UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

JUN 15 2DG 

l\1EMORANDUM 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

SUBJECT: BEAD Chemical Profile for Registration Review: Diphacinone (067701) and 

Diphacinone, sodium salt (067705) 

FROM: Colwell Cook, Biologist C~ Biological Analysis Branch 

THRU: 

TO: 

Cynthia Doucoure, Environmental Protection Specialist 

Science Information and Analysis Branch 

Elizabeth Hill, Economist 

Economic Analysis Branch 

Biological and Economic Analysis Division (7 

Amet Jones, Chief 

Biological Analysis Branc 

-) 

Diann Sims, Chief (~~~ Science Information and Analysis Branch 

Russell Wasem, Chemical Review Manager 

Risk Management and Implementation Branch I 

Pesticide Re-evaluation Division (7508P) 

Product Review Panel date: May 27, 2015 

Page 1 of 5 

c.~ 
SUMMARY 

Diphacinone was registered in 1960 and diphacinone, sodium salt was registered in 1962 as 

vertebrate control agents. Diphacinone is an indandione and considered a first generation 

anticoagulant rodenticide. Based on available proprietary data, diphacinone is reportedly used 

by consumers and Pest Control Operators (PCOs) in very small quantities (55-200 lbs a.i.). 

INTRODUCTION 

The purpose of this document is to convey usage information and a broad overview of the pest 

management roles of pesticides that are beginning to undergo registration review. The 

anticipated audience consists of the team of EPA staff current! y evaluating the registration status 

of diphacinone and diphacinone, sodium salt, and eventually the general public. This document 

builds upon the data BEAD provides in the Label Use Information System (LUIS) reports. The 

document is based on information and data available to BEAD as of April 2015 

HISTORY OF BEAD ASSESSMENTS FOR DIPHACINONE 

BEAD conducted an analysis of rodenticide bait use in 2006 (Chiri, 2006) which examined nine 

rodenticide products, including diphacinone. Diphacinone is considered a first-generation 

anticoagulant for use against commensal rats and mice and other rodents. This analysis 

concluded that rodenticides are necessary for managing rodents, which are a significant public 

health risk and are capable of causing significant economic damage and that rodenticide active 

ingredients are typically interchangeable and can be considered alternatives to one another. 

To date, BEAD has not reviewed any Section 18 Emergency Exemption Requests for the use of 

diphacinone; this should not be interpreted as a lack of benefits associated with the chemical. 

There are eight special local need labels for diphacinone, indicating that is needed for rodent 

control. 

COMMON FORMULATIONS AND APPLICATION METHODS 

Diphacinone is formulated as pelletized and granular baits, as well as powder formulations. 

These are applied via aircraft, bait boxes, cloth bags, hand bulb dusters, hand probes, spoons, 

spreaders, and trap/bait staions. Diphacinone sodium salt is formulated as a liquid and applied 

only indoors via bait stations. 

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USE SITES 

Agricultural Use Sites: 

Diphacinone is registered to control rodents in orchards, cropland, rangeland, and forest. 

Diphacinone, sodium salt is not registered for use in crops. 

Non-Agricultural Use Sites: 

Diphacinone is registered for use in and around animal burrows and buildings (industrial, 

commercial, agricultural and public), as well as noncrop areas (sewers, dumps, irrigation ditches, 

along fences, gullies, etc.). Diphacinone, sodium salt is registered for use inside of industrial, 

commercial, agricultural and public buildings. 

DIPHACINONE USAGE 

BEAD reviewed available public and proprietary agricultural data sources and found small 

quantities (55-200 lbs a.i.) of diphacinone reported to be used by consumers and Pest Control 

Operators (PCOs) in 2009 and 2011 as shown in Table 1 below. 

T a bl e 1 D. h . tpl acmone N on-agncu tura IU 

Sector 

Consumer Markets 

Consumer Markets 

PCO 

Sources: Klme & Company, 2009 

Proprietary Data, 2011 

Year 

2009 

2011 

2011 

sage 

Lbs A.I. Applied % of Total Lbs AI 

of Rodenticides 

Applied 

201 1.3 

185 1.2 

55 5.2 

BEAD also reviewed California data to determine if use of first generation anticoagulant 

rodenticides is increasing. Based on California DPR data from 2009-2013, diphacinone use 

increased by nearly 200% due to an increase in the area treated, while diphacinone sodium salt 

use has remained relatively low due in part to its sole use on non-agricultural sites as shown in 

Table 2 below. 

T a bl e 2 DIQJ . h acmone u . c rf sage m a 1 ornta: A ,g an dN on-ag 

Chemical Pounds A.I. Applied 

2009 2010 2011 2012 2013 

Diphacinone 44.91 52.67 72.63 96.36 133.54 

Diphacinone, <0.01 2.59 12.63 2.12 2.07 

Sodium Salt 

Source: California DPR, Pesticide Use Reporting, Summary Data, 2009-2013 

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BIOLOGICAL ASPECTS RELEVANT TO DIPHACINONE 

Diphacinone is an anticoagulant rodenticide. Anticoagulants work by inhibiting the formation of 

prothrombin, a critical component in blood clotting, leading to bleeding at capillaries, internal 

bleeding, and even death. Diphacinone, like other first generation anticoagulant rodenticides, 

requires multiple feedings for the rodent to acquire a lethal dose. 

ROLE OF DIPHACINONE IN PEST MANAGEMENT 

Diphacinone is registered for control of commensal rodents in and around homes, industrial and 

agricultural buildings and similar man-made structures, as well as in sewers; in wet or damp 

areas such as river banks, irrigation ditches, gullies, railroad tracks, loading areas, along fences, 

under granaries, garbage dumps, and landfills. Diphacinone is also used to control pocket 

gophers in rangeland, grain fields, forage crops, hay and alfalfa crops, vegetable crops, forest, 

nurseries, and noncrop areas, such as parks. 

Diphacinone is a critical component to a rodent management strategy. For a homeowner, along 

with sanitation and exclusion, diphacinone may be used in bait traps. Rodenticide baits, along 

with a variety of habitat modification and other pest management techniques, are used to reduce 

the damage caused by native and introduced rodents, as well as other pest mammals. Rodenticide 

baits are especially useful for rapidly reducing rodent numbers in cases of major infestations, 

including island eradication of introduced rodents. 

INFORMATION THAT MAY BE USEFUL FOR BEAD'S FUTURE WORK ON 

DIPHACINONE 

For future BEAD assessments, the following information would be helpful: usage data for nonag sites (lbs a.i. applied, typical number of applications per year, and maximum dose per year); 

and more detail about how diphacinone is used in agricultural to control vertebrate pests. 

REFERENCES 

California Department of Pesticide Regulation, Pesticide Use Reporting, Summary Data, 2009-

2013 

Chiri, A. 2006. Analysis of Rodenticide Bait Use. U.S. Environmental Protection Agency, 

Office of Chemical Safety and Pollution Prevention. 

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Kline & Company, 2009 

Proprietary Data, 2011 

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