UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

APR 2 9 2015 

MEMORANDUM 

OFFICE OF PREVENTION, PESTICIDES ANO 

TOXIC SUBSTANCES 

SUBJECT: BEAD Estimates for Applicator Exposure to Ethoprop (PC Code: 04 I l 0 l) From 

Applications Made to Potatoes in the Pacific Northwest. 

FROM: C

Bi

l

olog

ayton 

ical 

Myers, 

Analysis 

Ph.D.

Br

, 

anc

Bio

h 

logist 

~ 

( ~ 

Biological and Economic Analysis Division (7503P) 

THRU: Arnet Jones, Chief 

Biological Analysis Bran 1 

Biological and Economic Analysis Division (7503P) 

TO: Eric Miederhoff, CRM 

Risk Management and Implementation Branch III 

Pesticide Re-evaluation Division (7508P) 

Matthew Lloyd, CIH 

Risk Assessment Branch VII 

Health Effects Division (7509P) 

Product Review Panel: April, 22, 20 I 5 
Summary 

As part of a human hea lth risk assessment for registration review of ethoprop, OPP's Health 

Effects Division (HED) is evaluating potential cancer risks from occupationa l exposure to 

ethoprop. This memo provides estimates for the average/typical exposure of pesticide 

applicators to ethoprop for usage on potatoes in the Pacific Northwest, which HED has identified 

as the driver scenario for the chemical's cancer risk assessment. 

Using USDA-NASS data for average potato farm sizes in the Pacific Northwest, and using 

information on the typical field sizes for potatoes in the same region, BEAD estimates that a 

typical private applicator would apply ethoprop to potatoes about 5 days per year. BEAD's 

estimate is not upper-bound, because HED requires only an estimate of the typical/average 

exposure. However, some inherent conservatism is built into BEAD's estimate, so that any bias 

or error from uncertainty is in the direction of being more protective. Whil e BEAD does not 

have direct access to informat ion on commercial applications of ethoprop, based on input from 

industry experts and using the same assumptions on field sizes and number of fields treated per 

day, BEAD qualitatively estimates that 5-8 application days per year could be a reasonable 

estimate for commercial applicators of ethoprop on potatoes in the Pacific Northwest. 

Background 

Ethoprop is an organophosphate nematicide/insectic ide that is labeled for use on multiple 

agricultural crops in the United States, via soil-incorporated application. Ethoprop is used on 

potatoes for control of nematodes and problematic soil insect pests such as wirewom1s (EPA, 

Proprietary Data, 20 15; USDA-IPMC, 2000). It is labeled for one application per year on 

potatoes, and this application can either be made at-planting, or post-harvest, and is sometimes 

co-applied with a fumigant such as Vapam (WSPC, 20 15). 

As part of an occupational risk assessment for Registration Review of ethoprop, HED is 

evaluating potential cancer risks from exposure to cthoprop. Usage on potatoes in the Pacific 

Northwest has been identified as a driver scenario for the occupationa l cancer risk assessment 

because of the high application rates used to control nematodes, whi ch BEAD has previously 

verified (informally). OPP's cancer risk assessments model the expected occupational chronic 

exposure over a 30 year working period. HED has therefore indicated that they do not require 

upper-bound usage/exposure estimates, but rather need an average or ' typical' estimate for the 

number of days per year an applicator might apply ethoprop to potatoes. In the absence of 

information to inform appl icator exposure estimates, HED reverts to an assumption of 10 

application days per year for private applicators and 30 application days per year for commercial 

applicators. 

This memo provides BEAD's estimates for the average/typical exposure of private pesticide 

applicators to ethoprop from usage on potatoes in the Pacific Northwest. While BEAD has no 

direct source of information for commercial applicators of ethoprop, a surrogate qualitative 

estimate for commercial application is also briefly discussed, based on information provided to 

BEAD, HED, and PRD from industry and commodity experts (WSPC, 2015). 

2 
Method for Estimating Application Days per Y car 

To arrive at an ' average ' estimate for typical private applicator exposure days per year, BEAD 

estimates the average number of ethoprop appli cations per year (assuming one appli cation per 

day) as the number of potato fields per farm, further assuming all fields are treated every season. 

These two listed assumptions intentionally introduce a significant bias toward higher estimates of 

exposure. First, the assumption that every potato field is treated every year is an upper-bound 

usage assumption, since ethoprop can only be applied once per year to potatoes. Secondly, the 

assumption that a fanner would only apply ethoprop to one field per day is protective, because it 

is conceivable that more applications could be possible in fewer application days (HED assesses 

application days not the number of application). Therefore, by intentiona l design, BEAD's 

estimates are biased in a protective direction. With further regard to the upper-bound usage 

assumption, EPA's propri etary usage information indicates that a very small percentage of 

potatoes in Washington, Oregon, and Idaho are actuall y treated with ethoprop on an annual basis, 

with the average annual percent crop treated less than 5% for 2009-2012 (EPA Proprietary Data), 

in stark contrast to BEA D's assumption of l 00% treatment for potatoes. 

BEAD evaluated data on average fam1 sizes and average field sizes to calculate an estimate of 

the average number of fields present per farm, for commercial potato fa rms in the Pacific 

Northwest. Because almost all large potato farms in the Pacific Northwest are grown under 

center-pivot sprinkler irrigation (USDA-IPM Centers, 2000), BEAD further assumed that the 

reported typical ' pivot' size (125 acres) is a reasonable surrogate for typica l field size for 

commercial potatoes grown in the Pacific Northwest. This estimate of typical pivot size for 

production the Pacific Northwest has been provided to BEAD on numerous occasions via 

informational tours, informal communications with production and extension experts, and 

miscellaneous industry and extension literature. This estimate was also recently confirmed via 

communications with the Washington State Potato Commission (WSPC, 2015). Dividing the 

average potato farm size by this average field size of 125 acres then gives a reasonable 

approximation of the average number of fields per farm for Pacific Northwest potatoes. 

Using 2007 and 2012 data (USDA-NASS, 20 14), BEAD first calculated a " raw" average farm 

size for potato farms in Washington, Oregon, and Idaho by dividing the total reported potato 

acreage by the reported total number of potato farms for each state. Next, BEAD used the 

distribution of the number of farms by size for these same four states to select the farm size 

category that would include the median value for farm size. Because the mean value can be 

significantly affected by the presence of many very small farms or a few very large farms, a 

median farm size estimate is useful for comparison and context, because the median provides the 

farm size value at the middle of the farm size distribution. A median farm size estimate could 

reasonably be interpreted to be representative 'typical ' of farm sizes, so long as the distribution 

of fa rm sizes is reasonably close to normal. However, since farm sizes are only provided by 

discrete categories by NASS, BEAD cannot identify the true median value, and can only select 

the acreage range cohort/category where the median value would be located. 

For further protective bias (i.e., erring toward larger farm sizes, and thus more fields per farm 

and more application days) BEAD's presented distribution intentionally omits a large number of 

small potato fam1s less than 5 acres in size. Further, only processing potato acreage data is used 

3 
for calculation of the 2012 estimates, since an overview of available data showed that processing 

farms tended to be larger on the whole than farms producing potatoes for the fresh market 

(USDA-NASS, 2014). When comparing the average farm size with the respecti ve range 

category for median farm size, BEAD then selected the higher of these two values (and for a 

median range category, selected the upper limit acreage value from the respective acreage 

cohort/category) to further bias the estimate toward larger farm size. Finall y, the highest 

estimate for number of fields per farm (i.e., application days per year) from all the states was 

selected by BEAD as the typical value for all the Pacific Northwest states. Taken in total, these 

factors a ll serve to bias BEAD's estimates toward being more protective than would be the case 

if only the raw average values were reported. 

Estimates from the 2007 and 2012 Censuses of Agriculture 

For numerous vegetable crops, both the 2007 and 2012 Censuses of Agriculture (USDA-NASS, 

2014) provide estimates for the number of farms and the total production acreage by state. 

Additionally for potatoes, NASS provides a frequency distribution by state for fann size. The 

2012 Census also provides a breakdown of farm numbers and total acreage between fresh market 

and processing production, in addition to total production by state. This allows BEAD to 

provide estimates for typica l farm sizes that, while not upper-bound, are intentionally biased 

toward larger fa rm sizes as described above, for the purpose of providing a more protective 

estimate. 

Table 1 shows the farm size distribution data used to estimate the median potato farm size 

categories for the 3 leading potato production states in the Pacific Northwest: Idaho, Oregon, and 

Washington (USDA-NASS, 20 14). 

Table 2 shows the results for the calculation of the average number of potato fields per farm. 

4 
Table 1: Number of Farm by Farm Size Category and Average Acreage, Median Acreage, 

for Potatoes Grown in Idaho, Oregon, Washington, and North Dakota in 2007 (all 

potatoes) and 2012 (processing potatoes only). Values in BOLD Used for Calculation of 

Average Number of Fields per Farm.* 

2007 (All potatoes) 2012 (Processing potatoes only) 

# Farms by Acreage ID OR WA TD OR WA 

Category (Acres) 

5.0-14.9 7 7 11 3 I 2 

15.0-24.9 12 14 8 6 0 0 

25.0-49.9 43 19 16 24 15 6 

50.0-99.9 78 17 17 25 13 13 

100.0-249.9 167 29 78 86 14 45 

250.0-499.9 135 20 42 71 11 43 

500.0-749.9 78 4 26 42 5 24 

750.0-999.9 36 5 13 26 5 1 1 

>1000.0 92 8 40 54 8 28 

Total Acreage ( 1000 Acres) 351 36 157 146 27 124 

# Farms 703 345 618 344 99 238 

Avg. Farm Size (Acres) 499 104 254 424 272 521 

Median Farm Size 

Category Upper Limit 500 250 250 500 250 500 

(Acres) 

*Source: USDA-NASS, 2014. 

Table 2: Results for Average Number of Fields per Farm for Potatoes Grown in Idaho, 

0 regon, an d w as h" mg t on. 

2007 (All potatoes) 2012 (Processing potatoes only) 

ID OR WA ID OR 

Typical Farm Size 500 250 254 500 272 

Avg. Field Size (Acres) 125 125 125 125 125 

Avg. # Fields per Fam1 4.0 2.0 2.0 4.0 2.2 

Estimates for Commercial Applicators 

BEAD does not have direct access to information on commercial applications of ethoprop, other 

than limited available proprietary information on ' who applied' ethoprop on a total pounds or 

total acreage basis by state (i.e., there is not breakdown by individual applicators, only an 

indication on whether surveyed usage was done by a private applicator or a commercial 

applicator). Among Pacific Northwest states, data indicated that most applications made in 

Idaho and Oregon between 2009 and 2013 were made by private applicators. For Washington, 

more ethoprop applications were made by commercial applicators (EPA, Proprietary Data). 

5 

WA 

52 1 

125 

4.2 
While it provides some basic context, this measure conveys no information on the actual number 

of fields treated by individual applicators. 

However, information provided via phone conference to BEAD, BED, and PRD and via later 

follow-up correspondence with PRD (WSPC, 2015) indicated that most ethoprop applications 

(especially at-planting) are done by private applicators. A representative from a prominent 

commercial contract application company in the Pacific Northwest further indicated that 

approximately 5 ethoprop applications per year on potatoes would be typical for workers at that 

company. Another industry representative from a competing contract application company 

estimated that their commercial applicators would treat on average around 1,000 acres of 

potatoes per year with ethoprop. Using BEAD's previously discussed estimate of 125 acres as 

an average potato field size for the Pacific Northwest, and retaining the assumption of treating 

one field per day, it follows that commercial applicators with the second company would treat 

about 8 fields per year. Therefore, a qualitative estimate of 5-8 application days per year may be 

a reasonable approximation for commercial applications of ethoprop. However, BEAD reiterates 

here that it cannot independently verify such estimates independently, as there is no additional 

information available on ethoprop usage by commercial applicators that is currently available to 

BEAD, beyond what had been obtained from industry experts as described previously (WSPC, 

2015). 

Conclusion 

Based upon analysis of available data for typical farm and field sizes for potatoes grown in the 

Pacific Northwest, BEAD estimates that private applicators in this region would apply ethoprop 

approximately 5 days per year, based on an intentionally biased, protective estimate of the 

number of fields per potato farm. This figure is derived from available data from Washington, 

which had the largest mean potato farm size (521 acres). Taking this estimate and dividing by 

the typical fie ld size of 125 acres yields an estimate of 4.2 potato fields per farm, which BEAD 

rounds up to 5. Assuming one field is treated per day, and assuming every potato field is treated 

every year (an upper-bound usage assumption), this translates to an estimate of 5 application 

days per year for private applicators of ethoprop on potatoes. BEAD does not have direct access 

to information on commercial applications of ethoprop. However, based on input from industry 

experts and using the same assumptions on field size and number of fields treated per day, 

BEAD estimates that 5-8 application days per year could be a reasonable surrogate, qualitative 

estimate for commercial applicator exposure to ethoprop on potatoes in the Pacific Northwest. 

6 
References 

EPA, 2015. Proprietary Usage Data, 2009-2013. 

USDA-IPMC, 2000. Crop Profile for Potatoes in Idaho. USDA IPM Centers Crop Profile 

Document. www.ipmcenters.org/cropprofi I es/docs/I Dpotatoes.pdf 

USDA-NASS, 2014. U.S. Department of Agriculture, 2012 and 2007 Census of Agriculture: 

United States Summary and State Data Volume l, Geographic Area Series, Part 51. May 2014, 

Table 38. 

http://www.aucensus.usda.gov/Publications/2012/Full Report/Volume 1, Chapter I US/ 

Washington State Potato Commission, 2015. Personal communication and discussion of issues 

and industry practices via phone conference with WSPC, BEAD, HED, and PRD. March l 0, 

2015. 

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