ICP-OES assessment of heavy metal contamination in tropical marine sediments: A comparative study of two digestion techniques

Elemental Concentrations in the Shells of the Mussel Perna perna: Discrimination of Origin

The potential use of elemental concentrations and element:calcium (Ca) ratios as indicators of provenance for bivalve mollusks on the Brazilian coast is evaluated herein for the first time. The approach was applied to shells of the mussel Perna perna (target of extractive fisheries) from geographically close areas but under distinct environmental and anthropogenic influences. Both concentrations of the elements normalized by Ca and the total concentrations can be applied to discriminate the mussels' origin. However, the canonical approach using the total concentrations indicated variations regarding the discriminatory power, and the concentrations of the elements normalized by Ca were more robust in differentiating the provenance of the shells. The origin of mussels was better discriminated by six elementary ratios: Al:Ca, Fe:Ca, K:Ca, Mg:Ca, Mn:Ca and Na:Ca. Thus, monitoring studies aiming to discriminate the origin of P. perna individuals along their distribution based on these elementary ratios of the shell are recommended.

Determination of Minerals in Soft and Hard Cheese Varieties by ICP-OES: A Comparison of Digestion Methods

For sample preparation prior to mineral analysis, microwave digestion (~2 h) is quicker and requires lower acid volume as compared to dry (6-8 h) and wet digestion (4-5 h). However, microwave digestion had not yet been compared systematically with dry and wet digestion for different cheese matrices. In this work, the three digestion methods were compared for measuring major (Ca, K, Mg, Na and P) and trace minerals (Cu, Fe, Mn and Zn) in cheese samples using inductively coupled plasma optical emission spectrometry (ICP-OES). The study involved nine different cheese samples with moisture content varying from 32 to 81% and a standard reference material (skim milk powder). For the standard reference material, the relative standard deviation was lowest for microwave digestion (0.2-3.7%) followed by dry (0.2-6.7%) and wet digestion (0.4-7.6%). Overall, for major minerals in cheese, strong correlation was observed between the microwave and the dry and wet digestion methods (R² = 0.971-0.999), and Bland-Altman plots showed best method agreement (lowest bias), indicating the comparability of all three digestion methods. A lower correlation coefficient, higher limits of agreement and higher bias of minor minerals indicate possibilities of measurement error.

Ecotoxicological monitoring of potentially toxic elements contamination in Eucalyptus forest plantation subjected to long-term irrigation with recycled wastewater

Afforestation is an evergreen technology for restraining greenhouse gases (GHGs) emission and improving soil carbon sink in arid and semi-arid regions. Nonetheless, the long-term impact of woody forests irrigation using recycled wastewater resources remains inconclusive so far. For this purpose, the ecological risk benchmarks of potentially toxic elements (PTEs) were investigated on Eucalyptus forest plantation in order to gauge their bioavailability in the rhizospheric layer of Typic Torripsammentsoil and their accretion capacity in the biosphere. Water quality guidelines pointed to a moderate degree of restriction on use with elevated levels of PTEs. Notably, concentrations of As, B, Cd, Cr, Cu, Mn, Ni, V and Zn were above the permissible limits for irrigation. The geospatial mapping of PTEs concentration in soil pointed to elevated levels of most PTEs, particularly in the deforestated areas. Some of PTEs (Cd, Cu, Hg and Zn) showed values above the permissible limits. A spectrum of ecological risk indices showed considerable to high degree of contamination. Among PTEs, the water-soluble and exchangeable fractions showed high values of As, Cd and Hg (20.7, 17.2 and 11.0%, respectively). Sequential extraction showed variations among PTEs in their tendency to bind with different soil geochemical fractions: (i) carbonate (Cd, Zn and Cu), (ii) Fe-Mn oxides (Pb, Zn and Mn) and (iii) organic matter (B, Pb and Hg). Eight fungal species including Aspergillus flavus, Fusarium solani, Cephalosporimsp., Penicilliumsp., Rhizoctonia solani, Aspergillus niger, Botrytissp. and Verticilliumsp. were dominated in soil. Meanwhile, Agrobacteriumsp., phosphate solubilizing bacteria, nitrogen fixing bacteria and Escherichia coli were the dominant bacterial strains. Values of bioaccumulation index varied among PTEs, wherein B (5.15), Ni (1.98), Mn (1.62) and Cd (1.02) exhibited higher phytoextraction potentials. Other PTEs, however, exhibited values below 1.0 confirming their low phytoextraction potentials. Findings of this investigation, therefore, provide insights into biochemical signals of PTEs contamination in woody forest plantations and the urgent need to contextualize the large-scale utilization of recycled wastewater resources in such vulnerable areas.

Recent Progress on Ex Situ Remediation Technology and Resource Utilization for Heavy Metal Contaminated Sediment

Sediment is an important part of aquatic systems, which plays a vital role in transporting and storing metals. Due to its abundance, persistence, and environmental toxicity, heavy metal pollution has always been one of the hot spots in the world. In this article, the state-of-art ex situ remediation technology for metal-contaminated sediments is elaborated, including sediment washing, electrokinetic remediation (EKR), chemical extraction, biological treatment, as well as encapsulating pollutants by adding some stabilized/solidified materials. Furthermore, the progress of sustainable resource utilization methods, such as ecosystem restoration, construction materials (e.g., materials fill materials, partition blocks, and paving blocks), and agriculture use are reviewed in detail. Finally, the pros and cons of each technique are summarized. This information will provide the scientific basis for selecting the appropriate remediation technology in a particular scenario.

Gut microbiome and metabolome of sea cucumber (Stichopus ocellatus) as putative markers for monitoring the marine sediment pollution in Pahang, Malaysia

Antibiotic contamination in the marine environment forms an emerging threat to marine ecosystems. This study aimed to compare the gut and coelomic microbiota of Stichopus ocellatus with sediments between two coastal districts of Pahang, which potentially conferring as putative biomarkers for sediment pollution monitoring. The composition of the bacteria communities was determined using 16S rRNA V3-region gene amplicon sequencing, while hybrid whole-genome sequencing was employed to analyze the genome of Vibrio parahaemolyticus. The trace elements and antibiotic compositions were access using high-throughput spectrometry. The alpha- and beta-diversity of bacteria in gut and sediment samples from Kuantan differed substantially within (p-value = 0.017604) and between samples (p-value <0.007), respectively. Vibrio genera predominated in Kuantan samples, while Flavobacterium and Synechococcus_E genera predominated in Pekan samples. Vibrio parahaemolyticus revealed the presence of tet(35) and bla_CARB-33 genes that conceived resistance towards tetracycline and beta-lactam antibiotics, respectively, which were detected in sediment and gut samples.

Heavy Metal Contamination and Human Health Implications in the Chan Thnal Reservoir, Cambodia

Chan Thnal reservoir, built during the Pol Pot period, is the major water source for the people in Krang Chek commune, Kampong Speu Province, Cambodia. Metal pollution caused by agricultural activities, improper wastewater treatment, and municipal waste disposal poses serious environmental health problems. In this study, the concentrations of four potential toxic metals (i.e., Cd, Cu, Pb, and Zn) from six locations across the reservoir were investigated both in the water and sediment. The results reflected progressive deterioration and indicated moderate to heavy pollution from the metals. The metal levels in the water were in the order of Zn > Cu > Pb > Cd. The statistical analysis revealed primary sources of heavy metals contamination in the water. Cd, Cu, Zn, and Pb in the water likely originate from anthropogenic activities including agricultural runoff (i.e., the use of fertilizers and pesticides) and urban runoff (i.e., improper wastewater discharge and waste disposal). Among the four metals, the Pb levels in the water significantly exceeded the guideline for drinking water in all locations. The health risk assessment revealed serious non-carcinogenic risks of Pb intake in the children at the age below 10 and infants. Appropriate control and protection strategies are urgently needed to cut off the main Pb exposure pathway in pregnant women, children, and infants.

Method for analysis of environmental lead contamination in soils

A method for lead (Pb) detection in soil is presented. Pb is a dangerous environmental pollutant that is present in soils, posing a health risk to millions of people worldwide, and regular monitoring of Pb contamination in soils is essential to public health. Many sensitive methods for detection of heavy metals in solid matrices exist, but they cannot be performed on-site because they are costly (>$30 per sample), require trained personnel, and many classical sample preparation methods are not safe to bring into the field. We describe an alternative process, combining a safer sample preparation method with electrochemical analysis. The process requires minimal training, making it an attractive overall method for regular environmental screening of Pb in soils. Extract obtained from the soil is pH adjusted and analyzed using a stencil-printed carbon electrode and square wave anodic stripping voltammetry. In this work, a study of 15 neighborhood soils examining the concentration of Pb present post-extraction was performed to demonstrate the method. The limit of detection for the electrochemical analysis was calculated to be 16 ppb-well below the United States Environmental Protection Agency's action limit for Pb in soils (400 mg kg^-1 or 4000 ppb)-and third party inductively coupled plasma-optical emission spectroscopy analysis validated the results obtained in this study to within ±17% on average.

Cytogenetic, Serum Liver Enzymes and Liver Cell Pathology of the Hampala Barb Fish (Hampala macrolepidota) Affected by Toxic Elements in the Contaminated Nam Kok River Near the Sepon Gold-Copper Mine, Lao PDR

This study aimed to determine toxic element concentrations in aquatic environments, including water and sediment, and in the Hampala macrolepidota fish, and to evaluate chromosome abnormalities, serum liver enzyme changes and liver histopathological alterations in H. macrolepidota from the Nam Kok River near the Sepon gold-copper mine, Lao People’s Democratic Republic, as compared with a control area without mining activity. The results revealed significant differences (p < 0.05) in As, Ba, Cu, Fe, Mn, Ni, Se and Zn in water, in all of the studied potentially toxic elements in sediment, and in As, Ba, Cd, Cr, Cu, Mn, Ni, Se, and Zn in the fish between the study and control areas. A chromosome assessment demonstrated 6 types of chromosome abnormalities, among which centric gap had the highest total number of chromosome abnormalities. Percentage of chromosome abnormalities, percentage of cells with chromosome abnormalities and serum liver enzymes in H. macrolepidota were significantly different (p < 0.05) between the two studied areas and were higher in the contaminated fish than in the control fish. The observation of liver histopathological changes revealed cellular degeneration, such as nuclear damage, abnormal cytoplasmic mitochondria and the disintegration of rough endoplasmic reticulum. The results indicate that the contamination of potentially toxic elements in the Nam Kok River near the Sepon gold-copper mine area negatively affected chromosomes, serum liver enzymes and liver cell structures in H. macrolepidota.

Effects of Contamination by Heavy Metals and Metalloids on Chromosomes, Serum Biochemistry and Histopathology of the Bonylip Barb Fish Near Sepon Gold-Copper Mine, Lao PDR

The objectives of the present study were to determine the concentrations of heavy metals and metalloids in water, sediment and Osteochilus vittatus fish, and to assess chromosome aberrations, serum biochemical changes and histopathological alterations in O. vittatus from the Nam Kok river near the Sepon gold-copper mine, Lao People’s Democratic Republic compared with the reference area. The results showed that Fe, Mn and Ni in water, As and Cd in sediment as well as As, Cd, Cr, Mn and Ni in O. vittatus muscle samples near the gold-copper mine exceeded standard values. Furthermore, the chromosome assessment in O. vittatus revealed seven types of chromosome aberrations, and the highest total number of chromosome aberrations was a centromere gap. The total number of chromosome aberrations, cell number with chromosome aberrations and percentage of chromosome aberrations in O. vittatus as well as serum liver enzymes between the studied areas were significantly different (p < 0.05). The liver histopathological alterations of the fish near the gold-copper mine revealed atypical cellular structures as nuclear membrane degeneration, rough endoplasmic reticulum disintegration and abnormal cytoplasmic mitochondria. The results of this study suggested that heavy metal and metalloid contaminations from the Sepon gold-copper mine area negatively affect O. vittatus fish in terms of chromosomal defects, serum biochemical changes and liver histopathological appearances.

Microwave-Assisted Extraction of Trace Metals from Sediments using Dilute Hydrogen Peroxide and Dilute Nitric Acid Prior to their Determination by Inductively Couple Plasma-Optical Emission Spectrometry

Background and Objectives:

Contamination of aquatic sediments by trace metals is one of the global problems. This is because trace metals in sediments are persistent and nonbiodegradable. They may pose danger to flora and fauna since they can be released into freshwater systems. This study aimed at the development of microwave-assisted extraction using diluted hydrogen peroxide and nitric acid for extraction of trace elements from sediment samples prior to inductively coupled plasma optical emission spectrometry (ICP OES) determination.

Methods:

Response surface methodology (RSM) based on the Box-Behnken design was used for the optimization of factors affecting the microwave-assisted extraction process. The optimum conditions, for quantitative extraction of trace metals such as Cd2+, Cu2+, Cr2+, Pb2+ and Zn2+ were 16 min, 1.5 mol L-1 and 15% for extraction time, nitric acid concentration and H2O2 concentration, respectively.

Results and Discussion:

Under optimized conditions, the accuracy of the method was evaluated by analyzing loamy clay certified reference materials (CRM052) and the recoveries were above 92%, suggesting that the obtained results were in good agreement with the certified values. The developed method has shown reproducibility (RSD < 5%), as well as relative low limits of detection (0.02-0.09 μg g-1) and limit of quantitation (0.07-0.3 μg g-1). The developed analytical method was applied for extraction and the determination of trace metals in freshwater sediment samples.

Conclusions:

The method displayed advantages such as simplicity, rapidity, environmentally friendly and safe compared to classical methods that are based on concentrated acids.

Physiochemical characterization and systematic investigation of metals extraction from fly and bottom ashes produced from municipal solid waste

Incineration has emerged as one of the acceptable ways to treat municipal solid waste (MSW) due to its potential in reducing the mass and volume of the waste. However, it produces two major by-product residues, namely MSW-bottom ash (MSW-BA) and MSW-fly ash (MSW-FA). These residues have gained great attention to their hazardous nature and potential to be reused and recycled. In this paper, the physicochemical characterizations of the MSW-BA and the MSW-FA were performed, followed by a systematic investigation of metals extraction from MSW-BA and MSW-FA. Various extracting agents were used to investigate the possibility to extract 21 metals including cadmium (Cd), vanadium (V), chromium (Cr), and lead (Pb). It was revealed that some metals were present in a high amount in the MSW-BA while other metals were higher in the MSW-FA. Moreover, the energy-dispersive X-ray spectroscopy results revealed that the MSW-BA was dominated by oxygen (O) 55.4 ±0.6 wt%, silicon (Si) 22.5 ±0.3 wt%, and calcium (Ca) 18.5 ±0.2 wt%. On the other hand, the MSW-FA was enriched with Ca 45.2 ±0.5 wt%, and O 40.3 ±0.4 wt%. From the scanning electron microscopy, the MSW-BA was observed as flaky with an irregular surface that consisted of large pores, while, the MSW-FA was present as agglomerated particles and had a bimodal distribution. Moreover, Fourier transform infrared spectroscopy revealed that Al-Fe-OH, Al-Al-OH, Si-O, C-O, and C-H were some of the major functional groups present in the ashes. The F-tests concluded that the metal extraction from the MSW-BA and MSW-FA were significantly affected by the acid type. it is concluded that nitric acid and phosphoric acid were the best-suited acid for the MSW-BA while sulfuric acid and phosphoric acid for the MSW-FA. More than 11 wt% of Cd and 9 wt% of Cu were extracted from MSW-BA while 6 wt% of Pb and 4.5 wt% of V were extracted from the MSW-FA. The present methodology is an interesting development in metal extraction from the MSW-BA and the MSW-FA, which can develop in a cost-effective and sustainable option to utilize MSW.

Substituting HF by HBF4- an optimized digestion method for multi-elemental sediment analysis via ICP-MS/MS

Determination of elemental mass fractions in sediments plays a major role in evaluating the environmental status of aquatic ecosystems. Herewith, the optimization of a new total digestion protocol and the subsequent analysis of 48 elements in different sediment reference materials (NIST SRM 2702, GBW 07313, GBW 07311 and JMC-2) based on ICP-MS/MS detection is presented. The developed method applies microwave acid digestion and utilizes HBF₄ as fluoride source for silicate decomposition. Similar to established protocols based on HF, HBF₄ ensures the dissolution of the silicate matrix, as well as other refractory oxides. As HBF₄ is not acutely toxic; no special precautions have to be made and digests can be directly measured via ICP-MS without specific sample inlet systems, evaporation steps or the addition of e.g. H₃BO₃, in order to mask excess HF. Different acid mixtures with and without HBF₄ were evaluated in terms of digestion efficiency based on the trace metal recovery. The optimized protocol (5 mL HNO₃, 2 mL HCL, 1 mL HBF₄) allows a complete dissolution of the analyzed reference materials, as well as quantitative recoveries for a wide variety of certified analytes. Low recoveries for e.g. Sr, Ba and rare earth elements due to fluoride precipitation of HF-based digestions protocols, can be avoided by the usage of HBF₄ instead. Based on the usage of high purity HBF₄ all relevant trace, as well as matrix elements can be analyzed with sufficiently low LOQs (0.002 μg L^-1 for U up to 6.7 μg L^-1 for Al). In total, 34 elements were within a recovery range of 80%-120% for all three analyzed reference materials GBW 07313, GBW 07311 and JMC-2. 14 elements were outside a recovery range of 80%-120% for at least one of the analyzed reference materials.

Toxic heavy metals: impact on the environment and human health, and treatment with conducting organic polymers, a review

Water pollution by heavy metals has many human origins, such as the burning of fossil fuels, exhaust gases of vehicles, mining, agriculture, and incineration of solid and liquid wastes. Heavy metals also occur naturally, due to volcanoes, thermal springs activity, erosion, infiltration, etc. This water contamination is a threat for living beings because most heavy metals are toxic to humans and to aquatic life. Hence, it is important to find effective techniques for removing these contaminants in order to reduce the level of pollution of the natural waters. In this work, we have reviewed the toxicity of several heavy metals (mercury, lead, cadmium, chromium, nickel), their impact on the environment and human health, and the synthesis and characterization methods of conducting organic polymers (COPs) utilized for the removal of heavy metals from the environment. Therefore, this review was essentially aimed to present recent works and methods (2000-2020) on the environmental impact and toxicity of heavy metals and on the removal of toxic heavy metals, using chemically and/or electrochemically synthesized COPs. We have also stressed the great interest of COPs for the removal of toxic heavy metals from waters.

Investigation of potentially toxic elements in urban sediments in Belgrade, Serbia

Concentrations of 10 potentially toxic trace elements were measured in soil samples collected from 18 sites in urban areas of Belgrade, the capital and the largest city in Serbia. Samples were analysed in order to assess the extent of soil contamination and to distinguish natural and anthropogenic input. The results demonstrated a general Zn, Pb, and Cd enrichment in surface samples, hence, after comparison with guidelines, it has been determined that there is a potential risk for human health. In the surface and buried samples, traces of cooper were detected. The highest concentrations of Cr (121 ± 12.3 mg/kg) and Ni (94.9 ± 12.6 mg/kg) were found at a sediment depth of 2 m and should be ascribed to geogenic sources. The results of HCA and PCA analysis supported a natural origin of Co, Cu, Mn, Cr, and Ni, while Cd, Zn, and Pb originated from anthropogenic inputs. Based on the pollution indices, Cd made the most dominant contribution, posing a high contamination risk in the studied area. Results of Nemerow pollution index (PI_N) and potential ecological risk index (PER) demonstrated that pollution by heavy metals in sediments on several sites is moderately intense.

Quantification of the diagenesis-designating metals in sediments by ICP-MS: Comparison of different sample preparation methods

Concentrations of specific metals in sediments are of immense importance in geochemical studies related to diagenetic processes, and quantification can be most reliably performed by ICP-MS after bringing the sample into solution. It is the latter analytical operation that generates a discord as no common sample preparation approach has been yet accepted. To resolve this challenge, we compared different modes of acidic sample digestion (in open and closed systems, applying in the latter case conventional or microwave heating) using a lake sediment reference sample. It was shown that the sample treatment in an autoclave with resistance heating provides the best fit (relative deviation < 7%) to certified values for metals generally used as diagenetic proxies (U, Sm, Nd, Th, La, Sc, Sr, etc.). Furthermore, the thermally convective pressure digestion appears to be more cost-efficient than microwave-assisted digestion (because of lower reagent consumption and cheaper removable PFE liners), an important asset for systematic geochemical mapping. In order to prove the applicability of the developed digestion procedure for different sediments, a marine sample from the East Siberian Sea was analyzed independently in two laboratories and across all representative metals the results acquired were found in good agreement.

Effects of electronic waste on cytogenetic and physiological changes in snakehead fish (Channa striata)

The objectives of this study were to investigate cadmium (Cd), chromium (Cr), and lead (Pb) concentrations in water and sediment as well as the muscle, gill, and liver of snakehead fish (Channa striata) and to reveal chromosomal aberrations, changes in serum biochemical parameters, and histopathological alterations of fish from a reservoir near an electronic waste dumping area. Cd, Cr, and Pb concentrations were determined using inductively coupled plasma optical emission spectrometry. Chromosomal aberrations were studied in kidney cells using a conventional technique. The biochemical parameters were measured using an automated analyzer, and histopathological photographs were obtained using a transmission electron microscope. The results showed that heavy-metal concentrations in water and sediment did not exceed the standards, whereas Cd and Pb concentrations in the gill and liver exceeded the standards. The accumulation pattern of heavy metals in organ tissues was exhibited according to the following order: gill > liver > muscle. Five types of chromosomal aberrations were a centromere gap, single chromatid break, deletion, single chromatid gap, and fragmentation. The average percentages of chromosomal aberrations in polluted and reference C. striata were 4.60% and 1.00%, respectively. The statistical analyses of chromosomal aberration and biochemical parameters indicated that total protein, aspartate aminotransferase, and alanine aminotransferase significantly differed between the polluted and reference C. striata (p < 0.05). The liver histopathological alterations revealed atypical cellular structures, such as vacuolar appearance, nucleus degeneration, rough endoplasmic reticulum disintegration, abnormal cytoplasmic mitochondria, and deposition of heavy metals. Heavy-metal contaminations from electronic waste dumping areas affect fish in terms of chromosomal aberration, serum biochemistry, and histopathology.

What are the current analytical approaches for sediment analysis related to the study of diagenesis? Highlights from 2010 to 2018

This review is aimed at critical analysis of current and emerging capabilities of analytical methods as employed for sediment analysis. An emphasis is given to the most reliable experimental strategies used to acquiring analytical information that is relevant to study the diagenetic processes affecting the composition of sediments. Advanced analytical methodology in use basically rely on the application of mass spectrometry (or a few alternative techniques) to determine various inorganic elements, to measure their isotopic composition, to characterize organic matter, or to identify and quantify its principle components (biomarkers). Also brought into focus are sample preparation techniques which - given the complexity of sediment matrices and the diverse and multiple nature of analytes under scrutiny - are often a key for successful analysis.

Assessment of potentially toxic metal (PTM) pollution in mangrove habitats using biochemical markers: A case study on Avicennia officinalis L. in and around Sundarban, India

Spatial distribution of potentially toxic metals (PTMs) and their accumulation in mangrove Avicennia officinalis L. were studied along 8 locations in and around Sundarban mangrove wetland, India. Among 8 locations, S3 (Chemaguri) and S5 (Ghushighata) showed higher concentration of PTMs (Cd, Cr, Cu, Ni, Pb, Zn) characterized by higher enrichment factors (3.45-10.03), geo-accumulation indices (0.04-1.22), contamination factors (1.14-3.51) and pollution load indices (1.3-1.45) indicating progressive deterioration of estuarine quality and considerable ecotoxicological risk. Metal concentration in A. officinalis leaves showed significant correlation with sediment metals implying elevated level of bioaccumulation. Significant statistical correlation between photosynthetic pigments (Chlorophyll a, Chlorophyll b), antioxidant response (free radical scavenging and reducing ability) and stress enzymatic activity (Peroxidase, Catalase, Super-oxide dismutase) of A. officinalis with increasing metal concentration in the contaminated locations reflects active detoxification mechanism of the plant. The study indicates the potentiality of biomonitoring metal pollution using studied biochemical markers in mangrove habitats.

Impact of Heavy Metal Pollution on Ammonia Oxidizers in Soils in the Vicinity of a Tailings Dam, Baotou, China

Soil heavy metal pollution has received increasing attention due to their toxicity to soil microorganisms. We have analyzed the effects of heavy metal pollution on ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in soils in the vicinity of a tailings dam of Baotou region, China. Results showed that AOB were dominated with Nitrosomonas-like clusters, while AOA was dominated by group1.1b (Nitrososphaera cluster). Single Cd and Cr contents, as well as compound heavy metal pollution levels, had a significant negative impact on soil potential nitrification rate and both diversities of AOA and AOB. No clear relationship was found between any single heavy metal and abundance of AOA or AOB. But compound pollution could significantly decrease AOA abundance. The results indicated that heavy metal pollution had an obviously deleterious effect on the abundance, diversity, activity and composition of ammonia oxidizers in natural soils.

Rare earth elements profile in a cultivated and non-cultivated soil determined by laser ablation-inductively coupled plasma mass spectrometry

Rare earth elements (REEs) have several applications but the effects on environment are not well known. Therefore, the aim of this work is to establish a method for direct solid sample analysis by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) to evaluate the concentration and distribution of REEs in cultivated and non-cultivated soil. Samples were collected in two areas to 40 cm of depth. The LA-ICP-MS method is easy to be implemented and the sample treatment is very fast comprising only its drying, grounding and pressing as a pellet. The accuracy of the method was evaluated by using a certified reference material (BCR 667 - Estuarine Sediment, Institute for Reference Materials and Measurements (IRMM)) where good agreement with the certified values was obtained. Analyte recovery at two levels of concentration (2.5 and 15.0 μg g^-1) was also performed and recoveries in the range of 85%-120% were achieved, values that are acceptable for LA-ICP-MS analysis. In general, the concentration of the REEs is higher in the cultivated soil and increased from the surface to deeper layers, which can be a consequence of fertilizer application.

Insights on limits of detection, precision and accuracy in TXRF analysis of trace and major elements in environmental solid suspensions

In this work, the analytical capability of the total reflection X-ray fluorescence technique with the S2 PICOFOX spectrometer was investigated. A set of certified reference materials was prepared as solid particulate for TXRF analysis. Experimental data of sensitivity, limits of detection and recovery for many elements were obtained. Good sensitivity and limits of detection with a good recovery range of around 90-110% were achieved. Thus, the TXRF technique exhibits a good analytical potential for its applicability on different materials.

Root application of selenite can simultaneously reduce arsenic and cadmium accumulation and maintain grain yields, but show negative effects on the grain quality of paddy rice

Most current technologies can hardly simultaneously reduce the accumulation of arsenic (As) and cadmium (Cd) in crops. In this study, root application of selenite [Se (IV)] and selenate [Se (VI)] was used to assess their abilities to reduce the accumulation of As and Cd, and maintain the yields and quality of rice grains. The results show that Se (IV) showed a weaker ability than Se (VI) to maintain the grain contents of many essential elements, but a stronger ability to decrease As and Cd contents in rice grains, and maintain the yields, photosynthesis rate and stomatal conductance, and increase the grain contents of several amino acids (AAs), total Se, selenomethionine (SeMet) and selenocysteine (SeCys). The best outcomes resulted at a relatively high application of 5 mg kg^-1 Se (IV), reflecting in the highest total Se, SeCys and SeMet content (14.95, 118.70 and 864.73 μg kg^-1, respectively) in the grains, highest grain yield, and lowest grain As and Cd content (0.36 and 0.07 mg kg^-1, respectively). In addition, the application of 1-5 mg kg^-1 Se (IV) seemed to facilitate the formation of SeMet in the grains, but most inorganic Se in the grains were transformed into SeCys and SeMet under Se (VI) treatments. This study provides a new idea to resolve the problems of high accumulation of As and Cd in rice grains and insufficiency of Se intake in China.

Relationship between heavy metals and minerals extracted from soil clay by standard and novel acid extraction procedures

Strong acid digestions are commonly used to determine heavy metal (HM) contents in soils. In order to understand more fully the acid digestion processes, a logical step is to determine the extent of dissolution of mineral phases. The aims of this study were to compare the efficiency of extraction of HM by different acid digestions and to monitor the associated dissolution of the clay fraction. The context of the study was to develop a milder chemical extraction method (microwave-assisted 1 mol L^-1 HNO₃ closed system (NACS)), which recovers more reactive HM and with little dissolution of minerals. The different acid digestion methods dissolved different amounts of minerals from the clay fraction. Both aqua regia (AR) and EPA 3051 dissolved all of the Fe and Al oxides, and the dissolution of kaolin was limited to thinner particles (c dimension), smaller particles in a and b dimensions and grains with lower crystallinity. The lower recovery of HM for AR compared with EPA 3051 was related to the large amount of short-range order phases formed during the AR extraction as these phases have the capacity to re-adsorb HM. The new method (NACS) has the potential to replace other methods of determining bioavailable forms of HM, such as AR and EPA 3051. The contents of Pb, As, Co, Zn, and Cu determined by EPA 3051 and EPA 3052 were quite close.

Simultaneous determination of copper, cobalt, and mercury ions in water samples by solid-phase extraction using carbon nanotube sponges as adsorbent after chelating with sodium diethyldithiocarbamate prior to high performance liquid chromatography

Recently, a sponge-like material called carbon nanotube sponges (CNT sponges) has drawn considerable attention because it can remove large-area oil, nanoparticles, and organic dyes from water. In this paper, the feasibility of CNT sponges as a novel solid-phase extraction (SPE) adsorbent for the enrichment and determination of heavy metal ions (Co(2+), Cu(2+), and Hg(2+)) was investigated for the first time. Sodium diethyldithiocarbamate (DDTC) was used as the chelating agent and high performance liquid chromatography (HPLC) for the final analysis. Important factors which may influence extraction efficiency of SPE were optimized, such as the kind and volume of eluent, volume of DDTC, sample pH, flow rate, etc. Under the optimized conditions, wide range of linearity (0.5-400 μg L(-1)), low limits of detection (0.089~0.690 μg L(-1); 0.018~0.138 μg), and good repeatability (1.27~3.60 %, n = 5) were obtained. The developed method was applied for the analysis of the three metal ions in real water samples, and satisfactory results were achieved. All of these findings demonstrated that CNT sponges will be a good choice for the enrichment and determination of target ions at trace levels in the future.

Efficiency evaluation for remediating paddy soil contaminated with cadmium and arsenic using water management, variety screening and foliage dressing technologies

Paddy soils in many regions of China have been seriously polluted by multiple heavy metals or metalloids, such as arsenic (As), cadmium (Cd) and lead (Pb). In order to ensure the safety of food and take full advantage of the limited farmland resources of China, exploring an effective technology to repair contaminated soils is urgent and necessary. In this study, three technologies were employed, including variety screening, water management and foliage dressing, to assess their abilities to reduce the accumulation of Cd and As in the grains of different rice varieties, and meanwhile monitor the related yields. The results of variety screening under insufficient field drying condition showed that the As and Cd contents in the grains of only four varieties [Fengliangyouxiang 1 (P6), Zhongzheyou 8 (P7), Guangliangyou 1128 (P10), Y-liangyou 696 (P11)] did not exceed their individual national standard. P6 gained a relatively high grain yield but accumulated less As and Cd in the grains despite of the relatively high As and Cd concentrations in the rhizosphere soil. However, long-playing field drying in water management trial significantly increased Cd but decreased As content in the grains of all tested three varieties including P6, suggesting an important role of water supply in controlling the accumulation of grain As and Cd. Selenium (Se) showed a stronger ability than silicon (Si) to reduce As and Cd accumulation in the grains of Fengliangyou 4 (P2) and Teyou 524 (P13), and keep the yields. The results of this study suggest that combined application of water management and foliage dressing may be an efficient way to control As and Cd accumulation in the grains of paddy rice exposing to As- and Cd-contaminated soils.

Evaluation of sediment contamination with heavy metals: the importance of determining appropriate background content and suitable element for normalization

In the present study, concentrations of heavy metals (Cd, Cu, Co, Mn, Cr, Ni, Pb, and Zn) were determined at 35 river sediments in Serbia. The anthropogenic heavy metals input and quantification of the metal enrichment degree in sediments were estimated by calculating geo-accumulation indices (I(geo)) and enrichment factors (EF). These pollution indices have been calculated using different background values (continental crust and local background values) and different element used for normalization (Al and Fe), followed by result comparison. The EF values calculated with continental crust as background (minor to extremely severe enrichment) were higher than when regional background values were used (minor to moderate enrichment). Significant influence of background values on the I(geo) values is observed. Values of geo-accumulation index (<2) revealed that studied river sediments are remaining unpolluted to moderately polluted with Co, Mn, Cr, and Ni. Significant pollution in the sediments was observed for Cd, Cu, Pb, and Zn elements. The results of this study confirm the relevance of precise and accurate determining of local background concentrations while assessing sediment pollution. The values of EFs for studied elements were more influenced by the choice of background values than selection of element used for normalization. Our recommendation would be to use the local and regional background content in quantification of metal contamination in sediments, since these values differ and are site and region dependent.