# Characterizing Individual Sources Of Uncertainty in EFED Standard Aquatic Risk Assessments Using Best Available Data

Paul Hendley (Phasera Ltd.) 

# Jeffrey Giddings (Compliance Services International) based on research conducted for the 

# Pyrethroid Working Group (PWG)

**The Pyrethroid W**

**orking Group**  **(PWG) is a US task force whose members**  **include eight primary pyrethroid registrants (AMV**  **AC Chemical Corporation, BASF Corporation, Bayer**  **CropScience LP**  **, Cheminova**  **A/S, DuPont Crop Protection, FMC Corporation, Syngenta Crop**  **Protection LLC,**  **Va lent**  **U.S.A. Corporation).**  

## Assessing Risks to Endangered and Threatened Species from Pe sticides

3rd Interagency Wo rkshop on Joint Interim Approaches to NAS Recommendations October 6, 2014

# Examining individual sources of uncertainty
 

# Uncertainty is part of all risk assessments and is addressed through assumptions (explicit and implicit) about factors potentially affecting exposure and effects.  

# Components of uncertainty can be considered **individually** and examined using focused probabilistic analysis.  

# This is feasible because high - quality monitoring data are now available for many real - world variables such as:  

# Spatial data on hydrology and soils  

# Highly localized weather  

# Yearly field – by - field crop locations  

# Multi - year/site/AI water and sediment concentrations
2 October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved.

# May 1996: FIFRA SAP on risk assessment process

 

# “... current process cautious and protective in terms of adverse environmental effects but serves only as screen because it reveals little information on likelihood of damage ...”  

# SAP recommended that the process be expanded to include probabilistic assessments of risk, identify uncertainties.  

# Led to 1997 EPA initiation of ECOFRAM* panel. * E cological C ommittee O n F IFRA R isk A ssessment M ethods October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved. 3

# ECOFRAM Aquatic Exposure Concept
– Tiering

**Co ncentration**  **DI AGRAM**  **E**

**Key** Min Max

Me dian is area of m ost intense color 

### Ti**er 1** - S ingle value ideally at 90% ile of expected Tier 2 **Ti er 2**  - C onservative initial probabilistic estim ate **Ti er 3**  - R efined estim ate m ay include landscape/chemistry **Ti er 4** - M ost sophisticated - may included monitoring etc. **Re al W**  **orl d Actual Exp.**  may never be known exactly. 

## 0 **ppb (L**  **og Scale)** 

## Screening Level Assessment

October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved. 4

# PWG pyrethroid risk assessment - background
 

# Registration Review under way for 9 synthetic pyrethroids  

# Highly active insecticide class  

# ~30 year history of safe use  

# Vast range of US crops across the AIs  

# Economically significant for food production  

# Tier II exposure modeling indicated that  

# Plants and mollusks are not at risk, fish “on borderline”  

# Arthropods (including insects and crustaceans) are predicted to have substantial RQs for many crop uses

5 October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved.

# BUT large database of water/sediment monitoring indicates Tier II modeling overestimates pyrethroid concentrations
 

# Bulk water column EECs are much greater than concentrations measured in whole water samples . Example: deltamethrin use on cotton, soybeans, vegetables, and outdoor residential.

6 October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved.



## Modeling (ng/L) **Monitoring (ng/L)** Agricultural Re sidential Agricultural **(n=229)** Urban

**(n=420)** 90 th 

### % ile 46 - 569 125 90 th 

### % ile < RLa 

### <RL 95 th 

### % ile 62 - 691 158 95 th 

### % ile <RL <RL Max 73 - 761 162 99 th 

### % ile 2.8 16

a 

## RL = reporting limit, 0.5 - 1 ng/L for most samples **Conclusion: Statistically**  **valid monitoring**  **data are**  **at odds with Tier II exposure**  **predictions with potential**  **regulatory implications.** 

# Understanding role of sources of uncertainty**in EEC/monitoring discrepancy** **h elps both FIFRA and ESA assessments** 
 

## PWG set itself task to “Evaluate sources of uncertainty in standard FIFRA aquatic exposure modeling which contribute to more or less conservatism in exposure estimates and examine how their impact may be quantified using recent bestavailable data ”  

## Understanding the combined impact of individual sources of uncertainty allows for  

### More realistic aquatic EECs  

### Confidence in protective nature of assessments  

## For ESA, most effective if analysis is part of Step 1: avoid unwarranted may - affect determinations, narrow the scope of Step 2

October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved. **Number of species**  **of concern** 

Source: Intrinsik 7

# PWG’s approach to characterize potential uncertainties

October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved. 8

# Scope of PWG evaluation and data sources

 

## Initially identified ~ **70 sources of uncertainty** in the standard assessment of pyrethroids  

## Several non - conservative items, most are conservative or variable  

## Many are inherent in model algorithms  

## Focused on those related to standard modeling scenarios  

## e.g. wind speed/direction, extent of crop in watersheds, severity of selected soil/weather scenarios relative to national distribution, etc.  

## Sought **best -**  **available data sources**  to provide rigorous quantification of effect of each source of uncertainty (ideally via accepted models). Unfiltered government databases of environmental data (although not error free) have high credibility.  

## NASS CDL and Pesticide Use  

## NHD+  

## NEXRAD  

## USGS and CDPR monitoring data

October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved. 9

# Four examples of PWG analysis (out of ~70)

October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved. 10 

### Assumption **How this**  **issue is addressed**  **in the PWG exposure**  **analysis Potential**  **significance (SMA=**  **standard model**  **assumption) Minimum specified**  **application interval is always**  **used for aerial applications. Included.**  In real world, aerial foliar pyrethroid applications only made when needed due to insect pressure. This rarely necessitates more than two applications in close succession. **SMA** . Conservative. **Growers ignore instructions to avoid application**  **when imminent rainstorms are**  **anticipated. Included**  . In real world, insecticide applications are rarely made during or before rain due to tractor access issues and/or concerns about loss of efficacy due to washoff. **SMA** . Conservative.
**Regional use patterns and**  **application technologies**  **are not significantly different**  **from the national average. Included**  **except in special**  **cases** ( e.g. , California vegetables). In some areas there may be more or less PCA, PT

A, ground/air applications, etc. Insect pressure will vary spatially and by year , leading to region - specific application patterns. **PWG Hypothesis.**  **Variable.**
**Wind speed is always 10**  **mph for aerial applications**  **Included, Quantified**  **.** PWG modeling uses default fixed val ues. **SMA. Variable**  but largely very conservative.

# Example 1
– Wind speed co - occurrence for multiple applications
 

# Quantifies impact of model defaults for aerial applications (wind speed always 10 mph and temperature/RH are constant).  

# Retains p rotective assumption that wind direction is always toward water body.  

# Extracts wind speed, temperature and RH data from SAMSON stations for 6 times on all days.  

# Assumes aerial application sequence occurs at same time “N” days apart (repeated for different start dates) and employs labeled 150 - ft no - spray buffer & droplet size (medium coarse).  

# AgDrift computes drift load using specific wind speed, temperature and RH values for each aerial spray event over 30 years.  

# Resulting drift loads used as input to receiving water model (AGRO - 2014) to predict concentrations in water and sediment.

11 October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved.

# Drift loads for sequence of 4 or 2 aerial applications are over- estimated most of the time; time - of - day differences obvious

12 October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved.

**0 20**  **40 60**  **80 100** 

**0 20**  **40 60**  **80 100**  **120 140** **P r** **o b** **a b** **i l** **i t** **y (** **% )** 



### Pe **rc ent of Default**  **Annual Aerial**  **Drift Load**  

## MS Cot**ton -**  **Applic ation**  **Set 1**

**Default 0400**  **0800 1200**  **1600 2000**  **0000 0** 

**20 40**  **60 80**  **100**

**0 20**  **40 60**  **80 100**  **120 140**  **160 180**  **200 P** **r o** **b a** **b i** **l i** **t y** **( %** **)**



### Pe **rc ent of Default**  **Drift Load**  

## CA Onion **- Application**  **Set 1**

**Default 0400**  **0800 1200**  **1600 2000**  **0000**

**Conclusions: Except**  **at 12:00 and 16:00, drift loads substantially reduced compared**  **to default .**  **Applies to all AIs, not just pyrethroids.**  **NOTE: this does not take DIRECTION of wind into account!**  

## Default: no variation, 10 mph on every application over 30 - year period.

# Reduced drift loads can lead to substantial reductions in water concentrations

13 October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved. **4 aerial apps**  **2 aerial apps** 

**Magnitude of impact: Across range of crops, incorporating wind speed/drift**  **parameter distributions will**  **reduce 90**  **th percentile**  **EEC estimates for pyrethroids in sediment and water by**  **1.1 –**  **7X .**  **0.000 0.005**  **0.010 0.015**  **0.020**

**0 0.2**  **0.4 0.6**  **0.8 1** **C o** **n c** **e n** **t r** **a t** **i o** **n s** **, μ** **g /** **L**



## Ex**ceedance Probability**  

# MS Cot**ton 24 -**  **hr TW**

**A W ate**  **r Column**

**Default 0400** 

**0.000 0.002**  **0.004 0.006**  **0.008**

**0 0.2**  **0.4 0.6**  **0.8 1** **C o** **n c** **e n** **t r** **a t** **i o** **n s** **, μ** **g /** **L**



## Ex**ceedence Probability**  

# CA Onion 24**- hr TW** 

**A W ate**  **r Column**

**Default 0800**  

## (Sediment concentrations are also reduced in scenarios where erosion is not a major factor .)

# Example 2
– Landscape - related uncertainties
 

# PWG analysis identified two key assumptions inherent in standard EFED scenarios: 1. 

# Soil/landform/weather characteristics of Tier II scenarios reflect ~90 th 

# percentile runoff/erosion vulnerability for national distribution of chosen crop. 2. 

# Percent of cropped area (PCA) in realistic scale watersheds is 100% of the watershed area.  

# K ey government datasets were combined to create “added value” GIS layers to examine the impact of these assumptions on exposure predictions.

October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved. 14

# National Hydrography Data plus (NHD+) catchments are an excellent scale for regulatory assessment and uncertainty evaluation
 

## There are a large number of them (~2.5 million )

 

## Each includes a single stream reach  

## Entire US land area accounted for  

## NHD+ catchments comprise a range of areas highly relevant to farming practices at the local scale  

### 90 th 

### percentile ~2.4 mi 2  

### 50 th 

### percentile ~0.56 mi 2 

### (360A ) October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved. 15 **Cotton Soybean**  Catchments with crop, 2008 - 2012 **246,956 893,703**  Catchments with crop, 2012 **138,707 658,633** 

# Data processing example for NHD+ catchments
 

# Three catchments ( 90 - 650 acres ) with different landscape patterns  

# Different cropping density ( pink areas = cotton)  

# Proximity to flowing water (200m)  

# Crop in proximity to flowing water  

# Soils and cropping 

# A

**C B** 

0 0.5 1 0.25 Miles October 6, 2014 16 (c) 2014 Pyrethroid Working Group. All rights reserved.

# PWG has classified potential vulnerability to runoff/erosion of US EPA model scenarios using complete national assessment

October 6, 2014 17 (c) 2014 Pyrethroid Working Group. All rights reserved. 

### Conclusion: **Relative runoff/ erosion potential for standard FIFRA Tier II**  **scenarios varies and in some cases can be an overestimate and in others an underestimate of 90**  **th** 

### centile goal **MS Cotton and TX**  **cotton Tier II**  **scenarios at 97.5**  **th and 97.3**  **rd percentiles**  

## 57,720 soil/weather station

combinations on which cotton was cropped between 2008 - 2012

**MS Soybean**  **Tier II**  **scenario at 89.7**  **th percentile**  

## 229,110 soil/weather station combinations on which soybean was cropped between 2008 - 2012

# PCA in most catchments is much less than 100%

October 6, 2014 18 (c) 2014 Pyrethroid Working Group. All rights reserved. 

# PWG has classified distribution of watershed landscape compositions for every NHD+ catchment which NASS CDL reported as growing the crop - of- interest between 2008 and 2012.

**Conclusions: 10 -**  **to 200 -**  **m PCA**  **distributions at catchment scale vary**  **by crop but**  **assumption of 100% PCA is not supported! 86,853**  **catchments 90**  **th percentile = 3.2**  **%**



### Sunflower Cotton

**138,707 catchments**  **90 th**  **percentile = 13.7%**  

### Soybean

**658.633 catchments**  **90 th**  **percentile = 37.5%**  

## (Metric is percent cropped area (PCA) in 10 - to 200 - m zone around NHD+ stream segment)

# Incorporating PCA into FIFRA modeling scenarios

October 6, 2014 19 (c) 2014 Pyrethroid Working Group. All rights reserved. **CA Onion**  **MS**

**Soybean MS/TX**  **Cotton** Tier II 30 - year EEC distributions for standard MS & TX cotton scenarios **90 th**  **percentiles 0.012 μg/L**  EEC distributions for identical input but incorporating PCA distributions **90 th**  **percentiles 0.0016 ug/L** 

**Conclusions: Impact of watershed scale landscape**  **PCA on EECs is highly**  **significant. Effect varies by crop but remains dependent on Tier II** 

**soil/weather scenario selection.**  **Magnitude of impact: Across range of crops, PCA distributions reduce** 

**90 th**  **percentile EECs for sediment**  **and water by 3 -**  **10X.**

# What was learned

 

## PWG used this uncertainty approach to refine the pyrethroid risk assessment.  

## Including landscape thinking does not mean that aquatic EECs predicted by standard EFED scenarios will never occur, but that their probability of occurrence in the real world is much lower than Tier II estimates.  

## Another important learning was that there was a need for a further categorization of uncertainty. Two distinct regulatory questions apply for aquatic assessments.
October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved. 

## PWG NEXT STEP **– Select several potential**  **sources of uncertainty and categorize** 

**against these criteria.**
20

### Potential **source of uncertainty**  **Potential impact**  **Quantification Estimate**  **(EEC Multiplier) Impacts**  **single pond**  **scenario Impacts** 

**probability of**  **exposed ponds Systematic uncertainties in SPME KOC model inputs.**  Conservative. **1.25 –**  **1.4X due to correction factor used for model inputs. Y**  **Ad sorption**  **to aquatic plants/associated biofilms in water bodies**  **(quantified via EXA** **MS -**  **300 mg dry wt/L biomass).**  Conservative. **13X for water column, 2X for sediment and pore water. Y**  **Degradation by plant surfaces and associated biofilms.** Conservative. **Estimated 1.5 –**  **3X. Y**  **Variation in the number of applications made per season.** Conservative. **Estimated 1 –**  **1.5X. Y**  **Variation from modeled 30 year continuous cropping regimes.** Conservative. **1 –**  **1.3X. Y**  **Variation in frequency of applications.** Conservative. **Estimated 1 –**  **1.2X. Y**  **Incorporation of soil photolysis.** Variable
–non - conservative. **Estimated 0.7 –**  **1X. Y**  **Variable volume water body**  **– evaporation.**  Non conservative. **0.7 –**  **1X. Y**  **Variation in wind direction relative to water body.**  Conservative. **Estimated 1 –**  **1.3X. Y**  **Variable deposition/mixing of drift** Variable **0.5 -**  **2X -**  **creates more -**  **and less -**  **potentially exposure areas Y**  **Variable deposition/mixing of erosion** Variable **0.5 -** **2X -**  **creates more -**  **and less -**  **potentially exposure areas Y**  **Variation in wind speed at time of application.**  Conservative quantified
. **1.1 –**  **5X. Y**  **Interception of drift by intervening vegetation.** Conservative. **1 –**  **2X. Y**  **Effect of riparian buffers at**  **edge -** **of -** **field to**  **modify runoff/erosion.**  Conservative. **1 –**  **2X (effect mainly on sediment). Y**  **Variation in natural and man -**  **made filter strip widths.** Conservative. **1 –**  **2X (effect mainly on sediment). Y**  **Potential Drift deposition from >200 m.** Non conservative. **0.7 –**  **1.0X. Y**  **Distribution of PCA** 

**a cross potentially treated watersheds**  C onservative **Quantified. Typically 3 -**  **10X for sediment &**  **water for major crops**  **Y PCA**  **d istribution**  **PLUS full distribution of environmental**  **vulnerabilities** Variable **Quantified. 0.9 -**  **1.1 for water column. 0.5**  **- 2X for sediment and pore**  **water IN A DDITION**  **TO PCA**  **d istribution**  **Y Fraction of percent of crop area treated (PTA** **).** Conservative. **Water column 5.5X, 23X & 130X . Sediment**  **= 4X, 150X and 970X. (Onion, Soybean & Cotton) at 90th centile**  **Y Fraction of catchment area draining to watershed**  **exit (i.e., uncertainty about enclosed depressions).**  Conservative. **Estimated 1.1X –**  **1.3X. Y**  **Individual market share of pyrethroids nationally and by region.**  Conservative. **3 –**  **100X (deltamethrin > 100X both nationally and in CA ).**  **Y Variation in fraction of CoI in catchment treated on the same day.**  Conservative. **Estimated 1 –**  **1.8X. Y**  **Variation in actual rate of pyrethroid applied (GfK**  **Kynetec data).** Conservative. **1 –**  **1.15X. Y**  **Variation in selection of application methods (ground/air) and subsequent handling (banding/incorporation).**  Variable. Most likely to be conservative. **0.9 –**  **1.3X. Y**  **Variation in intervals between applications.**  Conservative. **Estimated 1 –**  **1.2X. Y**  **Fraction of watersheds with sediment /erosion control structures.**  Conservative. **1 –**  **1.4X (regional). (effect mainly on sediment). Y**  **Fraction of CoI area using conservation tillage, associated realism of LS CA** 

**a nd P parameters in models.**  Conservative. **0.8 –**  **1.1X (effect mainly on sediment). Y**  **Impact of sediment delivery ratios at field/catchment scales.** Conservative. **1 –**  **4X (effect mainly on sediment). Y**  October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved.

### Potential **source of uncertainty**  **Potential impact**  **Quantification Estimate**  **(EEC Multiplier) Impacts**  **single pond**  **scenario Impacts** 

**probability of**  **exposed ponds Systematic uncertainties in SPME KOC model inputs.**  Conservative. **1.25 –**  **1.4X due to correction factor used for model inputs. Y**  **Ad sorption**  **to aquatic plants/associated biofilms in water bodies**  **(quantified via EXA** **MS -**  **300 mg dry wt/L biomass).**  Conservative. **13X for water column, 2X for sediment and pore water. Y**  **Degradation by plant surfaces and associated biofilms.** Conservative. **Estimated 1.5 –**  **3X. Y**  **Variation in the number of applications made per season.** Conservative. **Estimated 1 –**  **1.5X. Y**  **Variation from modeled 30 year continuous cropping regimes.** Conservative. **1 –**  **1.3X. Y**  **Variation in frequency of applications.** Conservative. **Estimated 1 –**  **1.2X. Y**  **Incorporation of soil photolysis.** Variable
–non - conservative. **Estimated 0.7 –**  **1X. Y**  **Variable volume water body**  **– evaporation.**  Non conservative. **0.7 –**  **1X. Y**  **Variation in wind direction relative to water body.**  Conservative. **Estimated 1 –**  **1.3X. Y**  **Variable deposition/mixing of drift** Variable **0.5 -**  **2X -**  **creates more -**  **and less -**  **potentially exposure areas Y**  **Variable deposition/mixing of erosion** Variable **0.5 -** **2X -**  **creates more -**  **and less -**  **potentially exposure areas Y**  **Variation in wind speed at time of application.**  Conservative - quantified
. **1.1 –**  **7X. Y**  **Interception of drift by intervening vegetation.** Conservative. **1 –**  **2X. Y**  **Effect of riparian buffers at**  **edge -** **of -** **field to**  **modify runoff/erosion.**  Conservative. **1 –**  **2X (effect mainly on sediment). Y**  **Variation in natural and man -**  **made filter strip widths.** Conservative. **1 –**  **2X (effect mainly on sediment). Y**  **Potential Drift deposition from >200 m.** Non conservative. **0.7 –**  **1.0X. Y**  **Distribution of PCA** 

**a cross potentially treated watersheds**  C onservative **Quantified. Typically 3 -**  **10X for sediment &**  **water for major crops**  **Y PCA**  **d istribution**  **PLUS full distribution of environmental**  **vulnerabilities** Variable **Quantified. 0.9 -**  **1.1 for water column. 0.5**  **- 2X for sediment and pore**  **water IN A DDITION**  **TO PCA**  **d istribution**  **Y Fraction of percent of crop area treated (PTA** **).** Conservative. **Water column 5.5X, 23X & 130X . Sediment**  **= 4X, 150X and 970X. (Onion, Soybean & Cotton) at 90th centile**  **Y Fraction of catchment area draining to watershed**  **exit (i.e., uncertainty about enclosed depressions).**  Conservative. **Estimated 1.1X –**  **1.3X. Y**  **Individual market share of pyrethroids nationally and by region.**  Conservative. **3 –**  **100X (deltamethrin > 100X both nationally and in CA ).**  **Y Variation in fraction of CoI in catchment treated on the same day.**  Conservative. **Estimated 1 –**  **1.8X. Y**  **Variation in actual rate of pyrethroid applied (GfK**  **Kynetec data).** Conservative. **1 –**  **1.15X. Y**  **Variation in selection of application methods (ground/air) and subsequent handling (banding/incorporation).**  Variable. Most likely to be conservative. **0.9 –**  **1.3X. Y**  **Variation in intervals between applications.**  Conservative. **Estimated 1 –**  **1.2X. Y**  **Fraction of watersheds with sediment /erosion control structures.**  Conservative. **1 –**  **1.4X (regional). (effect mainly on sediment). Y**  **Fraction of CoI area using conservation tillage, associated realism of LS CA** 

**a nd P parameters in models.**  Conservative. **0.8 –**  **1.1X (effect mainly on sediment). Y**  **Impact of sediment delivery ratios at field/catchment scales.** Conservative. **1 –**  **4X (effect mainly on sediment). Y**  October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved.

# List includes quantitative and qualitative uncertainties  

# Worked examples show uncertainty impacts can be very significant.  

# Some items are pyrethroid specific but most apply to all AIs.  

# List is dominated by protective real world factors not considered in standard FIFRA EECs.  

# Magnitude of many effects quantified via models, others via Best Professional Judgment (BPJ).  

# Some factors appear to be significant but are difficult to quantify. These qualitative factors are mostly conservative and serve to build confidence in the protective nature of EECs.

23 October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved.

# To recap:

 

## Estimates of potential impacts of individual sources of uncertainty associated with standard FIFRA assessments have been developed.  

## Some uncertainties affect EECs in exposed water bodies, others affect the likelihood of a particular water body being exposed.  

## Several specific uncertainties were built into a full assessment which ultimately reduced pyrethroid RQs to acceptable levels.  

## Remaining sources of uncertainty were not built into assessment.  

## These remaining uncertainties will not all apply together but could provide at least 1 to 2 orders of magnitude of conservatism.  

## The non - included conservatisms and qualitative factors provide assurance that resulting risk assessments remain protective, and most would apply to all AIs.  

## T hese approaches have not involved modifying many basic standard protective FIFRA precepts, such as:  

## EECs based on maximum number of applications, maximum use rates  

## Using approved modeling approaches

24 October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved.

# Take home messages
 

# In many cases (including pyrethroids) large, statistically significant water monitoring databases indicate that EPA’s standard screening level (Tier II) EECs are highly protective.  

# Many individual sources of uncertainty which contribute to these conservative EECs have been identified, characterized, and in some cases quantified using probabilistic approaches.  

# Understanding the wide range of quantitative and qualitative uncertainty factors and their potential for modifying standard aquatic exposure estimates offers opportunities for reducing the numbers of may - affect determinations under ESA, as well as building confidence in the protective nature of refined exposure modeling.

25 October 6, 2014 (c) 2014 Pyrethroid Working Group. All rights reserved.