Assessment of the physicochemical conditions sediments in a polluted tidal flat colonized by microbial mats in Bahía Blanca Estuary (Argentina)

Preliminary assessment of the water quality of Rushikulya estuary based on the abundance of pathogenic bacteria

Estuaries are among the most dynamic ecosystems in coastal regions and are facing serious threats due to increasing anthropogenic activities. The aim of the present study is to evaluate the water quality of the Rushikulya estuary by analyzing the abundance of pathogenic bacteria in both its water and sediment. Water and sediment samples were collected from five different stations at the mouth of the Rushikulya estuary during the monsoon and post-monsoon seasons. These samples were analyzed to assess the abundance of pathogenic bacteria and environmental parameters. The results revealed that bacterial abundance is significantly higher in the sediment than in the water, possibly due to a longer residence time of pathogenic bacteria in the sediment. Seasonal observations indicated an increase in pathogenic bacterial abundance during the monsoon season, suggesting an impact from monsoonal discharge. Escherichia coli-like organism, faecal coliforms, Shigella-like organisms, and Vibrio cholera-like organisms were the dominant pathogenic bacteria in both the water and sediment of the Rushikulya estuary. The higher abundance of these pathogens and the results of statistical analysis, which showed a strong correlation between Total Streptococci and BOD (r = 0.79), indicate the influence of human settlement and the mixing of untreated sewage in the Rushikulya estuary. The elevated levels of E. coli, faecal coliforms, and Shigella-like organisms in the Rushikulya estuary raise significant concerns that require immediate attention.

Preliminary assessment of microbial mats in seawater metal remediation

Microbial mats have a special role in the removal of metals in marine environment. This study aimed to experimentally determine the efficiency of Cr removal from seawater by microbial mats. The effect of Cr on the microphytobenthic community and the influence of an aerated condition on the removal of metal and microorganisms were also considered. Hence, microbial mat samples were subdivided in 4 groups: submerged in Cr (chromium 2 mg/L without aeration), Cr + O₂ (chromium 2 mg/L with aeration), SW + O₂ (filtered seawater with aeration), and a control: SW (filtered seawater with neither chromium nor aeration). Water and microbial mat subsamples were used to determine Cr concentrations, organic matter content, granulometry, physicochemical parameters, chlorophyll a, phaeopigments, and quantitative analysis of the microphytobenthic community. Cr removal efficiency from seawater was 95% for the Cr treatment and 99% for the Cr + O₂ treatment. The abundance of cyanobacteria tended to decrease between the initial and final days of the assay, whereas the opposite trend was observed for diatoms. Two aspects are worth noting in the paper: microbial mats efficiently removed Cr from seawater at a concentration of 2 mg Cr/L and the removal of Cr by microbial mats was more efficient with water aeration.

Assessment of metal contamination in an urbanized estuary (Atlantic Ocean) using crabs as biomonitors: A multiple biomarker approach

Estuarine environments, which are complex and sensitive coastal system, and are the final receptacle of several human wastes. Consequently, biomonitoring contaminants, such as metals, within these environments and developing scientific-based tools to conserve them have become particularly importat in recent years. Therefore, in the present study, we determined the levels of certain metals (Cd, Cu, Pb, Zn, Mn, Ni, Cr and Fe) both in sediments and in a key ecological benthic species, the burrowing crab Neohelice granulata, in sites of the Bahía Blanca estuary (SW Atlantic Ocean) with different anthropogenic impacts. We combined these records with geochemical indices and enzymatic and non-enzymatic biochemical biomarkers as early warning signals of contamination and damage to establish an integrated metal contamination profile. Our results indicated that some metals like Cu moderately contaminate the estuary and that the primary input of metals in this area is due to malfunctioning sewage discharges. Crabs exhibited the following pattern of metal accumulation: Fe ≥ Cu > Zn > Mn > Ni > Cd. Pb and Cr were under the method detection limit, and Cu was probably bioaccumulated from sediments. Metal concentrations showed significant differences according to the sites and seasons (p > 0.05) and not strictly to the crab gender. Besides, a similar pattern was observed for biomarkers, and the integrated biomarker response allowed establishing different oxidative stress patterns, according not only to human impacts but also to the seasonal physiological needs of this species and environmental endpoints (salinity, temperature, and pH). This work demonstrates that environmental factors also affect the metal influx in crabs and the activity of biomarkers beyond the source and fate of these elements. This information is vital for future integrated monitoring programs.

Plastisphere on microplastics: In situ assays in an estuarine environment

In this study, the influence of the plastisphere on metals accumulation and weathering processes of polystyrene (PSMPs) and nylon microplastics (NyMPs) in polluted waters during a 129 day-assay were studied. MPs were characterized through scanning electron microscopy (SEM) with Energy dispersive X-ray (EDX), X-ray diffraction (XRD), attenuated total reflectance Fourier transformed infrared (ATR-FTIR) spectroscopy, contact angle, and thermogravimetric analysis (TGA). Also Cr, Mn, Zn, Cd, Pb, and Cu in the plastisphere on MPs were analyzed during the assay. Potentially pathogenic Vibrio, Escherichia coli, and Pseudomonas spp. were abundant in both MPs. Ascomycota fungi (Phona s.l., Alternaria sp., Penicillium sp., and Cladosporium sp.), and yeast, were also identified. NyMPs and PSMPs exhibited a decrease in the contact angle and increased their weights. SEM/EDX showed weathering signs, like surface cracks and pits, and leaching TiO₂ pigments from NyMPs after 42 days. XRD displayed a notorious decrease in NyMPs crystallinity, which could alter its interaction with external contaminants. Heavy metal accumulation on the plastisphere formed on each type of MPs increased over the exposure time. After 129 days of immersion, metals concentrations in the plastisphere on MPs were in the following order Cr ˃ Mn ˃ Zn ˃ Cu ˃ Pb ˃ Cd, demonstrating how the biofilm facilitates metal mobilization. The results of this study lead to a better understanding of the impact of marine plastic debris as vectors of pathogens and heavy metals in coastal environments.

First long-term assessment of metals and associated ecological risk in subtidal sediments of a human-impacted SW Atlantic estuary

The main objective of this article was to profile the metal accumulation, sources, pollution levels and trends during 6 years in a SW Atlantic coastal system (Bahía Blanca estuary). Subtidal sediment samples were taken from six stations with different human impacts, and chemical element analyses were performed using ICP-OES. As a result, metals tended to increase in time and differences were observed between a site profoundly impacted by sewage waters and the rest of the sampling stations. Values range from background levels to those considered toxic for the marine biota, as in the case of Cd and Cu. Besides, the geochemical analyses exhibited low to moderate pollution with probable adverse biological effects. Finally, the physicochemical parameters of the water column like pH and DO significantly decreased in time in all stations and temperature correlated with some metals, indicating a potential interaction.

Occurrence, distribution, and characterization of suspended microplastics in a highly impacted estuarine wetland in Argentina

Microplastics have been a global concern due to their potential and widespread risks to organisms and environments. In this study, we investigated the abundance, distribution, and characteristics of microplastics (MPs) in the surface waters of the Bahía Blanca Estuary (BBE), specifically in its inner and middle zone. The results showed the dominant shape of MPs were fibers, being black, transparent, and blue the main colors. The concentrations of MPs ranged from 182 to 33,373 items m^-3 with a mean value of 6162 items m^-3. The highest concentrations of MPs were detected in the middle zone of the estuary, a site that receives untreated sewage effluents from the city. The most abundant size ranges were from 0.5 to 1.5 mm (44.21%) and ˂0.5 mm (40.21%) and were predominant at all the sampling sites. The concentration of mesoplastics in the inner zone (16 items m^-3) presented larger values than in the middle zone (5 items m^-3). A wide variety of polymeric materials with predominance of microfibers such as cellulose-based, polyacrylonitrile, polyethylene terephthalate, and polypropylene were identified. Polyester/alkyd resins and poli(vinyl chloride) were also found. The analysis of MPs surface through SEM/EDX detected a variety of elements such as C, O, Si, Al, K, Ca, Cl, Ti, Fe, S, and P, indicating potential contaminant carriers in the water column. Some plastic particles presented a high degree of degradation on their surface morphology. Untreated sewage discharges appear to be a significant input of MPs. Therefore, the results provided in the present study should be considered by stakeholders interested in the management and conservation of this large coastal wetland with significant ecological and economic value.

Distribution of Butyltin Compounds in the Coastal Environment of the Bahía Blanca Estuary, Argentina

This study evaluates for the first time the distribution and accumulation of butyltin compounds (BTs) in different compartments such as seawater, sediments, suspended particulate matter (SPM), and mussels (Brachidontes rodriguezii) in the Bahía Blanca estuary. The samples were collected from six sampling sites with different anthropogenic impacts. A better visualization and interpretation of data was achieved using chemometric tools (Tucker4 model), which made it possible to reveal the main relationships among the variables. This analysis showed the presence of BTs in all the estuarine environmental compartments, even in sites with low human intervention. The relationships found among BTs levels, seasons, and environmental matrices show the importance of biological processes such as phytoplankton blooms and remobilization of sediments (by tidal dynamics and/or periodic dredging) in BTs distribution and degradation. In addition, partition coefficients showed that mussels mainly bioaccumulate tributyltin from sediment, water and, to a lesser extent, SPM.

Soil metal pollution assessment in Sarcocornia salt marshes in a South American estuary

Soil metal pollution in two Sarcocornia salt marshes within the Bahía Blanca estuary (Argentina, South America) was evaluated through pseudo-total and bioavailable metal levels and pollution indexes. Soil conditions were also studied. The pseudo-total metal concentrations were similar in both salt marshes and followed the same decreasing order: Fe > Zn > Cu > Cr > Ni > Pb > Cd. Bioavailable metals presented different patterns between salt marshes. The percentages of the bioavailable fraction varied between 28 and 80%, being higher than 60% for Cu, Zn and Pb. Organic matter ruled the distribution of all metals, except Pb. Using shale average concentration as background level, indexes did not show pollution nor enrichment, whereas using as background levels local values, anthropogenic enrichment was found for all metals and most metals showed moderate metal pollution. Our results showed that bioavailable metals levels and indexes using local background values provide an adequate assessment of metal pollution in salt marsh soils.

Chromium behavior in a highly urbanized coastal area (Bahía Blanca Estuary, Argentina)

The contamination of estuaries by heavy metals from anthropogenic activities in the industrial, domestic, and agricultural sectors is a global concern. In this study, the Cr, Fe, and Mn levels in the suspended particulate matter (SPM) were analyzed in estuarine waters from Bahia Blanca Estuary, during 2014-2015. The values of particulate Cr ranged from 7.33 to 35.20 μg g^-1, which could be associated to several anthropogenic sources. The positive correlations found between Cr and Chlorophyll-a, and Cr and particulate organic carbon (POC) suggest the strong influence of phytoplankton on the adsorption of this metal and on the increase of particulate Cr. Negative correlations were found between Cr and DO and between Cr and pH, which could indicate an increasing trend in the dissolved form of Cr. This study suggests that the physical-chemical characteristics of the water column as well as phytoplankton and POC dynamics influence the behavior of Cr in this estuary.

Influence of microphytobenthos on the sedimentary organic matter composition in two contrasting estuarine microhabitats

The influence of microphytobenthic community on the composition of sedimentary organic matter was evaluated in two Bahía Blanca estuary microhabitats contrasting in vegetation and hydrodynamic conditions; namely, S1 located in a Sarcocornia perennis saltmarsh with macroscopic microbial mats and S2 in a mudflat without macroscopic microbial mats or vegetation. Moisture, organic matter, chlorophyll a, phaeopigments, carbohydrates (CH), proteins (PRT), and abundance and structure of microphytobenthic community were evaluated in surface sediments. Higher moisture was observed at S2 and was related to the proximity of this site to the subtidal zone and the effect of the environmental variables temperature and rain. No significant differences were found in organic matter content between sites; however, at S1, a higher concentration was registered during winter and early spring associated to the period of higher microphytobenthic biomass. Chlorophyll a and phaeopigments were higher at S1, attributed to the higher microphytobenthos abundance at this site. Differences in microphytobenthos were observed not only in quantity but also in community structure since at S1 filamentous cyanobacteria dominated the community, whereas at S2, higher abundance of centric diatoms and the absence of cyanobacteria were observed during most of the study. S1 showed higher concentration of proteins and carbohydrates which could be attributed to the higher production of fresh organic matter by microphytobenthos. The total protein and carbohydrate concentrations allowed us to classify both microhabitats into the meso-oligotrophic category, contrasting with the classification made by other authors using water column proxies.

Microplastics and suspended particles in a strongly impacted coastal environment: Composition, abundance, surface texture, and interaction with metal ions

The composition and the interaction of the suspended particulate matter (SPM) with metal ions, along with the presence and characteristics of microplastics, were analyzed for the first time in the water column of the inner zone of Bahía Blanca Estuary during winter (June, July, and August) 2019. Surface analysis techniques (Scanning Electron Microscopy combined with Energy Dispersive X-ray Spectroscopy, X-ray Photoelectron Spectroscopy, and X-ray Diffraction) were employed to obtain an in-depth characterization of the particulate matter, suggesting the presence of Fe in our samples, with a mixture of Fe³⁺/Fe²⁺ oxidation states. Microplastics ranged in concentrations between 3 and 11.5 items L^-1, with an average of 6.50 items L^-1 (S.E: ±4.01), being fibers the most abundant type. Infrared Spectroscopy suggests that these fibers correspond to semi-synthetic cellulose-based and poly(amide) remains. We concluded that the SPM is a significant vehicle for metals which might have adverse effects on marine organisms.

Integrative assessment of the ecological risk of heavy metals in a South American estuary under human pressures

Biomonitoring of heavy metal pollution through the use of biomarkers could be a difficult task since the organisms' physiological changes could shift regarding natural factors (i.e., the season of the year) and due to the anthropogenic pressures of the environment. In the Southwest Atlantic Ocean, where most industrial and developing countries are settled, it is essential to address these concerns to generate information for the stakeholders and monitoring programs that aim to use biochemical biomarkers as early warning signals to detect heavy metal pollution. The present study intended to determinate the heavy metal concentrations in sediments and the hepatopancreas of the crab species Neohelice granulata as well as the ecological risk through the use of biomarkers and geochemical indices in sites with different anthropogenic pressures of the Bahía Blanca estuary (SW Atlantic Ocean) during the warm and cold season. The results showed low to moderate heavy metal pollution in the sediments by Cu with possible effects on the biota in a site with sewage waters' discharges. Except for GST that was explained by Cd, the biomarkers employed were not useful to assess spatial heavy metal pollution, and they might be ruled out by physiological seasonal variations rather than anthropogenic constraints, or another type of pollutants in the area.

Uptake and detoxification of trace metals in estuarine crabs: insights into the role of metallothioneins

The detoxification process of trace metals in the estuarine burrowing crab Neohelice granulata, after previously being exposed to anthropogenic pressures in the field, is described for the first time. The objectives of this study were (a) to assess the metal content (Cd, Cu, Pb, Zn, Mn, Ni, Cr, Fe) in the sediments and the uptake of these elements in the hepatopancreas of N. granulata; (b) to quantify trace metal concentrations in the hepatopancreas before and after the detoxification experiment; and (c) to relate this information to metallothionein (MT) induction or reversibility. The detoxification assay was performed for 25 days with artificial seawater under controlled conditions in a culture chamber. The results showed higher uptake and bioaccumulation of Zn and Cu from the sediments, and the hepatopancreas exhibited increased levels of Zn and lower concentrations of the rest of the metals and MTs after the assay, mainly Fe and Mn that were significantly lower. We conclude that trace metals could be translocated to and accumulated in the hepatopancreas, the main metabolic organ, and then eliminated under controlled conditions with corresponding reversibility of MTs. Graphical abstract.

Bioaccumulation of heavy metals (Hg, Cd and Ni) by sentinel crab (Macrophthalmus depressus) from sediments of Mousa Bay, Persian Gulf

The presence of heavy metals (HMs) in the environment can increase their risk of transfer to the food chain. The present study was conducted to investigate the bioaccumulation of HMs including Hg, Cd and Ni in soft and hard tissues of sentinel crab (Macrophthalmus depressus Rüppell, 1830) in sediments of Mousa Bay in northwest of the Persian Gulf. The average (mean ± SD) amounts of Hg, Cd and Ni in the sediments were 6.27 ± 3.66, 3.8 ± 1.48 and 71.6 ± 5.09 μg/g, whereas the relevant amounts for soft tissues were 6.16 ± 4.64, 3.3 ± 1.7 and 19.7 ± 3.96 μg/g, and for hard tissues were, 2.9 ± 1.67, 3.5 ± 1.35 and 10.44 ± 3.1 μg/g, respectively. Accordingly, soft tissues of the crab could be suitable bioindicators of Hg and Cd, whereas the hard tissues could be used as Cd bioindicator. Since the bioaccumulation of Ni was the most, it might have a higher risk among the metals to enter the food chain in the region.

Preliminary studies about the role of physicochemical parameters on the organotin compound dynamic in a South American estuary (Bahía Blanca, Argentina)

This work provides a preliminary study of the destination, mobility, and availability of tributyltin (TBT), dibutyltin (DBT), and monobutyltin (MBT) in contaminated sediments and water column within Puerto Rosales Port, located in the middle zone of the Bahía Blanca Estuary (Argentina). Therefore, this study presents the first comprehensive results of the role of several physicochemical parameters (temperature, pH, Eh, salinity, turbidity, organic matter, chlorophyll, and macronutrients) in behavior of organotin compounds (OTCs) in a marine-coastal ecosystem. The samples were collected seasonally in May, August, and November during 2014. Levels of OTCs were determined in sediments and water column samples by means of gas chromatography-mass spectrometry analysis. Degradation index analyses suggested not recent inputs of TBT at the area of study. However, results submitted a continuous input of TBT into the column water; further, its distribution and degradation pattern were shown to be influenced by salinity, turbidity, particulate organic matter, chlorophyll, and nitrates. These last two parameters, chlorophyll and nitrates, also were very important for sediment samples. Chlorophyll together with high temperatures recorded in the surface sediments triggers biodegradation process of TBT and DBT resulting in high MBT levels while nitrates seemed to promote debutylation process. Furthermore, pH appeared to influence drastically the adsorption/desorption activity of TBT and DBT in sediment. Finally, the Eh obtained suggested a degradation of TBT thanks to the presence of Fe (III) in this compartment. In addition, in fact, the results outlined a possible MBT additional input that contributes to the pollution observed in the study area. Graphical abstract Organotin compounds behavior according to several physicochemical parameters.

Magnetic nanotechnological devices as efficient tools to improve the quality of water: analysis on a real case

Magnetic nanoparticles (MNPs), based on iron oxide (magnetite) and ferrogel of gelatin and MNPs, were employed as efficient tools for the removal of heavy metals and nutrients from water samples from Bahia Blanca estuarine (BBE). An exhaustive adsorption performance of Cu, NO₃^-, and NO₂^- was conducted in batch using model solutions aiming to adjust the adsorption conditions. Adsorption studies using water simulating the real samples were also performed. Both kinds of nanomaterials demonstrated an efficiency between 60 and 80%, and 85% for the removal of heavy metals and NO₃^- and NO₂^-, respectively. Similar adsorption assays were performed using BBE water samples, employing the experimental conditions explored with model and simulated water. The reached efficiency was 30 and 45% for heavy metal and nutrient removal, respectively, using nanoparticles; meanwhile, ferrogels displayed a removal capacity around 50-60%. The nanoparticles showed structural instability by the leaching of iron to the medium after the adsorption processes. Ferrogels remained almost inalterable in terms of their integrity during the adsorption time. These materials showed satisfactory perspectives regarding their reuse possibilities. They were used for almost five repeated cycles of adsorption without losing efficiency on the adsorption. The results of this study suggest that MNPs and FGs appear as versatile and promising materials that may be considered as valid alternatives to the actual tools for the remediation of real water samples.

Response of microbial communities colonizing salt marsh plants rhizosphere to copper oxide nanoparticles contamination and its implications for phytoremediation processes

This study aimed to investigate Cu oxide nanoparticles (CuO NP) effect on microbial communities associated with salt marsh plants (Halimione portulacoides and Pragmites australis) rhizosphere and its implications for phytoremediation processes. Experiments were conducted, under controlled conditions, over one week. Rhizosediment soaked in the respective elutriate (a simplified natural medium) with or without plants, was doped with CuO NP or with Cu in ionic form. Microbial community in rhizosediments was characterized in terms of abundance (by DAPI) and structure (by ARISA). Metal uptake by plants was evaluated by measuring Cu in plant tissues (by atomic absorption spectroscopy). Results revealed significant metal uptake but only in plant roots, which was significantly lower (H. portulacoides) or not significant (P. australis) when the metal was in NP form. Microbial community structure was significantly changed by the treatment (absence/presence of Cu, ionic Cu or CuO NP) as showed by multivariate analysis of ARISA profiles and confirmed by analysis of similarities (Global test - one way ANOSIM). Moreover, in P. australis rhizosediments microbial abundance, bacterial richness and diversity indexes were significantly affected (increased or decreased) due to metal presence whereas in H. portulacoides rhizosediment microbial abundance showed a significant decrease, particularly when the metal was in NP form. Accordingly, Cu presence affected the response of the rhizosphere microbial community and in some cases that response was significantly different when Cu was in NP form. The response of the microbial communities to Cu NP might also contribute to the lower metal accumulation by plants when the metal was in this form. So, Cu NP may cause disturbances in ecosystems functions, ultimately affecting phytoremediation processes. These facts should be considered regarding the use of appropriate salt marshes plants to remediate moderately impacted areas such as estuaries, where NPs can be found.

Assessment of metal enrichment and their bioavailability in sediment and bioaccumulation by mangrove plant pneumatophores in a tropical (Zuari) estuary, west coast of India

Sediment collected from the estuarine mangroves of the Zuari estuary and Cumbharjua canal were analyzed to assess the concentration, contamination and bioavailability of metals. Mangrove pneumatophores were also analyzed to understand the metal bioaccumulation in mangrove plants. The results indicated the variation of metal concentrations in sediment along the estuary was attributed to changing hydrodynamic conditions, type of sediment and metal sources. Further, speciation studies revealed that Fe, Cr, Co, Ni, Cu and Zn were mainly of lithogenic origin and less bioavailable while high Mn content in the sediment raised concerns over its potential mobility, bioavailability and subsequent toxicity. The mangrove plants exhibited difference in metal accumulation due to variations in sediment parameters and metal availability, in addition to difference in plant species and tissue physiology that affect metal uptake. Moreover, the mangrove plants reflected the quality of the underlying sediment and can be used as a potential bio-indicator tool.