UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

Date: October 29, 2013 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

SUBJECT: Quizalofop-P-Ethyl: Review of Volatilization and Spray Drift Risk 

PC Codes: 128709,128711 

Decision No.: 482699 

Petition No.: NA 

Risk Assessment Type: NA 

TXRNo.: NA 

MRIDNo.: NA 

DP Barcode: D414696 

Registration No.: 352-341 

Regulatory Action: Registration Review 

Case No.: NA 

CAS No.: 100646-51-3 

40 CFR: 180.441 

FROM: Seyed 

Risk Assessment 

Tadayon, 

Branch 

ChemistV ~ 

Health Effects Division (7509P) 

Office of Pesticide Programs 

THROUGH: MichaelS. Metzger, Chief 

Risk Assessment Branch V 

Health Effects Division (7509P) 

Office of Pesticide Programs 

TO: Khue Nguyen, CRM 

Pesticide Re-evaluation Division (7508P) 

Office of Pesticide Programs 
I. ACTION REQUESTED 

The Pesticide Re-evaluation Division has requested a human health risk assessment for the 

potential exposures from volatilization and spray drift for various uses of quizalofop - p- ethyl. 

The most recent human health risk assessment for quizalofop-p-ethyl was completed on 12111112 

as part of the registration review process (Quizalojop-P-Ethyl, Summary of Human Health Risk 

Assessmentfor Registration Review, 0394192) and did not include an assessment of volatilization 

and spray drift. For details on hazard, toxicology, and risk estimates for dietary and occupational 

exposures see 0394192. 

II. CONCLUSION 

Spray drift and volatilization of quizalofop - p- ethyl from applications to crop and non-croplands 

do not result in exposure risks of concern. 

III. DETAILED CON SID ERA TIONS 

Quizalofop-p-ethyl is a selective herbicide used for the control of annual and perennial grasses in 

crop- and non-croplands. Presently, quizalofop-p-ethyl is registered for uses on canola, crambe, 

cotton, dry beans, dry and succulent peas, lentils, mint, snap beans, soybean, sugar beets, barley, 

flax, sunflower and wheat. There are no residential uses. 

Spray Drift 

Off-target movement of pesticides can occur via many types of pathways and it is governed by a 

variety of factors. Sprays that are released and do not deposit in the application area end up offtarget and can lead to exposures to those it may directly contact. They can also deposit on 

surfaces where contact with residues can eventually lead to indirect exposures (e.g., children 

playing on lawns where residues have deposited next to treated fields). The potential risk 

estimates from these residues can be calculated using drift modeling coupled with methods 

employed for residential risk assessments for turf products. 

The approach to be used for quantitatively incorporating spray drift into risk assessment include 

assessing exposures for children ( 1 to 2 years old) and adults who have contact with turf where 

residues are assumed to have deposited via spray drift thus resulting in an indirect exposure 

scenario. Aside from the predicted residues available for transfer, the routes of exposure and 

assessment methodology is analogous to how exposures to turf products are considered in risk 

assessment. 

In order to evaluate the drift potential and associated risks, an approach based on drift modeling 

coupled with techniques used to evaluate residential turfuses of pesticides was utilized. 

Essentially, a residential turf assessment based on exposure to deposited residues has been 

completed to address drift from the agricultural applications of quizalofop - p- ethyl. In the spray 

drift scenario, the deposited residue value was determined based on the amount of spray drift that 

may occur at varying distances from the edge of the treated field using the AgDrift (v2.1.1 ) 

model. Once the deposited residue values were determined, the remainder of the spray drift 
assessment was based on the algorithms and input values specified in the recently revised (20 12) 

Standard Operating Procedures for Residential Risk Assessment (SOPs). 

A screening approach was developed for situations where specific label guidance for application 

parameters is not available.

1

•

2 AgDrift is appropriate for use only when applications are made by 

aircraft, airblast sprayers, and groundboom sprayers. When AgDrift was developed, a series of 

screening values (i.e., the Tier 1 option) were incorporated into the model and represent each 

equipment type and use under varied conditions. The screening options specifically 

recommended in this methodology were selected because they are plausible and represent a 

reasonable upper bound level of drift for common application methods in agriculture. In all 

cases, each scenario is to be evaluated unless it is not plausible based on the anticipated use 

pattern (e.g., herbicides are not typically applied to tree canopies) or specific label prohibitions 

(e.g., aerial applications are not allowed). 

Risk Estimates from Lawn Deposition Adjacent to Applications 

The spray drift risk estimates are based on an estimated deposited residue concentration as a 

result of the screening level agricultural application scenarios. Quizalofop -p- ethyl is used on 

field crops and can be applied via aerial and groundboom equipments. Exposures were 

considered for 50 feet wide lawns where the nearest side of the property was directly adjoining 

the treated field (at field edge) and at varied distances up to 300 feet downwind of a treated field. 

Results are presented in Table 1 and indicate that there are no risks of concern from aerial or 

groundboom applications at the field edge. 

In addition to the screening level spray drift scenarios described above, additional results are 

provided which represent viable drift reduction technologies (DRTs) that represent potential risk 

management options. In particular, different spray qualities have been considered as well as the 

impact of other application conditions. 

A dermal toxicity endpoint was not selected for quizalofop -p- ethyl. Incidental oral risk 

estimates, using a chronic oral endpoint (0.9 mg/kg/day) were used for this assessment. The 

applicable Level of Concern is 100 so MOEs < 100 would be of concern. Children's (1 <2 year 

old) incidental oral risk estimates are above 100 from indirect exposure to quizalofop - p- ethyl 

related to spray drift and therefore no buffer zone for aerial or ground boom applications is 

required. 

2

http://www.epa.gov/ttnlscram/dispersion prefrec.htm 1 http://www.epa.gov/pesticides/science/residential-exposure-sop.html 
Volatilization 

Based on a WOE approach considering all the available hazard and exposure information for 

quizalofop, the HASPOC determined that a 28-day inhalation toxicity study in the rat is not 

required at this time. This approach considered all the available hazard and e"fosure information 

for quizalofop, including: (1) the low vapor pressure of quizalofop (8.3 x 10-1 mm Hg); (2) the 

low acute inhalation toxicity of quizalofop (Toxicity Category IV); and (3) the use of an oral 

POD established for the most sensitive endpoint/target organ system resulting in screening-level 

MOEs ranging from 2,900 to 211,000. 

HED also believes that there is the potential for bystander inhalation exposure to occur as a result 

of volatilization of quizalofop-p-ethyl. Volatilization can occur during the application process or 

thereafter. It can result from aerosols evaporating during application, while deposited sprays are 

still drying, or after as dried deposited residues volatilize. Quantitative risk assessments for 

quizalofop-p-ethyl inhalation exposures have not been previously conducted because no 

toxicological endpoints were identified. However, a Volatilization Screening Tool to estimate 

bystander's risk was used for quizalofop-p-ethyl assuming that inhalation toxicity is equal to oral 

toxicity. The screening tool utilized a number of physical and chemical properties to predict flux 

(e.g., the rate at which a chemical volatilizes off of a treated field); the AERSCREEN model to 

estimate air concentrations at different distances from a treated field; and chemical-specific 

human health toxicological data to estimate potential bystander inhalation risks. Using the 

screening tool, HED confirms that inhalation risks to bystanders from quizalofop-p-ethyl 

volatilization are not expected. 
1lc 1: Children Incidental Oral/Htl\1 Risk Summary (MOE) 

rp/Rate Group Spray Type/ Nozzle App Rate t:stimated At 10 feet 25 Feet 50 Feet 75 Feet 100 Feet 125 Feet ISO 200 Feet 250 Feet 300 Feet 

Configuration (lb ai/A) or Edoe Feet 

Adjusted 

TTR, 

(uwcm2) 

L - > ·- .. .. Flax (The hig~est appli~!ion. rate. f?~.!~~ o~ cr.ops) _ - _ . .... - - . I 

Aerial Fine to Medium 0.167 0.018 1,400 1,700 2,100 2,700 3,600 4,700 5,600 6,600 8,600 10,000 13,000 

Medium 10 Coarse 1,700 2,300 3.100 4,300 6,100 8,000 10,000 12,000 17,000 22,000 27,000 

Coarse to Very Coarse 1,900 2,900 4,300 6,700 9,600 13,000 16,000 20,000 27,000 35,000 44,000 

Very Fine 10 Fine 950 1,000 1,200 1,400 1,600 1,800 2,000 2,300 2.800 3,300 3,700 

AT401, M, 10 mph, 37% SO 1,500 1,900 2,500 3,400 4,500 5,900 7,200 8,400 11 ,000 14,000 17,000 

WASP, M, 10 mph, 37% SO 1,600 2,100 2,700 4. 100 5,600 7,200 8,800 10,000 14,000 17,000 20,000 

AT401 , C. 10 mph, 25% SD 1,800 2,500 3,600 5,300 7,500 9,800 12,000 15,000 21,000 27000 32,000 

WASP, C, I 0 mph, 25% SO 2,100 2,900 4,200 6,700 9,300 13,000 15,000 20,000 27,000 35,000 39,000 

AT401, VC, 10 mph, 20% SO 2,000 3,100 4,900 8,000 11 ,000 15,000 20,000 25,000 35,000 44 000 59,000 

WASP, VC, 10 mph 20% SO 2,600 4,000 6.200 9.800 14,000 19,000 25,000 29,000 44,000 51,000 59,000 

Groundboom Higjr Boom Verv line to Fine 1,900 3,800 6,300 10,000 14,000 18,000 21 ,000 25,000 32,000 44,000 51,000 

Low Boom Very fine to Fine 4,200 11,000 18,000 27 000 35,000 44,000 51,000 59,000 71 000 88.000 120,000 

High Boom Fine to 7,200 19,000 27,000 39,000 51,000 59,000 71,000 71 ,000 88,000 120,000 120,000 

Med iurn!Coarsc 

Low Boom Fine 10 11,000 29,000 44,000 59,000 71 ,000 88,000 120,000 120,000 180,000 180,000 180,000 

Medium/Coarse 

I Pineapple ., ·- ··-·, I 

Aerial Fine to Medium 0.21 0.023 1,100 1,300 1,700 2,200 2,900 3,700 4,500 5,200 6,900 8,300 10,000 

Medium to Coarse 1,300 1,800 2,400 3,400 4 900 6,400 8,000 9,700 13,000 18 000 22,000 

Coarse to Very Coarse 1,500 2,300 3.400 5,300 7,600 10,000 13,000 16,000 22 000 28,000 35,000 

Very Fine to Fine 750 830 920 1,100 1,200 1,400 1,600 1,800 2,200 2,600 3,000 

AT401 , M, l0mph,37%SO 1,200 1,500 2,000 2,700 3,600 4,700 5,700 6,700 8,800 11,000 13,000 I 

WASP, M, 10 mph, 37% SD 1,300 1,600 2,200 3,300 4,500 5,700 7,000 8,300 11 ,000 13,000 16,000 

AT401, C, 10 mph, 25% SO 1,400 2,000 2,800 4 200 6.000 7,800 9,700 12,000 17 000 22,000 26,000 

WASP, C, 10 mph, 25%SO 1,600 2,300 3,400 5,300 7,400 10,000 12,000 16,000 22,000 28,000 31,000 

AT401, VC, 10mph, 20%SO 1,600 2,400 3,900 6,400 9,100 12,000 16,000 20,000 28,000 35,000 47,000 

WASP, VC, 10 mph, 20% SO 2,000 3,200 4,900 7,800 11 ,000 15,000 20,000 23,000 35 000 40,000 47,000 

Groundboom HiJ! lr Boom VeT)• fine to Firre 1,500 3,000 5,000 8,000 11,000 14,000 17,000 20,000 26,000 35 000 40,000 

Low Boom Very fine to Fine 3,300 8,800 14,000 22,000 28 000 35,000 40,000 47,000 56 000 70 000 94,000 

High Boom Fine to 5,700 15,000 22,000 31 ,000 40,000 47,000 56,000 56,000 70,000 94,000 94,000 

Medium/Coarse 

Low Boom Fine to 8,500 23,000 35,000 47,000 56,000 70,000 94,000 94,000 140,000 140,000 140,000 

Medium/Coarse 

Vineyard 35,000 69,000 130,000 230 000 350,000 470,000 -·-- 560,000 700,000 940,000 I ,400,000 1,400,000 

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