Assessing cadmium and vanadium accumulation using diffusive gradient in thin-films (DGT) and phytoplankton in the Churchill River estuary, Manitoba

Bio-accessibility and mobilization dynamics of soil vanadium during a 48-year vegetation restoration in a vanadium titano-magnetite tailings reservoir

Bio-accessibility of vanadium (V) in soils determines the effectiveness of vegetation restoration in the vanadium titano-magnetite tailings reservoirs because of persistent V toxicity, yet the variations in the bio-accessibility and mobilization of V in the soils with vegetation restoration remain elusive. Here, the bio-accessibility and mobilization of V in the soil-water interface were investigated along a 48-year vegetation restoration chronosequence in the Majiatian tailings reservoir using the diffusive gradients in thin films technique (DGT) and DGT-induced flux model. We found a low concentration of DGT-extracted V along the vegetation restoration chronosequence and the V fraction was dominated by the residual form, indicating a low V bio-accessibility in the soils. The bio-accessibility of V increased along the chronosequence because of the increased V resupply from solid phase, especially from the organic V fraction and the clay bound V. Low supply coefficient (R = 0.25) revealed a limited release of V from solid phase to soil solution. The kinetic resupply processes of V and its key regulating parameters were stage-specific during the vegetation restoration. The pool size of labile V in the soils determined the rapid V supply at the early and late stages, while the low desorption rate of V from the solid to liquid phase regulated the slow supply regime at the middle stage. The results of the present study highlight the importance of the long-term monitoring of soil V mobilization in the tailings reservoir because of the increased bio-accessibility and the dynamic supply of V during the vegetation restoration.

Spatiotemporal characterization of vanadium at the sediment-water interface of a multi-ecological lake

As an emerging environmentally harmful metal, vanadium (V) deserves significant research attention due to its hazardous concentrations in aquatic environments. However, the research on the characterization of V in sediment-water interface (SWI) remains limited. In this study, seasonal sampling was conducted in algal- and macrophyte-dominated zones via the method of in situ high-resolution diffusive gradients in thin films (DGT). The concentration of dissolved V in water in algal-dominated regions (12 sites) exceeded the long-term ecotoxicology limit of 1.2 μg⋅L-1. Seasonal variations of chemical speciation of V were observed in three ecological sites. DGT-labile V at the SWI exhibited two basic patterns associated with eutrophic status, one showing sharply decreasing gradients in the vicinity of the SWI and the other showing the absence of diffusion gradient. Positive correlations were observed between the water-dissolved V and the DGT-labile V, indicating DGT-labile V is a sensitive indicator for the release of V from sediment into water. Moreover, the mobility of V was influenced by the reduction of Fe(hydr)oxides and complexation with organic matter, in particular, during periods of algal blooms. It is suggested that V contamination at the SWI of algal-dominated zones deserves additional attention.

Phytoplankton metabolite profiles from two Lake Ontario Areas of Concern reveal differences associated with taxonomic community composition

Water quality and phytoplankton community composition are important factors that can indicate freshwater ecosystem health. We combined water quality, phytoplankton community, and metabolomic data from algae and water sampled from two embayments in Lake Ontario, Hamilton Harbour and the Bay of Quinte, over ten weeks from August to October in the year 2020. Metabolomics was performed using liquid chromatography tandem mass spectroscopy (LC-MS/MS) to identify changes in intracellular metabolites within algae communities over time, and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was used to characterize putative isomers of extracellular metabolites at sub-ppb mass accuracy. Results from this study indicate that Hamilton Harbour and the Bay of Quinte are two very different ecosystems with respect to water quality, phytoplankton metabolites, and phytoplankton community composition. Community composition is strongly driven by conductivity and nitrates in Hamilton Harbour, while the opposite is true in the Bay of Quinte. Metabolites including α-aminobutyric acid and glycine were found in larger abundance within algal communities at both locations, while taurine was more predominant in algal communities from the Bay of Quinte. These metabolic profiles could reflect the different communities of phytoplankton, and be alternative indicators of algal bloom growth.

Assessing variability in the ratio of metal concentrations measured by DGT-type passive samplers and spot sampling in European seawaters

The current study evaluates the effect of seawater physico-chemical characteristics on the relationship between the concentration of metals measured by Diffusive Gradients in Thin films (DGT) passive samplers (i.e., DGT-labile concentration) and the concentrations measured in discrete water samples. Accordingly, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used to measure the total dissolved metal concentrations in the discrete water samples and the labile metal concentrations obtained by DGT samplers; additionally, lead and cadmium conditional labile fractions were determined by Anodic Stripping Voltammetry (ASV) and total dissolved nickel was measured by Cathodic Stripping Voltammetry (CSV). It can be concluded that, in general, the median ratios of DGT/ICP and DGT/ASV(CSV) were lower than 1, except for Ni (median ratio close to 1) and Zn (higher than 1). This indicates the importance of speciation and time-integrated concentrations measured using passive sampling techniques, which is in line with the WFD suggestions for improving the chemical assessment of waterbodies. It is the variability in metal content in waters rather than environmental conditions to which the variability of the ratios can be attributed. The ratios were not significantly affected by the temperature, salinity, pH, oxygen, DOC or SPM, giving a great confidence for all the techniques used. Within a regulatory context such as the EU Water Framework Directive this is a great advantage, since the simplicity of not needing to use corrections to minimize the effects of environmental variables could help in implementing DGTs within monitoring networks.

Labile metal assessment in water by diffusive gradients in thin films in shipyards on the Brazilian subtropical coast

Shipyards impact on estuarine environments because of the use of antifouling paints and petroleum products, which release trace metals that may remain in their bioavailable or labile form. Regardless of its importance, the relation between continuous input of trace metals (hotspot area) and their availability in the water column has been scarcely studied. This study evaluated seasonal variations in the concentrations of labile fractions of metals in shipyards located in estuarine areas on the Brazilian subtropical coast. These fractions were determined by the Diffuse Gradients in Thin Films (DGT) technique. Maximum labile fraction concentrations of Cr (0.3 μg L^-1), Ni (2.2 μg L^-1) and V (2.0 μg L^-1) are directly related to (i) their specific source: antifouling paints (for Cr), metal and steel alloys (for Cr and Ni) and petroleum products (for V), besides (ii) periods of intensive traffic and vessel repair. Additionally, variations in labile fractions of Ni and V in the Patos Lagoon estuary were influenced by salinity, which is known to affect metal desorption from surface sediments in resuspension events. Even though Cr is affected by the same processes, it is available as Cr(III) and does not represent any ecological risk in the study areas. Although the areas under study are affected by variations in physical and chemical conditions, shipyards were effectively hotspots of trace metals in their labile fraction in various estuarine systems in southeastern and southern Brazil. Thus, they represent areas where Ecological Risk Assessment, mainly of V, should be carried out.

Investigation on trace metal speciation and distribution in the Scheldt estuary

The biogeochemical behavior of Cd, Co, Cr, Cu, Ni and Pb along the historically polluted Scheldt estuary (Belgium - The Netherlands) was investigated in this study. As never studied before in this area, labile trace metals were measured using the passive sampling technique of Diffusive Gradients in Thin-films (DGT), while total dissolved and particulate trace metal concentrations were assessed using classic active sampling techniques. This dual approach allowed us to highlight the variations of trace metal speciation and distribution in the estuarine surface waters, considering environmental and physicochemical gradients along the transect. The large data set obtained was then compared with literature data of historical measurements along the Scheldt (from 1980 until now), but also from other estuaries. As emphasized by our results, trace metal mobility and partitioning along the Scheldt estuary was mainly driven by biogeochemical reactions which were strongly influenced by gradients of specific estuarine physico-chemical parameters, such as salinity, turbidity, temperature and so on. Hence, all species of trace metals displayed a non-conservative behavior. More precisely, dissolved labile fractions of trace metals showed higher levels in the middle estuary, where many solubilization and remobilization processes occurred due to turbulent mixing mechanisms and an increasing salinity. Our study confirmed the decreasing trend historically observed for particulate metals along the Scheldt, as well as the rising concentrations recorded for dissolved trace metals which might also lead to an increase of their labile fraction measured by the DGT. Finally, these preliminary results suggested that a more regular monitoring of labile metal along the Scheldt estuary is essential to have an in-depth understanding of trace metal speciation and to review bioavailability of trace metals within estuarine ecosystems.

Metal speciation of the Paraopeba river after the Brumadinho dam failure

On January 25, 2019, a tailings dam at the Córrego do Feijão iron ore mine (Brumadinho, Minas Gerais, southern Brazil) ruptured and released ~12 million m³ of mine tailings into the Paraopeba River, which is an important source of drinking water to a populous region. While water potability due to a strong increase in turbidity has been well documented, possible effects of metal contamination are yet to be addressed. We investigated the speciation of metals in the river water and desorption of metals from sediments as a means of supporting risk assessment, using the diffusive gradient in thin films (DGT) technique, desorption experiments and chemical speciation calculations. The results of the in-situ DGT monitoring revealed that the labile concentrations of metals were low in relation to the respective total and dissolved concentrations. Chemical speciation calculations showed that the heavy metals were not stable in the Paraopeba River. The desorption experiments suggested that sediments may release a limited amount of As and Cu, but large amounts of Mn into the river water. Higher concentrations of Fe and Mn indicated a possible association with the impact of mine tailings. In general, the total metal concentrations during the rainy season were higher than those during the dry season, whereas the reverse was generally the case for labile forms. This pattern reveals that metal speciation is intrinsically dependent on the seasonal variation of the hydrological conditions.

Distribution and availability of rare earth elements and trace elements in the estuarine waters of the Ría of Huelva (SW Spain)

Metal pollution in estuaries represents a serious environmental challenge, especially in areas affected by industrial and mining activities. This study investigates the metal partitioning and availability of rare earth elements (REE), Y and other trace metals (Ag, Tl, U and Cs) in the Ria of Huelva estuary (SW Spain), strongly affected by mining and industrial activities. A 30 h monitoring campaign was performed collecting periodic water samples and deploying diffusive gradient in thin films (DGTs) devices to determine the main factors controlling metal availability. The dissolved concentrations of U (3118-3952 ng/L) and Cs (284-392 ng/L) were in the same order of magnitude than those reported in other estuaries and coastal waters worldwide, however, REE (26-380 ng/L), Y (15-109 ng/L), Ag (14-307 ng/L) and Tl (29-631 ng/L) concentrations exceeded these values for the same salinities. Unlike most metals (i.e. Ag, Tl, U, Cs), which were mainly found in the dissolved form (87-100% of total), REE and Y were found in the particulate phase (22-36% of total). Metal lability was mainly related to the concentration in the water column following this order: U>REE>Y>Ag>Tl. A similar binding mechanism was observed for Tl and Cd, due to its chemical affinity. This relationship between chemical properties and absorption by DGT-resin was also observed for REE (and Y), Rb and Sr, which may cause bioaccumulation upon persistent exposure, considering the ability of these metals to cross the biological membranes. The lability of metals predicted by geochemical codes did not coincide with absorption of labile metals by DGTs due probably to the instability of complexes in contact with the DGT membranes, the inability of metals to form thermodynamically stable complexes or the absorption of colloids. From this work it can be concluded that DGT passive sampling should complement traditional sampling to monitor metal availability in aquatic environments.

An untargeted metabolomic approach for the putative characterization of metabolites from Scenedesmus obliquus in response to cadmium stress

Cadmium (Cd) is a widespread contaminant in aquatic systems and has a variety of toxicological implications on freshwater microorganisms. In this study, the green algae Scenedesmus obliquus was exposed to increasing Cd concentrations that inhibited growth by 20% (12.6 μmol L^-1), 30% (39.8 μmol L^-1) and 40% (83.2 μmol L^-1) and the metabolite profiles of released and cellular biomolecules were explored using an untargeted direct infusion high resolution Fourier transform ion cyclotron resonance mass spectrometry approach. In Cd untreated cultures, intrinsic differences in composition existed between released biomolecules and freeze-dried cells. Based on putatively characterized compound groups, a greater proportion of Cys-GSH isomers and carboxyamides were present in exudates whereas sugar isomers and phosphonic acids comprised most cellular metabolites. In cultures exposed to 83.2 μmol L^-1 Cd, an overall shift in metabolomic response across both released biomolecules and cellular components resulted in an increase of lipid-based esters, and Cys-GSH isomers. These two important metabolites are used in antioxidant defense mechanisms and reactive oxygen species prevention during cellular stress. The diversity of metabolites also decreased as Cd concentrations increased when compared to untreated cultures, suggesting that overall metabolites specialize upon metal stress. We show systemic shifts from sugar and carboxylic isomers to specialized proteins and lipid isomers to help S. obliquus cope with stress. These findings highlight the potential use of this green algae as a potential biosorbent and sheds light into the metabolomics of Cd toxicology and insights into microbial metal adaptation.

Metal partitioning and speciation in a mining-impacted estuary by traditional and passive sampling methods

This study deals with the metal partitioning and bioavailability of metal/loids in the estuary Ria of Huelva (SW Spain) which is strongly affected by historical mining and industrial activities. To address this issue, traditional (i.e., grab samples) and passive sampling (i.e., diffusive gradient in thin films, DGTs) was carried out in the outer part of the estuary during different tidal cycles in order to determine the dissolved and particulate metal/loid concentrations. The dissolved concentrations exceeded, by several orders of magnitude, those reported in other estuaries worldwide that are affected by anthropogenic activities. A spatial pattern was observed in the metal distribution; a decrease seaward was recorded for some of the elements associated with mining (e.g., Cu, Zn, and Cd), the opposite tendency is observed for others associated with harbor emissions (e.g., Sn, Ni, or Pb). A different metal/loid partitioning pattern was also observed; Fe, and to a lesser extent Pb and Sn, were chiefly found in the particulate matter, while the rest of the elements were mainly found in the dissolved form. The bioavailability of the metal/loids was studied by speciation using both geochemical modeling and DGTs; while concentrations in DGTs supported metal/loid speciation for Zn, Cd, Mn, Co, As, and Sb according to their affinity to form strong or weak complexes, some discrepancies were observed for other elements such as Cu, V, Fe, and Pb, which are prone to forming strong complexes. The main reason behind the unexpectedly high Fe and Pb DGTs concentrations may be associated with their presence in the colloidal particles passing through the DGT. There was a strong positive correlation between dissolved and DGT concentrations for Cd and Mn, and to a lesser extent for Fe and Cu, highlighting the direct relationship between the concentrations in water and availability to living organisms in the estuary.

Linking molecular and optical properties of dissolved organic matter across a soil-water interface on Akimiski Island (Nunavut, Canada)

Dissolved organic matter (DOM) plays a crucial role in terrestrial and aquatic carbon and biogeochemical cycles; however, molecular transformations between aquatic and terrestrial systems remain poorly understood due to the complexity and heterogeneity of DOM. In this study, we investigated the molecular diversity of aquatic DOM and adjacent soil derived water extractable organic matter (WEOM) from seven locations on Akimiski Island, Nunavut using a combination of absorbance spectroscopy and Fourier transform ion cyclotron mass spectrometry (FT-ICR-MS). Assigned elemental formula and Van Krevelen compositional analysis reveal compositional similarities in river, inland ponds and coastal pool sites for aquatic DOM and WEOM. More aromatic, oxygenated polyphenolic carbon rich molecules were found in aquatic DOM whereas WEOM was abundant in highly unsaturated aliphatic material. A total of 276 phenolic, unsaturated aliphatic, and vascular plant-derived polyphenolic molecules were identified as being conserved between WEOM and aquatic DOM at one river and two inland pond locations suggesting similar CHO sources from adjacent soils. Moreover, contributions of polyphenolic compounds in aquatic DOM and WEOM were greater at inland ponds than coastal pools, congruent with a greater aromaticity at inland sites. Our results highlight the similarities and differences in WEOM to aquatic DOM composition and how they range across surrounding watersheds that provide insight into the biogeochemical dynamics across a Canadian subarctic terrestrial-aquatic-continuum.

Combined use of diffusive gradients in thin film, high-resolution dialysis technique and traditional methods to assess pollution and bioavailability of sediment metals of lake wetlands in Taihu Lake Basin

The geochemical behavior of trace metals at the sediment/water interface in Taihu Lake, the third-largest fresh water lake in China, has been widely explored. However, information on metals in lake wetlands of the basin is lacking. Here, diffusive gradients in thin film (DGT), high-resolution dialysis technique (HR-Peeper) and traditional methods were jointly used to study the occurrence characteristics, pollution degree, bioavailability, and mobility of sediment metals in the northern lake wetlands of Jiaxing City in Taihu Lake Basin. The contents of Cr, Ni, Cu, Zn, As, Cd and Pb were 101, 52.8, 62.3, 184, 10.3, 0.4, and 39.8 mg/kg, respectively. The metals in the sediments were in an overall low enrichment level. The main form of Cd was acid-soluble (F1), and the other metals mainly existed in residual (F4) or oxidable (F3) forms. The mean DGT-labile contents (C_DGT) of Cr, Ni, Cu, Zn, As, Cd and Pb were 1.3, 1.2, 9.3, 6.7, 13.4, 0.7, and 0.8 μg/L, respectively. C_DGT-Cu and C_DGT-As were significantly and positively related to the Cu and As contents in pore water (C_sol). C_DGT-Cr, C_DGT-Cd, C_DGT-Pb, and C_DGT-Cu were significantly and positively related to C_F1-Cr, C_F1-Cd, C_F1-Pb, and C_F3-Cu, respectively. The stability of Cd was the worst with a mean risk assessment code of 40%, indicating a high risk of remobilization in the sediment. The remobilization risks of other metals were low or moderate. The C_DGT/C_sol ratio of Cd was also the largest, with a mean of 0.99, suggesting that the Cd resupplying ability from sediment solid to pore water was strong.

In situ arsenic speciation and the release kinetics in coastal sediments: A case study in Daya Bay, South China Sea

In-situ study on arsenic speciation and the release kinetics in marine sediments was scarce. In this study, the distributions of labile As and their speciation in coastal sediments of Daya Bay were obtained by separate diffusive gradients in thin films (DGT) probes. Results showed that the DGT-labile As(V) was the main speciation in surface sediments (from -20 to 0 mm) with a concentration range of 0.07-3.05 μg·L^-1, while the labile As(III) was the main speciation in deep layers of sediments (from -100 to -20 mm). In coastal areas, mariculture farms was the most dominated contributor to As(V) contamination in surface sediments. Both the apparent diffusion flux estimation and the DGT induced flux in sediments (DIFS) simulation indicated that As(V) contamination in surface sediments of mariculture, harbor and petrochemical areas suffered the potential risk of As(V) release into the overlying water from sediments. DIFS modeling also found that the sediments of mariculture farms were the main sediment As pools. Linear regression analysis indicated that the mobility of As mainly attributed to the As(V) in sediments.

Oxidative stress intensity-related effects of cadmium (Cd) and paraquat (PQ) on UV-damaged-DNA binding and excision repair activities in zebrafish (Danio rerio) embryos

Our earlier studies showed the inhibitory effects of cadmium (Cd) and paraquat (PQ) on the gene expression of DNA mismatch recognition proteins in zebrafish (Danio rerio) embryos. This study explored the effects of Cd and PQ on nucleotide excision repair (NER) capacity in zebrafish embryos. Exposure of embryos at 1 h post fertilization (hpf) to 3-5 μM Cd or 30-100 μM PQ for 9 h induced a 2-3-fold increase of oxidative stress, while a 6.5-fold increase of oxidative stress was induced by 200 μM PQ. Real-time RT-PCR detected a down-regulated xeroderma pigmentosum C (XPC) and an up-regulated UV-DDB2 gene expression in mildly-stressed embryos, whereas 8-oxoguanine DNA glycosylase (OGG1) gene expression increased with PQ exposure levels. NER of UV-damaged DNA was enhanced in weakly oxidant-stressed embryos as shown by a transcription-based DNA repair assay, yet repair activities of both UV and cisplatin-damaged DNA were inhibited in embryos exposed to 200 μM PQ. Band shift assay showed a suppression of cyclobutane pyrimidine dimer (CPD) binding activity in all stressed embryos. In contrast, (6-4) photoproduct (6-4PP) recognition activity was weakly stimulated except in embryos exposed to 200 μM PQ, revealing a link of NER capacity to 6-4PP binding. Our results showed that Cd and PQ imposed similar inducing effects on UV-DDB2 gene expression, NER of UV-damaged DNA and 6-4PP binding activity in zebrafish embryo under low levels of oxidative stress and NER capacity could be inhibited if the intensity of oxidative stress increased to a critical level.

Evaluation of free/labile concentrations of trace metals in Athabasca oil sands region streams (Alberta, Canada) using diffusive gradient in thin films and a thermodynamic equilibrium model

The Athabasca's oil sands exploitation is controversial due to its potential risks to water quality but little is known about the temporal changes in the most bioavailable fraction of metal, the free/labile species. In this study, diffusive gradient in thin films (DGT) and the Windermere Humic Aqueous Model (WHAM VII) equilibrium model were used to examine the temporal changes in free/labile metal (Cu, Ni, Zn, Pb) species in three tributaries of the north-flowing Athabasca River in the Athabasca oil sands region (AOSR). The influence of dissolved organic matter (DOM) composition (i.e. fulvic: humic ratio) on modeled Cu and Ni speciation showed a negligible effect on the labile concentration. The best agreements (92 ± 8%) between DGT-labile and WHAM calculated labile concentrations were found assuming the formation of iron oxyhydroxides (FeO(OH)). The agreement was only 70 ± 7% in the presence of inorganic colloidal aluminum oxyhydroxides (AlO(OH)) and in the absence of any inorganic colloids. Together these results suggest that a change in DOM composition had limited impacts on modeled free metal ion concentrations. Although the concentration of the main metal ligand (i.e. DOM), varied from 9 to 40 ppm, no significant temporal differences in the abundance of WHAM-modeled labile species were found, suggesting mobility and bioavailability of Cu, Ni, Pb and Zn were comparable over the 2003-2012 period.