Investigation of the Risk that Biosolids-derived Triclosan and Triclocarban Pose to Plants and Human Health
Triclosan and triclocarban are frequently detected in biosolids at relatively large concentrations, which generates concern that these chemicals may have an adverse effect on crop yield and accumulate in plants grown in biosolids-amended soil. The objective of this thesis was to determine whether biosolids-derived triclosan and triclocarban pose a risk to plants, or human health due to accumulation in plant tissue. In the laboratory, plants were grown in soil amended with biosolids that contained increasing concentrations of triclocan and triclocarban. In the field, plants were grown in soil amended with biosolids, which contained triclosan and triclocarban. Residues of triclocan and triclocarban in the edible tissue of plants from laboratory and field experiments did not exceed 5.5 and 5.7 ng/g dw. No consistent trend between exposure to triclosan or triclocarban and various measures of growth was observed for all species. Exposure to triclosan and triclocarban also did not have an effect on the colonization of the roots of lettuce and corn plants by arbuscular mycorrhizal fungi. The data collected in this thesis indicate that biosolids-derived triclosan and triclocarban represent a de minimis risk to crop yield. This thesis also evaluated the use of two models (i.e., BASL4 and DPU) to predict the concentration of eight pharmaceuticals and personal care products (PPCPs), including triclosan and triclcarban, in plant tissue grown in biosolids-amended soils for the purpose of characterizing exposure in human health risk assessment. Based on the simulation of various amendment scenarios, the DPU model more accurately predicted the residues of the eight PPCPs in plant tissue relative to the BASL4 model. Finally, an assessment was conducted to determine the risk that residues of PPCPs in plant tissue grown in soil amended with biosolids, manure, or wastewater pose to human health. The risk assessment determined that residues of PPCPs in plant tissue due to biosolids and manure amendment represents a de minimis risk to human health. However, the risk due irrigation with wastewater or the risk due the mixture of PPCPs present in plant tissue could potential pose a risk to human health, and therefore require further investigation.