Occurrence of micropollutants and enterobacteria in Ticino Valley: an insight of water contamination in an agricultural area with highly anthropogenic impact

This study investigates the groundwater quality of an aquifer located in medium-populated area of the Ticino Valley with strong agricultural vocation. Two monitoring campaigns were carried out according to the phases of rice cultivation (pre- and post-flooding) on the subsurface and surface irrigation network, Ticino River and wastewater effluents, highlighting a diffuse contamination. The isotopic analyses evidenced mixing phenomena, with both contributions from local rainfall and irrigation network. Combining chemical and microbiological approaches, the anthropogenic impact was evaluated by analysing a selection of traditional and emerging pollutants, such as pesticides, antibiotics and hormones, and assessing the extent of enterobacterial contamination and potential antibiotic resistance genes. Most of the investigated contaminants were found in concentrations from 0.1 ng/L to 632 ng/L, with the exception of Glyphosate and AMPA up to 5 and 20 μg/L, respectively. Even at these low concentrations, contamination of water resources is a serious issue because long-term exposure to such pollutants may cause detrimental effects. The most frequently detected pesticide was the fungicide Tricyclazole, while glucocorticoid Dexamethasone was the most frequent steroid hormone. Noteworthy is the ubiquity of Trimethoprim and a recurrent presence of fluoroquinolones. The occurrence of antibiotics at most sites, although at very low levels, is of environmental and public health concern, as they exert a selective pressure on bacterial populations, allowing the development of antibiotic resistant microbes, as highlighted by microbiological investigations. Indeed, a high microbial load was found in both campaigns, in particular in those sampling sites close to wastewater treatment plants, with the β-lactams and quinolones classes of antibiotics as the most affected by the phenomenon of resistance.