Approaches to herbicide (MCPA) pollution mitigation in drinking water source catchments using enhanced space and time monitoring

Phoebe A Morton,Rachel Cassidy,Stewart Floyd,Donnacha G Doody,W Colin Mcroberts,Philip Jordan

doi:10.1016/j.scitotenv.2020.142827

Phoebe A Morton, Rachel Cassidy + Show 4 more

Open Access

https://doi.org/10.1016/j.scitotenv.2020.142827

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Abstract

Freshwater occurrences of the selective acid herbicide 2-methyl-4-chloro-phenoxyacetic acid (MCPA) are an ongoing regulatory and financial issue for water utility industries as the number and magnitude of detections increase, particularly in surface water catchments. Assessments for mitigating pesticide pollution in catchments used as drinking water sources require a combination of catchment-based and water treatment solutions, but approaches are limited by a lack of empirical data. In this study, an enhanced spatial (11 locations) and temporal (7-hourly to daily sampling) monitoring approach was employed to address these issues in an exemplar surface water source catchment (384 km2). The spatial sampling revealed that MCPA was widespread, with occurrences above the 0.1 μg L−1 threshold for a single pesticide being highly positively correlated to sub-catchments with higher proportions of ‘Improved Grassland’ land use (r = 0.84). These data provide a strong foundation for targeting catchment-based mitigation solutions and also add to the debate on the ecosystems services provided by such catchments. Additionally, of the 999 temporal samples taken over 12 months from the catchment outlet, 25% were above the drinking water threshold of 0.1 μg L−1. This prevalence of high concentrations presents costly problems for source water treatment. Using these data, abstraction shutdowns were simulated for five scenarios using hydrometeorological data to explore the potential to avoid intake of high MCPA concentrations. The scenarios stopped abstraction for 4.2–9.3% of the April–October period and reduced intake of water containing over 0.1 μg L−1 of MCPA by 16–31%. This represents an important development for real-time proxy assessments for water abstraction in the absence of more direct pesticide monitoring data.

Highlights

In Europe, 37% of all drinking water is sourced from surface waters (Völker and Borchardt, 2019) such as rivers, lakes and impounding reservoirs, with proportions varying among countries depending upon geology, climate and legacy practices
Median methyl-4-chloro-phenoxyacetic acid (MCPA) concentrations at all spatial locations were below the drinking water limit of 0.1 μg L−1, with the highest median concentrations observed at D6 and D8, both on the Mourne Beg River (Table 1)
The highest MCPA concentration detected at any location was 8.97 μg L−1, which was on 5th June 2018 at D9 (Fig. 2), a small tributary that entered the main river at the confluence of the River Derg and Mourne Beg River

Summary

Introduction

In Europe, 37% of all drinking water is sourced from surface waters (Völker and Borchardt, 2019) such as rivers, lakes and impounding reservoirs, with proportions varying among countries depending upon geology, climate and legacy practices. In countries such as Ireland, Greece, the UK and Bulgaria, this proportion is much higher, accounting for >65% of source allocation (EPA, 2017a; European Topic Centre, 2016a, 2016b, 2016c, 2016d), while in Northern Ireland 99.9% of the public supply is sourced from surface water (NI Water, 2018). The EU Drinking Water Directive (DWD) stipulates that the maximum allowable concentration of a single pesticide in treated drinking water is 0.1 μg L−1 and the limit for the sum of all pesticides is 0.5 μg L−1 (Council of the European Commission, 1998)

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