Fate and transport of antibiotics in the agroecosystem: Uptake in the soil-plant system

Increasing stress on freshwater supplies, a result of increasing global population and climate change, has made necessary the reuse of wastewater as a source for irrigation. Wastewater, both municipal and agricultural, is a known reservoir for many emerging contaminants (ECs) including antibiotics. The use of wastewater for irrigation provides a pathway for antibiotics to enter the agroecosystem and the surrounding environment. With the emergence of antibiotic resistance as a global human health issue and the increased detection of human pharmaceuticals in various environmental compartments, an increased focus has been placed on the understanding of the fate and transport of these compounds. The focus of this dissertation research was to gain a better understanding of how antibiotic uptake is influenced by the soil-plant system when antibiotics are introduced into the system via irrigation water. Initially, a freeze and thaw cell lysing extraction method was developed and evaluated to extract and quantify four antibiotic compounds (ciprofloxacin, lincomycin, oxytetracycline, and sulfamethoxazole) from water, soil, and complex vegetative matrices. With this, a number of different environmental parameters were examined to determine their impacts on uptake into plants. First, subspecies variation in uptake potential in two cultivars of lettuce, lactuga sativa, revealed significantly higher uptake in cv. Greenstar compared to cv. Salad Bowl. Next, the influence of soil texture and drought conditions on the uptake of antibiotics from a single exposure of contaminated irrigation water showed that both variables impact antibiotic uptake, with the results being compound specific. In a follow up study, the influence of soil texture on antibiotic uptake by lettuce was studied with exposure to contaminated irrigation water throughout the entire growth cycle. Results reinforced the compound specific nature of soil texture effects and also revealed the time dependent nature of the uptake process and the influence of persistence both in soil and in the plant tissue. A final investigation was conducted to identify trends in uptake between various vegetables representing root, shoot, and fruit edible portions and showed distinct species level differences in uptake as well as compound specific differences in accumulation and translocation from various plant portions