Quantitative risk assessment of pesticides in drinking water under current and future climates
Risk assessment approaches have become critical for pesticide risk management and mitigation. Despite this, scientists and pesticide regulators have acknowledged the need to improve representation of variability in input data, and uncertainty in pesticide fate processes in existing approaches. Additionally, current methods are limited in their ability to represent the inherent uncertainty and variability associated with climate change, and therefore cannot inform future planning under changing climates. This thesis presents the development of a novel, practical risk assessment framework to assess the risks posed by pesticide contamination in drinking water under current and future climates, incorporating novel risk scoring systems, probabilistic risk modelling frameworks, and climate change projections. The main body of the thesis discusses the different stages involved in the development of the risk assessment framework. Firstly, a novel risk screening tool was developed to rank pesticide risks to human health, considering pesticide use, chronic health effects, environmental fate, and site-specific soil conditions. This approach incorporated both pesticide properties and site conditions in the scoring of pesticide mobility to enable more a realistic representation of the effects of location on pesticide transport; metabolite data was also used to inform overall risk scores based on EU recommendations. This method aids in identifying high-risk pesticides from a wide range of pesticides to better inform monitoring programs and further detailed risk assessments. Secondly, an existing deterministic simulation model was modified to better represent both site scenarios and transport processes involved in pesticide runoff to drinking water supplies. Additionally, a Monte-Carlo approach was utilised to enable probabilistic assessment and account for variability in pesticide properties, population characteristics, site conditions, and climatic factors. This framework enables farm advisors and catchment managers to predict concentrations of pesticides in drinking water supplies, quantify potential risks to human health arising from pesticide exposure, and implement risk mitigation measures using a practical and accessible probabilistic model. An Irish case study was used to illustrate the implementation of the framework to predict pesticide concentrations in surface water and assess health risks to adults and children at a grassland site typical of Irish agriculture. The results found pesticide concentrations exceeding EU drinking water limits for several pesticides, including MCPA, mecoprop, and 2,4-D, but indicated that health risks were low under current conditions despite these exceedances. Finally, this thesis investigates the impact of climate change on pesticide transport and health risks, integrating high-resolution climate model projections into the proposed probabilistic risk model. Standardised climate projections for Ireland were used to demonstrate how the probabilistic risk model developed in this thesis can be adapted for future climates. A risk assessment of pesticides for three timeframes (current, 2050, 2100), under two climate scenarios (RCP4.5 and RCP8.5) showed that pesticide risks will increase with future climate conditions. The study found significant regional variations, with higher risks in the south-west compared to the north-east of Ireland, and projected overall risk increases ranging from 18% to 85%, depending on the scenario and timeframe. Despite the projected increases in pesticide risk, the impact to human health remained below EU regulatory health thresholds even under worst-case climate conditions. This approach can be adapted to account for indirect impacts of climate change e.g. land-use, pest prevalence and agricultural policy, to better represent overall changes to pesticide risks under a changing climatic and legislative landscape. Overall, this research highlights the importance of incorporating site-specific conditions, variability in environmental and climatic factors, and future climate change projections into pesticide risk assessments. The methodologies developed provide robust tools for managing pesticide risks and can be adapted for various locations and conditions, thus informing future pesticide management, climate adaptation approaches, and public health protection strategies.
Risk assessment, Climate change, Probabilistic modelling, Water quality, Pesticides
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