Total petroleum hydrocarbons and heavy metals in road-deposited sediments in Tijuana,Mexico

Purpose

A study was carried out to evaluate the concentration of heavy metals (Pb, Cu, Cr, Cd, and Hg) and total petroleum hydrocarbons (TPH) in road-deposited sediments (RDS) from Tijuana, Mexico, and identify their possible sources.

Materials and methods

Thirty RDS samples were randomly collected during the dry season using a brush and dustpan and classified according to construction material, traffic intensity, and land use. Soil samples were collected from a nonurban area and their concentrations were used as background values. For TPH, the samples were quantified gravimetrically after Soxhlet extraction, whereas heavy metals were extracted by acid digestion and their concentrations were measured by atomic absorption spectrometry.

Results and discussion

The mean TPH concentrations for RDS were 4208 mg kg^?1 and ranged from 1186 to 9982 mg kg^?1. For heavy metals, mean concentrations were 31.8, 50.2, 17.1, 0.1, and 0.1 mg kg^?1 for Pb, Cu, Cr, Cd, and Hg, respectively. The Igeo results showed that RDS from Tijuana are moderately to strongly polluted with Pb and Cu and moderately polluted with Cr. Principal component analysis (PCA) showed that Pb, Cu, and Cr could have their origin in tire wear, brake pads, bearings, and bushings.

Conclusions

The findings of this study revealed that RDS from Tijuana are polluted with TPH and heavy metals and that their principal sources are anthropogenic activities.

     

Influence of pH on the release and chemical fractionation of heavy metals in sediment from a suburban drainage stream in an arid mine-based oasis

Purpose

The objectives of this study were to explore the influences of pH on the release of Cu, Zn, Cd, Pb, Ni, and Cr in sediments derived from the upstream, middle, and downstream reaches of Dongdagou stream in Gansu Province, Northwest China, and to examine the fractionation changes of heavy metals in the sediments after reaching their release equilibrium under different pH conditions.

Materials and methods

Sediment samples were obtained using a stainless steel grab sampler to collect the uppermost 10 cm of sediment from the channel bed. The pH-dependent release experiment was conducted in the solid-to-liquid ratio of 1:20 at different pH values (2, 4, 6, 8, 10, and 12) at room temperature. The total Cu, Zn, Cd, Pb, Ni, and Cr concentrations in the sediments were digested using an acid digestion mixture (HNO₃ + HF + HClO₄) in an open system. Metal fractionation of selected sediments was obtained using the Tessier sequential extraction procedure. Heavy metal concentrations in the samples were determined using atomic absorption spectrophotometry.

Results and discussion

The mean concentrations of heavy metals in sediments decreased in the following order: Zn (1676.67 mg kg^?1) > Pb (528.65 mg kg^?1) > Cu (391.34 mg kg^?1) > Cr (53.48 mg kg^?1) > Ni (34.27 mg kg^?1) > Cd (11.53 mg kg^?1). Overall, the solubility of Cu, Zn, Cd, Pb, and Ni decreased with increasing pH, and they were strongly released at pH 2. Moreover, the solubility of Cr increased with increasing pH, and its release was highest at pH 12. After reaching the release equilibrium of heavy metals under different pH conditions, the percentages of organic Cu, Zn, Cd, and Fe-Mn oxyhydroxide Pb decreased, compared to their initial fractions. The residual fractions of Ni and Cr were dominant, regardless of pH.

Conclusions

The average concentrations of Cu, Zn, Cd, and Pb in sediments were highly elevated compared with the soil background values in Gansu Province, China. The results of this pH-dependent release experiment showed that the release behaviors of Cu, Zn, Pb, and Cr followed an asymmetric V-shaped pattern, whereas Cd and Ni followed an irregular L-shaped pattern. The changes in the release of heavy metals in sediments were related to their redistribution between chemical fractionations.

     

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.

     

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.

     

Evaluation of palygorskite for remediation of Cd-polluted soil with different water conditions

Purpose

The study aimed at comparing the effects of different water managements on soil Cd immobilization using palygorskite, which was significant for the selection of reasonable water condition.

Materials and methods

Field experiment was taken to discuss the in situ remediation effects of palygorskite on Cd-polluted paddy soils, under different water managements, using a series of variables, including pH and extractable Cd in soils, plant Cd, enzyme activity, and microorganism number in soils.

Results and discussion

In control group, the pH in continuous flooding was the highest under three water conditions, and compared to conventional irrigation, continuous flooding reduced brown rice Cd by 37.9%, and brown rice Cd in wetting irrigation increased by 31.0%. In palygorskite treated soils, at concentrations of 5, 10, and 15 g kg^?1, brown rice Cd reduced by 16.7, 44.4, and 55.6%; 13.8, 34.5, and 44.8%; and 13.1, 36.8, and 47.3% under continuous flooding, conventional irrigation, and wetting irrigation (p < 0.05), respectively. The enzyme activity and microbial number increased after applying palygorskite to paddy soils.

Conclusions

Continuous flooding was a good candidate as water management for soil Cd stabilization using palygorskite. Rise in soil enzyme activity and microbial number proved that ecological function regained after palygorskite application.

     

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.

     

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.

     

Source identification and apportionment of soil cadmium in cropland of Eastern China: a combined approach of models and geographic information system

Purpose

Cadmium (Cd) is regarded as one of the most toxic heavy metals in the environment and can undermine the ecosystem function and human health at trace level due to its high toxicity. In order to reduce the anthropogenic Cd input into agricultural soil, it is of utmost importance to pinpoint the sources of Cd in soils and apportion their respective contributions.

Materials and methods

One hundred twenty-seven topsoil samples and 21 subsoil samples were collected from croplands of Meishan Basin, Changxing County, Zhejiang Province, Eastern China, and analyzed for concentrations of Cd and other heavy metals. Finite mixture distribution model (FMDM) was employed to fit the data to obtain the local soil Cd threshold value, a critical indicator to assess soil heavy metal contamination. Then, principal component analysis (PCA) and geographic information system (GIS) were used to identify the potential sources of Cd. Finally, positive matrix factorization (PMF) was applied to apportion the source contributions.

Results and discussion

Among the 127 topsoil samples, 71 were subject to Cd contamination with a mean concentration of 0.66 mg kg^?1 while the others were considered as background with a lower mean concentration of 0.145 mg kg^?1, close to the local background concentration of 0.142 mg kg^?1. Further, three components were extracted by PCA and interpreted as natural background, lead-acid battery manufacturing plants, and construction material associated activities, respectively. Additionally, most of the topsoil samples around the lead-acid battery manufacturing plants, construction material plants, and limestone/marble quarries were classified as Cd contaminated. However, PMF failed to get a successful portioning.

Conclusions

Lead-acid battery manufacturing plants and construction material associated activities were the main anthropogenic sources of soil Cd contamination. With the help of FMDM, it is possible to distinguish the contaminated soil and estimate the contribution of anthropogenic sources to soil Cd. The apportionment by PMF was not successful in this paper due to the high skewness or outliers of Cd concentration in sampling sites and violation of the assumption that all samples have the same sources.

     

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.

     

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

Purpose

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

Materials and methods

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

Results and discussion

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

Conclusions

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

     

The accumulation and transfer of arsenic and mercury in the soil under a long-term fertilization treatment

Purpose

The North China Plain (NCP) is a strategic grain production base in China with a wild distribution of fertile soils. During the past 20 years, high-input intensive agriculture with excess chemical fertilizer application has sustained high grain yields, but may have resulted in contamination of some elements in farmland. In this study, the accumulation and transfer of arsenic (As) and mercury (Hg) in typical Calcaric Fluvisols with long-term different fertilization practices were investigated.

Materials and methods

Field experiments with seven treatments were launched in 1989, and soil and plant samples were collected and analyzed periodically. The treatments include OM (organic manure), OM?+?NPK (50 % organic manure?+?50 % chemical fertilizer), NPK, NP, PK, NK, and CK (the control experiment with no fertilizer).

Results and discussion

With over 20 years (1989–2009) of cultivation, various extents of As and Hg accumulations were really observed in the soil. The higher As and Hg contents were found in P fertilizers than those in N, K, or OM fertilizers. As a result, the long-term P fertilization slightly promoted Hg accumulations with decreased soil Hg concentrations in the order of NPK?≈?NP?≈?PK?≈?OM?+?NPK?>?OM?>?NK?≈?CK, which was similar to the order of crop yields. At the tillage layer (0–20 cm), Hg accumulation in the soil was enhanced by crop production, due to the highly accumulated Hg in plant roots finally remained in the soil. However, no significant differences of soil As concentrations can be found between treatments with and without P fertilizers probably due to water leaching and plant uptake.

Conclusions

Soil As and Hg were mainly contributed by fertilizers, irrigation, and atmospheric deposition in recent years, but they did not exhibit in significant accumulations in the soil. The contents of As and Hg were not above the critical safe levels of soils for crop production (As, <30 mg kg^?1; Hg, <500 μg kg^?1). Arsenic and Hg tended to move downward in the soil profile and the movement was hindered by clay minerals.

     

A simple and economic method for simultaneous determination of 11 antibiotics in manure by solid-phase extraction and high-performance liquid chromatography

Purpose

A simple and highly efficient economic method for the analysis of 11 antibacterial drugs including two tetracyclines, three quinolones, four sulfonamides, chloramphenicol and tylosin, in livestock manure, was developed using solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC).

Materials and methods

The analytes were successively extracted by EDTA-McIlvaine solution and organic solvent mixture. The extracts were degreased with n-hexane and cleaned through SPE on a hydrophile-lipophile balance (HLB) cartridge. All compounds were determined on a C18 reverse phase column with gradient elution.

Results and discussion

Recoveries calculated from spiked samples of animal manures ranged from 62.65 to 99.16 % for 11 antibiotics with relative standard deviations of less than 10.0 %. Limits of detection ranged from 0.1 to 1.9 μg kg^?1, and limits of quantification ranged from 0.3 to 5.9 μg kg^?1.

Conclusions

The results show that SPE-HPLC is an inexpensive and practical method for rapid detection of multiple antibiotics in animal manure.

     

Management of human health risk in the context of kitchen gardens polluted by lead and cadmium near a lead recycling company

Purpose

At the global scale, gardening activities are often performed in urban areas with a historical background of pollution. In this study, a participatory program was developed with citizens concerned by gardening activities near a 50-year-old regulated lead recycling company, with the aim of co-constructing the tools for the assessment and management of potential sanitary risks induced by historic pollution with persistent (eco) toxic metals: lead and cadmium.

Materials and methods

Soils and vegetables (lettuce, leek, celery, carrot, chard, pumpkin, and celeriac) samples were collected from four kitchen gardens neighboring a 50-year-old secondary lead smelter. Both total and in vitro human bioaccessible metal concentrations in the cultivated plants were measured in relation to soil characteristics.

Results and discussion

The results showed that the soils of these gardens were slightly contaminated by metals (Pb, 77 to 236 mg kg^?1; and Cd, 0.5 to 1 mg kg^?1) in comparison with the natural geologic background. However, significant pollution of vegetables can occur especially with lead (Pb up to 9.8 mg kg^?1 in lettuce) and certainly as a result of direct foliar transfer. The washing of plants before consumption is therefore recommended in the context of atmospheric fallout of ultrafine particles enriched with metals.

Conclusions

Metal bioaccessibility measure integrates the influence of metal type, plant type, and soil physico-chemical properties. Based on the results, it is proposed that human bioaccessible fraction of metals may also be currently taken into account as well as total metal quantities and bioaccumulation factors in risk assessment studies performed in gardens. Overall, this study has led to reflections and functional recommendations aimed at reducing human exposure and to finally developing sustainable gardening practices.

     

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.

     

Historical sedimentary trends of mercury and other trace elements from two saltmarshes of the Marano and Grado lagoon (northern Adriatic Sea)

Purpose

Previous research conducted in the Marano and Grado lagoon (northern Adriatic Sea) has shown that this environment has been affected by trace metal contamination, especially by mercury (Hg), from both industrial (the chlor-alkali plant) and mining activities (Idrija mine, Slovenia). Sediment cores were collected from two different saltmarshes of this lagoon environment to evaluate the degree of the anthropogenic enrichments and the geochronology of Hg accumulation.

Materials and methods

Core subsampling was performed by cutting 1-cm thick slices at discrete intervals. Mercury determination was done differently from the other parameters in that the two long cores were subsampled at 1-cm intervals to obtain continuous concentration profiles. Samples were completely decomposed, using a mixture of mineral acids in a closed microwave system before being analysed for trace metal content using ICP-OES. Total Hg content in the solid phase was determined by DMA-80. ¹³⁷Cs was measured via gamma spectrometry. ²¹⁰Pb activity was measured via alpha-counting of its daughter, ²¹⁰Po, assuming secular equilibrium between the two isotopes.

Results and discussion

In saltmarsh sediments, Fe, Co, Li, Sc and V show no enrichment at both sites thus suggesting that they are essentially lithogenic elements. Conversely, enrichments are minimal (EF = <2) for As, Cd, Cr, Ni, Pb and Zn and moderate (EF = 2–5) for Cu and Mn and also for Pb and Zn but only in some levels of the sedimentary sequences. An exception is Hg, as expected due to the long-term input proceeding from the historical mining activity which has especially affected the eastern sector of the lagoon.

Conclusions

The core collected from the saltmarsh in the eastern lagoon (Grado) displays a better time resolution during the last century although the Hg background level has not been reached. Conversely, the core collected in the western sector (Marano) has recorded a longer and more complete history of Hg contamination, from the beginning of the peak of Hg extraction activity at the Idrija mine (1850). Both saltmarshes still receive Hg inputs and the sediment accumulation rates in the upper section appear to have increased over the last 10–20 years (from 0.30 to 0.45 cm year^?1 at Marano and from 0.30 to 0.74 cm year^?1 at Grado). Many of these morphological structures suffer erosive processes thus representing a potential source of contaminants associated with sediments, in particular Hg. Conservation and monitoring of saltmarshes should be taken into consideration also from this environmental point of view.

     

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.

     

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.

     

Spatial distribution and source apportionment of the heavy metals in the agricultural soil in a regional scale

Purpose

Understanding the spatial distribution and sources of soil heavy metals (HMs) in a large city helps prevent and control soil pollution. This study aimed to investigate the spatial patterns of soil HMs and identify their main sources in a regional scale.

Materials and methods

A total of 110 topsoil samples were collected from Tai’an City, China. Cd, Cr, Cu, Hg, Ni, Pb, and Zn concentrations in each soil sample were determined. Geostatistics, geographic information system (GIS), and positive matrix factorization (PMF) were used to explore the spatial distribution of seven soil HMs and to reveal the main sources of soil HMs in Tai’an City, respectively.

Results and discussion

Soil Cd, Cr, Pb, and Zn generally showed slight pollution levels in the study area. However, soil Hg and Cu contents reached moderate to heavy pollution levels in some areas. Soil Hg content increased from north to south across the city, and the highest Hg concentration was detected in Ningyang County. Soil Cd, Cu, and Zn distributions exhibited a similar pattern, and their contents increased from west to east; the highest Cd, Cu, and Zn concentrations were found in Xintai County. The highest soil Ni concentration was obtained in the northeast of Feicheng and Xintai counties. PMF analysis revealed the following four potential sources of agricultural soil HMs in Tai’an City: industrial and mining activities, agricultural activities, residential living activities, and business activities. Soil Hg mainly originated from residential living activities, which accounted for 75.3% of the total source. The main sources of soil Ni were residential living activities, agricultural activities, and industrial and mining activities, which account for 38.2, 27.50, and 25.1% of the total source, respectively. Soil Cu was mainly produced by agricultural activities (36.6%), followed by residential living activities (29.8%) and industrial and mining activities (25.8%).

Conclusions

PMF combined with GIS could be effectively applied to determine the main sources of HMs in agricultural soils in a regional scale.

     

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.

     

The forms and distribution of aluminum adsorbed onto maize and soybean roots

Purpose

The Al forms on maize and soybean roots were investigated to determine the main factors affecting the distribution of Al forms and its relationship with Al plant toxicity.

Materials and methods

Solution culture experiments were conducted to obtain the fresh roots of maize and soybean. KNO₃, citric acid, and HCl were used to extract the exchangeable, complexed, and precipitated forms of Al on the roots.

Results and discussion

The complexed Al was higher than the exchangeable and precipitated Al. Root CECs of soybean and maize were 77 and 55 cmol kg^?1, and functional groups on the soybean roots (262.4 cmol kg^?1) were greater than on maize roots (210.8 cmol kg^?1), which resulted in more exchangeable and complexed Al on soybean roots than on maize roots, and was one of the reasons for the increased Al toxicity to soybean. The total and exchangeable Al were the highest on the plant root tips and decreased gradually with increasing distance from the tips. Ca²⁺, Mg²⁺, and NH₄ ⁺ cations reduced the exchangeable Al on the roots. Oxalate and malate also reduced the adsorption and absorption of Al by roots, and the effect of oxalate was greater than malate.

Conclusions

Higher exchangeable and complexed Al on plant roots led to increased Al plant toxicity. Ca²⁺, Mg²⁺, and NH₄ ⁺ and oxalate and malate can effectively alleviate Al plant toxicity.