Page 2 of 16

(wheelchairs, metal bed frames, exteriors of toilets, cuntertops, metal surfaces, imaging 

equipment surfaces, metal, glass, acrylic, and porcelain) in hospitals, restrooms, schools, offices, 

gyms, and homes. Also, Mint-A-Kleen® a ready-to-use liquid product containing chlorhexidine 

gluconate was registered in 2010 for cleaning and control of microbial contamination in dental 

unit waterlines. 

There are three active ingredients in the chlorhexidine derivatives case 3038; however, 

one of these active ingredients, chlorhexidine dihydrochloride, does not have active registered 

products. This chemical is not being supported and is not addressed in this registration review. 

The chlorhexidine diacetate and chlorhexidine digluconate are the only active ingredients in the 

case with active products. For chlorhexidine diacetate a Reregistration Eligibility Decision 

(RED) was issued by EPA in September 1996 but no RED was issued by EPA for chlorhexidine 

digluconate.

Table 1. Registered Active Products of Chlorhexidine diacetate

Registration # Registration Name Company Name Formulation 

Type

% of Active 

Ingredient

1117-30 Fort Dodge Nolvasan 

Solution 

Fort Dodge Animal 

Health

Soluble 

Concentrate 2 

1117-48 Fort Dodge Nolvasan S Fort Dodge Animal 

Health

Soluble 

Concentrate 2 

1117-62 Chlorhexidine Diacetate Fort Dodge Animal 

Health Technical 99.3 

3573-74 Cougar The Procter & 

Gamble Company 

Soluble 

Concentrate 0.01 

3573-94 Chlorhexidine Diacetate The Procter & 

Gamble Company Technical 99.3 

Table 2. Registered Active Product of Chlorhexidine digluconate 

Registration # Registration 

Name Company Name Formulation Type

% of Active 

Ingredient

70467-3 BioSURF Micrylium 

Laboratories Liquid Spray 0.2

85298-2 Mint-A-Kleen® Anodia Systems Ready-to-use 

Liquid 0.12 

Use Patterns

EPA Reg. No.1117-30 

Nolvasan® Solution

Ch1orhexidine diacetate 
Page 3 of 16

Scented Disinfectant

Bactericide Virucide

For Animal Premises Use Only

Active Ingredient:

1,1’-Hexamethylenebis -5-(p-chlorophenyl) biguanide) diacetate 2% 

For cleaning, disinfection, deodorizing inanimate surfaces

For disinfection of veterinary or farm premises

For use in federally inspected meat, poultry, rabbit and egg establishments 

For dipping teats as an aid in controlling bacteria that causes mastitis.

For disinfection of inanimate objects to aid in control of bacteria and viruses

EPA Reg. No.1117-48 

Nolvasan® S 

Chlorhexidine diacetate

Scented Disinfectant

Bactericide Virucide

For Animal Premises Use Only

Active Ingredient:

1,1’-Hexamethylenebis [5-(p-chlorophenyl) biguanide] diacetate 2% 

For cleaning, disinfection, deodorizing 

For disinfection of veterinary or farm premises

For disinfection of inanimate objects to aid in control of bacteria and viruses

EPA Reg. No.1117-62 

Chiorhexidine Diacetate Technical 99.3%

This is a manufacturing use product for the formulation of indoor use antimicrobial hard surface 

disinfectant products. 

EPA Reg. No. 3573-74 

Cougar 

Active Ingredients:

Didecyl Dimethyl Ammonium Chloride 0.03%

Chlorhexidine Diacetate 0.01% 

Sanitizer: For use on hard non-porous floors. 

Sanitizing Cleaner. 

With Cougar Antibacterial solution, 99.9% of the bacteria* on floors are eliminated/killed.

All In-One mopping system. 

Antibacterial Cleaner

Cleans and kills/eliminates/removes 99.9% of bacteria* on dining area/cafeteria floors. 

Cleans and kills/eliminates 99.9% of bacteria* on public/school floors. 

Cleans, and removes bacteria*

Cleans and removes household bacteria* 

Cleans and Sanitizes.

Cleans and sanitizes floors wall-to-wall.

For use on all washable floors 

For use on/Great for vinyl glazed ceramic laminate, and finished wood floor surfaces. 
Page 4 of 16

For use on/Great for vinyl, glazed ceramic sealed marble laminate and finished wood floors. 

For vinyl, glazed ceramic, laminate, and finished wood floors. 

Great for! For Use on finished floors/glazed ceramic tile/vinyl surfaces.

Kills 99.9% of bacteria* and (helps) eliminate(s) odors (with fresh scent). 

Kills 99.9% of bacteria* and (helps) eliminate(s) odors in the air (with fresh scent). 

Kills and, prevents the spread of 99.9% of Enterobacter aerogenes/E. aerogenes on treated surfaces.

Kills and, prevents the spread of 99.9% of Staphylococcus aureus/S. aureus on treated surfaces. 

Kills/Eliminates/Removes 99.9% Enterobacter aerogenes/E. aerogenes

Kills/Eliminates/Removes 99.9% of bacteria*

Kills/Eliminates/Removes 99.9% of bacteria* on public/guest/school floors

Kills/Eliminatès/Removes 99.9% of bactéria* on floor/public restroom/lobby floors 

Kills/Eliminates/Removes 99.9% of household bacteria* 

Kills Eliminates/Removes 99.9% Staphylococcus aureus/S. aureus 

* Effective against/kllls/99.9% of Staphylococcus aureus and Enterobacter aerogenes. 

EPA Reg. No. 3573-94 

Chlorhexidine Diacetate Technical 99.3% 

This product is a manufacturing use product for the formulation of indoor use antimicrobial hard 

surface disinfectant products.

This product is a manufacture use product for formulation use only. 

EPA Reg. No. 70467-3 

BioSURF

Active Ingredients

Ethanol 70.5% 

Chlorhexidine gluconate 0.2% 

Tuberculocidal Canine Parvovirucidal Pseudomonacidal 

Hospital Hard Surface Disinfectant

BioSURF is a ready to use hard surface disinfectant for nonporous surfaces • One Step. 

For use on hard, non-porous imaging equipment surfaces 

Restrooms • Schools • The Office •The Gym •At Home. 

BioSURF Can be used on countertops metal surfaces and toilet exteriors. May be used on 

wheelchairs, metal bed frames and exteriors of toilets. BioSURF may be used on nonporous hard 

surfaces (imaging equipment, metal, glass, acrylic, and porcelain).

EPA Reg. No. 85298-2 

MINT-A-KLEEN®

Ready-to-use Liquid

Active Ingredient

Chlorhexidine digluconate 0.12% 

Dental Unit Waterline Cleaner

For the cleaning and control of microbial contamination in dental unit waterlines. For use in any 

dental unit. Ready to Use. Do Not Dilute. 
Page 5 of 16

Science Findings

The Agency has conducted a review of the available product chemistry, environmental 

fate, and ecotoxicity data for chlorhexidine diacetate and chlorhexidine digluconate. The 

findings are summarized below. 

All product chemistry data requirements have been satisfied for the active ingredients 

chlorhexidine diacetate and chlorhexidine digluconate. 

Table 3. Chemical Identity

Chlorhexidine diacetate Chlorhexidine digluconate

Chemical 

Name

1,1'- hexamethylene bis [5-(p-chlorophenyl) 

biguanide] Diacetate

2,4,11,13-Tetraazatetradecanediimidamide, N,N''-

bis(4-chlorophenyl)-3,12-diimino-, diacetate

1,1'-Hexamethylene bis(5-(4-chlorophenyl)

biguanide) digluconate

2,4,11,13-Tetraazatetradecanediimidamide, N,N"-

bis(4-chlorophenyl)-3,12-diimino, di-D-gluconate

Common 

Name

Chlorhexidine diacetate Chlorhexidine digluconate

Synonyms Chlorhexidine acetate Chlorhexidine gluconate

Trade 

Names 

Nolvasan, Arlacide A Bactigras, Hibitane 

acetate, Chlorhexidine acetate technical 

Hibitane chlorhexidine gluconate

Molecular 

Weight

625.55 g/mol 897.8 g/mol

PC Code 045502 045504 

CAS No. 56-95-1 18472-51-0

Molecular 

Formula

C22H30Cl2N10·2(C2H4O2) C22H30Cl2N10·2(C6H12O7)

Molecular 

Structure:

Chlorhexidine diacetate Chlorhexidine digluconate 
Page 6 of 16

Table 4. Product Chemistry Data Summary of Chlorhexidine diacetate and Chlorhexidine digluconate 

Guideline 

No.

Physical and Chemical 

Properties

Chlorhexidine diacetate

99.9%

Chlorhexidine digluconate

20% w/v Aqueous solution

(Technical)

830.1550 Product identity and 

composition

Refer to Table 3. Refer to Table 3. 

830.1600 Description of materials 

used to produce the 

product

CBI CBI

830.1620 Description of 

production process

CBI CBI

830.1650 Description of 

formulation process

CBI CBI

830.1670 Discussion of formation 

of impurities

CBI CBI

830.1700 Preliminary analysis CBI CBI 

830.1750 Certified limits CBI CBI

830.1800 Enforcement analytical 

method

Polarographic methods Polarographic methods

830.1900 Submittal of samples N/A NA

830.6302 Color White or almost white Clear, water white to amber liquid

830.6303 Physical State Powdered Solid

Microcrystalline powder

Liquid

830.6304 Odor Odorless or almost odorless Mild, practically odorless

Mild medicinal odor

It has a Bitter taste

830.6313 Stability to sunlight, 

normal and elevated 

temperature, 

metals/metal ions

Stable under ambient warehouse 

conditions to moisture and simulated 

sunlight.

Stability data at temperatures of 

25°C and 30°C over a 48 month 

period demonstrated that 

chlorhexidine acetate is stable in 

both amber glass bottles and in tin 

plate lever lid containers for a period 

of 48 months. Chlorhexidine acetate 

technical is transported in plastic 

bags inside fiberboard tin plate lever 

lid containers. 

The product is stable.

830.6314 Oxidation/Reduction: 

Chemical 

Incompatibility

Chlorhexidine acetate is compatible 

with an oxidizing agent (potassium 

permanganate), a reducing agent 

(zinc powder), water and carbon 

dioxide. No significant increase in 

temperature was observed with any 

mixture tested although in the case 

of potassium permanganate, a rise in 

temperature of approximately 4°C 

was detected upon initial mixing but 

this returned to ambient within 1 hr.

N/A

830.6315 Flammability N/A

Flash point > 100 °C 

N/A

Flash point: 376.7 °C

830.6316 Explodability N/A N/A
Page 7 of 16

Guideline 

No.

Physical and Chemical 

Properties

Chlorhexidine diacetate

99.9%

Chlorhexidine digluconate

20% w/v Aqueous solution

(Technical)

830.6317 Storage Stability Stability data at temperatures of 25° 

and 30°C over a 48 month period 

demonstrated that chlorhexidine 

acetate is stable in both amber glass 

bottles and in tin plate lever lid 

containers for a period of 48 months

Shelf-life is three years at 2-8°C.

Storage Temp: 2-8°C. 

830.6319 Miscibility N/A Miscible with water

830.6320 Corrosion 

Characteristics

Stability studies have shown that the 

physical condition of the product in 

tin plate lever lid containers is 

satisfactory. There is no evidence to 

suggest that product pack interaction 

would be a problem.

Non-corrosive in presence of 

glass.

830.6321 Dielectric breakdown 

voltage

N/A N/A

830.7000 pH 6.8 (in 1% solution)

7 in solution

20% solution (w/v) 6.0 – 6.8

(1% soln/water): Neutral.

830.7050 UV/Visible Absorption Not Reported. Not Reported.

830.7100 Viscosity N/A NR

830.7200 Melting point 158.7oC N/A

830.7220 Boiling point N/A The lowest known value is 100°C 

(212°F) (Water).

830.7300 Density Density: 1.2 g/cm3 Sp Gr: 1.06 at 20°C

Density: 1.06 g/mL at 25°C (lit.)

830.7370 Dissociation Constant N/A

pKa = 10.78 in water

1

830.7550 Partition coefficient (noctanol/water)N/A

Octanol/acetate buffer (pH 5) Log 

D=0.08

N/A

-0.33 (EPI Suite)

830.7840 Solubility in water Solubilizes

1.9 g/100 mL (20 oC)

Soluble in water.

Easily soluble in cold water.

Fully miscible. 

Miscible with water. 

830.xxxx Solubility in organic 

solvents

Ethanol...... 6.7 gm/100 ml

Glycerol.... slightly soluble

Propane..... slightly soluble

Soluble in ethanol & acetone.

Soluble in polar solvents such as 

lower alcohols, glycols and other 

polyols.

830.7950 Vapor pressure N/A

Chlorhexidine acetate is a solid 

which melts above 100 °C, vapor 

pressure is therefore not applicable.

The highest known value is 

17.535 mm of Hg (@ 20°C

(Water).

N/A = Not applicable; TGAI=Technical Grade Active Ingredient; CBI= Confidential Business Information
Page 8 of 16

Environmental Fate Summary

No definitive environmental fate assessment can be made because no data have been 

submitted regarding the chemical degradation, microbial metabolism or mobility of 

chlorhexidine derivatives. 

The Agency did not conduct an environmental fate assessment for chlorhexidine 

derivatives because of lack of data. However, the Agency needs to conduct an environmental 

fate assessment for disinfectant/sanitizers used in animal premises that may potentially pass 

through waste water treatment plants (WWTPs) and may be discharged into terrestrial and 

aquatic environments. For this assessment the Agency anticipates needing those data outlined on 

page 11 of this document. 

Water Quality

Chlorhexidine derivatives are not identified as a cause of impairment for any water 

bodies listed as impaired under section 303(d) of the Clean Water Act, based on information 

provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=88

5 . In addition, no Total Maximum Daily Loads (TMDL) have been developed for chlorhexidine 

derivatives, based on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id

=885&p_pollutant_group_name=PESTICIDES . More information on impaired water bodies 

and TMDLs can be found at http://www.epa.gov/owow/tmdl/. The Agency invites submission 

of water quality data for this pesticide. To the extent possible, data should conform to the quality 

standards in Appendix A of the OPP Standard Operating Procedure: Inclusion of Impaired 

Water Body and Other Water Quality Data in OPP’s Registration Review Risk Assessment and 

Management Process (see: http://www.epa.gov/oppfead1/cb/ppdc/2006/november06/session1-

sop.pdf ), in order to ensure they can be used quantitatively or qualitatively in pesticide risk 

assessments.

Ecological Effects Summary

The registrant has submitted ecological effects studies for both terrestrial and aquatic 

animals. These data are adequate to provide the Agency with sufficient information to determine 

appropriate label precautions, and may be seen in Tables 5 and 6 below. 

a. Toxicity to Terrestrial Animals 

(1) Birds, Acute and Subacute

Chlorhexidine diacetate is slightly toxic to practically nontoxic to avian species 

on an acute oral and subacute dietary basis.

Chlorhexidine digluconate is slightly toxic to avian species on an acute oral and 

subacute dietary basis.
Page 9 of 16

b. Toxicity to Aquatic Animals 

(1) Freshwater Fish

Chlorhexidine diacetate is moderately toxic to cold water fish and highly toxic to 

warm water fish.

Chlorhexidine digluconate is highly toxic to both cold and warm water fish. 

(2) Freshwater Invertebrates

Chlorhexidine diacetate is highly toxic to aquatic invertebrates.

Chlorhexidine digluconate is highly toxic to aquatic invertebrates. 

c. Toxicity to Aquatic Plants

(1) Freshwater Algae 

No algal toxicity data have been submitted. For the ecological risk assessment, 

including an endangered species assessment for all uses, the Agency anticipates 

needing the algal toxicity data outlined on page 11 of this document. 

Ecotoxicity data are adequate to provide the Agency with sufficient information to 

determine appropriate label precautions. 

Table 5. Ecotoxicity Data Summary for Chlorhexidine diacetate 

GUIDE

LINE

COMMON

NAME

TAXONOMIC 

NAME

TEST

TYPE

%

AI

STUDY

TIME

DOSE

TYPE

TOXI

CITY

TOX

LEVEL NOEL STUDY STATUS

TOX 

CATEGORY MRID

Avian Acute Oral Toxicity

850.2100 Bobwhite 

quail

Colinus 

virginianus

O 100 14 D LD50 2013 MGK 292 Acceptable Slightly 

toxic

42197501

Avian Subacute Dietary Toxicity

850.2200 Bobwhite 

quail

Colinus 

virginianus

D 100 8 D LC50 >5620 PPM 1780 Acceptable Practically 

nontoxic

42197502

850.2200 Mallard 

duck

Anas 

platyrhynchos

D 100 8D LC50 >5620 PPM 5620 Acceptable Practically 

nontoxic

42197503

Freshwater Fish Acute Toxicity

850.1075 Rainbow 

trout

Oncorhynchus 

mykiss

S 100 96 hr LC50 1871 PPB 900 Acceptable Moderately

toxic

42197504

850.1075 Bluegill 

sunfish

Lepomis 

macrochirus

S 100 96 hr LC50 600 PPB 300 Acceptable Highly toxic 42197505

Freshwater Invertebrate Acute Toxicity

850.1010 Water

flea

Daphnia 

magna

S 100 48 hr EC50 63 PPB 32 Acceptable Very highly 

toxic

42197506
Page 10 of 16

Table 6. Ecotoxicity Data Summary for Chlorhexidine digluconate

GUIDE

LINE

COMMON

NAME

TAXONOMIC 

NAME

TEST

TYPE

%

AI

STUDY

TIME

DOSE

TYPE

TOXI

CITY

TOX

LEVEL NOEL STUDY STATUS

TOX 

CATEGORY MRID

Avian Acute Oral Toxicity

850.2100 Mallard 

duck

Anas 

platyrhynchos

O 20.0 

Tech

14 D LD50 >2510

Eq to 502 

mg/kg ai

MGK Supplemental Slightly 

toxic

00030213

Avian Subacute Dietary Toxicity

850.2200 Mallard 

duck

Anas 

platyrhynchos

D 20.0 

Tech

8 D LC50 >10000

Eq to 2000 

ppm ai

PPM 4640 Supplemental Slightly 

toxic

124744

850.2200 Bobwhite 

quail

Colinus 

virginianus

D 20.0 

Tech

8D LC50 >10000

Eq to 2000

ppm ai

PPM >10000 Supplemental Slightly 

toxic

126034

Freshwater Fish Acute Toxicity

850.1075 Rainbow 

trout

Oncorhynchus 

mykiss

S 20.0 

Tech

96 hr LC50 2.3 PPM 1.21 Acceptable Highly toxic 00124743

850.1075 Bluegill 

sunfish

Lepomis 

macrochirus

S 20.0 

Tech

96 hr LC50 0.51 PPM 0.21 Acceptable Highly toxic 00124743

Freshwater Invertebrate Acute Toxicity

850.1010 Water

flea

Daphnia 

magna

S 20.0 

Tech

48 hr EC50 0.42

Eq to 84 

ppb

PPM Acceptable Very highly 

toxic

241539

045504

Adverse Ecological Incidents

There are no reported incidents in the Agency' s Ecological Incident Information System

(EIIS) regarding chlorhexidine derivatives. The absence of documented incidents does not 

necessarily mean that such incidents did not occur.

Ecological Effects Risk Assessment

An ecological risk assessment was not conducted on the chlorhexidine derivatives’s 

disinfectant/sanitizer use patterns described in this document. Chlorhexidine derivatives uses in 

animal premises and dental unit water lines that have potential for environmental exposure are 

down the drain disinfectant/sanitizer discharges. The Agency needs to conduct environmental 

fate and ecological risk assessments for disinfectant/sanitizers used in animal premises and dental 

unit water lines that potentially pass through waste water treatment plants (WWTPs) and may be 

discharged into terrestrial and aquatic environments. For this ecological risk assessment, 

including an endangered species assessment for all uses, the Agency anticipates needing the algal 

toxicity data outlined on page 11 of this document. 

The Agency has not conducted a risk assessment that supports a complete endangered 

species determination. The ecological risk assessment planned during registration review will 

allow the Agency to determine whether chlorhexidine derivatives’s use has “no effect or “may 

affect” federally listed threatened or endangered species (listed species) or their designed critical 

habitats. When an assessment concludes that a pesticide’s use “may affect” a listed species or its 

designated critical habitat, the Agency will consult with the U.S. Fish and Wildlife Service 

and/or National Marine Fisheries Services (the Services), as appropriate.
Page 11 of 16

Environmental Fate and Ecotoxicity Data Gaps and Anticipated Work 

Environmental fate and ecological risk assessments have not been conducted for 

chlorhexidine derivatives. The Agency needs to conduct environmental fate and ecological risk 

assessments for disinfectant/sanitizers used in animal premises and dental unit water lines that may 

potentially pass through waste water treatment plants (WWTPs) and may be discharged into 

terrestrial and aquatic environments. Therefore, the Agency anticipates needing the proposed 

environmental fate and ecotoxicity data for chlorhexidine derivatives and/or any of its major 

degradation products that are of potential concern for all registered uses of chlorhexidine derivatives. 

The following environmental fate and ecotoxicity data are needed to conduct an environmental fate 

and ecological risk assessment: 

• The Agency anticipates needing the following data to conduct a complete 

environmental fate assessment for animal premises and dental unit water lines uses: 

o (GLN 835.2120) Hydrolysis; 

o (GLN 835.2240) Photodegradation in water; 

o (GLN 850.6800) Modified Activated Sludge Respiration Inhibition; 

o (GLN 835.1110) Activated Sludge Sorption Isotherm; and

o (GLN 835.3110) Ready Biodegradability. 

• The Agency anticipates needing the following data in order to conduct a complete 

ecological risk assessment, including an endangered species assessment:

o (GLN 850.5400) algal toxicity (Tier II) using freshwater green alga, Selenastrum 

capricornutum.
Page 12 of 16

Appendix A. Environmental Fate Guideline Study Justifications

Guideline Number: 835.2120

Study Title: Hydrolysis

Practical Utility of the Data

1) What is the value of the study?

Data characterizing the rate of hydrolytic degradation of chlorhexidine derivatives and/or the formation 

and decline of degradates is important in determining the persistence and concentrations of chlorhexidine 

derivatives and potential degradates over time in various aquatic environments. For outdoor uses, 

chlorhexidine derivatives can reach surface water through direct contact or discharge to WWTPs. 

Chlorhexidine derivatives may also reach surface water or groundwater through run-off or leaching 

processes. The Agency will evaluate the potential risks of concern. 

2) How would the data be used?

The data would establish the significance of chemical hydrolysis as a route for degradation and identify, if 

possible, the hydrolytic transformation products formed that may adversely affect non-target organisms 

and may contaminate water and food source of aquatic organisms. The data would also help establish the 

hydrolytic half-life of chlorhexidine derivatives and possibly degradates, and assist in developing a 

degradation pathway.

3) How could the data affect the risk assessment?

The results of hydrolysis data would indicate if chlorhexidine derivatives is persistent or if it degrades 

into other products that may adversely affect nontarget organisms and may contaminate their food and 

water and possibly soil.

4) What is triggering the need for this data?

Hydrolysis data is needed to conduct the fate assessment to support material preservatives uses for 

chlorhexidine derivatives.

Guideline Number: 835.2240

Study Title: Photodegradation in water

Practical Utility of the Data

1) What is the value of the study?

Biocides introduced into aqueous systems in the environment can undergo photolytic transformation by 

sunlight. Results from the photolysis study will indicate the stability and persistence of chlorhexidine 

derivatives and potential degradates in an aquatic environment when exposed to sunlight. The Agency 

will evaluate the potential risks of concern.

2) How would the data be used?

The data would establish the significance of chemical photolysis as a route for degradation and identify, if 

possible, the photolytic degradation products formed that may adversely affect non-target organisms and 

may contaminate water and food source of aquatic organisms. The data would also help establish the 

photolytic half-life of chlorhexidine derivatives and possibly degradates, and assist in developing a 

degradation pathway.

3) How could the data affect the risk assessment?

The results of photolysis data would indicate if chlorhexidine derivatives are persistent or if they degrade 

into other chemical products that may adversely affect nontarget organisms by contaminating their food

supply. The results of the photolysis data would expand the understanding of the results of the hydrolysis 

data since environmental aquatic conditions usually involve exposure to sunlight. 
Page 13 of 16

Guideline Number: 835.2240

Study Title: Photodegradation in water

4) What is triggering the need for this data?

Aqueous photodegradation data is needed to conduct the fate assessment to support material preservative 

uses for chlorhexidine derivatives.

Guideline Number: 850.6800

Study Title: Modified Activated Sludge Respiration Inhibition

Rationale for Requiring the Data

The modified activated sludge, respiration inhibition test is needed to identify whether this pesticide 

could harm microorganisms found in biological wastewater treatment systems. The Agency will utilize 

these data to conduct the environmental fate assessment and to determining the potential impact of this 

chemical on waste water treatment plants (WWTPs) via effects on WWTP microbes. This test is also 

necessary to enable EPA to establish correct concentrations for use in the ready biodegradability test.

Practical Utility of the Data

1. How will the data be used?

The data will be used to assess exposure and risk to non-target endangered and non-endangered species. 

Exposure data are integral parts of the risk equation for determining the impact of pesticides to beneficial 

non-target organisms through direct exposure from their food sources and habitat. 

In addition, the data will be used to determine whether or not additional studies and/or label restrictions 

are needed. The study will identify the inhibitory effect of this chemical on the treatment plant’s 

microorganisms’ respiration at a particular concentration and will identify the EC50, the effective 

concentration at which the respiratory rate is reduced by 50%. EPA will use the data to determine the

chemical’s potential to directly harm the non-target organisms and/or the microbial treatment processes 

present in a WWTP. The data will also determine suitable non-inhibitory concentrations to be used in 

biodegradability tests.

2. How could the data impact the Agency’s future decision-making?

If the data show a high degree of respiratory inhibition, higher-tiered environmental fate studies may be 

required and the risk assessments for this chemical may need to be revised to address the impact of the 

potential risk. The risk assessment may result in the Agency requiring label restrictions that would be 

necessary for the products to meet the “no unreasonable adverse effects” requirements of FIFRA (e.g., 

changes to the directions for disposal). 

In addition, EPA is required by section 7(a)(2) of the ESA to ensure that any action it authorizes or takes 

“...is not likely to jeopardize the continued existence of any endangered or threatened species or result in 

the destruction or adverse modification of critical habitat” and to use the best scientific data available” in 

carrying out this obligation. The data EPA intends to call in are necessary to inform the determination 

required by the ESA as to whether continued registration of a pesticide is not likely to jeopardize the 

species or its critical habitat. Absent this data EPA may not be able to conclude that this pesticide will not 

harm endangered species and may therefore need to consider other limitations on the use of the pesticide in 

order to fulfill the Agency’s statutory obligations under the ESA. The lack of these data will limit the 

flexibility that the Agency and registrants have in coming into compliance with the ESA and could result in 

use restrictions which are unnecessarily severe.
Page 14 of 16

Guideline Number: 835.1110

Study Title: Activated Sludge Sorption Isotherm

Rationale for Requiring the Data

Data from this study are needed to determine the sorption potential of activated sludge for the removal 

of specific chemical compounds in biological wastewater treatment plants (WWTPs). If the chemical is 

not sorbed or biodegraded, then it would pass through a biological treatment system unaffected, 

potentially contaminating surface and drinking waters where it may then have the potential to adversely

affect nontarget organisms. EPA needs activated sludge sorption study data to assess the distribution of

the antimicrobial chemical among the solid, aqueous, and vapor phases of WWTPs. Specifically, this 

study identifies those chemicals which sorb to sludge biomass.

Practical Utility of the Data

1. How will the data be used?

The data will be used to assess exposure and risk to non-target endangered and non-endangered species. 

Exposure data are integral parts of the risk equation for determining the impact of pesticides to beneficial 

nontarget organisms through direct exposure from their food sources and habitat. 

In addition, the data will be used to determine whether or not additional studies and/or label restrictions are 

needed. If the data indicate that the chemical does not sorb to sludge and instead partitions more readily to 

water, then the chemical has the potential to pass through the WWTP and therefore could be discharged in 

to the aquatic environment. This determination could trigger further data requirements to assess the 

chemical’s impact upon release.

2. How could the data impact the Agency’s future decision-making? 

If the data show that the chemical negatively impacts the aquatic environment or the effectiveness of the 

WWTP, then the risk assessments for this chemical may need to be revised to reflect the magnitude of 

potential risk derived from the new data. The risk assessment may result in the Agency requiring label 

restrictions that would be necessary for the products to meet the “no unreasonable adverse effects” 

requirements of FIFRA (e.g., changes to the directions for disposal). 

In addition, EPA is required by section 7(a)(2) of the ESA to ensure that any action it authorizes or takes 

“...is not likely to jeopardize the continued existence of any endangered or threatened species or result in 

the destruction or adverse modification of critical habitat” and to use the best scientific data available” in 

carrying out this obligation. The data EPA intends to call in are necessary to inform the determination 

required by the ESA as to whether continued registration of a pesticide is not likely to jeopardize the 

species or its critical habitat. Absent this data EPA may not be able to conclude that this pesticide will not 

harm endangered species and may therefore need to consider other limitations on the use of the pesticide in 

order to fulfill the Agency’s statutory obligations under the ESA. The lack of these data will limit the 

flexibility that the Agency and registrants have in coming into compliance with the ESA and could result in 

use restrictions which are unnecessarily severe. 
Page 15 of 16

Guideline Number: 835.3110

Study Title: Ready Biodegradability

Rationale for Requiring the Data

For antimicrobial chemicals that go down-the-drain and reach a WWTP, as part of its screening-level 

environmental fate assessment, EPA will analyze the potential impact of the antimicrobial chemical on the 

microorganisms in the biological treatment processes of a WWTP. Biodegradation is an important 

environmental pathway in which the antimicrobial is broken down by bacteria. This study supplies 

information on the rate of breakdown and the completeness of the degradation to carbon dioxide and water. 

A ready biodegradability study would allow the Agency to determine whether the chemical achieves ‘‘pass 

levels’’ for ready biodegradability (e.g., 70% removal of dissolved organic carbon). 

Practical Utility of the Data

1. How will the data be used?

The data will be used to assess exposure and risk to non-target endangered and non-endangered species. 

Exposure data are integral parts of the risk equation for determining the impact of pesticides to beneficial 

non-target organisms through direct exposure from their food sources and habitat. 

In addition, the data will be used to determine whether or not additional studies and/or label restrictions 

are needed. If the chemical does not achieve a ‘‘pass level’’ for ready biodegradability, then the Agency 

would determine that the chemical has the potential to pass through the WWTP and therefore may be 

discharged in to the aquatic environment potentially resulting in exposure to non-target species. This 

determination would trigger further data requirements to assess the chemical’s impact on the aquatic 

environment upon release.

2. How could the data impact the Agency’s future decision-making? 

If the chemical is found to be readily biodegraded, then impact on WWTP would be identified as minimal 

and most likely no further studies or label restrictions would be required. If a low rate of biodegradability 

is identified, then higher-tiered environmental fate studies may be triggered and the risk assessments for 

this chemical may need to be revised to reflect the magnitude of potential risk derived from the chemical’s 

lack of biodegradability. The risk assessment may result in the Agency requiring label restrictions that 

would be necessary for the products to meet the “no unreasonable adverse effects” requirements of FIFRA 

(e.g., changes to the directions for disposal).

In addition, EPA is required by section 7(a)(2) of the ESA to ensure that any action it authorizes or takes 

“...is not likely to jeopardize the continued existence of any endangered or threatened species or result in 

the destruction or adverse modification of critical habitat” and to use the best scientific data available” in 

carrying out this obligation. The data EPA intends to call in are necessary to inform the determination 

required by the ESA as to whether continued registration of a pesticide is not likely to jeopardize the 

species or its critical habitat. Absent this data EPA may not be able to conclude that this pesticide will not 

harm endangered species and may therefore need to consider other limitations on the use of the pesticide in 

order to fulfill the Agency’s statutory obligations under the ESA. The lack of these data will limit the 

flexibility that the Agency and registrants have in coming into compliance with the ESA and could result in 

use restrictions which are unnecessarily severe.
Page 16 of 16

Appendix B: Ecological Guideline Study Justifications

Guideline Number: 850.5400

Study Title: Algal toxicity (Tier II) using freshwater green alga, Selenastrum Capricornutum

Practical Utility of the Data

1) What is the value of the study?

As part of an initial risk assessment, one indicator plant species is tested for phytotoxicity. This study 

would allow the Agency to categorize chlorhexidine derivatives as toxic or non-toxic to plants. If toxic, 

additional higher tier plant tests would be needed. An endangered species assessment for endangered or 

threatened plants is not possible without this study. 

2) How would the data be used?

This study would be used to evaluate the toxicity of chlorhexidine derivatives to non-target plants in 

terrestrial and aquatic ecosystems.

3) How could the data affect the risk assessment?

Adverse effects to non-target plants in terrestrial and aquatic ecosystems may result in mitigation to 

protect species at risk. Mitigation might include reduced label dosages, neutralization of effluents prior to 

discharge into water, restrictions on use in sensitive ecosystems or where endangered species are present, 

or other mitigation measures.

4) What is triggering the need for this data?

Increased concern from state regulators and the public to evaluate impacts on WWTP operations, 

endangered species, and persistence in the environment, since initial registration, have triggered the need 

for this study. Green algae are critical to ecosystem health and productivity.