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Wastewater from tanneries contains high concentrations of organic matter, chromium, nitrogen, and sulfur compounds. In this study, an artificial wetland is is used as the tertiary treatment in a tannery in León Gto., México. It consists of three subplots with an area of about 450 m2. Two subplots were planted with Typha sp. and the third with Scirpus americanus. Geochemical analyses along the flowpath of the wetland show that contaminants were effectively attenuated. The most probable number technique was used to determine rhizospheric microbial populations involved in the sulfur cycle and suggested that there were 104-10(6) cells g(-1) sediment of sulfate-reducing bacteria and 10(2)-10(5) of sulfur-oxidizing bacteria (SOB). Representatives of SOB were isolated on media containing thiosulfate. Phylogenetic analysis of 16S rRNA of SOB isolates shows that they belong to the genera Acinetobacter, Alcaligenes, Ochrobactrum, and Pseudomonas. Most of the isolates are organotrophic and can oxidize reduced sulfur compounds such as elemental sulfur or thiosulfate, accumulating thiosulfate, or tetrathionate during growth. All isolates can use reduced-sulfur compounds as their sole sulfur source and some can use nitrate as an electron acceptor to grow anaerobically. Our results illustrate the relevance of SOB in the functioning of the wetland constructed for tannery wastewater remediation.

The aim of this study was to examine lead (Pb) intestinal absorption, its mobilization and redistribution during lactation in rats chronically exposed to lead. Lead and calcium (Ca) concentrations were measured in blood, milk, femurs, liver and kidney samples obtained from pregnant and lactating mother rats which were subjected to different schedules of exposure to Pb: 158 days before and during lactation (group A), 144 days before lactation (group B) and 14 days only during lactation (group C). Results were compared to those of non-pregnant but Pb- exposed matched rats and non-exposed control rats. In groups A and B during lactation, Pb in blood (PbB), liver and kidney increased while Pb in bone decreased. Since there was not an external source of Pb in group B during lactation, the results indicate resorption of Pb in bone as the main source of Pb in the organism. In group A, there was an additional increase of PbB when compared to group B as a result of Pb intestinal absorption. In group C a significant increase in PbB due to intestinal absorption and deposit in bone was found when compared to non- pregnant 144 days old rats, suggesting that the three processes intestinal absorption, bone resorption and bone absorption were taking place. These data indicate that Pb stored in bone as a result of prior maternal exposure, should be considered as a major source of self intoxication and of Pb in milk available to suckling pups.

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