Submitted to: Annals of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2009
Publication Date: 8/31/2009
Citation: Dungan, R.S., Kim, J., Weon, H., Leytem, A.B. 2009. The Characterization and Composition of Bacterial Communities in Soils Blended with Spent Foundry Sand. Annals of Microbiology. 59(2):239-246.
Interpretive Summary: Sands are used by the foundry industry to create metalcasting molds and cores. After the sands have been used several times they are discarded due to a reduction in grain size. Most spent foundry sands (SFS) are landfilled, but there is interest in beneficially using them in manufactured soils. While SFSs generally contain low concentrations of metals and organics, concerns about their impact upon environmental receptors has not been adequately addressed. In this study we assessed the impact of spent sands from iron, aluminum, and steel foundries upon the soil bacterial community. Sandy loam and silty clay soils were blended with 30% SFS and were grown with and without perennial ryegrass. At 4 weeks and 6 months after initiation of the study samples were collected and DNA was extracted. To monitor bacterial community level changes, the DNA was amplified and subjected to denaturing electrophoresis to separate the products. Images of the banding patterns on the gels were taken and analyzed, which revealed that distinct communities were present at week 4 and month 6. Furthermore, the bacterial community structure differed between those with and without ryegrass. Diversity, which is used to assess the overall general health of ecosystems, was higher in the SFS-soil blends at week 4 when ryegrass was not present. By month 6 in treatments without ryegrass, the diversity in the sandy loam blends was similar to the control, while the diversity in all silty clay blends was greater than the control. A phylogenetic analysis of 309 isolates revealed that the soil controls and SFS-soil blends were dominated by common soil bacteria. The genera within each phylogenetic group was not largely influenced by the SFSs, as there was a fairly even distribution among the SFS-soil blends with and without ryegrass. Our results provide evidence that SFSs can bring about bacterial community level changes in soil; however, these changes are similar to that of blending soil with silica sand.
Technical Abstract: Spent foundry sands (SFSs) are a likely replacement for virgin aggregate used in manufactured soils, such as topsoils, potting soils, and landscaping mixes. While SFSs generally contain low concentrations of trace elements and xenobiotics, concerns about their impact upon environmental receptors has not been adequately addressed. To assess impacts upon the soil bacterial community, we amended sandy loam and silty clay soils with SFS from iron, aluminum, and steel foundries at a rate of 30% (dry weight basis). All soils and SFS blends were acclimated for 3 months prior to the initiation of the study, grown with or without perennial ryegrass, and then samples were aseptically collected at 4 weeks and 6 months. To monitor bacterial community level changes, 16S ribosomal DNA was amplified using PCR and subjected to denaturing gradient gel electrophoresis (DGGE). Cluster analyses of the DGGE banding patterns revealed that SFS blends from week 4 and month 6 produced unique clusters, with most ryegrass treatments clustering away from those without ryegrass. The diversity of the bacterial community, determined via the Shannon-Weaver index, revealed that diversity was generally higher in the SFS blends without ryegrass at both week 4 and month 6. At week 4, the highest diversity was present in the iron SFS blends (both soils without ryegrass). By month 6 in treatments without ryegrass, the diversity in the sandy loam blends was similar to the control, while the diversity in all silty clay blends was greater than the control. Phylogenetic analysis of bacterial isolates (total of 309) from the soils and SFS blends showed that they were dominated by Actinobacteria, Bacilli and Proteobacteria, with fewer numbers belonging to Bacteroidetes. Our results provide evidence that SFSs can bring about bacterial community level changes in soil; however, these changes are similar to that of blending soil with silica sand.