Stochastic modelling of pesticide transport to drinking water sources via runoff and resulting human health risk assessment.

A modelling framework was developed to facilitate a probabilistic assessment of health risks posed by pesticide exposure via drinking water due to runoff, with the inclusion of influential site conditions and in-stream processes. A Monte-Carlo based approach was utilised to account for the inherent variability in pesticide and population properties, as well as site and climatic conditions. The framework presented in this study was developed with an ability to integrate different data sources and adapt the model for various scenarios and locations to meet the users' needs. The results from this model can be used by farm advisors and catchment managers to identify lower risk pesticides for use for given soil and site conditions and implement risk mitigation measures to protect water resources. Pesticide concentrations in surface water, and their risk of regulatory threshold exceedances, were simulated for fifteen pesticides in an Irish case study. The predicted concentrations in surface water were then used to quantify the level of health risk posed to Irish adults and children. The analysis indicated that herbicides triclopyr and MCPA occur in the greatest concentrations in surface water, while mecoprop was associated with the highest potential for health risks. The study found that the modelled pesticides posed little risk to human health under current application patterns and climatic conditions in Ireland using international acceptable intake values. A sensitivity study conducted examined the impact seasonal conditions, timing of application, and instream processes, have on the transport of pesticides to drinking water.

Impact of historical legacy pesticides on achieving legislative goals in Europe.

Pesticides are widely used in agriculture to optimise food production. However, the movement of pesticides into water bodies negatively impacts aquatic environments. The European Union (EU) aims to make food systems fair, healthy and environmentally friendly through its current Farm to Fork strategy. As part of this strategy, the EU plans to reduce the overall use and risk of chemical pesticides by 50 % by 2030. The attainment of this target may be compromised by the prevalence of legacy pesticides arising from historical applications to land, which can persist in the environment for several decades. The current EU Farm to Fork policy overlooks the potential challenges of legacy pesticides and requirements for their remediation. In this review, the current knowledge regarding pesticide use in Europe, as well as pathways of pesticide movement to waterways, are investigated. The issues of legacy pesticides, including exceedances, are examined, and existing and emerging methods of pesticide remediation, particularly of legacy pesticides, are discussed. The fact that some legacy pesticides can be detected in water samples, more than twenty-five years after they were prohibited, highlights the need for improved EU strategies and policies aimed at targeting legacy pesticides in order to meet future targets.

Batch adsorption of herbicides from aqueous solution onto diverse reusable materials and granulated activated carbon.

This study reports the kinetics and isotherms of the adsorption of five herbicides, MCPA, mecoprop-P, 2,4-D, fluroxypyr and triclopyr, from aqueous solutions onto a range of raw and pyrolysed waste materials originating from an industrial setting. The raw waste materials investigated demonstrated little capability for any herbicide adsorption. Granulated activated carbon (GAC) was capable of the best removal of the herbicides, with >95% removal observed. A first order kinetic model fitted the data best for GAC adsorption of 2,4-D, while a pseudo-first order model fitted the data best for GAC adsorption of fluroxypyr and triclopyr, indicating that adsorption was via physisorption. A pseudo-second order kinetic model fitted the GAC adsorption of MCPA and mecoprop-P, which is indicative of chemisorption. The adsorption of the herbicides in all cases was best described by the Freundlich model, indicating that adsorption occurred onto heterogeneous surfaces.

A risk ranking of pesticides in Irish drinking water considering chronic health effects.

This paper presents a novel scoring system which facilitates a relative ranking of pesticide risk to human health arising from contaminated drinking water. This method was developed to identify risky pesticides to better inform monitoring programmes and risk assessments. Potential risk was assessed considering pesticide use, chronic human health effects and environmental fate. Site-specific soil conditions, such as soil erodibility, hydrologic group, soil depth, clay, sand, silt, and organic carbon content of soil, were incorporated to demonstrate how pesticide fate can be influenced by the areas in which they are used. The indices of quantity of use, consequence and likelihood of exposure, hazard score and quantity-weighted hazard score were used to describe the level of concern that should be attributed to a pesticide. Metabolite toxicity and persistence were also considered in a separate scoring to highlight the contribution metabolites make to overall pesticide risk. This study presents two sets of results for 63 pesticides in an Irish case study, (1) risk scores calculated for the parent compounds only and (2) a combined pesticide-metabolite risk score. In both cases the results are assessed for two locations with differing soil and hydrological properties. The method developed in this paper can be adapted by pesticide users to assess and compare pesticide risk at site level using pesticide hazard scores. Farm advisors, water quality monitors, and catchment managers can apply this method to screen pesticides for human health risk at a regional or national level.

An analysis of the spatio-temporal occurrence of anthelmintic veterinary drug residues in groundwater.

Anthelmintics are antiparasitic drugs used to control helminthic parasites such as nematodes and trematodes in animals, particularly those exposed through pasture-based production systems. Even though anthelmintics have been shown to be excreted into the environment in relatively high amounts as unmetabolized drug or transformation products (TPs), there is still only limited information available on their environmental occurrence, particularly in groundwater, which has resulted in them being considered as potential emerging contaminants of concern. A comprehensive study was carried out to investigate the occurrence of 40 anthelmintic residues (including 13 TPs) in groundwaters (and associated surface waters) throughout the Republic of Ireland. The study focused on investigating the occurrence of these contaminants in karst and fractured bedrock aquifers, with a total of 106 sites (88 groundwaters and 18 surface waters) samples during spring 2017. Seventeen anthelmintic compounds consisting of eight parent drugs and nine TPs were detected at 22% of sites at concentrations up to 41 ng L-1. Albendazole and its TPs were most frequently detected residues, found at 8% of groundwater sites and 28% of surface water sites. Multivariate statistical analysis identified several source and pathway factors as being significantly related to the occurrence of anthelmintics in groundwater, however there was an evident localised effect which requires further investigation. An investigation of the temporal variations in occurrence over a 13 month period indicated a higher frequency and concentration of anthelmintics during February/March and again later during August/September 2018, which coincided with periods of increased usage and intensive meteorological events. This work presents the first detections of these contaminants in Irish groundwater and it contributes to broadening our understanding of anthelmintics in the environment. It also provides insight to seasonal trends in occurrence, which is critical for assessing potential future effects and implications of climate change.

A Fuzzy Cognitive Map method for integrated and participatory water governance and indicators affecting drinking water supplies.

Drinking water governance is challenging with different perceptions and priorities among stakeholders in different countries. To make provision for drinking water protection in agricultural areas, governance systems need to be mapped for bottlenecks to be identified and solutions highlighted. To address this a system thinking approach was used in an explanatory network analysis of Fuzzy Cognitive Maps (FCM) that were created during face to face interviews with stakeholder representative groups (individuals, policy developers, researchers, and regulators). Two exercises were designed and facilitated to obtain stakeholder maps on A) the water governance framework from stakeholders' own perspective with a ranking of actors in terms of their perceived importance and B) a list of importance factors and how these were connected for the provision of good drinking water quality supplies in agricultural areas. Causal relationships were subsequently drawn around each subject allowing mapping. A graph theory Hierarchy Index (h) approach examined if stakeholder groups preferred top down hierarchical governance or a more inclusive democratic governance approach. Finally, an auto-associative neural network method was deployed on group maps for examination during steady-state conditions for three scenarios to be explored i.e. changing "Farmers knowledge", "best management practice (BMP) uptake" and "Farmers behaviour and belief" to the highest level of influence and seeing how the system reacted. Results of Exercise A showed that all stakeholder representative groups had a different perception of the water governance framework. Most stakeholder groups had a democratic point of view regarding water governance structures and the ranking and importance of the actors within the framework. Results of Exercise B demonstrated that most of the groups have similar opinions regarding the highest ranked factors affecting drinking water quality and the possible environmental ecological policy options. In this second exercise, only one representative group showed a democratic outlook whereas all others had a hierarchal outlook. Scenario testing of policy options enabled bottlenecks and possible solutions to be identified. By boosting "Farmers behaviour and belief" to the highest possible level, resulted in a large increase in other factors - a scenario where farmers could benefit from the outcome. This would be achieved by enhancing farmers' willingness and intention to participate and implement BMPs. Better results would be achieved if farmers believed in the method and could benefit from the outcome. Also keeping "Farmers knowledge" at the highest point had a positive influence on the other factors. This can be achieved by enhancing farmers training and knowledge transfer by local and national actors. This method is widely applicable and should be considered for more integrated and participatory approaches to drinking water governance.

An investigation of anticoccidial veterinary drugs as emerging organic contaminants in groundwater.

Intensification of the food production system to meet increased global demand for food has led to veterinary pharmaceuticals becoming a critical component in animal husbandry. Anticoccidials are a group of veterinary products used to control coccidiosis in food-producing animals, with primary prophylactic use in poultry production. Excretion in manure and subsequent land-spreading provides a potential pathway to groundwater. Information on the fate and occurrence of these compounds in groundwater is scant, therefore these substances are potential emerging organic contaminants of concern. A study was carried out to investigate the occurrence of anticoccidial compounds in groundwater throughout the Republic of Ireland. Twenty-six anticoccidials (6 ionophores and 20 synthetic anticoccidials) were analysed at 109 sites (63 boreholes and 46 springs) during November and December 2018. Sites were categorised and selected based on the following source and pathway factors: (a) the presence/absence of poultry activity (b) predominant aquifer category and (c) predominant groundwater vulnerability, within the zone of contribution (ZOC) for each site. Seven anticoccidials, including four ionophores (lasalocid, monensin, narasin and salinomycin) and three synthetic anticoccidials (amprolium, diclazuril and nicarbazin), were detected at 24% of sites at concentrations ranging from 1 to 386 ng L-1. Monensin and amprolium were the two most frequently detected compounds, detected at 15% and 7% of sites, respectively. Multivariate statistical analysis has shown that source factors are the most significant drivers of the occurrence of anticoccidials, with no definitive relationships between occurrence and pathway factors. The study found that the detection of anticoccidial compounds is 6.5 times more likely when poultry activity is present within the ZOC of a sampling point, compared to the absence of poultry activity. This work presents the first detections of these contaminants in Irish groundwater and it contributes to broadening our understanding of the environmental occurrence and fate of anticoccidial veterinary products.

A new sensitive method for the simultaneous chromatographic separation and tandem mass spectrometry detection of anticoccidials, including highly polar compounds, in environmental waters.

A sensitive and selective method was developed and validated for the determination of 26 anticoccidial compounds (six ionophores and twenty chemical coccidiostats) in surface and groundwater samples at parts-per-quadrillion (pg L-1) to parts-per-trillion (ng L-1) levels by ultra-high performance liquid chromatography with tandem mass spectrometry detection (UHPLC-MS/MS). A range of different analytical columns and mobile phase compositions were evaluated to enhance selectivity and retention of a number of highly polar and basic anticoccidials along with other non-polar coccidiostats. A combined separation, including these problematic polar compounds, was achieved on a phenyl-hexyl column, by binary gradient elution with water/acetonitrile using ammonium formate and formic acid as additives. The anticoccidial residues were extracted from raw, unfiltered, water samples (250 mL) using polymeric divinylbenzene solid phase extraction (SPE) cartridges, with subsequent elution (methanol:acetonitrile:ethyl acetate, 40:40:20, v/v) and concentration prior to determination. The method recovery (at a concentration representative of realistic expected environmental water concentrations based on literature review) ranged from 81% to 105%. The method was successfully validated for 26 anticoccidials, at four concentration levels, in accordance to Commission Decision 2002/657/EC and SANTE/11813/2017 guidelines. Trueness and precision, under within-laboratory reproducibility conditions, ranged from 88% to 111% and 0.9% to 10.3% respectively.

Improving the identification of hydrologically sensitive areas using LiDAR DEMs for the delineation and mitigation of critical source areas of diffuse pollution.

Identifying critical source areas (CSAs) of diffuse pollution in agricultural catchments requires the accurate identification of hydrologically sensitive areas (HSAs) at highest propensity for generating surface runoff and transporting pollutants. A new GIS-based HSA Index is presented that improves the identification of HSAs at the sub-field scale by accounting for microtopographic controls. The Index is based on high resolution LiDAR data and a soil topographic index (STI) and also considers the hydrological disconnection of overland flow via topographic impediment from flow sinks. The HSA Index was applied to four intensive agricultural catchments (~7.5-12km(2)) with contrasting topography and soil types, and validated using rainfall-quickflow measurements during saturated winter storm events in 2009-2014. Total flow sink volume capacities ranged from 8298 to 59,584m(3) and caused 8.5-24.2% of overland-flow-generating-areas and 16.8-33.4% of catchment areas to become hydrologically disconnected from the open drainage channel network. HSA maps identified 'breakthrough points' and 'delivery points' along surface runoff pathways as vulnerable points where diffuse pollutants could be transported between fields or delivered to the open drainage network, respectively. Using these as proposed locations for targeting mitigation measures such as riparian buffer strips reduced potential costs compared to blanket implementation within an example agri-environment scheme by 66% and 91% over 1 and 5years respectively, which included LiDAR DEM acquisition costs. The HSA Index can be used as a hydrologically realistic transport component within a fully evolved sub-field scale CSA model, and can also be used to guide the implementation of 'treatment-train' mitigation strategies concurrent with sustainable agricultural intensification.

Identifying contrasting influences and surface water signals for specific groundwater phosphorus vulnerability.

Two groundwater dominated catchments with contrasting land use (Grassland and Arable) and soil chemistry were investigated for influences on P transfer below the rooting zone, via the aquifer and into the rivers. The objective was to improve the understanding of hydrochemical process for best management practise and determine the importance of P transfer via groundwater pathways. Despite the catchments having similar inorganic P reserves, the iron-rich soils of the Grassland catchment favoured P mobilisation into soluble form and transfer to groundwater. Sites in that catchment had elevated dissolved reactive P concentrations in groundwater (>0.035 mg l(-1)) and the river had flow-weighted mean TRP concentrations almost three times that of the aluminium-rich Arable catchment (0.067 mg l(-1) compared to 0.023 mg l(-1)). While the average annual TRP flux was low in both catchments (although three times higher in the Grassland catchment; 0.385 kg ha(-1) compared to 0.128 kg ha(-1)), 50% and 59% of TRP was lost via groundwater, respectively, during winter periods that were closed for fertiliser application. For policy reviews, slow-flow pathways and associated time-lags between fertiliser application, mobilisation of soil P reserves and delivery to the river should be carefully considered when reviewing mitigating strategies and efficacy of mitigating measures in groundwater fed catchments. For example, while the Grassland catchment indicated a soil-P chemistry susceptibility, the Arable catchment indicated a transient point source control; both resulted in sustained or transient periods of elevated low river-flow P concentrations, respectively.

Quantifying faecal indicator organism hydrological transfer pathways and phases in agricultural catchments.

Faecal indicator organisms (FIOs) can impact on water quality and pose a health and environmental risk. The transfer of FIOs, such as Escherichia coli (E. coli), from land to water is driven by hydrological connectivity and may follow the same flowpaths as nutrients, from agricultural and human sources. This study investigated E. coli transfer in two catchment areas with high source and transport pressures. These pressures were: organic phosphorus (P) loading; human settlement; conduits and fissures in a grassland karst area; and clay rich and impermeable soils in a mixed arable area. The occurrence of E. coli and its transport pathways, along with the pathways of nutrients, were studied using a combination of targeted FIO sampling, during different hydrological phases and events, and high resolution nutrient analysis. The quick flow component in both catchments was found to be a more potent vector for E. coli, and was coincident with the total P flowpaths using a P Loadograph Recession Analysis (LRA). The karst grassland catchment was found to be a transport limited system and the mixed arable catchment a source limited system. Hence, despite the grassland catchment being a potentially higher FIO source, the E. coli loads leaving the catchment were low compared to the mixed arable catchment. E. coli load whole-event comparisons also indicated that the grassland karst transfers tended to be much lower on falling phases of runoff, while the arable catchment, over greywacke and mudstone geology, showed little change between the phases. Furthermore, the arable catchment showed asymptotic decline of sustained E. coli loads towards low flows, which may be indicative of chronic point sources. These results indicate the dominance of transport mechanisms over source mechanisms for mass E. coli loads and also chronic loads during low flow. These will be important considerations for risk assessment and mitigation.

Evaluating the critical source area concept of phosphorus loss from soils to water-bodies in agricultural catchments.

Using data collected from six basins located across two hydrologically contrasting agricultural catchments, this study investigated whether transport metrics alone provide better estimates of storm phosphorus (P) loss from basins than critical source area (CSA) metrics which combine source factors as well. Concentrations and loads of P in quickflow (QF) were measured at basin outlets during four storm events and were compared with dynamic (QF magnitude) and static (extent of highly-connected, poorly-drained soils) transport metrics and a CSA metric (extent of highly-connected, poorly-drained soils with excess plant-available P). Pairwise comparisons between basins with similar CSA risks but contrasting QF magnitudes showed that QF flow-weighted mean TRP (total molybdate-reactive P) concentrations and loads were frequently (at least 11 of 14 comparisons) more than 40% higher in basins with the highest QF magnitudes. Furthermore, static transport metrics reliably discerned relative QF magnitudes between these basins. However, particulate P (PP) concentrations were often (6 of 14 comparisons) higher in basins with the lowest QF magnitudes, most likely due to soil-management activities (e.g. ploughing), in these predominantly arable basins at these times. Pairwise comparisons between basins with contrasting CSA risks and similar QF magnitudes showed that TRP and PP concentrations and loads did not reflect trends in CSA risk or QF magnitude. Static transport metrics did not discern relative QF magnitudes between these basins. In basins with contrasting transport risks, storm TRP concentrations and loads were well differentiated by dynamic or static transport metrics alone, regardless of differences in soil P. In basins with similar transport risks, dynamic transport metrics and P source information additional to soil P may be required to predict relative storm TRP concentrations and loads. Regardless of differences in transport risk, information on land use and management, may be required to predict relative differences in storm PP concentrations between these agricultural basins.

The seasonality of phosphorus transfers from land to water: implications for trophic impacts and policy evaluation.

The Nitrates Directive regulations are a Programme of Measures under the EU Water Framework Directive to protect waters from agricultural transfers of nitrogen and phosphorus. Soil phosphorus management to an agronomic optimum and closed winter periods for organic and inorganic fertiliser amendments are among a suite of policy measures to curtail diffuse pollution at catchment scale. In this investigation, two intensive grassland and two arable catchments (7-12 km(2)) in the Republic of Ireland were studied to link a high resolution spatial survey (≤2 ha) of soil P availability with P delivery in receiving rivers; monitored on a sub-hourly basis over one year. Data indicated that source risk, as defined by soil P availability and organic P loading, was less important than mobilisation and hydrological transfer potential which increased delivery due to runoff flashiness as described by a hydrological metric during the winter. Overall, however, annual TP loads were low to moderate (0.175 to 0.785 kg ha(-1) yr(-1)). The data also highlighted, without exception, the influences of summer background P loading and subsequent ecologically significant P concentrations from persistent point sources. This may have implications for expected ecological status and recovery in these catchments, which appeared more at risk in catchments with little buffering in terms of summer base flow dilution. Wetter winters and drier summers under climate change scenarios would likely increase stream P concentrations both during storms and during baseflows and would be particularly magnified in those catchments with flashy runoff and suppressed baseflow. These seasonal insights into source-to-delivery functions and risk (re)assessment were only possible with high resolution (spatial and temporal) data collection and will be important in influencing expectations of policies that are evaluated at larger scales but with coarser resolution sampling.