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.

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.

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.

Short-term efficiency of epibenthic microbial mat components on phosphorus sorption.

Microbial mats may be an alternative tool for phosphorus (P) remediation of eutrophic coastal waters. The main objective of this work was to determine the importance that the living and non-living components of the mats have on P short-term sorption. Microbial mats were collected in the Paso Seco coastal flat, Argentina (40°38'3.32″S; 62°12'24.85″W), and incubated under controlled conditions in the lab. An adsorption curve was performed with the microbial mats. Active mats had a Freundlich constant 8.9-fold higher than underlying sandy sediments. Collected samples were then treated as follows: maintaining and disturbing their structural integrity (natural and autoclaved, respectively), and both conditions were incubated with filtered seawater, without and with phosphate addition (0 and 5 mg P L-1, respectively). Natural mats had a significantly-higher phosphate removal percentage than autoclaved ones, suggesting that living microorganisms increase P short-term sorption efficiency by ~25%, while non-living matter may account for the rest.

Heavy metal bioconcentration factors in the burrowing crab Neohelice granulata of a temperate ecosystem in South America: Bahía Blanca estuary, Argentina.

An extensive population of the burrowing crab, Neohelice granulata, inhabits the intertidal areas of the Bahía Blanca estuary, a moderately polluted temperate ecosystem located to the southwest of the province of Buenos Aires, Argentina. In order to determine the metal-accumulating ability of this species, concentrations of Cd, Cu, Pb, Ni, Zn, Mn, Cr, and Fe in soft tissues of adult specimens were measured. Subsequently, the bioconcentration factors (BCFs) of all heavy metals were determined using levels of concentrations previously obtained in intertidal sediments. The results showed concentrations above the detection limit in soft tissues of male and female crabs for all metals except Pb and Cr. BCF > 1 were obtained for Cd, Cu, and Zn, indicating that these metals are accumulated and biomagnified. However, BCF values < 1 were found for the rest of the metals (Mn, Ni, and Fe). The findings of metal accumulation in soft tissues of N. granulata is of great importance taking into account that this is a key species within this temperate ecosystem, playing a major role in the transference of pollutants to higher trophic levels.

Exceptionally high Cd levels and other trace elements in eggshells of American oystercatcher (Haematopus palliatus) from the Bahía Blanca Estuary, Argentina.

Concentrations of six trace metals were determined in the eggshells of American oystercatchers (Haematopus palliatus) from the Bahía Blanca estuary, Argentina. All metals measured in selected samples presented concentrations above the detection limit. Means found for Cu, Pb, Cr, Zn and Ni were as follow: 2.02±0.52, 7.23±2.33, 0.78±0.03, 2.22±1.13 and 6.05±0.89mg/kg dw. The mean concentrations of Cd found were surprisingly high: 13.28±3.38mg/kg dw. Previous studies made on prey items of the American oystercatchers showed low to medium concentrations of the six trace metals. This may indicate a possible transfer of the metals that are available in the environment through food chains. Our study indicates that American oystercatchers sequester heavy metals in their eggshells. Therefore the eggshells may be useful as biomonitors for trace metal contamination in the Bahía Blanca estuary.

Burrowing crab (Neohelice granulata) as a potential bioindicator of heavy metals in the Bahía Blanca estuary, Argentina.

Bioindicators can be used to determine spatial and/or temporal variations of heavy metals in a certain coastal or marine environments. This study investigated the potential use of the burrowing crab Neohelice granulata from two different locations in the Bahía Blanca estuary, a moderately polluted ecosystem. Concentrations of zinc (Zn), nickel (Ni), and lead (Pb) in soft tissues of male and female crabs were measured. In addition, concentrations of the three metals in eggs were compared with concentrations in female crabs. No geographical differences were found for any of the three metals, whereas sexual and seasonal differences were obtained for Zn and Ni, with the winter season posing lower concentrations. Moreover, the three metals were detectable in eggs and were lower than concentrations in female crabs (except for Zn). Finally, the usefulness of this species as a potential bioindicator of heavy-metal pollution within this estuarine ecosystem is discussed.

Heavy-metal concentrations in soft tissues of the burrowing crab Neohelice granulata in Bahía Blanca estuary, Argentina.

Copper (Cu), cadmium (Cd), and chromium (Cr) in soft tissues of male and female burrowing crab Neohelice granulate, as well as their eggs, were measured in two different locations in the Bahía Blanca estuary, a moderately polluted ecosystem, from October 2008 to August 2009. Differences between sexes, sites, and seasonality were assessed. Furthermore, metal levels in eggs were compared with metal levels in female crabs. The results showed no significant differences for Cu and Cd between sexes (Student t test p > 0.25 for both sites) and sites (two-way analysis of variance: Cu p = 0.82 and Cd p = 0.29). Nevertheless, seasonality was found, with winter having significantly lower concentrations for both metals. The range of Cu concentrations was between 96.92 and 152.18 µg g(-1) dry weight (dw), and the range of Cd concentrations was between 6.09 and 10.41 µg g(-1) dw. Cr concentrations could not be assessed because most of the values were lower than the detection limit. Although heavy metals in sediments were not measured in this study, a bioaccumulation process may be occurring for Cd because levels found during the entire sampling period were greater than levels in sediment from previous years. For Cu, a regulation process may be occurring considering that this is an essential metal and levels of Cu in N. granulata found in this study were between 1 and 2 orders of magnitude greater than levels in sediments. Finally, Cu and Cd levels in eggs were detectable, but they were lower than levels in female crabs. The importance of these findings is linked to the fact that metal accumulation seems to be occurring before hatch. The presence of heavy metals in soft tissues as well as in eggs of N. granulata is of great importance considering that this is a key species within the Bahía Blanca estuary; therefore, it plays a major role in the transference of pollutants to greater trophic levels.

Lead concentrations in zooplankton, water, and particulate matter of a southwestern Atlantic temperate estuary (Argentina).

This study presents for the first time valuable results of lead (Pb) accumulation in zooplankton from a southwestern Atlantic temperate estuary, the Bahía Blanca estuary, one of the most important and industrialized coastal environments of Argentina. It considers Pb concentrations in zooplankton organisms as well as in the dissolved and particulate phases. These fractions were analyzed on account of their important role in the biogeochemical cycles of trace elements in estuarine environments. In addition, the major physicochemical variables, i.e., nutrients, and pigment concentrations, and zooplankton composition and abundance, were also considered to understand Pb levels in the above-mentioned fractions. Samplings were performed from March to December 2005 with a bimonthly frequency and comprised a study area with stations located near industrial settlements and other stations a few kilometers far from these points. The results of the physicochemical variables and nutrients and pigments agreed with historic values for the estuary and did not present any evidence of abnormalities. Dissolved Pb presented a mean concentration of 2.15 ± 0.46 µg L(-1), whereas particulate Pb presented a mean concentration of 13.52 ± 3.07 µg g(-1) dry weight (dw). In the mesozooplankton, represented by copepods, the mean concentration was similar to the particulate fraction (13.38 ± 4.41 µg g(-1) dw), whereas in the macrozooplankton, represented by mysids, it was lower (9.81 ± 1.89 µg g(-1) dw). Thus, Pb concentrations were relatively high in the dissolved and particulate phases. Moreover, zooplankton accumulated important concentrations of this metal, which was mainly incorporated through suspended particulate matter (SPM). The source of Pb in all of these fractions is related to the industry discharges as well domestic sewage located near the sampling stations. Finally, through these results, it was possible to show the importance of zooplankton and SPM in the biogeochemical cycle of Pb as well as the interaction between these fractions in an estuarine and anthropogenic environment, such as the Bahía Blanca estuary.