Interactive effects of temperature and salinity on toxicity of zinc oxide nanoparticles towards the marine mussel Xenostrobus securis.

Growing application of zinc oxide nanoparticles (ZnO-NPs) in global market has led to the concern over their potential environmental impacts. Filter feeders like mussels are prone to nanoparticles due to their superior filter-feeding ability. Temperature and salinity of coastal and estuarine seawaters often vary seasonally and spatially, and their changes may jointly influence physicochemical properties of ZnO-NPs and thus their toxicity. This study, therefore, aimed to investigate the interactive effect of temperatures (15, 25 and 30 °C) and salinities (12 and 32 PSU) on physicochemical properties and sublethal toxicity of ZnO-NPs towards a marine mussel Xenostrobus securis, and to compare that with the toxicity caused by Zn2+ ions (zinc sulphate heptahydrate). The results revealed increased particle agglomeration but decreased zinc ion release of ZnO-NPs at the highest temperature and salinity condition (30 °C and 32 PSU). After exposure, ZnO-NPs significantly reduced survival, byssal attachment rate and filtration rate of the mussels at high temperature and salinity (30 °C and 32 PSU). Glutathione S-transferase and superoxide dismutase activities in the mussels were suppressed at 30 °C. These aligned with the augmented zinc accumulation with increasing temperature and salinity which could likely be attributable to increased particle agglomeration of ZnO-NP and enhanced intrinsic filtration rate of the mussels under these conditions. Together with the observed lower toxic potency of Zn2+ compared to ZnO-NPs, our results suggested that the mussels might accumulate more zinc through particle filtration under higher temperature and salinity, eventually resulting in elevated toxicity of ZnO-NPs. Overall, this study demonstrated the necessity to consider the interactive effect of environmental factors such as temperature and salinity during the toxicity assessment of nanoparticles.

Deciphering the mechanisms of zinc tolerance in the cyanobacterium Anabaena sphaerica and its zinc bioremediation potential.

Cyanobacteria adopt a variety of changes at proteomic and metabolic levels for surviving under harmful environmental conditions including heavy metal stress. The current study investigates the impact of zinc stress on the proteome of Anabaena sphaerica to get an insight into its molecular mechanisms of zinc tolerance. The study revealed three different aspects that were associated with the zinc tolerance in A. sphaerica: (i) the reduced expression of photosynthesis, nitrogen fixation, energy metabolism, respiratory, and transcriptional/translational proteins probably to conserve energy and utilizing it to sustain growth; (ii) the enhanced expression of metallothionein and ferritin domain protein All 3940 to chelate free zinc ions whereas upregulation of antioxidative proteins for detoxifying reactive oxygen species; and (iii) the expression of large numbers of hypothetical proteins to maintain the important cellular functions. Furthermore, over expressions of sulfate adenylyl transferase and cystathionine beta synthase along with the increased synthesis of peptidases and thiolated antioxidant proteins were also noticed which denoted cysteine synthesis under sulfur deprivation possibly by mobilizing the sulfur from dead cells and its channelization towards the production of thiolated antioxidants. Besides tolerating excess amount of zinc, A. sphaerica exhibited high zinc biosorption efficiency which confirmed its outstanding zinc bioremediation potential.

The roles of calcium and salinity in protecting against physiological symptoms of waterborne zinc toxicity in the euryhaline killifish (Fundulus heteroclitus).

In fresh water, environmental Ca ameliorates Zn toxicity because Ca2+ and Zn2+ compete for uptake at the gills. Zn toxicity is also lower in sea water, but it is unclear whether this is due to increased Ca2+ concentration, and/or to the other ions present at higher salinity. Using the euryhaline killifish, we evaluated the relative roles of Ca2+ (as CaNO3) versus the other ions contributing to salinity in protecting against physiological symptoms of Zn2+ toxicity. Killifish were exposed to a sublethal level of Zn (500 µg/L, as ZnSO4) for 96 h in either fresh water (0 % salinity) at low (1 mmol/L) and High Ca (10 mmol/L) or 35 ppt sea water (100 % salinity) at low (1 mmol/L) and High Ca (10 mmol/L). At 0 % salinity, High Ca partly or completely protected against the following effects of Zn seen at Low Ca: elevated plasma Zn, hypocalcaemia, inhibited unidirectional Ca2+ influx, inhibited branchial Na+/K+ATPase and Ca2+ATPase activities, and oxidative stress in gills, liver, intestine, and muscle. At 100 % salinity, in the presence of 1 mmol/L (Low Ca), Zn caused no disturbances in most of these same parameters, showing that the "non-Ca" components of sea water alone provided complete protection. However, for a few endpoints (inhibited intestinal Ca2+ATPase activity, oxidative stress in gill and liver), High Ca (10 mmol/L) was needed to provide full protection against Zn in 100 % salinity. There was no instance where the combination of 100 % salinity and High Ca failed to provide complete protection against Zn-induced disturbances in sea water.

Cellular Responses Induced by Zinc in Zebra Mussel Haemocytes. Loss of DNA Integrity as a Cellular Mechanism to Evaluate the Suitability of Nanocellulose-Based Materials in Nanoremediation.

Zinc environmental levels are increasing due to human activities, posing a threat to ecosystems and human health. Therefore, new tools able to remediate Zn contamination in freshwater are highly recommended. Specimens of Dreissena polymorpha (zebra mussel) were exposed for 48 h and 7 days to a wide range of ZnCl2 nominal concentrations (1-10-50-100 mg/L), including those environmentally relevant. Cellulose-based nanosponges (CNS) were also tested to assess their safety and suitability for Zn removal from freshwater. Zebra mussels were exposed to 50 mg/L ZnCl2 alone or incubated with 1.25 g/L of CNS (2 h) and then removed by filtration. The effect of Zn decontamination induced by CNS has been verified by the acute toxicity bioassay Microtox®. DNA primary damage was investigated by the Comet assay; micronuclei frequency and nuclear morphological alterations were assessed by Cytome assay in mussels' haemocytes. The results confirmed the genotoxic effect of ZnCl2 in zebra mussel haemocytes at 48 h and 7-day exposure time. Zinc concentrations were measured in CNS, suggesting that cellulose-based nanosponges were able to remove Zn(II) by reducing its levels in exposure waters and soft tissues of D. polymorpha in agreement with the observed restoration of genetic damage exerted by zinc exposure alone.

Efficient removal of zinc by multi-stress-tolerant yeast Pichia kudriavzevii A16.

Heavy metal bioaccumulation by growing microorganisms is a potential technique for treating the heavy metal pollution in food materials, e.g. fishery processing wastes. In this study, a multi-stress-tolerant yeast with high Zn tolerance and efficient Zn removal ability was screened and renamed as Pichia kudriavzevii A16 after identification. High salinity and low pH obviously increased the Zn bioaccumulation capacity of P. kudriavzevii A16, contributing to the increasing Zn removal rate of P. kudriavzevii A16 at 0.5 mmol/L Zn from 67.69% to 77.03% and 96.09%, respectively. P. kudriavzevii A16 displayed high specificity of Zn removal at high concentrations of Cu, while high concentrations of Cd significantly inhibited the Zn removal by restraining the yeast growth. P. kudriavzevii A16 possessed more powerful Zn removal ability than Saccharomyces cerevisiae CICC1211 under various environmental stresses. The multi-stress-tolerant P. kudriavzevii A16 can be developed into a potential Zn removal agent using in complex food environments.

Medicago sativa--Sinorhizobium meliloti Symbiosis Promotes the Bioaccumulation of Zinc in Nodulated Roots.

In this study we investigated effects of Zn supply on germination, growth, inorganic solutes (Zn, Ca, Fe, and Mg) partitioning and nodulation of Medicago sativa This plant was cultivated with and without Zn (2 mM). Treatments were plants without (control) and with Zn tolerant strain (S532), Zn intolerant strain (S112) and 2 mM urea nitrogen fertilisation. Results showed that M. sativa germinates at rates of 50% at 2 mM Zn. For plants given nitrogen fertilisation, Zn increased plant biomass production. When grown with symbionts, Zn supply had no effect on nodulation. Moreover, plants with S112 showed a decrease of shoot and roots biomasses. However, in symbiosis with S532, an increase of roots biomass was observed. Plants in symbiosis with S. meliloti accumulated more Zn in their roots than nitrogen fertilised plants. Zn supply results in an increase of Ca concentration in roots of fertilised nitrogen plants. However, under Zn supply, Fe concentration decreased in roots and increased in nodules of plants with S112. Zn supply showed contrasting effects on Mg concentrations for plants with nitrogen fertilisation (increase) and plants with S112 (decrease). The capacity of M. sativa to accumulate Zn in their nodulated roots encouraged its use in phytostabilisation processes.