Influence of temperature and salinity on heavy metal uptake by submersed plants

Trophic Transfer of Cd, Cu, Pb, Zn, P and Se in Dutch Storage Water Reservoirs

Heavy metals are naturally omnipresent in aquatic systems. Excess amounts of heavy metals can accumulate in organisms of pollution impacted systems and transfer across a food web. Analysing the food web structure and metal contents of the organisms can help unravel the pathways of biomagnification or biodilution and gain insight in trophic linkages. We measured heavy metals and other elements in mussel bank detritus and organisms of the Biesbosch reservoirs (the Netherlands) and linked those to stable isotopic signatures. The heavy metal contents (cadmium, copper, lead, and zinc) were often lowest in benthivorous, omnivorous and piscivorous species (mainly fish); whereas, phosphorus contents were lower in the autotrophs. Mussel bank detritus contained the highest amounts of heavy metals. The heavy metals were negatively correlated with δ15N values. For selenium no clear trend was observed. Furthermore, there was a negative correlation between fish length and some heavy metals. Based on all 20 analysed elemental contents, similarities between species became apparent, related to niche or habitat. This study confirms that elemental contents of species can differ between feeding guilds and/or species, which can be attributed to metabolic and physiological processes. The organisms in higher trophic levels have adaptations preventing metal accumulation, resulting in lower contents. Within the fish species biodilution occurs, as most metal contents were lowest in bigger fish. Overall, the metals did not seem to biomagnify, but biodilute in the food web. Metal analyses combined with isotopic signatures could thus provide insights in metal transfer and possible trophic linkages within a system.

Emergent properties of free-living nematode assemblages exposed to multiple stresses

Biological communities are currently facing multi-stressor scenarios whose ecological impacts are challenging to estimate. In that respect, considering the complex nature of ecosystems and types and interaction among stressors is mandatory. Microcosm approaches using free-living nematode assemblages can effectively be used to assess complexity since they preserve the interactions inherent to complex systems when testing for multiple stress effects. In this study, we investigated the interaction effects of three stress factors, namely i-metallic mixture of Cu, Pb, Zn, and Hg (control [L0], low, [L1] and high [L2]), ii- CO2-driven acidification (pH 7.6 and 8.0), and iii- temperature rise (26 and 28 °C), on estuarine free-living nematode assemblages. Metal contamination had the greatest influence on free-living nematode assemblages, irrespective of pH and temperature scenarios. Interestingly, whilst the most abundant free-living nematode genera showed significant decreases in their densities when exposed to contamination, other, less abundant, genera were apparently favored and showed significantly higher densities in contaminated treatments. The augmented densities of tolerant genera may be attributed to indirect effects resulting from the impacts of toxicity on other components of the system, indicating the potential for emergent effects in response to stress. Temperature and pH interacted significantly with contamination. Whilst temperature rise had potentialized contamination effects, acidification showed the opposite trend, acting as a buffer to the effects of contamination. Such results show that temperature rise and CO2-driven acidification interact with contamination on coastal waters, highlighting the importance of considering the intricate interplay of these co-occurring stressors when assessing the ecological impacts on coastal ecosystems.

Industrial wastewater treatment using floating wetlands: a review

Industrial wastewater generated from various production processes is often associated with elevated pollutant concentrations and environmental hazards, necessitating efficient treatment. Floating wetlands (FWs) have emerged as a promising and eco-friendly solution for industrial wastewater treatment, with numerous successful field applications. This article comprehensively reviews the removal mechanisms and treatment performance in the use of FWs for the treatment of diverse industrial wastewaters. Our findings highlight that the performance of FWs relies on proper plant selection, design, aeration, season and temperature, plants harvesting and disposal, and maintenance. Well-designed FWs demonstrate remarkable effectiveness in removing organic matter (COD and BOD), suspended solids, nutrients, and heavy metals from industrial wastewater. This effectiveness is attributed to the intricate physical and metabolic interactions between plants and microbial communities within FWs. A significant portion of the reported applications of FWs revolve around the treatment of textile and oily wastewater. In particular, the application reports of FWs are mainly concentrated in temperate developing countries, where FWs can serve as a feasible and cost-effective industrial wastewater treatment technology, replacing high-cost traditional technologies. Furthermore, our analysis reveals that the treatment efficiency of FWs can be significantly enhanced through strategies like bacterial inoculation, aeration, and co-plantation of specific plant species. These techniques offer promising directions for further research. To advance the field, we recommend future research efforts focus on developing novel floating materials, optimizing the selection and combination of plants and microorganisms, exploring flexible disposal methods for harvested biomass, and designing multi-functional FW systems.

Effect of redox potential on the heavy metals binding phases in estuarine sediment: Case study of the Musa Estuary

Heavy metals (HMs) exist in various chemical forms in marine sediments, and environmental factors like the redox potential (Eh) can affect labile-bound HMs, harming aquatic life and human health. This study utilized the Tessier sequential extraction to investigate how Eh affects the binding forms of elements, including Cd, Co, Cu, Ni, Pb, Zn, Fe, and Mn. The results revealed that decreasing Eh from 120 to 50 mV resulted in the release of weakly bound forms of Cd, Co, Ni, Pb, and Zn into the water, some of which were re-adsorbed by the residual fraction as Eh decreased further to -150 mV. Manganese was consistently bound to FeMn oxides, while Cu and Fe were predominantly associated with the more stable binding phase. Based on EF, Igeo, and CF, sediment was only polluted by As nearby an industrial zone, while water pollution indices indicated significant HMs contamination in all water samples.

Metals in Callitriche cophocarpa from small rivers with various levels of pollution in SW Poland

The anthropogenic impact of metals on aquatic environments is a risk for biota, and thus their levels must be controlled. Callitriche cophocarpa Sendtn. belongs to a genus with a potential for accumulation of elevated metal levels. Thus, it may provide consolidated evidence of contamination. Therefore, the aim of this investigation was to determine Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn in this species collected together with water and bottom sediments from rivers with various levels of pollution. Of these rivers, one less polluted and one more polluted was selected for the collection of C. cophocarpa for an experiment to compare its Cu and Zn concentration potential. Both metals were supplemented at concentrations 0.01, 0.02, 0.03, 0.05, 0.08 and 0.14 mg L-1 of Cu as CuSO4 × 5H2O and 0.4, 0.6, 0,9, 1,35, 2.03 and 3.04 mg L-1 of Zn as ZnSO4 × 7H2O, and in the binary design containing (mg·L-1) 0.01Cu + 0.4Zn, 0.02Cu + 0.6Zn, 0.03Cu + 0.9Zn, 0.05Cu + 1.4Zn, 0.08Cu + 2.03 Zn and 0.14Cu + 3.04Zn. The upper concentrations of Cr, Cu, Mn and Zn in C. cophocarpa shoots from both types of rivers as well as of Ni and Pb in shoots from more polluted rivers were higher than the values typical for toxicity thresholds with no visible harmful effects, which may indicate accumulation abilities of C. cophocarpa for these metals. Both roots and shoots of C. cophocarpa may be included in the group of macroconcentrators for bottom sediments with respect to Cd, Co, Cr, Cu, Fe, Mn, Ni and Zn and deconcentrators of Pb. Greater accumulation of most metals in roots than in shoots indicates their restricted mobility and translocation by C. cophocarpa to shoots. C. cophocarpa from the less polluted river and exposed to all experimental solutions contained significantly higher levels of Cu and Zn than that from the more polluted river exposed to identical experimental solutions. The plants collected from the more polluted river influenced by surplus of metals and living under chemical stress could probably limit further accumulation by developing a resistance mechanism. Cu and Zn contents in C. cophocarpa were higher when treated with separate metals than for binary treatment both in the more and less polluted river. Such research presenting the impact of a combination of metals could be important for understanding and explaining the interactions of these elements which may influence their bioavailability in nature as well as importance in the evaluation of the risk of environmental toxicity.

Salinity and temperature influence removal levels of heavy metals and chloride from water by wetland plants

Stormwater with low temperatures and elevated salinity, common in areas where deicing salt is used, might affect the removal of heavy metals by plants in stormwater treatment systems such as floating treatment wetlands. This short-term study evaluated the effects of combinations of temperature (5, 15, and 25 °C) and salinity (0, 100, and 1000 mg NaCl L^-1) on the removal of Cd, Cu, Pb, and Zn (1.2, 68.5, 78.4, and 559 μg L^-1) and Cl^- (0, 60, and 600 mg Cl^- L^-1) by Carex pseudocyperus, C. riparia, and Phalaris arundinacea. These species had previously been identified as suitable candidates for floating treatment wetland applications. The study found high removal capacity in all treatment combinations, especially for Pb and Cu. However, low temperatures decreased the removal of all heavy metals, and increased salinity decreased the removal of Cd and Pb but had no effect on the removal of Zn or Cu. No interactions were found between the effects of salinity and of temperature. Carex pseudocyperus best removed Cu and Pb, whereas P. arundinacea best removed Cd, Zu, and Cl^-. The removal efficacy for metals was generally high, with elevated salinity and low temperatures having small impacts. The findings indicate that efficient heavy metal removal can also be expected in cold saline waters if the right plant species are used.

Cadmium contributes to heat tolerance of a hyperaccumulator plant species Sedum alfredii

Hyperaccumulators are plant species that tolerate and accumulate very high concentrations of toxic metals, including Cd. Hyperaccumulation of heavy metals is reported to benefit plant biotic resistance; however, no prior study has examined the possible role of toxic metals on abiotic stress resistance in hyperaccumulators. A preliminary experiment found that Cd significantly improved plant growth of a hyperaccumulator, Sedum alfredii Hance, under heat stress. This study investigated the possible role of Cd in S. alfredii's heat resistance, using infrared thermography, transmission electron microscopy (TEM), real-time quantitative polymerase chain reaction (RTqPCR), and high-throughput sequencing. The results showed that high temperatures irreversibly damaged stomatal function, chloroplast structure, photosynthesis in S. alfredii, and lowered survival rates to 25%. However, Cd application significantly decreased the leaf temperature of S. alfredii and increased the survival rate to 75%. Cd penetrated the guard cells, restored stomatal function, and mitigated excessive water loss from S. alfredii under heat stress. Moreover, it activated antioxidant enzymes, promoted phytohormone biosynthesis, and upregulated a series of unigenes, thereby augmenting heat resistance in S. alfredii. These results indicate that Cd effectively improved thermotolerance in S. alfredii by regulating stomatal movement and antioxidant systems via upregulation of phytohormones and heat shock proteins.

Individual and mutual effects of elevated carbon dioxide and temperature on salt and cadmium uptake and translocation by rice seedlings

Plant kingdoms are facing increasingly harsh environmental challenges marked by the coexposure of salinity and pollution in the pedosphere and elevated CO₂ and temperature in the atmosphere due to the rapid acceleration of industrialization and global climate change. In this study, we deployed a hydroponics-based experiment to explore the individual and mutual effects of different temperatures (low temperature, T1: 23°C; high temperature, T2: 27°C) and CO₂ concentrations (ambient CO₂: 360 ppm; medium CO₂: 450 ppm; high CO₂: 700 ppm) on the uptake and translocation of sodium chloride (NaCl, 0.0, 0.2, 0.6, and 1.1 g Na/L) and cadmium nitrate (Cd(NO₃)₂·4H₂O, 0.0, 0.2, 1.8, and 5.4 mg Cd/L) by rice seedlings. The results indicated that Cd and Na exposure significantly (P< 0.05) inhibited plant growth, but T2 and medium/high CO₂ alleviated the effects of Cd and Na on plant growth. Neither significant synergistic nor antagonistic effects of Cd and Na were observed, particularly not at T1 or high CO₂. At increasing temperatures, relative growth rates increased despite higher concentrations of Cd and Na in both rice roots and shoots. Similarly, higher CO₂ stimulated the growth rate but resulted in significantly lower concentrations of Na, while the Cd concentration was highest at medium CO₂. Coexposure experiments suggested that the concentration of Cd in roots slightly declined with additional Na and more at T2. Overall, our preliminary study suggested that global climate change may alter the distribution of mineral and toxic elements in rice plants as well as the tolerance of the plants.

Increasing Temperatures Potentiate the Damage of Rare Earth Element Yttrium to the Crop Plant Triticum aestivum L

Given that increasing temperature may aggravate the toxicity of pollutants, it is a daunting challenge to evaluate the realistic risks of rare earth elements (REEs) under global warming. Here, we studied how elevated temperatures (27 and 32 °C) impact the effect of yttrium (Y) on wheat plants (Triticum aestivum L.) at concentrations not causing effects (0, 0.5, and 1 μM) at the control temperature (22 °C) in a hydroponic system. After 14 days of exposure, significant inhibition (p < 0.05, 29.5%) of root elongation was observed only at 1 μM of Y at 32 °C. Exposure to Y at 27 °C showed no visible effects on root length, but induced significant (p < 0.05) metabolic disorders of a range of carbohydrates and amino acids related to galactose, phenylalanine, and glutamate metabolisms. Such cases were even shifted to substantial perturbation of the nucleotide pool reallocation involved in the disruption of purine and pyrimidine metabolism at 32 °C. These observations were regulated by sets of genes involved in these perturbed pathways. Using weighted gene co-expression network analysis, the disorder of nucleotide metabolism was shown to be responsible for the aggravated Y phytotoxicity at the extreme high temperature. Although the temperature fluctuation considered seems to be in an extreme range, unexpected implications driven by high temperature cannot be neglected. Our findings thus reduce the gaps of knowledge in REE toxicity to plants under future climate warming scenarios and highlight the importance of incorporating environmental temperature into the framework of the risk assessment of REEs.

Changes in soil micronutrients along a temperature gradient in northern China

How climate warming affected terrestrial ecosystems received considerable attention. Soil micronutrients play a vital role in regulating the growth of all living organisms and thus make a significant contribution to plant production. However, the responses of soil micronutrients to climate warming still remained unclear. While soil sampling along a temperature gradient could reveal the long-term influence of climate warming on soil nutrient dynamics, the variations of soil micronutrients with temperature might be interfered by the effect of precipitation due to the collinearity between temperature and precipitation. Moreover, changes in soil micronutrients over broad geographical scale could be affected by soil texture. Hence, this study conducted a soil investigation across a temperature transect along the 400 mm isohyet in northern China to examine the responses of soil micronutrients to changing temperature and soil texture when the effect of precipitation was minimized. We observed that soil copper (Cu), manganese (Mn) and zinc (Zn) contents all decreased along the temperature gradient. Soil Cu, Mn and Zn contents were positively correlated with soil clay and silt contents and negatively correlated with soil sand content. Temperature and soil texture together accounted for 72.0 % of the variations in soil micronutrient contents. Temperature and soil texture individually explained 10.4 % and 48.0 %, and their shared variation explained 13.6 % of the variations in soil micronutrient contents. Moreover, soil parent material also exerted an effect on soil micronutrient contents. Our results suggested that climate warming might cause a decrease in soil micronutrient contents.

Investigating the effect of Eh and pH on binding forms of Co, Cu, and Pb in wetland sediments from Zambia

This study investigated binding forms of cobalt (Co), copper (Cu), and lead (Pb) in 28 sediment samples from inlet to outlet of three Zambian wetlands receiving mining effluents. Use was made of a modified Tessier metal binding fractions procedure. Due to storage artefacts, the original aim of investigating the effects of redox potential (Eh) changes, starting from extremely low Eh, was suspended. Instead, use was made of the new, not often explored opportunity for replicate sample division into three categories of varying redox potential and pH. Additionally, in line with the original research aim, two sediments from each wetland were investigated for their response to increasing Eh. The results showed overall high trace metal contents, with a need for remedial actions for Co and Cu in the first, Cu in the second, and Pb in the third wetland. Rather independent of Eh and pH, Co was often found in the residual fraction (F5), as well as in the oxidizable (F4) and reducible (F3) fraction. Cu was generally dominant in F5 and F4 fractions, with low F3 prevalence, indicating a high organic matter affinity. Pb distribution among binding forms showed small variations within and across wetlands, F5, F4, and F3 fractions dominating. In the above observations, statistical analysis showed that, among the 28 sediment samples across wetlands, the influence of Eh and pH on binding forms were generally found to be not significant, being 'overruled' by other sedimentological factors. With increasing Eh, the decrease in the oxidizable (F4) fraction was smaller than expected in eight of 18 tests. The Risk Assessment Code (RAC) method, based on the exchangeable fraction (F1) plus carbonate fraction (F2), showed that some sediments turned from "unsafe" to "safe," and vice versa, with increasing Eh. The "total metals method" does not show bioavailability, whereas RAC does not use the metal contents. Thus, the two methods should be used together to improve the prediction of potential toxicity.

Phytoremediation of heavy metals in soil and water: An eco-friendly, sustainable and multidisciplinary approach

Rapid industrialization, increased waste production and surge in agricultural activities, mining, contaminated irrigation water and industrial effluents contribute to the contamination of water resources due to heavy metal (HM) accumulation. Humans employ HM-contaminated resources to produce food, which eventually accumulates in the food chain. Decontamination of these valuable resources, as well as avoidance of additional contamination has long been needed to avoid detrimental health impacts. Phytoremediation is a realistic and promising strategy for heavy metal removal from polluted areas, based on the employment of hyper-accumulator plant species that are extremely tolerant to HMs present in the environment/soil. Green plants are used to remove, decompose, or detoxify hazardous metals in this technique. For soil decontamination, five types of phytoremediation methods have been used viz. phytostabilization, phytodegradation, rhizofiltration, phytoextraction and phytovolatilization. Traditional phytoremediation methods, on the other hand, have significant limits in terms of large-scale application, thus biotechnological efforts to modify plants for HM phytoremediation ways are being explored to improve the efficacy of plants as HM decontamination candidates. It is relatively a new technology that is widely regarded as economic, efficient and unique besides being environment friendly. New metal hyperaccumulators with high efficiency are being explored and employed for their use in phytoremediation and phytomining. Therefore, this review comprehensively discusses different strategies and biotechnological approaches for the removal of various HM containments from the environment, with emphasis on the advancements and implications of phytoremediation, along with their applications in cleaning up various toxic pollutants. Moreover, sources, effects of HMs and factors affecting phytoremediation of HMs metals have also been discussed.

Combined effects of temperature and nutrients on the toxicity of cadmium in duckweed (Lemna aequinoctialis)

Global anthropogenic changes are altering the temperature and nutrients of the ecosystem, which might also affect the extent of cadmium (Cd) toxicity in organisms. This study aimed to investigate the combined effects of temperature and nutrient availability (here, nitrogen [N] and phosphorus [P]) on Cd toxicity in duckweed (Lemna aequinoctialis). The growth parameters, nutrient uptake, and Cd tolerance of plantlets reached their highest values for duckweed grown in medium with 28 mg/L N and 2.4 mg/L P (N:P = 11.67) at 25 °C under 1 mg/L CdCl₂ exposure. Raising the temperature (from 18 °C to 25 °C) and levels of N and P (from 0.01 N/P to 2 N/P) enhanced photosynthetic capacity and nutrient uptake, thus promoting plant growth and diluting the toxic effects of Cd. Although Cd uptake increased with increasing temperature, duckweed with relatively high biomass exhibited a lower accumulation of the toxic metal because their growth rate exceeded Cd uptake rate. Increasing N and P supply also enhanced the tolerance of duckweed to Cd by limiting Cd bioavailability. Our study therefore suggests the importance of combined effects from temperature and nutrients for Cd toxicity and provides novel insights for a comprehensive analysis of Cd toxicity associated with the environmental factors of a particular ecosystem.

Utilization of Legume-Nodule Bacterial Symbiosis in Phytoremediation of Heavy Metal-Contaminated Soils

Simple Summary

The legume–rhizobium symbiosis is one of the most beneficial interactions with high importance in agriculture, as it delivers nitrogen to plants and soil, thereby enhancing plant growth. Currently, this symbiosis is increasingly being exploited in phytoremediation of metal contaminated soil to improve soil fertility and simultaneously metal extraction or stabilization. Rhizobia increase phytoremediation directly by nitrogen fixation, protection of plants from pathogens, and production of plant growth-promoting factors and phytohormones.

Abstract

With the increasing industrial activity of the growing human population, the accumulation of various contaminants in soil, including heavy metals, has increased rapidly. Heavy metals as non-biodegradable elements persist in the soil environment and may pollute crop plants, further accumulating in the human body causing serious conditions. Hence, phytoremediation of land contamination as an environmental restoration technology is desirable for both human health and broad-sense ecology. Legumes (Fabaceae), which play a special role in nitrogen cycling, are dominant plants in contaminated areas. Therefore, the use of legumes and associated nitrogen-fixing rhizobia to reduce the concentrations or toxic effects of contaminants in the soil is environmentally friendly and becomes a promising strategy for phytoremediation and phytostabilization. Rhizobia, which have such plant growth-promoting (PGP) features as phosphorus solubilization, phytohormone synthesis, siderophore release, production of beneficial compounds for plants, and most of all nitrogen fixation, may promote legume growth while diminishing metal toxicity. The aim of the present review is to provide a comprehensive description of the main effects of metal contaminants in nitrogen-fixing leguminous plants and the benefits of using the legume–rhizobium symbiosis with both wild-type and genetically modified plants and bacteria to enhance an efficient recovery of contaminated lands.

A comprehensive study on aquatic chemistry, health risk and remediation techniques of cadmium in groundwater

Cadmium (Cd), a non-essential trace element, it's intrusion in groundwater has ubiquitous implications on the environment and human health. This review is an approach to comprehensively emphasize on i) chemistry and occurrence of Cd in groundwater and its concomitant response on human health ii) sustainable Cd remediation techniques, iii) and associated costs. Current study is depending on meta-analysis of Cd contaminations in groundwater and discusses its distributions around the globe. Literature review primarily comprises from the last three decades online electronic published database, which mainly includes i) research literatures, ii) government reports. On the basis of meta-data, it was concluded that Cd mobility depends on multiple factors: such as pH, redox state, and ionic strength, dissolved organic (DOC) and inorganic carbon (DIC). A substantially high Cd concentration has been reported in Lagos, Nigeria (0.130 mg/L). In India, groundwater is continuing to be contaminated by Cd in the proximity of industrial, agricultural areas, high concentrations (>8.20 mg/L) were reported in Tamil Nadu and Maharashtra. Depending on chemical behavior and ionic radius cadmium disseminate into the food chain and ultimately cause health hazard that can be measured by various index-based assessment tools. Instead of chemical adsorbents, nanoparticles, phytoextraction, and bioremediation techniques can be very useful in the remediation and management of Cd polluted groundwater at a low-cost. For Cd pollution, the development of a comprehensive framework that links the hydro-geological, bio-geochemical processes to public health is important and need to be further studied.

Are mangrove forests reliable sinks of heavy metals due to phytoremediation and other mechanisms? A Sri Lankan perspective

We present a viewpoint regarding the prospects in Sri Lanka (a tropical island nation) to depend on mangroves in the remediation of heavy metal laden coastal environments. Sri Lanka has a rich array of lagoons and estuaries (total extent of 1580.17 km²) with ideal brackish water habitats to allow mangrove proliferation and for more restoration works. Furthermore, our estimates of Total Potential Ecological Risk (PER < 150) indicate that ecological risk from metallic contamination of coastal sediments is low, which means mangrove ecosystems would be ideal natural treatment systems for such low polluting environments (but as final cum tertiary treatment systems only). Mangroves are neither metal hyperaccumulators nor good phytoremediators (no ability to take up more than 5000 mg/kg dry weight of a given metal or exhibit a bioconcentration factor ≥ 1000), which means not very effective for high polluting environments.

Desert dust deposition supplies essential bioelements to Red Sea corals

Climate change-related increase in seawater temperature has become a leading cause of coral bleaching and mortality. However, corals from the northern Red Sea show high thermal tolerance and no recorded massive bleaching event. This specific region is frequently subjected to intense dust storms, coming from the surrounding arid deserts, which are expected to increase in frequency and intensity in the future. The aerial dust deposition supplies essential bioelements to the water column. Here, we investigated the effect of dust deposition on the physiology of a Red Sea coral, Stylophora pistillata. We measured the modifications in coral and Symbiodiniaceae metallome (cellular metal content), as well as the changes in photosynthesis and oxidative stress status of colonies exposed during few weeks to dust deposition. Our results show that 1 mg L^-1 of dust supplied nanomolar amounts of nitrate and other essential bioelements, such as iron, manganese, zinc and copper, rapidly assimilated by the symbionts. At 25°C, metal bioaccumulation enhanced the chlorophyll concentration and photosynthesis of dust-exposed corals compared to control corals. These results suggest that primary production was limited by metal availability in seawater. A 5°C increase in seawater temperature enhanced iron assimilation in both control and dust-enriched corals. Temperature rise increased the photosynthesis of control corals only, dust-exposed ones having already reached maximal photosynthesis rates at 25°C. Finally, we observed a combined effect of temperature and bioelement concentration on the assimilation of molybdenum, cadmium, manganese and copper, which were in higher concentrations in symbionts of dust-exposed corals maintained at 30°C. All together these observations highlight the importance of dust deposition in the supply of essential bioelements, such as iron, to corals and its role in sustaining coral productivity in Red Sea reefs.

Contributions of Wetland Plants on Metal Accumulation in Sediment

Wetlands, and especially salt marshes, are well-known sinks of metals, which limit toxic amounts of metals from entering the food chain. This study investigated metal concentrations (Cr, Cu, Fe, Mn, Ni, Pb, Zn) in a highly urbanised estuary, and compared vegetated rhizosediment (Salicornia tegetaria, Spartina maritima, and Zostera capensis) with bare sediment, in a depositional and non-depositional site, in the intertidal zone of the Swartkops Estuary. The samples were collected at two sites along the middle and lower reaches of the estuary and analysed using a Total X-ray Fluorescence (TXRF) spectrometer. It was found that the rhizosediment contained more metals and that metal concentrations in the sediment decreased as follows: S. tegetaria > S. maritima > Z. capensis > bare sediment. Although metal accumulation was similar in bare sediment for the depositional (Site B) and the non-depositional site (Site A), the rhizosediment displayed higher metal accumulation in the depositional site (Site B). However, regardless of site-specific depositional tendencies, rhizosediment displayed higher metal accumulation than bare sediment. These results indicate that vegetated sites and vegetated depositional sites should be the focus of monitoring metals in estuaries around the world.

Influence of Soil Salinity on Selected Element Contents in Different Brassica Species

Climate changes in coastal regions cause increased soil salinity, a well-known type of environmental stress for a high number of agricultural crop species, including Brassicaceae, whose growth and development, and consequently the crop quality and yield, are affected by salinity stress. The aim of the present study is to investigate the effect of salt stress on micro- and macro-element homeostasis in different Brassica crops. Kale (Brassica oleracea var. acephala), white cabbage (B. oleracea var. capitata) and Chinese cabbage (B. rapa ssp. pekinensis) were grown hydroponically and treated with 200 mmol/L sodium chloride for 24 h to mimic short-term salt stress. The contents of Al, Ca, K, Mg, Na, B, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V and Zn were determined in the roots and leaves of the salt-treated plants and corresponding controls by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. While Al, Ca, K, Mg and Na were determined in the mg/g range, the contents of the other elements were found at the µg/g level. A statistical analysis of the obtained data showed that the applied salt treatment significantly influenced the single-element contents in different plant parts. The major elements Ca, K and Mg were mainly unaffected in the more-salt-tolerant kale and white cabbage under salinity stress, while K and Mg were significantly decreased in the more-sensitive Chinese cabbage. The levels of micro-elements were found to be species/variety specific. In general, potentially toxic elements were accumulated in the roots of salt-treated plants to a higher extent than in the corresponding controls.

Plant–Metal Interactions in the Context of Climate Change

Expanding fundamental understanding of the complex and far-reaching impacts of anthropogenic climate change is essential for formulating mitigation strategies. There is abundant evidence of ongoing damage and threat to plant health across both natural and cultivated ecosystems, with potentially immeasurable cost to humanity and the health of the planet. Plant–soil systems are multi-faceted, incorporating key variables that are individually and interactively affected by climatic factors such as rainfall, solar radiation, air temperature, atmospheric CO2, and pollution. This synthesis focuses on climate effects on plant–metal interactions and related plant–soil dynamics. Ecosystems native to metalliferous soils incorporate vegetation well adapted to metal oversupply, yet climate-change is known to induce the oversupply of certain immobile soil metals by altering the chemistry of non-metalliferous soils. The latter is implicated in observed stress in some non-metal-adapted forest trees growing on ‘normal’ non-metalliferous soils. Vegetation native to riverine habitats reliant on flooding is increasingly at risk under drying conditions caused by anthropogenic water removal and climate change that ultimately limit plant access to essential trace-metal nutrients from nutrient poor sandy soils. In agricultural plant systems, it is well known that environmental conditions alter soil chemistries and plant responses to drive plant metal toxicity stress. These aspects are addressed with reference to specific scenarios and studies linking climate to plant–metal interactions, with emphasis on land plants.

Metal Bioaccumulation and Oxidative Stress in Ulva laetevirens in the Venice Lagoon: Early Warning Biomarker for Metal Bioaccumulation

Transitional water systems (TWSs) may be threatened by various metals originating from increased agricultural, industrial activities, or urban effluents. Macroalgae are one of the biological quality elements used to monitor and assess the health status of TWS due to their structural and functional key role in marine ecosystems. Here, metal accumulation from the macroalgae Ulva laetevirens Areschoug (1854) and oxidative stress by lipid peroxidation (LPO) biomarker were investigated during four sampling seasons from three sampling sites (SMM: Santa Maria del Mare; PM: Porto Marghera; SG: San Giuliano) of Venice Lagoon, affected by different anthropogenic stressors. The metal pollution index (MPI) scores for U. laetevirens increased in the order SMM < PM < SG (sea inlet < industrial area < Osellino River estuary), with average values per site of 2.99, 4.37, and 6.33, respectively. The level of LPO was statistically correlated with the concentration of toxic metal(loid)s (As, Pb, Hg) measured in macroalgae, and seasonality affected both levels of LPO and metal bioaccumulation, with peak values during spring and summer. These findings highlighted the efficiency and usefulness of the oxidative stress test (LPO) on the common macroalga U. laetevirens as an early warning signal for health assessment in aquatic ecosystems.

Influence of low temperature on comparative arsenic accumulation and release by three Pteris hyperaccumulators

Arsenic (As) hyperaccumulator Pteris ferns are renowned for their capacity to accumulate As and have been used to remediate As-contaminated environmental. However, there is less information on how they perform under low temperature though it is important for practical phytoremediation. The purpose of this study was to identify the effect of temperature on As accumulation by three As hyperaccumulators, Pteris multifida, Pteris cretica and Pteris vittata. Ferns were cultured with 5 mg/L As addition under 25 °C to 5 °C for 15 days. The results showed that dropping of temperatures reduced As accumulation by P. vittata moderately but not P. multifida and P. cretica until 10 °C. At 5 °C, all ferns discontinued As accumulation, and the morphology showed necrosis in P. vittata, wherein P. multifida and P. cretica kept healthy. The As distribution showed that As was mainly accumulated in fronds, while P. multifida stored partial As in its root. Both translocation factor and As efflux showed that temperate zone ferns manage As more strictly as compared to P. vittata. Our findings demonstrated that temperature should be considered when applying Pteris ferns for As phytoremediation, and P. multifida could be the most suitable fern for treating As-contaminated water in temperate zone area.

Global patterns of accumulation and partitioning of metals in halophytic saltmarsh taxa: A phylogenetic comparative approach

The current study represents the first attempt to analyse quantitatively, within a phylogenetic framework, uptake and partitioning patterns of copper (Cu), zinc (Zn), cadmium (Cd) and lead (Pb) in extant saltmarsh taxa globally, and to assess associations of these patterns with various plant traits indicative of their halophytic adaptations. Despite saltmarsh being diverse taxonomically, most saltmarsh taxa accumulate metals to roots at, or above, unity (> 1). Further, there is significant translocation from roots to shoot for Cu, Zn and Cd (≤ 1), however, Pb is less mobile (TF = 0.65). Patterns of accumulation were similar among families, except greater Cd accumulation to roots in members of Juncaceae. Patterns of uptake to roots and translocation to leaves were broadly similar among plant type, plant form, habitat and photosynthetic mode. Zinc is lower in the leaves of salt-secreting species for some closely related taxa, suggesting some species co-excrete sodium (Na⁺) and Zn²⁺ through glands in leaf tissue. Salinity tolerance has no relationship to metal uptake and translocation. Translocation of Zn is greater at lower Zn sediment exposures, reflecting its active uptake and essentiality, but such bias does not affect outcomes of analyses when included as a covariate.

Trophic Transfer of Radioactive Micronutrients in a Shallow Benthic Food Web

The Baltic Sea is one of the most polluted seas in the world, with widespread eutrophication and radionuclide contamination. Using key species of the Baltic Sea, the effects of eutrophication on uptake and trophic transfer of the radioactive micronutrients commonly found in nuclear power plant effluents were investigated experimentally using the brown macroalgae Fucus vesiculosus and the grazers Idotea balthica and Theodoxus fluviatilis in a controlled environment. Rapid uptake of 54 Mn, 57 Co, and 65 Zn from water was observed in all biota; and eutrophication combined with grazing pressure strongly influenced the uptake in F. vesiculosus. Uptake of 54 Mn, 57 Co, and 65 Zn to I. balthica and T. fluviatilis grazing on F. vesiculosus were also observed. The results indicate that ecosystems could be open for further trophic transfer as radionuclides accumulate quickly in the producers and are transferred to primary consumers. Environ Toxicol Chem 2021;40:1694-1705. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

New challenges of marine ecotoxicology in a global change context

Currently, research agenda in marine ecotoxicology is facing new challenges with the emergence of newly and complex synthetized chemicals. The study of the fate and adverse effects of toxicants remains increasingly complicated with global change events. Ecotoxicology had provided for a decades, precious scientific data and knowledge but also technical and management tools for the environmental community. Regarding those, it is necessary to update methodologies dealing with these issues such as combined effect of conventional and emergent stressors and global changes. In this point of view article, we discuss one hand the new challenges of ecotoxicology in this context, and in the other hand, the need of updating agenda and methodologies currently used in monitoring programs and finally recommendations and future research needs. Among recommendations, it could be cited the necessity to perform long-term experiments, the standardization of sentinel species and taking benefit from baseline studies and omics technologies.

Constructed wetland, an eco-technology for wastewater treatment: A review on types of wastewater treated and components of the technology (macrophyte, biolfilm and substrate)

Constructed wetland (CW) represents an efficient eco-technological conglomerate interweaving water security, energy possibility and environmental protection. In the context of wastewater treatment technologies requiring substantial efficiency at reduced cost, chemical input and low environmental impact, applications of CW is being demonstrated at laboratory and field level with reasonably high contaminant removal efficiency and ecological benefits. However, along with the scope of applications, role of individual wetland component has to be re-emphasized through related research interventions. Hence, this review distinctively explores the concerns for extracting maximum benefit of macrophyte (focusing on interface of pollutant removal, root radial oxygen loss, root iron plaque, endophyte-macrophyte assisted treatment in CW, and prospects of energy harvesting from macrophyte) and role of biofilm (effect on treatment efficiency, composition and factors affecting) in a CW. Another focus of the review is on recent advances and developments in alternative low-cost substrate materials (including conventional type, industrial by-products, organic waste, mineral based and hybrid type) and their effect on target pollutants. The remainder of this review is organized to discuss the concerns of CW with respect to wastewater type (municipal, industrial, agricultural and farm wastewater). Attempt is made to analyze the practical relevance and significance of these aspects incorporating all recent developments in the areas to help making informed decisions about future directions for research and development related to CW.

Warming enhances the cadmium toxicity on macrophyte Myriophyllum aquaticum (Vell.) Verd. seedlings

Due to a close contact with water column, submerged macrophytes are easily disturbed by environment change in freshwater ecosystems, especially at the seedling stage. In recent decades, freshwater ecosystems have been subject to severe cadmium (Cd) pollution, which can cause toxic effects on the growth of submerged macrophytes. Moreover, the temperature rise resulting from climate warming and water level decline may further aggravate such effect, especially in shallow lakes. Here, we investigated the independent and interaction effects of Cd exposure levels (0, 0.5, 1, and 2.5 mg L^-1) and temperature (15, 25, and 30 °C) on morphological and physiological traits of Myriophyllum aquaticum (Vell.) Verd. Seedlings generated from propagules and seeds. The temperature rise and Cd exposure generally resulted in a significant increase of Cd concentrations and antioxidant enzyme activities in leaves, as well as a decrease of chlorophyll a and b concentrations. The number and length of leaves generated from propagules always show a downward trend with the increase of Cd exposure, regardless of the temperature. Moreover, the lowest leaf number and length always occurred at high temperature (i.e. 30 °C) when the Cd exposure level increased to 1 and 2.5 mg L^-1. For the seedlings generated from seeds, the temperature rise caused an increase of leaf emergence rate under low Cd exposure levels, but resulted in a significant decrease with the Cd exposure level. This study indicates the negative effects of Cd exposure and temperature rise on submerged macrophytes at the seedling stage, and highlights that temperature rise would enhance Cd toxicity.

Accumulation of elements by submerged (Stuckenia pectinata (L.) Börner) and emergent (Phragmites australis (Cav.) Trin. ex Steud.) macrophytes under different salinity levels

Accumulation of essential/beneficial and non-essential chemical elements by submerged (Stuckenia pectinata (L.) Börner) and emergent (Phragmites australis (Cav.) Trin. ex Steud.) rooted macrophytes in three water bodies was studied as dependent on water salinity (specific conductivity) and main environmental factors (temperature, pH of water, growing period, element contents in water and sediments). Inductively coupled plasma optical emission spectrometry (ICP - OES) was used for the element detection in the plants, sediments, and water. Multivariate statistics redundancy analysis (RDA) showed that investigated factors together explained 37.8 - 44.7% and 29.9 - 42.6% of the essential/beneficial and non-essential elements variability, respectively, whereas salinity was one of the main factors determining the accumulation of a number of elements (Mg, S, Na, Li, Sr, Sb) by the macrophytes. A decrease in the essential element contents (K, P, N, Cu, Zn) was observed in both species of the macrophytes during the growing season. Environmental factors (salinity, growing period, and pH) were more significant than the element contents in water and the sediments for the essential/beneficial element accumulation by two species of the macrophytes. The element contents in the sediments to a greater extent determined non-essential element accumulation by P. australis than by S. pectinata. The study showed that the efficiency of using P. australis and S. pectinata for remediation of aquatic ecosystems contaminated by heavy metals should not decrease with a salinity increase.

Trace metal dynamics in soils and plants along intertidal gradients in semi-arid mangroves (New Caledonia)

Trace metal dynamics were investigated in mangroves developing in semi-arid New Caledonia, where Avicennia and Rhizophora stands grow in the upper and lower intertidal zone, respectively. We collected soil samples and mangrove tissues in an undisturbed site, a mining-influenced site and in a mining and aquaculture-influenced site. Differences in duration of immersion and organic matter (OM) cycling resulted in a sharp decrease of metal concentrations in soils and plants from landside to seaside. Both species were tolerant to metals mainly via exclusion, (i.e. metal bioaccumulation restricted to roots and leaf litter). Strong correlations (p < 0.05) were found between Na and Fe, Mn, Cu and Zn in green and senesced leaves of Avicennia marina, indicating a possible role of those metals in mechanisms to cope with hypersaline conditions. Increasing metal pollution, aridity and sea-level rise are likely to result in a decrease in mangrove efficiency in filtering trace metals seaward.

Screening the Capacity of 34 Wetland Plant Species to Remove Heavy Metals from Water

Floating treatment wetlands (FTWs), consisting of vegetated rafts, may reduce heavy metal levels in polluted water, but the choice of plant species for efficient metal removal needs to be further investigated. We screened the capacity of 34 wetland plant species to remove metals dissolved in water to identify suitable species for FTWs. The plants were grown hydroponically for 5 days in a solution containing 1.2 µg Cd L-1, 68.5 µg Cu L-1, 78.4 µg Pb L-1, and 559 µg Zn L-1. Results show large variation in metal removal rate and capacity between the investigated species. The species with highest removal capacity could remove up to 52-94% of the metals already after 0.5 h of exposure and up to 98-100% of the metals after 5 days of exposure. Plant size contributed more to high removal capacity than did removal per unit of fine roots. Carex pseudocyperus and C. riparia were the most efficient and versatile species. The findings of this study should be considered as a starting point for further investigation of plant selection for improved water purification by FTWs.

Evaluation of cadmium hyperaccumulation and tolerance potential of Myriophyllum aquaticum

Enrichment of the hyperaccumulator bank is important for phytoremediation, and studying new hyperaccumulators has become a research hotspot. In this study, cadmium (Cd), the main representative factor of heavy-metal-polluted water, was the research object, and the Cd bioenrichment ability and tolerance of Myriophyllum aquaticum were studied for the first time. The experiment was conducted for 28 days by establishing experimental groups with different Cd concentrations (0, 10, 20, 40, 80, and 160 mg/L). The results show that M. aquaticum is a new Cd hyperaccumulator. There was no notable damage in the 40 mg/L Cd treatment group, and the Cd enrichment ability of M. aquaticum reached 17,970 ± 1020.01 mg/kg, while the bioconcentration factor (BCF) reached 449.25. At the same time, the antioxidant system (superoxide dismutase (SOD) and peroxidase (POD)) and proline (Pro) levels of M. aquaticum maintained normal plant physiology, but there were physiological anomalies in M. aquaticum at high concentrations and under long-term treatment. The results show that M. aquaticum has a high Cd bioenrichment ability and tolerance in water and can be used for phytoremediation of river water polluted by Cd.

Assessment of metal/metalloid occurrence in rivers with their accumulation in macrophyte case study with Myriophyllum alterniflorum

Water quality monitoring with integrative tools is a main issue of concern for environment assessment. Submerged aquatic macrophyte can be a good candidate for the evaluation of contaminant content in rivers. Indeed, owing to their habitat, aquatic macrophytes interact directly with surface water; they can absorb contaminants and thus allow to detect their presence in water. In situ studies were conducted over 28 days in five aquatic environments, affected by different levels of anthropogenic pressure (domestic wastewater plant, industrial activities), during two field campaigns. We have investigated whether the accumulation of some metals and a metalloid (As) in Myriophyllum alterniflorum could be used to detect their occurrence in river waters. Our results demonstrated that long time bioaccumulation was correlated with the contaminant levels in water. However, the water composition and the duration of exposure affected the studied pollutants' absorption. On an operational point of view, the optimal duration of exposure of Myriophyllum alterniflorum to assess the water quality is conditioned by the contaminant contents in waters that can induce different defense mechanisms as the reduction of pollutant absorption and their efflux. In addition, the nutrient concentration influenced the accumulation of pollutants since the higher the nutrient level, the higher the essential metal accumulation was observed.

Cellular Responses of Gelidium floridanum (Gelidiales, Rhodophyta) Tetraspores Under Heat Wave and Copper Pollution

Spore settlement and development are bottlenecks for resilience of habitat-forming macroalgal species. These processes are directly related to temperature, a global stressor protagonist of ocean warming. The toxic effects of local pollutants such as copper may be worsened under a global warming scenario. Therefore, in this paper, we investigated the effects of increased temperature combined with elevated concentrations of copper on the viability, photosynthetic pigments, and ultrastructure of Gelidium floridanum tetraspores. Tetraspores were cultivated on slides with sterilized seawater or seawater enriched with CuCl₂ , and incubated under 24°C or 30°C for 24 h. Tetraspores cultivated with copper 3.0 μM under 30°C had lower viability. Both temperature and copper had a significant effect on phycocyanin and phycoerythrin concentrations. Samples cultivated with copper under 30°C presented a heavily altered cellular structure, with vesicles throughout the cytoplasm, chloroplasts with altered structure and cells with degenerated cytoplasm and cell walls. Our findings show that temperature and copper significantly affect the viability, photosynthetic pigments, and ultrastructure of G. floridanum tetraspores, presenting an additive interaction for the physiology of this seaweed's early stages.

Salt Tolerance and Desalination Abilities of Nine Common Green Microalgae Isolates

In recent years, decline of freshwater resources has been recognized as one of the main environmental problems on global level. In addition to the increasing extent of primary salinization due to climate change, secondary salinization caused by human interventions is also a significantly increasing problem, therefore, the development of various chemical-free, biological desalination and removal procedures will become increasingly important. In the present study, the salinity tolerance, salinity, and nutrient reducing ability of nine common freshwater microalgae species from the genera Chlorella, Chlorococcum, Desmodesmus, Scenedesmus, and Monoraphidium were investigated. Our results proved that the studied green microalgae species are halotolerant ones, which are able to proliferate in environments with high salt concentrations. Furthermore, most of the species were able to reduce conductivity and remove significant amounts of chloride (up to 39%) and nutrients (more than 90% nitrate). The results proved that nitrate removal of the studied species was not influenced by salt concentration, only indirectly via growth inhibition. However, the results also highlighted that N:P ratio of the medium has primarily importance in satisfactory phosphorous removal. It can be concluded that assemblages of the studied microalgae species could be able to adapt to changing conditions even of salt-rich wastewaters and improve water quality during bioremediation processes.

Bacteria-assisted phytoremediation of fuel oil and lead co-contaminated soil in the salt-stressed condition by chromolaena odorata and Micrococcus luteus

Bioremediation of lead-petroleum co-contaminated soil under salt-stressed condition has been investigated. In this study, the co-contaminated soil (780 mg kg^-1 Pb and 27,000 mg kg^-1 TPHs) under the high salinity (EC 7.79 ds m^-1) was used as a model soil to be remediated by Chromolaena odorata inoculated with Micrococcus luteus. The results showed that salt stress caused a marked reduction in dry biomass and stem height, and high accumulation of proline. The presence of salt did not affect the total amount of chlorophyll in plant tissues. No toxicity symptoms were evident from plant morphology after three months of exposure. Drastic differences in the accumulation patterns of Pb in C. odorata grown on saline and non-saline soils were observed and indicated that salinity negatively affected Pb uptake and accumulation. A high rate of degradation of TPHs was observed in non-saline soils with or without bacterial inoculation. Salinity stress showed no significant different in the proportion of TPH degradation with added or non-added M. luteus. The tolerance of C. odorata and M. luteus to moderate concentrations of Pb and fuel oil made them very good candidates for the use in bacteria-assisted phytoremediation of lead-fuel oil co-contaminated soils under the mild saline soils.

Ecological risk assessment of metals in sediments and selective plants of Uchalli Wetland Complex (UWC)-a Ramsar site

Wetlands act as kidneys of land and facilitate remediation of metals and other harmful pollutants through uptake by aquatic macrophytes. The aim of the present study was to investigate metal concentrations in sediments and plants, sources of metal origin, and contamination level in Uchalli Wetland Complex. Sediment samples were collected from 15 randomly selected sites. Metal concentrations (Cd, Pb, Ni, Cu, Zn, Cr, As, Mn) in sediments and macrophytes were determined during summer and winter seasons using the inductively coupled plasma technique. Metal concentrations in sediments during summer and winter seasons were in the order as follows: As > Mn > Zn > Cr > Ni > Cd > Pb > Cu and As > Mn > Zn > Cr > Ni > Pb > Cd >Cu respectively. All analyzed metals were within European Union (EU) limits. In macrophytes, these metals were in the order as follows: Mn > As > Ni > Zn > Cr > Cd > Cu > Pb and As > Mn > Zn > Ni > Cr > Cd > Pb during summer and winter seasons respectively. Contamination degree (C_d) (1.023-5.309) for these lakes showed low contamination during both seasons; mC_d values (below 1.5) showed very little contamination degree, while the pollution load index (0.012 to 0.0386) indicated no metal pollution in these lakes. PCA applied on sediment showed that Pb, Zn, Cr, Cu, and Cd had anthropogenic sources of origin. As and Mn were due to natural processes while Ni could be resultant of both anthropogenic and natural sources. PCA on macrophytes showed that Ni, Pb, Cr, Zn, Cu; Cd, As; Mn had anthropogenic, natural, and anthropogenic + natural sources of origin. The study concluded that metal concentrations in sediments were not up to dangerous level.

Characterization of Nutrient and Metal Leaching in Roadside Ditches Maintained with Cool and Warm Season Grasses

Roadside ditches play an important role in the quantity and quality of receiving waters. Very little, however, is known about the fate and transport of nutrients and trace metals in roadside ditches, especially their leaching to shallow groundwater. This study sought to document selected water quality constituent levels in infiltrated water (i.e., leachate) in roadside ditches maintained with permanent vegetation. Leachate sampling wells were installed in four roadside ditches, and water samples were collected from the wells following major rainfall events during the years 2016 and 2017. The samples were analyzed for nutrient and metal concentrations. Results indicated that nutrient concentrations in the water samples range from 0.00600 to 0.0107 mg/L for orthophosphate (PO4–P), 0.00500 to 6.80 mg/L for nitrate (NO3–N), 0 to 0.007 mg/L for nitrite (NO2–N), and 0.0100 to 314 mg/L for chloride (Cl−). Concentrations of the metals examined varied between 0.0100 and 104 mg/L in water samples. While there was no specific pattern in both nutrient and metal concentrations when roadside ditches maintained with cool season grass were compared to those of warm season grass ditches, results suggest that grass types will likely affect differently uptake of nutrients and metals in the ditches.

Environmental variations mediate duckweed (Lemna minor L.) sensitivity to copper exposure through phenotypic plasticity

Environmentally mediated sensitivity of Lemna minor to copper (Cu) was evaluated for the first time in three experiments: the effects of two levels of nutrient concentration, light irradiance or Cu pre-exposure were tested. Various Cu concentrations (ranging from 0.05 to 0.25 mg/L) were used to assess the sensitivity of L. minor to this metal, using one common strain previously acclimatized to two different levels of light intensity, nutrient enrichment and Cu pre-exposure. Our results showed a phenotypic plastic response of the relative growth rates based on frond number and fresh mass production, and maximum quantum yield of photosystem II (F_v/F_m). Growth was affected by the three environmental conditions both prior and during Cu exposure, whereas F_v/F_m was mostly affected during Cu exposure. Copper significantly influenced all the parameters measured in the three experiments. Environmental conditions significantly modified L. minor sensitivity to Cu in all experiments, with up to twofold difference depending on the treatment. Growth rate was the parameter that was most impacted. Our study revealed for the first time the existence of phenotypic plasticity in L. minor sensitivity to chemical contamination, and implies that environmental context needs to be taken into account for a relevant risk assessment.

Tolerance Mechanisms to Copper and Zinc Excess in Rhizophora mucronata Lam. Seedlings Involve Cell Wall Sequestration and Limited Translocation

Rhizophora mucronata is a common mangrove growing in habitats subjected to heavy metal (HM) contamination. Understanding their physiological responses to copper (Cu) and zinc (Zn) excess and underlying tolerance mechanisms is crucial to assess impacts of metal pollution on mangrove community. Seedlings were treated with Cu or Zn (0, 50 or 100 mg per plant) by means of a single addition. At day 3 and 7, Cu and Zn accumulation, photosynthetic efficiency, superoxide dismutase and peroxidase activity, non-protein thiols, reactive oxygen species and lipid peroxidation in roots and leaves were measured. R. mucronata restricted Cu and Zn translocation, thus accumulated HM mainly in roots while kept the leaves unaffected. However, high root HM did not induce oxidative stress nor anti-oxidative defense as HM were largely deposited in cell wall. We concluded that HM tolerance strategies of R. mucronata seedlings are exclusion and restriction of translocation to the vital photosynthetic tissue.

Effects of various warming patterns on Cd transfer in soil-rice systems under Free Air Temperature Increase (FATI) conditions

Global warming has become an important research topic in different disciplines around the world, especially in the fields of environment quality and food security. As a potential problem in soil environments, cadmium (Cd) contamination of rice under global warming conditions has not been thoroughly investigated. In this study, the fate of Cd in soil-rice systems under various warming patterns was studied via pot experiments under Free Air Temperature Increase (FATI) conditions. The patterns of warming included different temperatures (0.5 °C and 0.8 °C), different day-night durations (nighttime, daytime, and the whole day), and different warming stages (WSx) (including WS1 (seedling to tillering), WS2 (jointing to booting), WS3 (heading), WS4 (grain filling to milk ripening)). At harvest, samples of different rice tissues were collected and the Cd concentrations were measured. The results showed that warming significantly increased Cd concentrations in grain by 1.45 and 2.31 times, which was positively correlated with the two temperature increases (0.5 °C and 0.8 °C), respectively. Both daytime and nighttime warming significantly increased the Cd concentration in grain, and the daytime dominated Cd translocation from roots to shoots. In addition, warming in individual growth stages contributed to increases in Cd accumulation in grain by 31.6% (WS1), 15.0% (WS2), 20.6% (WS3), and 32.8% (WS4), respectively. Specifically, warming during the vegetative phase boosted Cd translocation from roots to shoots, while warming during maturation further increased Cd uptake and remobilization into grain. The projected results could provide a new and in-depth understanding of the fate of Cd in soil-rice systems under global warming conditions in Cd contaminated areas.

The influence of an electric field on growth and trace metal content in aquatic plants

It is known that both natural and artificial electric fields (EF) affect plants physiological parameters as well as germination, growth and yield. The present article describes results of a preliminary experiment on the impact of electric field on aquatic plants biogeochemistry. The objective of the present study was the assessment of the influence exerted by the electric field on growth and trace metals content of Elodea canadensis. In a laboratory experiment plants were exposed to the field intensity of 54 kV m^-1 for 7 days. The plants length was measured and the content of Fe, Mn, Ni, Pb, and Zn was determined using atomic absorption spectrometry (AAS). Results showed that the application of electric field slightly enhanced the growth of E. canadensis shoots. The content of Mn and Ni was significantly lower, and Pb and Zn significantly higher in plants exposed to the electric filed, while Fe content did not differ between control and EF treatment. This provides a rationale for further studies on biological effects of electric field in trace metal contaminated waters and application of an electrically enhanced phytoremediation.

Salinity-dependent nanostructures and composition of cell surface and its relation to Cd toxicity in an estuarine diatom

The interactions between metal and phytoplankton are affected by salinity in estuarine environments. While water chemistry is an important factor regulating the metal bioavailability in phytoplankton, the physiological adaptation of the algae cells may also change their intrinsic response to metals. In this work, we tried to interpret the salinity-dependent Cd toxicity in a pennate diatom Nitzchia closterium from a biological side. As with many studies, we observed Cd toxicity to the diatom increased with decreasing salinity. However, changing free Cd ion concentrations may be partly responsible for the enhanced Cd toxicity. Multiple evidences showed that diatom cells acclimated at low salinity had stronger intrinsic Cd adsorption capacity. Salinity significantly affected not only the nanostructures but also the biochemical composition in the cell surface of the diatom. Diatom cells grown at lower salinity had a lower surface potential, higher specific surface area, and more sulfur-containing groups in the cell wall, leading to stronger Cd binding capacity in the cells. Meanwhile, more Si was present as poly-silicic acid when the salinity decreased. The change of Si content and speciation in the cell wall are also considered a major reason for the variations of Cd surface binding. Our study provided new clues for the salinity-dependent metal toxicity in marine diatoms.

Ocean warming and copper pollution: implications for metabolic compounds of the agarophyte Gelidium floridanum (Gelidiales, Rhodophyta)

Ocean warming is increasing and scientific predictions suggest a rise of up to 4°C in sea water temperatures. The combination of a polluted and warmer environment may be detrimental for aquatic species, especially for primary producers such as seaweeds. This study investigated the potential for interactive effects of an increased seawater temperature in a copper-rich environment on the photosynthetic pigments and metabolic compounds of the red seaweed Gelidium floridanum. Seaweed samples were cultivated in a factorial design with temperature (24°C and 30°C), copper (0 and 3 μM), and time (7 and 14 d). The exposure of G. floridanum to copper and 30°C for 7 d resulted in a lower concentration of chlorophyll a, smaller phycobiliprotein rods and lower concentration of soluble sugars. After 14 d of cultivation, a higher concentration of chlorophyll a and soluble sugars could be observed on seaweeds cultivated under 30°C. The accumulation of carotenoids and the release of phenolic compounds indicated specific protective mechanisms against temperature and copper, respectively. Overall, seaweeds grew less when exposed to copper 3 μM at 30°C.

Identifying the Key Information and Land Management Plans for Water Conservation under Dry Weather Conditions in the Border Areas of the Syr Darya River in Kazakhstan

Due to an increase in poorly planned anthropogenic activities, the water quality of several Asian big rivers is highly being affected. Although the assessment of heavy metal contents is vital to develop and design sustainable water management plans, several areas in Central Asia such as Kazakhstan do not have recent studies available that evaluate this situation. One representative example of this lack of information is the Syr Darya River. Thus, this study carried out the first approach to a water quality assessment in Kazakhstan’s Syr Darya River, where a massive expansion of irrigation canals, pastures in middle- and lower-reaches and an increase in industrialization and population have lowered its potential water capacity. To achieve this goal, various physicochemical parameters were analyzed for forty-three water samples along the river under dry weather conditions at 25 cm water depth. The obtained results were analyzed using standard methods (e.g., Multi N/C 2100 S analyzer or an atomic absorption spectrometer) and evaluated by multivariate techniques (cluster analysis (CA), principal component analysis (PCA), and non-metric multidimensional scaling (NDMS)) and a heavy metal pollution index (HPI). In the CA, five cluster groups were obtained. It is important to remark that the first cluster consists of the highest number of water sampling points (8). The last cluster is made up of only one point, which shows the highest difference against the other sites in our model. The NDMS also confirmed that some specific points along the river are different. Five components were extracted from the PCA: (1) COD (chemical oxygen demand), Zn, Cu, Pb, Ni and Mn; (2) Cu, Cd, Ni and Co; (3) T (water temperature), pH and DO (dissolved oxygen); (4) T and Fe; and (5) COD and OC (organic carbon). The HPI showed very high values (279.9), which were locally confirmed in some hotspots close to the Aral Sea, industrialized areas and agricultural fields. Therefore, our results demonstrate that, under dry weather conditions, surface water resources could be mismanaged in the Syr Darya River in Kazakhstan in specific areas. For the future, considering the important role that agriculture and pasture play in the Kazakh economy, we insist upon the importance of applying water quality control measures applying nature-based solutions and efficient management plans. Moreover, we confirmed the necessity to conduct further research related to sampling under other weather situations such as wet and cold conditions, different river water depths and other locations considering specific land uses, for example, grazing, mining, railways or industries.

Functional and structural biomarkers to monitor heavy metal pollution of one of the most contaminated freshwater sites in Southern Europe

This study evaluated the biological effects of highly polluted freshwater environment (Regi Lagni channels, S Italy) on the aquatic moss Leptodictyum riparium, exposed in bags at three sites representative of different environmental conditions and characterized by different heavy metal burdens. Bioaccumulation, ultrastructural alterations, Reactive Oxygen Species (ROS) production, antioxidant enzymes activity and DNA damage were assessed. To better evaluate the biological response of the moss species to heavy metals, the same biological parameters were assessed also in L. riparium samples cultured in vitro using metal mixtures at the same concentrations as measured at the 3 field exposure sites. Heavy metals were accumulated into the moss tissues causing severe ultra-structural damages at higher concentration case studies, and the ROS production as well as the activity of the enzyme followed a concentration-dependent increase. However, the DNA damage trend suggested a threshold effect that changed between field and in vitro experiment. The enrichment factor suggests that the concentration in the most polluted site is close to the upper limit of L. riparium to accumulate metals. Overall, combining measures of the morpho-functional traits at different level contribute to improving the knowledge about the tolerance of L. riparium to heavy metal stress, suggesting that this moss could be suitable for biomonitoring activity in field conditions.

Using Myriophyllum aquaticum (Vell.) Verdc. to remove heavy metals from contaminated water: Better dead or alive?

This study aimed to investigate the potential of the invasive macrophyte Myriophyllum aquaticum to remove heavy metals. The elements tested were Cd, Cr, Ni, and Zn, in single-metal trials, and experiments were performed with both the living and dead biomass of the plant. In respect of metal removal by living plants, the element that was removed the most was Zn, though Cd showed the highest concentration in plant shoots. The metal negative effect on plant growth was, therefore, more important than the level of metal concentration in plant tissue in determining the removal percentages. All the metals were mostly accumulated in the roots, where a considerable fraction of the element was simply adsorbed to root cell wall, except in the case of Cr. In shoots, the fraction of the adsorbed metal was extremely low in respect to roots, thereby implying a lower apoplastic binding capacity. As regards a possible use of the dead biomass for metal removal, we proposed the generation of a hybrid biosorbent enclosing the dried and grounded plant biomass in cotton bags to improve its handling and its adsorption capacity, in view of a valid alternative to reduce the problems of packed beds. Cadmium-and especially Zn-were the elements removed most efficiently with respect to the other metals. On comparing the removal percentages of the living biomass and the hybrid biosorbent, our data deposed in favour of the use of M. aquaticum as dead biomass for a possible application of this invasive macrophyte in the biological treatment of metal-contaminated water. Our findings may be beneficial to metal removal application accompanying wetland management, devising a possible use of M. aquaticum waste material after its removal from the invaded habitats.

Cadmium uptake kinetics in parts of the seagrass Cymodocea nodosa at high exposure concentrations

Background

Seagrass species have been recommended as biomonitors of environmental condition and as tools for phytoremediation, due to their ability to concentrate anthropogenic chemicals. This study aims to provide novel information on metal accumulation in seagrasses under laboratory conditions to support their use as a tool in the evaluation and abatement of contamination in the field. We investigated the kinetics of cadmium uptake into adult leaf blades, leaf sheaths, rhizomes and roots of Cymodocea nodosa in exposure concentrations within the range of cadmium levels in industrial wastewater (0.5–40 mg L⁻¹).

Results

A Michaelis–Menten-type equation satisfactorily described cadmium accumulation kinetics in seagrass parts, particularly at 0.5–5 or 10 mg L⁻¹. However, an S equation best described the uptake kinetics in rhizomes at 5 mg L⁻¹ and roots at 10 and 20 mg L⁻¹. Equilibrium concentration and uptake rate tended to increase with the exposure concentration, indicating that seagrass displays a remarkable accumulation capacity of cadmium and reflect high cadmium levels in the surrounding medium. Concerning leaf blades and rhizomes, the bioconcentration factor at equilibrium (range 73.3–404.3 and 14.3–86.3, respectively) was generally lower at higher exposure concentrations, indicating a gradual reduction of available binding sites. Leaf blades and roots accumulated more cadmium with higher rate than sheaths and rhizomes. Uptake kinetics in leaf blades displayed a better fit to the Michaelis–Menten-type equation than those in the remaining plant parts, particularly at 0.5–10 mg L⁻¹. A marked variation in tissue concentrations mainly after the steady state was observed at 20 and 40 mg L⁻¹, indicative of the stress induced on seagrass cells. The maximum concentrations observed in seagrass parts at 5 and 10 mg L⁻¹ were comparatively higher than those previously reported for other seagrasses incubated to similar exposure concentrations.

Conclusions

Cymodocea nodosa displays a remarkable cadmium accumulation capacity and reflects high cadmium levels in the surrounding medium. Kinetic models satisfactorily describe cadmium uptake in seagrass parts, primarily in adult leaf blades, at high exposure concentrations, permitting to predict cadmium accumulation in field situations. Cymodocea nodosa appeared to be a valuable tool in the evaluation and abatement of cadmium contamination in coastal areas.