Uptake Kinetics and Subcellular Compartmentalization Explain Lethal but Not Sublethal Effects of Cadmium in Two Closely Related Amphipod Species

Selenium nanoparticles: Enhanced nutrition and beyond

Selenium is a trace nutrient that has both nutritional and nutraceutical functions, whereas narrow nutritional range of selenium intake limits its use. Selenium nanoparticles (SeNPs) are less toxic and more bioavailable than traditional forms of selenium, suggesting that SeNPs have the potential to replace traditional selenium in food industries and/or biomedical fields. From the perspective of how SeNPs can be applied in health area, this review comprehensively discusses SeNPs in terms of its preparation, nutritional aspect, detoxification effect of heavy metals, nutraceutical functions and anti-pathogenic microorganism effects. By physical, chemical, or biological methods, inorganic selenium can be transformed into SeNPs which have increased stability and bioavailability as well as low toxicity. SeNPs are more effective than traditional selenium form in synthesizing selenoproteins like glutathione peroxidases. SeNPs can reshape the digestive system to facilitate digestion and absorption of nutrients. SeNPs have shown excellent potential to adjunctively treat cancer patients, enhance immune system, control diabetes, and prevent rheumatoid arthritis. Additionally, SeNPs have good microbial anti-pathogenic effects and can be used with other antimicrobial agents to fight against pathogenic bacteria, fungi, or viruses. Development of novel SeNPs with enhanced functions can greatly benefit the food-, nutraceutical-, and biomedical industries.

Cadmium accumulation and isotope fractionation in typical protozoa Tetrahymena: A new perspective on remediation of Cd pollution in wastewater

Cadmium (Cd) pollution threatens water safety and human health, which has raised serious public concern. Tetrahymena is a model protozoan, possessing the potential to remediate Cd contaminated water given the rapid expression of thiols. However, the mechanism of Cd accumulation in Tetrahymena has not been well understood, which hinders its application in environmental remediation. This study elucidated the pathway of Cd accumulation in Tetrahymena using Cd isotope fractionation. Our results showed that Tetrahymena preferentially absorb light Cd isotopes, with Δ^114/110Cd_{Tetrahymena-solution} = -0.20 ± 0.02‰ ∼ - 0.29 ± 0.02‰, which implies that the intracellular Cd is probably in the form of Cd-S. The fractionation generated by Cd complexation with thiols is constant (Δ^114/110Cd_{Tetrahymena-remaining solution} ∼ -0.28 ± 0.02‰), which is not affected by the concentrations of Cd in intracellular and culture medium, nor by the physiological changes in cells. Furthermore, the detoxification process of Tetrahymena results in an increase in cellular Cd accumulation from 11.7% to 23.3% with the elevated Cd concentrations in batch Cd stress culture experiments. This study highlights the promising application of Cd isotope fractionation in Tetrahymena for the remediation of heavy metal pollution in water.

Metal bioaccumulation in stygophilous amphipod Synurella ambulans in the hyporheic zone: The influence of environmental factors

Given the increasing need to protect vulnerable freshwater ecosystems and make them more resilient to human use and climate change, biomonitoring of the hyporheic zone (HZ), which plays a critical role in pollution attenuation, is essential. The aim of the present study was to assess the potential of the amphipod species Synurella ambulans as a bioindicator of metal contamination in the HZ of the Sava River (Croatia). Amphipods were collected during the four seasons at two sampling sites (average sampling depth 55 cm) differing in type (agricultural and urban) and intensity (diffuse and point source contamination) of anthropogenic influence, one located upstream (Medsave), and the other downstream (Jarun) of the wastewater treatment plant discharge. Concentrations of Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Rb, Sn, Zn, Ca, K, Mg and Na were measured in the interstitial water, sediments and specimens of S. ambulans by HR ICP-MS. Physicochemical parameters (temperature, DO, O₂ saturation, pH, conductivity, alkalinity, total water hardness, COD_KMnO4, nutrients) were measured in the interstitial water, while organic carbon was measured in the interstitial water and sediments. Metal concentrations in interstitial water and sediments were below thresholds set by environmental quality standards. Metal concentrations in S. ambulans were classified as follows: higher at the Jarun site (Al, Cr, Fe, Ni, Pb, Sn), higher at the Medsave site (Cd, Cu, Rb) and mostly comparable at both sites (Co, Mn, Zn). Bioaccumulation factors were generally higher at Jarun, with average values ranging from 322 to 143,278 L kg^-1. Bioaccumulation of metals in S. ambulans depended on various environmental factors, with metal exposure level and dissolved macro elements showing the strongest association with metals accumulated in S. ambulans. The findings provided the first evidence on the suitability of S. ambulans as a good bioindicator of chronic metal contamination in the HZ.

Organ-specific accumulation of cadmium and zinc in Gammarus fossarum exposed to environmentally relevant metal concentrations

One of the best approaches for improving the assessment of metal toxicity in aquatic organisms is to study their organotropism (i.e., the distribution of metals among organs) through a dynamical approach (i.e., via kinetic experiments of metal bioaccumulation), to identify the tissues/organs that play a key role in metal regulation (e.g., storage or excretion). This study aims at comparing the organ-specific metal accumulation of a non-essential (Cd) and an essential metal (Zn), at their environmentally relevant exposure concentrations, in the gammarid Gammarus fossarum. Gammarids were exposed for 7 days to ¹⁰⁹Cd- or ⁶⁵Zn-radiolabeled water at a concentration of 52.1 and 416 ng.L^-1 (stable equivalent), respectively, and then placed in clean water for 21 days. At different time intervals, the target organs (i.e., caeca, cephalons, intestines, gills, and remaining tissues) were collected and ¹⁰⁹Cd or ⁶⁵Zn contents were quantified by gamma-spectrometry. A one-compartment toxicokinetic (TK) model was fitted by Bayesian inference to each organ/metal dataset in order to establish TK parameters. Our results indicate: i) a contrasting distribution pattern of concentrations at the end of the accumulation phase (7^th day): gills > caeca ≈ intestines > cephalons > remaining tissues for Cd and intestines > caeca > gills > cephalons > remaining tissues for Zn; ii) a slower elimination of Cd than of Zn by all organs, especially in the gills in which the Cd concentration remained constant during the 21-day depuration phase, whereas Zn concentrations decreased sharply in all organs after 24 h in the depuration phase; iii) a major role of intestines in the uptake of waterborne Cd and Zn at environmentally relevant concentrations.

Differences in the subcellular distribution of cadmium and copper in the gills and liver of white sturgeon (Acipenser transmontanus) and rainbow trout (Oncorhynchus mykiss)

Recent studies have shown that white sturgeon (Acipenser transmontanus) are more resistant to cadmium (Cd) compared to rainbow trout (Oncorhynchus mykiss), whereas they are more sensitive than rainbow trout when exposed to copper (Cu). Differences in the subcellular distribution of metals among species could be one of the factors responsible for the differences in the sensitivity to metals. Although, subcellular distribution has been studied extensively in many species with many metals, its direct role in species-specific differences in the sensitivity has not been well studied. The objective of this study was to evaluate the role of subcellular distribution of metals in species-specific differences in the sensitivity to metals between sturgeon and trout. We compared the subcellular distribution of metals Cd and Cu in the cellular debris, heat-stable proteins, heat-denatured fraction, metal-rich granules, and organelles fractions from the gills and liver after exposure of juveniles of both species to 1.25 and 20 μg/L Cd and Cu for 8 days, respectively. Sturgeon diverted a higher amount of Cd towards biologically inactive metal pool (BIM) and a lower amount towards the biologically active metal pool (BAM) compared to trout in both tissues. This explained why sturgeon are able to tolerate a relatively higher exposure level to Cd compared to trout. For Cu, there was no statistically significant species-specific differences in the amounts diverted towards either BAM or BIM; hence, white sturgeon's greater sensitivity to Cu was not explained by its subcellular distribution strategies.

Intergenerational effects of resuspended sediment and trace metal mixtures on life cycle traits of a pelagic copepod

Multiple stressors like metal toxicity, organic compounds and sediment pollution from the Seine estuary are raising concern and novel toxicological approaches are needed to better assess and monitor the risk. In the present study, the copepod Eurytemora affinis from the Seine, was exposed to two different sources of contaminants, which were resuspended polluted sediments and a mixture of trace metals (dissolved phase). The exposure continued for four generations (F0, F1, F2, F3) where F0 is a generation for acclimation to the exposure condition and F3 is a generation for decontamination followed without any exposure, to detect possible maternal carryover effects of pollutants (F0 - F2) and the role of recovery (in F3). Higher accumulation of metals resulted in higher mortalities at both exposure conditions, with particularly F1 being the most sensitive generation showing highest bioaccumulation of metals, highest mortality, and smallest population size. Copper accumulation was highest of all metals in mixture from both the resuspended sediment and the combined trace metal treatment. A significantly lower naupliar production was seen in copepods exposed to resuspended sediment compared to trace metal exposed copepods. However, the decontamination phase (F3) indicated that E. affinis pre-exposed to resuspended sediment had a higher ability to recover the total population size, increase naupliar production, and depurate accumulated Cu. The population exposed to a trace metal mixture showed lower recovery and lower ability to discharge accumulated toxic metals indicating its greater effect on our experimental model when compared to resuspended sediment.

Changes of cellular stress response related hsp70 and abcb1 transcript and Hsp70 protein levels in Siberian freshwater amphipods upon exposure to cadmium chloride in the lethal concentration range

The induction of cellular stress response systems, heat shock protein hsp70/Hsp70 and multixenobiotic transporter abcb1, by cadmium chloride (CdCl₂) was explored in amphipod species with different stress adaptation strategies from the Lake Baikal area. Based on the lethal concentrations (LC) of CdCl₂, the sensitivities of the different species to CdCl₂ were ranked (24 hr LC50 in mg/L CdCl₂ (mean/95% confidence interval)): Gammarus lacustris (1.7/1.3–2.4) < Eulimnogammarus cyaneus (2.9/2.1–4.0) < Eulimnogammarus verrucosus (5.7/3.8–8.7) < Eulimnogammarus vittatus (18.1/12.4–26.6). Conjugated dienes, indicating lipid peroxidation, were significantly increased after 24 hr exposures to 5 mg/L CdCl₂ only in the more CdCl₂-sensitive species G. lacustris and E. cyaneus. Upon treatment with 0.54 to 5.8 mg/L CdCl₂ for 1, 6 and 24 hrs, hsp70 transcript levels were generally more increased after the longer exposure times and in the more CdCl₂-sensitive species. Relating the CdCl₂ exposure concentrations to LCx values revealed that across the species the increases of hsp70 transcript levels were comparatively low (up to 2.6-fold) at CdCl₂ concentrations ≤LC50. Relative hsp70 transcript levels were maximally increased in E. cyaneus by 5 mg/L CdCl₂ (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\hat {=}$\end{document}= ˆLC70) at 24 hrs (9.1-fold increase above the respective control). When G. lacustris was exposed to 5 mg/L CdCl₂ (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\hat {=}$\end{document}= ˆLC90) for 24 hrs, the increase in hsp70 was in comparison to E. cyaneus considerably less pronounced (3.0-fold increase in hsp70 levels relative to control). Upon exposure of amphipods to 5 mg/L CdCl₂, increases in Hsp70 protein levels compared to untreated controls were highest in E. cyaneus at 1 and 6 hrs (5 mg/L CdCl₂\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\hat {=}$\end{document}= ˆ LC70) and in E. verrucosus at 24 hrs (5 mg/L CdCl₂\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\hat {=}$\end{document}= ˆ LC45). Thus, when the fold increases in Hsp70 protein levels in the different amphipod species were related to the respective species-specific LCx values a similar bell-shaped trend as for hsp70 transcript levels was seen across the species. Transcript levels of abcb1 in CdCl₂exposed individuals of the different amphipod species varied up to 4.7-fold in relation to the respective controls. In contrast to hsp70/Hsp70, abcb1 transcripts in CdCl₂ exposed individuals of the different amphipod species did not indicate similar levels of induction of abcb1 at equal LCx levels across the species. Induction of hsp70 and abcb1 genes and Hsp70 proteins by CdCl₂ in the lethal concentration range shows that these cellular responses are rather insensitive to CdCl₂ stress in the examined amphipod species. Furthermore, the increase of expression of these cellular defense systems at such high stress levels suggests that induction of these genes is not related to the maintenance of normal metabolism but to mitigation of the effects of severe toxic stress.

Alleviative Effects of C60 on the Trophic Transfer of Cadmium along the Food Chain in Aquatic Environment

C₆₀ could enhance the accumulation of pollutants in organisms, but their effects on higher trophic levels remain unknown. In the present study, the transfer of C₆₀ from Daphnia magna to zebrafish (Danio rerio) and its effects on Cd transfer were investigated. The results showed that C₆₀ could be transferred from D. magna to zebrafish through dietary exposure and accumulate mainly in the intestines, but biomagnification was not observed. The presence of C₆₀ promoted accumulation of Cd in D. magna. However, it decreased Cd burden in the higher trophic level (zebrafish), displaying an alleviative effect on the trophic transfer of Cd along the food chain. To explore the underlying mechanisms, the release of Cd from D. magna in digestive fluids and changes in zebrafish digestive physiology were further investigated. The results showed that C₆₀ did not inhibit Cd release from D. magna, but stimulated the digestive tracts of zebrafish to excrete Cd earlier and in a greater amount, which consequently lowered assimilation efficiency of Cd in zebrafish. Overall, the present study showed the trophic transfer of C₆₀ in the aquatic food chain and revealed the effects of C₆₀ on trophic transfer of Cd along the food chain in aquatic environment.

Population response of the estuarine copepod Eurytemora affinis to its bioaccumulation of trace metals

We evaluated the acute toxicities of metals cadmium (Cd), copper (Cu) and nickel (Ni) to a widely-distributed copepod Eurytemora affinis isolated from the Seine estuary. Both sexes of adult E. affinis were exposed separately to the three metals at concentration gradients to determine its 50% lethal concentration (LC50). After 4 days of exposure, both males and females showed a higher sensitivity to Cu (male LC50: 25.0 μg.L^-1 and female LC50: 38.0 μg.L^-1) than to Ni (male LC50: 90.0 μg.L^-1 and female 161.0 μg.L^-1) and Cd (male LC50: 127.8 μg.L^-1 and female LC50: 90.0 μg.L^-1). To assess for the first time, the extend of metal bioaccumulation and its effect at population scale, late stages (>200 μm) were collected and exposed to each metal at the concentration of 1/3 LC50, and to their mixture during 144 h without feeding. The Cd concentration consistently increased with time until the end of the experiment, whereas the Ni and Cu concentrations reached a plateau after 24 h and 72 h exposure, respectively. The results revealed that the copepods could accumulate Cu faster than Ni and Cd either in the treatment alone (0.58 L g^-1.d^-1) or in the three-metal mixture (0.72 L g^-1.d^-1) after 50% of exposure time (72 h). The number of individuals decreased in copepod populations except for the Cd treatment, where the number of nauplii increased. In addition, all treatments of metal exposure negatively affected bacterial densities in the copepod cultures, where the Cu treatment showed a negative remarkable effect compared with Cd and Ni treatment did.

Selenium Stimulates Cadmium Detoxification in Caenorhabditis elegans through Thiols-Mediated Nanoparticles Formation and Secretion

Antagonism between heavy metal and selenium (Se) could significantly affect their biotoxicity, but little is known about the mechanisms underlying such microbial-mediated antagonistic processes as well as the formed products. In this work, we examined the cadmium (Cd)-Se interactions and their fates in Caenorhabditis elegans through in vivo and in vitro analysis and elucidated the machinery of Se-stimulated Cd detoxification. Although the Se introduction induced up to 3-fold higher bioaccumulation of Cd in C. elegans than the Cd-only group, the nematode viability remained at a similar level to the Cd-only group. The relatively lower level of reactive oxygen species in the Se & Cd group confirms a significantly enhanced Cd detoxification by Se. The Cd-Se interaction, mediated by multiple thiols, including glutathione and phytochelatin, resulted in the formation of less toxic cadmium selenide (CdSe)/cadmium sulfide (CdS) nanoparticles. The CdSe/CdS nanoparticles were mainly distributed in the pharynx and intestine of the nematodes, and continuously excreted from the body, which also benefitted the C. elegans survival. Our findings shed new light on the microbial-mediated Cd-Se interactions and may facilitate an improved understanding and control of Cd biotoxicity in complicated coexposure environments.