UNITED STATES ENVIRONMENTAL PROTECTION 

AGENCY 

WASHINGTON D.C., 20460 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

PC Code: 108501 

DP Barcodes: 416208, 

416209,416286 

DATE: September 4, 2014 

MEMORANDUM 

SUBJECT: Pendimethalin: Drinking Water Assessment, and Ecological Risk Assessment for 

New Use on hops and multiple crop group/subgroup conversions including Low 

Growing Berry Subgroup 13-07G, Onion Subgroups 3-07 A & B, Sunflower 

Subgroup 20B, Citrus Fruit Group 10-10, Pome Fruit Group 11-10, Stone Fruit 

Group 12-12, and Fruiting Vegetable Group 8-10. 

FROM: Ibrahim Abdel-Saheb, Ph.D., Environmental Scientist ~ -.....~~ -~- 2-A \~ Elizabeth Donovan, Biologist ~..:tktr- ~ j J Lj V'-1 

Environmental Risk Branch 6 

Environmental Fate and Effects Divison (7507P) 

THRU: Mark Corbin, Branch Chief A I. ~ r ~ Environmental Risk Branch 6 ~ V 

Environmental Fate and Effects Divison (7507P) 

TO: Kable B. Davis, Product Manager Team 25 

Emily Schmid, Risk Manager Reviewer 

Herbicide Branch 

Registration Division (7505P) 

Barbara Madden, Minor Use Team Leader 

Sidney Jackson, Risk Manager Reviewer 

Risk Integration, Minor Use, and Emergency Response Branch 

Registration Division (7505P) 
EFED was asked to perform a drinking water assessment (DP Barcode (416286)), and an 

ecological risk assessment for the herbicide pendimethalin "Prowl H20" (DP Barcodes 416208 

& 41 6209, EPA registration No. 241-418) for a new use on hops and multi ple crop 

group/subgroup conversions including Low Growing Berry Subgroup 13-07G, Onion Subgroups 

3-07 A & B, Sunflower Subgroup 20B, Citrus Fruit Group 10-10, Pome Fruit Group 11-1 0, 

Stone Fruit Group 12-12, and Fruiting Vegetable Group 8-10. None of the proposed uses are at a 

higher application rate than currently registered uses listed on label EPA Reg. No. 241-418. 

Thus; these subgroups are not assessed in this document. 

According to the pendimethalin new use petition, the maximum single application of Prowl 1-bO 

is either a single application of 1 lb ai/acre or 4 lbs ai/acre with sequential applications with an 

interval of 30 days or more. The label limits the maximum cumulative total application rate to 4 

lb ai/acre of Prowl H20 per year. 

On December 15, 2010 ((DP Barcode 378514), EFED completed Section 3 new use of 

pendimethalin on Edamame and Cool- and Warm-Season Forage Grass; with a maximum 

application rates 1.52 lbs a. i./acre to 4.00 lbs a.i./acre, respectively with an annual maximum 

application rate of 4 lb ai/acre. 

Since the application rate for the new proposed use on hops is similar to the previously assessed 

application rate of 4 lbs a.i./acre (2010 Risk assessment), the proposed new uses will yield 

estimated exposure concentrations (EEC) similar to those presented in the 2010 grass assessment 

as shown in Table 1 below. Thus; while the current assessment yields slightly higher exposure 

and hence risk quotients (RQ) EFED believes that the risk profile for the current new use is 

substantially similar to the risk profile in the earlier assessment 

Table 1. Estimated Environmental Concentrations (ppb) for pendimethalin use on hops. 

2010 2014 

Peak ( 1-in-1 0 yr) 11.9 12.7 

21-day Avg ( 1-in-1 0 yr) 4.13 3.34 

60-day Avg ( 1-in-1 0 yr) 2.81 2.5 I 

A summary of that assessment follows. 

Based on the available data, the 2010 risk assessment concluded that pendimethalin is classified 

as highly toxic to fish and aquatic invertebrates and slightly toxic to birds and mammals on an 

acute basis. On a chronic basis, pendimethalin results in reduced egg production in freshwater 

fish and reduced production of young in freshwater invertebrates. Chronic toxicity data are not 

available for estuarine/marine fish and invertebrates. In terrestrial animals, chronic effects of 
pendimethalin result in reduced avian body weight and decreased number of pups born and pup 

weight in mammals. Pendimethalin is classified as practically non-toxic to terrestrial insects. 

Based on the available terrestrial plant toxicity data, pendimethalin is toxic to plants, with 

monocots having greater sensitivity to exposure via seedlings, whereas dicots are more sensitive 

to exposure of foliar surfaces. 

The results of this screening-level risk assessment indicate that the proposed new uses of 

pendimethalin have the potential for direct acute effects to listed freshwater fish, 

estuarine/marine mollusks, and aquatic vascular and non-vascular plants (including risk to nonlisted aquatic non-vascular plants). Although pendimethalin partitions to the sediment, risks to 

benthic invertebrates are not expected because predicted sediment exposure concentrations based 

on the proposed new uses are significantly lower than sediment concentrations where no effects 

were observed to midge larvae. With respect to terrestrial animals, direct acute and chronic 

effects to listed and non-listed birds and mammals are possible including chronic effects to 

piscivorous mammals via ingestion of pendimethalin residues in aquatic biota. ln addition, risks 

to terrestrial plants are also predicted. 

In addition, for human health, the EFED Drinking Water memorandum for pendimethalin 

(0 334061 , 05/08/2007) use on bearing grapes, cabbage, asparagus, and artichoke yields the 

highest acute exposure concentration of77.7 ~-tg/1 and the highest chronic exposure concentration 

of 6.00 ~-t g/L. Estimated drinking water concentrations (EDWCs) for this proposed Section 3 new 

use are not expected to exceed the values for bearing grapes, cabbage, asparagus, and artichoke. 

Data gaps for this assessment include the following: 

No foliar dissipation studies were supplied by the registrant. Therefore, the default assumption 

foliar half-life of 35 days was used to calculate pendimethalin residue concentrations on 

terrestrial food items. Pendimethalin is a persistent compound in some environments. 

Laboratory field dissipation studies in soil under aerobic conditions demonstrate a half-life of 

approximately 72-172 days, and field dissipation studies in the Midwest similarly show halflives ranging from 84-147 days. lfthe foliar dissipation half-life is similar to or greater than the 

available soil half-life data, the default assumption of a 35-day half-life may underestimate 

exposure to terrestrial mammals and birds. 

No chronic estuarine/marine fish and non-mollusk invertebrate data are available for 

pendimethalin. 

All terrestrial plant testing was conducted with the active ingredient (TGAI - technical grade 

active ingredient) and did not include solvent controls. The use of TEP (typical end-use product) 

instead ofTGAI is recommended for all terrestrial non-target plant studies. Testing with only the 

TGAI may underestimate toxicity to plants because the TEP may include a solvent or adjuvant 

which results in additive or synergistic toxicity. 

In addition, since the previous risk assessment was published, the Agency has issued guidance for 

the conduct and data needed to conduct the risk assessment to assess pesticide risk to bees 

(US EPA eta!. , 2014 ). This guidance document indicates that if exposure of bees to a pesticide is 
expected, a Tier I screening-level risk assessment is conducted. The Tier I assessment is intended 

to be sufficiently conservative that chemicals that pass the screen are considered to represent a 

relatively low risk of adverse effects to bees. Tier I toxicity data that are generally needed to 

complete screening-level risk assessments include acute contact toxicity data to adult honey bees 

(honey bees serving as a surrogate for all bee species), acute and chronic oral toxicity to adult 

honey bees, and acute and chronic oral toxicity to juvenile (i.e. larval) honey bees. If risk 

concerns are identified in the screening-level assessment, it may be refined using data that further 

define exposure or through additional data including Tier II semi-field or full-field toxicity tests. 

The current new use on hops and various crop group conversions include ground and aerial 

applications to a wide range of crops where spray drift may land on blooming non-target plants 

and could result in residues in pollen and nectar (which could then be transported to the hive). 

Additionally, pendimethalin is highly persistent and is systemic and can move in both xylem and 

phloem. Although pendimethalin uptake is primarily through the foliage, root uptake is also 

possible. Therefore, pendimethalin residues may be present in pollen and nectar either through 

transport from leaf tissues affected by spray drift or from root uptake from plants grown where 

pendimethalin was previously applied. Residues can in tum be brought back to bee colonies 

where in-hive bees including young adult and developing brood (i.e. , eggs, larvae and pupae) may 

be exposed. Therefore, exposure at all bee life stages would be expected. 

Since exposure of bees to pendimethalin residues is expected, Tier I honey bee laboratory toxicity 

data are needed to conduct the screening-level risk assessment. Acute contact toxicity data is 

available that indicates picloram residues are practically non-toxic to honey bees on an acute 

contact basis. However, no data is available that evaluate pendimethalin's toxicity from the oral 

exposure route to adult and larval bees on an acute or chronic basis. 

Therefore, the Agency is requesting Tier I laboratory toxicity data for acute and chronic oral 

toxicity for both adult and larval honey bees in order to complete the risk assessment for bees, as 

is further detailed in the attached data rationale tables. Should the screening level risk 

assessment identify that there are risk concerns to bees, mitigation measures may need to be 

considered or the registrant may conduct Tier II effects studies (e.g. 850.3040 guideline studies) 

that reduce uncertainty by characterizing pendimethalin's effects at the whole-colony level. 

References 

USEPA, PMRA and CDPR, 2014. Guidance for Assessing Pesticide Risks to Bees. Office of 

Pesticide Programs, USEPA, Washington D.C. Health Canada Pest Management Regulatory 

Agency, Ottawa, ON, Canada. California Department of Pesticide Regulation, Sacramento, CA. 

June 23, 2014.