Year of Publication

2008

Degree Name

Doctor of Philosophy (PhD)

Document Type

Dissertation

College

Agriculture

Department

Soil Science

First Advisor

Dr. Elisa M. D'Angelo

Abstract

The entire stretch of the Ohio River is under fish consumption advisories due to contamination with polychlorinated biphenyls (PCBs). In this study, natural attenuation and biostimulation of PCBs and microbial communities responsible for PCB transformations were investigated in Ohio River sediments.

Natural attenuation of PCBs was negligible in sediments, which was likely attributed to low temperature conditions during most of the year, as well as low amounts of available nitrogen, phosphorus, and organic carbon. Moreover, surface sediments were relatively oxidized, as indicated by the prevalence of aerobic bacteria such as beta- Proteobacteria, alpha-Proteobacteria, Sphingobacteria, and Nitrospira in 16S rRNA sediment clone libraries. On the other hand, several reductive dechlorinators were detected in sediments, including Dehalococcoides, Desulfitobacterium spp. which suggested that reductive dechlorination might be possible in sediments under certain biogeochemical conditions.

Considerable amounts of PCBs were transformed by reductive dechlorination (80% in 177 days by pattern N) when sediments were maintained under anaerobic conditions, amended with nutrients and organic carbon, and incubated at 25 ºC in lab microcosms. Analysis of 16S rRNA clone libraries from these treatments revealed that Bacteroidetes, Chloroflexi and Firmicutes were enriched and Proteobacteria were depleted compared to clone libraries from treatment without organic amendments. Reductive dechlorination was decreased in sediments incubated at 10 and 40 ºC, and was not affected by FeSO4 amendments compared to unamended sediments incubated at 25 ºC.

Transformations of PCB-153 were investigated in sediments under anaerobic, aerobic and sequential anaerobic and aerobic conditions. Transformations were only observed in treatments with an anaerobic phase, which occurred by reductive dechlorination by pattern N. Neither PCB-153 nor dechlorination products PCB-99 or PCB-47 were transformed under aerobic conditions. Analysis of 16S rRNA clone libraries revealed that Bacteoridetes, Chloroflexi, and Firmicutes were enriched under anaerobic conditions and Proteobacteria were enriched under aerobic conditions.

Results from this study revealed that natural attenuation and biostimulation were not effective at removing PCBs from Ohio River sediments. Hence, other remediation methods will need to be employed to decrease PCB levels in this ecosystem.

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