Leaves of Phragmites australis as potential atmospheric biomonitors of Platinum Group Elements

Biodynamics and Environmental Concentrations of the Platinum Group Elements in Freshwater Systems

Growing reliance on platinum group elements (PGEs) as critical minerals for emerging technologies raises concerns regarding their ecotoxicological behavior. We studied their environmental fate in various inorganic and biological matrices from Canada using ICP-MS/MS analysis. Our findings confirmed previously published rhodium, palladium, and platinum concentration gradients from road dust to sediments, soils, and water, but differed from the literature reporting high biological contamination, which was not observed in our study. We also conducted experiments using a predator-prey model by exposing Chaoborus americanus to PGE mixtures for 24 h and to contaminated prey (Daphnia magna) for 8 days, followed by a 3-day excretion period. We estimated water uptake rate constants (kuw = 1.6-3.5 mL g-1 d-1), assimilation efficiencies (AEs = 0.024-32.2%), and efflux rate constants (ke = 0.51-0.69 d-1) for four PGEs. Overall, Chaoborus showed poor bioaccumulation and low trophic transfer of the PGEs, which were rapidly excreted. Experimental results supported low detection of PGEs in wild organisms, underscoring the need for caution when interpreting studies reporting high PGE levels in biological matrices. Nonetheless, this study improves our understanding of the PGEs' environmental fate, revealing correlations with several quantitative ion character-activity relationships (QICARs) and highlighting chemical bond softness (σParr) as a predictor of biological assimilation and excretion.

Tree Physiological Variables as a Proxy of Heavy Metal and Platinum Group Elements Pollution in Urban Areas

Physiological variables (the content of chlorophyll, flavonoids and nitrogen, together with Fv/Fm) and the content of ten heavy metals (As, Cd, Cu, Hg, Mn, Ni, Pb, Sb, V and Zn) and two platinum group elements (PGEs: Pd and Rh) were measured in the leaves of 50 individuals of Ligustrum lucidum trees regularly distributed in the city of Logroño (Northern Spain). Three of these variables increased with increasing physiological vitality (chlorophyll, nitrogen and Fv/Fm), whereas flavonoids increased in response to different abiotic stresses, including pollution. Our aim was to test their adequacy as proxies for the pollution due to heavy metals and PGEs. The three vitality indicators generally showed high values typical of healthy plants, and they did not seem to be consistently affected by the different pollutants. In fact, the three vitality variables were positively correlated with the first factor of a PCA that was dominated by heavy metals (mainly Pb, but also Sb, V and Ni). In addition, Fv/Fm was negatively correlated with the second factor of the PCA, which was dominated by PGEs, but the trees showing Fv/Fm values below the damage threshold did not coincide with those showing high PGE content. Regarding flavonoid content, it was negatively correlated with PCA factors dominated by heavy metals, which did not confirm its role as a protectant against metal stress. The relatively low levels of pollution usually found in the city of Logroño, together with the influence of other environmental factors and the relative tolerance of Ligustrum lucidum to modest atmospheric pollution, probably determined the only slight response of the physiological variables to heavy metals and PGEs.

The efficiency of trace element uptake by seagrass Cymodocea serrulata in Rabigh lagoon, Red Sea

The search for solutions to environmental pollution has been on the increase, with many questions recently as to which marine organisms can bioaccumulate trace elements in the marine ecosystem. Cadmium, Cr, Cu, Fe, Mn, Ni, Pb, and Zn concentrations in sediment, seawater, and seagrass compartments (root, rhizome, and leaf blade) were determined at Rabigh lagoon, Red Sea. This is to provide an insight into the potential of Cymodocea serrulata to bioaccumulate trace elements and as a good candidate to biomonitor these elements in a natural aquatic ecosystem. Results revealed significant variations in trace element concentrations across the three compartments of C. serrulata and the sites, with site S8 located in the most closed part of the lagoon recording the highest concentrations for all the trace elements. The translocation factor (TF_rhizome/root = 1.00) of trace elements was higher in the root compartment. This implies that the root compartment is a better bioindicator of trace elements and has more potential to be utilized for biomonitoring. A significant positive correlation (p < 0.01) was established between the trace element concentrations in sediment, seawater, and the three compartments of C. serrulata except for Mn concentration in the compartments. The seagrass C. serrulata can be used for biomonitoring of trace elements in marine ecosystems as our results provide information on its capacity to bioaccumulate these elements. This is one of the key characteristics of a typical bioindicator of aquatic pollutants.

Trace metal accumulation in seagrass and saltmarsh ecosystems of India: comparative assessment and bioindicator potential

Coastal macrophytes serve as bioindicators of coastal trace metal contamination. In this study, trace metal levels in India's seagrass and saltmarsh ecosystems were assessed for their suitability as bioindicators of metal contamination. Trace metal accumulation and bioindicator potential of both seagrasses and saltmarshes were found to be metal and species-specific. Higher concentrations of Cu, Fe, Mg and Mn were found in the tissues of seagrasses, while saltmarshes showed higher accumulation of Cd, Cr, Hg, Ni, Pb and Zn. The leaves of seagrasses are suitable bioindicator of metals in the water column, while the roots and rhizomes of saltmarshes/seagrasses are suitable bioindicators of metals in the sediment. This study proposes the development of a monitoring network using seagrasses and saltmarss as model organisms for short and long-term monitoring of coastal metal contamination. Determining the phytotoxic levels of trace metals in seagrasses and saltmarsh is important for monitoring plant die-offs and loss.

Phragmites australis as a dual indicator (air and sediment) of trace metal pollution in wetlands - the key case of Flix reservoir (Ebro River)

Evaluation of trace metal pollution in an environmentally complex context may require the use of a suite of indicators. Common reed, Phragmites australis, is a well-known biomonitor of sediment pollution. Here, we show its potential for also assessing air pollution. The plant panicles, holding silky hairs with high surface to volume ratio, are appropriate collectors of atmospheric contaminants, which perform independently from root bioconcentration. We applied the dual value of common reed as an indicator of trace metal pollution to the case of a chlor-alkali plant in the Ebro river bank (Spain). This factory had historically damped waste to the shallow Flix reservoir. Extensive common reed meadows are growing on the top of the waste, in a nearby nature reserve across the reservoir and a meander immediately downriver. Three replicated individuals from a total of 11 sites were sampled, and the trace metal content measured in the main plant compartments (roots, rhizomes, stems, leaves, and panicles). Panicles and roots showed a much larger concentration of trace metals than the other plant compartments. Levels of Hg, Cu, and Ni were markedly higher in panicles at the factory and nearby points of the reserve and lowered at the meander. In contrast, Cd, Zn, and Mn in roots increased from the factory to the meander downriver. We conclude that panicles show recent (less than a year) airborne pollution, whereas roots indicate the long-term transport of pollutants from the waste in the shoreline of the factory to downriver sedimentation hotspots, where they become more bioavailable than in the factory waste. The Hg spatial pattern in panicles agree with air measurements in later years, therefore, confirming the panicles suitability for assessing airborne pollution and, consequently, Phragmites as a potential dual biomonitor of air and sediments.

How polluted are cities in central Europe? - Heavy metal contamination in Taraxacum officinale and soils collected from different land use areas of three representative cities

The level of environmental contamination can vary according to different types of land use. The aim of the present study was to determine the relations among Cd, Pb, Ni and Cr content in plants (Taraxacum officinale) and soils for 10 types of land use in the urban areas of representative cities for central Europe region (Warsaw, Poznan and Wroclaw in Poland). Descriptive statistical analysis, as well as cluster analysis and principal component analysis, heatmaps and Andrews curves, was performed to identify relations between HMs and land use, as well as differences between particular cities. The investigations revealed variation among sites, plant organs and cities. The content (mg kg^-1 DW) in soils, roots and leaves for Cd varied between 0.4 and 3.6, 0.4-2.8 and 0.5-3.9, Cr ranged between 23.2 and 40.6, 14.0-26.1 and 15.8-24.8, Ni varied between 2.1 and 13.2, 0.2-42.1 and 0.0-3.9, while Pb varied between 27.0 and 231.5, 4.3-34.2 and 3.0-9.5, respectively. It was possible to note some tendencies. Nickel was the element with the highest content in the roots (up to 42.1 mg kg^-1 DW) in comparison to leaves and soils and the highest bioaccumulation factor (up to 15.0). This means that the main source of Ni might be contamination of the soil. The cluster analysis of standardized HM levels in leaves revealed that cadmium is a different from the other three elements, which might be related to the translocation factor, for which this element was found to have the highest levels at many sites.

Urban Allotment Gardens for the Biomonitoring of Atmospheric Trace Element Pollution

This study evaluates the results of the characterization of air pollution in urban green areas using edible plants. To this purpose, we examined the effect of location (i.e., three different levels of pollution), substrate (peat moss and vermiculite), and plant species (oilseed rape [ L.] and kale [ L.]) on the accumulation of trace elements on leaves. A total of 36 samples of unwashed leaves were digested with HNO-HO and analyzed for 27 elements by inductively coupled plasma mass spectrometry. Considering the location, plants exposed next to the road showed higher contents of traffic-related elements, and additionally, outdoors samples were enriched in marine aerosol ions. Cadmium and Pb concentrations did not exceed the European legal maximum levels for vegetables, so their consumption would be safe for human health. Results support the hypothesis that edible plants such as kale and rapeseed could be used as bioindicators of atmospheric pollution.

Perspectives on using marine species as bioindicators of plastic pollution

The ever-increasing level of marine pollution due to plastic debris is a globally recognized threat that needs effective actions of control and mitigation. Using marine organisms as bioindicators of plastic pollution can provide crucial information that would better integrate the spatial and temporal presence of plastic debris in the sea. Given their long and frequent migrations, numerous marine species that ingest plastics can provide information on the presence of plastic debris but only on large spatial and temporal scales, thus making it difficult to identify quantitative correlations of ingested plastics within well-defined spatio-temporal patterns. Given the complex dynamics of plastics in the sea, the biomonitoring of marine plastic debris should rely on the combination of several bioindicator species with different characteristics that complement each other. Other critical aspects include the standardization of sampling protocols, analytical detection methods and metrics to evaluate the effects of ingested plastics in marine species.

Seagrass Halophila stipulacea: Capacity of accumulation and biomonitoring of trace elements

This study aimed to shed further light on the capacity of the seagrass Halophila stipulacea to accumulate and biomonitor the elements As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, and Zn, present in water and sediments. Results showed that the organs of H. stipulacea accumulate different levels of trace elements, whose concentrations decrease mainly in the order of roots>rhizomes>leaves. The seagrass H. stipulacea showed levels of trace elements similar to those found in other Mediterranean seagrasses, e.g. Posidonia oceanica and Cymodocea nodosa. This study showed that H. stipulacea could act as a promising bioindicator of several elements, present in sediments, including As, Cd, Cu, Mn, Ni and Zn.

Trace elements in Mediterranean seagrasses and macroalgae. A review

This review investigates the current state of knowledge on the levels of the main essential and non-essential trace elements in Mediterranean vascular plants and macroalgae. The research focuses also on the so far known effects of high element concentrations on these marine organisms. The possible use of plants and algae as bioindicators of marine pollution is discussed as well. The presence of trace elements is overall well known in all five Mediterranean vascular plants, whereas current studies investigated element concentrations in only c. 5.0% of all native Mediterranean macroalgae. Although seagrasses and macroalgae can generally accumulate and tolerate high concentrations of trace elements, phytotoxic levels are still not clearly identified for both groups of organisms. Moreover, although the high accumulation of trace elements in seagrasses and macroalgae is considered as a significant risk for the associated food webs, the real magnitude of this risk has not been adequately investigated yet. The current research provides enough scientific evidence that seagrasses and macroalgae may act as effective bioindicators, especially the former for trace elements in sediments, and the latter in seawater. The combined use of seagrasses and macroalgae as bioindicators still lacks validated protocols, whose application should be strongly encouraged to biomonitor exhaustively the presence of trace elements in the abiotic and biotic components of coastal ecosystems.

Development of polyethyleneimine-loaded core-shell chitosan hollow beads and their application for platinum recovery in sequential metal scavenging fill-and-draw process

Polyethyleneimine (PEI)-loaded chitosan hollow beads (CHBs) were fabricated through the ionotropic gelation process using sodium tripolyphosphate (TPP) as a counter polyanion. The CHBs were loaded with hydrophilic PEI in pre- and/or post-loading methods. Hence, the sorbent could possess a large number of amine groups which were able to function as the binding sites to recover platinum metal ions. The enhancement of the amine groups was confirmed by Fourier transform infrared spectroscopy (FTIR). Isotherm and kinetic studies were carried out to evaluate the sorption performance of the sorbents. The maximum Pt(IV) uptake by the PEI-loaded CHBs was estimated to be 815.2±72.6mg/g, which was much higher than that of a commercial ion exchange resin, Lewatit^® MonoPlus TP214 (330.2±16.6mg/g). A sequential metal scavenging fill-and-draw process was operated using the PEI-loaded CHBs sorbents for ten cycles and the Pt(IV) recovery efficiency was kept above 97.4% even after the last cycle. These results indicated that the ionic polymer-loaded hydrogel hollow beads can be a novel platform to design high-performance sorbents able to recover and/or scavenge anionic precious metal ions even from trace metal solutions.

Probability of foliar injury for Acer sp. based on foliar fluoride concentrations

Fluoride is considered one of the most phytotoxic elements to plants, and indicative fluoride injury has been associated over a wide range of foliar fluoride concentrations. The aim of this study was to determine the probability of indicative foliar fluoride injury based on Acer sp. foliar fluoride concentrations using a logistic regression model. Foliage from Acer nedundo, Acer saccharinum, Acer saccharum and Acer platanoides was collected along a distance gradient from three separate brick manufacturing facilities in southern Ontario as part of a long-term monitoring programme between 1995 and 2014. Hydrogen fluoride is the major emission source associated with the manufacturing facilities resulting with highly elevated foliar fluoride close to the facilities and decreasing with distance. Consistent with other studies, indicative fluoride injury was observed over a wide range of foliar concentrations (9.9-480.0 μg F^- g^-1). The logistic regression model was statistically significant for the Acer sp. group, A. negundo and A. saccharinum; consequently, A. negundo being the most sensitive species among the group. In addition, A. saccharum and A. platanoides were not statistically significant within the model. We are unaware of published foliar fluoride values for Acer sp. within Canada, and this research provides policy maker and scientist with probabilities of indicative foliar injury for common urban Acer sp. trees that can help guide decisions about emissions controls. Further research should focus on mechanisms driving indicative fluoride injury over wide ranging foliar fluoride concentrations and help determine foliar fluoride thresholds for damage.

Assessment of palladium footprint from road traffic in two highway environments

Palladium (Pd) is an emerging eco-toxic pollutant from vehicle catalytic converters, emitted worldwide for more than two decades. Nowadays, the spatial extent of Pd fallout is growing along roads, but its subsequent fate in neighboring terrestrial ecosystems has not been extensively addressed yet. Two sites representative of contrasted natural environments (field, forest) but located under similar ambient conditions were selected to isolate and analyze the specific impact of vehicular Pd, along highway A71, France. Pd impregnation was assessed along 200-m-long transects perpendicular to the highway. Contents were measured in soils, earthworms, plant communities of the right of way (ROW), and the neighboring field (crop weeds), as well as in a moss, and bramble and ivy leaves in the forest. The direct impact of Pd fallouts appears to be confined in the grassy verge of the highway: ROW soils ([Pd] = 52-65 ng g(-1)), earthworms ([Pd] = 18-38 ng g(-1)), and plant community ([Pd] = 10-23 ng g(-1)). Pd footprint is pointed out by the accumulation index calculated for earthworms and plant communities even though transfer coefficients indicate the absence of bioaccumulation (TCs < 1). An indirect longer range transfer of Pd is identified, induced by hydric transport of organic matter.