Ian M. RamboFollow


Biological Sciences


Smith, David, C

Advisor Department

Oceanography, Graduate School of




Hexachlorocyclohexane, bioremediation, marine microbiology, aerobic degradation, Spanish, persistent organic pollutant


Hexachlorocyclohexanes (HCHs) are a family of chlorinated organic compounds that were previously used as agricultural insecticides. HCHs are recognized as persistent organic pollutants due to their toxicity, recalcitrant properties, and tendency to bioaccumulate in food webs. Although HCH was first synthesized in 1825, its use was not widespread until the discovery of the insecticidal activity of the γ-HCH isomer in 1942. γ-HCH and its toxic waste isomers α-HCH and β-HCH were banned from production and use by the United Nations in 2009, yet these chemicals still present environmental problems due to their persistence in soils and surface waters. HCHs continue to be introduced into aquatic ecosystems via rain and groundwater. Bioremediation of HCH-contaminated soil and water by bacteria is a viable option for restoring these areas.

Aerobic biodegredation of HCH by soil bacteria has been studied extensively, yet the HCH degrading potential of aerobic bacterioplankton in the ocean water column has not. Certain bacteria are able to utilize toxic compounds like HCH as carbon sources, and in environments where HCH concentrations are high, HCH-degrading species have the potential to out-compete other members of the microbial community and alter the greater ecological landscape.

This study focuses on the effects that α, β, and γ-HCH isomers have on aerobic marine bacterial communities. These isomers were chosen due to their higher prevalence in the environment compared to other HCH isomers, as well as their toxicity. Water samples from Narragansett Bay were spiked with α, β, and γ-HCH to select for bacterial species able to tolerate or utilize these compounds. Bacteria isolated from these seawater incubations were used in subsequent HCH degradation experiments. Mass spectrometry was used to quantify the concentrations of each HCH isomer over time in order to calculate degradation rates. Comparisons of experimental and control samples highlight possible bacterial population trends in HCH-contaminated environments. Isolation of marine bacteria capable of degrading HCH in situ has potential for bioremediation of contaminated waters.