Assessment of the use of industrial by-products to remediate a copper- and arsenic-contaminated soil

Copyright © 2004 ASA, CSSA, SSSATwo water treatment sludges (WTS-A, WTS-B), two red muds (RM), and red gypsum (RG), all rich in iron oxy-hydroxides, were added to a soil highly polluted with As and Cu at 2% (w/w) to reduce metal bioavailability. Because the amendments increased soil pH to approximately 6, a lime treatment to the same pH and an unamended treatment were included for comparison. All the amendments had significant positive effects on the soil microbial biomass and growth of ryegrass (Lolium multiflorum Lam. cv. Avance), but only WTS-A improved lettuce (Lactuca sativa L. cv. Tom Thumb) growth. The mineralization of added ammonium nitrogen was not significantly affected by the treatments, while a physiologically based extraction test (PBET) showed that bioaccessibility of As was low (<5%) and decreased only in the WTS-A treatment. Concentrations of As in soil pore water and extractable As only decreased in the WTS and RG treatments. In contrast, Cu concentrations in soil pore water and extractable Cu decreased in all treatments, by more than 84% in the WTS, RM, and RG treatments. Non-isotopically exchangeable As and Cu were present in colloids in the soil pore water. Untreated soil had <4% isotopically exchangeable As and this decreased by approximately 50%, with WTS, RM, and RG. The labile Cu pool represented a large proportion (34%) of the total Cu pool, and the isotopically exchangeable and soluble Cu were strongly correlated with soil pH. Acidification of the treated soils showed that the labile As and Cu both increased in the treated soils compared with untreated soils. The significance of the treatment effects on soil fertility and potential off-site transport of As and Cu to ground water are discussed.Enzo Lombi, Rebecca E. Hamon, Gerlinde Wieshammer, Mike J. McLaughlin and Steve P. McGrat

Culturable bacteria from Zn- and Cd-accumulating Salix caprea with differential effects on plant growth and heavy metal availability.

Aims: To characterize bacteria associated with Zn ⁄ Cd-accumulating Salix caprea regarding their potential to support heavy metal phytoextraction. Methods and Results: Three different media allowed the isolation of 44 rhizosphere strains and 44 endophytes, resistant to Zn ⁄Cd and mostly affiliated with Proteobacteria, Actinobacteria and Bacteroidetes ⁄ Chlorobi. 1-Aminocyclopropane- 1-carboxylic acid deaminase (ACCD), indole acetic acid and siderophore production were detected in 41, 23 and 50% of the rhizosphere isolates and in 9, 55 and 2% of the endophytes, respectively. Fifteen rhizosphere bacteria and five endophytes were further tested for the production of metal-mobilizing metabolites by extracting contaminated soil with filtrates from liquid cultures. Four Actinobacteria mobilized Zn and ⁄ or Cd. The other strains immobilized Cd or both metals. An ACCD- and siderophore-producing, Zn ⁄ Cd-immobilizing rhizosphere isolate (Burkholderia sp.) and a Zn ⁄ Cd-mobilizing Actinobacterium endophyte were inoculated onto S. caprea. The rhizosphere isolate reduced metal uptake in roots, whereas the endophyte enhanced metal accumulation in leaves. Plant growth was not promoted. Conclusions: Metal mobilization experiments predicted bacterial effects on S. caprea more reliably than standard tests for plant growth-promoting activities. Significance and Impact of the Study: Bacteria, particularly Actinobacteria, associated with heavy metal-accumulating Salix have the potential to increase metal uptake, which can be predicted by mobilization experiments and may be applicable in phytoremediation

Jornadas ICT. 2004

Jornadas ICT. 200