Stimulating and toxic effect of chromium on growth and photosynthesis of a marine chlorophyte.

Marine phytoplankton can interchange trace metals in various biochemical functions, particularly under metal-limiting conditions. Here, we investigate the stimulating and toxicity effect of chromium (Cr) on a marine Chlorophyceae Osetreococcus tauri under Fe-replete and Fe-deficient conditions. We determined the growth, photosynthesis, and proteome expressions of Osetreococcus tauri cultured under different Cr and Fe concentrations. In Fe-replete conditions, the presence of Cr(VI) stimulated significantly the growth rate and the maximum yield of photochemistry of photosystem II (Fv /Fm ) of the phytoplankton, while the functional absorption cross-section of photosystem II (σPSII ) did not change. Minor additions of Cr(VI) partially rescued phytoplankton growth under Fe-limited conditions. Proteomic analysis of this alga grown in Fe-replete normal and Fe-replete with Cr addition media (10 µM Cr) showed that the presence of Cr significantly decreased the expression of phosphate-transporting proteins and photosynthetic proteins, while increasing the expression of proteins related to carbon assimilation. Cr can stimulate the growth and photosynthesis of O. tauri, but the effects are dependent on both the Cr(VI) concentration and the availability of Fe. The proteomic results further suggest that Cr(VI) addition might significantly increase starch production and carbon fixation.

Tradeoffs between pH, dissolved organic carbon, and mineral ions regulate cadmium uptake by Solanum hyperaccumulators in calcareous soil.

Soil solution pH and dissolved organic carbon (DOC) influence cadmium (Cd) uptake by hyperaccumulators but their tradeoff in calcareous soils is unclear. This study investigated the mechanisms of Solanum nigrum L. and Solanum alatum Moench in calcareous soil using a combination of concentration gradient experiments (0.6-100 mg Cd kg-1) and soil solution composition analysis. The results showed that the soil solution pH of S. nigrum remained stable despite Cd stress. On average, the soil solution pH of S. alatum was 0.23 units higher than that of S. nigrum, although pH decreased significantly under high Cd stress. In addition, the concentrations of potassium (K) and calcium (Ca) in the soil solution of S. nigrum increased and decreased under low and high levels of Cd stress, respectively. In S. alatum, the K and Ca concentrations in the soil solution generally increased with increasing Cd stress levels. Moreover, the level of DOC in the soil solution of both plants was higher under Cd stress compared to the control, and a gradually increasing trend with Cd stress level was observed in S. alatum. Consequently, the bioconcentration factors of the roots (2.62-19.35) and shoots (1.20-9.59) of both plants were >1, while the translocation factors were <1, showing an obstacle of Solanum hyperaccumulators in transferring Cd into their aboveground parts. Redundancy analysis revealed that the Cd concentration in S. nigrum roots was significantly negatively correlated with the soil solutions of K and Ca. In contrast, Cd concentrations in S. alatum roots and shoots were significantly positively correlated with soil solution DOC, K, and Ca but negatively correlated with pH. Our results suggest that calcareous soil neutralizes the acidity of released protons but does not affect cation exchange, inhibiting DOC in assisting the translocation of Cd within plants.

Residual loads from tilapia farming on the sediment of a Brazilian reservoir.

This study investigated the sediment geochemistry of a fish farming area in net cage tanks in the Rosário reservoir, Brazil. Three areas were investigated: reference (RA), fish farming (FFA), and dispersion (DA). The results were analyzed through correlation, similarity, principal component analysis, comparison with legislation, sediment quality guidelines, and sediment pollution indices. The mean concentrations for RA, FFA, and DA areas were respectively: Cu (mg.kg-1) 37.74, 62.23, and 71.83; Mn (mg.kg-1) 22.55, 66.48, and 55.90; Zn (mg.kg-1) 9.13, 114.83, and 94.27; Fe (%) 0.28, 0.40, and 0.43; OM (%) 15.84, 21.95, and 18.45; TOC (%) 1.86, 3.69, and 6.05; TN (mg.kg-1) 2365.00, 5015.00, and 3447.51; TP (mg.kg-1) 780.00, 6896.00, and 2585.50; ORP (mV) -95.50, -135.20, and -127.10; pH 6.60, 6.58, and 6.05; <63 µm 90.59, 78.68, and 87.30. Statistically, the influence of fish farming on sediment, organic matter, and pollutant sedimentation was demonstrated. Cu and Zn concentrations were below sediment quality guidelines. Regarding legal limits (resolution 454/2012/CONAMA), nutrients in the FFA area exceeded by 60% (TN) and 100% (TP), while in DA and RA areas they were 100% lower. TOC was 100% lower in all areas. Organic matter exceeded the limit by 100% in all areas. Pollution indices resulted in: low contamination factor 78%; unpolluted for 87% of pollution load and 83% of combined pollution; moderately polluted for 75% of the Nemerow index. The greatest impacts and influence of farming on pollutant sedimentation were more concentrated in the fish farming area. In terms of legal aspects and pollution indices, fish farming produced low levels of trace metal pollution and nutrient concentrations exceeded legal limits.

Elemental geochemical evidence for the river-derived sources of trace metals in surface sediments from Hangzhou Bay, East China Sea.

Coastal estuaries are often heavily subject to riverine influences by the inputs of sediment from terrestrial sources. Hangzhou Bay (HZB) is threatened by the riverine derived trace metals from two large rivers of Qiantang River (QTR) and Yangtze River (YZR). However, previous studies mainly focused on the incidental transport from the largest river in China (YZR) and failed to simultaneously evaluate the contributions of these two rivers, especially the directly flowing river of QTR, by their trace elemental geochemical composition and distribution. Herein, a comprehensive study identified the river-derived sources of multiple trace metals in surface sediments which transported from both of the rivers. The sampling stations were separated into three regions of YZR, HZB, and QTR based on their spatial distributions of sediment grain size and components. The significant variations for most of the trace metals concentrations, except for Cd, Th, and U, were found among three regions (χ2 ≥ 8.22, p ≤ 0.016). The highest concentrations in HZB were mainly resulted from the grain size effect (68.82% of the total variance), while the highest concentrations of Sr, Cd, and Ba in YZR and Zr and Hf in QTR were attributed to the anthropogenic source (11.90%) and mineral composition (6.21%) of river basins. After normalized the diversity of multiple trace metals concentrations and the influence of grain size by ratios of Igeo and EFLi, three regions were effectively distinguished. It was indicated that As, Cd, and Sb were enriched in the sediments of rivers by anthropogenic source (EFLi > 1.5 and/or Igeo > 1). The results evidenced that, after removing the influence of grain size, elemental geochemical composition of the surface sediments confidently identified the river-derived anthropogenic sources of the enriched trace metals from two major rivers, and largely from YZR.

Manganese reductive dissolution coupled to Sb mobilization in contaminated shooting range soil.

A "redox-stat" RMnR bioreactor was employed to simulate moderately reducing conditions (+ 420 mV) in Sb-contaminated shooting range soils for approximately 3 months, thermodynamically favoring Mn(IV) reduction. The impact of moderately reducing conditions on elemental mobilization (Mn, Sb, Fe) and speciation [Sb(III) versus Sb(V); Fe2+/Fe3+] was compared to a control bioreactor RCTRL without a fixed redox potential. In both bioreactors, reducing conditions were accompanied by an increase in effluent Sb(V) and Mn(II) concentrations, suggesting that Sb(V) was released through microbial reduction of Mn oxyhydroxide minerals. This was underlined by multiple linear regression analysis showing a significant (p < 0.05) relationship between Mn and Sb effluent concentrations. Mn concentration was the sole variable exhibiting a statistically significant effect on Sb in RMnR, while under the more reducing conditions in RCTRL, pH and redox potential were also significant. Analysis of the bacterial community composition revealed an increase in the genera Azoarcus, Flavisolibacter, Luteimonas, and Mesorhizobium concerning the initial soil, some of which are possible key players in the process of Sb mobilization. The overall amount of Sb released in the RMnR (10.40%) was virtually the same as in the RCTRL (10.37%), which underlines a subordinate role of anoxic processes, such as Fe-reductive dissolution, in Sb mobilization. This research underscores the central role of relatively low concentrations of Mn oxyhydroxides in influencing the fate of trace elements. Our study also demonstrates that bioreactors operated as redox-stats represent versatile tools that allow quantifying the contribution of specific mechanisms determining the fate of trace elements in contaminated soils. KEY POINTS: • "Redox-stat" reactors elucidate Sb mobilization mechanisms • Mn oxyhydroxides microbial reductive dissolution has a major role in Sb mobilization in soils under moderately reducing conditions • Despite aging the soil exhibited significant Sb mobilization potential, emphasizing persistent environmental effects.

Single-cell visualization and quantification of trace metals in Chlamydomonas lysosome-related organelles.

The acidocalcisome is an acidic organelle in the cytosol of eukaryotes, defined by its low pH and high calcium and polyphosphate content. It is visualized as an electron-dense object by transmission electron microscopy (TEM) or described with mass spectrometry (MS)-based imaging techniques or multimodal X-ray fluorescence microscopy (XFM) based on its unique elemental composition. Compared with MS-based imaging techniques, XFM offers the additional advantage of absolute quantification of trace metal content, since sectioning of the cell is not required and metabolic states can be preserved rapidly by either vitrification or chemical fixation. We employed XFM in Chlamydomonas reinhardtii to determine single-cell and organelle trace metal quotas within algal cells in situations of trace metal overaccumulation (Fe and Cu). We found up to 70% of the cellular Cu and 80% of Fe sequestered in acidocalcisomes in these conditions and identified two distinct populations of acidocalcisomes, defined by their unique trace elemental makeup. We utilized the vtc1 mutant, defective in polyphosphate synthesis and failing to accumulate Ca, to show that Fe sequestration is not dependent on either. Finally, quantitation of the Fe and Cu contents of individual cells and compartments via XFM, over a range of cellular metal quotas created by nutritional and genetic perturbations, indicated excellent correlation with bulk data from corresponding cell cultures, establishing a framework to distinguish the nutritional status of single cells.

Persistent deep water anoxia in the eastern South Atlantic during the last ice age.

During the last glacial interval, marine sediments recorded reduced current ventilation within the ocean interior below water depths of approximately >1,500 m [B. A. Hoogakker et al., Nat. Geosci. 8, 40-43 (2015)]. The degree of the associated oxygen depletion in the different ocean basins, however, is still poorly constrained. Here, we present sedimentary records of redox-sensitive metals from the southwest African margin. These records show evidence of continuous bottom water anoxia in the eastern South Atlantic during the last glaciation that led to enhanced carbon burial over a prolonged period of time. Our geochemical data indicate that upwelling-related productivity and the associated oxygen minimum zone in the eastern South Atlantic shifted far seaward during the last glacial period and only slowly retreated during deglaciation times. While increased productivity during the last ice age may have contributed to oxygen depletion in bottom waters, especially on the upper slope, slow-down of the Late Quaternary deep water circulation pattern [Rutberg et al., Nature 405, 935-938 (2000)] appears to be the ultimate driver of anoxic conditions in deep waters.

Evaluating washing techniques to eliminate external contamination of trace elements in bat fur and bird feathers.

Non-invasive proxies, such as fur and feathers, are likely to be increasingly used to assess the potential exposure of chemicals, including trace metals and metalloids. However, the amount of external contamination is usually unknown, and there is no standard method for removing external contamination of trace metals in fur or feathers. To date, 40 % of studies published related to the measurement of trace metal levels in fur or the hair of non-human mammals and 24 % of studies in feathers do not state any washing methods or did not wash the samples before analysis. We assessed three washing techniques to remove external contamination of arsenic (As), lead (Pb), and zinc (Zn) from bat fur. We selected the three most frequently used fur washing methods from literature. To test these methods, fur samples from great flying foxes (Pteropus neohibernicus neohibernicus, n=15 individuals) from Papua New Guinea preserved over eight decades (AMNH, USA) were used. Percentages of trace metal removed are 87.19 % (SD= 12.28), 92.99 % (SD= 5.5) and 88.57 % (SD= 9.33) for As, 54.72 % (SD= 31.64), 55.89 % (SD= 37.87), and 53.93 % (SD= 41.28) for Pb, and 74.03 % (SD= 22.96), 22.93 % (SD= 73), and 24.95 % (SD= 49.5) for Zn using M2, M3, and M4, respectively. We also assessed four washing techniques to remove external contamination of arsenic (As), mercury (Hg), and zinc (Zn) from bird feathers. We identified the four most prevalent washing techniques in the literature used for feathers. We used feathers from the great horned owl (Bubo virginianus) and the great blue heron (Ardea herodias) to test these methods. Percentages of trace metal removed are 34.35 % (SD= 44.22), 69.22 % (SD= 36.5), 62.59 % (SD= 48.37), and 80.89 % (SD= 14.54) for As, 66.97 % (SD= 13.26), 29.4 % (SD= 67.06), 49.68 % (SD= 42.33), and 28.88 % (SD= 69) for Hg, and <0 % (SD= 80.1), 0 % (SD= 29.55), 11.23 % (SD= 47.73), and 57.09 % (SD= 21.2) for Zn using M2, M3, M4, and M5, respectively. This study shows the importance of washing fur and feather samples prior to trace metals analyses in ecotoxicology and biomonitoring studies.

Plastics and plastic-bound toxic metals in municipal solid waste compost from Sri Lanka.

This study examined plastics and toxic metals in municipal solid waste compost from various regions in Sri Lanka. Plastics were extracted using density separation, digested using wet peroxidation, and identified using Fourier Transform Infra-Red Spectroscopy in Attenuated Total Reflection mode. Compost and plastics were acid-digested to quantify total Cd, Cu, Co, Cr, Pb, and Zn concentrations and analyzed for the bioavailable fraction using 0.01 M CaCl2. Notably, plastics were highly abundant in most compost samples. The main plastic types detected were polyethylene, polypropylene, and cellophane. However, the average Cd, Cu, Co, Cr, Pb, and Zn levels were 0.727, 60.78, 3.670, 25.44, 18.95, and 130.7 mg/kg, respectively, which are well below the recommended levels. Zn was the most bioavailable (2.476 mg/kg), and Cd was the least bioavailable (0.053 mg/kg) metal associated with compost. The Contamination factor data show that there is considerable enhancement of Cd and Cu, however, Cr, Cu, Co, and Pb are at low contamination levels. Mean geo accumulation index values were 1.39, 1.07, - 1.06, - 0.84, - 0.32, and 0.08 for Cd, Cu, Co, Cr, Pb, and Zn. Therefore, the contamination level of compost samples with Cd and Cu ranges from uncontaminated to contaminated levels, whereas Co, Cr, Pb, and Zn are at uncontaminated levels. Despite no direct metal-plastic correlation, plastics in compost could harm plants, animals, and humans due to ingestion. Hence, reducing plastic and metal contamination in compost is crucial.

Comparative analysis of sediment quality indices using different reference values in an environmental protection area in Southeastern Brazil.

Contamination of aquatic ecosystems by potentially toxic elements (PTEs) is a concerning environmental issue, given their persistence, toxicity potential, and ability to accumulate in living organisms. Several studies have been conducted to assess the contamination of aquatic ecosystems by PTEs, using pollution and ecological risk indices that rely on the concentration of these elements in aquatic sediments. However, many of these studies use global reference values for calculating the indices, which can lead to misleading interpretations due to substantial variations in PTEs concentrations influenced by the geological characteristics of each region. Therefore, the use of regional reference values is more appropriate when available. This study aimed to investigate variations in the results of five indices, employing global, regional, and quality reference values, based on sediment samples collected from rivers in the Ipanema National Forest, a protected area in Brazil exposed to various anthropogenic pressures. The results revealed that elements such as Al, Fe, and Mn exceeded the limits allowed by legislation in water samples, while As and Cr surpassed the limits in sediment samples. Comparative analysis highlighted significant discrepancies in the results of the indices when global reference values were used compared to regional and quality reference values, especially for As and Ba. Thus, this study underscores the importance of establishing specific regional values for an accurate assessment of sediment quality and the risks associated with contamination by PTEs in different regions worldwide.

Trace metal speciation trends in Mazowe dam, Zimbabwe, a typical sub-tropical dam ecosystem impacted by gold mining and agriculture.

The present study aimed to assess trace metal speciation trends in the water and sediments of Mazowe Dam, a typical sub-tropical dam ecosystem impacted by gold mining and agriculture in Zimbabwe. The elements studied include Al, As, Cd, Co, Cr, Cu, Hg, Fe, Mn, Ni, Pb, and Zn. Elemental speciation in the water column was determined using Visual MINTEQ version 3.1 geochemical computer modelling, while speciation in the sediment phase was determined using sequential extraction techniques. For each element, the data obtained were subjected to extensive correlation analysis to identify intra- and inter-metal species interactions in the water column and the sediment phase, as well as across the water-sediment interface. Possible mechanisms to account for the observed species interactions are proposed. In the water column, Co was predicted to have the highest number of chemical species (9), Cd and Zn (8), Mn and Fe (7), Ni (6), Pb (5), Al and Cu (3), Cr, Hg, and As have the least (2). In the sediment, Al, As, Co, Cr, Cu, Fe, Ni and Fe mainly exist in the residual fraction, while Zn and Mn concentrations in fractions vary per sampling site, with no fraction that is dominant across the sampling sites. Equilibrium exchange reactions across the water-sediment interface were observed e.g., for Cd species /FA2Cd (aq) and Co species /FACo+2G (aq), and /FA2Co (aq). This study is valuable in highlighting trace metal speciation in a tropical dam ecosystem in Africa and adds to the growing knowledge about the behaviour of trace metals in aquatic ecosystems in the region and globally.

Mapping soil trace metal distribution using remote sensing and multivariate analysis.

Trace metal soil contamination poses significant risks to human health and ecosystems, necessitating thorough investigation and management strategies. Researchers have increasingly utilized advanced techniques like remote sensing (RS), geographic information systems (GIS), geostatistical analysis, and multivariate analysis to address this issue. RS tools play a crucial role in collecting spectral data aiding in the analysis of trace metal distribution in soil. Spectroscopy offers an effective understanding of environmental contamination by analyzing trace metal distribution in soil. The spatial distribution of trace metals in soil has been a key focus of these studies, with factors influencing this distribution identified as soil type, pH levels, organic matter content, land use patterns, and concentrations of trace metals. While progress has been made, further research is needed to fully recognize the potential of integrated geospatial imaging spectroscopy and multivariate statistical analysis for assessing trace metal distribution in soils. Future directions include mapping multivariate results in GIS, identifying specific anthropogenic sources, analyzing temporal trends, and exploring alternative multivariate analysis tools. In conclusion, this review highlights the significance of integrated GIS and multivariate analysis in addressing trace metal contamination in soils, advocating for continued research to enhance assessment and management strategies.

Characterization of soil trace metal pollution, source identification, and health risk assessment in the middle reaches of the Guihe River Basin.

The natural environment, as well as human production and survival, is intrinsically dependent on soil. This study comprehensively assessed the pollution status, health risks, and sources of trace metals in the middle reaches of the River Gui Basin (MRGB) utilizing the geoaccumulation index, potential ecological risk index (PERI), and human health risk evaluation method. The findings of this study provide the following key insights: (1) only Cu and Pb levels in the MRGB soils did not exceed the background values established for soils in Weifang City (WFC). (2) The geoaccumulation status in most areas of the MRGB ranged from non-polluted to mildly polluted, with the overall ecological risk classification ranging from mild to moderate. (3) The cumulative non-carcinogenic risk for humans in the MRGB remained within acceptable limits, whereas the carcinogenic risk indices fell within tolerable levels. Oral ingestion emerged as the primary exposure pathway for both non-carcinogenic and carcinogenic health risks. (4) Cu, Zn, Ni, and Cr concentrations in MRGB soils primarily stemmed from natural sources associated with parent rocks, with Zn exhibiting additional influence from anthropogenic factors. In contrast, Pb, Cd, Hg, and As concentrations were predominantly driven by anthropogenic sources. Although the soils in the MRGB typically exhibited mild-to-moderate contamination levels, the contamination levels of Hg and Cd were notably more severe. As and Cr were significant health hazards. Most soil contamination sources are attributed to anthropogenic factors, warranting heightened attention from the relevant authorities.

Bioaccumulation and Health Risk Assessment of Potentially Toxic Metals in Citrus Limetta & Citrus Sinensis Irrigated by Wastewater.

The aim of this study was to evaluate the impact of different irrigation sources on the levels of potentially toxic metals (Cd, Cr, Fe and Mn) in the edibles of citrus fruits (Citrus sinensis and Citrus limetta). The samples of fruit, soil and water were collected from two locations (fresh water irrigated-FW I and sewage water irrigated-SW II) within the city of Sargodha. The samples utilized in the study for metal analysis were prepared utilizing the wet acid digestion method. Metal determination was performed using Atomic Absorption Spectrometry (AAS). The potentially toxic metal values in the citrus samples ranged from 0.010 to 0.063, 0.015 to 0.293, 6.691 to 11.342 and 0.366 to 0.667 mg/kg for Cd, Cr, Fe and Mn, respectively. Analysis of Citrus limetta and Citrus sinensis indicated that the highest concentration of Cr, Fe and Mn is observed at the sewage water irrigation site (SW-II), whilst the minimum levels of Cr, Fe and Mn were observed at the fresh water irrigation site (FW-I). The results show that the levels of these metals in soil and fruit samples meet the acceptable guidelines outlined by USEPA and WHO. It was found that the metal pollution constitutes a potential threat to human health due to the HRI values for Cd, Cr, and Fe being above 1, despite the DIM values being below 1. Regular monitoring of vegetables irrigated with wastewater is highly recommended in order to minimise health risks to individuals.

Evaluation of the Effects of Wastewater Irrigation on Heavy Metal Accumulation in Vegetables and Human Health in the Cauliflower Example : Heavy Metal Accumulation in Cauliflower.

The goals of the present research were to determine the heavy metal contents in the water-soil-cauliflower samples in industrial wastewater irrigated areas and to assess the health risks of these metals to the people. Metal analyses were carried out using the atomic absorption spectrophotometer equipped with a graphite furnace. The metal readings in the cauliflower specimens ranged from 1.153 to 1.389, 0.037 to 0.095, 0.61 to 0.892, 0.625 to 0.921, 1.165 to 2.399, 0.561 to 0.652, 0.565 to 0.585, 0.159 to 0.218 and 1.268 to 1.816 mg/kg for Cd, Co, Cr, Cu, Fe, Ni, Pb, Zn and Mn, respectively. Statistics revealed that, with the exception of Pb and Co (p > 0.05), there was no statistically significant variation in the metal concentrations in the cauliflower samples according to the irrigation type. Pb, Ni, and Cr had HRI values below 1.0 and did not seem to be a hazard to human health, in contrast to Cd, Co, Cr, Cu, Fe, Ni, Pb, Zn and Mn, which glanced to constitute a health risk. Regular monitoring of vegetables irrigated with wastewater is strongly advised to reduce health hazards to people.

Biometals in Alzheimer disease: emerging therapeutic and diagnostic potential of molybdenum and iodine.

The current ageing trend of the world population has, in part, accounted for Alzheimer disease (AD) being a public health issue in recent times. Although some progress has been made in clarifying AD-related pathophysiological mechanisms, effective intervention is still elusive. Biometals are indispensable to normal physiological functions of the human body-for example, neurogenesis and metabolism. However, their association with AD remains highly controversial. Copper (Cu) and zinc (Zn) are biometals that have been investigated at great length in relation to neurodegeneration, whereas less attention has been afforded to other trace biometals, such as molybdenum (Mo), and iodine. Given the above context, we reviewed the limited number of studies that have evidenced various effects following the usage of these two biometals in different investigative models of AD. Revisiting these biometals via thorough investigations, along with their biological mechanisms may present a solid foundation for not only the development of effective interventions, but also as diagnostic agents for AD.

Regulatory mechanisms of sulfur metabolism affecting tolerance and accumulation of toxic trace metals and metalloids in plants.

Soil contamination with trace metals and metalloids can cause toxicity to plants and threaten food safety and human health. Plants have evolved sophisticated mechanisms to cope with excess trace metals and metalloids in soils, including chelation and vacuolar sequestration. Sulfur-containing compounds, such as glutathione and phytochelatins, play a crucial role in their detoxification, and sulfur uptake and assimilation are regulated in response to the stress of toxic trace metals and metalloids. This review focuses on the multi-level connections between sulfur homeostasis in plants and responses to such stresses, especially those imposed by arsenic and cadmium. We consider recent progress in understanding the regulation of biosynthesis of glutathione and phytochelatins and of the sensing mechanism of sulfur homeostasis for tolerance of trace metals and metalloids in plants. We also discuss the roles of glutathione and phytochelatins in controlling the accumulation and distribution of arsenic and cadmium in plants, and possible strategies for manipulating sulfur metabolism to limit their accumulation in food crops.

Machine learning based on the graph convolutional self-organizing map method increases the accuracy of pollution source identification: A case study of trace metal(loid)s in soils of Jiangmen City, south China.

Rapid economic development and industrialization may include environmentally harmful human activities that cause heavy-metal accumulation in soils, ultimately threatening the quality of the soil environment and human health. Therefore, accurate identification of pollution sources is an important weapon in efforts to control and prevent pollution. The self-organizing map (SOM) method is widely used in pollution source identification because of its capacity for visualization of high-dimensional data. The SOM ignores the graph structure relationship among chemical elements in soils; the SOM analysis of pollution sources has high uncertainty. Here, we propose a new analysis method, i.e., the graph convolutional self-organizing map (GCSOM), which uses a graph convolutional network (GCN) to extract the graph structure relationship among the chemical elements in soils, then performs data visualization using an SOM. We compared the performances of GCSOM and SOM, then assessed the pollution source characteristics of trace metal(loid)s (TMs, mostly heavy metals) in Jiangmen City using the GCSOM. Our experimental results showed that the GCSOM is superior to the SOM for identification of TM sources, while the TMs in the soil of Jiangmen originate from three main sources: agricultural activities (mainly in Taishan City, Jiangmen), traffic emissions (mainly in Xinhui and Pengjiang Districts), and industrial activities (mainly in Xinhui District). The risk assessment indicated that the risk of all TMs was within threshold.

Joint effects of temperature and copper exposure on developmental and gene-expression responses of the marine copepod Tigriopus japonicus.

There is growing contamination of copper (Cu) in the marine environment, particularly after the ban of organotin compounds and the increase of the use of Cu-based antifouling paints. Although there are increasing research interests in temperature-dependent chemical toxicity to aquatic organisms, most existing studies focused on acute impacts of chemicals at high concentrations. This study aimed to investigate the interacting effect of temperature and copper exposure at environmentally relevant concentrations on survival and development in the marine copepod Tigriopus japonicus with a partial life-cycle toxicity test. Expressions of five stress response genes in the copepod, namely two glutathione S-transferases (GST-S and GST-O), two heat shock proteins (HSP70 and HSP90), and glutathione reductase (GR) were also investigated. The copepod's survival was significantly impaired at 15 °C after development to adult stage, while its developmental time reduced significantly with increasing temperature. Copper at the two environmentally relevant test concentrations had no significant impacts on these apical endpoints whereas the interaction between Cu and temperature was more significant in modulating gene expressions. GST-S, GST-O and HSP90 genes in copepods exposed to 100 µg Cu L-1 were significantly upregulated at 20 °C. At 32 °C, most genes were either insignificantly expressed or down-regulated, compared to the control, likely suggesting that thermal stress inhibited the copepod's antioxidative defense system. Overall, the results revealed that the joint Cu and thermal stresses have significantly elicited antioxidative system in the copepods. It clearly demonstrated the need for more fundamental studies about potential impacts of different environmental factors such as temperature on chemical toxicity under realistic scenario of marine pollution.

Dynamic modelling the effects of ionic strength and ion complexation on trace metal speciation during anaerobic digestion.

Dosing trace metals into anaerobic digestors is proven to improve biogas production rate and yield by stimulating microorganisms involved in the metabolic pathways. Trace metal effects are governed by metal speciation and bioavailability. Though chemical equilibrium speciation models are well-established and widely used to understand metal speciation, the development of kinetic models considering biological and physicochemical processes has recently gained attention. This work proposes a dynamic model for metal speciation during anaerobic digestion which is based on a system of ordinary differential equations aimed to describe the kinetics of biological, precipitation/dissolution, gas transfer processes and, a system of algebraic equations to define fast ion complexation processes. The model also considers ion activity corrections to define effects of ionic strength. Results from this study shows the inaccuracy in predicting trace metal effects on anaerobic digestion by typical metal speciation models and the significance of considering non-ideal aqueous phase chemistry (ionic strength and ion pairing/complexation) to define speciation and metal labile fractions. Model results show a decrease in metal precipitation and increase in metal dissolved fraction and methane production yield with increase in ionic strength. Capability of the model to dynamically predict trace metal effects on anaerobic digestion under different conditions, like changing dosing conditions and initial iron to sulphide ratio, was also tested and verified. Dosing iron increases methane production and decreases hydrogen sulphide production. However, when iron to sulphide ratio is greater than 1, methane production decreases due to increase in dissolved iron which reaches inhibitory concentration levels.