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The UK Pesticide Load Indicator (PLI) is a multi-component indicator, which combines data on the usage of different pesticide active substances in UK agriculture with information on their propensity to persist, bioaccumulate, or be lost via surface run-off or leaching, as well as information on their relative toxicity to wildlife. Data are derived from the UK Pesticide Usage Survey (PUS) and the Pesticide Properties Database (PPDB). The PLI supplements traditional metrics such as the ‘total mass of pesticides applied’ and the ‘total area treated’ by considering the changing mixture of different substances applied through time and the effect of their varying chemical or biochemical properties. The PLI consists of 4 environmental fate and 16 ecotoxicity metrics. It does not quantify harm or reflect environmental outcomes, as it does not account for any mitigation practices or calculate exposure of real wildlife populations. Instead, the aim of the PLI is to illustrate relative trends in the potential pressure on the environment arising from the use of pesticides, to help inform UK policy decisions and the assessment of policy intervention.
The PLI was originally adapted from an indicator developed by the Danish government, but it has since gone through multiple phases of revision and alignment to the UK policy context. This report outlines the results of Phase 4 (conducted 2022-23), which focused on:
a) Making the scope of the PLI calculation explicit through development of a protocol for assessing a substance’s suitability for inclusion. This permits the inclusion of biopesticides and micro-organisms within the indicator alongside more conventional pesticide treatments.
b) Removal of the previous aggregation step and its replacement with an approach which shows information on relative trends across all 20 individual metrics.
c) Revisions and improvements to the visualisation tool based on the requirements of Defra policy teams.
d) Simplification, streamlining, and documentation of backend calculations and processes, allowing these to be easily maintained on an ongoing basis.
e) Consideration of how the PLI might integrate with other reporting around pesticide usage, including the recently proposed Total Applied Toxicity (TAT).
In addition to highlighting the changes made to the indicator and serving as a revised reference document for the calculation, this report also examines cases where the PLI might be used in practice. The PLI was developed for a wide range of uses including characterising trends in load within the UK landscape and examining the impact of changes in policy such as the approval or withdrawal of active substances or products and initiatives such as those recently introduced under the Sustainable Farming Incentive scheme (SFI).
With respect to general trends in load within arable crops, the overall trend in total mass of active substances applied per hectare of cropped land increased by approximately 16% between 2010 and 2018 and then decreased by 23% between 2018 and 2020. The 20 PLI metrics calculated over the same period show different trends, both to one another and to that suggested by overall mass of pesticide applied. Most of the fate metrics (except for drain flow) track the trend in mass applied between 2010 and 2018. However, the majority of the ecotoxicity metrics show declining trends in load over the same period, which contrasts with the trend in mass applied and may reflect a shift towards the use of less toxic active substances. Whilst the majority of PLI metrics showed a decline between 2018 and 2020, matching the trend in mass applied, the magnitude of the changes varied substantially and there were contrasting trends for some of the ecotoxicity metrics. For example, there was a very large proportional decline in load on bees (which decreased by 77% and 98% for contact and oral exposure respectively); no statistical change for load on acute toxicity for birds and mammals; and increased load on parasitic wasps. The ability of the PLI to characterise these different trends, and to link change to the contribution of specific active substances, greatly enhances the ability of policy makers to understand the impact of actions and to support the development of targeted policy. How the PLI responds to policy change has been explored in detail in this report with the example of the withdrawal of neonicotinoid seed treatments on oilseed rape.
The PLI is one of a broader family of pesticide indicators which explore changes in the mixture of pesticides applied over a given geographic scope and time. One similar indicator is the recently published TAT (a novel international standard for reporting of the potential impacts of pesticides), which although not identical shows sufficient similarity with the PLI to draw comparisons and explore the possibility of alignment. The key difference between the PLI and TAT lies in the underlying data sources for the ecotoxicity assessment and how these are aggregated. In this respect, the PLI has a more transparent link to the underlying measurements, whereas the TAT aggregates across multiple species and study types. Despite these differences, the two indicators are sufficiently similar to be calculated within the same framework, and should a policy need emerge, the TAT could be calculated and displayed alongside the PLI.
The goal of developing the PLI was to provide an exploratory tool that facilitates access to improved information about the potential environmental impacts associated with pesticide use and to provide a tool for exploring relative tends associated with the changing mixture of active substances applied over time. When compared to previous monitoring efforts, which have largely been dependent on the total mass of pesticide applied (irrespective of the properties of active substances), the PLI has been highly successful in adding a greater resolution and ‘colour’ to the discussion around the potential effects of pesticide usage and the potential impacts of policy intervention. Phase 4 marks the transition between the PLI as a research prototype to a stable deployed system. The PLI has undergone a substantial realignment from an initial application of the Danish system to something that is much more targeted and aligned to the needs of UK policy. It fills an important gap in the current UK reporting system with respect to pesticide usage and it is likely to be a useful component of decision making going forwards. While work on the indicator will continue, particularly with the annual inclusion of further PUS surveys, the core processes of the PLI are now established to the point where the indicator is ready for routine operational deployment, as a part of a wider suite of indicators that reflect different elements of the socio-economic context and decision-making processes around pesticide use.
Original languageEnglish
PublisherDepartment for Environment, Food and Rural Affairs (Defra)
Commissioning bodyDepartment for Environment, Food and Rural Affairs (Defra)
Number of pages77
Publication statusPublished - 11 Jul 2023


  • pesticide
  • load
  • Indicator
  • PPDB


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