Several tasks were performed within RESOURCE to accomplish the project objectives. Target analytical methodologies and protocols were developed to analyze selected antibiotics and ARGs in both manure (mostly pig slurry) and groundwater. A streamlined protocol for DOM characterization in groundwater, and subsequent statistical analysis, was set-up. Comprehensive field monitoring studies were performed, collecting both groundwater and manure, in areas with intensive livestock production and where groundwater is also used as a drinking water source. Besides analyzing antibiotics and ARGs in manure, their reduction under different treatment technologies was also evaluated as a strategy to reduce potential environmental and human health risks.
Results showed a widespread occurrence of antibiotics widely used in animal husbandry in animal manure (i.e. pig slurry) at high concentrations (from high µg L-1 to even mg L-1). Some of these antibiotics were also present in groundwater samples, mostly at low concentrations (ng L-1). Nevertheless, in some cases, they even reached remarkable levels (µg L-1). Genes conferring resistance to the antibiotic classes detected were also found in both manure and groundwater, with values from 4×102 to 5×106 copy numbers/L water in groundwater. The reduction of antibiotics during manure treatment was moderate (from 40% up to even complete elimination for some compounds), suggesting that its treatment prior to field application is a suitable alternative to reduce environmental risks. DOM analysis revealed that most molecular formulas were CHO compounds, while a remarkable percentage contained nitrogen and sulphur (~15-20%, respectively) as well. The use of van Krevelen diagrams (plots of H/C versus O/C atomic ratios) showed that all our samples were dominated by molecules falling in the lignin-like region. Finally, we could also establish relationships between antibiotics and DOM composition. The analysis of groundwater samples along different seasons showed large variability in the compounds detected and their concentrations. This hinders the assessment of groundwater quality for public uses as well as the implementation of efficient monitoring strategies.
Project results were disseminated through different strategies, such as: (i) the publication of open-access journal articles (two papers are under preparation and will be submitted once completed); (ii) oral and poster contributions in national and international conferences; (iii) the organization of a workshop with stakeholders, farmers and end-users: (iv) the elaboration of an open-access technical guide about the reduction of antibiotics in manure treatment and to draft guidelines for a safe manure reuse; (v) disseminating the project activities and results at the institute’s annual newsletter, 10th anniversary conference “Water research in perspective: beyond 2020” and the EU Climate Change Initiative, all open to the general public and (vi) the presentation of a master thesis, among others.
