Page 2 of 15

dietary basis; and moderately toxic to freshwater fish and invertebrate. For the ecological 

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

requires the acute avian oral toxicity data, acute freshwater invertebrates toxicity data, 

acute freshwater fish toxicity data, and algal toxicity data.

Introduction

The first product containing 1-(2-Hydroxyethyl)-2-alkyl*-2-imidazoline (*as in 

fatty acids of tall oil) hereafter called alkyl imidazoline, was registered in the United 

States in 1970. Currently, one end use product is registered for use as a microbiocide in 

fuel oil storage tanks (See Table 1 below).

Alkyl imidazoline is a microbiocide/microbiostat used in fuel and oil storage tank 

bottom water. It is used to prevent the growth of slime-forming bacteria and fungi which 

might interfere with the use and quality of oils and fuels in storage tanks. Formulation 

includes one soluble concentrate liquid product, with 25% active ingredient. Product is 

loaded and applied through a closed delivery system that has a proportioning pump or 

siphon type feeder to meter the pesticide product directly from the product container into 

the fuel oil as it is pumped into storage tanks. Product is not intended for homeowner use 

or for use in or around residences.

There are two active ingredients in the Alkyl imidazolines Case 3010; however, 

one of these active ingredients, 2-heptadecentyl-2-imidazoline (PC Code: 046612; CAS 

No.: 30968-43-5), does not have active registered products. This chemical is not being 

supported and is not addressed in this registration review. 1-(2-Hydroxyethyl)-2-alkyl-2-

imidazoline (as in fatty acids of tall oil) is the only active ingredients in the case with 

active products. A Reregistration Eligibility Decision (RED) was issued by EPA for 

Alkyl imidazolines in 19951

.

Table 1. Registered Product of 1-(2-Hydroxyethyl)-2-alkyl-2-imidazoline (as in fatty acids of tall oil)

Registration

No.

Registration 

Name

Company

Name

Formulation 

Type

% of Active

Ingredient

68708-3 NALCO 2210

Fuel Oil Treatment

Nalco Energy Services, 

L.P.

Ready-to-use 

Solution 25

EPA Reg. No. 68708-3

2210 Fuel Oil Treatment

NALCO Energy Services, L.P.

Active Ingredient:

l-(2-hydroxyethyl)-2-alkyl (C18)*-2-imidazoline... 25.0%

*As in Tall Oil Fatty Acids.

2210 Fuel Oil Treatment Is Intended For Industrial Use Only.

 1 http://www.epa.gov/oppsrrd1/REDs/3010red.pdf
Page 3 of 15

For Use with Closed Delivery Systems Only

To inhibit sludge formation, to disperse existing sludge and to control filter - plugging 

bacteria and fungi in fuel oil storage tanks and feed lines, use 40 to 80 ppm of 2210 Fuel 

Oil Treatment based on fuel oil. Higher dosage may be required to completely inhibit 

some bacteria not considered to be factors in filter plugging.

Feed 2210 Fuel Oil Treatment by means of proportioning pump or siphon type feeder 

directly from drum or other container to the fuel oil as it is pumped into storage tanks.

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

environmental fate, and ecotoxicity data for 1-(2-Hydroxyethyl)-2-alkyl*-2-imidazoline 

(*as in fatty acids of tall oil). The primary source of information for this assessment was

the 1995 Alkyl imidazolines RED. The findings are summarized below.

Product Chemistry Summary (Nalco PR-471/NALCO 2210 - 25 % AI)

Common Name: Nalco PR-471, Alkyl imidazoline

Chemical Name: 1-(2-hydroxyethyl)-2-alkyl*-2-imidazoline (*as in

fatty acids of tall oil)

1H-Imidazole-1-ethanol, 4,5-dihydro-, 2-nortall-oil 

alkyl derivatives.

2-Alkyl*-2-imidazoline-1-ethanol *(as in fatty acids 

of tall oil)

Trade and Other Names: Nalco 2210, Fuel-prep 1000

OPP Chemical Code: 046609

CAS Registry Number: 61791-39-7

Case: 3010

Chemical Family: Fatty Acid Salt

Ave. Molecular Formula: C22H40-44N2O

Ave. Molecular Weight: 350.58

Molecular Structure:

R= Nortall Oil

Color: Clear to slightly hazy - amber

Physical State: Liquid

Odor: Slight, “amine-like”

Hydrocarbon

Stability: Product is stable in presence of metal and metal 

ions at normal temperature and temperatures up to 
Page 4 of 15

200°C. Product darkens on long-term exposure to 

sunlight. The imidazoline can react with water to 

form the amide.

Oxidation/Reduction: N/A, the product contains neither oxidizing nor 

reducing agents.

Flammability-Flash Point: Flash point: 151°F

Explodability: N/A, the product contains no explosive agents.

Storage Stability: After one year of storage, the ring clouse was found 

at 80.48%.

Miscibility: Soluble in kerosene, toluene, heptane @ 0.01, 0.1, 

1.0, and 10 volume %. Insoluble in water at all 

cited %.

Corrosion Characteristics: Not Provided.

Dielectric breakdown

voltage: N/A, the product is not used around electrical 

equipment.

pH: N/A, product hydrocarbon soluble, not soluble in 

water.

20% in isopropyl alcohol = 11.2

UV/Visible absorption: Not provided.

Viscosity: 97 cps @ 60oF

Melting point: This material is a mixture and has no true melting 

point (i.e. each component of the mixture melts at a 

different temperature). Determination of this 

endpoint is not applicable.

Boiling Point: This material contains long-chain hydrocarbons that 

degrade at much lower temperatures than those at 

which they would be expected to boil. 

Determination of this endpoint is not applicable.

Density: 0.940 ± .005 g/ml at 25°C or 7.6 lbs/gal

Specific gravity: 0.91-0.93 @ 60°F

Dissociation Constant: Product is a mixture. No value can be obtained.
Page 5 of 15

Log Ko/w or log P: Product is a mixture. No value can be obtained.

This material has surfactant properties and will 

accumulate at the interface between hydrophobic 

and hydrophilic phases rather than equilibrating 

between the two phases. It will remain in the 

organic phase (fuel/oil) in any mixture with water. 

Determination of this endpoint is not applicable.

Its affinity to the organic (fuel) phase of the 

mixture.

Solubility: Insoluble in water (8 mg/L in water).

This material is a mixture and has no single value 

for water solubility. Determination of this endpoint 

is not applicable.

Soluble in kerosene, toluene, heptane @ 0.01, 0.1, 

1.0, and 10 volume percent. Insoluble in water at 

all cited percent.

Vapor Pressure: <0.1 mm Hg at 25°C.

This material is a large complex molecule with 

long-chain hydrocarbons that are non-volatile. 

Determination of this endpoint is not applicable.

Enforcement Analytical

Method: Not provided.

All product chemistry data requirements have been satisfied for the active 

ingredient 1-(2-hydroxyethyl)-2-alkyl*-2-imidazoline (*as in fatty acids of tall 

oil). (Source: MRIDs 42434701, 43126801, 42434702, 42434703, 43379001, 

43373101 & 44402001).

Environmental Fate Summary

No risk assessment was performed for alkyl imidazoline at the time of the 

registration. The Agency has not received any guideline environmental fate studies on 

alkyl imidazoline which are required to conduct an environmental fate assessment for 

material preservatives (including alkyl imidazoline) used in fuel oil storage tanks. For 

this assessment the Agency anticipates needing those data outlined on page 9 of this 

document.
Page 6 of 15

Water Quality

1-(2-hydroxyethyl)-2-alkyl*-2-imidazoline (*as in fatty acids of tall oil) is 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 the Agency’s National 

Pesticides Cause of Impairment of Waters website (searched April 7, 2011)2. In addition, 

no Total Maximum Daily Loads (TMDL) have been developed for 1-(2-hydroxyethyl)-2-

alkyl*-2-imidazoline (*as in fatty acids of tall oil), based on information provided at the 

Agency’s National Pesticide TMDL web site (searched April 7, 2011)3

http://www.epa.gov/owow/tmdl/

. More 

information on impaired water bodies and TMDLs can be found at 

. 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

No ecological risk assessment was performed for alkyl imidazolines at the time of 

the registration. Available ecotoxicity guideline studies and the results are summarized 

in Table 2. The Agency's conclusions for the terrestrial and aquatic effects studies are as 

follows.

a. Toxicity to Terrestrial Animals

Birds, Acute

No avian acute oral toxicity data have been submitted. For the ecological 

risk assessment, including an endangered species assessment for all uses, 

the Agency anticipates needing the avian acute oral toxicity data outlined 

on page 9 of this document.

Birds, Subacute

Alkyl imidazoline is practically nontoxic to avian species on subacute 

dietary basis.

Mammals, Acute

Alkyl imidazoline has slight oral toxicity.

 2 . http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=885 3

http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id=885&p_p

ollutant_group_name=PESTICIDES
Page 7 of 15

There is currently no 2-generation rat repro study and the human health 

scoping document identifies this study as a data gap.

b. Toxicity to Aquatic Animals

Freshwater Fish and Invertebrates

Alkyl imidazoline is moderately toxic to freshwater fish, with the LC50

values ranging from 1.07 -1.17 and to Daphnia magna, a freshwater 

aquatic invertebrate with EC50 value as 1.7 ppm. However, these studies 

were found invalid and must be repeated.

c. Toxicity to Aquatic Plants

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 9 of 

this document.

Table 2. Ecotoxicity Data Summary for 1-(2-hydroxyethyl)-2-alkyl*-2-imidazoline (*as in fatty acids of tall oil)

GUIDE

LINE

COMMON

NAME

TAXONOMIC 

NAME

TEST

TYPE

%

AI

STUDY

TIME

DOSE

TYPE

TOXI

CITY

TOX

LEVEL NOEL STUDY STATUS

TOX 

CATEGORY MRID

Avian Subacute Dietary Toxicity

850.2200

(71-2a)

Bobwhite

quail

Colinus

virginianus

D 100 8 D LC50 >5000 PPM 3180 Acceptable Practically 

nontoxic

44004901

Freshwater Fish Acute Toxicity

850.1075

(72-1)

Rainbow

trout

Oncorhynchus

mykiss

S 25

100

96 hr LC50 1.07

2.7

ppm N.R

2.2.

Invalid Moderately 

toxic

43373102

44004902

850.1075

(72-1)

Bluegill 

sunfish

Lepomis 

macrochirus

S 25 96 hr LC50 1.17 ppm N.R. Invalid Moderately 

toxic

43373102

Freshwater Invertebrate Acute Toxicity

850.1010

(72-2)

Water

flea

Daphnia

magna

S Form

TEP

48 hr EC50 1.7 ppm <1.3 Invalid Moderately 

Toxic

43379002

Terrestrial Mammalian Acute Oral Toxicity

81-1 SpragueDawley 

Rats

------ ---- 85±3% ----- LD50

(Males)

LD50

(Females)

LD50

(Combined)

1948

1880

1932

mg/kgbw----- Acceptable Slightly 

toxic

III

42293001

Test Type—D: dietary; S: static.

% AI—Form: TEP: typical end-use product

Tox Level—ppm: parts per million (equivalent to milligrams per kilogram-diet (mg/kg-diet) for dietary exposure and milligrams per 

liter (mg/L) for aquatic exposures)

Toxicity—N.R.: not reported

Categories of acute toxicity for aquatic organisms (U.S. EPA, 2004) based on EC50/LC50(mg/L): < 0. 1 very highly toxic; 0.1-1 

highly toxic; >1-10 moderately toxic; >10-100 slightly toxic; >100 practically nontoxic. 

Categories of acute toxicity to terrestrial animals, avian and mammalian (U.S. EPA, 2004). LC50 (ppm): < 50 very highly toxic; 50 

- 500 highly toxic; 501 – 1000 moderately toxic; 1001-5000 slightly toxic; >5000 practically non-toxic. LD50 (mg/kg bw): < 10 very 

highly toxic; 10 - 50 highly toxic; 51 - 500 moderately toxic; 501-2000 slightly toxic; >2000 practically non-toxic.
Page 8 of 15

Adverse Ecological Incidents

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

System (EIIS) regarding 1-(2-hydroxyethyl)-2-alkyl*-2-imidazoline (*as in fatty acids of 

tall oil). The absence of documented incidents does not necessarily mean that such 

incidents did not occur.

Ecological Effects Risk Assessment

Alkyl imidazoline, is used as a preservative and fungicide to inhibit slime-forming 

bacteria and fungi growth in fuel oil storage tank bottom water. An ecological risk 

assessment was not conducted on the alkyl imidazoline’s use pattern described in this 

document as a microbiocide in fuel oil. The Agency needs to conduct environmental fate 

and ecological risk assessments for alkyl imidazoline’s fuel oil treatment use pattern 

listed in this document. For this ecological risk assessment, including an endangered 

species assessment for fuel oil treatment use, the Agency anticipates needing the 

ecological effects data outlined on page 9 of this document to characterize alkyl 

imidazoline’s toxicity to birds, fish, and aquatic invertebrates.

The Agency has not conducted a risk assessment for alkyl imidazoline that 

supports a complete endangered species effects determination. The ecological risk 

assessment planned during registration review will allow the Agency to determine 

whether alkyl imidazoline use has “no effect” or “may affect” federally listed threatened 

or endangered species (listed species) or their designated 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 9 of 15

Environmental Fate and Ecotoxicity Data Gaps and Anticipated Work

Environmental fate and ecological risk assessments have not been conducted for 

1-(2-hydroxyethyl)-2-alkyl*-2-imidazoline (*as in fatty acids of tall oil). The Agency 

needs to conduct environmental fate and ecological risk assessments for alkyl 

imidazoline’s (*as in fatty acids of tall oil) fuel oil treatment use pattern listed in this 

document. Therefore, the Agency anticipates needing the proposed environmental fate 

and ecotoxicity data for alkyl imidazoline and/or any of its major degradation products 

that are of potential concern for all registered uses of alkyl imidazoline. 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 fuel oil treatment uses:

o (GLN 835.2120) Hydrolysis;

o (GLN 835.2240) Photodegradation in water

o (GLN 850.6800) Modified Activated Sludge Respiration Inhibition;

o (GLN 835.3110) Ready biodegradability, (GLN 835.3220) Porous Pot 

Test, or (GLN 835.3280) Simulation Tests to Assess the Biodegradability 

of Chemicals Discharged to Wastewater4

.

• The Agency anticipates needing the following ecotoxicity data in order to 

conduct a complete ecological risk assessment, including an endangered 

species assessment:

o (GLN 850.2100) Acute Avian Oral Toxicity;

o (GLN 850.1010) Acute Freshwater Invertebrates Toxicity;

o (GLN 850.1075) Acute Freshwater Fish Toxicity; and

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

Selenastrum capricornutum.

 4 The results of the Activated Sludge Respiration Inhibition Test (ASRI) determine which of these 

biodegradation tests are required. If the ASRI test EC50 is less than or equal to 20 mg/L, then either the 

Biodegradation in Activated Sludge Study or the Porous Pot Test is required. If the ASRI test EC50 is 

greater than 20 mg/L, then the applicant must choose either: (i) Ready Biodegradability or (ii) 

Biodegradation in Activated Sludge or the Porous Pot Test. If the antimicrobial passes the ready 

biodegradability study, then no further testing is required. If, however, the antimicrobial fails the ready 

biodegradability study, then the Biodegradation in Activated Sludge or the Porous Pot study is required.
Page 10 of 15

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 alkyl imidazoline and/or the formation and decline 

of degradates is important in determining the persistence and concentrations of alkyl imidazoline and 

potential degradates over time in various aquatic environments. Alkyl imidazoline can reach surface water 

through direct contact or discharge to WWTPs. Alkyl imidazoline 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 alkyl imidazoline 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 alkyl imidazoline 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 fuel oil treatment uses for alkyl 

imidazoline.

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 alkyl imidazoline 

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 alkyl imidazoline 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 alkyl imidazoline is persistent or if it degrades into 

degradation products that may adversely affect nontarget organisms and may contaminate their food. 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 11 of 15

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 alkyl imidazoline.

Guideline Number: 850.6800; OECD 209

Study Title: Modified Activated Sludge, Respiration Inhibition Test for Sparingly Soluble 

Chemicals; Activated Sludge Respiration Inhibition Test

Rationale for Requiring the Data

An activated sludge, respiration inhibition test (ASRI) is needed to identify whether this pesticide could 

harm activated sludge microorganisms found in biological wastewater treatment systems. The Agency 

will use these data to determine the potential impact of this chemical on waste water treatment plants 

(WWTPs) as a result of respiration inhibition of activated sludge microorganisms. This test is also 

necessary to enable EPA to establish correct concentrations for use in the biodegradability test, if that 

test is determined to be adequate for assessing biodegradation potential. Furthermore, the results of the 

Activated Sludge Respiration Inhibition Test (ASRI) determine which biodegradation test is required. If 

the ASRI test EC50 is less than or equal to 20 mg/L, then either the Biodegradation in Activated Sludge 

Study or the Porous Pot Test is required. If the ASRI test EC50 is greater than 20 mg/L, then the applicant 

must choose either: (i) Ready Biodegradability or (ii) Biodegradation in Activated Sludge or the Porous Pot 

Test. If the antimicrobial passes the ready biodegradability study, then no further testing is required. If, 

however, the antimicrobial fails the ready biodegradability study, then the Biodegradation in Activated 

Sludge or the Porous Pot study is required.

Practical Utility of the Data

1. How will the data be used?

The data will be used to assess potential adverse effects to activated sludge microorganisms. In addition, 

the data will be used to determine whether or not label restrictions are needed. The study will identify the 

inhibitory effect of this chemical on the treatment plant’s microorganisms’ respiration at different 

concentrations of the test substance and will identify the EC50, the effective concentration of the test 

substance at which the respiration rate is 50% of that shown by the control under conditions in this 

guideline. 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 indicate a high degree of activated sludge respiration inhibition, a more rigorous test for 

biodegradation in wastewater treatment will be required than the ready biodegradability test. Also, if a 

high degree of respiration inhibition is demonstrated and biodegradation and/or sorption is indicated to be 

negligible, the Agency may require label restrictions or mitigation measures to insure that activated sludge 

microorganisms will not be adversely impacted.
Page 12 of 15

Guideline Numbers: 835.3110, 835.3220, or 835.3280

Study Titles: Ready Biodegradability, Porous Pot Test, or Simulation Tests to Assess the 

Biodegradability of Chemicals Discharged to Wastewater (also referred to as Biodegradation in 

Activated Sludge), respectively

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 results supply

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

and water. A ready biodegradability study would allow the Agency to determine whether or not the 

chemical achieves ‘‘pass levels’’ for ready biodegradability (e.g., 70% removal of dissolved organic 

carbon). The results of the Activated Sludge Respiration Inhibition Test (ASRI) determine which of these 

three biodegradation tests are required. If the ASRI test EC50 is less than or equal to 20 mg/L, then either 

the Biodegradation in Activated Sludge Study or the Porous Pot Test is required. If the ASRI test EC50 is 

greater than 20 mg/L, then the applicant must choose either: (i) Ready Biodegradability or (ii) 

Biodegradation in Activated Sludge or the Porous Pot Test. If the antimicrobial passes the ready 

biodegradability study, then no further testing is required. If, however, the antimicrobial fails the ready 

biodegradability study, then the Biodegradation in Activated Sludge or the Porous Pot study is required.

Practical Utility of the Data

1. How will the data be used?

The data from a biodegradation study will be used to determine the percent removal of the antimicrobial as 

a result of biodegradation of the antimicrobial by activated sludge microorganisms. Percent removal via 

biodegradation is a key input used to determine concentrations of the antimicrobial in surface water 

immediately downstream of wastewater treatment plants. The concentrations of antimicrobial pesticide 

immediately downstream of wastewater treatment plants are 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 activated sludge microorganisms would be 

identified as highly biodegradable (90% removal via biodegradation). This result would be used in 

conjunction with wastewater treatment plant influent volume and measurement endpoints for aquatic 

organisms to determine concentrations of antimicrobial pesticide downstream of wastewater treatment 

plants. If high inhibition of activated sludge microorganisms (i.e., EC50 less than or equal to 20 mg/L) is 

determined in an activated sludge respiration inhibition test, then higher-tiered wastewater treatment plant 

(WWTP) biodegradation studies and/or an activated sludge sorption isotherm study may be triggered. If 

results of higher-tier WWTP biodegradation tests indicate low or negligible removal by biodegradation, the 

risk assessments for this chemical would 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).
Page 13 of 15

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.

Appendix B: Ecological Guideline Study Justifications

Guideline Number: 850.2100

Study Title: Acute avian oral toxicity

Practical Utility of the Data

1) What is the value of the study?

The Agency currently does not have any acceptable acute avian oral toxicity data for alkyl imidazoline. 

This study would allow the Agency to categorize alkyl imidazoline as toxic or non-toxic to birds. If the 

avian acute oral LD50 (TGAI testing) is less than or equal to 100 mg a.i./kg, additional higher tier bird test 

would be needed.

2) How would the data be used?

This study would be used to evaluate the toxicity of alkyl imidazoline to non-target birds in terrestrial and 

aquatic ecosystems.

3) How could the data affect the risk assessment? 

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

species at risk.

4) What is triggering the need for this data?

Acute avian oral toxicity study is required to establish the toxicity of a pesticide to birds.

Guideline Number: 850.1075 

Study Title: Acute Freshwater Fish Study (2 species) 

Guideline Number: 850.1010 

Study Title: Acute Toxicity Freshwater Invertebrates Study

Practical Utility of the Data

1) What is the value of the study?

Invertebrates serve as food for fish, birds, and crustaceans. The protection of non-target invertebrates is 

essential to the food chain in any healthy ecosystem. Sport fishing and commercial fishing have a 

high impact on the United States economy. The acute toxicity tests are designed to measure 

mortality during short term (48 hours for Daphnids and 96 hours for fish) aquatic exposure to a 

range of concentrations of the pesticide in water.

2) How would the data be used?

The data would allow the Agency to determine acute risk to freshwater fish and invertebrates from water 

column exposure to alkyl imidazoline. The effects data would be used to determine the likelihood that 
Page 14 of 15

Guideline Number: 850.1075 

Study Title: Acute Freshwater Fish Study (2 species) 

Guideline Number: 850.1010 

Study Title: Acute Toxicity Freshwater Invertebrates Study

Practical Utility of the Data

the acute risks can potentially impact aquatic communities, either by direct effects on fish and 

invertebrates or by indirect effects on other organisms by reducing their food sources. Also, by refining 

the assessment, the Agency would be able to determine whether the mitigation imposed as part of the 

registration review process was appropriate for alkyl imidazoline. 

If future endangered species risk assessments are performed without these data, the Agency would have 

to assume that alkyl imidazoline "may affect" endangered species directly or indirectly, and use of alkyl 

imidazoline might need to be restricted in areas where endangered species could be exposed. The lack 

of these data will limit the flexibility the Agency and registrants have in coming into compliance with 

the Endangered Species Act and could result in use restrictions for alkyl imidazoline which are 

unnecessarily severe.

Acute freshwater invertebrate and fish toxicity data would be used to describe the concentrationresponse curves and determine 48-h and 96-h LC50’s (concentrations calculated to kill 50% of the 

population) along with 95% confidence intervals. Additionally, a NOEC for 48 and 96 h are reported.

3) How could the data affect the risk assessment?

There are many freshwater invertebrates and fish species that are listed as threatened and 

endangered in the United States. Daphnia magna is considered as a surrogate species to represent all 

freshwater invertebrates in the risk assessment process. Oncorhynchus mykiss (Rainbow trout) and 

Lepomis macrochirus (bluegill sunfish) are considered surrogate species to represent all freshwater 

fish species in the risk assessment process. As part of the acute risk assessment for aquatic 

animals, the lowest EC50 or LC50 for freshwater invertebrates and fish are used in the RQ equation. 

An acute RQ > 0.5 would indicate an acute LOC, defined as the potential for acute risk to nontarget organisms which may warrant regulatory action in addition to restricted use classification. 

An acute RQ > 0.1 would result in an acute restricted use LOC, defined as the potential for acute 

risk to non-target organisms, which may be mitigated through restricted use classification. An 

acute RQ > 0.05 would fall under the LOC for acute endangered species.

4) What is triggering the need for this data?

Data are needed in order to conduct an ecological risk assessment for the use of alkyl imidazoline as a 

microbiocide/microbiostat in fuel oil storage tanks and determine the acute toxicity of alkyl imidazoline 

to freshwater fish and invertebrates using acute toxicity studies.

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 alkyl imidazoline 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?
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Guideline Number: 850.5400

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

Practical Utility of the Data

This study would be used to evaluate the toxicity of alkyl imidazoline 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.