than those in the initial soil. Wet cultivation enhanced plant Cd concentration but reduced Zn accumulation compared to dry cultivation. Zn bioavailability was strongly affected by soil water status but failed to reduce Cd uptake by amaranth. Irreversible or slowly reversible changes occurred in Cd and Zn solubility and phytoavailability as soil water-saturated status was altered by periodic flooding events.

Conclusions

Dry cultivation with lower soil water content ensured high production with low Cd in the edible part of this leaf vegetable and so remains the recommended irrigation regime.

     

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.

     

Competitive sorption of linear alkylbenzene sulfonate (LAS) surfactants and the antibiotics sulfamethoxazole and ciprofloxacin in wastewater-irrigated soils of the Mezquital Valley,Mexico

Purpose

The increasing reuse of wastewater for irrigation introduces surfactants and antibiotics into the environment. How these two kinds of compounds interact with regard to their sorption processes in soil is not clear.

Materials and methods

We performed batch experiments to investigate the sorption of linear alkylbenzene sulfonates (LAS) and its effect on sorption of sulfamethoxazole and ciprofloxacin in irrigated and non-irrigated soils with different organic matter (OM) contents.

Results and discussion

LAS sorption was non-linear in the presence of the antibiotics, and as general trend, it increased with rising OM content of soils. Free LAS was also removed from solution by complexation with Ca²⁺. Dissolved organic compounds released from soils with OM contents ≥18.4 g kg^?1 further reduced LAS sorption. Sorption of sulfamethoxazole was reduced by LAS sorption only in one soil with a small OM content of 9.5 g kg^?1.

Conclusions

The strong sorption of ciprofloxacin is not affected by LAS. Sulfamethoxazole sorption only competes with LAS sorption in organic matter-poor soils. Accumulation of organic matter in soils, for example due to long-term wastewater irrigation, provides extra sorption capacity for LAS and sulfamethoxazole so that competition for sorption sites is reduced.

     

Micro/nanostructured hydroxyapatite structurally enhances the immobilization for Cu and Cd in contaminated soil

Purpose

The presence of high copper (Cu) and cadmium (Cd) contamination in soils around mining areas has raised serious health concerns. Improving hydroxyapatite (HAP) adsorption capacity for Cu and Cd is important if its application potential in heavily contaminated soils is to expand.

Materials and methods

The micro/nanostructured HAP (mnHAP) was synthesized using a template-induced method to improve the HAP immobilization of Cu and Cd in contaminated soils. Commercial and synthetic HAPs were evaluated as amendments in Cu and Cd remediation tests with 1.5 and 3.0 % addition level for 90 days, and soils without HAP materials (0.0 %) were designated as the controls; each treatment was repeated three times. The materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N₂ adsorption, and scanning electron microscopy (SEM)-energy-dispersive spectra (EDS) and then quantitatively determined the Cu and Cd contents by inductively coupled plasma (ICP) and inductively coupled plasma mass spectrometry (ICP-MS).

Results and discussion

The mnHAP was more effective in immobilizing Cu and Cd than the two commercial HAPs. After treatment with mnHAP at the 3.0 % addition level for 90 days, the contaminated soils showed 55.2 and 84.8 % reductions in Cu and Cd concentrations in the toxicity characteristic leaching procedure (TCLP) leaching procedure, respectively. The experimental data indicated that the enhanced Cu and Cd immobilization by mnHAP was due to the increases of surface area and the improvement of structure and newly introduced carboxylate groups on its surface.

Conclusions

These findings show that regulating the structure and surface properties of HAP can enhance Cu and Cd immobilization in soils.

     

Type of organic carbon amendment influences pH changes in acid sulfate soils in flooded and dry conditions

Purpose

Acid sulfate soils (ASS) are common in wetlands and can pose an environmental threat when they dry because oxidation of pyrite may cause strong acidification. Addition of organic matter can stimulate sulfate reduction during wet periods and minimize acidification during dry periods. However, the effect of the organic amendment may depend on its composition.

Materials and methods

Three wetland acid sulfate (sulfuric, hypersulfidic, and hyposulfidic) soils collected from different depth in one profile were used. The soils, unamended or amended with 10 g C kg^?1 as glucose, wheat straw, pea straw, or Phragmites litter, were incubated for 18 weeks under flooded conditions (“wet period”) followed by 10 weeks during which the soils were maintained at 100 % of maximum water-holding capacity (“dry period”).

Results and discussion

During the wet period, the pH decreased in the control and with glucose to pH 3–4, but increased or was maintained in residue-amended soils (pH at the end of the wet period about 7). In the dry period, the pH of the control and glucose-amended soils remained low, whereas the pH in residue-amended soils decreased. However, at end of the dry period, the pH was higher in residue-amended soils than in the control or glucose-amended soils, particularly with pea straw (C/N 50).

Conclusions

Amendment of acid sulfate soils with plant residues (particularly those with low to moderate C/N ratio) can stimulate pH increase during flooding and reduce acidification under oxidizing conditions.

     

Sustainability of in situ remediation of Cu- and Cd-contaminated soils with one-time application of amendments in Guixi,China

Purpose

In situ immobilization of heavy metal-contaminated soils with the repeated incorporation of amendments can effectively reduce the bioavailability of soil heavy metals. However, the long-term application of amendments would lead to the destruction of soil structure and accumulation of soil toxic elements, ultimately affecting food security and quality. Thus, the sustainability of the amendments in a heavy metal-contaminated soil was evaluated from 2010 to 2012.

Materials and methods

Batch field experiments were conducted in the soils, which were amended with apatite (22.3 t ha^?1), lime (4.45 t ha^?1), and charcoal (66.8 t ha^?1), respectively. The amendments were applied only one time in 2009, and ryegrass was sown each year. Ryegrass and setaria glauca (a kind of weed) were harvested each year. Concentrations of copper (Cu) and cadmium (Cd) were determined by batch experiments. Five fractions of Cu and Cd were evaluated by a sequential extraction procedure.

Results and discussion

Ryegrass grew well in the amended soils in the first year, but it failed to grow in all the soils in the third year. However, setaria glauca could grow with higher biomass in all the amended soils. The treatment of apatite combined with plants was more effective than lime and charcoal treatments in removing Cu and Cd from the contaminated soils by taking biomass into account. Apatite had the best sustainable effect on alleviating soil acidification. The Cu and Cd concentrations of CaCl₂-extractable and exchangeable fractions decreased with the application of amendments. Moreover, apatite and lime could effectively maintain the bioavailability of Cu and Cd low.

Conclusions

Apatite had a better sustainable effect on the remediation of heavy metal-contaminated soils than lime and charcoal. Although all the amendment treated soils did not reduce soil total concentrations of Cu and Cd, they could effectively reduce the environmental risk of the contaminated soils. The findings could be effectively used for in situ remediation of heavy metal-contaminated soils.

     

Nitrogen compound pollution associated with the use of sewage sludge compost and limestone outcrop residue under saline irrigation

Purpose

The use of composted sewage sludge and limestone outcrop residue in land rehabilitation, soil improvement, and technosol making can influence the mobility of nitrogen compounds in groundwater.

Materials and methods

This experiment analyzed this source of possible pollution under an experimental design based on the use of columns (0–30 cm) formed by both wastes and a heavy irrigation regime. Two waters of different quality (saline and non-saline) were used for irrigation. The presence of nitrate, nitrite, and ammonium in the leachates was checked.

Results and discussion

The environmental risk due to the presence of nitrogen species associated with the use of these materials was very low in general, although nitrate was the most important compound affected by the use of sewage sludge compost and saline water.

Conclusions

The combination of saline water for irrigation with the compost has to be seriously considered as a source of pollution for surface and ground waters, and the use of both resources may be a key factor to be studied (low-quality water and sewage sludge compost).

     

Simultaneous immobilization of lead,cadmium, and arsenic in combined contaminated soil with iron hydroxyl phosphate

Purpose

Combined contamination of lead (Pb), cadmium (Cd), and arsenic (As) in soils especially wastewater-irrigated soil causes environmental concern. The aim of this study is to develop a soil amendment for simultaneous immobilization of Pb, Cd, and As in combinative contaminated soil.

Materials and methods

A soil amendment of iron hydroxyl phosphate (FeHP) was prepared and characterized, and its potential application in simultaneous immobilization of Pb, Cd, and As in combined contaminated soil from wastewater-irrigated area was evaluated. The effects of FeHP dosage, reaction time, and soil moisture on Pb, Cd, and As immobilization in the soil were examined.

Results and discussion

The immobilization efficiencies of Pb, Cd, and As generally increased with the increasing of FeHP dosage. With FeHP dosage of 10 %, the immobilization percentages of NaHCO₃-extractable As and DTPA-extractable Pb and Cd reached 69, 59, and 44 %, respectively. The equilibrium time required for immobilization of these contaminants was in the following order: NaHCO₃-extractable As (0.25 days) < DTPA-extractable Cd(3 days) < DTPA-extractable Pb (7 days). However, the immobilization efficiencies of Pb, Cd, and As have not changed much under soil moisture varied from 20 to 100 %. According to the results of the sequential extraction, the percentages of Pb, Cd, and As in residual fractions increased after the application of FeHP amendment, while their percentages in exchangeable fractions decreased, illustrating that FeHP can effectively decrease the mobilities and bioavailabilities of Pb, Cd, and As in the soil. Moreover, the application of FeHP will not have soil acidification and soil structure problem based on the soil pH measurements and soil morphology.

Conclusions

FeHP can immobilize Pb, Cd, and As in the combinative contaminated soil from wastewater irrigation area simultaneously and effectively. Thus, it can be used as a potential soil amendment for the remediation of Pb, Cd, and As-combined contaminated soil.

     

Effect of rice planting on the nutrient accumulation and transfer in soils under plastic greenhouse vegetable-rice rotation system in southeast China

Purpose

Greenhouse vegetable-rice crop rotations have rapidly expanded in the southeast of China in recent years. However, how rice planting affects nutrient accumulation and transfer in soils during plastic greenhouse vegetable cultivation is still poorly understood. The aim of this research was to characterize the nutrient accumulation and vertical distribution of greenhouse soil under long-term greenhouse vegetable-rice rotation.

Materials and methods

The nutrient accumulation and transfer between greenhouse eggplant-summer rice (GER) and greenhouse eggplant-summer fallow (GEF) without plastic cover in the Changxing city, Zhejiang province of China, were compared. The soil nutrient contents were determined in the surface soil samples collected from both the GER and GEF systems after eggplant harvest and after summer cultivation as well as the soils collected from both systems at different soil depths after summer cultivation. The nitrogen concentration of the surface water and groundwater samples collected during the flooding water time in GER was also measured.

Results and discussion

Both the GER and GEF soils showed obvious accumulation of nutrients at the 0–20-cm soil depth after eggplant harvest. However, compared with the summer fallow without plastic cover in GEF, rice planting in GER sharply reduced the nutrients in soils at the 0–20-cm layer. The NO₃ ^?-N, Olsen-P, and available K in the soil of GER decreased from 25, 159, and 144 to 8, 127, and 120 mg kg^?1, respectively. Nutrient contents in all different soil depths in GER were lower than those in GEF at equivalent soil depths. The nitrogen content of groundwater in GER showed unobvious enhancement during flooding water time.

Conclusions

Rice planting during the summer after greenhouse vegetable cultivation could reduce the nutrient accumulation in soil. Flooding water in summer did not increase nutrient leaching in comparison with fallow without plastic cover during the summer. Thus, rice can be regarded as a suitable catch crop for greenhouse vegetable cultivation.

     

Effects of saline water irrigation and fertilization regimes on soil microbial metabolic activity

Purpose

Irrigation and fertilization can change soil environment, which thereby influence soil microbial metabolic activity (MMA). How to alleviate the adverse effects by taking judicious saline water irrigation and fertilization regimes is mainly concerned in this research.

Materials and methods

Here, we conducted a field orthogonal designed test under different saline water irrigation amount, water salinity, and nitrogen fertilizer application. The metabolic profiles of soil microbial communities were analyzed by using the Biolog method.

Results and discussion

The results demonstrated that irrigation amount and fertilizer application could significantly change MMA while irrigation water salinity had no significant effect on it. Medium irrigation amount (30 mm), least (50 kg ha^?1) or medium (350 kg ha^?1) N fertilizer application, and whatever irrigation water salinity could obtain the optimal MMA. Different utilization rates of carbohydrates, amino acids, carboxylic acids, and polymers by soil microbial communities caused the differences of the effects, and D-galactonic acid γ-lactone, L-arginine, L-asparagine, D-glucosaminic acid, Tween 80, L-threonine, and D-galacturonic acid were the indicator for distinguishing the effects.

Conclusions

The results presented here demonstrated that by regulating irrigation water amount and fertilizer application, the effects of irrigation salinity on MMA could be alleviated, which offered an efficient approach for guiding saline water irrigation.

     

New alternative method of benzo[a]pyrene extractionfrom soils and its approbation in soil under technogenic pressure

Purpose

The optimization of benzo[a]pyrene extraction conditions by subcritical water extraction method from soils is the purpose of the research. The optimal conditions for benzo[a]pyrene recovery are 30-min extraction by water in a special steel cartridge at 250 °C and 100 atm.

Materials and methods

Studies were conducted on the soils of monitoring plots subjected to Novocherkassk Power Station emissions. Monitoring plots were established at different distances from the Novocherkassk Power Station (NPS; 1.0–20.0 km).

Results and discussion

It was shown that the use of water in subcritical state as a solvent for benzo[a]pyrene extraction from soil allows to avoid large volumes of organic solvents and to decrease the time of sample preparation. It is shown that the maximum benzo[a]pyrene maintenance was observed in soils of the monitoring plots located most close (to 5 km) to a pollution source in the area of the prevailing direction of a wind rose. Dynamics of pollutant accumulation in soils depend on number of Novocherkassk state district power station emissions.

Conclusions

The method of benzo[a]pyrene subcritical water extraction from soil was developed and approbated during long-term monitoring researches of technogenic polluted territories. The optimum conditions for benzo[a]pyrene extraction from soil have been determined: the soil is treating by subcritical water at 250 °C and 100 atm of pressure for 30 min. Trends in the accumulation of benzo[a]pyrene in soil zones of the thermal power plant influence have been researched over a 5-year period of monitoring observations by subcritical water extraction method. Benzo[a]pyrene accumulation in soils depends on the technogenic emissions to the atmosphere from Novocherkassk power station and on the soil physical and chemical properties.

     

Effects of phosphate on trace element accumulation in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.): a 5-year phosphate application study

Purpose

Phosphate (P) fertilizers are being widely used to increase crop yield, especially in P-deficient soils. However, repeated applications of P could influence trace element bioaccumulation in crops. The effects of 5-year P enrichment on trace element (Cu, Zn, Cd, Pb, As, and Hg) accumulation in Oryza sativa L. were thus examined.

Materials and methods

Two paddy soils with different initial P availabilities were amended with and without P fertilizer from 2009 to 2013. Trace elements and P levels in rice and soils were analyzed.

Results and discussion

In soil initially with limited P, P amendment enhanced grain Pb, As, and Hg concentrations by 1.8, 1.5, and 1.4-fold, respectively, but tended to decrease the grain Cd level by 0.73-fold, as compared to the control. However, in soil initially with sufficient P, P amendment tended to reduce accumulation of all examined elements in rice grain.

Conclusions

Phosphate amendment in initially P-limited and P-sufficient soils had different effects on trace element availability in soil (as reflected by extractable element) and plant physiology (growth and metal translocation), resulting in contrasting patterns of trace element accumulation in rice between the two types of soils. Our study emphasized the necessity to consider the promoting effects of P on Pb, As, and Hg accumulation in grain in initial P-deprived soil.

     

Shifts of archaeal community structure in soil along an elevation gradient in a reservoir water level fluctuation zone

Purpose

Although archaea play an important role in nutrients cycling, the archaeal community in a reservoir water-level fluctuation zone (WLFZ) remains unclear. An elucidation of archaeal community responding to the environmental variables is essential to understand the nutrients dynamics in WLFZ. This study focused on the response of the archaeal community structure and abundance to the periodic water flooding along an elevation gradient in the WLFZ of the Three Gorges Reservoir.

Materials and methods

Along the elevation gradient (152–175 m) of the study area, soil samples in the beginning and late stages of water flooding were collected to investigate the influence of water flooding on the archaeal community in soil, using quantitative PCR and Illumina high-throughput sequencing approaches.

Results and discussion

An increase of archaeal abundance from 3.8?×?10⁸ to 3.8?×?10⁹ copies (g d.w.s)^?1 on average was observed after water flooding. The archaeal abundance was positively correlated with the contents of ammonium, organic matter, and moisture in soil and with the accumulated flooding time. Higher diversity was observed in dry samples (non-flooded soil samples) rather than wet samples (flooded soil samples). The Thaumarchaeota were predominant in most of the dry samples. Interestingly, high proportions of Candidatus Nitrososphaera were observed in the transition zone, while euryarchaeotal methanogens dominated the wet samples. The proportion of methanogens decreased dramatically in the dry samples at higher elevations, which was associated with the decrease of the moisture content and the probably increase of available oxygen in soil.

Conclusions

Archaeal abundance, diversity, and community composition shifted along an elevation gradient and were influenced by water flooding. The increased archaea abundance after water flooding and elevation related community composition and diversity indicated that water flooding was a key dynamic environmental variable in the WLFZ.

     

Vinasse irrigation: effects on soil fertility and arbuscular mycorrhizal fungi population

Purpose

The aim of this research was to determine the vinasse irrigation effects on the arbuscular mycorrhizal fungi (AMF) population (total spore abundance (TSA), richness, relative abundance, and diversity indices) and soil parameters and nutrients at high doses. The irrigation of soil with vinasses derived from sugarcane, beet, or alcohol production is a common practice around the world. Little is known about how this affects the AMF community and soil nutrients.

Materials and methods

The spider plant (Chlorophytum comosum, (Thunb.) Jacques), a mycorrhizable plant, was used to investigate the effect of 4 months of frequent vinasse irrigation (0, 25, 50, 75, and 100% vinasse concentration) on AMF and soil characteristics, e.g., electrical conductivity (EC), pH, mineral N, available P, Na⁺, K⁺, Ca²⁺, and Mg²⁺.

Results and discussion

The vinasse irrigation decreased the TSA, AMF richness and diversity after 4 months, regardless of vinasse concentration. The vinasse irrigation did not acidify the soil, but the EC, mineral N and available P increased. The biomass of C. comosum decreased (77–81%) after vinasse irrigation for 4 months.

Conclusions

Frequent irrigation with vinasse at concentrations ≥50% increases EC, K⁺, Na⁺, Mg²⁺, Ca²⁺ and available P in the soil, and decreases the amount of AMF spores, richness and diversity, which is not desirable in agricultural soils.

     

Effect of the size of variable charge soil particles on cadmium accumulation and adsorption

Purpose

The size of soil particles strongly affects the accumulation and adsorption of heavy metals which partly controls the co-transport of heavy metals by soil colloids. However, the effect of the size of soil particles on the accumulation and adsorption of heavy metals in the colloidal dimension has seldom been studied. In this study, variable charge soils were selected and separated into five size fractions to elucidate the effect of the size of soil particles on Cd accumulation and adsorption.

Materials and methods

Five soil particle size fractions (>10, 10–1, 1–0.45, 0.45–0.2 and <0.2 μm) were obtained from Cd-contaminated soil by natural sedimentation and fractional centrifugation. The concentrations and species of Cd were measured in various sized soil particles. Batch adsorption experiments of Cd on the obtained soil particles were conducted under different pH values and concentrations of NaCl.

Results and discussion

Generally, the concentration of Cd increased with decreasing soil particle sizes, and the Cd proportion of exchangeable and carbonate fraction decreased from 43.84 to 17.75% with decreasing particle size. The soil particles with a size of 10–1 and <0.2 μm possessed a stronger adsorption ability than the other fractions in most cases. Moreover, the Cd adsorption capacities of the soil particles increased with increasing pH values and decreasing concentrations of NaCl, especially for soil particles containing more organic matter (OM) and variable charge minerals.

Conclusions

Smaller soil particles are more capable of accumulating Cd and make Cd more stable. The adsorption capability of Cd is negatively related to the particle size and NaCl concentration and is positively related to the pH. The effects of the size of variable charge soil particles on Cd accumulation and adsorption are attributed to the differences in the physicochemical properties among various soil particle size fractions. This study contributes to the understanding of the co-transport of heavy metals in soil by soil colloids.

     

Sorption and transport of sulfonamides in soils amended with wheat straw-derived biochar: effects of water pH,coexistence copper ion,and dissolved organic matter

Purpose

Sulfonamides are widely used for the prevention and treatment of bacterial infections, hard-degraded contaminants distributed in the environment if they are discharged into the soil and water. Biochar could probably influence the geochemical behavior of ionized antibiotics in the soils.

Materials and methods

To determine the sorption/desorption of three representative sulfonamides (SAs) in soils amended with biochar, we investigated the effects of water pH, Cu²⁺, and dissolved humic acid on the sorption of sulfamethoxazole (SMX), sulfamethazine (SMZ), and sulfadiazine (SD) onto two different soil samples (S1 pH?=?5.13 and S2 pH?=?7.33) amended with wheat straw-derived biochar (size 0.5～0.6 mm).

Results and discussion

Batch experiments showed that the sorption/desorption isotherms of SAs on soil with/without biochar followed the Freundlich model. The biochar had a strong adsorption potential for SMX, SMZ, and SD both in S1 and S2 at low water pH. Except for SMX, the presence of Cu²⁺ inhibited the sorption of SMZ and SD through competing hydrophobic adsorption region in soils. HA suppressed the sorption of three sulfonamides in soil S2 by electrostatic repulsion under alkaline condition. The soil leaching column experiments showed the SA transport in soils, and S1 and S2 amended with biochar (0.5 and 1.0 wt%) brought about 12–20 % increase in SMX, SMZ, and SD retention compared to the untreated soil.

Conclusions

The results indicated that the presence of biochar effectively mitigated the mobility of ionized antibiotics such as SMX, SMZ, and SD in soils, which helps us reconsider the potential risk of antibiotics in the environment.

     

Comparison of ammonium fertilizers,EDTA, and NTA on enhancing the uptake of cadmium by an energy plant,Napier grass (<Emphasis Type="Italic">Pennisetum purpureum</Emphasis> Schumach)

Purpose

The aim of this study was to quantify the effect of enhanced agronomic practices on cadmium (Cd) accumulation in the high-biomass energy plant Napier grass (Pennisetum purpureum Schumach).

Materials and methods

Potted-plant experiments were performed to investigate the effects of ammonium fertilizers and chelating agents, alone or in combination, on the growth, accumulation of Cd, and phytoextraction efficiency of P. purpureum on Cd-contaminated soil. The fertilizers included ammonium nitrate, ammonium sulfate, and ammonium chloride. The chelating agents included ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA).

Results and discussion

The addition of ammonium fertilizers and chelating agents generally stimulated growth of P. purpureum, and the shoots accounted for 90.1–94.1% of the total biomass. The concentrations of Cd in different parts of P. purpureum plants were in the order root > leaf > stem. Ammonium chloride alone showed effectiveness in increasing root and shoot Cd concentrations compared to other amendments alone. Both EDTA alone and NTA alone significantly decreased root Cd concentration and increased shoot Cd concentration, while EDTA alone was more efficient on shoot and total Cd accumulation than that by NTA alone. The total accumulation of Cd in P. purpureum ranged from 1.10 to 2.05 mg per plant with 47.3–73.5% of Cd accumulation concentrated in shoots. The results indicate that P. purpureum can remove more Cd through phytoextraction than that by other hyperaccumulators.

Conclusions

Ammonium chloride led to the highest total Cd accumulation. Ammonium chloride applied alone or in combination with either EDTA or NTA resulted in the most effective agronomic approaches for P. purpureum phytoextraction of soil Cd.

     

Characterization of soil physico-chemical parameters and limitations for revegetation in serpentine quarry soils (NW Spain)

Purpose

Quarrying activities in areas with serpentinized rocks may have a negative impact on plant growth. Quarry soils generally offer hostile environments for plant growth due to their low-nutrient availability, low organic matter, and high-trace metal content.

Materials and methods

In order to determine the factors that can limit plant revegetation, this study was carried out in two serpentine quarries in Galicia (NW Spain): one abandoned in 1999 and the other still active.

Results and discussion

The results show that in soils developed in the abandoned quarry, the limitations for revegetation were: moderate alkaline pH (7.87–8.05), strong Ca/Mg (<1) imbalance, low N (<0.42 mg kg^?1) and P (<2 mg kg^?1) content, and high total heavy-metal content (Co 76–147 mg kg^?1; Cr 1370–2600 mg kg^?1; and Ni 1340–2040 mg kg^?1). The limitations were much less intense in the soils developed in the substratum in the active quarry, which were incipient soils poorly developed and permanently affected by the quarrying activity.

Conclusions

Restoration work should be geared toward establishing a stable diverse vegetation cover, including serpentinophile species, which would provide the necessary modifications to correct nutritive imbalances and improve soil quality.

     

Heavy metal and PCB spatial distribution pattern in sediments within an urban catchment—contribution of historical pollution sources

Purpose

This work analyzes polychlorinated biphenyl (PCB) and heavy metal contamination in fluvial sediments and soils in an urban catchment, according to the geo-accumulation index and to soil and sediment quality guidelines. The catchment is located in Coimbra, Portugal, being affected by frequent flooding, and its main stream is a tributary to one of the major rivers in Portugal (Mondego). Given the presence of industrial activities over time, some inputs of pollutants are expected, but so far, the legacy of historic pollution in this catchment has not yet been investigated.

Materials and methods

Twenty-five samples were collected from nine sampling sites at the depths of 0–20, 20–40 and 40–60 cm (to provide a historic perspective) along longitudinal profiles (streamlines) and in soils downstream of pollution sources. These samples were analyzed for six heavy metals (Cu, Cr, Pb, Cd, Zn, Ni), organic carbon, pH and ten PCBs (IUPAC numbers 28, 30, 52, 101, 138, 153, 166, 180, 204, 209).

Results and discussion

Total PCB concentrations ranged 0.47–5.3 ng g^?1 dry weight (dw), and levels increase from the bottom to the top layers, suggesting an increased input over the last 100 years. PCB congener distribution shows the dominance of hexachlorobiphenyls, especially PCB138, suggesting the existence of local sources. PCB levels did not exceed sediment quality levels, placing sediments/soil under class 1 (not contaminated) or class 2 (trace contamination) with respect to PCB. All six metals exceeded the lowest effect level for sediment quality criteria, and three (Cd, Pb and Zn) largely exceeded the clean levels for dredged materials, placing sediments in class 5 (heavily contaminated). Sampling site S1 presented the highest concentrations of Zn, Pb and Cd, and historic vehicle traffic was identified as the most likely source, given the vertical and horizontal profiles.

Conclusions

High levels of Pb, Cd and Zn were found in fluvial sediments at some locations of the Loreto catchment, likely from historic traffic sources. This urban area is frequently affected by flooding events and is currently being subject to urban redevelopment. During these events/actions, historic pollutants in the sediments might surface and be redistributed, impacting the downstream ecosystem of the major Mondego River or increasing the risk of exposure of the urban population.

     

Metal accumulation and hydraulic performance of bioretention systems after long-term operation

Purpose

Stormwater bioretention systems are widely used to treat diffuse infiltration of runoff from paved surfaces and roofs. Substantial questions remain about the hydraulic performance and the accumulation of pollutants in systems over the long term. Data of metal accumulation of systems with operational times >10 years currently is limited. This study deals with the accumulation of metals in a variety of long-term operational bioretention systems (11–22 years) to derive further operation recommendations for the water authorities.

Materials and methods

The hydraulic conductivity of the bioretention systems in field was measured using a double ring infiltrometer. Media soil samples from 22 diverse designed systems were collected across the surface and at intervals up to a depth of 65 cm to determine the spatial accumulation of Zn, Cu, Pb and Cd. Leaching experiments of selected bioretention media soils were derived to assess the metal leachability by water.

Results and discussion

The hydraulic performance of most bioretention systems still met the technical guidelines of Germany even after long-term operation. Considerable metal accumulation occurred in the topsoil (0–20 cm). Median concentrations of all metals are highest at the soil surface (0–10 cm), decreasing with increasing depth. High concentrations were determined at the inflow points of the runoff waters, whereas concentrations at more than 1.5 m distance from the inflow were only slightly increased compared to the initial soil concentrations. Leachability tests have shown that most of the metals deposited in bioretention soils are only slightly water soluble. No concentrations exceeding the threshold values of the German Soil Contamination Ordinance for the pathway soil to groundwater could be determined.

Conclusions

The hydraulic conductivity of the bioretention systems is given even well after long-term operation. Most of the metal accumulation is concentrated in the top 20 cm; concentrations decrease rapidly and mostly reach background/initial concentrations after depths of 30 cm. The water-soluble metals are all below the trigger values of the German Soil Act. This underlines the strong retention capacity of long-term bioretention systems after long-term operational times.