UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASH I NGTON

, D

. C

. 20460

OFFICE OF CHEMICAL SAFETY
AND POLLUTION PREVENTION

P C Cod e: 128931

DP B a rcod e: 426789

D a t e: March 24

, 2016

MEM O RAN D U M

SUBJECT :

TO :

F RO M:

T HR U : Di camba DGA: Second Addendum to the Environmenta l Fate and Ecological
Risk Assessment for Dicamba DGA salt and its Degradate

, 3,6-dichlorosa li cylic

ac i d (DCSA) for th e Section 3 New Use on D i camba-Tolerant Soybean

Grant R owland

, Ri s k Manager Reviewer Kathryn Montague

, Product Manager 23
Daniel Kenny

, Branch Chief

Herb i cide Branch Registration Division (7505P)

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Michael Wagman, Biologist ' /YI_(/

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William P. Eckel, PhD.

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Mark Corb i n, Branch Chief

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Monica Wait

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Environmental Risk Branch 6 

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This is an addendum to the Environme n tal Fate and Effects D i vis i on ' s (EFED) ecological risk

assessment for dicamba DGA salt ( C l arity ® formu l at i on or M1691

, EPA Reg No. 524-582) and
its degradate, 3,6-dichlorosalicyclic acid (DCSA)

, for the proposed new use on d i camba

- tolerant soybean. It includes analysis of information t h at was not previously included in the origina l soyb e an new use r isk assessment (USEPA

, 2011, DP 378444)

. Since the original risk

assessment was co n ducted

, the registrant

, Monsanto

, has submitted:

1) fie l d tria l data that impacts EFED ' s prev i ous analysis of spray drift

, 2) data for incidents and inqu i ries from the use of dicamba DGA salt

,2 3) laboratory volatility data for dicamba DGA and DMA salt formulations

, and 4) terrestrial plant reproductive effects data

.

Additionally, this addendum includes analysis conducted by EFED regarding :

5) the implication of new mammalian chronic effects endpoints for parent dicamba and the
metabolite DCSA from the Health Effects Division (HED ; USEPA 2016, D37836 6+ ), 6) a revised T

- REX run using refined estimates of foliar dissipation half

- lives and variable application rates, 7) the potential for effects to beneficial terrestrial invertebrates

, 8) effects posed by runoff , and 9) potential synergistic intera ctions with glyphosate

.



### 1. Spray Drift and Buffers (Field Trial Data)

In the first a ddendum to the EFED Section 3 risk assessment for dicamba DGA salt for use on

dicamba

- tolerant soybeans (D404138, 5/20/14), EFED estimated that the distance from the appli cation site to where no effects are observed to sensitive plants (based on the NOAEC for the most sensitive apical endpoint of plant height for the most sensitive tested species, non

- dicamba tolerant soybeans) range d from 10 0 to 175 feet (for the 0.5 lb a .e. /A tolerant

- soybean post

emergent application rate)

. However, based on a weight of evidence approach and refined AgDri f t modeling for coarser droplet spectra (coarse to ultra

- course droplet distribution), EFED refined this distance to 124 feet (rounded up to 125 feet) or to 107 feet if label language were to restrict the droplet size to solely extra

- coarse and ultra

- coarse droplet sizes ).

EFED further refined this analysis after receiving more information including a spray drift deposition stu dy submitted by BASF (MRID 49067704)

. In light of this information, Monsanto proposed that the spray drift buffer distance be reduced to 70 feet for M1691 Herbicide using the TTI 11004 nozzle at application spray pressures ≤ 63 psi. EFED ’s subsequent anal ysis for

submitted field trial data (presented below) , however, indicates that a larger buffer may be necessary in order to limit potential effects to sensitive plants to the sprayed field. Linking this data to our previous modeling efforts and empl o ying a weight of evidence approach , EFED proposes that the label should be modified to include language to maintain a 100 to 110 foot downwind buffer when applying at the 0.5 lbs a .e ./A application rate. The July 2015

amended labels subsequently submitted by Monsanto include d a 110 foot buffer and 220
foot buffer for 0.5 and 1 .0 lbs a.e ./A application rates
, respectively.

Field Trial Data Discussion

Subsequent to EPA’s 5/20/2014 a ddendum, Monsanto presented information from academic field research that had not previously been submitted to the Agency for review. EPA requested data from these field trials and Monsanto submitted the raw data (MRID 49612701 pg. 51 ) on 4/13/2015 along with a response document (MRID 49570501 pg. 1 ). Monsanto’s response document included an analysis that the 70 foot buffer would be protective of the no

- effect3 distance for sensitive plants ( the “no

- effect” distance is based on the most se nsitive NOAEC for the apical endpoint of plant height for the most sensitive tested species, non

- dicamba tolerant soybeans) for 7 of the 9 submitted trials and a proposed rationale for why it may not have been protective in the remaining 2 trials. The r esponse document also included Monsanto’s statement that the field trial data are not suitable for use in EPA’s regulatory decision

- making process, but overall support the then

- proposed 70 foot buffer.

While EFED agrees that the field trial data are gene rally not suitable for regulatory decision

making, we believe that they demonstrate add itional uncertainty that the previously proposed 70

foot buffer w ould be sufficient to prevent potential effects to non

- target plants that are off the

field. In an atte mpt to conduct a quantitative evaluat ion of the field trial data, EFED considered

that the data could reasonably represent a dose

- response effect, with higher treatment doses expected to be closer to the application site. In this context, the distances fa rthest from the application site were considered to be likely to have little to no dicamba residues and loosely were considered controls. EFED then considered that plant heights and yield (similar to our apical endpoints of plant height and biomass from t he standard vegetative vigor plant ecotoxicity tests) at the closer distances ( i.e. treatment groups) could be compared to those of plants at the “control” distances using statistical hypothesis tests, similar to our standard statistical methodologies for data evaluation of ecotoxicity tests. In an effort to streamline the data analysis process, EFED used standard t

- tests in Excel to conduct the analysis.

T his statistical analysis indicate d that a majority (5/9) of the field trial s provide d evidence that the proposed 70 foot buffer would not be sufficient to keep any effects to sensitive plants’ apical endpoints contained to the field. Three of the nine trial sites had significant inhibitions compared to the “control groups” at distances greater than EFE D’s refined buffer of 125 feet, though EFED notes Monsanto’s rationale for the greater distances in two of those sites (Monmouth, IL and Haubstadt, IN) might be due to applications not conforming to the currently proposed label

restrictions for M

- 1691 Herb icide. The maximum “no effect” spray drift distance that EFED determined for the remaining site (Rower, AR) was 147.5 feet.

Since these field trials involved no true controls and residue analysis was not conducted to

confirm the lack of residues i n the f a rthest plants, the magnitude of an effect seen between “treatment” groups and true control plants m ight be higher than what this analysis indicates.

These field trials were all conducted at the 0.5 lbs a. e ./A (maximum single post

- emergent applicati on rate) and all were conducted using the TTI11004 nozzle in accordance with the label directions. The operating pressures varied across the sites from 30 psi to 50 psi (other than for the Haubstadt trial site, for which nozzle pressures were not recorded ), which is less than the labeled maximum operating pressure of 63 psi. Higher operating pressures than used in these field trials (but within the proposed labeled directions for use ), may result in an increase d proportion of finer spray droplets and cons equently result in effects at distances greater than

observed in these field trials. The specific process, results and conclusions that EFED used in evaluating Monsanto’s submitted field trial data and relating it as an additional lin e of evidence

in dete rmining an appropriate buffer that would result in no adverse effects to EPA’s apical4 endpoints for terrestrial plants (the most sensitive taxa to the herbicide dicamba) , is discussed immediately below.

Details of EFED’s Process to Determine a “No Effect” Spray Drift Buffer from the Available

Field Trial ( MRID 49612701 pg. 51 ) Data:

Transects (at each site or for each swath, where multiple swaths were tested) were combined to determine mean soybean (non dicamba

- tolerant) plant heights (14 & 28 DAT) or yiel ds at set
distance s

. The f a rthest two distances for which plant height or yield data were recorded were

considered “controls

, ” though there are considerable uncertainties to this approach . Specifically, no true controls were used, no residue analysis was conducted to confirm that these plants were not exposed to dicamba (or other chemical) residues, data were only recorded when there was at least 5% visual response (which could have been due to a number of factors including potential dicamba residues) and for many of these “controls” the height/yield endpoint may not have been recorded in all transects, resulting in a lower sample size (n) for controls and therefore a decreased power in the statistical t

- test.

All analyses were conducted in MS Excel. Me ans for each distance towards the sprayer were compared to the “control” means to determine the percent inhibition at each distance. T

- tests (1

- tailed, assumed equal variances unless an F

- test {p<0.05} showed unequal variances) were conducted to compare t he endpoints of the treatment distances to the controls. Since these were field tests and had considerable uncertainties surrounding the controls, EFED considered significance at the (α=) 0.1 level which increases the conservatism of the analysis . The bu ffer for a “no effect” distance at each site was considered the first distance greater than the maximum distance which had a significant decrease compared to the control group. For example, at the Brooksville, MS site

, the furthest distance which exhibite d a significant decrease (p<0.10) in height at 28 DAT compared to the control group was 86.25 feet. The next highest distance at

which soybean heights were measured was 96.25 feet ( not significant, p=0.19), which therefore

was considered the “no effect” di stance buffer for that site.

Results of the Analysis of the Field Trial ( MRID 49612701 ) Data

After reviewing th is field trial data, EFED made the following findings. Of the nine field trials

discussed above

, a majority ( five ) provide evidence that a 70 fo ot buffer may not be sufficient

, and four provide evidence that a 100 foot buffer may not be sufficient ( Table 1 ). With a buffer

distance of 125 feet for a 0.5 lb a.e ./A application rate, 3 sites (33%) would provide evidence that a larger buffer might be necessary, with Monsanto stating (and subsequently providing information) that two of these (Monmouth and Haubstadt) may not have followed the currently proposed label by either using a different formulation or applying when wind speed was lower than requi red by the current proposed draft label.5 Table 1 . Distance (in feet) from Site of Application to a "No Effect" *

Site Height (ft.)
14 DAT Height (ft.)
28 DAT Yield (ft.) Comments

Brooksville,
MS 46.25 96.25 66.25

Rower, A R 7.9 20.6 248.7* * 14 DAT “controls” had only n=2. 28 DAT controls
had n=3. * *Note , for yield, after the 12% inhibition at 223.4’, no treatment group was significantly (p<0.1) inhibited compared to controls (inhibitions ranged from 1.03

— 23.75% after this ) . The higher inhibitions were not significant due to the use of the nonequal variance t

- test, but would have been had we assumed equal variances). Therefore, using best professional judgment informed by the data and t

test res ults , EFED has reduced the n o effect distance for this endpoint to 147.5’ , after which all inhibitions at shorter distances were > 10% (other
than only 1.1% inhibition at 7.9 feet). W. Lafeyette,
IN 66.25 26.25 No Data 14 DAT “controls” had n=3, 28 DAT “controls”
had n=2 Scott, MS 26.25 26.25 66.25 Jackson, TN 16.25 16.25 16.25 Yield “controls” had n=4. Kirkwood, IL 116.25 116.25 16.25

Monmouth,
IL Swath 1 74.2 137.8 0 14 DAT controls had n=4, 28 DAT controls had n=3, Yield controls had n=3 Monmouth,
IL Swath 2 53 95.4 254.4 1 4 DAT controls had n=3, 28 DAT controls had n=2, Yield controls had n=2 Haubstadt,
IN Swath 1 30 80 10 Swath 1 only took measurements to a maximum of 100 feet. 14 DAT controls had n=5, 28 DAT
controls had n=3 Haubstadt,
IN Swath 2 40 80 150 14 DAT cont rols had n=3, 28 DAT controls had n=3, Yield controls had n=2 Gilbert, IA

Swath 1 N/A N/A N/A This swath was not evaluated as no field measurements were taken past 30 feet. Gilbert, IA

Swath 2 35 15 5 14 & 28 DAT and Yield controls had n=4. For yield, no distance had lower mean yield compared
to controls. * Distance based on Plant Height after 14 and 28 days after treatment (DAT) and Yield (α = 0.10). No effect” indicates no reduction in plant height or biomass relative to controls. In controls, the

s ample size (n) is considered 6 (or 10 for Brooksville, MS and Scott, MS trial sites) unless otherwise noted in the comments section where fewer controls may affect the power of the test.6 Weight of Evidence Conclusions

After reviewing the field trial da ta submitted to EPA, EFED finds that there is considerable uncertainty around the use of a 70 foot in

- field buffer with the intent to keep any adverse effects (related to our apical endpoints of plant height and biomass) on the field , as the majority of th e sites appeared to have effects on plant height at distances past this . T hough the quality of this

field trial data is not suitable for the purpose of establishing an appropriate buffer distance (especially as the lack of true controls may mean that the magnitude of effects to true control plants could be greater than indicated here), EFED believes this data provides a line of evidence

that an in

- field buffer greater than 70 feet is warranted to ensure protection of listed species, such

as that determined in our previous risk assessment addendum (D404138, 5/20/14) which used a refined modeling approach extracting out the coarse, extra

- coarse and ultra

- coarse droplet spectra to determine an average 124 foot buffer (rounded up to 125 feet) or solely the extr a
coarse and ultra

- coarse droplet spectra for an estimated average distance of 107 feet (rounded up to 110 feet) for a 0.5 lbs a.e ./A application. The draft label only supports the use of one nozzle ( Tee Jet® TTI11004 ) with a maximum operating pressure o f 63 psi which restricts droplet spectra to ultra

- coarse and extremely coarse

.

Using a weight of evidence approach ( covering the refined modeling analysis conducted in the previous risk assessment addendum, the spray drift deposition study submitted by BASF (MRID 49067704) and the submitted field trial data discussed here), EFED concluded that the label should be modified to include language to maintain a 100 to 110 foot downwind buffer when applying at the 0.5 lbs a.e ./A application rate and with the described nozzles restricting the droplet spectra extra

- c oa rse and ultra

- coarse

. The July 2015 amended labels subsequently submitted by Monsanto included a 110 foot buffer and 220 foot bu ffer
for 0.5 and 1 .0 lbs a.e./A application rates, respectively.

Further data that may help refine this estimate would be field trial data with actual controls (and/or residue analysis to indicate a lack of dicamba or other herbicide treatments), larger control sample sizes and transect replication, field measurement s provided regardless of whether plant visual response (damage) was observed or not, a greater number of swaths at each trial site (reflective of typical practices in soybean agriculture) and using the maximum labeled nozzle operating pressure.



### 2. Incidents

Incident Reports Submitted by Monsanto (2012

- 2014)

Monsanto provided information for 73 incidents involving the M1691 formulation from 2012 to 2014. In their response document (MRID 49612701 pg. 68 ), Monsanto notes that observations were solely qualitati ve visual estimates and that no measurements of apical endpoints such as plant height or yield were taken. Monsanto further note d that the incidents related either to seed production activities or to activities performed as part of the product developm ent process relating to product stewardship

. T he y stated that current proposed label requireme nt s were not in7 place in 2012, that all of these incidents either did not follow all of the current draft lab el requirements (including tank mixture s wi th additional pesticide active ingredients such as glyphosate , nozzle type, wind

- speed, wind direction, spray volume, etc.) or they were a result of other factors ( e.g. burndown application, heavy rainfall, equipment contamination, spillage, etc.)
and tha t the percentage of incidents as a function of the number of applications made has decreased in each subsequent year since 2012.

EFED has conducted an initial review of th ese incident s and generally agrees with Monsanto that
the incidents resulted from applications not in accordance with current ly proposed draft label language or were attributed to other (non

- dicamba) factors. However, four incidents (Inquiries 19, 20, 24, and 30) from 2014 lacked sufficient information in the report (such as on tank mixture, application rates, nozzles, wind direction & speed, equipment speed, buffer distance, spray volume & pressure or boom height ) to determine whether their occurrence followed applications that were in accordance with the current proposed draft labe l requirements. Although , as Monsanto notes, much of this data arises from se ed production activities or activities related to the product development process and were not generated for purposes of risk assessment, EFED does not discount that they could be suggestive of potential incidents in the
field and they could provide useful information to that end

.

EFED also acknowledges that the incident observations are qualitative measures of visual injury ( e.g. leaf spotting or curling) . Nonetheless, the information presented in these incidents may be
useful if future labels incorporate changes such as potential tank mixes with additional a ctive ingredients or additional nozzle types , since some of these incidents include information on tank mixes and nozzle types which would be relevant in the case where those changes are made to the
label

.

Mi ssouri and Arkansas Case file s

The Missouri Department of Agriculture (MDA) has submitte d information for incidents occurring from 2013 to 2015 and the Arkansas Plant Board (APB) has submitted information for
incidents occurring in 2015

, regarding observ ations of dicamba

- type damage to non

- tolerant plants following either preemergence or postemergence applications to dicamba

- tolerant (DT) soybeans or cotton. Similar to the incidents reported by Monsanto for 2012

- 2014, all of the incidents were qualitative visual estimates and no observations or measurements of apical endpoints such as plant height or yield were taken.

2013

- 2014 Incidents

MDA has notified EPA of two incidents following potential dicamba applications that occurred
in 2013 and 2014. In 201 3, dicamba

- type damage was observed in a non

- DT soybean field (MO
Case File #81513M00701, EIIS Incident report number I026579

- 001) . The only dicamba application in the area was reported to be a Clarity herbicide application on DT

- soybeans 2,800
feet from the damaged field. The air temperature and humidity at the time of dicamba application were reported to be 82 0 F and 55%, respectively. Dicamba residues were found in

one foliage sample taken from the affected field at 42 μg/kg

. In the other two samples, dicamba residues were not detected (limit of detection not reported, but a limit of quantification of 3.88 μg/kg )

. The case file submitted to the agency did not originally determine the cause of the dicamba damage

. I n subsequent co mmunication with the Age ncy ( 2015 letter from D. Slade, MDA to Grant Rowland, EPA ), MDA concluded that the application of C larity herbicide was not transported to the affected site by spray drift, but by later volatilization.

In their response document (MRID 49612701 pg. 1 , s ubmitted prior to MDA’s December, 2015
letter ), Monsanto note d that it has reviewed the complete incident report from the Missouri Department of Agriculture (MRID 49612701 pg. 75). Monsanto state d that the report indicate d that 1) there wa s potential the crop visual injury response was observed prior to the dicamba application, 2) MO Department of Agriculture did not come to a definitive conclusion on the primary cause of the incident and 3) other plausible explanations were not investigated, such as
tempe rature inversion, alternative sources of dicamba, such as leaking equipment or damage from other herbicides. Therefore, Monsanto conclude d that the incident d id not provide
evidence that the observed plant response was a result of exposure to vapor drift of dicamba
residues. Monsanto also included this incident in their description of the 73 incidents from 2012

- 2014 discussed previously in this section and noted that this incident would not comply with the current proposed label requirements

, as M1691 was tank mixed with glyphosate and other adjuvants.

EPA notes that MDA has now completed their investigation of this incident, measured residues indicating the presence of dicamba residues on the affected site, concluded that dicamba
volatilization rather than drift was the likely cause of the damage and initiated enforcement action against the applicator for allowing the product to move from the target field. The climatic conditions at the time of application were slightly outside of the range of conditions from the available laboratory studies on dicamba DGA salt’s volatility. Given that effects to EPA’s apical endpoints of plant height and biomass were not measured, there is uncertainty whether this
incident indicates that volatilization followin g dicamba applications may result in impacts to apical endpoints beyond the proposed spray drift buffer of 110 feet for a 0.5 lb/A application. However, based on the available data, a volatilization buffer equal to the spray drift buffers, and
extendin g in all directions f r o m the treated field, is justified. The current proposed labels only apply a unidirectional spray drift buffer in the direction wind is blowing. Further discussion of volatility is provided in Section 3 below.

MDA also notified E PA of an incident in 2014 (MO Case File #072214MO0701) where “dicamba type” damage was observed on a non

- DT cotton field where the only nearby dicamba application would have been a C larity herbicide application on DT

- soybeans, 2.2 miles from the
affected s ite. As with the other incidents, the provided information only indicated observations of visual injury and not effects to apical en dpoints such as plant height and yield. Residue samples taken from the affected site failed to detect dicamba residues. It is unclear whether this
incident was also included in Monsanto’s submitted information on the 73 incidents from 2012

- 2014 (discussed previously in this section). Wi th the current information available

, and due to the lack of identified dicamba residues, it is uncertain whether the damage observed in the incident was a result of dicamba applications or due to some other unidentified cause. If the observed damage was caused by dicamba, th e n given the large distance between the affected site and the nearest known dicamba application, it would likely have been a result of volatilization

, rather than spray drift.9 2015 Incidents

Missouri and Arkansas recently submitted to EPA a total of 15 incidents in 2015 that might be
attributed to dicamba use (12 in Arkansas and 3 in Missouri). The information indicates that these incidents resulted from 6 separate instances of applications of dicamba

, with 8 of the incidents (7 f rom Arkansas and 1 from Missouri) being a result of a single instance of a post

emergent dicamba application to DT

- cotton of Strut herbicide (active ingredient Dicamba DGA),
tank

- mixed with glyphosate and applied at two times the labeled rate for the pro posed Clarity/M1691 post

- emergent use. V isual observations of plant damage extended to 1320 feet (1/4 mile) from the application site . The remaining incidents were pre

- emergent applications of dicamba or at this time remain uncertain as to whether any application of dicamba was made.

Conclusions Regarding Incident Information 2012

— 2015

For the purposes of the registration of dic amba on dicamba

- tolerant soybean , the incident information available at this time indicates that the vast majority of incid ents occurred following applications that were not made according to the current draft label requirements. Label requirements that were not followed included tank mixes with other active ingredients and adjuvants, higher application rates, and application s with different nozzle types and climatic conditions than permitted according to the draft label. Quantitative measurements of yield loss or decreased plant height were not made in any of the incident descriptions. Currently, EPA has no methodology for r elating qualitative estimates of visual damage to quantitative effects to apical endpoints.

Most of these incidents were likely caused by spray drift off the field following the application. The only incident where volatility of dicamba residues has bee n concluded to be the cause of the
incident by a regulatory agency (MDA for MO Case File #81513M00701, EIIS Incident report
number I026579

- 001 ) was a n incident where the application was a lso made as a tank mix of glyphosate, additional adjuvants

, and dicam ba . However, EFED believes that this d ifference from the draft label is unlikely to have impacted the ability of dicamba residues to volatilize
since th e different active ingredient s and adjuvants are generally presumed to have disassociated
from each ot her by the time any volatilization would occur

. R ather , the volatilization may have
been more likely impacted by the climatic conditions (temperature and humidity) in the days following the application which fall outside of the range of submitted laborat ory data conditions

. Additional discussion and characterization of volatility is provided in the next section.



### 3. Volatility

After reviewing data submitted to EPA relating to the volatility of dicamba, E FED ha d concerns regarding the volatility of dicamba , and possible post

- application, vapor

- phase off

- site transport that might damage non

- target plants. Monsanto responded to these concerns with a submission (MRID 49612701 pg. 143) that acknowledge d the long

- recognized volatility of dicamba and
describe d m easurements of the volatilization in the different formulations.10 Th e information submitted to address EFED’s concerns wa s helpful, but the submission d id not include enough detail to verify the measurements in the studies

. EFED determined that i t woul d be useful also to perform volatility experiments under varied conditions of temperature and relative humidity, because these factors seem to be important in field conditions

.

The registrant has agreed to place directional, in

- field spray drift buffers of 110 feet for the 0.5 lb

a. e ./A application rate and 2 2 0 feet for the 1.0 lb a. e ./A application rate. One open literature study (Egan and Mortensen 2012), directly addresses the potential for volatilization and transport of dicamba, and the potential for damage to the most sensiti ve tested species, soybean (non
dicamba

- tolerant ). Based on damage assessments of non dicamba

- tolerant soybean plants placed near treated fields after spray drift from a 0.5 lb/A DGA salt application had dissipated, the
authors estimated the ex posure at distance by correlation to known dose

- damage correlations. They estimated that the 95% upper bound vapor exposure would drop below the soybean NOAEC at approximately a distance of 25 meters (82 feet). This is well within the 110

- foot spray drif t buffer proposed for the 0.5

- lb/A rate. Thus, based on at least one study, this buffer
distance should be adequate to protect against volatilization exposure for EPA’s apical endpoints of plant height and yield

. However

, consideration should be made as t o whether this buffer distance should be applied on all sides of the field, rather than the currently labeled uni

directional buffer according to wind direction.

The incident described by MDA in the previous section (MO Case File #81513M00701, EIIS
Inci dent report number I026579

- 001) provides limited information that the proposed 110 to 220

- foot spray drift buffers would not be adequate to limit off

- site plant damage due to post

application volatilization. However, since the incident only qualitatively describes visual damage, while the buffer is intended to be protective of apical endpoints of height and yield, t his remains an uncertainty , and would benefit from additional field trial data under varied conditions of temperature and relative humidity. Based on the best available data for dicamba residues from vapor drift compared to effects on apical endpoints, EFED believes t hat a 110 foot buffer for the 0.5 lb ae/A application rate should be adequate to protect against effects on non

- target plants from volatilization of dicamba residues. This analysis similarly suggests that a 220

- foot buffer is protective for the 1.0 lb ae/ A application rate , though this may be overly conservative since the 1.0 lb ae/A rate is for pre

- emergent applications that may be applied under conditions less conducive to vapor drift ( e.g. cooler temperatures )



### 4. Potential Effects on Terrestrial Plant Reproduction

E FED is aware of published literature associating dicamba applications with effects to soybean

progeny. These studies indicate potential effects to the quantity and reproductive quality of
future soy bean generations following dicamba applications that would not be observed in the guideline vegetative vigor and seedling emergence studies EFED typically uses to assess risk to terrestrial plants. Therefore, t h e s e data raise a potential concern that has not been directly
addressed in OPP assessments , should these effects occur at lower exposures than the effects observed in the guideline terrestrial plant studies

. In meetings and email correspondence in January/February, 2015

, OPP asked whether Monsant o was aware of this issue. Monsanto requested the references that OPP was aware of, so that they could independently review them.11 Monsanto reviewed the open literature references provided by OPP and stated that no ne of the
studies described effects on progeny at application rates lower than OPP ’s lowest available regulatory endpoint from the available vegetative vigor plant study (0.000261 lb dicamba a.e./A equivalent to 0.29 g a.e./ha, based on plant height) , therefore any mitigations ( i.e. spray drift buffers) based on the plant height endpoint would be protective for effects to progeny

.

The open literature studies examined seeds/pod, seed weight, seed quality, delayed maturation, pod malformation, reduced germination or progeny emergence, and malformed progeny. The vast majority of the studies did not investigate effects at rates as low as the NOAEC from the available vegetative vigor study. Monsanto’s review of the available information indicated that
the lowest effects endpoint reported fro m these studies was for delayed maturation of soybeans at rates as low as 0.56 g a.e./A from Kelley et al. (2005), which would still be almost 2 times less sensitive than the regulatory endpoint based on plant height that E FED has used in its risk

assessme nts. Monsanto conclude d that the open literature studies d id not contain information
that indicate d that the in

- field buffer based on plant height that is on the draft label would not also be protective of these reproductive effects.

EFED acknowledges M onsanto’s submission of their analysis of the open literature data for effects to progeny , but to date has not independently reviewed each of these studies

. However, for the following reason , EFED does not believe the information would change its risk

a ssessments. The most sensitive endpoint reported in the open literature was a LOAEC of 0.56 g a.e./A for delayed maturation of soybeans (Kelley et al

., 2005; no NOAEC reported)

. As EFED’s determination for risk to listed plant species is based on the most sensitive apical endpoint ( i.e.

, the NOAEC for soybean plant height from the available vegetative vigor study with dicamba
DGA , 0.000261 lb dicamba a.e./A equivalent to 0.29 g a.e./ha, based on plant height ), less sensitive endpoints reported in the liter ature for effects to progeny would not impact EPA’s risk

assessments. EFED’s policy regarding open literature is that typically if endpoints from the open
literature are not more sensitive than guideline endpoints , than further analysis is not required (U SEPA, 2011b)



### 5. Revised Terrestrial Vertebrate Endpoints

Parent Dicamba

The risk assessment for the proposed new use on soybeans (USEPA, 2011. D378444) used the chronic endpoint from the rat 2

- generation study (MRID 43137101), a NOAEL of 45 mg/kg

- bw, based on decreased pup weight at 136 mg/kg

- bw compared to the concurrent controls. HED recently reanalyzed the data from this study ( USEPA, 201 6

, D431873 ) in comparison to the historical control database range and determined that the NOAEL and LOAEL shou ld be raised to 136 and 450 mg/kg

- bw, respectively

, because pup weights in each generation in the 136 mg/kg

- bw treatment group were within the historical control range and above the historical control mean for the F1, F2A and F2B generations. The revised T

- REX run presented in S ection
6 of this addendum reflects the adjusted chronic endpoint for parent dicamba

.

Metablolite DCSA12 Following preliminary review of a rat 2

- generation study with DCSA (MRID 47899517), t he risk assessment for the proposed new us e on soybeans (USEPA, 2011 D378444) used a chronic
NOAEL endpoint of 37 mg/kg/d based on decreased parental bodyweight in the 362 mg/kg/d
treatment group

. However, since that assessment was completed , the chronic endpoint was
revised in the final DER revi ew (USEPA, 2012) and a recent memorandum for a benchmark dose analysis (USEPA, 2016) was completed to reflect the observed statistically significant
decreas es (6

- 9%) in offspring weight on 14 and 21 post

- natal days (PND) . The DER review
from 2012 conside red the LOAEL from effects to pup weight to be based on the male pre

- mating dose of 37 mg/kg/d, with a corresponding NOAEL of 4 mg/kg/d. The recent benchmark dose analysis conducted by HED (USEPA, 2016) determined BMD 5 (estimated benchmark dose [BMD] to r esult in 5% body weight change in pups from background levels) and BMDL 5 (the
lower 95% confidence level on the BMD 5 ) based on both the male pre

- mating dose and the
female lactation dose and noted that female lactation doses are more reflective (than male

premating doses) of pup exposure during the nursing period wh en the pup body weight
decreased . This analysis concluded that the pup weight LOAEL and NOAEL threshold values based on the dam lactation doses would be 78 mg/kg/d and 8 mg/kg/d , respectively

. HED also
calculated a BMD 5 (estimated benchmark dose to result in 5% body weight change in pups from background levels) and BMDL 5 (the lower 95% confidence level on the BMD 5 ) of 38.6 and 34.9 mg/kg/d, respectively

, based on the female lactation doses. In the revised T

- REX analysis below, EFED used the NOAEL value of 8 mg/kg/d for risk estimation and further characterized the risk using the BMDL 5 of 34.9 mg/kg/d for DCSA effects to mammals.

No chronic data is available for the effects of the DCSA degrada te to birds (or reptiles or
terrestrial

- phase amphibians, for which birds are surrogates). As a highly conservative approach, EPA will consider the toxicity differential for chronic effects between parent dicamba and the metabolite DCSA and apply a simila r ratio to estimate chronic effects to avian organisms. Therefore, a factor of 17 x (based on the chronic endpoints of 136 m g/kg

- bw for parent dicamba
and 8 mg/kg

- bw for DCSA) is applied to the dicamba chronic NOAEC of 695 mg/kg

- diet for the mallard duck, to result in a highly conservative estimate of a chronic NOAEC of 40.9 mg/kg

- diet for birds for DCSA. This is considered a highly conservative approach as the chronic mammalian endpoint is based on effects to pups who would have been continually exposed to
DCSA residues in utero and throughout lactation while chicks in the avian reproduction test would not be exposed to DCSA residues while still in the eg g or post hatch.



### 6. Revised T

- REX Analysis for Parent Dicamba and Quantitative Assessment of DCSA Exposur e and Risk

Dicamba

- specific Half

- Life

In the risk assessment for the proposed new use on soybeans (USEPA, 2011), E FED modeled the dicamba residues using a single application (the T

- REX model available at the time of the assessment was incapable of runnin g applications with variable rates) and used the default foliar dissipation half

- life value of 35 days. However, E FED has refined this analysis by modeling the residues using the maximum potential application rates with minimum application intervals (a 1
lb a. e ./A application followed by two 0.5 lb a. e ./A applications with a seven day interval between each application) ; a chemical

- specific foliar dissipation half

- life value for parent dicamba13 (described below) ; and the new chronic mammalian endpoint for p arent dicamba (described previously in Section 5 )

.

EFED used residue data by Jimenez (1994; MRID 43370701) to calculate a dicamba specific foliar dissipation half

- life. According to the available Health Effects Division (HED) review (DP Barcode 207649, 3/11/1996), this study was acceptable for use in risk assessment and indicated that there was no difference in foliar dissipation data between the various tested dicamba salt
formulations (DMA, DGA and sodium salt formulations) . Therefore, data for all dic amba salt
formulations tested were used to calculate the final foliar half

- life value.

Half

- lives were calculated for each set of residue decline data based on the NAFTA Guidance for Evaluating and Calculating Degradation Kinetics in Environmental Media and using the PestDF package in the R statistical program. Each equation was evaluated for appropriateness before
inclusion in the final half

- life calculation. Individual decline data and estimated foliar half

- life
values are available in Table 2

. A sum mary of this information is provided in the table below. The upper 90 th percentile, one tailed, confidence interval of 8.4 days was used to calculate
refined EECs in this assessment.

Table 2. Dicamba Half

- Life (days) in Foliage
Arithmetic
Mean Standard
Deviation Max Value Min Value Number of
Values Upper 90%
CL on the

mean 7.3 6.6 43.7 1.11 99 8.4

Parent Dicamba T

- REX Analysis

Modeled maximum r esidue values (EECs) determined using this refined approach were slightly higher (~15%) than those determ ined in the original dicamba

- tolerant soybean Section 3 assessment, but would not have impacted the screening

- level risk conclusions for any assessed
taxa. The previous risk assessment (2011) concluded that there was potential for direct adverse
eff ects to mammals from chronic exposures of dicamba (max chronic RQ was 2.31 for small mammals consuming short grass). Following the refinements presented in this section (3 applications of dicamba to include the two post

- emergent applications at the 0.5 lb a

. e

. /A rate, foliar dissipation half

- li fe decreased from 35 days to 8.4 days, and an increase in the mammalian chronic endpoint from 45 mg/kg

- bw to 136 mg/kg

- bw ) , there are no longer any exceedances for any size class of mammal consuming any dietary item (max RQ = 0. 84 , see Appendix 1 for full

T

- REX input and output)

DCSA Metabolite Exposure Analysis

Since the chronic toxicity endpoints are more sensitive for DCSA than dicamba and DCSA residues were higher than dicamba residues within dicam ba

- tolerant soybean plant tissues (see below), EFED separately assessed the chronic exposure to DCSA residues for birds and
mammals.14 The available data indicate that DCSA has similar acute toxicity as parent dicamba, but is substantially more toxic on a chronic basis to mammals. In conventional soybean plants, DCSA residues following dicamba applications prior t o planting were less than 2% of total dicamba residues in forage, hay and seed (MRIDs 43814101 and 44089307; max of 0.130 ppm DCSA

,
see Appendi x 2 ) and would not be above toxicity thresholds for any taxa

. However, in dicamba

tolerant soybean plants, dicamba is converted to DCSA and its glycosidic conjugates following demethylation of the aromatic methoxy moiety of dicamba (USEPA, 2013. HED resid ue chemistry summary) and in comparison to dicamba use on conventional soybeans, the maximum
residues of DCSA in dicamba

- tolerant soybean field trials following one 1

- lb/A pre

- emergent application and two 0.5

- lb/A post

- emergent applications were a substant ially higher proportion
of dicamba

- related residues in forage, hay and seed ( Appendix 2 and MRID 47899524; 76%

-- 88% of total dicamba

- related residues ). The empirical data from MRID 47899524 found mean s and maximum s, respectively, of DCSA concentrations of 17.0 and 51.3 ppm

, in forage 7

- 10 days following the last application, 32.2 and 61.1 ppm in hay 13

- 15 days following the last application and 0.059 and 0.440 ppm in seeds 73

- 98 days after the last application. EFED use d the
maximum measured values from t he empirical data on forage, hay and seeds to assess risk to
terrestrial vertebrates. There is some uncertainty in this approach as the maximum DCSA residues appear to be slightly increasing (16%) between forage at 7

- 10 days and hay at 13

- 15 days, however this could be due to the difference between fresh er forage and drier hay, where DCSA has become more concentrated compared to the overall plant biomass

, rather than due to
additional conversion of dicamba residues to DCSA . Additionally, the amount of addi tional
dicamba available to potentially convert to DCSA appears limited after this point as the maximum residues of dicamba were only 2.62 and 1.16 ppm in forage and hay, respectively.

Based on the available plant metabolism data for DCSA on non

- DT plan ts, EFED assumed that any exposure for terrestrial vertebrates occurs as a result of feeding solely on DCSA in DT

soybean and no exposure to DCSA is expected for terrestrial vertebrates feeding off the field,
even if dicamba residues should occur followin g spray drift or volatilization. This is because the
conversion of dicamba to DCSA in plants is only expected to occur in crops modified to be
tolerant to dicamba.

DCSA Effects Assessment

No effects data are available for the chronic effects of DCSA to birds. EFED conservatively assumed that the ratio of parent dicamba to DCSA toxicity ( 17 x differential) from the mammalian toxicity data could be applied to the chronic effects endpoint for birds , resulting in a chronic avian endpoint of 40.9 mg/kg

- bw . However, since the DCSA chronic endpoint for mammals is based on effects to pups who were continually exposed in utero in the study, it may
be conservative to assume that this toxicity differential in mammals for parent dicamba and DCSA would be equival ent for chicks who would not be exposed to DCSA residues during their gestation in the egg (beyond initial maternal transfer into the egg during egg development)

.

Using the empirical dataset for DCSA residues in DT

- soybean crops (as described above) , the maximum residues in soybean forage and hay tissue were 61.1 ppm and in seeds were 0.440

ppm. Residues in arthropods (as a dietary item for birds and mammals consuming insects that15 have consumed soybean tissues with DCSA residues) were assumed to follow th e Kenaga nomogram relationship between broadleaf plants and arthropods for spray applications and therefore were considered to contain 42.5 ppm. This is likely conservative, given that the residues from the nomogram are for external residues in food items following a spray application while the actual exposures would be internal residue concentrations in the plant. A screening assessment using this empirical data for the exposure values results in exceedances of the chronic
LOC for all size classes of mam mals consuming soybean forage and hay tissue or consuming insects that had consumed soybean tissues with DCSA residues (RQs range from 1 .1

— 3.3
, Table 3 ) , for small birds consuming forage and hay tissue or insects that had fed on DT

- soybean
tissues , ( RQs r ange from 1.2

— 1.7

, Table 4 ) and medium birds feeding on forage/hay tissue (marginal exceedance of 1.0 ) but no exceedances occurred for any si ze mammalian or avian granivore consuming soybean grain (max granivore RQ of < 0.01)

.

Table 3 . Dose

- based exposu re, body

- weight adjusted chronic endpoints and risk quotients for mammals consuming DT

- soybean tissues containing DCSA residues ( maximum 61.1 mg/kg in forage/hay, 0.44 mg/kg in seeds) or consuming arthropods that had fed on DT

- soybean tissues (assumed to c ontain 42.5 mg/kg DCSA). Bold RQ values exceed the LOC.

Size Class (g) Dietary Item Food Intake (k

- diet/d) Dose

- based EEC (mg/kg

- bw) Adjusted NOAEL (mg/kg

- bw) RQ

Small (15g) Forage/Hay 0.0143 58.25 6.2 3.3
Seed 0.00318 0.09 6.2 < 0.01 Arthropod 0.0143 40.52 6.2 2.3
Medium (35g) Forage/Hay 0.0231 40.33 14.2 2.8
Seed 0.00513 0.06 14.2 < 0.01 Arthropod 0.0231 28.05 14.2 2.0 Large (1000g) Forage/Hay 0.153 9.35 17.6 1.5
Seed 0.0340 0.01 17.6 <0.01 Arthropod 0.153 6.50 17.6 1.1

Table 4. Dose

- based exposure and risk quotients for birds consuming DT

- soybean tissues containing DCSA residue s (chronic endpoint assumes a 17 x differential in toxicity be tween parent dicamba and DCSA for birds).

Size Class (g) Dietary Item Food Intake (k

- diet/d) Dose

- based
E EC (mg/kg

bw) NOAEC (mg/kg

- bw) RQ

Small (20g) Forage/Hay 0.0228 69.65 40.9 1.7
Seed 0.0051 0.11 40.9 < 0.01 Arthropod 0.0228 48.45 40.9 1.2
Medium (100g) Forage/Hay 0.0649 39.65 40.9 1.0
Seed 0.0144 0.06 40.9 <0.01 Arthropod 0.0649 27.58 40.9 0.7 Large (1000g) Forage/Hay 0.291 17.78 40.9 0.4
Seed 0.065 0.03 40.9 <0.01 Arthropod 0.291 12.37 40.9 0. 3

While this assessment used the comparison of the maximum residues detected with the chronic mammalian endpoint, there is some uncertainty due t o the limited temporal sampling of DCSA
residues in DT

- soybean tissues (forage from days 7

- 10, hay from days 13

- 15 and seeds from16 days 73

- 98) and therefore understanding formation/decline rates is not possible (to better understand potential maximum residu es). Plant metabolism studies that track DCSA residues over time in all parts of DT

- soybean plants following post

- emergent applications would decrease this uncertainty. In the absence of this, EFED has used the best available data and the maximum

measure d residues to evaluate the chronic exposure.

As noted above, EFED calculated t hese RQs based on the female lactation dose NOAEL endpoint of 8 mg/kg/d from the DCSA 2

- generation study where reductions of up to 9% pup body weight were observed 2

- 3 week s post birth at the next highest dose (78 mg/kg/d). If the

BMDL 5 (the lower 95% confidence level on the estimated benchmark dose to result in a 5% body weight change in pups from background levels) of 34.9 mg/kg/d calculated by HED (EPA, 2016) for DCSA wa s used in place of the NOAEL , the n the maximum residues from the empirical data in soybean hay would be below the threshold dose for all size classes of mammals feeding on soybean plant tissue or soybean

- consuming arthropods (RQs would range from
0.35

— 0. 76 for mammals feeding on tolerant soybean tissue s and 0.24

— 0.53 for mammals feeding on arthropods having consumed soybean tissue s).



### 7. Terrestrial Invertebrates Risk Characterization

The initial 2011 risk assessment for dicamba use on tolerant plants ( s oybean use D378444

, 3/8/2011 ) was conducted prior to EPA developing methods to quantitatively evaluate risks to pollinators. Consequently, that assessment included no quantitative analysis of the risk to beneficial terrestrial invertebrates posed by dica mba use patterns

. B ased on the acute contact data for the honey bee

, the 2011 assessment qualitatively concluded that direct effects to listed terrestrial insect species were not expected.

In June 2014, President Obama issued a memorandum 1 establishing a Pollinator Health Task Force, co

- chaired by USDA and EPA, to create a National Pollinator Health Strategy that promotes the health of honey bees and other pollinators (including birds, bats, butterflies, and insects) . Consistent with this Presidential me morandum

, the Office of Pesticide Programs (OPP)
has been evaluating its own risk assessment methods to more quantitatively characterize pesticide risks to bees . This evolution has identified additional honeybee life stage testing and longer duration effe cts tests for adults (i.e., larval acute and chronic studies, and adult chronic studies) as potentially important to the risk assessment process

.

This addendum document explains additional lines of evidence not considered in the 2011 risk

assessment to b etter characterize the risk posed by dicamba uses to terrestrial invertebrates and
ascertain if the lack of additional bee studies (including chronic adult honey bee data and acute and chronic larval honey bee data) is a significant limitation to making a more definitive
characterization. The characterization of the chronic risks to adult and larval bees presented here is a novel approach using the best available data. However, this approach is not meant to preclude potential requests for additional terre strial invertebrate data or represent a new framework for EPA assessments for estimating potential risks to beneficial terrestrial

1 h ttps://www.whitehouse.gov/the

- press

- office/2014/06/20/presidential

- memorandum

- creating

- federal

- strategy

promote

- health

- h oney

- b17 invertebrates. EPA’s established methodology for evaluating risks to pollinators can be found in the Guidance for Assessing P esticide Risks to Bees (USEPA, 2014) and relies on a full suite of honey bee laboratory data including acute and chronic effects studies to adult and larval honey bees to fully estimate risk to bees.

Acute Contact and Dietary Exposure to Adult Honey Bees

On an acute contact exposure basis, dicamba is classified as ‘practically non

- toxic’ to non

- target insects including honey bees (honey bee acute contact LD 50 > 91 μg a.e./bee (MRID 00036935 )

. If an RQ were calculated for terrestrial invertebrates

, 2 us ing this non

- definitive LD 50 (conservatively assuming that the highest tested dose would res ult in 50% mortality where in that study, mortality at that dose was only 2.5% ) and determining acute contact exposure fr om a direct spray of dicamba as the maxi mu m single application rate (1.0 lbs a. e ./A) * 2.7 μg a. e ./bee (upper bound for contact exposures from a direct spray of 1 lb a

. e

. /A, based on work by Kock and Weisser, 1997) , the resultant RQ would be 0.03 (2.7/ 91) or 1 order of magnitude less th an the terrestrial invertebrate LOC (0.4). Given that the actual dose that would result in 50% mortality is likely considerably higher than 100 μg a.e./bee, this analysis can be considered highly conservative. Although this is for only a single applicati on of dicamba, it may be considered an appropriate estimate of exposure from a direct spray as there is a 7

- day minimum interval between applications and the lifespan of a bee as a forager is 4

- 5 days (Winston, 1987)

. Therefore, the risk to adult honey be es posed by contact with residues of dicamba in spray drift is
considered low.

Acute dietary data for non

- target insects has not been submitted to the Agency. However, a review of the EU Footprint Pesticide Properties Database reported an acute oral va lue for honey bees that indicates dicamba is also practically non

- toxic to non

- target insects on an oral exposure basis (honey bee acute oral LC 50 > 100 μg a.e./bee ). If an RQ were calculated for terrestrial
invertebrates

, 2 using this non

- definitive LC 5 0 (and again, conservatively assuming that the highest tested dose would result in 50% mortality) and determining acute dietary exposure of dicamba residues of 32.12 μg/bee/bee/day (1.0 lb a. e ./A * 110 μg a. e ./g {upper

- bound residue for tall grass from T

- REX } * 0.292 g/day {pollen consumption rate} , the resultant RQ would be 0.32 (32.12/ 100) or slightly below the proposed terrestrial invertebrate LOC (0.4). Given that the actual dose that would result in 50% mortality is likely considerably hig her than 100 μg a.e./bee, this analysis can be considered highly conservative.

Chronic Oral Exposures to Adult and Larval Honey Bees

Approach The Office of Pesticide Program’s overview of the FIFRA risk assessment process (USEPA 2004) states the followi ng:

In some instances, a core study may not be available for a particular data requirement listed in 40 CFR 158. In this case

, the risk assessment team may

2 The employed methodology for calculating an RQ for pollinators was first proposed in the 2012 Pollinator Risk Assessment Framework SAP White Paper, and subsequently validated by the panel. The White Paper is accessible online at regulations.gov, under docket EPA

- HQ

- OPP

- 2012

- 0543

.18 consider other sources of information to address the data gap .... P rofessional judgment is used by the risk assessment team to determine the utility of the available supplemental data for the proposed risk assessment. (page 36 USEPA 2004)

EFED has employed, for the last decade, an acute to chronic ratio approach (USEPA 1999, Mount et al. 2003) to addr ess data uncertainty for a variety of endpoints including survival, growth, development, and reproduction effects from prolonged exposure. The process uses mathematical relationships observed between acute and chronic exposure effects endpoints
conducted w ith one organism to draw inferences on the potential effects endpoints associated with longer duration exposures in another organism, where only acute exposure effects endpoints
have been measured. Consistent with this approach, an evaluation of the inver tebrate data
uncertainties for dicamba focus es on the acute and chronic toxicity data for other invertebrates to determine a relative relationship between the acute toxicity endpoints and the chronic endpoints. This relationship is then examined relative to the acute toxicity data available for the dicamba equivalence (a.e.) endpoints for bees to estimate a chronic endpoint for terrestrial invertebrates. The estimated chronic/developmental endpoint is compared to available exposure information to
determin e if a presumption of risk is or is not supported by these lines of evidence.

Aquatic invertebrates were selected for this approach 1) because they represent a relatively closer taxonomy to terrestrial invertebrates than would be achieved for tested verte brate species and 2) because of a lack of a specific taxonomically

- based mechanism of action for invertebrate responses to dicamba DGA salt . Moreover, the chronic data avai lable for aquatic invertebrates includes measures of effects on survival, reproduct ion, growth, and development milestones over protracted exposure windows, which are conservatively applicable to the growth, development and survival measurement endpoints expected from acute and chronic bee larval and adult bee
chronic studies.

Analysis
The available data from the soybean risk assessment for honeybees and for freshwater
invertebrates are summarized below:

Acute Daphnia magna E C 50 > 100 mg a.e./L MRID 40094602

Chronic Daphnia m agna NOAEC = 42 mg a.e./L 3 MRID 48718007

Acute Honey bee con tact LD 50 > 91 μg a.e./bee MRID 00036935

Acute Honey bee oral LD 50 > 100 μg a.e./bee EU Footprint Database 4

Although the acute daphnid data are non

- definitive, a comparison of the acute and chronic endpoints, in the case of D. magna , indicates generall y low acute and chronic toxicity to aquatic invertebrates with a relationship between the acute median lethal toxicity threshold (EC 50 ) and the chronic no observed adverse effect concentration (NOAEC) of > 2.38 (>100/42 = >2.38).

3 Test material was dicamba BAPMA salt

4 EU Pesticide Properties Database (PPDB), http://sitem.herts.ac.uk/aeru/ppdb/en/Reports/213.htm19 Applying the minimum that this factor could be to the available honey bee median lethal endpoint would yield e stimate s of chronic endpoint s of 38 μg a.e./bee for contact exposure and

42 μg a.e./bee for oral exposure . Although these estimates may lack conservatism since the ratio of acute to chronic toxicity in the daphnid data se t may be greater than 2.38, the estimated endpoint s may still be conservative si nce the acute value s for bees were also not definitive ( i.e.

, the highest do s e tested was below lethal levels so an ac tual LD 50 /LC 50 were not demonstrated)

, so the actual acute median lethal value is likely to be greater and yield higher (less sensitive)

estimates of chronic effect threshold.

Following EPA’s framework for assessing pesticide risks to bees (USEPA, 201 4), t he acute contact estimated exposure level from dicamba DGA is 2.7 μ g a.e./bee for the max imum 1 lb

a. e ./A application rate . This exposure level is over an order of magnitude lower than the

estimated contac t

- based bee chronic NOAEC of 38 μ g a.e./bee. The acute dietary estimated exposure level for adult honeybees is 32.12 μg/bee/day for the maximum 1 lb a. e ./A application

rate , which is also lower than the ACR

- estimated oral exposure chronic bee endpoint of 42 μg a.e./bee . In both case s , the estimated exposure level is below the estimated chronic toxicity endpoint for survival, developmental, and reproducti ve effects for honeybees under prolonged

exposures , even without conside ring that the acute endpoints in honeybees are very conservative

estimates.

Adult honeybee effects following chronic exposure effects are adequately addressed by th is approach as well because the endpoint for such a test is survival under prolonged expos ure and the underlying chronic exposure endpoints used in the approach were conducted at levels producing no adult invertebrate mortality. Also it is reasonable to expect that effects measures under longer term studies are a conservative surrogate for sho rt duration exposure effects (e.g.,
an acute larva study measuring survival).

Because honeybee risk assessment results serve as a surrogate for assessing risks to other
terrestrial invertebrates , the finding s above indicate no concern for risks to th e ta xon overall

. However, t here are uncertainties inherent in the evaluation:

1. D. magna chronic studies incorporate long exposure periods and measure survival, growth and development of a juvenile crustacean life stage, which are also evaluated endpoints in acute and chro nic for larval honeybee studies , but the mechanism of action may not be exactly a match for non

- crustacean arthropods such as larval insects. However, given that very similar aquatic effects extrapolations are made across a variety of aqua tic invertebrate taxa, including insects, the uncertainty herein is no greater than the acceptable level of uncertainty in the aquatic invertebrate extrapolations routinely employed for aquatic effects characterizations.

2. Routes of exposure between aquat ic organism toxicity tests and honeybee tests are not the same. Exposure media in aquatic invertebrate testing is via water, but for chronic exposure studies feeding occurs so some oral exposure via diet is p robable

. Larval honeybee testing involves both dietary and dermal exposure under the laboratory testing conditions, and adult chronic honeybee studies involve dietary20 exposure. However, for a chemical such as dicamba DGA salt , once dissociated in test solution to the free acid, the exposure differenc es are likely not biologically significant as the uptake for the hydrophilic acid is likely diffusion across the membrane with other water soluble compounds and therefore absorption for either the gut or gill would be similar , though metabolic pathways may be different following uptake through the gill compared with the gut

.

The refined investigation in this document considered other lines of evidence and focused on:

1. A long standing EFED approach to consider the relationship between acute and chronic endp oints in the complete dataset for one organism to draw inferences on the same endpoints for another organism when data are lacking (i.e.

, inferring survival, growth and development effects levels for terrestrial invertebrate developmental life stages and s urvival in organisms following prolonged exposure); and

2. Comparison of resulting extrapolated invertebrate development, growth and reproduction endpoints under chronic exposure conditions to estimated levels of

exposure.

Considering all lines of evidence , it is reasonable to conclude that risks are likely to be low to larval and adult honey bees under the conditions described in the soybean risk assessment
scenarios of use as the empirical data demonstrate low acute and chronic toxicity to other similar

t axa ( i.e. aquatic invertebrates ) , low acute toxicity to adult honey bees and based on the ACR analysis presented here, chronic toxicity to adult and larval honey bees is also anticipated to be
low

. Additionally, dicamba will be reassessed in registration review [ beginning in summer, 2016 ]

. EPA intends to use Registration Review to facilitate submittal of additional pollinator data and is also revising the existing insect pollinator data requirements in CFR Part 158 (revision anticipated in 2017) to requi re additional data necessary to complete risk assessments
consistent with the risk assessment framework. C onsistent with current use of bee endpoints as a surrogate for other terrestrial invertebrates, there is sufficient information to preclude concern for direct terrestrial invertebrate risks and any attendant indirect effects mediated through these organism s.

No data is available for the acute or chronic toxicity of dicamba’s degradate DCSA to honey

bees or other pollinators (the EU footprint database does however report a 14

- D LC 50 of > 1000 mg/kg for earthworms) . However, given the low DCSA residues meas ured in dicamba

- tolerant seeds (max measured residue of 0.440 ppm), exposures to honey bees and other pollinators from DCSA residues in pollen and n ectar of dicamba

- tolerant soybean are anticipated to be low.

As noted above for terrestrial vertebrate sp ecies, based on the available plant metabolism data for

DCSA on non

- DT plants, EFED assumed that any exposure for terrestrial in vertebrates occurs as a result of feeding solely on DCSA in DT

- soybean plant tissues and no exposure to DCSA is expected for ter restrial in vertebrates feeding off the field, even if dicamba residues should occur following spray drift or volatilization

.21 

### 8. Runoff

The Agency considers spray drift exposure to be the principal risk issue associated with the proposed label use of dic amba DGA salt, owing to a variety of lines of evidence, including past experience with other dicamba formulations and associated spray drift incident reporting. However, in the following paragraphs the Agency provides an explicit consideration of the

runo ff risks and effects of proposed mitigation to limit off

- site runoff in listed species effects
determination.

An important component of the model used for terrestrial risk assessment (TerrPlant) is the assumption that the mass of pesticide running of f the treated field is directly related to the pesticide’s solubility in water. In the case of dicamba DGA salt , the dissociated salt yields highly
soluble dicamba acid. The TerrPlant model assumes that the high solubility of the acid results in

a runoff mass of 5 percent of the field

- applied mass. The model also includes an assumption that
the non

- target plant receptors in the runoff zone are exposed to a single pulse of the total mass. The TerrPlant model does not account for any pesticide degradation o r partitioning, nor does it account for the temporal aspects of runoff associated with meteorological events (i.e., runoff follows precipitation events that exceed field capacity of the soil). According to the original ecological risk assessment (USEPA, 2011a) , dicamba is not environmentally persistent. Therefore, TerrPlant is likely providing a highly conservative estimate of runoff loading at any given time because the processes of degradation and partitioning combined with the stochastic

natur e of runoff are impo rtant limiting factors for dicamba

.

A refined characterization of potential pesticide runoff is routinely considered in aquatic system exposure modeling through the use of the Surface Water Concentration Calculator (SWCC).
EFED has tu rned to this model to ascertain the extent to which explicit consideration of degradation, partitioning, and stochastic runoff events would lead to a more mechanistically appropriate runoff exposure estimate than is possible using TerrPlant. Using the SWCC Missouri cotton scenario run for the cotton risk assessment (D404823) and assuming one application of
dicamba DGA at 1 pound per acre, followed by two half

- pound applications at seven

- day
intervals , EFED has determined that the total yearly mass of dicamb a in runoff from a 10 hectare (24.7 acre) treated field is ~0.0 55 % of the applied mass (see Appendix 3 for calculations). Using these assumptions in TerrPlant ( total 2 lb ae/A application and a 0.0 55 % runoff fraction), and the most sensitive endpoint of 0. 000261 for the NOAEC for soybeans, the maximum RQ is less than the LOC of 1.0 by a factor of at least 2 (RQs range from <0.1 to 0.48, see Appendix 3 ).

Combining the predictions of SWCC modeling and the expectation that much of the off

- site plant communi ty will not experience foliar contact with dicamba DGA in runoff sheet flow

, EFED conclude s that all available lines of evidence support a “no effects” determination for runoff exposure for off

- field listed plants for the proposed labeled use of dicamba DG A

.



### 9. Herbicide Interactions (Synergism)

Mixtures of herbicides, such as those applied in tank mixtures, may cause synergistic, antagonistic, or additive effect in non

- target plants, compared to the effects of the individual herbicides. The patent and lite rature studies cited below indicate that combinations of dicamba22 and glyphosate may cause effects that range from synergistic to antagonistic, depending on the plants tested and the doses used.

In the case of dicamba and glyphosate, a patent application ( Satchivi and Wright 2011) filed by DowAgrosciences LLC claimed synergistic effects in Chenopodium album (common lambsquarters) and Commelina benghalensis (dayflower), but no synergism in Conyza
canadensis (Horseweed/marestail).

Flint and Barrett (1989a) studied the combined effects of dicamba and glyphosate on field bindweed ( Convolvulus arvensis ) and found synergistic inhibitory effects on the root system. Flint and Barrett (1989b) also studied interactions between dicamba and glyphosate in Johnsongrass ( Sorghum halepense ). They found antagonistic effects of dicamba on shoot and root fresh weights, compared to lower rates of glyphosate alone.

Kelley et al. (2005) studied the interactions of dicamba with four herbicides, including glyphosate, in non

- GMO soybeans. Dicamba was not found to be synergistic with glyphosate considering plant injury and yield loss as endpoints.

Olszyk et al. (2015) tested the interaction of dicamba and glyphosate (at three different rates) in eight plant species, including big bluestem ( Andropogon gerardii ), Milkweed ( Ascelepiassyriaca spp.), purple node joe pye weed ( Eutrochium purpureum ), soybean ( Glycine max ), evening primrose ( Oenothera biennis ), slender knodding smartweed ( Polygonum lapathifolium ), Canada goldenrod ( Solida go canadensis ), and purple top tridens ( Tridens flavus ). Generally, antagonistic effects were found in plant growth endpoints and the study authors concluded that no combination of dicamba with differing glyphosate rates produced a synergistic response fo r any species.

The current draft label for dicamba use on tolerant soybean and cotton plants specifies that tank mixes may only be used for products that have been tested and found not to have unreasonable adverse effects on the spray drift propertie s of M1691 Herbicide. EFED believes that guideline laboratory studies of effects to terrestrial plants should be required for any product or tank mixture combining dicamba and other active ingredients to assess risks associated with any tank
mixture for use on dicamba

- tolerant soybeans or cotton. Testing of such products should include the standard suite of tested species from the already submitted dicamba and tank mixed active ingredien t vegetative vigor studies as well as those that the open literature and patent data indicate potential for synergistic effects

.

References :

Egan, JF and DA Mortensen, 2012. Quantifying vapor drift of dicamba herbicides appli ed to soybean. Environ. Toxicol. Chem. 31(5) 1023

- 1031, 2012.

Flint, JL and Barrett, M. , 1989a. Effects of Glyphosate Combinations with 2,4

- D or Dicamba on field Bindweed ( Convolvulus arvensis ). Weed Science, 1989, 37: 12

- 18.

Flint, JL and Barrett, M. 1898b. Antagonism of Glyphosate Toxicity to Johnsongrass ( Sorghum23 halepense ) by 2,4

- D and Dicamba. Weed Science, 1989, 37: 700

– 705.

Kelley, KB, LM Wax, AG Hager and DE Riechers, 2005. Soybean response to plant growth regulator herbicides is affec ted by other postemergence herbicides. Weed Science, 2005, 53: 101

- 112.

Koch, H. and p. Weisser. 1997. Exposure of honey bees during pesticide application under field conditions. Apidologie, 28:439

— 447.

Olszyk, D, T, Pfleeger, EH Lee and M Plocher, 2 015. Glyphosate and dicamba herbicide tank mixture effects on native plant and non

- genetically engineered soybean seedlings. Ecotoxicolgy, 2015, 24:1014

- 1027.

Satchivi, N and Wright, T, 2011. Synergistic herbicidal composition containing a dicamba
der ivative and a glyphosate derivative. World Intellectual Property Organization publication no. WO 2011/140020 A2., 10 November 2011.

Slade, D. 2015 (Missouri Department of Agriculture, Jefferson City, MO) . Letter to: Grant Rowland (Environmental Protecti on Agency, Washington D.C.), 2015 Dec 15.

USEPA, 2011. Ecological Risk Assessment for Dicamba and its Degradate, 3,6

- dichlorosalicylic acid (DCSA), for the Proposed New Use on Dicamba

- Tolerant Soybean (MON 87708).
Environmental Fate and Effects Division. Office of Pesticide Programs. Office of Chemical Safety and Pollution Prevention, Washington, D.C. DP 378444. March 8, 2011.

USEPA, 2011b. Evaluation Guidelines for Ecological Toxicity Data in the Open Literature.
Environmental Fate and Effects Divis ion. Office of Pesticide Programs. Office of Chemical Safety and Pollution Prevention, Washington D.C. May 16, 2011.

USEPA, 2012. Data Evaluation Record for MRID 47899517. Health Effects Division. Office of Pesticide Programs, Washington D.C. December 7, 2012.

USEPA, 2014. Guidance for Assessing Pesticide Risks to Bees. Environmental Fate and Effects
Division. Office of Pesticide Programs. Washington, D.C. June 23, 2014.

USEPA, 2016. 3, 6

- Diclorosalicyclic acid (DCSA): Benchmark Dose Analys is of a Reproduction Study . Health Effects Division. Office of Pesticide Programs, Washington D.C. March, 2 , 2016. D431873

.

Winston, M.L. 1987. The Biology of the Honey Bee. Harvard University Press, Cambridge,
MA. ISBN 0

- 674

- 07409

- 2.24 

### Appendix 1 : T

- R EX Inputs and Ou t puts for Dicamba Use on Dicamba

Tolerant Soybeans

Application No. Rate Day of Application

Chemical Name: Application Rate (lb ai/acre 1 1 0 The value in G6 must be zero

Seed Treatment? (Check if yes) FALSE Seeding Rate (lbs/acre) 2 0.5 7

Use: 166.7 3 0.5 14

Product name and form: 4

% A.I. (leading zero must be entered for formulations <1% a.i.): 5

Application Rate (lb ai/acre) 1 6

Half-life (days): 8.4 7

Application Interval (days): 8

Number of Applications: 9

Are you assessing applications with

variable rates or intervals? yes 10

You MUST specify application day 11

12

What body weight range is assessed (grams)? Birds Mammals 13

Small 20 15 14

Medium 100 35 15

Large 1000 1000 16

17 18
19

20

21

22

23

24

25

26

27
28

29
30

Note: Sources of wildlife diet are assumed to be available for less than one year for this model.

Endpoints

Avian

Endpoint Toxicity value Indicate test species

below Optional Test Organism Body weight (g) Optional Test Species Name Toxicity Value Reference (MRID)

LD50 (mg/kg-bw) 188.00 1

LC50 (mg/kg-diet) 10000.00 1

NOAEL (mg/kg-bw) 1

NOAEC (mg/kg-diet) 695.00 2

1.15 Mammalian 1

Acute Study Chronic Study

350 350

Endpoint Toxicity value Reference (MRID)
LD50 (mg/kg-bw) 2740.00

LC50 (mg/kg-diet) Reported Chronic Endpoint 136.00 1

Is dietary concentration (mg/kg-diet) reported from

the available chronic mammal study? (yes or no) no

yes no

Enter dietary concentration (mg/kg-diet)

Estimated Chronic Diet Concentration Equivalent to Reported Chronic Daily Dose 2720 mg/kg-diet based on

standard FDA lab rat

conversion 100.00%

Enter the Mineau et al. Scaling Factor Assessed Species Inputs (optional, use defaults for RQs for national level assessments)

Size (g) of mammal used in toxicity study Default rat body weight is 350 grams You MUST specify application day in Columns F and G - you may enter up to 30 applications Chemical Identity and Application Information

Dicamba

8

Reset Model25 Summary of Risk Quotient Calculations Based on Upper Bound Kenaga EECs

Table X. Upper Bound Kenaga, Acute Avian Dose

- Based Risk Quotients

Size
Class (grams) Adjusted
L D50 EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

20 135.44 299.47 2.21 137.26 1.01 168.45 1.24 18.72 0.14 117.29 0.87 4.16 0.03

100 172.42 170.77 0.99 78.27 0. 45 96.06 0.56 10.67 0.06 66.88 0.39 2.37 0.01

1000 243.55 76.46 0.31 35.04 0.14 43.01 0.18 4.78 0.02 29.94 0.12 1.06 0.00

Table X. Upper Bound Kenaga, Subacute Avian Dietary Based Risk Quotients

LC50 EECs and RQs

Short Grass Tall Grass Broadleaf
Plants Fruits/Pods/Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

10000 262.94 0.03 120.52 0.01 147.91 0.01 16.43 0.00 102.99 0.01

Size class not used for dietary risk quotients

Table X. Upper Bound Kenaga, Chronic Avian Dietary Based Risk Quotients26 NOAEC (ppm) EECs and RQs

Short Grass Tall Grass Broadleaf
Plants Fruits/Pods/Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

695 262.94 0.38 120.52 0.17 147.91 0.21 16.43 0.02 102.99 0.15

Size class not used for dietary risk quotients

Table X. Upper Bound Kenaga, Acute Mammalian Dose

- Based Risk Quotients

Size
Class (grams) Adjusted
LD50 EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds Arthropod s Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

15 6022.06 250.70 0.04 114.90 0.02 141.02 0.02 15.67 0.00 98.1893 0.0163 3.4819 0.0006

35 4872.49 173.26 0.04 79.41 0.02 97.46 0.02 10.83 0.00 67.8619 0.0139 2.4065 0.0005

1000 2107.50 40.17 0.02 18.41 0.01 22.60 0.01 2.51 0.00 15.734 0.0075 0.5579 0.0003

Table X. Upper Bound Kenaga, Acute Mammalian Dietary Based Risk Quotients

LC50 (ppm) EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

0 262.94 #DIV/0! 120.52 #DIV/0! 147.91 #DIV/0! 16.43 ##### 102.99 #DIV/0!

Size class not used for dietary risk quotients27 Table X. Upper Bound Kenaga, Chronic M ammalian Dietary Based Risk Quotients

NOAEC (ppm) EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds/Large
Insects Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

2720 262.94 0.10 120.52 0.04 147.91 0.05 16.43 0.01 102.9 9 0.04 Size class not used for dietary risk quotients

Table X. Upper Bound Kenaga, Chronic Mammalian Dose

- Based Risk Quotients

Size
Class (grams) Adjusted
NOAEL EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods /Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

15 298.90 250.70 0.84 114.90 0.38 141.02 0.47 15.67 0.05 98.19 0.33 3.48 0.01

35 241.85 173.26 0.72 79.41 0.33 97.46 0.40 10.83 0.04 67.86 0.28 2.41 0.01

1000 104.61 40.17 0.38 18. 41 0.18 22.60 0.22 2.51 0.02 15.73 0.15 0.56 0.0128 

### Appendix 2. Dicamba Crop Field Trial Residue Data Which Include the
Determination of the DCSA Metabolite.

Table 1 . Summary of Residues from Conventional Asparagus Crop Field Trials with DCSA as a D icamba
Residue of Concern

. 1

Formulation 2 Total Application Rate (lb ae/A) PHI (days) N 3 Residue of
Concern Combined Residues (ppm)

Min. Max. LAFT 5 HAFT 5 Median 5 Mean 5 SD 5

4 lb ae/gal
DGA SL

, 4 lb ae/gal
DGA SL , and
2 lb ae/gal Na
SL Single post

em ergence broadcast application of

0.5 lb ae/A 1 24 Parent 0.266 3.274 0.304 3.144 0.604 0.967 0.852

DCSA 4 <0.01 0.071 <0.01 <0.040 0.011 0.014 0.0069

Total 0.271 3.192 0.314 3.166 0.622 0.981 0.854

1 Asparagus data are taken directly from MRID Nos. 43245206 and 43425803 (D204488, D204809, and D209229, L. Cheng, 07/14/1997) used for tolerance re

- assessment in the 2005 RED

. 2 Test applications included the dimethylamine (DMA), diglycolamine (DGA), and sodium (Na + ) salt formulations.

3 number of sa mples

. 4 DCSA is the 3,6

- dichloro

- 2

- hydroxybenzoic acid metabolite.

5 Values based on per

- trial averages. LAFT = lowest average field trial, HAFT = highest average field trial, SD = standard deviation. For computation of the LAFT, HAFT, median, mean, and standard deviation, values < LOQ are assumed to be at the LOQ (0.01 ppm).

Table 2 . Summary of Residues from Conventional Soybean Crop Field Trials (Seed) with DCSA as a
Dicamba Residue of Concern

. 1, 2

Formulation 3 Total Application Rate (lb ae/A) PHI (days) N 4 Residue of
Concern Combined Residues (ppm)

Min. Max. LAFT 6 HAFT 6 Median 6 Mean 6 SD 6

4 lb ae/gal

D M A SL Single 0.5 lb ae

pre

- plant

treatment followed by a

single post

emergence application of

2.0 lb ae/A 7 24 Parent 0.027 8.10 0.038 7.40 0 .72 1.022 1.703

DCSA 5 <0.01 0.130 <0.01 <0.048 .014 0.02 0.015

5

- OH
dicamba <0.01 0.360 <0.01 0.26 0.01 0.043 0.071

Total 0.047 8.14 0.084 7.44 0.768 1.085 1.713

1 Soybean grain data are for the 1X rate which used a 0.5 lb ae/A treatment made at 14

- days pre

- planting followed by a 2.0 lb
ae/A treatment made at 7

- days prior to harvest taken directly from MRID Nos. 43814101 (D223283, S. Knizner, 07/29/1996) and 44089307 (D228703, S. Chun, 07/16/1998) used for tolerance reassessment in the 200 5 RED.

2 T he registrant was not supporting tolerances for soybean forage and hay at this time in lieu of a feeding restriction placed o n the label. However, data were included for these commodities in the study submissions acquired using a single 0.5 lb a e/A treatment
made at 14

- days pre

- planting (0.25x the maximum rate). Total residues of dicamba (parent, DCSA, and 5

- OH dicamba) were
<0.03

- <0.097 ppm in soybean forage and <0.03

- <0.04 ppm in soybean hay.

3 Test applications included the dimethylamin e (DMA ) salt formulation.

4 number of samples

. 5 DCSA is the 3,6

- dichloro

- 5

- hydroxybenzoic acid metabolite.

6 Values based on per

- trial averages. LAFT = lowest average field trial, HAFT = highest average field trial, SD = standard deviation. For computat ion of the LAFT, HAFT, median, mean, and standard deviation, values < LOQ are assumed to be at the LOQ (0.01 ppm).29 Table 3

. Summary of Residues from Dicamba

- Tolerant Cotton Crop Field Trials with DCSA as a Dicamba
Residue of Concern

. Commodit y Analyte Total App.

Rate
lb ae/A (kg ae/ha) PHI (days) Residue Levels (ppm) 1

n Sample
Min. Sample
Max. LAFT 2 HAFT 2 Median Mean Std. Dev.

TRT 2 (Applications at Preemergence, 6

- leaf stage, and first white flower + 15 days; EP: Clarity)

Undelinted
Co tton seed Dicamba 2.0 (2.2) 49

- 105 13 < 0.02 < 0.02 < 0.02 < 0.02 0.02 0.02 N/A

5

- OH Dicamba 13 < 0.02 < 0.02 < 0.02 < 0.02 0.02 0.02 N/A

DCSA 13 < 0.02 0.23 < 0.02 0.23 0.02 0.04 0.06

Combined Residues 13 < 0.06 < 0.28 < 0.06 < 0.28 0.06 0.09 0.06

Gin bypr oducts Dicamba 2.0 (2.2) 82

- 84 3 < 0.04 < 0.04 < 0.04 < 0.04 0.04 0.04 N/A

5

- OH Dicamba 3 < 0.04 < 0.04 < 0.04 < 0.04 0.04 0.04 N/A

DCSA 3 0.39 1.73 0.43 1.58 0.67 0.89 0.61

Combined Residues 3 < 0.47 < 1.82 < 0.53 < 1.66 0.75 0.97 0.61
TRT 3 (Application s at Preemergence, first open boll stage, and 7 days prior to harvest; EP: Clarity)

Undelinted
Cotton seed Dicamba 2.0 (2.2) 6

- 8 13 0.06 1.97 0.06 1.38 0.65 0.64 0.43

5

- OH Dicamba 13 < 0.02 0.02 < 0.02 < 0.02 0.02 0.02 N/A

DCSA 13 < 0.02 0.25 < 0.02 0. 16 0.03 0.05 0.05

Combined Residues 13 < 0.12 < 2.24 < 0.10 < 1.56 0.71 0.71 0.48
TRT 4 (Applications at 6

- leaf, first white flower + 15 days, first open boll, and 7 days prior to harvest; EP: Clarity)

Undelinted
Cotton seed Dicamba 2.0

- 2.1 (2.2

- 2.4) 6

- 8 13 0.09 1.54 0.12 1.42 0.47 0.61 0.41

5

- OH Dicamba 13 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 N/A

DCSA 13 0.02 0.27 0.02 0.27 0.06 0.08 0.07

Combined Residues 13 < 0.13 < 1.83 < 0.16 < 1.72 0.56 0.71 0.48
TRT 4 (Applications at 6

- leaf, first white fl ower + 15 days, first open boll, and 7 days prior to harvest; EP: Clarity)

Gin byproducts Dicamba 2.0 (2.2) 6

- 7 3 3.09 23.6 3.13 23.0 14.9 13.7 10.0

5

- OH Dicamba 3 < 0.04 0.04 < 0.04 < 0.04 0.04 0.04 N/A

DCSA 3 1.70 6.29 1.78 6.17 4.50 4.15 2.22

Co mbined Residues 3 < 4.83 29.9 < 5.06 < 29.6 19.7 18.1 12.2
TRT 5 (Applications at 6

- leaf, first white flower + 15 days, first open boll, and 7 days prior to harvest; EP: MON 11968)

Undelinted
Cotton seed Dicamba 2.0 (2.2) 7

- 8 4 0.17 0.72 0.20 0.62 0.41 0. 41 0.23

5

- OH Dicamba 4 < 0.02 < 0.02 < 0.02 < 0.02 0.02 0.02 N/A

DCSA 4 0.02 0.17 0.02 0.12 0.04 0.06 0.04

Combined Residues 4 < 0.21 < 0.91 < 0.24 < 0.76 0.47 0.49 0.27

1 Except for sample min/max, values reflect per trial averages; n = no. of field trials. For calculation of median, mean, and standard deviation, the LOQ (0.02 ppm each analyte in undelinted cotton seed and 0.04 ppm for each analyte in cotton gin byproducts) was used for any results reported as <LOQ in Table C.3. Combined residues o f dicamba, 5

- OH dicamba, DCGA, and DCSA are expressed in parent equivalents. Individual analyte results are reported as per se. N/A = Not applicable.

2 LAFT = lowest

- average

- field

- trial; HAFT = highest

- average

- field

- trial.30 Table 4

. Summary of Residu es from Dicamba

- Tolerant Soybean Crop Field Trials with DCSA as a
Dicamba Residue of Concern

. Commodity Total Applic.
Rate
lb a.e./A (kg a.e./ha) PHI (days) Residue Levels a, b (ppm)

N Min. Max. HAFT Median (STMdR) Mean (STMR) Std. Dev.

DCGA c
Fora ge 1.96

- 2.04 (2.19

- 2.28) 7

- 10 44 0.356 5.90 5.27 1.93 2.02 1.02

Hay 13

- 15 44 0.167 7.26 7.19 2.00 2.66 1.91

Seed 73

- 98 44 <0.011 0.135 0.131 0.017 0.032 0.029

DCSA

Forage 1.96

- 2.04 (2.19

- 2.28) 7

- 10 44 8.92 51.3 50.4 15.0 17.0 8.00

Hay 13

- 15 44 12.2 61.1 60.7 31.9 32.2 11.2

Seed 73

- 98 44 0.010 0.440 0.439 0.033 0.059 0.089

Dicamba

Forage 1.96

- 2.04 (2.19

- 2.28) 7

- 10 44 <LOQ 2.62 2.47 0.068 0.374 0.603

Hay 13

- 15 44 <LOQ 1.16 1.01 0.051 0.130 0.216

Seed 73

- 98 44 <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ

5

- O H Dicamba

Forage 1.96

- 2.04 (2.19

- 2.28) 7

- 10 44 <LOQ 0.009 0.009 0.005 0.006 <LOQ

Hay 13

- 15 44 <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ

Seed 73

- 98 44 <LOQ <LOQ <LOQ <LOQ <LOQ <LOQ

a Concentrations of the individual analytes are reported as dicamba equivalents

b Va lues < LOQ are assumed to be at the LOQ.

C DCGA residues were quantitated by a non

- validated method31 

### Appendix 3 : Runoff Calculations from SWCC and Resulting RQ values in
TerrPlant

Summary of Water Modeling of dicamba and the USEPA Standard Pond

Estim ated Environmental Concentrations for dicamba are presented in Table 1 for the USEPA standard pond with the MScottonSTD field scenario. A graphical presentation of the year

- to

- year peaks is presented in Figure 1 . These values were generated with the Surfac e Water Concentration Calculator (SWCC Version 1.106). Critical input values for the model are
summarized in Tables 2 and 3

.

This model estimates that about 22% of dicamba applied to the field eventually reaches the water body. The main mechanism of trans port from the field to the water body is by runoff (76.7% of the total transport), followed by spray drift (23.1%) and erosion (0.18%). In the water body, pesticide dissipates with an effective water column half

- life of 106.0 days. (This value does not inc lude dissipation by transport to the benthic region; it includes only processes that result in removal of pesticide from the complete system.) The main source of dissipation in the water column is metabolism (effective average half

- life = 107.2 days) follo wed by photolysis (9502 days) and volatilization (141341.2 days). In the benthic region, pesticide dissipates very slowly (622.2 days). The main source of dissipation in the benthic region is metabolism (effective average half

- life = 622.2 days). The pest icide is about evenly distributed in the benthic region between the pore water and sorbed to sediment.

Table 1. Estimated Environmental Concentrations (ppb) for dicamba.

Peak (1

- in

- 10 yr) 42.2

4

- day Avg (1

- in

- 10 yr) 41.7

21

- day Avg (1

- in

- 10 yr) 40.1

60

- day Avg (1

- in

- 10 yr) 35.6

365

- day Avg (1

- in

- 10 yr) 13.8

Entire Simulation Mean 8.49

Table 2. Summary of Model Inputs for dicamba.

Scenario MScottonSTD

Cropped Area Fraction 1

Koc (ml/g) 13.4

Water Half

- Life (days) @ 25 °C 72.9

Benthic Half

- Life (d ays) @ 25 °C 423

Photolysis Half

- Life (days) @ 40 10532 °Lat

Hydrolysis Half

- Life (days) 0

Soil Half

- Life (days) @ 25 °C 18

Foliar Half

- Life (days) 35

Molecular Wt 221

Vapor Pressure (torr) 3.41E

- 5

Solubility (mg/l) 6100

Table 3. Application Schedul e for dicamba.

Date (Mon/Day) Type Amount (kg/ha) Eff. Drift

04/16 Ground 1.12 0.99 0.05

04/23 Ground 0.56 0.99 0.05

04/30 Ground 0.56 0.99 0.05

Figure 1. Yearly Peak Concentrations33 Table 4. Alternative dicamba runoff analysis based on MS cot ton SWCC run at 2 lb/A (maximum annual application rate for dicamba based on a 1 lb a. e ./A application and two
0.5 lb a. e ./A applications.

Sources Contribution
factor Total mass (kg) based on 30 years Total mass applied over 30 year period Percentage of
di camba over 30 year period Average
annual loss (%)

Runoff 0.7669 11.14
672 1.66 0.055
Erosion 0.0018 0.02634 0.0039 0.00013
total 0.7687 11.17 1.7 0.056

Comparison of the most sensitive terrestrial and aquatic endpoints for use in the runoff
calcula tions.

Comparing most sensitive IC 25 /NOAEC for non

- vascular aquatic plants and terrestrial plants. Most sensitive species are the blue green algae (IC 50 /NOAEC of 0.061/0.005 mg ae/L) and soybean IC 25 /NOAEC of 0.000513/0.000261 lbs ae/A.

To compare, ass ume exposure is equivalent to a 1

- acre field covered with 1 inch of water. Therefore the EEC in lb/A that compares to an IC 50 of 0.061 mg ae/L for blue

- green algae can be considered following E quation 1 below:

Equation 1.
EEC lb a. e ./Acre = ( Z mg/L ) * ( 102,790 L water/ Acre

- in) * (1 inch) * (1 lb/ 453,592 mg)

w hich reduces to:

Equation 2.
EEC lb a.e ./Acre = ( Z mg/L ) * (0.226613) EEC lb ai/A = 0.061 mg/L * 0.226613 = 0.0138 and the EEC in lb/a that compares to a NOAEC of 0.005 mg ae/L for blue

- green algae would be EEC lb ae/A = 0.005 mg/L * 0.226613 = 0.0011. These endpoints are approximately 1

- 2 orders of magnitude less sensitive than the soybean endpoints. Therefore, the soybean endpoints should
be used in the revised TerrPlant runoff claculation s.

Table 5. RQ values calculated in TerrPlant for plants in dry and semi

- aquatic areas exposed to Dicamba DGA salt t hrough runoff. Conservative assumptions of 2 lb a.e/A application rate and 0.06% loss through runoff and erosion.

Plant Type Listed Sta tus Dry Semi

- Aquatic

Monocot non

- listed <0.1 <0.1

Monocot listed <0.1 <0.1

Dicot non

- listed 0.17 0.26

Dicot listed 0.32 0.48