Tricosan in greywater: Implications for reuse

Greywater is household wastewater containing all used water except sewage. In order to conserve water, it has been proposed to use greywater for irrigational purposes. If this was the case, greywater would travel straight from the house to outside for use, minimizing the need for installing pipelines and such to carry the water elsewhere. However the widespread use of a variety of antibacterial and there subsequent presence in greywater raises concerns regarding impact on environment and health. Our research looked at the possible modification of microbial communities within the soil due to the presence of a commonly used antibacterial agent, triclosan. Along with the community structure, we also looked at any antibiotic resistance due to the constant exposure to triclosan. This experiment involved of three groups: control, greywater only and greywater with triclosan. Each group consisted of four soil filled columns treated with their designated solutions on a weekly basis. The effluent was collected from each column and cultured onto plates. Isolates were then taken from the plates for further testing. Our findings show that under constant exposure, the community structure did, in fact, change showing two very distinct heterotrophic populations between those that were treated with triclosan and those that were not. It was also seen that due to the exposure to triclosan, resistance to the four tested antibiotics (ampicillin, chloramphenicol, streptomycin and tetracycline) increases. Our results indicate that triclosan in greywater can have significant impacts on soil microbes. The changing of the microbial community structure could lead to a change in available nutrients and the form those nutrients are found. While the antibacterial products may be present in very minute concentrations, their constant presence may be selecting for bacteria that are resistant to all types of antibiotics, thus making it harder to treat. It is possible that all this is avoidable by treating the greywater before using it or by removing antibacterial products. In congruence with our data, there is a need for further investigation.