UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

MAR 2 6 2015 

OFFICE OF PREVENTION, PESTICIDES AND 

TOXIC SUBSTANCES 

MEMORANDUM 

SUBJECT: 

FROM: 

THRU: 

TO: 

Estimates of Crop Irrigation for Endothall Registration (DP# 426243) 

Derek Berwald, Economist 

Economic Analysis Branch 

Biological and Economic Analysis Division (7503P) · 

Timothy Kiely, Chief Q l~ Economic Analysis Branch \J ) lM. 

Biological and Economic Analysis Division ( 3P) 

Garland Waleko, Chemical Review Manager 

Risk Management and Implementation Branch 2 

Pesticide Re-evaluation Division (7508P) 

Product Review Panel: .March, 11,2015 

1 
Summary 

As part of a dietary risk assessment for Registration Review of endothall, OPP's Health Effects 

Division is evaluating potential risks from exposure to endothall from irrigation water. This 

memo provides estimates for the percentage of crops that may be exposed to endothall that EPA 

is reasonably certain will not be exceeded. For crops that may be exposed to endothall by 

irrigation water, the maximum percent that could be exposed is the share of production of that 

crop from irrigated land. This document provides estimates ofthe percent of various 

<.:•)mmouities that could be exposed to endothall via irrigation water. The commodities in this 

memo were chosen by the Health Effects Division. These estimates of the percentage of the 

commodities that may be exposed to endothall in irrigation water in this document are unlikely 

to be exceeded. In addition to the commodities in this memo, endothall can be applied directly 

to potatoes and cotton, but they are not discussed here. 

EPA used two methods to estimate percent crop irrigated, which were combined to make the 

final estimates shown in Table 1. The preferred method, used where data on irrigated production 

are available, is an estimate of the share of total production that is irrigated. Estimates from this 

method are provided for barley, com, dry edible beans, oats, peanuts, rice, sorghum, soybeans, 

sugarbeets, sugarcane, and wheat, shown in Table 2. Where data on irrigated production are not 

available, EPA estimated the percent crop irrigated by determining the percentage of United 

States production of a crop that is grown in 17 western states where endothall may be used, 

shown in Table 3. The 17 western states are Arizona, California, Colorado, Idaho, Kansas, 

Montana, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, Oregon, South Dakota, 

Texas, Utah, Washington, and Wyoming. These states are the states where large scale water 

projects predominate, and where other chemicals are used in canals for weed control. These 

types of irrigation projects are relatively rare in other patts of the country. 

Use of these estimates in the exposure assessment is conservative, because it is the equivalent of 

assuming l 00% of irrigated crops are irrigated with water from endothall-treated canals. 

In fact, even in areas with surface water delivery systems, all irrigation canals may not be treated 

with endothall, and even if they are, may only be treated periodically. Even in the heavily 

irrigated areas of the West, some crops, such as dryland grains, are not irrigated. Some irrigated 

production is irrigated directly from wells, rather than from water transported in surface canals. 

The final column of Table 1 shows BEAD's estimates of the maximum share of crops that may 

be treated with endothall, using the estimates from Table 2 based on irrigation data when 

available. or using the state production estimates from Table 3 when necessary. 

2 
Table 1. Estimated Percent Crop Treated with Endothall for 

Dietary Risk Assessment 

Estimated 

Share of Percent Crop 

Share of Production Treated for 

Irrigated in the Dietary Risk 

Production West 1 Assessment 

Apple n/a 78% 78% 

Fresh market n/a 84% 84% 

Processing n/a 49% 49% 

Juice n/a 22% 22% 

Canned n/a 55% 55% 

Barley for grain 40% 40% 

Corn for grain 21% 21% 

Dry Beans 35% 35% 

Grape n/a 97% 97% 

Fresh market n/a 99% 99% 

Processing n/a 96% 96% 

Green Peas n/a 42% 42% 

Oats for grain 8% 8% 

Peanut for nuts 34% 34% 

Rice 100% 100% 

Sorghum for grain 19% 19% 

Soybean for beans 12% 12% 

Strawberry n/a 92% 92% 

Fresh market n/a 90% 90% 

Processing n/a 100% 100% 

Sugarbeetforsugar 37% 37% 

Sugarcane for sugar 54% 54% 

Watermelon n/a 38% 38% 

Wheat for grain 13% 13% 

Source: USDA 2015a, 2015b, 2015c, 2014, EPA calculations. ! Arizona, California, Colorado, Idaho, Kansas, Montana, Nebraska, Nevada, 

New Mexico, North Dakota, Oklahoma, Oregon, South Dakota, Texas, Utah, 

Washington, and Wyoming. Estimates are only provided for certain crops. 

3 
Background 

Endothall is an herbicide registered for control of plants in water bodies. Normal methods for 

estimating the percent crop treated for a pesticide are inappropriate in this case, because the 

pesticide is not directly applied to the crop. Potential exposure occurs via irrigation water, 

except for potatoes and cotton, where the chemical can be applied directly to the crop. 

Most of the water that goes through a canal to irrigate crops will not be treated. Instead, 

endothall is periodically injected into irrigation water to keep weed populations down. Because 

the water in the canal is rapidly turned over, after several hours most if not all of the endothall 

will no longer be in the canal systems. Furthermore, much production can receive water that is 

not delivered from surface water canals. 

Method for Estimating Percent Commodity Treated 

For some crops, the estimates in this memo are based on yield and acreage data for irrigated and 

non-irTigated crops from the 2012 Census of Agriculture (USDA 2014). The estimates provided 

will be an upper bound on the percentage of crops that may have been irrigated with water from 

canals that were treated with endothall, because some of the irrigated crops are not grown in 

areas where endothall is used nor irrigated with surface water. 

Other crops that are important to the dietary risk assessment do not have data on irrigated and 

non-irrigated production available. For these crops, this memo provides estimates of the amount 

of the crop grown in 17 western states where endothall use is expected. These are states where 

substantial amounts of water are transported through open canai systems to be used for irrigation. 

It is these systems where weed control is important and endothall exposure is more likely. Other 

states do not have large scale irrigation projects that transport water through surface canals. 

Estimates from the 2012 Census of Agriculture 

For select crops, the 2012 Census of Agriculture (USDA 20 14) provides estimates of the acres 

and yield from farms with irrigation, farms without irrigation, and farms where some of the crop 

is irrigated. This information is used to estimate maximum share of production that could have 

been exposed to irrigation water. Using this information we provide estimates of the share of 

production irrigated for those crops where the data are available. These crops are barley, com, 

dry edible beans, oats, peanuts for nuts, rice, sorghum, soybeans, sugarbeets, sugarcane, and 

wheat. 

Table 2 shows the estimated percent of the commodity that has been irrigated for the food crops 

for which data are available. To estimate the production from the irrigated acres, the first step is 

to estimate the crop production from irrigated land. Using the data in Table 2, the irrigated yield 

is multiplied by the irrigated acreage, which is the acreage from farms where the entire crop is 

irrigated plus the irrigated acreage from partially irrigated farms. To get an estimate of the share 

of the crop irrigated, this is divided by an estimate oftotal production. To estimate total 

4 
production from the information in Table 2, the yield is multiplied by the acreage for each type 

of farm, and these are added together. Taking wheat as an example, estimated production from 

irrigated fam1land is (2,064,900 acres + 1,303,265 acres) x 81.8 bushels/acre= 275,515,897 

bushels, which is the numerator for our percentage calculation. Total estimated production is 

2,064,900 acres x 81.8 bushels/acre+ (1 ,303,265 acres + 3,549,686 acres) x 43.0 bushels per 

acre+ 42,122,375 acres x 42.9 bushels per acre= 2, 184,635,601 bushels. Dividing estimates for 

production from irrigated land by the estimate of total production yields an estimate of the share 

of production that has been irrigated, in this case 13%. The estimates for all the food crops with 

available data in the census are in the last column of Table 2. 

Note that the data available in the Census of Agriculture only provides overall yield for farms 

where only part of the crop is irrigated, although it does provide total production and irrigated 

and dryland acreage data. For this analysis, BEAD assumed the yield from the irrigated acreage 

on partially irrigated farms to be equal to the average yield per acre from irrigated farms. In 

addition the implied yields for the non-irrigated portion of partly irrigated farms are lower than 

non-irrigated farms. with the exception of peanuts and sugarbeets. This is further evidence that 

this method tends to provide conservative estimates. 

These estimates are based on only one year of data, but they are similar to estimates from 2012, 

based on 2007 data (EPA 20 12). However, it is unlikely that the amount of acreage irrigated will 

change a large amount from one year to the next, because irrigation equipment is an expensive 

capital investment. In some cases, weather conditions may cause water availability to change, 

which may cause growers to change irrigation decisions. 

ote that these are estimates of the amount of the crop irrigated, not the amount of the crop that 

may have endothall residues. Not all of the crop that is irrigated will be grown in areas where 

endothall is likely to be used, and even in the West, where endothall use for irrigation is 

expected, not all systems will necessarily be using endothall. Therefore, BEAD is reasonably 

certain the share of crops that are actually exposed to endothall will not exceed the estimates of 

irrigated acreage in Table 2. 

5 
-able 2. Share of Crop Production Irrigated - -· Entire crop irrigated Part of crop irrigated None of crop irrigated EPA 

Average Estimated 

Yield Acres Acres not Average Average Share of 

Per Yield Yield Per Production 

:rop Farms Acres Acre Farms irrigated irrigated Per Acre Farms Acres Acre Irrigated• 

larley for grain (bushels) 3,892 692,023 100.7 765 159,670 211,532 58.1 14,010 2,220,680 55.8 40% 

:orn for grain (bushels) 20,040 6,202,712 171.1 21,211 6,616,357 6,947,141 129.4 307,279 67,646,835 111.1 21% 

)ry edible beans, excluding Iimas (cwt) 2,758 429,218 22.8 226 44,288 50,983 18.5 3,912 1,118,308 17.8 34% 

)ats for grain (bushels) 905 51,076 87.1 356 8,056 15,311 66.2 33,777 1,004,255 59.4 8% 

>eanuts for nuts (polllnds) 1,239 304,922 4,362.0 1,262 216,751 265,710 4,347.7 4,060 834,248 3,875.1 34% 

\ice (cwt) 5,591 2,693,759 74.3 - - - - - - 100% 

;orghum for grain (bushels) 1,848 377,681 80.7 1,617 248,725 499,499 56.3 16,572 4,016,194 47.7 19% 

;oybeans for beans (bushels) 8,124 2,978,353 49.4 16,246 4,179,061 4,691, 518 41.0 278,593 64,255,848 37.6 12% 

;ugarbeets for sugar (tons) 1,436 394,588 32.8 50 7,209 24,771 28.2 2,427 822,913 26.2 37% 

;ugarcane for sugar (tons) 195 N/A 35.7 21 N/A N/A 35.1 450 401,816 34.7 54%b 

Nheat for grain, all (bushels) 8,520 2,064,900 81.8 6,766 1,303,265 3,549,686 43.0 132,346 42,122,375 42.9 13% 

;ource: USDA 2014 and EPA Calculations 

Assumes irrigated acres on farms where only part of the crop is irrigated obtain t he same yield as acres on farms where the entire crop is irrigated 

Some data on acreage for sugarcane were not released by USDA, as shown in the table. However, using the total production of sugarcane for sugar reported in USDA 2015X (30,500 

housand tons) and subtracting off the non-irrigated production in this table (401,816 acres x 34.7 thousand tons = 13,943 t housand tons) leaves yields total production from irrigated and 

>artially irrigated farms of 16,577 tons, or 54% of total production. 

6 
Crop Estimates for Other Dietary Crops of Concern 

Endothall residues on some crops for which irrigation data are not available are of particular 

concern to EPA based on residue trials and dietary habits. These crops are peas, watermelon, 

strawberries, apples, and grapes. For these crops BEAD provides estimates of the proportion of 

the crop that is grown in the 17 western states (Arizona, California, Colorado, Idaho, Kansas, 

Montana, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, Oregon, South Dakota, 

Texas, Utah, Washington, and Wyoming), which are the states that are potential users of 

endothall in irrigation water (Table 3). According to the Farm and Ranch Irrigation Survey 

(USDA 2004), almost 70% of the irrigated acreage in. the United States is in the 17 western 

states, and about 87% of the irrigation water applied to crops is in these western states, which 

correspond to the states served by Bureau of Reclamation water projects. In the West large scale 

water delivery systems are important to agriculture; these are the systems that may use endothall 

for irrigation. Agriculture in the East, where it is less arid, does not require large scale water 

transfe rs, although endothall may be used for drainage systems and water bodies. 

The share of the crop grown in the 17 western states can be used as a crude measure of the share 

of the crop that may come in contact with endothall. These estimates are the best that can be 

made with the available data, and they likely overestimate the crop that will encounter endothall 

treated water because not all production in the western states will be irrigated with water from 

canals that have been treated with endothall. Not all irrigation systems use endothall, some crop 

production is irrigated with wells that do not require weed control, and some crops such as wheat 

and oats may be farmed without irrigation, even in the arid West. As an example of the degree 

to which this method can overestimate potential exposure to endothall, recall that the data on 

irrigated production showed that an estimated 13% of wheat is irrigated. Using the share of 

production in the 17 western states indicates that up to 78% (not shown in Table 3) of wheat 

could have potentially been exposed to endothall. This is an example where a majority of 

production is in the West, but relatively little wheat is irrigated. 

Where available, estimates of the crop grown in the 17 western states are provided for different 

end-uses of the particular crop. This information can be useful for dietary risk estimates, which 

are based on consumption of specific food products. The estimates of the amount grown in the 

17 western states are provided in Table 3. 

Peas 

Only two western states are important producers of green peas for processing, whi ch can appear 

in baby foods. In 2012, about 128,000 tons were produced in Washington State, and about 

41 ,000 tons in Oregon. Production in these two states was about 42% of US production of about 

407.000 tons (USDA 20 15a). 

7 
Watermelon 

Four western states produce enough watermelon to show up in the USDA data, Arizona, 

California, Oklahoma, and Texas. California and Texas produced about 6,800,000 cwt. and 

5,400,000 cwt. in 2012, respectively. Arizona produced abaout 1,200,000 cwt., and Oklahoma 

only produced about 348,000 cwt. Together, the almost 13,700,000 cwt. ofwatermelon 

represented about 38% ofUS production of about 36,200,000 cwt. in 2012 (USDA 2015a). 

Strawberries 

California is the major strawberry producing state in the United States. In 2012, California 

produced about 27,600,000 cwt. of strawberries, and Oregon another 213,000 cwt., and 

Washington about 103,000 cwt. Together, the three states produce about 92% of the total US 

strawberries. About 90% of the fresh market strawberries come from the western states of 

California, Washi ngton and Oregon, and almost all the processing strawberries come from the 

same three states, accounting for almost all strawberries used for processing (USDA 20 15b ). 

Apple 

Available data on apple production covers the production for the western states of Arizona, 

California, Idaho, Oregon, Utah, and Washington, with Washington being by far the largest 

producer. Combined these states accounted for about 78% oftotal US apple production in 2012, 

with over 72% of the total coming from Washington alone (USDA 2015b). The west has a much 

larger share of fresh apple production (84%) than it does with apples used for processing; less 

than half of processing apples come from the western states. 

Grapes 

California was the largest producer of grapes in 2012, accounting for almost 9 1% of total 

.production. The 17 western states combined accounted for about 97% of total production. 

Looking at the end uses of these grapes, the picture is similar. About 99% of fresh grapes were 

from the western states in 2012, and about 96% of the processed grapes (USDA 20 15b ). 

8 
Table 3. Share of Production of Specific Crops in the 17 Western States, 2012 

Western States Western 

Crop US Production Production States Share 

Green Peas (Tons) 407,250 169,040 42% 

Watermelon (1,000 cwt.) 36,153 13,726 38% 

Strawberries (1,000 cwt.) 30,520 27,962 92% 

Fresh Market 24,552 21,995 90% 

Processing 5,968 5,967 100% 

Apple (Million Pounds) 8,927 6,961 78% 

Fresh Market 6,595 5,539 84% 

Processing 2,332 1,152 . 49% 

Juice 749 164 22% 

Canned 1,112 610 55% 

Grapes (Tons) 7,524,443 7,287,450 97% 

Fresh Market 962,983 957,150 99% 

Processing 6,561,460 6,330,300 96% 

Source: USDA 2015a, 2015b, 2015c, EPA Calculations 

The 17 Western states are Arizona, California, Colorado, Idaho, Kansas, 

Montana, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, Oregon, 

South Dakota, Texas, Utah, Washington, and Wyoming. 

9 
References 

EPA 2012. Berwald, Derek and Bill Phillips II. Updated Estimates of Percent Commodity 

Exposed to Endothall via Irrigation (DP# 369862, 369863). November 19, 2012. 

USDA 2004. US Department of Agriculture, National Agricultural Statistics Service, The 

Census of Agriculture, Farm and Ranch Irrigation Survey (2003) Volume 3, Special 

Studies Part 1. November 2004. Available here: 

http://www .agcensus. usda. gov /Publications/2002/FRIS!index.asp 

USDA 20 15a. US Department of Agriculture, National Agricultural Statistics Service, 

Vegetables 2014 Summary. January 2015. Available here: 

http://usda.mannlib.cornell.edu/usdalcurrentNegeSumrn!VegeSumm-01-29-2015.pdf 

USDA 2015b. US Department of Agriculture, National Agricultural Statistics Service, 

Noncitrus Fruits and Nuts 2014 Preliminary Summary. January 2015. Available here: 

http://usda.mannlib.cornell.edu/usdalcurrent/NoncFruiNu/NoncFruiNu-01-23-2015.pdf 

USDA 20 15c. US Department of Agriculture, National Agricultural Statistics Service, Crop 

Production 2014 Summary. January 2015. Available here: 

http:/ /usda.mannlib.cornell.edu/usda/current/CropProdSu/CropProdSu-0 1-12-

20 15 _revision. pdf 

USDA 2014. US Department of Agriculture, 2012 Census of Agriculture: United States 

Summary and State Data Volume: 1, Geographic Area Series, Part 51. May 2014, Table 

36. Available here: 

http://www.agcensus.usda.gov/Publications/2012/Full_Report/Volume_ l ,_Chapter_ l_U 

S/usvl.pdf 

10