No abstract

The contamination of sediments caused by the deposition of industrial residues from titanium dioxide production, in sand dunes near a wetland was assessed through atomic absorption spectrometry. The contamination occurred near a shallow freshwater wetland called Jauá Lake, along the coast of Camaçari, Bahia, Brazil. Five core samples were collected, including a reference site, from Jauá Lake and one from a small lake, near the deposition site. Cores were cut in 20-cm sections. Fractions <63 μm were analysed for copper, cadmium, zinc, iron, lead, aluminium, mercury and titanium. Metal concentrations on the upper layer of sediments were, as a whole, higher than in lower ones. Concentrations from the reference site were similar to those from the other sites in Jauá Lake. Absolute values of most metals in the sediments of the Dunas Lake located near the contamination site were higher than in all other stations. The hypothesis, that:: (1) contamination coming from groundwater would contaminate the sediment; and (2) there would be a gradient of decreasing contamination from sites near the residue deposit to sites located further away, were rejected. The continuous removal of groundwater may have contributed to the reduction of further contamination. It is recommended that future studies examine the concentration of metals in plants and the role of plants in metal bioavailability.

Metals are often spilled by industries into inland water environments, with adverse consequences. Numerous papers have reported that heavy metals produce massive destruction of algae. Nevertheless, algal populations seem to become tolerant when they have had previous exposures to heavy metals. Because the mechanisms allowing heavy metal tolerance of algae are not yet known, the present study analyzed the effect of hexavalent chromium on growth and photosynthetic performance of Dictyosphaerium chlorelloides, stressing on the adaptation mechanisms to chromium contamination. Growth and photosynthetic performance of algal cells were inhibited by Cr(VI) at 10 mg/L, and the 72-h median inhibition concentration was established as 1.64 and 1.54 mg/L, respectively. However, after further incubation for a three month period in an environment with 25 mg/L of chromium, some rare, chromium-resistant cells occasionally were found. A Luria-Delbrück fluctuation analysis was performed to distinguish between resistant algae arising from rare, spontaneous mutations and resistant algae arising from physiological adaptation and other adaptive mechanisms. Resistant cells arose only by spontaneous mutations before the addition of chromium, with a rate of 1.77 x 10(-6) mutants per cell division. From a practical point of view, the use of both chromium-sensitive and chromium-resistant genotypes could make possible a specific algal biosensor for chromium.

No abstract