Greywater Reuse: Impact of Triclosan on Soil Microorganisms

Open Access
Harrow, Danielle Irene
Graduate Program:
Environmental Pollution Control
Master of Science
Document Type:
Master Thesis
Date of Defense:
March 30, 2012
Committee Members:
  • Katherine H Baker, Thesis Advisor
  • Yen Chih Chen, Thesis Advisor
  • Shirley Elizabeth Clark, Thesis Advisor
  • Triclosan
  • Antibiotic Resistance
  • Greywater
The use of greywater for irrigation results in the direct discharge of trace quantities of personal care products and antimicrobial agents to the environment. The presence of antibacterial compounds (e.g. triclosan) in greywater raises concerns regarding potential impacts of these materials on the environment and human health. Our research examined the impact of triclosan on soil microbial communities using soil filled pots irrigated with greywater (synthetic) only or greywater with triclosan. Functional diversity of the heterotrophic microbial community was assayed. Soil samples were cultured for viable heterotrophic bacteria and triclosan-resistant heterotrophic bacteria in the two treatments. Isolates were evaluated for resistance to multiple antibiotics and used to quantify tetracycline resistance genes. Under constant exposure, the community structure, showed two very distinct heterotrophic assemblages between soils treated with triclosan and the control soil. There were statistically significant increases in the number of heterotrophic organisms resistant to triclosan when the two soils were compared. The frequency of the tet a gene increased significantly in subsamples irrigated with greywater with triclosan as well as the proportion of bacterial isolates resistant to multiple antibiotics in these soil samples. Our results indicate that triclosan in greywater can have significant impacts on soil microbes. This in turn can affect the types of available nutrients within the soil. While antibacterial products may be present in trace concentrations in greywater, repeated exposure to soil organisms may be selecting for bacteria resistant to multiple types of antibiotics. Therefore, our results indicate that greywater should be treated to remove antibacterial agents before its use in lawn irrigation. Alternatively, the use of antibacterial containing products should be significantly reduced.