Metal contamination of bed sediments in the Irwell and Upper Mersey catchments,northwest England: exploring the legacy of industry and urban growth

Purpose

Manchester is often heralded as the first industrial city. Large volumes of physical and liquid contaminants were released into its river network throughout the industrial period up to the latter part of the twentieth century. Water quality has improved dramatically in recent decades, but, given their environmental significance, it is important to ascertain the extent to which a legacy of contamination persists in the modern bed sediments.

Materials and methods

Fine-grained bed sediments were sampled at 40 sites in the Mersey and Irwell catchments. Sediments were wet sieved to isolate the <63-μm grain size fraction. Metal concentrations were determined using XRF. Particle size characteristics were also measured. Sediments were subjected to a five-step sequential extraction procedure to ascertain the environmental significance of metal concentrations. Alongside archival research of past industry, enrichment factors, multivariate statistical techniques and conditional inferences trees were used to identify sources of heavy metals.

Results and discussion

Bed sediment-associated heavy metal(loid) concentrations were as follows: As (9.89–110 mg kg^?1), Cr (76.5–413 mg kg^?1), Cu (53.1–383 mg kg^?1), Pb (80.4–442 mg kg^?1) and Zn (282–1020 mg kg^?1). Enrichment factors ranged from moderate to extremely severe, with Pb showing the greatest enrichment across the catchments. Chemical mobility was generally low, but metal(loid) partitioning identified the influence of anthropogenic sources. Statistical analysis highlighted a number of point sources associated with former industrial sites that operated during the industrial period. Conditional inference trees highlighted the role of the textile industry on Cu concentrations in addition to indicating the complexity of sources, fluxes and stores of sediment-associated contamination throughout the system.

Conclusions

Fine-grained sediment-associated metal(loid)s in the Mersey and Irwell catchments are anthropogenically enriched. Concentrations also exceed sediment quality guidelines. A lack of distinct spatial patterning points to a complex network of contaminant inputs across the catchments, even in the headwaters. Whilst potential modern urban sources are likely to be important, spatial patterns and multivariate/data mining techniques also highlighted the importance of releases from former industrial sites as well as the reworking of historically contaminated floodplains and soils.

     

Trace metals in the soils of Water Conservation Area of Florida Everglades: Considerations for ecosystem restoration

Purpose

Inorganic contaminants present a major challenge for the restoration of aquatic ecosystems. The objectives of this study were to determine the extent of trace metal contamination and investigate the influence of different plant communities on trace metal accumulation in the soils of the Florida Everglades.

Materials and methods

Soil samples (n?=?117) were collected from 0 to 10-cm depth using a stainless steel coring device from sites with three dominant plant communities—cattail, sawgrass, and slough—of Water Conservation Area-2A (43,281 ha) of Florida Everglades.

Results and discussion

The mean pH in soils collected from three plant communities was 6.75–6.82, whereas electrical conductivity was slightly greater in the sawgrass (0.69 dS m^?1) than cattail (0.58 dS m^?1) and slough (0.40 dS m^?1). Mean reduction–oxidation potential was greatest in cattail (?113 mV) than sawgrass (?85.3 mV) and slough (?48.3 mV) soils. Among 11 trace metals (As, B, Co, Cr, Cu, Mn, Mo, Na, Ni, Pb, Zn) found in soil samples, Na had the greatest contents and was greater in cattail (2070 mg kg^?1) and sawgrass (1735 mg kg^?1) than slough (1297 mg kg^?1). Four trace metals (B, Cu, Mo, Ni) were significantly greater in cattail than sawgrass and slough. Whereas, Mn was significantly lower in cattail (31 mg kg^?1) than both sawgrass (84 mg kg^?1) and slough (51 mg kg^?1). Cattail also had significantly lower Cr (1.97 mg kg^?1) and Pb (10 mg kg^?1) than sawgrass (Cr 2.5 mg kg^?1; Pb 20.8 mg kg^?1). As (<6.9 mg kg^?1), Co (<1.3 mg kg^?1), and Zn (<17.2 mg kg^?1) were not significantly different among soils collected from three plant community-dominant sites. Contents of Cd and Se were below the method detection limits (Cd 0.01 mg L^?1; Se 0.2 mg L^?1) and are not reported.

Conclusions

None of the trace metals in the soils exceeded the US Environmental Protection Agency sediment toxicity thresholds. Results from this study provided baseline concentrations of trace metals, which can be used to measure the success of restoration efforts in Florida Everglades.

     

Evaluation of Mercury,Lead, Arsenic,and Cadmium in Some Species of Fish in the Atrato River Delta,Gulf of Urabá, Colombian Caribbean

The concentrations of mercury, lead, cadmium, and arsenic were evaluated in 96 samples, 12 by each one of the following eight fish species: snook (Centropomus undecimalis), crevalle jack (Caranx hippos), Serra Spanish mackerel (Scomberomorus brasiliensis), southern red snapper (Lutjanus purpureus), blue runner (Caranx crysos), Atlantic tarpon (Megalops atlanticus), ladyfish (Elops saurus), and Atlantic goliath grouper (Epinephelus itajara), which were collected during 1 year in the Atrato River Delta in the Gulf of Urabá, Colombian Caribbean. Three fish were caught from each of the following sites the community usually uses to catch them (known as fishing grounds): Bahía Candelaria, Bahía Marirrío, Bocas del Roto, and Bocas del Atrato. The quantification of metals was performed by microwave-induced plasma-optical emission spectrometry. The Pb concentration fluctuated from 0.672 to 3.110 mg kg^?1, surpassing the maximum permissible limit (MPL?=?0.3 mg kg^?1) for human consumption for all species. The Hg concentration ranged between < Limit of detection and 6.303 mg kg^?1, and in the crevalle jack and Atlantic tarpon, concentrations exceeded the MPL (0.5 mg kg^?1). The levels of Cd and As were not significant in the studied species and did not exceed the MPL (0.05 mg kg^?1).     

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.

     

Optimization of arsenic and pentachlorophenol removal from soil using an experimental design methodology

Purpose

In this study, a soil-washing process was investigated for arsenic (As) and pentachlorophenol (PCP) removal from polluted soils. This research first evaluates the use of chemical reagents (HCl, HNO₃, H₂SO₄, lactic acid, NaOH, KOH, Ca(OH)₂, and ethanol) for the leaching of As and PCP from polluted soils.

Materials and methods

A Box–Behnken experimental design was used to optimize the main operating parameters for soil washing. A laboratory-scale leaching process was applied to treat four soils polluted with both organic ([PCP] _i ?=?2.5–30 mg kg^?1) and inorganic ([As] _i ?=?50–250 mg kg^?1, [Cr] _i ?=?35–220 mg kg^?1, and [Cu] _i ?=?80–350 mg kg^?1) compounds.

Results and discussion

Removals of 72–89, 43–62, 52–68, and 64–98 % were obtained for As, Cr, Cu, and PCP, respectively, using the optimized operating conditions ([NaOH]?=?1 N, [cocamidopropylbetaine] _i ?=?2 % w w^?1, t?=?2 h, T?=?80 °C, and PD?=?10 %).

Conclusions

The use of NaOH, in combination with the surfactant, is efficient in reducing both organic and inorganic pollutants from soils with different levels of contamination.     

Cadmium contamination of sediments in the water reservoirs in Silesian Upland (southern Poland)

Purpose

Cadmium (Cd) is considered a toxic element and its concentrations are relevant to human health and the environment. Therefore, the purpose of the study was to determine the extent to which the bottom sediments of water bodies (artificial lakes and ponds) in the Silesian Upland in southern Poland are contaminated with Cd; an attempt was also made to determine the factors that condition spatial differences in the concentration of this element between individual water bodies in the region.

Materials and methods

Measurements of the Cd content in bottom sediments were carried out in 35 water bodies in southern Poland in 2011 and 2012. Depending on the surface area and morphometric characteristics, from two to nine samples representative in terms of sediment thickness were collected in each water body. Cadmium concentrations were determined for 92 0.25 g aliquots using the TD-ICP method.

Results and discussion

Cadmium content in all samples (0.7–580.0 mg kg^?1) was higher than the natural range of concentrations for this element in the Earth’s crust (0.1–0.3 mg kg^?1) and the geochemical background for Poland (0.5 mg kg^?1) and, with a few exceptions, was also higher than the preindustrial concentration (1.0 mg kg^?1) and the regional geochemical background (2.5 mg kg^?1). Adopting natural Cd concentrations in the Earth’s crust (0.1–0.3 mg kg^?1) as the baseline for the geoaccumulation index (I_geo), the sediments examined can be classified as extremely and heavily contaminated (and moderately contaminated in a small number of cases). The assessment of sediment quality based on I_geo, with the regional geochemical background (2.5 mg kg^?1) adopted as the baseline, results in non-contaminated and moderately contaminated sediments being dominant with a far smaller number of heavily and extremely contaminated ones.

Conclusions

In the case of several water bodies, Cd concentrations were at record levels that have not been found anywhere else in the world. On the basis of the I_geo, sediments of varying quality were found—from virtually uncontaminated to extremely contaminated. The I_geo index as an indicator of the quality of bottom sediments is a measure that requires careful interpretation, especially when different concentration levels regarded as natural are used for determining its value.

     

The bioaccumulation of Cd in rice grains in paddy soils as affected and predicted by soil properties

Purpose

The area of cadmium (Cd)-contaminated soil in China is increasing due to the rapid development of the Chinese economy. To ensure that the rice produced in China meets current food safety and quality standards, the current soil quality standards for paddy soils urgently need to be updated.

Materials and methods

We conducted a pot experiment with 19 representative paddy soils from different parts of China to study the effects of soil properties on bioaccumulation of Cd in rice grains. The experiment included a control, a low treatment concentration (0.3 mg kg^–1 for pH?<?6.5 and 0.6 mg kg^–1 for pH?≥?6.5), and a high treatment concentration (0.6 mg kg^–1 for pH?<?6.5 and 1.2 mg kg^–1 for pH?≥?6.5) of Cd salt added to soils.

Results and discussion

The results showed that the Cd content in grains of the control and low and high Cd treatments ranged from 0.021 to 0.14, 0.07 to 0.27, and 0.12 to 0.33 mg kg^–1, respectively. Stepwise multiple regression analysis indicated that soil pH and organic carbon (OC) content could explain over 60 % of the variance in the (log-transformed) bioaccumulation coefficient (BCF) of Cd in grains across soils. Aggregated boosted trees analysis showed that soil pH and OC were the main factors controlling Cd bioavailability in paddy soils. Validation of the models against data from recent literature indicated that they were able to accurately predict the BCF in paddy soils.

Conclusions

These quantitative relationships between the BCF of Cd in grains and soil properties are helpful for developing soil-specific guidance on Cd safety threshold value for paddy soils.     

Trace element content in soil after a sediment-laden flood in northern Chile

Purpose

Arid and hyper-arid zones worldwide are reservoirs of chemical compounds, among them are various trace elements. With climate change, abnormal precipitation is occurring in arid and hyper-arid mountainous zones, which in turn is increasing the displacement of trace elements from mountainous to populated areas. The objective of this study was to evaluate trace element displacement of a sediment-laden flood in the Copiapó River Basin on March 24–25, 2015.

Materials and methods

Sixty topsoil samples were taken from 20 agricultural fields. Soil organic matter content, pH, electrical conductivity, and particle size were determined according to accepted procedures in Chile. Samples were acid-digested to determine total Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Se, and Zn content by flame atomic absorption spectroscopy. Hydride generation AAS was used for As and Se determination, and Hg was quantified by cold vapor AAS. Detection limits were 0.2, 0.05, 0.1, and 5.0 mg kg^?1 for Cd, Hg, Se, and Mo, respectively. Correlation and principal component analyses were made, and theoretical distribution functions were fitted to each element.

Results and discussion

Metal concentration showed a strong correlation between SOM and particle size, explaining the first component from the principal component analysis. All trace elements correlated well between each other except for Mo and Se. Mo values were consistently below detection levels (<5.0 mg kg^?1). Expected values for the elements were (95% of probability): 13–37 g Al kg^?1, 10–50 mg As kg^?1, <0.2–0.6 mg Cd kg^?1, 13–25 mg Cr kg^?1, 27–281 mg Cu kg^?1, 27–40 g Fe kg^?1, <0.05–6.5 mg Hg kg^?1, 516–1.080 mg Mn kg^?1, 7–24 mg Ni kg^?1, 13–50 mg Pb kg^?1, 0.2–0.6 mg Se kg^?1, and 61–172 mg Zn kg^?1. Concentrations of As, Cu, and Hg were consistently above national standards.

Conclusions

The authors conclude that the trace element contents in sediments deposited by the event are within expected values based on soil data in Chile.

     

Distinguishing between natural and anthropogenic sources for potentially toxic elements in urban soils of Talcahuano,Chile

Purpose

The objectives of this study were (1) to determine the concentrations and background concentrations of Ba, Co, Cr, Mn, and Ni in the urban soils of Talcahuano (Chile); (2) assess the level of contamination in the urban soils based on different pollution indexes; and (3) to identify natural or anthropogenic sources in order to obtain a spatial distribution of the pollutants.

Material and methods

A total of 420 samples were collected from the study area as follows: 140 topsoil samples (TS) (0–10 cm), 140 subsoil samples (SS) (10–20 cm), and 140 deep soil samples (DS) (150 cm). The soils were characterized, and the concentrations of Ba, Co, Cr, Mn, and Ni were analyzed by atomic absorption photospectrometry following aqua regia digestion. Correlations and principal component analysis combined with spatial analysis were implemented in order to distinguish the sources and their classification as geogenic or anthropogenic. Several simple and robust statistical methods were applied to datasets in order to explore their potential in the evaluation of a useful and robust background values. The degree of contamination along with the geoaccumulation index, enrichment factor, and contamination factor were also evaluated.

Results and discussion

The median concentrations obtained for various elements includes Ba 461 mg kg^?1, Co 82.7 mg kg^?1, Cr 134 mg kg^?1, Mn 311 mg kg^?1, and Ni 56.1 mg kg^?1. In general, the concentrations of Ba, Co, Cr, Mn, and Ni decrease with depth. Correlations and principal component analysis suggest that Cr, Mn, and Ni are contributed by external sources. The spatial distribution of Cr, Mn, and Ni in TS displays a spatial pattern extending along industrial environments and emission sources.

Conclusions

The estimated background values determined with the iterative 2σ-technique includes 536 mg kg^?1 for Ba, 95.9 mg kg^?1 for Co, 208 mg kg^?1 for Cr, 464 mg kg^?1 for Mn, and 90.5 mg kg^?1 for Ni. The geochemical index, enrichment factor, and the contamination factor register a moderate to considerable contamination in some soil samples.

     

Effects of Single,Binary and Quinary Mixtures of Phenanthrene and Its N-PAHs on <Emphasis Type="Italic">Eisenia fetida</Emphasis> in Soil

It is now acknowledged that aromatic hydrocarbons present in contaminated soils occur in mixtures. The effect of single, binary and quinary mixtures of phenanthrene and selected nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs) were investigated on the survival, growth and behavioural index of earthworms (Eisenia fetida) over a 21-day incubation in soil. The results showed that the LC₅₀ values ranged from (not detected) ND–329.3 mg kg^?1 (single mixture), ND–219.8 mg kg^?1 (binary mixtures) to 148.4 mg kg^?1 (quinary mixture), while the EC₅₀ values (based on weight loss) ranged from 13.3–148.4 mg kg^?1 (single mixture), 63.8–148.4 mg kg^?1 (binary mixture) to 24.2 mg kg^?1 (quinary mixture). Greater impacts were recorded where N-PAHs are present with phenanthrene. Further, behavioural index of E. fetida was affected after 24-h exposure to N-PAH-amended soils. Among the N-PAHs however, benzo[h]quinoline recorded the greatest impact on the survival, growth and behavioural index of E. fetida in soil. Findings from this study showed that three ring-N-PAHs are more toxic than phenanthrene as expected from their physico-chemical properties. The binary and quinary mixtures of phenanthrene and N-PAHs in soil intensified toxicity, suggesting that PAHs-N-PAHs mixtures represent greater risk to soil biota.     

Cumulative effects of repeated chlorothalonil application on soil microbial activity and community in contrasting soils

Purpose

Chlorothalonil (CTN) has received much attention due to its broad-spectrum antifungal function and repeated applications in agriculture production practice. An incubation experiment was conducted to study the accumulating effects of CTN repeated application on soil microbial activities, biomass, and community and to contrast the discrepancy of effects in contrasting soils.

Materials and methods

Different dosage CTN (5 mg kg^?1, T1, and 25 mg kg^?1, T5) was applied into two contrasting soils at 7-day intervals. Soil samples were taken 7 days after each application to assess soil enzyme activities and gene abundances. At the end of incubation, the soil samples were also taken to analyze microbial communities in the two test soils.

Results and discussion

Soil fluorescein diacetate hydrolysis (FDAH) and urease activities were inhibited by CTN repeated applications. After 28 days of incubation, bacterial 16S rRNA gene abundances in T1 and T5 treatments were significantly lower than those in the CK treatments (46.4 and 36.6 % of the CK treatment in acidic red soil, 53.6 and 37.9 % of the CK treatment in paddy soil). Archaeal 16S rRNA gene abundances of T1 and T5 treatments were observed the similar trends (56.1 and 40.8 % of the CK treatment in acidic red soil, 45.6 and 43.7 % of the CK treatment in paddy soil). Repeated applications at 25 mg kg^?1 exerted significantly negative effects on the Shannon-Weaver, Simpson and McIntosh indices.

Conclusions

Microbial activity, biomass, and functional diversity were significantly inhibited by repeated CTN application at the higher dosage (25 mg kg^?1), but the inhibitory effects by the application at the recommended dosage (5 mg kg^?1) were erratic. More emphasis needs to be placed on the soil type and cumulative toxicity from repeated CTN application when assessing environmental risk.

     

Geochemical monitoring of organic and inorganic pollutants in the sediment of the Eastern Posavina (Serbia)

Purpose

The aim of this study was to obtain a complete picture of the geochemical character of the sediment in the eastern Posavina region, Serbia, an area which has thus far not been systematically investigated. Geological mapping and impact assessment were thus carried out for this area.

Materials and methods

Sediments were sampled (from 0 to 0.5 m depth) in four locations in eastern Posavina between 2002 and 2014. Eight heavy metals (Ni, Zn, Cd, Cr, Cu, Pb, As and Hg) and a wide variety of organic parameters (16 EPA polycyclic aromatic hydrocarbons (PAHs), mineral oils, selected pesticides and polychlorinated biphenyls (PCBs)) were monitored. Metals were analysed by flame and graphite atomic absorption spectrometry, and gas chromatography with mass detection was used for the PAH analyses. The origins of the monitored substances were classified using geoaccumulation index (I _geo), ecological risk index (RI) and principal component analysis (PCA/FA).

Results and discussion

The sediments all contained higher heavy metals concentrations than the upper continental crust (UCC), suggesting dynamic natural and anthropogenic processes in this unique region. Significant variations (RSD values from 13 to 190) were observed for Cd (0.001–80.00 mg kg^?1), Hg (0.01–5.40 mg kg^?1), mineral oil (2.00–1851 mg kg^?1) and the sum of 16 EPA PAHs (0.003–5.57 mg kg^?1). The I _geo index classified the pollution risk due to Cr as strong, Cd, Zn and Hg as moderate to strong and Ni as moderate. Based on PCA/FA analysis, the parameters were grouped somewhat differently, with anthropogenic activity found to be responsible for much of the Hg, Cd and Cr pollution present in the sediments.

Conclusions

The analysis revealed eight heavy metals (Ni, Zn, Cd, Cr, Cu, Pb, As and Hg), the sum of 16 EPA PAHs and mineral oil as parameters of great interest for this unique region. These parameters must be the focus of future monitoring programs, in support of appropriate remediation techniques and/or dredging activities, which are required in order to comply with the new Serbian regulations and the relevant EU recommendations.

     

Plant growth and heavy metal bioavailability changes in a loess subsoil amended with municipal sludge compost

Purpose

The effects of municipal sludge compost (MSC) as a soil amendment are often studied in agricultural soil or topsoil contaminated with heavy metals. However, little is known about the effects of MSC amendments on plant growth and heavy metal bioavailability in subsoil. This study was conducted to investigate the effects of MSC application on plant growth and the mobility and bioavailability of Cd, Cu, and Zn in an amended soil-plant system.

Materials and methods

A pot experiment was performed to evaluate the translocation of heavy metals to broad bean (Vicia faba L.) grown in loess subsoil previously amended with different application rates of MSC. The subsoil and MSC were homogeneously mixed to achieve six soil-amended treatments (total weight of 8 kg in each pot) in 0, 0.5, 2, 6, 15, and 30% mass ratios (MSC/total). Soil samples amended with MSC were aged for 60 days before sowing. Soil and plant samples were collected after 120 days of growth. Plant height was periodically measured until harvest. The total quantities of heavy metals and their different fractions were analyzed by using graphite furnace atomic absorption spectroscopy (GF-AAS).

Results and discussion

Compared with the control soil (0% treatment), the average biomass growth rates from the 0.5 to 30% treatments ranged from 14.5 to 170.4% (increasing order), respectively. Cd (0.42–1.85 mg kg^?1) and Cu (14.95–23.01 mg kg^?1) mainly concentrated in the plant roots, and Zn (22.06–36.48 mg kg^?1) mainly concentrated in the plant stems and leaves. Fortunately, the metal concentrations in the edible plant parts (0.03–0.1 mg kg^?1) remained below the Chinese national standard thresholds (0.2 mg kg^?1), possibly because of the alkaline soil pH (8.60–7.74), organic matter (7.4–65.9 g kg^?1) bound to metals, and translocation of less metal to the edible plant parts by biochemical modulation.

Conclusions

MSC can enhance subsoil fertility and promote plant development, especially in the 30% treatment. The mobility and bioavailability of heavy metals suggest that Cd is the element needing to be monitored during MSC application. High organic matter content and alkaline pH are the most important factors for controlling Cd levels. More work is required to determine the long-term impacts of sludge amendment on the soil and environment.

     

Root system responses of hyperaccumulator Solanum nigrum L. to Cd

Purpose

Though phytoremediation is an important technology for remedying heavy metal-contaminated soils, hyperaccumulation mechanism, especially in root, is still less known.

Materials and methods

Pot culture experiment was used to explore the tolerance mechanism of a cadmium (Cd) hyperaccumulator Solanum nigrum L. by determining the main root traits compared to the non-hyperaccumulator Solanum melongena L. (cultivar name Liaoqie 3) in the same plant family.

Results and discussion

The total root lengths, total root surface areas, and total root volumes of S. nigrum were not significantly decreased (p?<?0.05) compared to their controls when Cd spikes were lower than 20 mg kg^–1. However, the abovementioned three factors of S. melongena were significantly decreased (p?<?0.05) when 20 mg kg^–1 of Cd was spiked. By contrast, S. nigrum showed stronger tolerance to Cd. In addition, S. nigrum showed all Cd hyperaccumulator characteristics, i.e., a Cd hyperaccumulator. S. melongena was a non-Cd hyperaccumulator.

Conclusions

These results indicated that root trait can be a factor of hyperaccumulation because of strong tolerance to Cd.     

Pilot-scale counter-current acid leaching process for Cu,Pb, Sb,and Zn from small-arms shooting range soil

Purpose

The main objective of this study was to evaluate the potential of a counter-current leaching process (CCLP) on 14 cycles with leachate treatment at the pilot scale for Pb, Cu, Sb, and Zn removal from the soil of a Canadian small-arms shooting range.

Materials and methods

The metal concentrations in the contaminated soil were 904?±?112 mg Cu kg^–1, 8,550?±?940 mg Pb kg^–1, 370?±?26 mg Sb kg^–1, and 169?±?14 mg Zn kg^–1. The CCLP includes three acid leaching steps (0.125 M H₂SO₄?+?4 M NaCl, pulp density (PD)?=?10 %, t?=?1 h, T?=?20 °C, total volume?=?20 L). The leachate treatment was performed using metal precipitation with a 5-M NaOH solution. The treated effluent was reused for the next metal leaching steps.

Results and discussion

The average metal removal yields were 80.9?±?2.3 % of Cu, 94.5?±?0.7 % of Pb, 51.1?±?4.8 % of Sb, and 43.9?±?3.9 % of Zn. Compared to a conventional leaching process, the CCLP allows a significant economy of water (24,500 L water per ton of soil), sulfuric acid (133 L H₂SO₄ t^–1), NaCl (6,310 kg NaCl t^–1), and NaOH (225 kg NaOH t^–1). This corresponds to 82 %, 65 %, 90 %, and 75 % of reduction, respectively. The Toxicity Characteristic Leaching Procedure test, which was applied on the remediated soil, demonstrated a large decrease of the lead availability (0.8 mg Pb L^–1) in comparison to the untreated soil (142 mg Pb L^–1). The estimated total cost of this soil remediation process is 267 US$ t^–1.

Conclusions

The CCLP process allows high removal yields for Pb and Cu and a significant reduction in water and chemical consumption. Further work should examine the extraction of Sb from small-arms shooting range.     

Fractionation of chromium in tannery sludge-amended soil and its availability to fenugreek plants

Purpose

Fenugreek (Trigonella foenum-graecum L.) is a medicinal plant with antidiabetic effects. Chromium has been related to better glucose tolerance in humans. The objective of this study was to determine whether tannery sludge could be used for Cr biofortification of fenugreek.

Materials and methods

Soil was mixed with tannery sludge containing 6.03 g Cr kg^?1. All Cr was in the form of Cr(III). Three treatments were disposed: control without sludge, and two treatments with 10 and 20 g sludge kg^?1, respectively. Control and the 10 g sludge kg^?1 treatments received NPK fertilizer to adjust the concentrations of major mineral nutrients to similar levels in all treatments. Soils were potted and planted with fenugreek. Plants harvested at the initial flowering stage were analysed for total Cr, Fe, Zn and Pb. Sequential soil extraction was applied to obtain operationally defined soil Cr fractions.

Results and discussion

Total Cr in all treatments was below or within the allowable range for agricultural soils (100–150 mg kg^?1). In control soils, most Cr was in the residual fraction (HF/HClO₄ digest). Tannery sludge-amended soils incorporated most Cr into the moderately reducible fraction (oxalic acid/ammonium oxalate extract). In fenugreek shoots, Cr concentrations reached 3.2 mg Cr kg^?1, a higher concentration than that reported for other leafy vegetables. Lead concentrations in plant shoots from this treatment were enhanced but hardly exceeded 1 mg Pb kg^?1.

Conclusions

Tannery sludge-amended soils containing Cr within the range of permissible concentrations can increase shoot Cr in fenugreek. Only sludge with low Pb concentrations should be used for Cr biofortification of fenugreek.     

A novel heavy metal chelating agent sixthio guanidine acid for in situ remediation of soils contaminated with multielements: its synthesis,solidification, biodegradability,and leachability

Purpose

The main objectives of the study were to (1) develop a one-step facile procedure for synthesizing a new chemical amendment agent with three chelating groups for solidifying multiple heavy metals, called sixthio guanidine acid (SGA), using guanidine hydrochloride and carbon disulfide as raw reactants and (2) assess its biodegradability, solidification effectiveness, and leachability in remedying soils contaminated with multiple heavy metals of various concentrations compared with other traditional amendment agents.

Materials and methods

Polluted soil samples were collected near a metalliferous mining site of Qixiashan in the southeast of Nanjing, China. Their concentrations were determined at 22.15–320 mg kg^?1 for As, 3.30–29.31 mg kg^?1 for Cd, 115.66–158.65 mg kg^?1 for Ni, 165.04–1677.06 mg kg^?1 for Pb, and 355.6–2426.91 mg kg^?1 for Zn. Biodegradability of SGA was assessed in accordance with GB/T 21831-2008 and OECD-301D. Total concentration of heavy metals was determined according to ISO11466:1995. A modified three-step sequential Community Bureau of Reference (BCR) extraction procedure was used to examine speciation of heavy metals in the soil sample, and concentrations of heavy metals were measured by using inductively coupling plasma optical emission spectrometry (ICP-OES). Leachate extraction tests were carried out before and after the soil sample was solidified with different amendments in accordance with HJ/T 557-2009.

Results and discussion

It is found that the optimal conditions for SGA synthesis are a molar ratio of 4:1, a reaction temperature of 40 °C, and a reaction time of 2 h. Under such conditions, SGA yield is achieved as high as 91.5 %. The bioavailability and mobility of As, Cd, Ni, Pb, and Zn in highly contaminated soils can be reduced via using SGA. Our results indicate that SGA is nonbiodegradative and much more effective than other traditional chemical amendment agents in that it is highly effective in comprehensively solidifying As, Cd, Ni, and Pb.

Conclusions

SGA has the potential for comprehensive in situ remediation of soils contaminated with several heavy metal elements of various concentration levels, and such findings may be used as a guide to design new chemical amendment agents for rehabilitating soils contaminated with heavy metals.

     

Behavior of Metals Under Different Seasonal Conditions: Effects on the Quality of a Mexico–USA Border River

Spatial and seasonal mobilization trends of metals in surface water were evaluated in the US–Mexico San Pedro River (SPR). Water samples were collected at five sampling stations for the analysis of dissolved oxygen, pH, electric conductivity, sulfates, and metals (Cd, Cu, Fe, Mn, Pb, and Zn). Quality of the water was characterized through Ecological Criteria of Water Quality (ECWQ) established in Mexico and Water Quality Criteria (Environmental Protection Agency (EPA)). High total metal concentrations were detected as follows: Fe?>?Cu?>?Mn?>?Zn?>?Pb?>?Cd. Metal concentrations were slightly higher in dry season than in rainy season: Cd (below detection limit (BDL)–0.21 mg L^?1), Cu (BDL–13 mg L^?1), Fe (0.16–345 mg L^?1), Mn (0.12–52 mg L^?1), Pb (BDL–0.48 mg L^?1), and Zn (0.03–17.8 mg L^?1). Low pH and dissolved oxygen values as well as high sulfate content were detected in both seasons. High values of metals (Cd, Cu, Fe, Mn, Pb, Zn) were detected at station E1 representing pollution source, as well as at stations E2 (Cd, Cu, Fe, Mn), E3 (Fe, Mn, Pb), and E4 and E5 (Fe, Mn). Detected concentrations exceeded maximum permissible established in ECWQ and Water Quality Criteria (EPA). Efflorescence salts on sediments in the dry season could increase levels of metals in water column. This study provides valuable information on the potential mobility of metals in surface water of SPR located in an arid environment where transport processes are strongly linked to climate. The information derived from this study should help the regional and national authorities to address present environmental regulations.     

Pine Bark Amendment to Promote Sustainability in Cu-Polluted Acid Soils: Effects on <Emphasis Type="Italic">Lolium perenne</Emphasis> Growth and Cu Uptake

The establishment of a complementary grass cover on vineyard soils can promote sustainability of the affected environment. In this work, we used an acid vineyard soil with total Cu concentration 188 mg kg^?1 to study the influence of pine bark amendment on Lolium perenne growth and Cu uptake. The results indicate that the pine bark amendment did not cause a significant increase in the mass of the shoots of Lolium perenne, but favored the root biomass: 0.034 g for control and 0.061 g for soil samples amended with 48 g kg^?1 of pine bark. Moreover, the pine bark amendment decreased Cu concentration in both, shoots (50 mg kg^?1 for control soil and 29 mg kg^?1 for soil amended with 48 g kg^?1 pine bark) and roots (250 mg kg^?1 for control soil and 64 mg kg^?1 for soil amended with 48 g kg^?1 pine bark). The main factor responsible for these results was a significant decrease of the most mobile fractions of Cu in the soil. Those fractions were extracted using ammonium acetate, ammonium chloride, sodium salt of ethylene-diamine-tetraacetic acid (EDTA-Na), and diethylene-triamine-pentaacetic acid (DTPA).     

Short-term exposure to carbaryl and UV radiation increases the reproduction output of the collembolan Folsomia candida

Purpose

Ecotoxicological risk assessment of chemical compounds is considered more accurate when mixtures of chemicals and/or interactions between chemicals and natural stressors are considered. To further simulate natural conditions, under which organisms are often exposed to combinations of natural and anthropogenic stressors, the combined exposure of a widely used insecticide, carbaryl, under UV radiation was evaluated. It is more than likely that soil organisms are confronted with a combination of chemical exposure and increasing UV irradiance on the terrestrial habitat. Considering the heterogeneity of contamination in field soils and the probability of collembolan to avoid contaminated soil (less time under exposure), combined effects of carbaryl and ultraviolet radiation were evaluated, by using a short exposure to Folsomia candida.

Materials and methods

Single exposures to carbaryl and UV radiation were performed, and adult mortality and number of laid and hatched eggs were reported. Following the results, a combined exposure was carried out, using the same conditions performed previously in the single tests. Organisms were exposed simultaneously to carbaryl (from 1 to 7 mg kg^?1) and UV doses (from 1,121.29 to 3,795.26 J m^?2), the last corresponds to 1 to 4 h of exposure. Mortality was reported, and organisms were left to lay eggs in culture boxes.

Results and discussion

Both ultraviolet radiation and high concentrations of carbaryl as single stressors increased the number of produced eggs of F. candida, with significant differences at higher concentrations (4, 5.5, and 7 mg kg^?1) of carbaryl and an EC50 of 5.93 mg kg^?1. In the case of UV radiation, statistical differences were found at all concentrations compared with control, with an EC50 of 1,248.24 J m^?2. In both cases, no significant mortality was observed. When combined, both stressors acted independently on egg production, showing additivity of effects (independent action (IA) model to data on laid eggs; SS?=?0.00056; r2?=?0.75; p?Conclusions This study highlights the importance of taking UV exposure conditions into account when assessing the impact of pesticides to soil biota and looking for more realistic scenarios while showing that soil sheltering occurs only up to a certain extent and that indirect effects can be observed. The opposite trends on responses obtained under standardized tests and short exposures to carbaryl provided some insight on the possible effects of carbaryl during collembolan life cycle.