Dissolved Cd Concentrations Research Articles

Organic matter addition promotes Cd immobilization in alkaline paddy soils

Straw incorporation into the soil is a common agricultural practice, but its effect on soil cadmium (Cd) mobility is not well understood. We added 0–20 g kg−1 organic matters (OMs) with different C/N ratios to three spiked alkaline paddy soils that contained a realistically low concentration of total Cd (0.94 mg kg−1), and then investigated soil Cd solubility in alternate watering conditions. As current physical and chemical methods have difficulties in accurately determining the distribution and speciation of Cd in soil at a low concentration, we measured multiple soil properties to identify key factors regulating dissolved Cd concentration. For all three soils, pH and dissolved Cd concentration both decreased after flooding and increased after subsequent drying. OM addition significantly reduced soil Cd solubility at both flooding and drying stages. Random forest and linear regressions further confirmed that soil total organic carbon, rather than pH, dissolved organic carbon, or total inorganic carbon as previously suggested, was the primary predictor of Cd solubility. OMs with different C/N ratios had similar effects on soil Cd solubility, whereas the effect of OM addition rate depended on soil type. The results demonstrated the potential of straw incorporation for the remediation of Cd-contaminated alkaline paddy soils, through mechanisms that differ from those reported for acid soils.Graphical

Effects of blast furnace slag on the immobilization, plant uptake and translocation of Cd in a contaminated paddy soil

The potential toxicity of Cd to soil and rice plant severely threaten human health. This study was conducted to investigate the remediation effects of blast furnace slag (BFS) on the bioavailability of Cd in a contaminated paddy soil from a perspective of soil solution chemistry. Batch experiments, pot culture experiments, and principal analysis (PCA) were used to study the effects and mechanisms of BFS addition changing Cd chemical behavior and Cd toxicity. Results indicated that BFS facilitated Cd adsorption in soils, increased pH, Eh, and EC values in soil solution, whereas reduced dissolved Cd content. BFS amendment was efficient in decreasing root Cd intake and Cd upward transport in rice plant, with the Cd translocation factor in brown rice decreased by ∼ 75% (BFS treatment, 6‰ wt) relative to Cd treatment, which in turn increased rice biomass and grain yield. PCA indicated that the dissolved Cd concentration had a close relationship with soil pH and metal concentration in soil solution. Results from this study indicated that BFS had potential ability for either immobilization or remobilization of Cd in soils, and the findings have important implications for Cd-polluted soil remediation or other resource utilization with slag-based materials.

Cd transfers during marine sediment resuspension over short and long-term period: Associated risk for coastal water quality

Cadmium (Cd) is a highly toxic metal, regularly monitored uniformly for water quality across Europe, but scarcely for sediments. This study was designed to compare the kinetics of Cd remobilization and the amplitude of its transfers with different marine sediments. The results showed a highly reproducible transfer kinetics. Dissolved Cd was strongly and quickly removed from the dissolved phase (from 5 min up to 7 h). Then, the dissolved Cd concentration increased progressively to reach a maximal value after two weeks of mixing. The influence of the resuspension intensity representing light wind-induced resuspension up to dredging operations was observed after 2 weeks. The intensity of the sediment resuspension clearly impacted the amplitude of Cd remobilization, dissolved Cd ranging from a few ngL−1 to few hundreds of ngL−1, exceeding the maximal dissolved Cd concentration accepted by the European Union Water Framework Directive (WFD-2008/105 32/EC).

Factors controlling the temporal variability and spatial distribution of dissolved cadmium in the coastal Salish Sea

Cadmium (Cd) is a transition metal that can be toxic to aquatic biota even at low levels. The adverse effects of Cd are of particular concern in waterbodies along the eastern margin of the Pacific Ocean, where anthropogenic inputs are superimposed on the naturally elevated oceanic concentrations. While the accumulation of Cd in marine bivalves is well documented, few studies have investigated the cycling of dissolved Cd in estuarine and coastal waters that are susceptible to Cd enrichment. Here we examine the temporal and spatial variations of dissolved Cd in the coastal waters of Salish Sea in the northeast Pacific, with a focus on the Strait of Georgia (SoG). We find that the distribution of dissolved Cd in the Salish Sea is largely governed by conservative mixing between the upwelled Pacific water and freshwater discharge from the Fraser River, with a biological overprint transferring some of Cd from surface to deep water. Anthropogenic loadings of Cd from municipal effluent are negligible compared to natural inputs. Spatially, dissolved Cd and salinity gradually decrease as the Pacific source water flows landward from Juan de Fuca Strait into the SoG. Time-series sampling in the southern SoG reveals a small but significant decrease of dissolved Cd concentrations in the SoG deep layer over a winter stagnation period. We attribute this decline to diffusive removal, as driven by Cd sulfide precipitation in suboxic porewaters. The intermittent stagnation of the SoG deep layer provides a natural “benthic chamber” to estimate elemental exchange between deep water and sediment on a basin-scale, which could be valuable for studying the biogeochemical cycling of other trace metals.

Assessment of potential variability of cadmium and copper trace metals using hindcast estimates.

Trace metals are vital to primary productivity and play an essential role as main components in regulating oceanic biogeochemical cycles. Dissolved and particulate trace metals within the water column may vary due to primary production, temperature, and nutrient changes, factors that may also vary spatially and temporally. Furthermore, assessment of trace metals mainly relies on in situ observation, and so wide-area investigation of trace-metal concentration may be challenging and subject to technical constraints. A specific approach is therefore necessary that combines biogeochemical proxies, satellite data, and trace-metal linear correlation. This study aims to assess the potential spatio-temporal variability of sea surface cadmium (Cd) and copper (Cu) concentrations in Indonesian seas and surrounding areas. The correlations of Cd and Cu concentrations with primary production and nutrient data were used to convert hindcast satellite data into estimates of the metals' concentrations. The potential variability of trace metals can be determined by overlaying both data. Indonesia's Fisheries Management Areas (FMAs) were used for data clustering and analysis. The results show that Cd and Cu trace metals have similar distribution patterns throughout the year. However, dissolved Cu has a more diverse coverage area than dissolved Cd, including within the Halmahera, Seram, and Maluku Seas (FMAs 716 and 717), the Makassar Strait (FMA 717), and the Java-Sumatra upwelling area (FMA 573). Both Cd and Cu concentrations in the Java-Sumatra upwelling region follow the periodic upwelling pattern. Overall, both Cd and Cu show a declining trend in concentration from 2012 to 2019. It is estimated that dissolved Cd concentration declined from 1500-2000pmol/kg in 2012 to 1000-1500pmol/kg in 2019 for all locations. Dissolved Cu concentration decreased from 30-35nmol/kg in 2012 to 25-30nmol/kg in 2019. Estimated dissolved Cd and Cu follow the linear functions of silicate (SiO4), nitrate (NO3), and primary productivity. The fluctuation of anthropogenic activities and global warming are likely to indirectly impact the decline in metal concentrations by affecting nutrients and primary productivity.

High cadmium pollution from sediments in a eutrophic lake caused by dissolved organic matter complexation and reduction of manganese oxide

Eutrophication and metal pollution are global environmental problems. The risk of metal pollution is high in the eutrophic lakes because of high mobility of metal in sediments. However, the mechanism of cadmium (Cd) mobility in sediments is still unclear. Here we study the mobilization of Cd in sediments from the eutrophic Lake Taihu via monthly field monitoring of mobile Cd using diffusive gradient in thin films (DGT) and high resolution dialysis (HR-Peeper) techniques. We found a high mobility of Cd in sediments in February and March, resulting from reductive dissolution of Mn oxide mediation by high microbial activities, as shown by the similarities in distribution patterns of DGT-labile Cd and Mn. A two orders of magnitude increase in dissolved Cd concentrations (about 28 μg L−1) was observed in May and June, with dissolved Cd concentrations in overlying water about 110 times higher than the criteria continuous concentration set by Environmental Protection Agency. Hourly changes were found to coincide and correlate between dissolved Cd and dissolved organic matter (DOM) under simulated anaerobic conditions, strongly suggesting that the sudden outbreak of Cd pollution observed in the field resulted from the complexation of DOM with Cd in sediments. This was further supported by the NICA-Donnan model that more than 71% of dissolved Cd in the pore water in May and June was present as Cd-DOM complexes. Three components of DOM including humic-, tryptophan-, and tyrosine-like components in the sediments in June was identified using the fluorescence excitation emission matrix-parallel factor analysis. We found that Cd was stable complexed with tyrosine-like component. The Fourier transform infrared and two-dimensional correlation spectroscopy further revealed that Cd was bound to phenolic OH, alkene CC, alcoholic CO, aromatic CH, and alkene CH groups. Our study effectively promotes the understanding of Cd mobilization in sediments and highlights the risk of sudden Cd pollution events in the eutrophic lakes.

Effects of plant species and traits on metal treatment and phytoextraction in stormwater bioretention

To study effects of plant species selection on total and dissolved metal treatment performance of bioretention systems (BRS), 12 sets of columns were prepared, each planted with one of 12 species that are either widely used in BRS or have potentially important traits for metal removal (ability to hyperaccumulate metals, C4 photosynthesis, or ability to form mycorrhiza). Artificial stormwater was applied to half of the columns during all of a 31-week test period, while treatment of the others included a 5-week long dry period to test interactive effects of drying and plant traits on BRS metal treatment in more realistic alternating wet and dry conditions. Concentrations of metals (dissolved and total) in the effluent significantly differed between most columns with different plants, and the differences in concentrations of dissolved metals after the dry period were particularly important. Mean dissolved Cd concentrations exceeded Swedish reference values in effluents from BRS with two of the plant species, while mean dissolved Zn concentrations exceeded them in effluents from BRS with three of the species (and non-vegetated controls). Dissolved Cu leaching was observed in effluents from BRS with five of the plant species after the dry period, and mean concentrations exceeded Swedish reference values in effluents from all the BRS (including the constantly watered systems). Some support in terms of metal concentrations in shoots and shoot/soil ratios was obtained for using hyperaccumulators in BRS to remove metals from filter material. For example, Armeria maritima (a hyperaccumulator with the lowest shoot biomass) and Miscanthus sinsenis (a C4 plant with the highest biomass production) took up similar amounts of metals despite large differences in biomass. However, no significant correlations between effluent metal concentrations and plants’ metal uptake were found, possibly because of the short duration of the experiment. The results indicate that root biomass affected effluent metal concentrations more strongly. Root biomass was often positively correlated with total and (particularly) dissolved effluent metal concentrations. Further experiments with different soil metal concentrations, organic matter analyses and stronger focus on root characteristics are recommended, including additional tests of effects of hyperaccumulators and mycorrhiza on metal treatment and phytoextraction.

Liming effects on dissolved and colloid-associated transport of cadmium in soil under intermittent simulated rainfall

Liming has been regarded as an effective measure to reduce the bioavailability and mobility of cadmium (Cd) in soil. However, its effect on Cd transport in colloid-associated form remains unclear. In this study, relative importance of dissolved and colloid-associated transport of Cd was explored in columns packed with moist soil aggregates (diameter <2 mm) under intermittent simulated rainfall of distilled water or 5 mmol L−1 CaCl2 solution. The Cd2+/Ca2+ exchange selectivity coefficient determined in column experiments displayed gradual decreases with decreasing ionic strength. It is proposed that the exchange selectivity coefficient determined by repeated batch extraction can be used to predict Cd discharge in dissolved form in column effluent. Colloid-associated Cd was the main Cd form in the first flushing effluent sample upon resuming infiltration of distilled water. Otherwise, Cd was transported mainly in dissolved form, accounting for 81–93 % and 54–72 % of total Cd discharge for unlimed soils and limed soils, respectively. Liming remarkably reduced dissolved Cd concentration but only slightly enhanced colloidal Cd transport. Cd was enriched on colloids, and the enrichment factor was enhanced by liming. Colloidal Cd transport through preferential pathways (e.g., macropores, shrinkage cracks, tile drains) should be paid due attention.

Sulfur controlled cadmium dissolution in pore water of cadmium-contaminated soil as affected by DOC under waterlogging

Cadmium (Cd) precipitation and dissolution in pore water is associated with dissolved organic carbon (DOC)-induced reduction-oxidation of sulfur (S) under waterlogging and is vital for controlling the bioavailability in paddy soil. A 120-day soil incubation experiment, including application of sulfur (S, 30 mg kg−1) and wheat straw (W, 1.0%) alone or in combination (W + S) into Cd-contaminated paddy soil under waterlogging, was conducted to investigate the dynamic of dissolved Cd and its relationship with DOC, S2−, Fe2+, pH, Eh and pe + pH in soil pore water. The results showed that the lowest dissolved Cd concentration was observed in the W + S-treated soil pore water among all treatments when the soil Eh remained at lower values during the period of 15–60 days of incubation, which could be attributed to CdS precipitation and/or co-precipitation of Cd absorbed by FeS2 because of the reduction in sulfur. The application of S resulted in a Cd rebound in the pore water irrespective of W addition when the Eh began to increase from its lowest values during the period of 45–75 days of incubation, and SOB genera were observed in the S added soil. This could be attributed to re-dissolution of the precipitated Cd in soils under the SOB-driven oxidation of sulfide such as CdS and FeS2. In conclusion, DOC-driven reduction-oxidation of sulfur controls Cd dissolution in the pore water of Cd-contaminated paddy soil under waterlogging conditions. Further studies are required to investigate the interaction of sulfur and SOM-induced DOC on Cd bioavailability in rice-planted paddy soils.

Physical and biogeochemical controls on the distribution of dissolved cadmium and its isotopes in the Southwest Pacific Ocean

Cadmium stable isotope ratios (δ114Cd) have become a useful tool for oceanographers investigating the biogeochemical and physical processes that affect the nutrient-like distribution of the bioactive trace metal cadmium (Cd) throughout the oceans. Here, we present a meridional transect of dissolved Cd and δ114Cd from Japanese GEOTRACES section GP19 along 170°W from 64°S in the Southern Ocean to the equatorial Pacific. Along the GP19 section, the deep ocean (>1500 m) shows small variability in dissolved Cd (0.75–0.9 nmol kg−1) and a homogeneous δ114Cd signature (+0.26 ± 0.06‰, 2SD, n = 60; relative to NIST SRM-3108). Adding these data to previously published work allows us to calculate a deep Pacific and Southern Ocean (>1500 m) mean δ114Cd of +0.26 ± 0.10‰ (2SD, n = 436). Higher in the water column, depth profiles of Cd along the GP19 section exhibit a strong vertical gradient from a maximum (up to 0.9 nmol kg−1) at 1500–2000 m up to depleted surface waters (<0.001 nmol kg−1 in the equatorial Pacific). This gradient in dissolved Cd concentration is associated with changes in dissolved δ114Cd, with values higher (+0.4 to +0.6‰) than the deep ocean average at intermediate depths (300–1500 m), and then a further increase towards high δ114Cd values (up to +0.9‰) in the surface ocean. Both patterns could be explained by one-dimensional biological cycling including preferential uptake of isotopically light Cd by phytoplankton, and such processes likely explain the surface patterns. At intermediate depths, however, the observed strong vertical Cd concentration and isotopic gradients instead result from the lateral isopycnal transport of Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water (SAMW), both of which carry distinctly lower pre-formed Cd concentrations and higher δ114Cd values. These pre-formed signatures, which are imparted during water-mass formation in the Southern Ocean, are clearly conserved into the lower latitude Pacific as these water masses travel northward.Overall, the distribution of Cd and δ114Cd along the GP19 section is remarkably well explained by large scale mixing of water mass endmembers with defined δ114Cd signatures, emphasizing the importance of surface Southern Ocean processes for the distribution of trace metals such as Cd in the subsurface Southwest Pacific. At the regional scale, however, two other processes may overprint this mixing relationship. First, by comparison with the nearby Southeast Pacific GP16 section, we find that the δ114Cd signature of equatorial intermediate water masses shows little zonal variation across the equatorial Pacific, despite becoming enriched in dissolved Cd due to remineralization. We propose that this uniformity is explained by complete utilization of Cd in the surface tropical Pacific and remineralization of Cd with an isotopic signature similar to intermediate waters, therefore conserving the southern-sourced isotopic signature. Similarly, the observed increase of about 30% in deep ocean Cd concentrations from the South to the North Pacific is associated with a near-constant δ114Cd signal. These observations enable us to constrain the net δ114Cd of Cd added by remineralization to the deep ocean, with the caveat that such a signal is integrated over the entire Pacific, and that remineralization under different oceanic regimes such as HNLC areas may add Cd with different isotopic compositions to deep waters. Second, at GP19 stations close to the equator, subtle Cd depletion (relative to phosphate) is observed associated with low-oxygen subsurface waters, consistent with other studies from the North Pacific. Discerning the effects of such processes on Cd isotopic distributions is an important step to a more detailed understanding of the biogeochemical cycling of Cd in the modern ocean, and the application of δ114Cd as a tracer of past deep water circulation.This article is part of a special issue entitled: “Cycles of trace elements and isotopes in the ocean – GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.

Cadmium cycling in the water column of the Kuroshio-Oyashio Extension region: Insights from dissolved and particulate isotopic composition

We measured dissolved and particulate Cd isotopic composition in the water column of a meridional transect across the Kuroshio-Oyashio Extension region in a Japanese GEOTRACES cruise to investigate the relative influence of physical and biogeochemical processes on Cd cycling in the Northwestern Pacific Ocean. Located at 30–50°N along 165°E, the transect across the extension region possesses dramatic hydrographic contrast. Cold surface water and a relatively narrow and shallow thermocline characterizes the Oyashio Extension region in contrast to a relatively warm and highly stratified surface water and thermocline in the Kuroshio Extension region. The contrasting hydrographic distinction at the study site provides us with an ideal platform to investigate the spatial variations of Cd isotope fractionation systems in the ocean. Particulate samples demonstrated biologically preferential uptake of light Cd isotopes, and the fractionation effect varied dramatically in the surface water of the two regions, with relatively large fractionation factors in the Oyashio region. Based on the relationship of dissolved Cd concentrations and isotopic composition, we found that a closed system fractionation model can reasonably explain the relationship in the Kuroshio region. However, using dissolved Cd isotopic data, either a closed system or steady-state open system fractionation model may explain the relationship in the surface water of the Oyashio region. Particulate δ114/110Cd data further supports that the surface water of the Oyashio region matches a steady-state open system model more closely. Contrary to the surface water, the distribution of potential density exhibits comparable patterns with Cd elemental and isotopic composition in the thermocline and deep water in the two extension regions, showing that physical processes are the dominant forcing controlling Cd cycling in the deep waters. The results demonstrate that Cd isotope fractionation can match either a closed or open system Rayleigh fractionation model, depending on the relative contribution of physical and biogeochemical processes on its cycling.

Release of cadmium in contaminated paddy soil amended with NPK fertilizer and lime under water management

Agricultural soils contaminated with cadmium (Cd) pose a risk to receiving surface water via drainage or runoff. A 90-day laboratory incubation experiment was conducted to investigate the release characteristics and transformation of Cd from contaminated paddy soil amended with agrochemical (NPK fertilizer) and lime (L) under water management regimes of continuous flooding (F) and drying-wetting cycles (DW). The result showed that the dissolved Cd concentrations in overlying water of the fertilizer treatment under flooding (NPK+F) and drying-wetting (NPK+DW) reached up to 81.0 μg/L and 276 μg/L, and were much higher than that from the corresponding controls without NPK fertilizer addition at the end of experiment. The Cd concentration showed significantly negative correlation with overlying water pH, but positive correlation with soil redox potential and concentrations of dissolved total nitrogen, sulfate and manganese in overlying water (P < 0.05), indicating that drying-wetting cycles and N fertilizer addition may enhance soil Cd release. The Cd concentrations in overlying water from all treatments except NPK+L+F treatment exceeded the Cd threshold limit of Chinese Environmental Quality Standards for Surface Water (10 μg/L Grade V) and poses potential risk to surface water quality. Meanwhile, the proportion of Cd in the acid-soluble fraction from all incubated soil except NPK+L+F treatment increased compared to before incubation. The results indicated that continuous flooding was a reasonable water management candidate coupled with lime addition for immobilizing soil Cd.

Air-Filled Porosity as a Key to Reducing Dissolved Arsenic and Cadmium Concentrations in Paddy Soils.

Simultaneous suppression of rice ( L.) uptake of As and Cd is challenging because these toxic elements are immobilized under contrasting redox conditions. Given the notion that oxygen diffusion governs redox conditions in temporarily drained paddy soil, we assume that the key to simultaneous suppression of dissolved As and Cd concentrations is air-filled porosity (AFP) of soil. The objectives of this study were to reveal relationships between AFP and dissolved As and Cd concentrations in paddy soils and to identify the optimum water management, in terms of AFP, for simultaneous reduction of As and Cd. Dissolved As and Cd concentrations were determined in soil cores collected at different depths and times during rice growing seasons. Dissolved As concentrations were appreciable (>3 µg L) only when AFP was below a threshold value of 0.04 to 0.10 m m, suggesting that dissolved As was rapidly immobilized once AFP exceeded the threshold value on drainage. Dissolved Cd concentrations were roughly proportional to AFP, with higher concentrations associated with lower soil pH. Although dissolved As concentrations tended to be low in soil samples with high dissolved Cd concentrations and vice versa, both concentrations were low when AFP was slightly above the threshold value for As immobilization. The results suggest that dissolved As and Cd can be simultaneously kept at low levels by appropriate water management practices that produce AFP slightly above the threshold value for As immobilization.

Dissolved Trace and Minor Elements in Cryoconite Holes and Supraglacial Streams, Canada Glacier, Antarctica

Here we present a synthesis of the trace element chemistry in melt on the surface Canada Glacier, Taylor Valley, McMurdo Dry Valleys (MDV), Antarctica (~78°S). The MDV is largely ice-free. Low accumulation rates, strong winds, and proximity to the valley floor make these glaciers dusty in comparison to their inland counterparts. This study examines both supraglacial melt streams and cryoconite holes. Supraglacial streams on the lower Canada Glacier have median dissolved (<0.4 µm) concentrations of Fe, Mn, As, Cu, and V of 71.5, 75.5, 3.7, 4.6, and 4.3 nM. All dissolved Cd concentrations and the vast majority of Pb values are below our analytical detection (i.e. 0.4 and 0.06 nM). Chemical behavior did not follow similar trends for eastern and western draining waters. Heterogeneity likely reflects distinctions eolian deposition, rock:water ratios, and hydrologic connectivity. Future increases in wind-delivered sediment will likely drive dynamic responses in melt chemistry. For elements above detection limits, dissolved concentrations in glacier surface melt are within an order of magnitude of concentrations observed in proglacial streams (i.e. flowing on the valley floor). This suggests that glacier surfaces are an important source of downstream chemistry. The Fe enrichment of cryoconite water relative to N, P, or Si exceeds enrichment observed in marine phytoplankton. This suggests that the glacier surface is an important source of Fe to downstream ecosystems.

Leaching of cadmium and tellurium from cadmium telluride (CdTe) thin-film solar panels under simulated landfill conditions

A crushed non-encapsulated CdTe thin-film solar cell was subjected to two standardized batch leaching tests (i.e., Toxicity Characteristic Leaching Procedure (TCLP) and California Waste Extraction Test (WET)) and to a continuous-flow column test to assess cadmium (Cd) and tellurium (Te) dissolution under conditions simulating the acidic- and the methanogenic phases of municipal solid waste landfills. Low levels of Cd and Te were solubilized in both batch leaching tests (<8.2% and <3.6% of added Cd and Te, respectively). On the other hand, over the course of 30days, 73% of the Cd and 21% of the Te were released to the synthetic leachate of a continuous-flow column simulating the acidic landfill phase. The dissolved Cd concentration was 3.24-fold higher than the TCLP limit (1mgL−1), and 650-fold higher than the maximum contaminant level established by the US-EPA for this metal in drinking water (0.005mgL−1). In contrast, the release of Cd and Te to the effluent of the continuous-flow column simulating the methanogenic phase of a landfill was negligible. The remarkable difference in the leaching behavior of CdTe in the columns is related to different aqueous pH and redox conditions promoted by the microbial communities in the columns, and is in agreement with thermodynamic predictions.

Acartia tonsa eggs as a biomonitor to evaluate bioavailability/toxicity of persistent contaminants in anoxic/sulfidic conditions: The case of cadmium and nickel

The evaluation of toxicity due to persistent pollutants in anoxic aquatic environments has met with various problems, as most test organisms can not withstand oxygen lack and exposure to free sulfide. We evaluated the suitability of the eggs of the brackish copepod Acartia tonsa for bioassays in anoxic/sulfidic conditions: when exposed to deep hypoxia and free sulfide, the eggs become quiescent and are able to resume hatching after restoring normoxic conditions. Tests with cadmium and nickel were performed in normoxic and deeply hypoxic conditions and in anoxic water containing H2S or H2S+FeSO4 on an equimolar basis. Active and quiescent eggs showed equivalent sensitivity to the metals, both suffering significant reductions in hatching success at 89μM Cd and 17μM Ni. As expected on the basis of the SEM/AVS model, Cd toxicity was almost completely suppressed in presence of sulfides. Dissolved Cd concentration drastically dropped and hatching success was generally >80%, as against values <6% observed in sulfide-free water, indicating that the applied experimental procedure can simulate metal-sulfide interaction. Ni toxicity was only slightly reduced by the presence of sulfides. High dissolved Ni concentrations were detected and mean hatching percentages were ≤32%, suggesting that Ni bioavailability/toxicity was only partially controlled by excess reactive sulfides. The results suggest that A. tonsa eggs could be a useful biomonitor to evaluate toxicity due persistent contaminants in anoxic conditions and the role of sulfides in reducing metal bioavailability/toxicity.

Effects of algae growth on cadmium remobilization and ecological risk in sediments of Taihu Lake

Indoor simulation experiment with 2.76 L microcosms using sediment from Taihu Lake were conducted to investigate the relationship between algae bloom and heavy metals release into a lake aquatic environment. The results showed that Microcystic aeruginosa (M. aeruginosa) growth can enhance cadmium (Cd) mobilization from sediments to overlying water due to increasing pH and DO content of overlying water and changing the redox condition of surface sediment (0–2 cm) from weak oxidation to weak reduction. The dissolved Cd concentration in overlying water can be decreased during algal growth process. The remobilization of Cd from sediment can effectively reduce the ecological risk of total Cd in sediments. The results of this study showed that both Igeo and Eri can be used to effectively evaluate the ecological risk of heavy metal Cd in different fractions.

The cadmium–phosphate relationship in the western South Atlantic — The importance of mode and intermediate waters on the global systematics

The correlation between dissolved cadmium (Cd) and phosphate (PO4) in the modern ocean has been extensively studied. However, factors that cause the non-linearity in this global correlation are still largely debated and poorly constrained. In this study, we present vertical and meridional distributions of Cd concentrations along the GEOTRACES GA02 Leg 3 transect (53°S to 0°S) in the western South Atlantic. The vertical profiles of dissolved Cd show typical nutrient-like distributions, matching those of the macronutrient PO4. In the surface ocean, low Cd concentrations of 0.34–45pmolkg−1 are measured at all stations sampled. Below the fluorescence maxima, Cd concentrations increase with depth, reaching maxima at the depths of, or slightly below, the oxygen minimum. Similarly, surface waters have very low dissolved Cd/PO4 ratios, followed by a sudden decrease at depths corresponding to the fluorescence maxima, below which the Cd/PO4 ratios increase with depth.These variations in Cd and Cd/PO4 ratios are consistent with phytoplankton uptake in the surface ocean at higher Cd/PO4 ratios compared to deep water Redfield Cd/PO4 ratios, and remineralization of high Cd/PO4 organic particles as they sink to depth. In addition, a comparison of Cd and PO4 distributions in waters within the depth range of Subantarctic Mode Water (SAMW) in our study and those in the source regions suggests that SAMW plays an important role in the non-linearity of the Cd–PO4 correlation in the global ocean. On the other hand, intermediate waters at the equatorial stations display significantly lower Cd compared to the southern stations in this study. We attribute this to the influence of low-Cd waters originating in the oxygen-depleted zone (ODZ) of the Angola Basin that are brought in via the Benguela and Equatorial Currents. In the deep ocean (>1000m), the meridional distributions of dissolved Cd concentrations and Cd/PO4 ratios reflect mixing between North Atlantic Deep Water (NADW) (low nutrients, low Cd/PO4 ratios) and Antarctic Bottom Water (AABW) (high nutrients, high Cd/PO4 ratios), showing that dissolved Cd and PO4 can reliably trace deep ocean circulation in the modern ocean.

Evolution of cadmium tolerance and associated costs in a Gammarus fossarum population inhabiting a low-level contaminated stream.

Deciphering evolutionary processes occurring within long-term contaminated wild populations is essential for the ecological risk assessment of persistent chemical contaminations. Using field populations of Gammarus, a commonly-used genus in aquatic ecotoxicology, the present study sought to gain insights into the extent to which long-term exposure to metals in the field could effectively lead to shifts in toxicological sensitivities. For this, we identified a Gammarus population inhabiting a stream contaminated by cadmium (Cd). We compared the Cd-exposure and Cd-sensitivity of this population to those of five reference populations. Active biomonitoring determined in different years and seasons that significant levels of Cd were bioavailable in the contaminated site. Laboratory sensitivity tests under common garden conditions established that this long-term field exposure led to the development of a moderate Cd tolerance, which was maintained after a 3-week acclimatization in the laboratory, and transmitted to offspring produced under clean conditions. The potential physiological costs of tolerance were assessed by means of feeding rate measurements (in the laboratory and in situ). They revealed that, unlike for reference populations, the feeding activity of organisms from the tolerant population was greatly decreased when they were maintained under laboratory conditions, potentially indicating a high population vulnerability to environmental perturbations. Because dissolved Cd concentrations in water from the contaminated site were low (averaging 0.045 µg L(-1)) and below the current European environmental quality standard for Cd for inland surface waters (fixed at 0.08 µg L(-1) in soft water environments), this case study sheds light onto the extent to which current environmental quality standards are protective against potential adverse outcomes of adaptive and micro-evolutionary processes occurring in contaminated environments.

Biogeochemical cycling of cadmium isotopes along a high-resolution section through the North Atlantic Ocean

Cadmium (Cd) is a bioactive trace element in the oceans, with a nutrient-like distribution that closely matches dissolved phosphate. Seawater-dissolved stable Cd isotope ratios (δ114Cd) are a relatively new parameter, which show much promise for furthering our understanding of the biogeochemical cycling of Cd in the oceans. Here we present a high-resolution paired section of dissolved Cd concentrations and dissolved δ114Cd from 21 open-ocean stations along the US GEOTRACES GA03 transect through the North Atlantic Ocean. Dissolved Cd concentrations along the section are strongly influenced by water-mass distribution and the cycling of Cd. The highest dissolved Cd concentrations (400–540pmolkg−1) are associated with Antarctic-sourced water masses, whilst biological uptake in the surface ocean results in a strong vertical gradient in dissolved Cd towards the surface, reaching as low as 0.03pmolkg−1 in western surface waters. Dissolved δ114Cd is also characterized by a vertical gradient from ∼+0.2‰ in the deep ocean to +2‰ to +5‰ in the Cd-depleted surface ocean (relative to NIST SRM 3108). This variability in δ114Cd can be ascribed to mixing of Antarctic and North Atlantic water masses, together with fractionation due to in situ biological uptake of light Cd in the very surface ocean. Subtle deviations from this overall pattern of dissolved Cd concentration and dissolved δ114Cd are observed within low-oxygen waters off North Africa, where a dissolved Cd deficit relative to phosphate is associated with higher dissolved δ114Cd values. Together with elevated particulate Cd and Ba, this suggests that Cd sulfide precipitation is occurring within the water column of the North Atlantic, constituting a potentially important sink for isotopically light Cd. Additionally, the first measurements of dissolved δ114Cd within a hydrothermal plume at the Mid-Atlantic Ridge show that Cd is scavenged from the dissolved phase, leaving the remnant dissolved Cd isotopically heavier. Constraining the significance of these marine sinks for dissolved Cd is important, not only for our understanding of the marine biogeochemical cycling of Cd in the modern oceans, but also for the successful application of the microfossil Cd/Ca proxy and the development of δ114Cd as a tracer for past-ocean biogeochemical cycling.