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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 < 0.025 to 176.722 mg·kg−1 DW, with an overall proportion of V > 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.

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The mercury concentrations in wastewater and sewage sludge of a stabilization pond system have been evaluated. The system is built by three parallel facultative ponds followed by two systems of three maturation ponds in series. The samples of wastewater and sludge were digested using nitric acid and placed into a Parr-type bomb for 4 h at 110 degrees C. Mercury was measured by Cold Vapour Atomic Absorption Spectrometry (CV-AAS) at 253.7 nm with sodium tetrahydroborate as reductant. The methodologies were checked with an USEPA quality control sample, a standard reference material from NIST and with another method of mineralization (cold mineralization) showing good results. Concentrations of mercury in wastewater between 1.47 +/- 0.75 microgl(-1) have been found at the entrance of the system and 0.74 +/- 0.0 microgl(-1) at the exit, while in sludge the results were between 0.29 +/- 0.12 microgkg(-1) in the facultative pond and 0.04 +/- 0.02 microgkg(-1) in the second maturation pond (exit).