Clopyralid in Drinking Water

Clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) is a selective herbicide used for control of broadleaf weeds, especially thistles and clovers.

As with all individual pesticides the EU legal limit for Clopyralid is 0.10 micrograms/litre in drinking water.

When it is found in drinking water it is usually a small amount above the EU legal limit

There is no WHO health-based guideline values set for Clopyralid in drinking water.

4-chloro-2-methylphenoxyacetic acid (MCPA) in Drinking Water

MCPA accounts for 75pc of all exceedances in water

Tradenames: Mortone, Agritox, M50, Lupo

The four most commonly detected compounds accounting for pesticide exceedances in drinking-water in Ireland are MCPA, 2,4-D, Mecoprop and Clopyralid

Irish Water pointed out the detection of 81 pesticide and herbicides exceedances in public drinking water supplies in Ireland in 2020, an increase of 5 from 2019.

MCPA, the active substance in many herbicide products used to control thistles, docks and rushes, is still the most commonly detected pesticide in drinking water.

Where MCPA enters a stream it can be detected in surface water (drinking water abstraction point) a long way from where it was applied, >30km.

MCPA is the most popular grassland spray by far, and the fact it is highly soluble means it is prone to run-off and leaching

Under the Drinking Water Directive, the limit for a single pesticide in drinking water is 0.1 μg/L and for the sum of all pesticides is 0.5 μg/L.

The River Derg flows east from Donegal across the border into Country Tyrone, where it supplies 16 million litres per day to nearly 40,000 people in Northern Ireland. However, concentrations of the pesticide MCPA have been detected up to 4.33 μg/L at the NI Water drinking water abstraction point and up to 8.97 μg/L in River Derg tributaries.

These concentrations were detected by the Agri-Food and Biosciences Institute (AFBI) and Ulster University (UU) as part of the Source to Tap project.

Source to Tap is monitoring water quality in the River Derg to assess the impact of a financial incentive scheme for agriculture that aims to improve drinking water quality in the catchment.

The Source to Tap monitoring program is focused on MCPA, which is primarily used in Ireland to reduce the cover of rushes (Juncus species) on grazing land.

MCPA is preferred over other herbicides as it does not kill grass and can therefore be sprayed, whereas other herbicides such as glyphosate must be wiped, requiring additional equipment.

The majority of the high concentrations occurred in late spring/early summer and late summer/early autumn, which coincides with peak periods for MCPA application.

Additionally, MCPA is highly soluble and the majority of high concentrations coincide with storm events when rainfall would have washed pesticides into the river.

However, peaks occur that are not associated with rainfall, which could be caused by farming activities such as spraying too close to water courses or accidental spills.

Interestingly, MCPA was present in river water over the entire year, albeit at low concentrations over winter, indicating a persistent source to the river system, either from water stored in the soil or from groundwater.

Note: there are no plans to use predictive modelling for substances with high usage in Ireland but for which little or no monitoring data is available (Source: National Aquatic Environmental Chemistry Group (NAECG) minutes 18/01/2021)

PESTicide MANagement for better water quality

Project AttributeProject Details
Project TitlePESTicide MANagement for better water quality
EPA Project Code2019-HW-LS-3
Lead OrganisationNational University of Ireland Galway (NUIG)
CoordinatorMark Healy
EPA Research 2014 – 2020 Theme(s)Sustainability: Theme 2: Health & Wellbeing
EPA Research Pillars
Project Start and End DatesStart: 03/02/2020
End (if applicable): 02/02/2023
Revised End Date (if applicable):
EPA Project TypeLarge Scale Project
EPA Award TypeSTRIVE – Project Based Awards
Current Project StatusGrant Awarded
Total Funding Amount425598.40
Project Abstract/DescriptionThis project will use a DPSIR (drivers, pressures, state, impacts, responses) approach to assess how drinking water and human health may be affected by pesticide use in Ireland. The project will evaluate the drivers and pressures for the use of pesticides in Ireland and a semi-quantitative pesticide risk ranking will utilise all available data to identify pesticides of concern (WP1). The pathway of loss from the source of pesticide use to the receptor will be identified in WP2. This WP will comprise controlled laboratory mesocosm experiments to understand the impact of soil type and land use on pesticide leaching and surface runoff. In WP 3, the response of the receptor will be evaluated. This will be conducted at urban and catchment scale, and will utilise most of the study sites of the Agricultural Catchments Programme, which have already been extensively characterised and monitored. Baseline monitoring will be conducted for one year, before a low-cost, passive, in-situ technology will be placed in the streams draining the catchments. The project will develop a citizen science network through collaboration with stakeholders (WP 4). WP 5 will address project management and communication to the EPA and stakeholders. Final technical report focusing on the drivers, pressures and impacts of pesticide use on receiving waters and human health in Ireland. This will provide quantitative information, which will inform policies. This project will develop solutions for pesticides in the environment by examining, at field-scale, the efficacy of in-situ, low-cost, passive remediation technologies for pesticide mitigation. Publication of a minimum of five peer reviewed publications from project findings in internationally recognised journals. Materials will be prepared as part of general outreach activities in the NUIG Ryan Institute (reaching > 50,000 members of the general public in 2018 (e.g., Science week) and volunteer formation. These materials will inform the general public and interested third parties about PEST-MAN. Create a website and different profiles in twitter and Facebook to disseminate the obtained results, announce volunteer formation activities, share formation material, and coordinate volunteer actions. A “ResearchGate” project page will be created. This online resource is designed to help researchers discuss publications, create exposure for their own work and connects with colleagues. The results will be presented in leading engineering, soil and microbiological conferences and workshops.
EPA Scientific OfficerRachelClarke