Occurrence, fate, and transport of human and veterinary antibiotics in the watershed

Abstract

Antibiotics have been used to abate infections for humans, not only to prevent diseases but also to enhance the growing efficiency as growth promoters for animals. However, antibiotics released in the environment can cause adverse effects producing antibiotic resistant bacteria in the ecosystem and potentially human health issues. Consequently, researchers have begun to study antibiotics to evaluate the occurrence, transport, and fate in several environmental compartments. The first objective of this study was to identify the presence of antibiotics in both aqueous and sediment matrices of the watershed with newly developed solid phase extraction (SPE) methods combined with high performance liquid chromatography tandem mass spectrometry (HPLC/MS/MS) techniques. The selected watershed, Cache la Poudre River is located in Northern Colorado, and combines effluents from two wastewater treatment plants (WWTP) and runoffs from several animal feeding operations (AFO) making it suitable for studying human and animal antibiotics. The measured concentration levels of antibiotics in water was generally less than 1 μg/L but as much as a 1000 times higher concentration was detected in sediment, indicating the importance of studying this matrix for better environmental risk assessment. The second objective was to verify transport mechanisms of antibiotics focused on veterinary antibiotics from source to environment. To evaluate rainfall effects on surface runoff and leaching behavior of veterinary antibiotics, rainfall simulation and column leaching experiments were conducted. Depending on the sorption and persistence of individual antibiotics, different characteristics were observed. In particular, these studies revealed that colloids could act as carriers to move even strongly sorbed antibiotics deeper into the subsurface and possibly cause contamination in groundwater. The last objective was to compare two animal waste management approaches, stockpiling and composting, for minimizing the release of antibiotics prior to application in the field as fertilizer. Composting was shown to be more effective to degrade antibiotics and can be suggested as an alternative strategy to reduce the antibiotics in the environment. Although there is no regulation regarding handling or treatment of wastes with residual antibiotics, adverse effects have been identified and there are concerns about possible human health risk. As a result, continued research on antibiotics in the environment should be pursued.