Transport and risk assessment of antibiotics in the use of treated water in agricultural irrigation

In this thesis study, 20 commonly used antibiotics and 4 of their metabolites, totaling 24 target pollutants, were selected. Raw wastewater, secondary treated wastewater, water treated with ultrafiltration (UF), multilayer sand filter and ultraviolet (MMF/UV), and groundwater samples from the Konya Advanced Wastewater Treatment Plant were used to irrigate lettuce and corn plants. The presence of antibiotics in irrigation water and their transfers to lettuce and corn were evaluated. Antibiotic concentrations in water, soil samples, and plant samples divided into roots, stems, and edible parts after harvest were measured using liquid chromatography-mass spectrometry (LC-MS). Health risks for children and adults were calculated based on antibiotic concentrations in the edible parts of the plants. Ecological risks for aquatic organisms, such as algae, daphnia, and fish, as well as soil organisms, were assessed using antibiotic concentrations in irrigation water and soil. Health risk assessments were also conducted for scenarios involving the consumption of irrigation water as drinking water and ingestion of soil. All target antibiotics and metabolites were detected in water samples, while no antibiotic residues were found in groundwater. The highest antibiotic concentrations were found in raw wastewater, ranging from 1932.77 to 22117.78 ng/L. Metabolite concentrations in raw wastewater ranged from 185.69 to 1108.29 ng/L. Macrolides (MLs) were the most abundant antibiotic class in raw wastewater. Azitromycin (AZI), clarithromycin (CLA), and doxycycline having the highest concentration. While antibiotic removal was generally limited, the UF process achieved the highest removal efficiency. Roxithromycin (ROX) was not removed in any treatment process. Sulfamethoxazole (SMX), ROX, and clindamycin (CLI) were found to be resistant to biological degradation. Negative removal values observed for some antibiotics were attributed to reversion from metabolites to parent compounds and the release of antibiotics adsorbed onto suspended solids back into the system. Antibiotics exhibited different transport and transformation mechanisms in lettuce and corn depending on their physicochemical properties. Macrolides (MLs) and quinolone (QN) antibiotics accumulated at the highest levels in lettuce and corn, respectively. Many antibiotics showing a tendency to move from the roots to other plant parts. The highest antibiotic accumulation was observed in lettuce and corn irrigated with raw wastewater. Lettuce showed the highest antibiotic accumulation in the edible parts, while corn exhibited higher concentrations in the stems compared to the edible parts. Antibiotic concentrations in the edible parts of lettuce and corn were measured at 651.52-1045.10 ng/g and 190.06-578.24 ng/g, respectively. In the soil where these plants were grown, antibiotic concentrations were 322.73-490.57 ng/g for lettuce and 148.00-263.00 ng/g for corn. Health risks, both carcinogenic and non-carcinogenic, from consuming lettuce and corn, were evaluated. For children, the hazard index (HI) values for non-carcinogenic risk from consuming lettuce and corn were 3.23×10-3–7.33×10-3 and 3.07x10-3-1.17x10-2, respectively, with lower values for adults. Since all HI values were below the threshold, no non-carcinogenic health risk was anticipated. The total carcinogenic risk (TCR) values for antibiotic-related cancer risk from consuming these plants were in the 10-7 range for both children and adults, indicating no significant carcinogenic risk. Using the toxicity threshold concern (TTC) approach, the required consumption amounts of lettuce and corn to pose a health risk were determined to be much higher than actual consumption levels, suggesting no health risk from eating these plants irrigated with various water sources. Monte Carlo simulation results, based on 100,000 iterations, also predicted no antibiotic-related health risks. Health risks from drinking antibiotic-contaminated water and ingesting contaminated soil were evaluated. It was generally concluded that there would be no health risk from consuming reclaimed water. However, seasonal variations could increase antibiotic concentrations, posing a high HI values for wastewater. No health risks were found for soil ingestion. Ecological risk assessments for daphnia, algae, fish, and soil organisms revealed that the highest risk quotient (RQ) value was in raw wastewater, recorded in February. Algae showed the highest RQ, while fish had the lowest.