Ecological risk by potentially toxic elements in surface sediments of the Lake Maracaibo (Venezuela)

The evaluation of potential ecological risk of aquatic sediments associated with the presence of potentially toxic elements (PTE) determines its degree of danger on native biota. In this work, the potential ecological risk of V, Ti, Cr, Ni, Cu, Zn, As, Se, Cd, Sn, Hg and Pb in superficial sediments is explained in three different areas of Lake Maracaibo: El Tablazo Bay, Strait of Maracaibo and the lake itself, through a multi-guideline approach (elemental enrichment (enrichment factor, contamination degree, pollutant load index and geo-accumulation index), sediment quality guidelines and risk assessment code). The PTE levels ranged from Ti > Pb > Zn > Cr > Cu > Ni > As > Cd > Se > Hg > Sn. The PTE concurrent effect on biota was El Tablazo Bay > lake > Strait of Maracaibo. The superficial sediments of Lake Maracaibo constitute a medium with a high potential ecological risk on estuarine biota. This is mainly due to the levels of As in El Tablazo Bay, Cd in the Strait of Maracaibo and Pb in the lake area. This represents a latent toxicity hazard for native biological communities and other associated organisms

Developments in the study and applications of bacterial transformations of selenium species

Microbial bio-transformations of the essential trace element selenium are now recognized to occur among a wide variety of microorganisms. These transformations are used to convert this element into its assimilated form of selenocysteine, which is at the active center of a number of key enzymes, and to produce selenium nanoparticles, quantum dots, metal selenides, and methylated selenium species that are indispensable for biotechnological and bioremediation applications. The focus of this review is to present the state-of-the-art of all aspects of the investigations into the bacterial transformations of selenium species, and to consider the characterization and biotechnological uses of these transformations and their products

Detoxification, active uptake, and intracellular accumulation of chromium species by a methane-oxidizing bacterium

Despite the wide-ranging proscription of hexavalent chromium, chromium (VI) remains among the major polluting heavy metals worldwide. Aerobic methane-oxidizing bacteria are widespread environmental microorganisms that can perform diverse reactions using methane as the feedstock. The methanotroph Methylococcus capsulatus Bath, like many other microorganisms, detoxifies chromium (VI) by reduction to chromium (III). Here, the interaction of chromium species with M. capsulatus Bath was examined in detail by using a range of techniques. Cell fractionation and HPLC-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) indicated that externally provided chromium (VI) underwent reduction, and was then taken up into the cytoplasmic and membranous fractions of the cells. This was confirmed by X-ray photoelectron spectroscopy (XPS) of intact cultures that indicated negligible chromium on the surface of, or outside, the cells. Distribution of chromium and other elements within intact and sectioned cells, as observed via transmission electron microscope (TEM) combined with energy-dispersive X-ray spectroscopy (EDX), and electron energy loss spectroscopy (EELS), was consistent with the cytoplasm/membrane location of the chromium (III), possibly as chromium phosphate. The cells could also take up chromium (III) directly from the medium in a metabolically dependent fashion, and accumulate it within the cells. These results indicate a novel pattern of interaction with chromium species distinct from that observed previously with other microorganisms. They also suggest that M. capsulatus, and similar methanotrophs may contribute directly to chromium (VI) reduction, and accumulation in mixed communities of microorganisms that are able to perform methane-driven remediation of chromium (VI)