Investigating veterinary drugs in groundwater

While the use of veterinary drugs is ubiquitous on Irish farms, very little is known about their subsequent impacts on the environment. In this article, Damien Mooney discusses his research into two commonly used veterinary anti-parasitic drugs and a newly-developed analytical method to determine the presence or otherwise of such contaminants in Irish groundwaters.

Due to increased intensification of the food production system, veterinary drugs have become a critical component in animal husbandry in Ireland and more broadly within the European Union.

The administration of such substances can potentially lead to their occurrence in environmental waters, primarily as a result of excretion in faeces and urine, either directly on farmland or via land spreading in manure or slurry.

This has led to veterinary drugs being considered as potential emerging groundwater contaminants of concern.


This research specifically focused on investigating two groups of antiparasitic veterinary drugs that are most commonly used in Irish agriculture, the anthelmintics (used to control parasitic worms in food producing animals exposed to pasture-based diets) and the anticoccidials (used to treat coccidiosis, an intestinal parasitic disease, which is predominant in poultry).

One of the main reasons that these are considered as emerging contaminants is because there is only limited information available on their environmental occurrence, fate and ecotoxicity, particularly in groundwaters.

This dearth of information has been attributed (in part) to a lack of suitably sensitive analytical methodologies for detecting these contaminants at environmentally relevant concentrations. There is also no regulatory monitoring of these drugs in environmental waters and no definitive legislative limits specific to natural waters or drinking water. This is despite the fact that up to 90% of the
administered dose can be excreted by the animal into the environment.


The main objective of the research was to develop new analytical methods and apply them to investigate the occurrence of these contaminants in Irish groundwater.

A comprehensive, highly sensitive analytical method was developed, validated and applied to investigate the occurrence of 40 anthelmintic compounds (including 13 breakdown products) and 26 anticoccidial compounds, respectively.

In brief, contaminants were extracted from the raw water samples using a technique called solid phase extraction, which acts like a “chemical filter” to isolate any contaminants from large volumes of water. The filtered contaminants were then identified and quantified by liquid chromatography tandem mass spectrometry (LC-MS/MS), which is considered the most powerful technique for analysing veterinary drugs in complex samples.

This method was applied in two separate studies, for each of which sampling sites were selected to be representative of different animal production systems and varied hydrogeological settings throughout Ireland.

This involved sampling a range of rural groundwater sites across the country, including water bodies being abstracted for potable use by Irish Water and by privately sourced group water schemes (GWSs).

The sites selected were from a network of existing abstraction and monitoring points being utilised by group water schemes (43 in all), the Environmental Protection Agency of Ireland, the Geological Survey Ireland and Teagasc (as part of its Agricultural Catchments Programme).


17 different anthelmintic compounds were detected across 22% of the 106 sites (including 22 group water schemes) that were sampled in 2017, with concentrations in the order of 1-41 parts per

Monthly sampling was carried out over 13 months, at eight karstic springs, including four from which group water schemes abstract their raw water.

The results showed seasonal variation, with increased frequency and concentration of anthelmintics in groundwater between March-April and again during August-September. The research highlighted the importance of anthelmintic usage patterns (as well as extreme rainfall events) in understanding the occurrence of anthelmintics in groundwaters that are most sensitive to contamination.

Overview of potential source and pathways for anthelmintic occurrence in groundwater (from


In a separate study in 2018, 109 sites (including 11 GWSs) were sampled for the 26 anticoccidials. 7 different compounds were detected at 24% of sites, with concentrations in the range of 1-386 parts per trillion. The anticoccidials detected were in line with expected usage. Statistical analysis shows that the presence of poultry farms and poultry manure landspreading is a significant driver of the occurrence of anticoccidial compounds in groundwaters.

Figure 2: overview of potential source and pathways for anticoccidial occurrence in groundwater (from


Although there are no legislative limits set to determine the safe levels of these contaminants in water, the detected concentrations in this study were an order of magnitude lower than the levels permissible in foods of animal origin that are intended for human consumption.

Even so, this study highlights the fact that these veterinary pharmaceuticals are occurring in our groundwaters and may, therefore, need to be considered with regard to potential groundwater quality and environmental concerns.

This is especially so given that their use is anticipated to continue, and possibly increase, as a result of agricultural intensification and climate change.

Analytical methods

The analytical method developed as part of this study is considered the most comprehensive method currently available for application to environmental water samples. Its application will allow for more comprehensive studies to be carried out in the future, providing more information on the fate of anthelmintics and anticoccidials in environmental waters.


Damien has recently completed a PhD on this topic and is also the primary author of two papers that have been published on foot of his research. “Investigating veterinary antiparasitic drugs as emerging contaminants in Irish groundwater” is available at and ‘An investigation of anticoccidial veterinary drugs as emerging organic contaminants in groundwater’ can be read in full at

This work formed part of the Groundwater Challenge of the Irish Centre for Research in Applied TGeosciences (iCRAG) and was undertaken as a collaboration between Trinity College Dublin, the Teagasc Walsh Fellow Scheme. This work was partly supported by a grant from Science Foundation Ireland (No.13/RC/2092) and under the European Regional Development Fund and by industry partners.