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Assessing the impact of agriculture on Spanish groundwater

Reusing manure as a fertiliser can lead to a degradation of natural water resources. By analysing dissolved organic matter together with antibiotics and antibiotic resistance genes, RESOURCE has developed a novel method for assessing water quality.

Food and Natural Resources

75 % of the EU’s population rely on groundwater for their drinking water supply, while in agriculture it is widely used for irrigation. However, groundwater quality can be compromised by the so-called contaminants of emerging concern. These include veterinary antibiotics, pharmaceuticals, antibiotic resistance genes and pesticides. RESOURCE, a research project undertaken with the support of the Marie Skłodowska-Curie Actions programme, evaluated animal manure as a source of groundwater contamination in Spanish agricultural areas with intensive livestock production. The project confirmed that using animal manure as a fertiliser results in antibiotics and antibiotic resistance genes reaching groundwater systems. “Information about groundwater quality is still scarce,” says Meritxell Gros from the Catalan Institute for Water Research, the project host. “Our findings highlight the importance of proper manure management practices to prevent groundwater pollution.”

Groundwater samples as fingerprints

Spain has several regions where intensive livestock production has resulted in large surpluses of manure which, through its use in agricultural fields, is degrading natural water resources. RESOURCE set out to analyse the better-known contaminants, in this case antibiotics and antibiotic resistance genes. This they supplemented with the novel approach of characterising dissolved organic matter (DOM). DOM is a combination of numerous substances, such as humic and fulvic acids, polysaccharides, proteins, lipids, nucleic acids, soluble microbial products and synthetic organic chemicals. The team used high-resolution mass spectrometry followed by statistical analysis to unravel the DOM composition in the groundwater samples. “We wanted to explore the use of DOM as a fingerprint of water quality, instead of just focusing on the classical approach of analysing organic contaminants,” explains Gros. The analysis of samples from different seasons showed large variability in concentrations of antibiotics and antibiotic resistance genes. The team are now investigating the cause of these differences. DOM analysis showed that groundwater samples were dominated by components similar to lignin, with only small amounts of protein-like substances. This was surprising as previous studies of surface water using DOM have found significant traces of protein or tryptophan like substances. “Maybe these compounds are retained by the soils or degraded by microorganisms, so don’t reach groundwater. We should explore this further,” adds Gros. “And despite generally finding low concentrations of antibiotics, between a microgram and nanogram per litre, it is remarkable that they reach groundwater at all! The same goes for the low traces of antibiotic resistance genes found.” Field sampling was conducted in Osona and la Selva, two regions with some of the highest livestock production in Spain.

Prevention is better than cure

By reducing the amount of antibiotics in water supplies, RESOURCE contributes to the fight against antibiotic resistance, in line with the EU’s One Health Action Plan. It also supports the EU’s Water Framework Directive 2000/60/EC set up to protect inland surface waters, and transitional, coastal and groundwater bodies, with the Groundwater Directive 2006/118/EC developed alongside it. “We hope our methodology for assessing groundwater quality using DOM as an indicator, and our data on the occurrence of antibiotics and antibiotic resistance genes, will be useful for future regional monitoring programmes,” says Gros. To take the work forward the team are exploring options for expanding the study areas. They are considering carrying out nationwide monitoring of groundwater quality in hotspots with high livestock densities and are working towards the open-access publication of their results.

Keywords

RESOURCE, groundwater, drinking water, agriculture, contaminants, antibiotics, manure, dissolved organic matter, livestock, irrigation

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