Pest Management Regulatory Agency: Aquatic exposure modelling for exposure assessment in support of the regulation of pest control products in Canada

Transcription

1 Pest Management Regulatory Agency: Aquatic exposure modelling for exposure assessment in support of the regulation of pest control products in Canada 242nd ACS National Meeting August 28, 2011 Greg Malis, Ian Kennedy, Lizanne Avon, Émilie Larivière. Environmental Assessment Directorate Ottawa, Ontario, Canada

2 Introduction to Canadian water modelling General modelling aspects Model features Modelling scenarios General approach to modelling Monitoring data Comparison

3 Modelling in Canada Use of Canadian scenarios to model: Estimated environmental concentrations (EECs) in surface waters for ecological risk assessment Pesticide Root Zone Model (PRZM)/EXposure Analysis Modeling System (EXAMS) EECs in drinking water supplies for the human health risk assessment Surface Water: PRZM/EXAMS Groundwater: LEACHM (Leaching Estimation and Chemistry Model)

4 Factors affecting pesticide levels in water Labels Pesticide use Registrant studies Fate Assessment Crops Pesticide levels in water Pesticide properties Hydrology Weather soil properties Varies with site

5 Modelling Environmental Fate of Pesticides Precipitation (and irrigation) PRZM EXAMS Foliar washoff Spray Drift Leaching LEACHM Volatilization Diffusion

6 PRZM Model Processes Foliar deposition Foliar washoff L ea c h i n g Transformation

7 Sediment Depth 5cm Water depth 2.74m, 5.33m or 0.8m Outflow EXAMS Model Processes Spray drift Transformation Water P h o t o t r a n s f o r m a t i o n V ol a ti l i z a ti o n Transformation Sediment Completely mixed

8 LEACHM Model Processes Addition of rainfall and/or irrigation water Addition of chemical: Surface application or soil incorporated Evaporation of water Volatilization of chemical Segment 1 Segment 2 Segment 3 Segment n Transport (Advection & Diffusion) Biotransformation Hydrolysis Partitioning (gas solution soil) water table Calculated groundwater concentration

9 Model Scenarios The data describing the soil, crop and weather characteristics of a site. Represent areas across Canada of major agricultural activity. Incorporate representative soil, weather and plant growth information. Surface water bodies drinking water: reservoir and dugout environmental exposure: small pond

10 Model Scenarios receiving water bodies Drinking water US EPA Index reservoir (based on Shipman reservoir in Illinois 5.3 hectare surface area with 2.74 m depth, drainage area is hectares) a prairie dugout (0.05 hectare surface area with 5.4 m depth, drainage area is 4 hectares) Environmental exposure the ecoscenario represents a permanent water body (1 hectare surface area with 0.8 m depth, drainage area is 10 hectares) 0.15 m depth used for amphibian assessment

11 Scenario Locations

12 General Approach Use tiered approach (Level 1 and Level 2) Level 1 drinking water: to screen out pesticides that do not pose any drinking water concern, and allow for simplified use expansions For surface water, uses PRZM/EXAMS with most vulnerable scenarios For groundwater, uses highest EECs out of all 11 scenarios If Level 1 concentration is unacceptable, move to a Level 2 assessment Ecoscenario Level 1 is a direct overspray assessment. PRZM/EXAMS starts with level 2, using region specific rate/use information and scenarios

13 Level 1 - General Approach Fate inputs to models modified from PMRA Science Policy Note (SPN) , Estimating the Water Component of a Dietary Exposure Assessment 80 th percentile half-lives in environmental media (e.g., soil, water) Terrestrial field dissipation DT50s are not used in modelling 20 th percentile K OC or K d coefficients where multiple values exist Note modeling inputs are being discussed as part of a NAFTA groundwater modelling project

14 Level 1 - General Approach (continued) Assumptions about use: Label information Highest rate and max. number of applications Shortest time interval between applications The pesticide is applied every year of the simulation Range of starting application dates 100% of the watershed is assumed to be cropped 100% of the crop is assumed to be treated with pesticide For drinking water assessment, we report both 90 th percentile of daily and yearly average concentrations for surface water and groundwater EECs For ecological assessment, we report 90 th percentile of daily, 96-hour, 21-day, 60-day, 90-day and yearly average concentrations for ecoscenario EECs

15 Transformation products PRZM does not correctly handle formation and decline of transformation products LEACHM handles only the case of 100% conversion PMRA typically simplifies by handling transformation products in one of two ways 1. Combined residues calculate the combined half-life, and then model all compounds of interest together assume all compounds have similar phys. chem. characteristics as the parent 2. Treat separately assume that transformation products are applied to the soil surface then same as the parent compound. assume pulse application rather than slow formation missing phys. chem. Data 3. For groundwater, if possible, simulate transformation using LEACHM Requires sufficient transformation product fate data When compounds have differing KOC

16 Level 2 General Approach Case-by-case approach Use pattern items considered include: restricting the modelling to scenarios that reflect the current or proposed uses and relevant application dates of the pesticide percent cropped area agricultural practices (e.g. crop rotation, resistance management) Refinements are intended to be more accurate, not just less conservative PMRA tries to choose reasonably conservative inputs at Level 1 Use expansion could require additional modelling

17 Modelling data quality Modelled EECs are intended to be a realistic upper bound Uncertainty and the degree of conservatism are not easily characterized due to Simplification of processes in the models Uncertainty in fate data Quantitative effect of choice of generally conservative inputs Not all model assumptions and parameters are conservative. LEACHM neglects preferential flow Degradation rates from lab studies conducted at 20 C or 25 C which may not reflect a colder Canadian climate (PRZM)

18 Use of Monitoring Data When available, PMRA considers monitoring data (surface and groundwater) for re-evaluation and special reviews Evaluate the quality of data received Experimental design Spatial and temporal conditions Available ancillary data Data sources Environment Canada, Department of Fisheries and Oceans, Provincial Ministries US data: NAWQA, USDA, STORET databases Registrant Literature

19 Comparison to other jurisdictions EPA Surface water similar to PMRA Tier 1 EPA GENEEC and FIRST, PMRA PRZM/EXAMS Tier 2 both use PRZM/EXAMS Different scenarios US chooses chemical parameters differently EPA Groundwater different SCI-GROW is a regression based on field (PGW) studies SCI-GROW is based on single application (taken as maximum yearly total) SCI-GROW is considered valid for K OC between 13 and 180 L/kg OC EU uses different models

20 NAFTA groundwater modelling project Intended to harmonize Canada and US groundwater modelling Common conceptual model Common numerical model (i.e. modelling program) Mostly common guidance on scenario creation and input parameter selection Completion within 2011

21 Future directions NAFTA projects Groundwater, degradation kinetics, PGW guidance Surface water modelling Canadian reservoir and watershed scenario development, Percent Crop Area (PCA), probabilistic, variable volume pond, watershed model Study improvements Link sorption and degradation, field aerobic soil lab study improvements, plant uptake and metabolism, more evenly distributed data, second chemical spike, sterile control Model advancements Model advancements will require more parameters and will increase the complexity of choosing them. Examples include; time dependent sorption, transformation products, nonlinear sorption isotherm

22 Questions

23 Input parameter comparison with US and EU Sorption EU EPA PMRA Freundlich isotherm where model allows Linear isotherm using K f Half-life Geometric mean Mean or median or 3x or 90% confidence t 1/2 temperature correction t 1/2 moisture correction Foliar interception Linear isotherm using K d 80 th percentile of calculated halflives Yes Yes Occasionally Yes No No Removed from application GW: none SW: PRZM Run length? GW: none SW: PRZM