2 

residential pet exposure and the second section addresses the request for an alternatives 

assessment. 

I. 2,4-D and Residential Pets 

During the public comment period on NRDC’s petition, Beyond Pesticides raised an 

issue unrelated to those raised in the NRDC petition. Specifically, Beyond Pesticides is 

concerned about the use of 2,4-D for lawn care and the possible association of cancer in pets due 

to this exposure. In support of its claim that there is a relationship between 2,4-D treated lawns 

and canine cancer, Beyond Pesticides cited several studies (Glickman et al. 2004, Hayes et al. 

1991, Hayes et al. 1995, Reynolds et al. 1994). 

EPA evaluated the studies cited by Beyond Pesticides and the studies do not change the 

Agency’s current conclusions. The two studies conducted by Hayes et al. in 1991 and 1995 

focused on an epidemiological evaluation (i.e., case control study) of the relationship between 

2,4-D use on lawns and the incidence of malignant lymphoma in companion dogs. This 

evaluation used a hospital-based recall questionnaire approach. There were several criticisms of 

this paper which were addressed in 1995 by Hayes et al., including issues associated with the 

exposure assessment process and the uncertainties associated with low odds ratios. 6 The authors 

acknowledged major weaknesses with the studies were a lack of environmental or personal 

sampling and possible recall bias. Further, significant uncertainty exists due to the lack of 

exposure data. In addition, the 2005 RED required that, in order for a product to be eligible for 

reregistration, label language needed to be added restricting pet access to treatment areas during 

and immediately after application. All labels now have this language, which changes the use 

patterns that existed during the time of the Hayes studies in the early 1990s because now pets 

should not be in the treatment area during or immediately after application. Further, the authors 

concurred with several commenters that the studies do not prove that 2,4-D exposure in a home 

environment is a cause of malignant lymphoma in companion dogs. Therefore, Hayes et al does 

not impact the Agency’s previous assessment. 

Reynolds et al. 1994 attempted to supplement Hayes et al. by attempting to refine the 

ability to predict exposures from lawn herbicides like 2,4-D by collecting exposure 

characteristics using an interview/questionnaire approach and by monitoring of 2,4-D in pet 

urine. They concluded that gathering data via owner questionnaires could be a good surrogate 

predictor of exposure. Among 44 dogs potentially exposed to 2,4-D-treated lawns an average of 

10.9 days after application, 2,4-D concentrations greater than or equal to 10.0 μg/l were found in 

33 dogs (75%) and concentrations of ≥50 μg/l were found in 17 (39%). Among 15 dogs with no 

known exposure to a 2,4-D-treated lawn in the previous 42 days, 4 (27%) had evidence of 2,4-D 

in urine, one at a concentration of ≥50 μg/l . The odds ratio for the association between exposure 

to a 2,4-D-treated lawn and the detection of ≥50 μg/l 2,4-D in urine was 8.8 (95% confidence 

interval, 1 .4-56.2). Dogs exposed to lawns treated within 7 days before urine collection were 

more than 50 times as likely to have 2,4-D at concentrations ≥50 μg/l than dogs with exposure to 

a lawn treated more than one week previously (odds ratio = 56.0; 95% confidence interval, 10.0-

312.2). The highest mean concentration of 2,4-D in urine (21 3 mg/l) was found in dogs sampled 

 

6

 U.S. EPA, 2,4-D: Evaluation of Data Identified In NRDC Petition and Associated Documents (March 27, 2012) at 

65-66 (hereinafter HED). 
3 

within two days after application of the herbicide. The authors indicated that these findings 

demonstrate that dogs living in and around residences with recent 2,4-D lawn treatment, absorb 

measurable amounts of the herbicide for several days after application and, thus, may constitute a 

useful animal model for evaluating the effects of herbicides on the induction of lymphoid cancer. 

EPA believes the use of interviews/questionnaires may have some utility as a surrogate means of 

predicting exposures in epidemiological research. However, with regard to the specific issue of 

establishing a model specific to 2,4-D exposure and cancer induction the results are incomplete 

and have considerable uncertainty, which is consistent with the findings of the investigators who 

concluded that additional research on this matter is needed.7

 

In summary, the studies cited by Beyond Pesticides, in its comments to support its 

assertion that 2,4-D has been shown to induce lymphoma in pets, did not address key 

uncertainties (lack of sampling, timing of the studies, and recall bias) in the study results. In 

particular, Beyond Pesticides failed to note the relatively weak association between exposure and 

lymphoma onset described by Hayes et al. Further, because these studies were conducted prior 

to the risk mitigation measure identified in the RED, and now reflected on all 2,4-D product 

labels (i.e., limiting pet access during and immediately following application), the resulting new 

use patterns should result in reduced exposure. As such, while the Agency concurs that perhaps 

additional research is warranted, it does not believe that there is evidence of critical animal 

health issues which warrant changes to its current conclusions. 

C. Alternatives Assessment for 2,4-D 

Beyond Pesticides and New York State’s Department of Environmental Conservation and 

Department of Health submitted comments stating that a comprehensive evaluation of 

alternatives to 2,4-D is needed. They assert that the evaluation should include a comparison of 

environmental fate characteristics, application rates and methods, efficacy, and risks 

(incorporating both toxicological properties and estimated exposures) to public health and nontarget organisms. These commenters felt that there are viable organic lawn management 

practices that eliminate the need for 2,4-D, as well as non-chemical alternatives to be considered. 

Generally, the Agency does not assess alternatives where it has not identified any risks of 

concern. Where a pesticide has no risks of concern, it is unnecessary to consider the risk profiles 

of alternative pesticides in determining whether the pesticide being assessed will cause 

unreasonable adverse effects on the environment. Further, EPA may not deny registration to a 

pesticide because it is non-essential. See 7 U.S.C. § 136a(c)(5). 

EPA evaluated the studies cited in the Petition and public comments and concluded that 

the studies do not alter the Agency’s current conclusion that 2,4-D does not present a risk of 

concern. Many of the studies and their deficiencies are specifically addressed in this response or 

in EPA’s separate Order addressing tolerances. EPA’s complete analysis of all the studies cited 

in the Petition and public comments can be found in the EPA’s 2,4-D: Evaluation of Data 

Identified In NRDC Petition and Associated Documents located in docket number EPA-HQOPP-200-0877. Because the studies cited by the Petition and in public comments do not alter the 

 

7

 Id. 
4 

Agency’s conclusions that 2,4-D does not present a risk of concern, the Agency does not believe 

it is appropriate or necessary to conduct an alternatives assessment at this time.