Role of indigenous microorganisms and organics in the release of iron and trace elements from sediments impacted by iron mine tailings from failed Fundão dam.

After Fundão Dam failure in 2015, most of Gualaxo do Norte River in Doce River Basin in Brazil became silted by iron mining tailings consisting mainly of fine-grained quartz, hematite, and goethite. Previous work pointed to the possibility of reductive dissolution of iron and manganese from tailings, leading to mobilization of iron, manganese and trace elements. Several microorganisms were shown to reduce Fe(III) to Fe(II) and Mn(III, IV) to Mn(II) "in vitro", but their roles in mobilization of Fe and trace elements from freshwater sediments are poorly understood. In this work, bottom sediments and water collected in Gualaxo do Norte River were used to build anoxic microcosms amended with acetate, glucose or yeast extract, in order to access if heterotrophic microorganisms, either fermenters or dissimilatory Fe reducers, could reduce Fe(III) from minerals in the sediments to soluble Fe(II), releasing trace elements. The Fe(II) concentrations were measured over time, and trace elements concentrations were evaluated at the end of the experiment. In addition, minerals and biopolymers in bottom sediments were quantified. Results showed that organic substrates, notably glucose, fuelled microbial reduction of iron minerals and release of Fe(II), Mn, Ba, Al and/or Zn from sediments. In general, higher concentrations of organic substrates elicited mobilization of larger amounts of Fe(II) and trace elements from sediments. The results point to the possibility of mobilization of huge amounts of iron and trace elements from sediments to water if excess biodegradable organic matter is released in rivers affected by iron mine tailings.

A case study of in situ oil contamination in a mangrove swamp (Rio De Janeiro, Brazil).

Mangroves are sensitive ecosystems of prominent ecological value that lamentably have lost much of their areas across the world. The vulnerability of mangroves grown in proximity to cities requires the development of new technologies for the remediation of acute oil spills and chronic contaminations. Studies on oil remediation are usually performed with in vitro microcosms whereas in situ experiments are rare. The aim of this work was to evaluate oil degradation on mangrove ecosystems using in situ microcosms seeded with an indigenous hydrocarbonoclastic bacterial consortium (HBC). Although the potential degradation of oil through HBC has been reported, their seeding directly on the sediment did not stimulate oil degradation during the experimental period. This is probably due to the availability of carbon sources that are easier to degrade than petroleum hydrocarbons. Our results emphasize the fragility of mangrove ecosystems during accidental oil spills and also the need for more efficient technologies for their remediation.

Characterization of hydrocarbonoclastic bacterial communities from mangrove sediments in Guanabara Bay, Brazil.

Hydrocarbonoclastic bacterial communities inhabiting mangrove sediments were characterized by combining molecular and culture-dependent approaches. Surface sediments were collected at two sampling sites in Guanabara Bay (Rio de Janeiro, Brazil) and used to inoculate in vitro enrichment cultures containing crude oil to obtain hydrocarbonoclastic bacterial consortia. In parallel, in situ mesocosms (located in the Guapimirim mangrove) were contaminated with petroleum. Comparison of bacterial community structures of the different incubations by T-RFLP analyses showed lower diversity for the enrichment cultures than for mesocosms. To further characterize the bacterial communities, bacterial strains were isolated in media containing hydrocarbon compounds. Analysis of 16S rRNA encoding sequences showed that the isolates were distributed within 12 distinct genera. Some of them were related to bacterial groups already known for their capacity to degrade hydrocarbons (such as Pseudomonas, Marinobacter, Alcanivorax, Microbulbifer, Sphingomonas, Micrococcus, Cellulomonas, Dietzia, and Gordonia groups). Other strains, with high capacity for degrading hydrocarbons (aliphatic or aromatic), were related to isolates from hydrothermal vents that have not been thus far detected in hydrocarbon-contaminated sites, nor described for their ability to grow or degrade petroleum hydrocarbons. Degradation studies showed the ability of Marinobacter, Alcanivorax and Sphingomonas isolates to degrade both PAH and alkane compounds. Our results point out the rich microbial diversity of the mangroves, whose potential for hydrocarbon degradation is promising for future studies on pollutant bioremediation.