Dissemination of antibiotics through the wastewater–soil–plant–earthworm continuum

Authors: Ashworth, Daniel; Ibekwe, Abasiofiok - Mark; MEN, YUJIE - University Of California, Riverside; Ferreira, Jorge

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2022
Publication Date: 10/29/2022
Citation: Ashworth, D.J., Ibekwe, A.M., Men, Y., Ferreira, J.F. 2022. Dissemination of antibiotics through the wastewater–soil–plant–earthworm continuum. Science of the Total Environment. 858. Article 159841. https://doi.org/10.1016/j.scitotenv.2022.159841.
DOI: https://doi.org/10.1016/j.scitotenv.2022.159841

Interpretive Summary: In arid regions such as the southwestern United States, farmers increasingly use water that has been recycled to irrigate their crops. This reuse of treated municipal wastewater (TMW) in agriculture may lead to the addition of contaminants such as antibiotics to the soil. Antibiotics are important as they may lead to the development of antibiotic resistance in agricultural systems, i.e., through the food chain, which could lead to serious human health concerns. We therefore studied the dissemination of the antibiotics trimethoprim, sulfamethoxazole, and sulfapyridine through the water–soil–plant–earthworm continuum under greenhouse/laboratory conditions. When used “as-collected” to irrigate spinach and radish crops, the TMW did not lead to any transfers of these compounds from the soil into plants owing to their low concentrations in the TMW. However, when we spiked the TMW to produce higher concentrations of these compounds, they were taken up by the plant roots and found in the edible plant parts. In subsequent studies, contaminated plant materials were fed to earthworms and showed the potential to bioaccumulate in the earthworm tissues. Such transfers may imply that these compounds could also be transferred to humans, which may have implications for the development of antibiotic tolerance and associated human health concerns. These issues can perhaps be lessened through high levels of TMW purification to effectively remove these compounds.

Technical Abstract: Under the ongoing climate change scenario, treatedmunicipal wastewater (TMW) is a potential candidate for irrigated agriculture but may result in the exposure of agricultural environments to antibiotics. We studied the transfers of trimethoprim, sulfamethoxazole, and sulfapyridine in the TMW–soil–plant–earthworm continuum under greenhouse/laboratory conditions. Irrigation of potted spinach and radish with as-collected TMW resulted in no transfers of antibiotics into soil or plants owing to their low concentrations in the tertiary-treated TMW. However, TMW spiked with higher antibiotic concentrations led to transfers through this continuum. High initial inputs, slow soil degradation, and chemical speciation of the antibiotics, coupled with an extensive plant-root distribution, were important factors enhancing the plant uptake of antibiotics. In microcosm studies, transfers from vegetable materials into earthworms were low but showed potential for bioaccumulation. Such food chain transfers of antibiotics may be a driver for antibiotic resistance in agricultural systems, which is an area worthy of future study. These issues can perhaps be mitigated through high levels of TMW purification to effectively remove antibiotic compounds.