Comparative analysis of heavy metal accumulation and bioindication in three seagrasses: Which species is more suitable as a bioindicator?

Trace metal pollution gradients in a tropical seagrass ecosystem

Trace metals are one of the most serious pollutants in tropical seagrass meadows given their persistence and toxicity. Whereas quantity is frequently measured, there is no information on the spatial extent of metal pollution in these systems. Here, we use an island in Indonesia (Barang Lompo) as a model system to study the impact radius of two major and eight trace metals in sediment and seagrass leaves. We provide evidence for exponential decay in both the metal pollution index and concentrations of most metals with increasing distance from the island (k = -0.01 to -0.08 m-1). Consequently, there is an impact radius of approximately 100 m around the island. The comparative analysis of both seagrass species further revealed interspecific differences in metal loads. This study highlights the importance of assessing the spatial extent of metal pollution in addition to its quantity.

Comparison of metals in eelgrass (Zostera marina L.) and the environment across the North Pacific Ocean: Environmental processes drive source delivery

Seagrass beds play a critical role in biodiversity maintenance, serving as nursery habitats for fisheries, and aiding in carbon and sediment sequestration in the ecosystem. These habitats receive dissolved and particulate material inputs, like nutrients and heavy metals, affecting both plant health and the ecosystem. Eelgrass (Zostera marina L.), sediments, and water were randomly collected at twenty sites along the temperate North Pacific coasts of Asia and North America to assess heavy metals concentrations (Cr, Cu, Zn, Cd, and Pb). This aimed to understand heavy metal distribution and accumulation patterns in eelgrass tissues, revealing crucial factors influencing metal accumulation. The sampling included various areas, from pristine marine reserves to human-influenced zones, covering industrial, agricultural, and aquaculture regions, enabling a thorough analysis. This study's uniqueness lies in comparing heavy metal distributions in eelgrass tissues with sediments, uncovering unique accumulation patterns. Aboveground eelgrass tissues mainly accumulated Cd, Zn, and Cu, while belowground tissues stored Cr and Pb. Aboveground eelgrass tissues proved reliable in indicating Cd and Pb concentrations in sediments. However, the correlation between Cu, Zn, and Cr in eelgrass tissues and environmental concentrations seemed less direct, requiring further investigation into factors affecting metal accumulation in seagrass. Human activities are probable major contributors to heavy metal presence in Asian marine environments, whereas oceanographic processes serve as primary metal sources in North American Pacific estuaries. Critical discoveries emphasize the necessity for ongoing research on phytotoxic thresholds and in-depth studies on the complex connections between seagrass physiology and environmental metal concentrations. Understanding these dynamics is crucial for evaluating the broader impact of heavy metal pollution on coastal ecosystems and developing effective conservation measures.

Identification of anthropogenic source of Pb and Cd within two tropical seagrass species in South China: Insight from Pb and Cd isotopes

Seagrass beds are susceptible to deterioration and heavy metals represent a crucial impact factor. The accumulation of heavy metal in two tropical seagrass species were studied in South China in this study and multiple methods were used to identify the heavy metal sources. E. acoroides (Enhalus acoroides) and T. hemperichii (Thalassia hemperichii) belong to the genus of Enhalus and Thalassia in the Hydrocharitaceae family, respectively. Heavy metal concentrations in the two seagrasses followed the order of Cr > Zn > Cu > Ni > As > Pb > Co > Cd based on the whole plant, and their bioconcentration factors were 31.8 ± 29.3 (Cr), 5.7 ± 1.3 (Zn), 7.0 ± 3.8 (Cu), 3.0 ± 1.9 (Ni), 1.2 ± 0.3 (As), 1.7 ± 0.9 (Pb), 9.1 ± 11.1 (Co) and 2.8 ± 0.6 (Cd), indicating the intense enrichment in Co and Cr within the two seagrasses. The two seagrasses were prone to accumulate all the listed heavy metals (except for As in E. acoroides), especially Co (BCFs of 1124) and Cr (BCFs of 2689) in the aboveground parts, and the belowground parts of both seagrasses also accumulated most metals (BCFs of 27) excluding Co and Pb. The Pb isotopic ratios (mean 208Pb/204Pb, 207Pb/204Pb and 206Pb/204Pb values of 38.2054, 15.5000 and 18.3240, respectively) and Cd isotopic compositions (δ114/110Cd values ranging from -0.09‰ to 0.58‰) within seagrasses indicated the anthropogenic sources of Pb and Cd including coal combustion, traffic emissions and agricultural activities. This study described the absorption characteristics of E. acoroides and T. hemperichii to some heavy metals, and further demonstrated the successful utilization of Pb and Cd isotopes as discerning markers to trace anthropogenic origins of heavy metals (mainly Pb and Cd) in seagrasses. Pb and Cd isotopes can mutually verify and be helpful to understand more information in pollution sources and improve the reliability of conclusion deduced from concentrations or a single isotope.

Transcriptome Analysis Reveals the Stress Tolerance Mechanisms of Cadmium in Zoysia japonica

Cadmium (Cd) is a severe heavy metal pollutant globally. Zoysia japonica is an important perennial warm-season turf grass that potentially plays a role in phytoremediation in Cd-polluted soil areas; however, the molecular mechanisms underlying its Cd stress response are unknown. To further investigate the early gene response pattern in Z. japonica under Cd stress, plant leaves were harvested 0, 6, 12, and 24 h after Cd stress (400 μM CdCl2) treatment and used for a time-course RNA-sequencing analysis. Twelve cDNA libraries were constructed and sequenced, and high-quality data were obtained, whose mapped rates were all higher than 94%, and more than 601 million bp of sequence were generated. A total of 5321, 6526, and 4016 differentially expressed genes were identified 6, 12, and 24 h after Cd stress treatment, respectively. A total of 1660 genes were differentially expressed at the three time points, and their gene expression profiles over time were elucidated. Based on the analysis of these genes, the important mechanisms for the Cd stress response in Z. japonica were identified. Specific genes participating in glutathione metabolism, plant hormone signal and transduction, members of protein processing in the endoplasmic reticulum, transporter proteins, transcription factors, and carbohydrate metabolism pathways were further analyzed in detail. These genes may contribute to the improvement of Cd tolerance in Z. japonica. In addition, some candidate genes were highlighted for future studies on Cd stress resistance in Z. japonica and other plants. Our results illustrate the early gene expression response of Z. japonica leaves to Cd and provide some new understanding of the molecular mechanisms of Cd stress in Zosia and Gramineae species.

A review of metal contamination in seagrasses with an emphasis on metal kinetics and detoxification

Seagrasses are important foundation species in coastal ecosystems, and they provide food and habitat that supports high biodiversity. However, seagrasses are increasingly subjected to anthropogenic disturbances such as metal pollution, which has been implicated as a significant factor driving seagrass losses. There have been several reviews synthesizing the metal concentrations in seagrasses and evaluating their utility as biomonitors for metal pollution in the coastal environment at the local scale. However, the interpretation of metal data in seagrass biomonitors requires a more mechanistic understanding of the processes governing metal bioaccumulation and detoxification. In this review, the progress and trends in metal studies in seagrasses between 1973 and 2022 were analyzed to identify frontier topics in this field. In addition, we tried to (1) analyze and assess the current status of metal contamination in seagrasses on a global scale by incorporating more metal data from tropical and Indo-Pacific seagrasses, (2) summarize the geochemical and biological factors governing metal uptake and loss in seagrasses, and (3) provide an up-to-date understanding of metals' effects on seagrasses and their physiological responses to metal challenges. This review improves our understanding of the highly variable metal concentrations observed in the field.

Eco-Physiological Responses of Avicennia marina (Forssk.) Vierh. to Trace Metals Pollution via Intensifying Antioxidant and Secondary Metabolite Contents

Mangrove is one of the most precious ecosystems with the greatest losses due to climate change, human activities, and pollution. The objective of this study is to assess the accumulation and distribution of some trace metals (Cu, Cd, Ni, Pb, and Zn) in sediments and Avicennia marina roots and leaves and to discuss the antioxidant potential of A. marina under metallic pollution stress. Sediments, leaf, and root samples of A. marina were collected from five sites along the Red Sea Coast of Egypt. Several ecological pollution indices, including the geo accumulation index (Igeo), contamination factor (CF), pollution load index (PLI), bioconcentration factor (BCF), and translocation factor (TF), were used to assess the pollution load. Cu, Cd, Ni, Pb, and Zn average concentrations in sediments were 167.4, 0.75, 110.65, 39.79, and 220 μg g^-1, respectively, and the average values of these metals in A. marina roots were 44.9, 0.5, 87.96, 39.02, and 54.68 μg g^-1, respectively, while in leaves their concentration were 50.46, 0.5572, 88.24, 40.08, and 56.08 μg g^-1, respectively. The values of the Igeo, CF, and PLI index indicated that location 1 and 5 are moderate-to-heavily contaminated sites. On the other hand, leaves and roots of A. marina grown in polluted locations 1 and 5 showed high accumulation of malondialdehyde (MDA), low chlorophyll a and chlorophyll b contents concomitant with a decrease in total soluble sugars. High total antioxidant capacity was associated with a significant increase in activity levels of antioxidant enzymes (Catalase, Polyphenol oxidase, Polyphenol peroxidase, and Ascorbic acid oxidase), accumulation of secondary metabolites (total phenols, flavonoids, and tannins), and proline and carotenoids content increase. Overall, the present study suggests that the mangrove habitat of the Egyptian Red Sea coast is under the stress of anthropogenic activities, which necessitates a conservation plan to avoid further contamination and protect the unique biota of this distinctive habitat.

Macroalgae for biomonitoring of trace elements in relation to environmental parameters and seasonality in a sub-tropical mangrove estuary

Being a resourceful ecosystem, mangrove estuaries have always been subjected to trace elements (TEs) contamination, and therefore, the biomonitoring approach holds immense potential for surveilling the aquatic environment. To investigate the potentiality of mangrove macroalgae as biomonitors, estuarine water, intertidal-sediment, and macroalgal samples were collected from the Pasur River estuary of Sundarbans mangrove ecosystem, Bangladesh, and afterward studied through Atomic Absorption Spectrometer to quantify the levels of six concerned TEs (Fe, Mn, Zn, Cu, Pb, and Cd). This study utilized the geo-environmental and ecological indices and sediment characterization approaches (sediment quality guidelines-SQGs) for assessing the contamination scenario of the adjacent environment to macroalgae whereas the performance of studied algal groups was evaluated using Bio-contamination factor, Comprehensive bio-concentration index, and Metal accumulation index. Metal occurrence scheme in the water followed the order of Fe > Zn > Mn > Pb > Cd while Fe > Mn > Zn > Cu > Pb > Cd for both sediment and macroalgae. Both Pb and Cd exceeded the guideline limit in estuarine water and the indices approach manifested low to moderate contamination with enrichment from anthropogenic origin of Mn, Zn, and Cu in sediment. Moreover, the SQGs revealed rare biological effects of Cu on an aquatic community. Within algal samples, Chlorophyta contributed the highest biomass production, followed by Phaeophyta and Rhodophyta. Statistical relationship disclosed the influence of environmental variables on TE's accumulation in Chlorophyta. By contrast, hydrochemical's association showed prevalence over the TEs accumulation process for Phaeophyta and Rhodophyta. Bioaccumulation performance analysis revealed that the ability to accumulate TEs in macroalgal groups varied with seasons. Therefore, biomonitoring with macroalgae for the region of interest might require further temporal considerations.

Comparisons of diatoms and fishes as toxic metal bioindicator: a case study of an A-class wetland in northwest Turkey under effect of an intensive paddy cultivation stress

In this research, diatoms as the first step and fishes as the last step of the food chain were compared as toxic metal accumulation bioindicator in an A-class wetland in Turkey. Bioaccumulations of potentially toxic elements (PTEs) were determined in liver, gill and muscle tissues of two commercially consumed fish species Carassius gibelio and Cyprinus carpio and in frustules of epiphytic diatom communities living on submerged macrophytes. Samples were collected seasonally from the Gala Lake, which is among the best stopover habitats of birds migrating between Europe and Africa, considering the paddy harvest period that is a major stress factor for the ecosystem. Also, potential human health risks associated with the consumption of fishes and consumption - dermal contact of diatoms were evaluated both for summer - before paddy harvest (BPH) and autumn - after paddy harvest (APH) periods. As a result of this research, the investigated toxic metal concentrations were increased significantly in diatoms in the APH period, while less significant exchanges were recorded in fishes. The bioaccumulations of PTEs were ranked as follows: Zn > Mn > Se > Cu > B > Cr > Ni > As > Pb > Cd for C. gibelio; Zn > Mn > Se > Cu > B > Cr > As > Ni > Pb > Cd for C. carpio; and Mn > Zn > Se > Pb > B > Ni > Cr > Cu > As > Cd for diatom frustules. Although the HI values in diatoms detected in the APH period were statistically significantly higher (about 1000 times; p < 0.05) than detected in the BPH period, they were less than the limit of 1 in both seasons. However, the HI coefficients of fishes were quite higher than the limit (an average of 23.59 for C. gibelio and 19.18 for C. carpio), which means quite high probable non-carcinogenic health risks for humans. Furthermore, the CR coefficients of Cr, Ni and As in muscle tissues of fishes were considerably higher than the limit of 10-4, which reflects a significant carcinogenic health risk for consumers. The data showed that although the fishes at the top of the food chain bioaccumulate the PTEs in their tissues much higher than the diatoms at the bottom of the food chain, the diatoms are much more sensitive to changes in the environmental conditions than the fishes and they are more effective biological tools as toxic metal accumulation bioindicators.

Multi-leveled insights into the response of the eelgrass Zostera marina L to Cu than Cd exposure

Seagrass beds are recognized as critical and among the most vulnerable habitats on the planet; seagrass colonize the coastal waters where heavy metal pollution is a serious problem. In this study, the toxic effects of copper and cadmium in the eelgrass Zostera marina L. were observed at the individual, subcellular, physiologically biochemical, and molecular levels. Both Cu and Cd stress significantly inhibited the growth and the maximal quantum yield of photosystem II (Fv/Fm); and high temperature increased the degree of heavy metal damage, while low temperatures inhibited damage. The half-effect concentration (EC₅₀) of eelgrass was 28.9 μM for Cu and 2246.8 μM for Cd, indicating Cu was much more toxic to eelgrass than Cd. The effect of Cu and Cd on photosynthesis was synergistic. After 14 days of enrichment, the concentration of Cu in leaves and roots of Z. marina was 48 and 37 times higher than that in leaf sheath, and 14 and 11 times higher than that in rhizome; and the order of Cd concentration in the organs was root > leaf > rhizome > sheath. Heavy metal uptake mainly occurred in the organelles, and Cd enrichment also occurred to a certain extent in the cytoplasm. Transcriptome results showed that a number of photosynthesis-related KEGG enrichment pathways and GO terms were significantly down-regulated under Cd stress, suggesting that the photosynthetic system of eelgrass was severely damaged at the transcriptome level, which was consistent with the significant inhibition of Fv/Fm and leaf yellowing. Under Cu stress, the genes related to glutathione metabolic pathway were significantly up-regulated, together with the increased autioxidant enzyme activity of GSH-PX. In addition, the results of recovery experiment indicated that the damage caused by short-term Cd and Cu stress under EC₅₀ was reversible. These results provide heavy metal toxic effects at multiple levels and information relating to the heavy metal resistance strategies evolved by Z. marina to absorb and isolate heavy metals, and highlight the phytoremediation potential of this species especially for Cd.

Environmental settings of seagrass meadows control rare earth element distribution and transfer from soil to plant compartments

The role of seagrass meadows in the cycling and accumulation of rare earth elements and yttrium (REEY) is unknown. Here, we measured the concentration of REEY in the different compartments of Halodule wrightii (shoots, rhizomes, and roots) and soils in seagrass meadows near sandy beaches, mangroves, and coral reefs in the Todos os Santos Bay, Brazil. We provide data on the accumulation dynamics of REEY in seagrass compartments and demonstrate that plant compartments and soil properties determine accumulation patterns. The ∑REEY in soils were ~1.7-fold higher near coral reefs (93.0 ± 5.61 mg kg^-1) than near mangrove sites (53.9 ± 31.5 mg kg^-1) and were slightly higher than in sandy beaches (81.7 ± 49.1 mg kg^-1). The ∑REEY in seagrasses varied between 35.4 ± 28.1 mg kg^-1 near coral reefs to 59.2 ± 21.3 mg kg^-1 near sandy beaches, respectively. The ∑REE bioaccumulation factor (BAF) was highest in seagrass roots near sandy beaches (BAF = 0.67 ± 0.48). All values of ∑REE translocation are <1, indicating inefficient translocation of REE from roots to rhizome to shoot. PAAS normalized REE was enriched in light REE (LREE) over heavy REE (HREE). The REEY accumulation in Halodule wrightii revealed a low potential of the seagrass to act as a sink for these elements. However, their bioavailability and potential uptake may change with soil properties. Our results serve as a basis for a better understanding of REE biogeochemical cycling and its fate in the marine environment. REE have experienced increased use as they are central to new technologies revealing an urgent need for further investigations of potential impacts on coastal ecosystems.

Nutritional composition, heavy metal content and in vitro effect on the human gut microbiota of Talitrus saltator, an underutilized crustacean from the Atlantic coast

In this study, an undervalued marine crustacean (Talitrus saltator) was characterized in terms of nutritional and heavy metal composition and its potential to affect human gut microbiota. Nutritional analysis of this crustacean revealed that it complies with the criteria established in European legislation to include nutritional claims in their labeling, such as "source of fiber," "low in fat," "low in sugars" and "high in protein." The analysis of the heavy metal content did not reveal any risk derived from the presence of Cd, Hg, or Pb, whereas essential metals contained in 100 g exceeded the minimum daily requirements recommended in Europe for Zn (19.78 mg/kg), Cu (2.28 mg/kg), and Fe (32.96 mg/kg). Using an in vitro system, the effect of T. saltator on the human colonic microbiota shows some beneficial effects, such as fermentation-maintained populations of Bifidobacterium or Lactobacillus, did not increase Firmicutes phylum counts, decreased the Firmicutes/Bacteroidetes ratio, and stimulated 11 metabolic pathways with respect to baseline. These results are unusual in a high protein content-food. However, negative effects were also found in gut microbiota relative proportions, such as an increase in the Proteobacteria phylum and especially some opportunistic bacteria from this phylum, probably due to the antimicrobial effect of chitin on other groups more sensitive to its effect. This work shows for the first time the effect of T. saltator on human colonic microbiota using and in vitro system. The presence of chitin in its composition could provide some beneficial effects by modulating the microbiota, but as T. saltator is a high-protein food, more studies should be carried out showing these benefits.

Assessment of Cd bioavailability using chemical extraction methods, DGT, and biological indicators in soils with different aging times

Total cadmium (Cd) cannot be used to accurately assess the ecological risk of Cd pollution in soil. Currently there is no universally recognized method to evaluate Cd bioavailability in soil. In this study, chemical extraction methods, diffusive gradients in thin films (DGT) and bioindicator methods were used to evaluate Cd bioavailability in soils with the same properties but different aging times. Results indicate that aging decreased the Cd bioavailability in soil and its toxicity to barley. This was primarily due to a decrease in the proportion of ion-exchangeable Cd. Correlation analyses were conducted on the Cd bioavailable content obtained via the soil extraction methods and the toxicity effect of barley. Results showed that the order of the minimum value of the linear regression determination coefficient (R²) of chemical extraction methods and DGT was as follows: DGT-Cd (0.7385, p < 0.05) > total Cd (0.6931, p < 0.05) > acetic acid-Cd (0.6078) > ion-exchangeable Cd (0.5933) > DTPA-Cd (0.5842) > CaCl₂-Cd (0.4980) > water-soluble Cd (0.4602). The order of minimum value of R² of biological indicators of barley was integrated biomarker response (IBR) (0.8501, p < 0.01) > length (0.6492) > dry weight (0.6320) > fresh weight (0.4980) > Cd concentration (0.4602). The root is more suitable for indicating the plant uptake and accumulation of Cd in soil. Meanwhile, the shoot can effectively evaluate the toxic effect of Cd stress on plants. DGT is more suitable to reflect Cd bioavailability to barley compared to chemical extraction methods, Furthermore, it can be used to evaluate stable polluted soil with longer aging time. In the study of the bioavailability of heavy metals in soil, IBR can be used as a reliable reference index to contribute to the comprehensive evaluation of metal bioavailability in addition to considering plant uptake.

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.

Spatial and seasonal metal variation, bioaccumulation and biomonitoring potential of halophytes from littoral zones of the Karachi Coast

Coastal wetlands primarily serve as natural sinks of trace metals and their importance for phytoremediation is well known at global level. There are some reports on trace metal availability in soil sediments of the Karachi coast but studies on accumulation and translocation to harvestable (Shoot) parts among halophytes of the littoral zones have not been conducted. Hence, phytoremediation potential of six naturally existing halophytes (Aeluropus lagopoides, Arthrocnemum macrostachyum, Atriplex stocksii, Avicennia marina, Cressa cretica and Suaeda fruticosa) was assessed for cleaning metal (Mn, Zn, Pb and Cr) polluted soils of the Karachi coast. Seasonal (winters, pre and post-monsoon summers) and spatial (three littoral zones: viz., site - I: Sandspit, site - II: Do-Dariya/Clifton and site - III: Korangi creek) variations in soil and plant metals of the Karachi coast were studied. Soil Zn, Pb and Cr were generally higher in winters, Mn and organic matter in summers (7-11%) while pH values ranged between 7.15 and 7.5 in all seasons at site - III. All tested species had potential for cleaning Pb through their harvestable part (shoots) with A. stocksii as prominent candidate (16 mg kg^-1) at site - I. Cressa cretica emerged as exclusive candidate for Zn phytoremediation (96 mg kg^-1) at site - I, while S. fruticosa, A. macrostachyum and A. lagopoides showed bioaccumulation in pre-monsoon summers at site II. Aeluropus lagopoides with higher Mn in post monsoon summers (62 at site - III and 53 mg kg^-1 at site - II) and Cr (7.1 mg kg^-1 at site - II and 14 mg kg^-1 at site - III) appeared exclusive bioindicator with potential of for cleaning all metals (Mn, Zn, Pb and Cr) at different sites. Metal bioaccumulation at study sites appeared species specific and varied seasonally among tested halophytes.

Seasonal variation of heavy metals in seagrasses along Thondi coast, Palk Bay, India

The present study deals with the bioaccumulation of heavy metals in different seagrass species (Syringodium isoetifolium, Halodule pinifolia, Cymodocea serrulata, Halophila ovalis) along Thondi coast and decaying seagrass offshore. Heavy metal concentrations in the seagrass samples were analysed during the period of April 2019 to March 2020 using atomic absorption spectrophotometry. Among the heavy metals assayed, the level of manganese was higher (15.62 ± 1.02 mg/kg) and chromium was the least metal observed (0.002 mg/kg). One-way ANOVA revealed significantly higher level of heavy metals in summer season, while it gradually decreased through pre-monsoon to monsoon season (P < 0.05). Cadmium and chromium were observed to be below detectable levels in the seagrass species. S. isoetifolium was found to bioaccumulate higher levels of heavy metals than the other seagrass species studied. Elucidation of heavy metal levels in the dead and decayed seagrass offshore revealed a higher level of heavy metals than live seagrass species.

Trophic transfer of heavy metals through aquatic food web in a seagrass ecosystem of Swan Lagoon, China

The Swan Lagoon is a national nature reserve and an important spawning ground in China. In this study, we evaluated the concentration of heavy metals (Cd, Cr, Cu, Pb, and Zn) in different aquatic organisms (aquatic plants, crustaceans, mollusks, and fish), in order to examine their trophic transfer in food web. The results showed that the concentrations of Cd, Cu, Pb, and Zn were considerably higher in mollusks, whereas Cr concentrations were significantly higher in aquatic plants than in mollusks, crustaceans, and fish (p < 0.01). Heavy metals exhibit different patterns of trophic transfer in food web. Cd, Cr, Cu, and Pb tended to be efficiently biodiluted with increasing trophic levels in food web (trophic magnification factor, TMF < 1; p < 0.05). The concentration of Zn increased with increasing trophic level; however, it exhibited a TMF of only 1.03, and was not significantly correlated with δ¹⁵N (p > 0.05), indicating neither biomagnification or biodilution in the food web.

Programmed responses of different life-stages of the seagrass Ruppia sinensis to copper and cadmium exposure

Seagrass meadows are recognized as crucial and are among the most vulnerable habitats worldwide. The aquatic plant genus Ruppia is tolerant of a wide salinity range, and high concentrations of trace metals. However, the tolerance of its early life stages to such trace metal exposure is unclear. Thus, the current study investigated the trace metal-absorbing capacity of three different life-history stages of Ruppia sinensis, a species that is widely distributed in China, by observing toxic symptoms at the individual, subcellular, and transcription levels. The seedling period was the most vulnerable, with visible toxic effects at the individual level in response to 50 μM copper and 500 μM cadmium after 4 days of exposure. The highest concentrations of trace metals occurred in the vacuoles and cytoplasmic structures of aboveground tissues. Genes related to signal identification and protein processing were significantly downregulated after 4 days of exposure to copper and cadmium. These results provide information relating to the strategies evolved by R. sinensis to absorb and isolate trace elements, and highlight the phytoremediation potential of this species.

Heavy metal concentrations in the macroalgae, seagrasses, mangroves, and crabs collected from the Tuticorin coast (Hare Island), Gulf of Mannar, South India

This study investigates the concentration of heavy metals in the macroalgae, seagrasses, mangroves, and crabs collected from Hare Island, Gulf of Mannar Marine Biosphere Reserve. The concentration of heavy metals ranged between 0.06 (Hg)-259 (Fe) μg/g in macroalgae, 0.09 (Pb)-377 (Fe) μg/g in seagrasses, 0.112 (Cd)-122 (Fe) μg/g in mangroves, and 0.11 (Cd) -240 (Fe) μg/g in crabs. The levels of heavy metals in the analyzed samples were found below the maximum residual limits (MRLs) prescribed by various National and International agencies. The result suggests that exposure to the analyzed metals through macroalgae consumption does not cause potential health risks to consumers (target hazard quotient (THQ), estimated exposure dose (EED), and hazard index (HI) <1). Hence, this study concludes that macroalgae that grow in the Gulf of Mannar regions are safe for human consumption and are suitable to prepare food supplements and bioceutical products.

Seagrass vegetation affect the vertical organization of microbial communities in sediment

Seagrasses represent high primary productivity and provide important ecosystem services to the marine environment. Seagrass-associated microbial communities are playing essential ecological functional roles in biogeochemical cycles. However, little is known about the effect of seagrass vegetation on microbial communities in sediment. In the present study, the sediment cores of seagrass bed (dominated by Zostera japonica and Zostera marine) and degradation area in Swan Lake (China) were sampled; then, biogeochemical parameters were analyzed, and microbial community composition was investigated by using high-throughput sequencing of the 16S rRNA gene. The results showed that the presence of seagrass could lead to a decrease in the richness and diversity of the microbial community. In the vertical direction, a pronounced shift from Proteobacteria-dominated upper layers to Chloroflexi and Crenarchaeota-dominated deep layers in all sediment cores were observed. Besides, Bathyarchaeia is more abundant at degradation area, while Vibrionaceae, Sulfurovum and Lokiarchaeial overrepresent at the seagrass bed area. Vibrionaceae was abundant in the rhizosphere of Z. marina and Z. japonica, and the proportions reached 84.45% and 63.89%, respectively. This enrichment of Vibrio spp. may be caused by the macrobenthic species near the seagrass rhizosphere, and these Vibrio spp. reduced the diversity and stability of microbial community, which may lead to the degradation of seagrass. This study would provide clues for the distribution patterns and niche preferences of seagrass microbiome. The conservation strategy of seagrass would be further elucidated from the perspective of the microbiome.

Influence of variable salinity and low light on copper accumulation in the potential seagrass bioindicator, Zostera muelleri

Utilising a potential coastal trace element bioindicator requires understanding its accumulation patterns under varying environmental scenarios. The present study aimed to understand, from two experiments, the influence and effect of low light (15.3 μmol photons m^-2 s^-1) and variable salinity (normal 36 and reduced 29) on Zostera muelleri accumulating variable Cu concentrations (control, low 5 μg L^-1 and high 50 μg L^-1) in order to determine its capability as a potential trace element bioindicator. Initial (24 h) leaf Cu concentration was in proportion to exposure Cu concentrations, irrespective of manipulated environmental conditions, suggesting passive accumulation. Final below-ground Cu concentrations, during the low light experiment, significantly increased over time, suggesting active Cu accumulation. Zostera muelleri leaves could act as a Cu bioindicator at times of reduced light and salinity while further interpretation is required of below-ground Cu concentrations. It is recommended that Z. muelleri could be utilised as a Cu bioindicator.

Coastal bays and coral cays: Multi-element study of Chelonia mydas forage in the Great Barrier Reef (2015-2017)

There is increasing interest in understanding potential impacts of complex pollutant profiles to long-lived species such as the green sea turtle (Chelonia mydas), a threatened megaherbivore resident in north Australia. Dietary ingestion may be a key exposure route for metals in these animals and marine plants can accumulate metals at higher concentrations than the surrounding environment. We investigated concentrations of 19 metals and metalloids in C. mydas forage samples collected from a group of offshore coral cays and two coastal bays over a period of 2-3 years. Although no samples exceeded sediment quality guidelines, coastal forage Co, Fe, and V concentrations were up to 2-fold higher, and offshore forage Sr concentrations were ~3-fold higher, than global seagrass means. Principal Component Analysis differentiated coastal bay from coral cay forage according to patterns consistent with underlying terrigenous-type or marine carbonate-type sediment geochemistry, such that coastal bay forage was higher in Fe, Co, Mn, Cu, and Mo (and others) but forage from coral cays was higher in Sr and U. Forage from the two coastal bays was differentiated according to temporal variation in metal profiles, which may be associated with a more episodic sediment disturbance regime in one of the bays. For all study locations, some forage metal concentrations were higher than previously reported in the global literature. Our results suggest that forage metal profiles may be influenced by the presence of some metals in insoluble forms or bound to ultra-fine sediment particles adhered to forage surfaces. Metal concentrations in Great Barrier Reef forage may be present at levels higher than expected from the global seagrass literature and appear strongly influenced by underlying sediment geochemistry.

A Machine Learning Approach in Analyzing Bioaccumulation of Heavy Metals in Turbot Tissues

Metals are considered to be one of the most hazardous substances due to their potential for accumulation, magnification, persistence, and wide distribution in water, sediments, and aquatic organisms. Demersal fish species, such as turbot (Psetta maxima maeotica), are accepted by the scientific communities as suitable bioindicators of heavy metal pollution in the aquatic environment. The present study uses a machine learning approach, which is based on multiple linear and non-linear models, in order to effectively estimate the concentrations of heavy metals in both turbot muscle and liver tissues. For multiple linear regression (MLR) models, the stepwise method was used, while non-linear models were developed by applying random forest (RF) algorithm. The models were based on data that were provided from scientific literature, attributed to 11 heavy metals (As, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, Ni, Zn) from both muscle and liver tissues of turbot exemplars. Significant MLR models were recorded for Ca, Fe, Mg, and Na in muscle tissue and K, Cu, Zn, and Na in turbot liver tissue. The non-linear tree-based RF prediction models (over 70% prediction accuracy) were identified for As, Cd, Cu, K, Mg, and Zn in muscle tissue and As, Ca, Cd, Mg, and Fe in turbot liver tissue. Both machine learning MLR and non-linear tree-based RF prediction models were identified to be suitable for predicting the heavy metal concentration from both turbot muscle and liver tissues. The models can be used for improving the knowledge and economic efficiency of linked heavy metals food safety and environment pollution studies.

Heavy metals accumulation in seagrasses collected from Palk Bay, South-eastern India

Metals such as Cd, Pb, Cu and Zn were analysed in five seagrass species from five locations of the Palk Bay coast of south-eastern India. The maximum Cd concentration (2.83 ± 0.08 μg g^-1) was recorded in Syringodium isoetifolium on the Mallipattinam coast in the post-monsoon season, and the Cu (29.54 ± 1.03 μg g^-1) in Enhalus acoroides of the Thondi coast during monsoon season. The maximum concentrations of Pb (3.12 ± 0.14 μg g^-1) and Zn (52.66 ± 0.88 μg g^-1) were observed in S. isoetifolium and Cymodoceae rotundata on the Devipattinam and Karangadu coasts, respectively, during the monsoon season. The metal concentrations obtained in different seagrass species varied significantly among species, and no clear monsoon season had a clear effect on the accumulation of heavy metals in the investigated seagrass species. S. isoetifolium has higher capacity for Cd and Pb accumulation than other tested seagrass species.

Comparative assessment of heavy metal accumulation and bio-indication in coastal dune halophytes

This study aimed at assessing heavy metals (Fe, Mn, Zn, Cu, Cr and Pb) in four perennial halophytes (viz. Heliotropium bacciferum, Halopyrum mucronatum, Ipomoea pes-caprae and Salsola imbricata) growing at two sites on the Karachi coast. Site - II, closer to the Industrial area had higher bioavailability as well as translocation factor (TF) for most of the heavy metals and Na⁺ where soil sediments had lower pH (approximately 7.5), higher salinity (EC) and organic matter (OM). Site - I which was far from Industrial area had comparatively higher bio-concentration factor (BCF) and lower TF for metal ions and soil pH of 8.1-9. Metal accumulation in plants was both site and species specific. Extractable concentration of shoot Pb in all tested halophytes was above normal of the threshold values (i.e., >0.3 mg kg^-1) while Mn (<50 mg kg^-1) and Cu (<40 mg kg^-1) were within permissible limits. Salsola imbricata had highest Na⁺ at both sites (site - I = 73; site - II = 98 mg kg^-1) with and 10 mg kg^-1 extractable shoot Pb at site - I. Ipomea pes-caprae also accumulated shoot Pb higher than normal (site - I = 3.3; site - II = 0.8 mg kg^-1) with lowest Na⁺ content. Heliotropium bacciferum had higher extractable Pb (site - I = 10.5; II = 2.75) with >20 mg kg^-1 Na⁺ in shoot while maintaining > 1 TF for Pb, Cu, Mn and Zn at site - I and all tested metals at site - II. Halopyrum mucronatum had highest shoot Fe (644 mg kg^-1), Zn (63 mg kg^-1) and Cr (9.2 mg kg^-1) at site - II and above threshold values of Pb at both sites (site - I = 8.2; site - II = 2.5 mg kg^-1) which makes this species an ideal bio-indicator candidate while other species could be potentially used for Pb phytoremediation.

Foraminifera as bioindicators of water quality: The FoRAM Index revisited

Coral reefs worldwide are degrading at alarming rates due to local and global stressors. There are ongoing needs for bioindicator systems that can be used to assess reef health status, the potential for recovery following destructive events such as tropical storms, and for the success of coral transplants. Benthic foraminiferal shells are ubiquitous components of carbonate sediment in reef environments that can be sampled at minimal cost and environmental impact. Here we review the development and application of the FoRAM Index (FI), which provides a bioindicator metric for water quality that supports reef accretion. We outline the strengths and limitations of the FI, and propose how it can be applied more effectively across different geographical regions.

A living plant cell-based biosensor for real-time monitoring invisible damage of plant cells under heavy metal stress

Heavy metals inevitably cause invisible or visible damage to plants, leading to significant economic losses. Therefore, it is necessary to develop a method for timely monitoring the damage of plants under the stress of heavy metals. Here, vitronectin-like proteins (VN) on the surface of plant cells is as an important biomarker for monitoring damage of plants under the stress of heavy metals. A living plant cell-based biosensor is constructed to monitor invisible damage of plant cells induced by cadmium [Cd(II)] or lead [Pb(II)]. To fabricate this sensor, l-cysteine was first modified on the glassy carbon electrode followed by the modification of anti-IgG-Au antibody. Then, the living plant cells, incubated with the anti-VN, were modified onto the electrode. The sensor worked by determining the change in electrochemical impedance. Cd(II) and Pb(II) was detected in the linear dynamic range of 45-210 and 120-360 μmol·L^-1, respectively. And the detection limit of Cd(II) and Pb(II) of this biosensor was 18.5 nmol·L^-1 [with confidence interval (95%) 18.4-18.6 nmol·L^-1] and 25.6 nmol·L^-1 [with confidence interval (95%) 25.4-25.8 nmol·L^-1], respectively. In both Arabidopsis and soybean, when the content of VN increased by about 20 times under the stress of Cd(II) or Pb(II), which means when the electron-transfer resistance increased by 35%, chlorophyll content showed significant decrease about 17%. Therefore, by establishing a quantitative relationship among the content of biomarker, the electron-transfer resistance and chlorophyll content in plant cells, the invisible damage of plants under the stress of heavy metals was detected. These results can provide a reference method for early-onset warning systems for heavy metal pollution in the environment.

Trace elements in the seagrass Posidonia oceanica: Compartmentation and relationships with seawater and sediment concentrations

Seagrasses are employed to assess trace element levels in seawater and sediments; however, their capacity as bioindicators of trace elements in seawater has been recently questioned, due to the scarcity of a significant seagrass-seawater relationship. In the aim to provide an insight into trace element accumulation in the seagrass Posidonia oceanica, Cd, Co, Cr, Cu, Ni and Pb concentrations in seawater, sediments, and several seagrass compartments (adult leaf blades, intermediate leaf blades, adult leaf sheaths, juvenile leaves, orthotropic rhizomes, plagiotropic rhizomes, and roots of plagiotropic rhizomes) from the coasts of Thrace, Greece were determined. Uni- and multivariate data analyses were applied. A comparison with reported element concentrations revealed that this coastal area can be generally classified as an area of no marked Cd, Co, Cr, Cu, Ni and Pb anthropogenic enrichment. Trace elements showed a non-uniform distribution among seagrass compartments; adult leaf blades displayed the highest mean Cd and Ni concentrations, adult leaf blades, plagiotropic rhizomes and roots the highest mean Co concentrations, juvenile leaves the highest mean Cu concentration, and plagiotropic rhizomes the highest mean Cr and Pb concentrations, indicating that the accumulation varies with element, compartment and compartment age. Cd, Cr and Ni in adult leaf blades reached mean tissue-seawater accumulation factors of 10³, while Co of 10⁴, implying that this seagrass is a strong accumulator of these elements from solution. Cd, Co, Cr, and Ni concentrations in leaf compartments, particularly adult leaf blades, positively correlated with their concentrations in seawater, and Pb concentrations in plagiotropic rhizomes and roots with sediment Pb concentration. Thereby, P. oceanica could be regarded as a biondicator for Cd, Co, Cr and Ni in seawater, and for Pb in sediments. The results presented provide an insight on trace element accumulation in P. oceanica, and can be utilized for the design of biomonitoring programs.

Macrobenthos functional trait responses to heavy metal pollution gradients in a temperate lagoon

Biological traits analysis (BTA) can help identify the effect of various contaminants on functional trait composition of macrobenthos. However, the effects of bioavailable heavy metals on functional traits of macrobenthos communities remain to be examined. We sampled macrobenthos communities and assessed environmental variables over gradients of heavy metal pollution in Swan Lagoon, China. The RLQ and fourth-corner approaches were used to investigate the response of functional traits to heavy metal pollution. Our findings suggested that macrobenthic functional traits can be used to distinguish the effects of heavy metals and other environmental variables and isolate the corresponding species associated with heavy metal contamination. The macrobenthos at highly contaminated sites comprised taxa of sub-surface deposit-feeders, second-order opportunistic species, and tube-builders, mainly represented by the polychaeta Cirriformia tentaculata and Cirratulus chrysoderma. At less contaminated sites, indifferent species, species attached to seagrass, and crawlers were observed. The results confirm that BTA can provide new insights into the response of macrobenthic functional traits to heavy metal pollution in coastal lagoons.