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A review of the pesticide MCPA in the land‐water environment and emerging research needs

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Abstract Due to its high solubility and poor adsorption to the soil matrix, the post‐emergence herbicide 2‐methyl‐4‐chlorophenoxyacetic acid (MCPA) is susceptible to transport into surface and groundwater bodies, where it can result in compromised water quality and breaches of legislative standards. However, there is still poor understanding of catchment scale dynamics and transport, particularly across heterogeneous hydrogeological settings. While it is known that MCPA degrades under aerobic conditions, negligible breakdown can occur in anaerobic environments, potentially creating a legacy in saturated soils. Fast runoff pathways post application are likely transport routes, but the relative contribution from the mobilization of legacy MCPA from anaerobic zones has yet to be quantified, making the delineation of MCPA sources encountered during monitoring programs challenging. While ecotoxicological effects have been examined, little is known about the interaction of MCPA (and its degradation products) with other pesticides, with nutrients or with colloids, and how this combines with environmental conditions to contribute to multiple stressor effects. We examine the state of MCPA knowledge, using case study examples from Ireland, and consider the implications of its widespread detection in waterbodies and drinking water supplies. Research themes required to ensure the sustainable and safe use of MCPA in an evolving agricultural, social and political landscape are identified here. These include the need to identify mitigation measures and/or alternative treatments, to gain insights into the conditions governing mobilization and attenuation, to map pathways of migration and to identify direct, synergistic and antagonistic ecotoxicological effects. This article is categorized under: Water and Life > Stresses and Pressures on Ecosystems Science of Water > Water Quality
Trends between 2004 and 2016 in (a) the number of reported pesticides failures for public water supplies in the Republic of Ireland (reproduced from EPA, ) of which 81% are sourced from surface water (EPA, ) and (b) the mean raw water concentration of MCPA in Northern Ireland (data provided by Northern Ireland Water). The dashed line on (b) represents the drinking water standard limit of 0.1 μg/L
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River discharge (15 min frequency; data from Department for Infrastructure NI), weekly MCPA concentrations (data provided by Northern Ireland Water) and seven‐hourly MCPA concentrations (data provided by AFBI) in a river in Northern Ireland during the summer period of 2018. River discharge is shown as a gray line, weekly MCPA concentrations are gray circles and seven‐hourly MCPA concentrations are black circles. Note that both discharge and MCPA concentrations are displayed on a logarithmic scale. The data highlight the importance of sample resolution for insights on MCPA magnitude and process relationships
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River discharge (15 min frequency; data from Department for Infrastructure NI) and MCPA loads (data provided by Northern Ireland Water) in a river in Northern Ireland shown for (a) a full year (2014) and (b) the summer period only, when high loads are likely coincident with application and rainfall/runoff events but do not reduce to zero during inter‐storm periods throughout the year. River discharge is shown as a gray line and MCPA loads are black diamonds. Note that both discharge and MCPA loads are displayed on a logarithmic scale
[ Normal View | Magnified View ]
River discharge (15 min frequency; data from Department for Infrastructure NI) and MCPA concentrations (data provided by Northern Ireland Water) in a river in Northern Ireland shown for (a) a full year (2014) and (b) the summer period only, when high concentrations are likely coincident with application and rainfall/runoff events. River discharge is shown as a gray line and MCPA concentrations are black diamonds. Note that both discharge and MCPA concentrations are displayed on a logarithmic scale
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