Toxicity of imidacloprid to the earthworm Eisenia andrei and collembolan Folsomia candida in three contrasting tropical soils

Purpose

Imidacloprid is a widely used seed dressing insecticide in Brazil. However, the effects of this pesticide on non-target organisms such as soil fauna still present some knowledge gaps in tropical soils. This study aimed to assess the toxicity and risk of imidacloprid to earthworms Eisenia andrei and collembolans Folsomia candida in three contrasting Brazilian tropical soils.

Materials and methods

Acute and chronic toxicity assays were performed in the laboratory with both species in a tropical artificial soil (TAS) and in two natural soils (Oxisol and Entisol), at room temperature of 25 °C. The ecological risk was calculated for each species and soil by using the toxicity exposure ratio (TER) and hazard quotient (HQ) approaches.

Results and discussion

Acute toxicity for collembolans and earthworms was higher in Entisol (LC₅₀?=?4.68 and 0.55 mg kg^?1, respectively) when compared with TAS (LC₅₀?=?10.8 and 9.18 mg kg^?1, respectively) and Oxisol (LC_{50collembolans}?=?25.1 mg kg^?1). Chronic toxicity for collembolans was similar in TAS and Oxisol (EC_{50 TAS}?=?0.80 mg kg^?1; EC_{50 OXISOL}?=?0.83 mg kg^?1), whereas higher toxicity was observed in Entisol (EC₅₀?=?0.09 mg kg^?1). In chronic assays with earthworms, imidacloprid was also more toxic in Entisol (EC₅₀?=?0.21 mg kg^?1) when compared to TAS (EC₅₀?=?1.89 mg kg^?1). TER and HQ values indicated a significant risk of exposure of the species to imidacloprid in all soils tested, and the risk in Entisol was at least six times higher than in Oxisol or TAS.

Conclusions

The toxicity and risk of imidacloprid varied significantly between tropical soils, being the species exposure to this pesticide particularly hazardous in very sandy natural soils such as Entisol.

     

Evaluating the mercury distribution and release risks in sediments using high-resolution technology in Nansi Lake,China

Purpose

Mercury (Hg) and methylmercury (MeHg) are easily released from sediments to overlying water and cause secondary contamination. In general, Hg concentrations are low in natural aquatic environments, but Hg toxicity is high. Therefore, it is important to assess the mobility and release risks of Hg and MeHg from surface sediment using in situ high-resolution sampling techniques.

Methods

The profile distribution of Hg and MeHg was obtained for samples from Weishan sub-lake (WL) and Dushan sub-lake (DL) of Nansi Lake, China, by high-resolution dialysis (HR-Peeper probes) and the diffusive gradients in thin films (DGT) technique at mm-resolution. Furthermore, Hg mobility and release risks in sediments were evaluated by combining BCR (European Community Reference Bureau) extraction and DGT-measured data.

Results

The soluble concentrations of Hg in surface sediments in WL and DL were 21.70 and 19.38 ng L^?1 and the DGT-labile concentration of Hg were 8.21 and 10.30 ng L^?1, respectively. The soluble and labile Hg and MeHg concentrations were higher in the surface sediments (from??40 to 0 mm) than in deep sediments. The distribution of the labile-Hg was controlled by the ferrimanganic (hydr)oxide and total nitrogen rather than organic carbon content. The non-residual components accounted for a greater proportion of the interface, which further confirmed Hg was more active on the surface layer of the sediment. The resupply ability indicated that the release of Hg from sediment was insufficient to maintain the initial concentration in the porewater before consumption. The MeHg fluxes in WL (6.18 ng m^?2 day^?1) were twice those in DL (2.89 ng m^?2 day^?1), and the risk assessment code revealed a higher risk in the surface layer (25.21–61.88%) than in the deep layer (0–27.75%).

Conclusions

Dissolved Hg and MeHg accumulated on the surface of the sediments and were more active than in the deeper sediments. The DGT-labile state can be used for a better understanding of the bioavailability and mobility of Hg. The diffusion direction of Hg and MeHg was from sediment to the overlying water. The release risks of Hg and MeHg from surface sediments (especially in WL) were found to be worthy of concern.

     

Response of phosphorus fractions to land-use change followed by long-term fertilization in a sub-alpine humid soil of Qinghai–Tibet plateau

Purpose

Identification of phosphorus (P) species is essential to understand the transformation and availability of P in soil. However, P species as affected by land use change along with fertilization has received little attention in a sub-alpine humid soil of Tibet plateau.

Materials and methods

In this study, we investigated the changes in P species using Hedley sequential fractionation and liquid-state ³¹P-NMR spectroscopy in soils under meadow (M) and under cropland with (CF) or without (CNF) long-term fertilization for 26 years in a sub-alpine cold-humid region in Qinghai–Tibet plateau.

Results and discussion

Land-use change and long-term fertilization affected the status and fractions of P. A strong mineralization of organic P (OP) was induced by losing protection of soil organic matter (SOM) and Fe and Al oxides during land-use change and resulted in an increase of orthophosphate (from 56.49 mg kg^?1 in M soils to 130.07 mg kg^?1 in CNF soils) and great decreases of orthophosphate diesters (diester-P, from 23.35 mg kg^?1 in M soils to 10.68 mg kg^?1 in CNF soils) and monoesters (from 336.04 mg kg^?1 in M soils to 73.26 mg kg^?1 in CNF soils). Long-term fertilization boosted P supply but failed to reclaim soil diester-P (from 10.68 mg kg^?1 in CNF soils to 7.79 mg kg^?1 in CF soils). This may be due to the fragile protection from the combination of SOM with diester-P when long-term fertilization had only improved SOM in a slight extent.

Conclusions

These results suggest that SOM plays an important role in the soil P cycling and prevents OP mineralization and losses from soil. It is recommended that optimization of soil nutrient management integrated with SOM was required to improve the P use efficiency for the development of sustainable agriculture.

     

Trace elements and polycyclic aromatic hydrocarbons in road gully sediments from different land uses,Hong Kong

Purpose

This study investigated the concentrations of cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), zinc (Zn), and polycyclic aromatic hydrocarbons (PAHs) in sediments collected from gully pots for road drainage in Hong Kong. The presence and intensity of anthropogenic contamination of road gully sediments were assessed. Identifications of potential sources of trace elements and PAHs were performed to help understand the situation for future control of pollution to the land and aquatic environments.

Materials and methods

Gully sediment samples were collected from gully pots of 18 roads that are potentially exposed to different pollution sources in Hong Kong. The selection of roads considered different road features, adjacent land uses, and traffic volumes. Composite samples were collected for the analysis of trace elements (Cd, Cr, Cu, Pb, Ni, and Zn) and PAHs by an accredited environmental testing laboratory. Geo-accumulation index (I_geo), contamination factor (C_f), modified degree of contamination (mC_d), ecological risk factor (Er), and pollution load index (PLI) were used to assess the level of ecological risk of trace element contamination. Positive matrix factorization (PMF) and PAH diagnostic ratios were applied to identify the sources of trace elements and PAHs.

Results and discussion

Elevated trace element concentrations were commonly found in gully sediments. The concentrations of Zn (267–3700 mg kg^?1) were the highest compared to the other trace elements. Noticeable high concentrations of Cu (27–1020 mg kg^?1), Pb (21–332 mg kg^?1), and Cr (14–439 mg kg^?1) were found in all samples. The PAH contents were moderate to high (0.6 to 24.7 mg kg^?1). Commercial/industrial emissions and road features that cause frequent acceleration-deceleration and turning events showed important influences on the contaminant levels. Strong correlations between the concentrations of Cd, Cr, Pb, and Zn were identified, implying that these trace elements are likely from common sources. The contamination assessment indices reflect significant sediment pollution. The ecological risk ranges from the considerable/moderate-risk class to over the high-risk class.

Conclusions

The collected gully sediments are identified as highly contaminated and need to be isolated from the environment upon final disposal. Through the comprehensive analysis of the collected data, this study provides a detailed insight into the contaminant levels of road gully sediments and potential sources of contamination. Disposal of gully sediments and potential impacts due to release of contaminants into the downstream aquatic environment during rainstorm events should receive attention and need further investigation.

     

Effects of NTA on Pb phytostabilization efficiency of Athyrium wardii (Hook.) grown in a Pb-contaminated soil

Purpose

Chelate-assisted phytoremediation with biodegradable chelates has been considered to be a promising technique to enhance phytoremediation efficiency, while little information is available on phytostabilization. This study aims to assess NTA-assisted phytostabilization of Pb-contaminated soils by Athyrium wardii (Hook.).

Materials and methods

A pot experiment was carried out to investigate the effects of different application days (1, 3, 5, 7, 10, 14, 21) of nitrilotriacetic acid (NTA) on plant growth, Pb accumulation, and Pb availability in rhizosphere soils of A. wardii grown in soils contaminated with low (200 mg kg^?1) and high (800 mg kg^?1) concentrations of Pb.

Results and discussion

With the application of NTA, better growth for A. wardii was observed when treated with NTA for 5–14 days for both low and high Pb soils, suggesting potential harvest time. Pb concentrations and Pb accumulation in underground parts of A. wardii grown in low and high Pb soils increased with increasing application time of NTA generally. Similar changes were also found for bioaccumulation coefficients (BCFs) of A. wardii. The greatest remediation factors (RFs) for underground parts and whole plant of A. wardii were observed for NTA application time of 7 and 5 days for low and high Pb soils, suggesting the greatest remediation efficiency. Furthermore, plant growth, BCF, and RF of A. wardii grown in low Pb-contaminated soils were greater than those grown in high Pb-contaminated soils. Pb availability in rhizosphere soils of A. wardii grown in low Pb soils was lower than those in high Pb-contaminated soils.

Conclusions

It seems to be the optimum for A. wardii to phytostabilize slightly Pb-contaminated soils with the application of NTA for 7 days as taking plant growth, Pb remediation efficiency, and environmental risk into consideration.

     

Optimization of portable X-ray fluorescence spectrometry for the assessment of soil total copper concentrations: application at an ancient smelting site

Purpose

Copper (Cu) is the earliest anthropogenic metal pollutant, but knowledge of Cu soil concentrations at ancient metalworking sites is limited. The objective of this work was to examine the ability of portable X-ray fluorescence to quantify Cu in soils at such sites.

Materials and methods

Using a Bruker Tracer III-SD pXRF, we examine factory “scan” settings versus simple instrument parameter changes (a reduction in energy settings from 40 to 12 kV) to target analysis for Cu. We apply these to a set of uncontaminated samples (n?=?18, <?92 mg Cu kg^?1) from Central Thailand and compare results to standard wet chemistry analysis (aqua regia digestion and ICP-OES analysis). We then apply the optimized method to a set of highly contaminated samples (n?=?86, <?14,200 mg Cu kg^?1) from a known ancient smelting site.

Results and discussion

We demonstrate that simple changes to factory recommended “scan” settings can double the sensitivity of Cu determination via pXRF (“optimized limit of determination” of 19.3 mg kg^?1 versus an initial value of 39.4 mg kg^?1) and dramatically improve the accuracy of analysis. Changes to other results for other elements are variable and depend on concentration ranges, soil matrix effects, and pXRF response for the individual element. We demonstrate that pXRF can accurately determine Cu across a wide concentration range and identify grossly contaminated soil samples.

Conclusions

We conclude that pXRF is a useful tool to rapidly screen and analyse samples at remote sites and can be applied to ancient metalworking sites. Simple optimization of the pXRF settings greatly improves accuracy and is essential in determining comparative background concentrations and “unaffected” areas. Application to other elements requires further element and matrix specific optimization.

     

Mercury Cycling in Lake Gordon and Lake Pedder,Tasmania (Australia). II: Catchment Processes

The sources and concentrations of total mercury (total Hg) and methylmercury (MeHg) in the upper catchment of the Lake Gordon/Lake Pedder system in Tasmania, Australia were investigated. The catchment area, which contains over 50% wetlands, is located in a temperate region with no obvious point sources of mercury. Surface waters in the region had concentrations of total Hg ranging from 1.2 to 14.4 ng L^-1 and MeHg from < 0.04 to 1.4 ng L^-1. MeHg concentrations were seasonally dependent, with the highest concentrations occurring in summer. Sediments/soils in the catchment had concentrations of total Hg ranging from 4.0 to 194 ng g^-1 and MeHg from <0.02 to 20.1 ng g^-1. The low concentrations of total Hg confirmed that this region is pristine as regards mercury and has no geological enrichment of total Hg. The highest total Hg and MeHg concentrations in both sediment/soils and waters were found in bogs whereas the lowest concentrations typically occurred on the wetlandplains. MeHg concentrations, in bog and swamp sediments were correlatedwith the organic matter content (r = 0.942, P < 0.001). Acid volatile sulfide (AVS) measurements indicate that in most sediments AVS was greater than total Hg. Given the high reactivity of inorganic mercury and sulfide, this suggests that most of the particulate mercury in sediments is present as mercuric sulfide. The yield of MeHg from the catchment was estimated to be 3.2 mg ha^-1 yr^-1 and is higher than published rates measured in non-contaminated temperate catchments in the northern hemisphere. The higher yield was attributed to the generally warmer climatic conditions that favour net methylation and the relatively high rainfall (2–3 m yr^-1) of the region, which supplies reactive inorganic mercury to the active zones ofmercury methylation and also flushes MeHg from the catchment.     

Phytoextraction of cobalt (Co)-contaminated soils by sweet alyssum (Lobularia maritima (L.) Desv.) is enhanced by biodegradable chelating agents

Purpose

Combining biodegradable chelating agents with phytoextraction is an efficient technique to amend metal-contaminated soils, but most studies have addressed remediation efficiency rather than a comprehensive understanding of the interactions among plant stress, metal accumulation, and metal bioavailability. This study aimed to investigate the effects of biodegradable chelating agents on improving the efficiency of phytoextraction for cobalt (Co)-contaminated soil by sweet alyssum (Lobularia maritima (L.)) and to explore the interrelationships among plant stress, Co accumulation, and Co bioavailability.

Materials and methods

Sweet alyssum (three plants per pot) was grown in pots containing soil with Co added at 0, 40, and 60 mg kg^?1, respectively. After 70 days of growth, we added four biodegradable chelating agents (EDDS, NTA, CA, and OA) at various concentrations (0, 2.5, 5.0, and 7.5 mmol kg^?1). The plants were harvested after 7 days, and the biomass, reactive oxygen species (ROS) parameters, Co concentrations of the shoot and root, and available Co content in the soil were analyzed.

Results and discussion

The results demonstrate that chelating agents significantly (p?<?0.05) improved the phytoextraction capability of sweet alyssum and influenced plant growth and stress. The capability of EDDS to activate Co was higher than that of other chelating agents at identical concentrations in Co-contaminated soils. Furthermore, we observed that a moderate concentration (40 mg kg^?1) of Co could promote plant growth and that high concentrations of Co (60 mg kg^?1) and EDDS (7.5 mmol kg^?1) cause enhanced stress to plant growth, even resulting in lower shoot Co accumulation than that in the moderate EDDS treatment (5.0 mmol kg^?1).

Conclusions

The present study demonstrates that the application of EDDS may be a better choice for Co phytoextraction than NTA, CA, and OA; nevertheless, a high concentration of EDDS may enhance the negative effects on plant growth, physiological traits, and Co accumulation.

     

Phosphorus desorption from calcareous soils with different initial Olsen-P levels and relation to phosphate fractions

Purpose

Calcareous soils are characterized by high pH and phosphorus (P) fixation capacity. Increasing application of P fertilizer recently has significantly improved soil P concentration, especially available P (Olsen-P) and inorganic phosphate (P_i) fractions. However, there are few data available on the ability of soils with different initial Olsen-P levels to continuously supply P (i.e., P desorption capacity) to crops without additional P fertilization and on which P_i fraction exerts the greatest influence on P desorption capacity.

Materials and methods

Five soils with different initial Olsen-P levels (0.5, 14.3, 38.4, 55.4, 72.3 mg kg^?1, hereafter refer as OP1, OP2, OP3, OP4, and OP5) but similar other soil properties were selected to evaluate the capacity of P desorption and its relationship with P_i fractions. Soil P was sequentially extracted once daily for 16 consecutive days using Olsen solution.

Results and discussion

The content and proportions of dicalcium phosphate fraction (Ca₂-P), octacalcium phosphate fraction (Ca₈-P), aluminum phosphorus fraction (Al-P), and iron phosphorus fraction (Fe-P) in P_i increased significantly with the increase of initial Olsen-P (P?<?0.01). Applied P fertilizer was mostly stored as Ca₈-P in the soil. Soil P desorbed reached an equilibrium after 16 extractions for all soils, and P desorption capacity (12–358 mg kg^?1) showed a significant linear relationship with initial Olsen-P (P?<?0.01), with an increase of 4.2 mg kg^?1 desorbed P per 1 mg kg^?1 increase of initial Olsen-P. Ca₂-P exerted the conclusive effect on P desorption in the first four extractions, but Ca₈-P played a more important role in the 16 extractions.

Conclusions

Ca₈-P was the greatest potential pool for P desorption after Ca₂-P was depleted. P desorption capacity was significantly linearly related to initial Olsen-P (P?<?0.01). Different fertilizer use strategies were developed based on P desorption capacity for soils with different initial Olsen-P levels. The present study provided basic data on how to reduce effectively the application amount of chemical P fertilizer.

     

Lanthanides and yttrium in the sediments of the lower Minho River (NW Iberian Peninsula): imprint of tributaries

Purpose

Rare earth elements have been used as sediment tracers in river, estuarine and coastal environments but rarely applied as fluvial tributary tracers. Lanthanides (Ln) and yttrium (Y) were quantified in fluvial sediments of the Minho River lower course (NW Iberian Peninsula), where the catchment contains heterogeneous lithologies, to define the characteristic imprints of tributaries and their relevance in the riverine system.

Materials and methods

Surface sediments were sampled at 36 points in the lower Minho riverbed and its nine main tributaries.The <?2-mm fraction was sieved and ground, and ≈?100 mg was completely acid-digested with HF and aqua regia in closed Teflon bombs at 100 °C for 1 h. The residue was evaporated, re-dissolved with HNO₃ and Milli-Q water, heated 20 min at 75 °C and diluted to 50 cm³ with Milli-Q water. Lanthanides and yttrium were determined using a quadrupole ICP-MS equipped with a Peltier impact bead spray chamber and a concentric Meinhard nebuliser. Blanks accounted for less than 1% of the element concentrations in the samples. The precision and accuracy of the analytical procedures were controlled through reference materials AGV-1 and MAG-1.

Results and discussion

Contents ranged from 22 to 153 mg Ln kg^?1 and 1.5–22.9 mg Y kg^?1 and ES-normalised light-heavy Ln fractionation, (L_N/H_N), varied between 0.6 and 2.6. These wide ranges, together with Eu and Ce anomalies and element-by-element Ln, varied with changes in parental rocks of the lower Minho basin. Minho sediments showed negative Ce anomalies (0.81?±?0.29) and positive Eu anomalies (1.23?±?0.18). Sediments received traces of granitic pegmatites and gneissic peralkaline rocks from two tributaries: the Gadanha (22.9 mg Y kg^?1; 83 mg Ln kg^?1; 0.60 L_N/H_N; 0.51 Eu/Eu*; 0.88 Ce/Ce*) and the Louro (15.9 mg Y kg^?1; 110 mg Lnkg^?1; 0.97 L_N/H_N; 0.69 Eu/Eu*; 1.49 Ce/Ce*). The Tamuxe tributary, flowing through a slate and quartzite fault, provided the lowest source (1.6 mg Y kg^?1; 28 mg Ln kg^?1; 2.48 L_N/H_N; 1.01 Eu/Eu*; 0.55 Ce/Ce*).

Conclusions

Lanthanide and Y signatures in sediments may be used to trace land-tributary-river influences. The imprints are observed downstream of fluvial confluences but not in all cases, responding to basin lithological changes, particularly for pegmatites and peralkaline rocks. The general REE trend is described using Y contents only. Tributaries, which are responsible for one-fifth of the Minho water load, provide one-half of their sediments. Non-homogeneous sediment patterns may be magnified in dammed rivers such as the Minho.

     

Microbiological analysis of cadmium-contaminated sediments during biostabilization with indigenous sulfate-reducing bacteria

Purpose

Sulfate-reducing bacteria (SRB) have received particular attention in the bioremediation of sediments contaminated with heavy metals. In this study, indigenous SRB were used to stabilize Cd in sediments spiked with different Cd concentrations (≤ 600 mg kg^?1).

Materials and methods

The study investigated the Cd leaching efficiency from sediments after 166 days (d) of biotreatment and assessed the bacterial community and bacteria relationship in sediments during SRB biostabilization.

Results and discussion

The study found that the Cd leaching efficiency of sediments was reduced by 18.1–40.3% (29.4 ± 8.7%) after 166 days of biotreatment. During the biostabilization, the bacterial community in sediments significantly changed, particularly after 61 days of biotreatment. At the family level, the identified dominant bacteria (mean abundance > 3%) included Bacillaceae, norank Nitrospira, Anaerolineaceae, Nitrospinaceae, Streptococcaceae, and Hydrogenophilaceae. The study also speculated the complex relationships between these bacteria. The relative abundance of Desulfobacteraceae and Desulfobulbaceae in sediments was enhanced after biotreatment. Bacillaceae and Streptococcaceae may play a negative role in Cd biostabilization and inhibited SRB biological activity. However, Anaerolineaceae and Hydrogenophilaceae may have commensalism and mutualism relationships, respectively, with typical SRB. The presence of Nitrospinacea and norank Nitrospira may reduce the inhibitive effect of denitrifying bacteria on SRB, thereby exhibiting a positive effect on biologic sulfate reduction and Cd biostabilization.

Conclusions

Indigenous SRB treatment increased Cd stability in sediments and changed bacterial community. During SRB biostabilization, complex relationships between bacteria in sediments were speculated, including competition, syntrophism, and antagonism. These results provide insights for better regulating and controlling SRB biostabilization.

     

Response of soil C:N:P stoichiometry,organic carbon stock,and release to wetland grasslandification in Mu Us Desert

Purpose

Wetlands in Mu Us Desert have severely been threatened by grasslandification over the past decades. Therefore, we studied the impacts of grasslandification on soil carbon (C):nitrogen (N):phosphorus (P) stoichiometry, soil organic carbon (SOC) stock, and release in wetland-grassland transitional zone in Mu Us Desert.

Materials and methods

From wetland to grassland, the transition zone was divided into five different successional stages according to plant communities and soil water conditions. At every stage, soil physical and chemical properties were determined and C:N:P ratios were calculated. SOC stock and soil respirations were also determined to assess soil carbon storage and release.

Results and discussion

After grasslandification, SOC contents of top soils (0–10 cm) decreased from 100.2 to 31.79 g kg^?1 in June and from 103.7 to 32.5 g kg^?1 in October; total nitrogen (TN) contents of top soils (0–10 cm) decreased from 3.65 to 1.85 g kg^?1 in June and from 6.43 to 3.36 g kg^?1 in October; and total phosphorus (TP) contents of top soils (0–10 cm) decreased from 179.4 to 117.4 mg kg^?1 in June and from 368.6 to 227.8 mg kg^?1 in October. From stages Typha angustifolia wetland (TAW) to Phalaris arundinacea L. (PAL), in the top soil (0–10 cm), C:N ratios decreased from 32.2 to 16.9 in June and from 19.0 to 11.8 in October; C:P ratios decreased from 1519.2 to 580.5 in June and from 19.0 to 11.8 in October; and N:P ratios decreased from 46.9 to 34.8 in June and changed from 34.9 to 34.0 in October. SOC stock decreased and soil respiration increased with grasslandification. The decrease of SOC, TN, and TP contents was attributed to the reduction of aboveground biomass and mineralization of SOM, and the decrease of soil C:N, C:P, and N:P ratios was mainly attributed to the faster decreasing speeds of SOC than TN and TP. The reduction of aboveground biomass and increased SOC release led by enhanced soil respiration were the main reasons of SOC stock decrease.

Conclusions

Grasslandification led to lowers levels of SOC, TN, TP, and soil C:N, C:P, and N:P ratios. Grasslandification also led to higher SOC loss, and increased soil respiration was the main reason. Since it is difficult to restore grassland to original wetland, efficient practices should be conducted to reduce water drainage from wetland to prevent grasslandification.

     

Plant Availability and Uptake of Lead, Zinc, and Cadmium in Soils Contaminated with Anti-corrosion Paint from Pylons in Comparison to Heavy Metal Contaminated Urban Soils

Red lead (Pb₃O₄) has been used extensively in the past as an anti-corrosion paint for the protection of steel constructions. Prominent examples being some of the 200,000 high-voltage pylons in Germany which have been treated with red lead anti-corrosion paints until about 1970. Through weathering and maintenance work, paint compounds and particles are deposited on the soils beneath these constructions. In the present study, six such “pylon soils” were investigated in order to characterize the plant availability and plant uptake of Pb, Cd, and Zn. For comparison, three urban soils with similar levels of heavy metal contamination were included. One phase extractions with 1 M NH₄NO₃, sequential extractions (seven steps), and extractions at different soil pH were used to evaluate the heavy metal binding forms in the soil and availability to plants. Greenhouse experiments were conducted to determine heavy metal uptake by Lolium multiflorum and Lactuca sativa var. crispa in untreated and limed red lead paint contaminated soils. Concentrations of Pb and Zn in the pylon soils were elevated with maximum values of 783 mg Pb kg⁻¹ and 635 Zn mg kg⁻¹ while the soil Cd content was similar to nearby reference soils. The pylon soils were characterized by exceptionally high proportions of NH₄NO₃-extractable Pb reaching up to 17% of total Pb. Even if the relatively low pH of the soils is considered (pH 4.3–4.9), this appears to be a specific feature of the red lead contamination since similarly contaminated urban soils have to be acidified to pH 2.5 to achieve a similarly high Pb extractability. The Pb content in L. multiflorum shoots reached maximum values of 73 mg kg⁻¹ after a cultivation time of 4 weeks in pylon soil. Lime amendment reduced the plant uptake of Pb and Zn significantly by up to 91%. But L. sativa var. crispa cultivated on soils limed to neutral pH still contained critical Pb concentrations (up to 0.6 mg kg⁻¹ fresh weight). Possible mechanisms for the exceptionally high plant availability of soil Pb derived from red lead paint are discussed.     

Two-year fluctuation of Cd bioavailability in a remediated rice field under different water managements

Purpose

Based on two consecutive years of field-scale trials, under different water managements, we illustrated the persistence of remediation effect of palygorskite on a Cd-polluted rice field.

Materials and methods

The Cd uptake by a plant, pH and Cd chemical extractability, available P/K, and extractable Zn/Cu in paddy soils were used to evaluate the influence of palygorskite on Cd immobilization and soil fertility index.

Results and discussion

In contrast to the 1st year, at 0–1.5% palygorskite applied dose in soils, 0.025 M HCl–extractable Cd in continuous flooding reduced by 12.1–19.0%, and that in wetting irrigation increased by 10.9–18.9% in the 2nd year (p?<?0.05). The toxicity characteristic leaching procedure Cd reduction of 3.0–11.4% and increase of 8.9–12.0% were obtained under above-mentioned water managements (p?<?0.05). Compared with the 1st year, at different clay additional concentrations, grain Cd in continuous flooding reduced by 7.0–11.3%, and that in wetting irrigation increased by 6.5–10.8% in the 2nd year (p?<?0.05). Although trace elements in clay treated soils declined, they had no influence on the grain yield due to a minimum value higher than the critical value of 1.5 mg kg^?1 for Zn and 2.0 mg kg^?1 for Cu. The available P in continuous flooding took on a maximum increase of 8.2% in the 2nd year (p?<?0.05).

Conclusions

Two consecutive years of field-scale in situ demonstration tests revealed that continuous flooding was a preferable water management regime for Cd immobilization using palygorskite in the rice field. There were no remarkable differences in extractable Zn/Cu between 2 years.

     

Distribution and provenance implication of rare earth elements and Sr-Nd isotopes in surface sediments of Jiulong River,Southeast China

Purpose

The purposes of this paper are to investigate the geochemical characteristics of rare earth elements (REEs) in the surface sediments of Jiulong River, southeast China, to probe the provenance compositions of the sediments, and to analyze the potential anthropogenic influence on REEs in the sediments. REEs and Sr-Nd isotopes were selected as the tools because REEs can be used to identify the anthropogenic effects on sediments and Sr-Nd isotopes have been widely known as powerful tracers for provenance analysis.

Materials and methods

Fifty-three samples of surface sediments (0~5 cm) were collected from Jiulong River. The concentrations of REEs and Sr-Nd isotopic compositions in the surface sediments were determined by inductively coupled plasma mass spectrometry (ICP-MS) and thermal ionization mass spectrometry (TIMS), respectively. The chondrite-normalized and WRAS-normalized REEs patterns, enrichment factor, plots of La-Th-Sc and La/Yb-∑REE, and plots of ε_Nd(0) vs ⁸⁷Sr/⁸⁶Sr and ε_Nd(0) vs δEu are presented.

Results and discussion

The mean concentration of ΣREEs in the surface sediments of Jiulong River was 254.25 mg kg^?1. The mean values of ΣLREEs (227.6 mg kg^?1), ΣHREEs (26.64 mg kg^?1), and (La/Yb)_N ratios (9.24) suggested an enrichment of LREEs compared to HREEs. Negative Eu anomalies were observed in the surface sediments. The distribution patterns of REEs in the surface sediments from different areas of Jiulong River were remarkably similar. The values of ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, and ε_Nd(0) were 0.714091~0.733476, 0.511875~0.512271, and ??14.88~??7.16, respectively. The plots of ε_Nd(0) vs ⁸⁷Sr/⁸⁶Sr, ε_Nd(0) vs 1/[Nd], and ε_Nd(0) vs δEu indicated that the sediments in Jiulong River were mainly derived from natural geological processes and the REEs might be also influenced by anthropogenic activities such as Fujian Pb-Zn deposit, coal ash, and industrial sludge.

Conclusions

The REEs in the surface sediments at different sites are similar in geochemical characteristics, with a right-inclined distribution pattern and higher enrichment of light REEs (LREEs) compared to heavy REEs (HREEs), and a negative Eu anomaly but no evidence of Ce anomaly. The sediments in Jiulong River were mainly derived from natural geological processes (granite and magmatic rocks), and the REEs in the sediments were also influenced by anthropogenic activities (Fujian Pb-Zn deposit, coal ash, and industrial sludge).

     

河北板蓝根产地土壤-植物中镉铅汞砷含量特征及其污染评价

采用野外调查和室内分析相结合的方法,研究了河北省安国市和蔚县板蓝根产地土壤-植物中Cd、Pb、Hg、As含量特征及其在菘蓝中的累积特性,并对板蓝根产地土壤和草药中Cd、Pb、Hg、As污染状况进行了评价,为该地区安全、合理地发展中草药生产提供数据支撑和科学依据。结果表明,安国市和蔚县板蓝根产地土壤中重金属Cd、Pb、Hg、As含量差异不大,土壤重金属含量的变异系数在11.70%~97.65%。以《土壤环境质量标准》(GB 15618—1995)一级标准值进行评价,综合污染指数评价结果显示45%板蓝根种植区土壤Cd、Pb、Hg、As污染等级为警戒限,其他处于清洁水平;而以《土壤环境质量标准》二级标准值进行评价,种植区单项污染指数及综合污染指数结果均0.7,土壤环境清洁。此外,菘蓝地上部(大青叶)Cd、Pb、Hg、As平均含量分别为0.22 mg·kg~(-1)、0.89 mg·kg~(-1)、0.04 mg·kg~(-1)、0.25 mg·kg~(-1),对重金属的富集能力表现为CdHgPbAs;菘蓝地下部(板蓝根)Cd、Pb、Hg、As含量均值分别为0.14 mg·kg~(-1)、0.57 mg·kg~(-1)、0.04 mg·kg~(-1)、0.26 mg·kg~(-1),对重金属的富集能力表现为CdHgAsPb。所有菘蓝样品中Pb、Hg、As含量均未超出《药用植物及制剂进口绿色行业标准》(WM2—2001),大青叶9.09%样品中Cd超标,且Cd平均污染指数0.7,属警戒限污染等级。因此,在中药材GAP(良好的农业规范)产地环境质量评价时,除板蓝根产地土壤完全符合土壤环境质量二级标准外,也不应忽视板蓝根和大青叶吸收和累积重金属的自身特性。     

Mercury methylation,uptake and bioaccumulation by the earthworm Lumbricus terrestris (Oligochaeta)

To date, most studies about mercury (Hg) methylation and bioaccumulation have focused on aquatic ecosystems. In contrast, information regarding the biogeochemical cycle of Hg in terrestrial ecosystems is scarce. Considering the relevance of earthworms in soils, it is very important to study their role in the bioaccumulation and transformation of Hg species (inorganic Hg, IHg, and monomethylmercury, MeHg). The aim of this experimental study was to compare the uptake and bioaccumulation of MeHg and IHg in the earthworm Lumbricus terrestris exposed to soils freshly spiked with inorganic Hg as well as historically contaminated soils. The study consisted of a 28-day uptake phase in Hg (spiked and natural) contaminated and non-contaminated soils followed by a 14-day depuration phase in non-contaminated soils. Soils were characterized by determining not only Hg concentrations (total Hg, MeHg and acid-labile Hg) but also analysed for other physicochemical parameters that can influence the fate of Hg within the earthworm–soil system. Mercury species were determined in earthworms (whole organism) exposed to Hg contaminated and non-contaminated soils. Mercury availability in soils seems to be the main factor controlling the uptake and bioaccumulation of Hg species because, according to kinetic data, the spiked IHg was more readily assimilated and methylated by earthworms. Bioaccumulation factors (BAFs) for MeHg and total Hg were also higher in spiked than in naturally Hg-contaminated soils. In addition, BAFs for MeHg (ranging from 0.8 to 17.3) were higher than those for total Hg (between 0.02 and 0.62) which suggests that MeHg was more easily bioaccumulated by this earthworm species and also that earthworms may actively contribute to MeHg production in soils.     

Washing agents from sewage sludge: efficiency of Cd removal from highly contaminated soils and effect on soil organic balance

Purpose

To compare Cd removal from different soils with three washing agents recovered from sewage sludge (dissolved organic matter (DOM), soluble humic-like substances (HLS), soluble humic substances (SHS)). Also, to investigate how washing with these agents changes soil organic-matter composition (OM).

Materials and methods

Sandy clay loam (S1) and clay (S2) highly contaminated with Cd (300 mg kg^?1) were washed with DOM, HLS, or SHS solutions at various pHs, and with various washing times and washing modes (single or double). Cd distribution and OM composition were determined (including content of humic substances (HS), fulvic fraction (FF), labile humic acids (L-HA), and stable humic acids (S-HA)).

Results and discussion

Cd removal proceeded with pseudo-second-order kinetics. Equilibrium was reached in 30 min (S1) and 60 min (S2). DOM, HLS, and SHS removed 75–82% of Cd from S1, and 80–87% from S2. The most mobile fraction of Cd was removed after one wash. S2 retained more OM, including HS, than S1. Although washing did not change the HA/FF ratio in most variants, washing with DOM and HLS increased the percentage of L-HA in both soils. Washing with SHS increased S-HA content in both soils, but the percent content of S-HA was similar to that in the unwashed soil.

Conclusions

DOM, HLS, and SHS derived from sewage sludge can effectively remediate clay and sandy clay soils highly contaminated with Cd. Washing with an SHS solution can increase the content of the most stable carbon forms (HA), which is beneficial for carbon sequestration in remediated soils.

     

Mercury distribution and speciation in floodplain soils and uptake into native earthworms (Diplocardia spp.)

Historically as part of its national security mission, the U.S. Department of Energy's Y-12 National Security Facility in Oak Ridge, TN acquired a significant fraction of the world's supply of elemental mercury. During the 1950s and 1960s, a large amount of elemental mercury escaped confinement and is still present in the watershed surrounding the Y-12 facility. Earthworms are key components in natural food chains, providing a food source for many small mammals and important food sources for small birds. The objectives of this study were to investigate the current status of mercury distribution and speciation and determination of mercury bioavailability to native earthworms in floodplain soils of East Fork Poplar Creek (EFPC) after decades of U.S. Department of Energy's remediation. The present study clearly shows that the total mercury in a tested floodplain field of EFPC was significantly below the US Department of Energy target 400 mg Hg/kg. The major mercury form in the current floodplain soils of EFPC is mainly the non-cinnabar mercury bound form in soil silicates (4 M HNO₃-extractable residual fraction). The results show strong linear relationships between mercury concentrations in native earthworms (both mature and immature groups) and the non-cinnabar mercury form. Native earthworms may be used as a potential mercury ecological bio-indicator (bio-marker) for demonstrating mercury bioavailability and ecotoxicity in the ecosystem.     

Effects of water and organic manure coupling on the immobilization of cadmium by sepiolite

Purpose

Natural sepiolite (SP) has proven effective on the in-situ immobilization remediation of Cd-contaminated soils. But the practical remediation effect may largely influenced by water management and the application of organic manure. The effects of chicken manure (CM) on SP-amended soils were investigated under normal and saturated water conditions using a pot experiment with Brassica campestris L.

Materials and methods

Cd-contaminated paddy soils were amended with CM, SP, and CM?+?SP with no amendment as control. The amount of sepiolite was 0.5% (w/w, the same below) either in SP or CM?+?SP amended soils, while the amount of CM was 0.5, 1.0, and 2.0% in CM and CM?+?SP-amended soils. The plant metal contents, fresh weight, and soluble sugar content of plant edible parts were measured on harvest. Soil Cd was extracted by diethylenetriaminepentaacetic acid (DTPA) and HCl to estimate the mobility of heavy metal. Soil pH and dissolved organic matter (DOM) of rhizosphere soil were determined. The electronegative charges of soils were also measured using the zeta potential.

Results and discussion

The application of CM and increasing soil moisture on SP-amended soil increased plant growth to a greater extent than the application of SP alone. The application of CM along with the increase of soil moisture decreased Cd uptake and translocation in plants grown on SP-amended soil compared to the application of SP alone. Cd content of edible plant parts reached a minimum of 0.24 mg kg^?1 with the application of 2.0% CM on SP-amended soils under water-saturated conditions, which was approximately 50% lower than the Cd concentration found when applying SP alone.

Conclusions

The results of this study suggest that the application of sepiolite on Cd contaminated soil can effectively reduce Cd uptake by B. campestris L., and the addition of CM combined with effective water management also appears to further reduce Cd absorption and accumulation.