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

Thermochemical conversion of microbial mats: A case study on Cr(VI) removal from freshwater

In response to increasing anthropogenic pollution and metal accumulation in aquatic environments, bioremediation has gained great importance. Microbial consortia are emerging as a promising solution due to their diverse pollutant metabolizing pathways. This study evaluates the role of biotic and abiotic components in microbial mats for Cr(VI) removal from freshwater. For this purpose, microbial mats were modified by high-temperature treatments using an autoclave and a muffle furnace, and modified and unmodified mats, both chemically characterized by SEM-EDS, ATR-FTIR, XRD, and XPS, were used in Cr(VI) removal assays. The concentrations of total Cr and Cr(VI) were measured, which were initially 15 mg/L and after 17 days reached values between 0.22 and 4.99 mg/L depending on the treatment. The removal efficiency was nearly 99% in unmodified mats, while in autoclaved ones it reached 95% and in calcined mats 67%. These findings demonstrate that all components contribute to Cr removal. Both trivalent and hexavalent Cr penetrated the porous structure reaching deep layers where they were adsorbed by electrostatic attraction or complex formation with the mat components, while the insoluble compounds formed, such as Cr2O3 and CrPO4, precipitated on the mat. Microbial mats with all their components, including their living microbial communities, provide abundant sites for surface removal phenomena and offer greater potential for the reduction of Cr(VI) to Cr(III), thereby achieving higher Cr removal efficiency.

The behaviour of particulate trace metals in marine systems: A review

Changes in the ocean temperature, seawater acidity, and oxygen level are parts of global change that may indirectly impact the biogeochemical cycles of trace metals in the marine system, particularly for the particulate phase. The different factors influencing the level of particulate trace metals are interesting topics for investigation. Following up on marine research in the estuary and coastal areas, we specifically review the distribution of particulate trace metals. This review aims to provide an overview of the progress of studies on particulate metals in the marine environment and to understand the factors that influence the level of particulate metals. Spatially, the distribution of particulate trace metals decreases towards the sea due to the influence of salinity, while the temporal distribution portrays the unique feature of each location that differences in metal sources and phytoplankton bloom periods might cause.

Novel method of removing metals from estuarine water using whole microbial mats

This study addresses the limited understanding of chromium-microbial mat interactions in estuarine tidal flats. The aims were to evaluate (1) the efficiency of the microbial consortium in Cr(III) removal from seawater; (2) the elemental and mineralogical composition of the microbial mat as a natural system in the Cr removal, (3) the effects of metal on microphytobenthos, and (4) possible interactions of Cr with other metals present in the consortium. Microbial mats were exposed to Cr(III) solutions at different concentrations (2-30 mg Cr/L). Analysis such as metal concentration, organic matter content, chlorophyll a and phaeopigment concentrations, abundance of diatoms and cyanobacteria, SEM-EDS, and XRD were performed. Most of the Cr(III) was deposited, as chromium oxide/hydroxide, on the surface of all microbial mat components. The complete microbial mat, comprising sediments, detritus, EPS, and diverse microorganism communities, exhibited a remarkable capacity to accumulate Cr(III), retaining over 87% in the solution.

Chromium removal by microbial mats: understanding the effect of salinity and pH

Environmental contamination by chromium represents a serious public health problem. Therefore, it is crucial to develop and optimize remediation technologies to reduce its concentration in the environment. The aims of this study were to evaluate the uptake of chromium by live and complete microbial mats in experimental mesocosms under different pH and salinity conditions to understand how these factors affect the microphytobenthic community and, consequently, how chromium removal process is influenced. Microbial mats from the estuarine environment were exposed to 15 mg Cr/L under different pH (2, 4, and 8) and salinity (2, 15, and 33) conditions. Salinity, redox potential, and pH were measured throughout the trial in solutions and in microbial mats, while total Cr determinations were performed at the end of the assay. The results demonstrated that the removal efficiency of Cr by microbial mats was significantly improved in solutions at pH 2, remaining unaffected by variations in salinity. Notably, both cyanobacteria and diatoms showed remarkable resistance to Cr exposure under all conditions tested, highlighting their exceptional adaptability. Microbial mats have proved to be effective filters for reducing the concentration of chromium in aqueous solutions with varying pH and salinity levels.

Enhancing copper and lead adsorption in water by in-situ generation of calcium carbonate on alginate/chitosan biocomposite surfaces

Chitosan (CS) and sodium alginate (SA)-based biocomposites (CSA) were prepared with the in-situ generation of Calcium Carbonate (CSAX_Ca) through a simple, straightforward, economical, and eco-friendly procedure. Different drying conditions (X) were tested to achieve suitable structural and surface characteristics to enhance adsorption capacity: freeze-dried (L), vacuum-dried with methanol (M), and freeze-dried + vacuum-dried with methanol (LM). Temperature and adsorbent dosage effects on the adsorption capacity of Cu2+ or Pb2+ were examined. Results showed that the higher-yielding biocomposite (CSALM_Ca) exhibited rapid adsorption and good diffusion properties, achieving removal above 90 % within contaminant initial concentration ranges of 10-100 mg/L. At 35 °C, a pseudo-second-order kinetic and the Langmuir model effectively described kinetics and isotherms, revealing maximum adsorption (qe, max) of 429 mgCu2+/L and 1742 mgPb2+/g. Characterization through FTIR, XRD, and SEM of the as-prepared adsorbents confirmed the presence of CaCO3 in vaterite and calcite forms and the influence of drying conditions on the material morphology. Post-adsorption material characterization, in combination with adsorption findings, revealed chemisorption processes involving Ca2+ ion exchange for Cu2+ or Pb2+, resulting in surface-insoluble compounds. The best-performing material showed that after three reuse cycles, the removal of Cu2+ and Pb2+ decreased to 75 % and 62 %, respectively.

Geochemical elements in suspended particulate matter of Ensenada de La Paz Lagoon, Baja California Peninsula, Mexico: Sources, distribution, mass balance and ecotoxicological risks

The present study aimed to evaluate multi-element concentrations (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Sr) in suspended particulate material (SPM) collected from Ensenada de La Paz (ELP) lagoon, Baja California Sur, Mexico in two different periods (September and May) to comprehend their origin, geochemical behavior, mass transfer and associated ecotoxicological risks. The 24 hr variation coefficient of volumetric SPM levels were found to be 51.7% in September and 40.5% in May, signifying the effects of oceanic waters. The calculated enrichment factor (EF) values for all the studied elements were of higher magnitude because of the high surface area and oxide nature of SPM, and in this study, Mo had the highest EF of 46.77 probably due to its origin from continental weathering. From the ecotoxicological perspective, the integrated toxic risk index revealed low toxic risk to the benthic community. However, the mean-ERM-Quotient calculated using the particulate concentrations of As, Cd, Cr, Cu, Ni, Pb indicated 9% probability of toxicity to biota. The comprehensive geochemical and ecotoxicological assessment of particulate metal concentrations in the ELP lagoon signify low to moderate contamination.

Chemical-analytical characterization and leaching of heavy metals associated with nanoparticles and microplastics from commercial face masks and the abundance of personal protective equipment (PPE) waste in three metropolitan cities of South America

In this study, we surveyed the presence of personal protective equipment (PPE) waste on the streets of Bogotá-Colombia, Lima-Perú, and Mar del Plata-Argentina. Furthermore, this work is also focused on the release capacity of Ag, Cu, and Zn metals associated with nanoparticles, and microplastics (MPs) from textile face masks (TFMs) and disposable face masks. According to our results, an association between low-income areas and PPE waste was found, which may be related to the periodicity of waste collection and economic activity. Polymers, like polypropylene, cotton-polyester, and additives, such as CaCO₃, MgO, and Ag/Cu as nanoparticles, were identified. TFMs released high levels of Cu (35,900-60,200 μg·L^-1), Zn (2340-2380 μg·L^-1), and MPs (4528-10,640 particles/piece). Metals associated with nanoparticles leached by face masks did not present any antimicrobial activity against P. aeruginosa. Our study suggests that TFMs may leach large amounts of polluting nano/micromaterials in aquatic environments with potential toxicological effects on organisms.

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.

Microplastics in bivalves, water and sediments from a touristic sandy beach of Argentina

This study assesses for the first time the concentrations of microplastics (MPs) in sediments, water and two human-consumed mussels with different ecological traits (Amarilladesma mactroides and Brachidontes rodriguezii) in a touristic sandy beach of Argentina. MPs were characterized through FTIR and SEM/EDX techniques. All the samples presented MPs with similar concentrations as other human-impacted coastal areas of the world, being black and blue fibers of < 0.5 and 0.5-1 mm the most abundant. SEM images exhibited cracks and fractures with clay minerals and microorganisms adhered to MPs surface. EDX spectrums showed potentially toxic elements, such as Cr, Ti, and Mo. FTIR identified polymers such as cellulose, polyamides, and polyacrylates in most of the samples analyzed. Our study demonstrates that microplastic pollution is a common threat to sandy beaches in Argentina, worsened by plastic particles carrying metal ions with potential toxic effects to the biota, including A. mactroides, an endangered species.