Organochlorine compounds in a Brazilian watershed with sugarcane and intense sediment redistribution.

Until 1985 persistent organochlorine compounds such as aldrin [(1alpha,4alpha,4abeta,5alpha,8alpha,8abeta)-1,2,3,4,10,10-hexachloro-1,4,4a,5,8,8a-hexahydro-1,4:5,8-dimethanonaphthalene] and heptachlor (1,4,5,6,7,8,8-heptachloro-3a,4,7,7a-tetrahydro-4,7-methano-1H-indene) were recommended and used as insecticides on a large scale in sugarcane (Saccharum officinarum L.) cropping in Brazil. The environmental impact of these applications was not investigated in the past neither prior to nor after their restriction of use in Brazil. In a case study conducted during 1999, organochlorine insecticides were investigated in soils, colluviums, submerged sediments, and organisms in a watershed located in a traditional sugarcane-growing region in the southeastern region of Brazil. The results indicated that past applications of organochlorine insecticides (prior to 1985) do not represent an environmental threat at the present time. Most insecticides applied in the past were not detected or were present only in amounts that were below the detection limit. The organochlorine compounds lindane [(1alpha,2alpha,3beta, 4alpha,5alpha,6beta)-1,2,3,4,5,6-hexachlorocyclohexane] and heptachlor that remained on the market after 1985 for purposes other than for soil application were still detectable in significant amounts in soils, sediments, and soil organisms (heptachlor in form of the epoxide metabolites). This may suggest that these residues were originated from applications after 1985. These compounds showed a capacity for accumulation in sediments and soil organisms. The enrichment ratio from soils to sediments was 2 to 3 times and from soils to organisms up to 20 times.

Bacterial functional redundancy along a soil reclamation gradient.

A strategy to measure bacterial functional redundancy was developed and tested with soils collected along a soil reclamation gradient by determining the richness and diversity of bacterial groups capable of in situ growth on selected carbon substrates. Soil cores were collected from four sites along a transect from the Jamari tin mine site in the Jamari National Forest, Rondonia, RO, Brazil: denuded mine spoil, soil from below the canopy of invading pioneer trees, revegetated soil under new growth on the forest edge, and the forest floor of an adjacent preserved forest. Bacterial population responses were analyzed by amending these soil samples with individual carbon substrates in the presence of bromodeoxyuridine (BrdU). BrdU-labeled DNA was then subjected to a 16S-23S rRNA intergenic analysis to depict the actively growing bacteria from each site. The number and diversity of bacterial groups responding to four carbon substrates (L-serine, L-threonine, sodium citrate, and alpha-lactose hydrate) increased along the reclamation-vegetation gradient such that the preserved forest soil samples contained the highest functional redundancy for each substrate. These data suggest that bacterial functional redundancy increases in relation to the regrowth of plant communities and may therefore represent an important aspect of the restoration of soil biological functionality to reclaimed mine spoils. They also suggest that bacterial functional redundancy may be a useful indicator of soil quality and ecosystem functioning.