Page 2 of 27

Executive Summary

Sodium is a broad spectrum antimicrobial compound. Sodium omadine is registered for 

use as a material preservative in metalworking cutting fluids, adhesives, caulks, paints (in-can), 

janitorial products (in-container), and hides/leather /leather products (surfaces). Sodium 

omadine was first registered in the United States in 1968 for use as a material preservative. A 

Reregistration Eligibility Decision (RED) was issued by EPA for sodium omadine in January 

1996. Currently there are six companies that have twelve active registrations. One of these 

products is registered as a technical with an active ingredient declaration of 40%, and one is 

registered as an intermediate manufacturing use product with active ingredient declarations of 

41.57%. The remaining ten products are end-use products with active ingredient declarations of 

1.2 to 41%; these products consist of soluble ready-to-use solutions and a flowable soluble 

concentrate. All product chemistry data requirements have been satisfied for this active 

ingredient.

At the time of the RED, risk assessments were not conducted for industrial microbiocides 

unless products had a once-through cooling water system use. To regulate these industrial 

microbiocide uses and associated risks to the aquatic environment, the Agency required that 

labels for sodium omadine products that require discharges to aquatic environments comply with 

a National Pollutant Discharge Elimination System (NPDES) permit. As part of the registration 

review process, risk assessments for material preservatives such as the metalworking cutting 

fluids will be conducted. 

To conduct these assessments, the Agency data base for evaluating the environmental 

fate and transport of sodium omadine is incomplete. Because of the down drain antimicrobial 

uses, the Agency anticipates needing activated sludge sorption isotherm, activated sludge 

respiration inhibition, one of four waste biodegradability tests (ready biodegradability, porous 

pot test, or one of two simulation tests) for material preservatives that potentially pass through 

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

environments. Additionally, an aquatic photolysis study is needed. Based on environmental fate 

information currently inhouse, sodium omadine is essentially stable with half-life of at least 23 

days, but no acceptable photolysis in water data has been submitted. 

Sodium omadine is moderately toxic to avian species on an acute oral basis and slightly 

toxic to avian species on a subacute dietary basis; slightly toxic to mammals on an acute oral 

basis; and very highly toxic to freshwater fish and aquatic invertebrates. For the ecological risk 

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

needing algal toxicity data, a freshwater fish early life stage study, an invertebrate life cycle 

study, and a resubmittal of a rainbow trout acute toxicity study. From the information available

coldwater rainbow trout are more acutely sensitive to sodium omadine than bluegill sunfish, but 

the degree is unknown because the study did not provide a definitive LC50 value for the rainbow 

trout (i.e, 96-h LC50 < 7.3 ppb sodium omadine). To conduct a quantitative risk assessment a 

definitive acute toxicity value for this more sensitive species is needed.
Page 3 of 27

Introduction

Sodium omadine was first registered in the United States in 1968 for use as a material

preservative. Twelve products containing sodium omadine are currently registered which are 

listed in Table 1. They are used in metalworking cutting fluids, cooling and lubricating fluids, 

adhesives, caulks, patching compounds, sealants, pastes and grouts, paints (in-can), inks, 

sponges, janitorial products (in-container), hides/leather /leather products (surfaces), aqueous 

analytical and diagnostic reagents used in chemical and clinical analysis, aqueous synthetic fiber 

lubricating (spin finishes), carrageenan based gels used in solid air fresheners, dry wall and 

gypsum, pearlite, plaster-like, mineral used in manufacture of tile, chrome or vegetable tanned 

leather, for the dry film preservation of natural, and synthetic adhesives, latexes, urethane foams, 

caulks, patching compounds, sealants, architectural paints, industrial paints and coatings 

(including wood coatings), glues, in-can preservation of latex emulsions used in adhesives,

laundry rinse additives, laundry detergents, carpet cleaners, surface cleaners, floor cleaners,

pigment slurries, building materials such as joint cements and concrete additives, materials in the 

textile, paper, polishes waxes, protein solutions, ceramic glazes, fire extinguishing materials, 

cleaning solutions and detergents as a materials preservative. A Reregistration Eligibility 

Decision (RED) was issued by EPA for sodium omadine in January 19961

.

Table 1. Registered Products of Sodium omadine

Registration

#

Registration

Name

Company

Name

Formulation

Type

% of Active 

Ingredient

1258-843 Sodium Omadine 40% 

Aqueous Solution Arch Chemicals, Inc. Ready-to-Use Solution 40

1258-990 Triadine 10 Arch Chemicals, Inc. Ready-to-Use 

Solution 6.56

1258-1205 Triadine 20 Industrial 

Microbiostat Arch Chemicals, Inc. Ready-to-Use Solution 3.69

1258-1213 Sodium Omadine 10% 

Aqueous Solution Arch Chemicals, Inc. Ready-to-Use Solution 10

1258-1238 Sodium Omadine-E 10% 

Aqueous Solution Arch Chemicals, Inc. Soluble Concentrate 10

10350-56 Sodium Pyrithione 3M Soluble 

Concentrate 41

39967-26 Preventol WB Plus Lanxess Corporation Soluble 

Concentrate 1.2

43813-48 Sodium Pyrion 40% 

Aqueous Solution Janssen PMP Soluble Concentrate 40

43813-49 Sodium Pyrion 40% MP Janssen PMP Technical 

Chemical 40

 1

http://www.epa.gov/oppsrrd1/REDs/0209.pdf
Page 4 of 27

Registration

#

Registration

Name

Company

Name

Formulation

Type

% of Active 

Ingredient

63898-2 Tomicide S API Corporation Soluble 

Concentrate 41

87772-1 Phicide Sodium 

Manufacturing Concentrate Dublinchem, Inc Formulation Intermediate 41.57

87772-2

Phicide Sodium (Sodium 

Pyrithione 41% Aqueous 

Solution) 

Dublinchem, Inc

Soluble 

Concentrate 41

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

fate, and ecotoxicity data for sodium omadine. The primary source of information for this 

assessment was the 1996 Sodium omadine RED. The findings are summarized below.

The physical and chemical properties of the 90% TGAI and 40% TGAI Sodium omadine

are shown below

A. Product Chemistry Summary of the Sodium omadine (Min. 90% TGAI Solid)

Common Name: Sodium omadine

Sodium pyrithione

Chemical Name: Sodium omadine exists as a mixture of two

tautomeric forms:

1-hydroxy-2(1H)- pyridinethione, sodium salt and

2-pyridinethio-1-oxide, sodium salt.

2-(1H)-Pyridinethione, 1-hydroxy-, sodium salt

2-Mercaptopyridine-N-oxide sodium salt

Trade and Other Names: Omadine ® sodium,

sodium 2-pyridinethiol 1-oxide,

sodium 1-hydroxypyridine-2-thione,

sodium 2-mercaptopyridine-N-oxide

OPP Chemical Code: 088004

CAS Registry Number: 15922-78-8

Case No.: 0209

Chemical Family: Mercaptan 

Pyridine
Page 5 of 27

Molecular Formula: C5H4NOSNa; C5H5NOS.Na

Molecular weight: 149.16 g/mole

Molecular Structure:

Color: Technical sodium omadine is an off-white solid powder.

Physical State: Solid, powder

Odor: None to Mild odor.

Stability: Sodium omadine is stable at 100°C for 120 hours, and at 

pH's above 7 but is in equilibrium with omadine acid below 

pH 7. The recommended pH range is 7-12. 

Will gradually degrade when exposed to light and should 

be packaged in brown or opaque container.

Oxidation/Reduction: Not an oxidizer or reducing agent. Do not contain oxidizing 

or reducing agents.

Flammability Not required because the product does not contain 

combustible liquids.

Explodability: Not explosive. Contains no explosive ingredients.

Storage Stability: Stable: 3 month sample shows no degradation.

Accelerated storage stability (thermal stability) shows no 

degradation.

Stability: Its assay will remain unchanged after 2 years' 

storage while avoiding light.
Page 6 of 27

97% Powder pH 7.14: The results revealed that there were 

no significant changes in the physical and chemical 

properties viz, appearance (color, physical state, odor), pH 

and active ingredient of the test substance after the 

accelerated storage for a period of 14 days at 54 ± 2°C.

Miscibility: Not required because the product is not an emulsifiable 

liquid and is not to be diluted with petroleum solvents.

Corrosion Characteristics: Not corrosive to packaging material. No corrosion of 

metals.

Dielectric breakdown voltage: Not applicable for products not intended to be used around 

electrical equipment.

pH: 10% in water 9.4 – 9.8;

2% in water: 8.7;

The mean pH of sodium pyrithione solid 97% was

7.11 ± 0.03 at 21.1 °C.

UV/Visible absorption: The UV-Visible absorption spectra of sodium pyrithione 

solid 97% were determined at three different pH levels 

[viz., pH-7.15 (neutral solution), pH - 1.97 (acidic solution)

and pH 12.86 (basic solution)].

The UV absorbance was 0.255, 0.688 and 1.350 at 

wavelength 331.0, 281.0, and 243.0 nm respectively for 

neutral solution and the molar absorption coefficient (ε) 

was 3990.61, 10766.82 and 21126 76, respectively.

The UV absorbance was 0.287, 0.587 and 0.733 at 

wavelength 331.0, 271.0 and 218.0 nm respectively for 

acidic solution and the molar absorption coefficient (ε) 

4681.89, 9575.86 and 11957.59, respectively.

The UV absorbance was 0.229, 0.683 and 1.444 at

wavelength 332.0, 282.0 and 243.0 nm, respectively for 

basic solution and the molar absorption coefficient (ε) was 

3735.73, 11141.92 and 23556.28, respectively.

Viscosity: Not applicable for solid products.

Melting point: 252-257°C, Decomposes.

Boiling Point: Not applicable for solids.

Density: Bulk Density: 0.5 g/ml
Page 7 of 27

The mean density of sodium pynthione solid 97% was 

0.7043 ± 0.0013 g/cm3 at 20 ± 1 °C.

Dissociation Constant (pKa):The mean dissociation constant of sodium pyrithione solid 

97% was 5.61 ± 0.21 at 20°C.

Particle Size: 65 to less than 25 μ (90% Na omadine).

Log Ko/w: Not applicable.

-2.72 (Source: EPI Suite).

Solubilities: The average value was 54.74 w/w % which is equivalent to 

120.95 g per 100 ml of H2O.

The solubility of sodium pyrithione solid 97% in buffer 

water (pH 5.01) was> 1000 g/L at 20 ± 1 °C.

The solubility of sodium pyrithione solid 97% in buffer 

water (pH 7.03) was> 1000 g/L. at 20 ± 1 °C.

The solubility of sodium pyrithione solid 97% in buffer 

water (pH 9.05) was> 1000 g/L at 20 ± 1 °C.

Vapor Pressure: 7 x 10-8 mm Hg at 22°C.

2.23 x 10-10 mm Hg (Source: EPI Suite).

Henry's Law Constant: 2.47E-008 atm-m3

/mole at 25°C (Source: EPI Suite).

Enforcement Analytical

Method: Iodometric determination

Ultravoilet Determination

Titrimetric Method

Amperometric Titration

Product Chemistry Summary of Sodium omadine (40% of TGAI Solution)

Color: Clear amber; dark or light yellow or amber transparent 

liquid.

Physical State: Clear liquid.

Odor: None to Mild odor.

Stability: Stable under normal conditions.

Sodium omadine is unaffected by pH values above 7. 

Below 7, it is in equilibrium with omadine acid.
Page 8 of 27

Will gradually degrade when exposed to light and should 

be packaged in brown or opaque container.

Oxidation/Reduction: Not an oxidizer or reducing agent. Do not contain oxidizing 

or reducing agents.

No temperature change was recorded during 24 hours and 

no corrosion or pitting was detected.

Flammability Not required because the product does not contain 

combustible liquids.

Explodability: Not explosive. Contains no explosive ingredients.

Storage Stability: There were no significant chemical changes in any of the 

samples over the period of the study of 12 months. There 

were no visible changes in the appearance of the products 

over the period of the study.

Miscibility: Not required because the product is not an emulsifiable 

liquid and is not to be diluted with petroleum solvents.

Corrosion Characteristics: Not corrosive to packaging material. No corrosion of 

metals.

There was no evidence of corrosion to any of the 

containers. The sodium omadine 40% solution remained a 

clear, amber-colored liquid in all containers.

Dielectric breakdown voltage: Not applicable for products not intended to be used around 

electrical equipment.

pH: 8.5-10.5 or 9.8.

UV/Visible absorption: The UV-Visible absorption spectra of sodium pyrithione 

solid 97% were determined at three different pH levels 

[viz., pH-7.15 (neutral solution), pH - 1.97 (acidic solution) 

and pH 12.86 (basic solution)].

The UV absorbance was 0.255, 0.688 and 1.350 at 

wavelength 331.0, 281.0, and 243.0 nm respectively for 

neutral solution and the molar absorption coefficient (ε) 

was 3990.61, 10766.82 and 21126 76, respectively.

The UV absorbance was 0.287, 0.587 and 0.733 at 

wavelength 331.0, 271.0 and 218.0 nm respectively for 
Page 9 of 27

acidic solution and the molar absorption coefficient (ε) 

4681.89, 9575.86 and 11957.59, respectively.

The UV absorbance was 0.229, 0.683 and 1.444 at 

wavelength 332.0, 282.0 and 243.0 nm, respectively for 

basic solution and the molar absorption coefficient (ε) was 

3735.73, 11141.92 and 23556.28, respectively.

Viscosity: The viscosity of the five batches ranged from 9.94 to 11.89 

cps. The average value was 10.98 cps.

Melting point: Not applicable.

Boiling Point: 105oC – 109oC.

Density: 10.2 lb/gal;

Sp. Gr. at 25oC 1.22 (1.19-1.26 g/ml).

Dissociation Constant (pKa): 4.56 + 0.01 at 21.9°C.

Log Ko/w: Not applicable.

Solubilities: Soluble.

Vapor Pressure: 19 mm Hg @ 25 °C.

Enforcement Analytical

Method: Iodometric determination

Ultravoilet Determination

Titrimetric Method

Amperometric Titration

All product chemistry data requirements have been satisfied for the active 

ingredient sodium omadine (Source: MRIDs 00159036, 00159037, 00159038, 00159039, 

40170101, 40974101, and 41189901; 471266-4, -5, -6, -9, -10, -12, -14, -15, -16, 

448431-01 & 449976-01).
Page 10 of 27

B. Environmental Fate Summary

No environmental fate assessment was performed for sodium omadine at the time of the 

registration. Available environmental fate guideline studies and the results are summarized 

below.

The Agency's conclusions for the degradation, studies are as follows.

In the hydrolysis study, measurements at each combination of concentration (10 mg/l or 

100 mg/l), temperature (5 °C or 40 °C), and pH (4, 7, or 10), indicate that a half-life of 23 days 

was obtained at 40 °C, pH 10, and 10 mg/l concentration. At other levels of concentration, 

temperature, and pH, sodium omadine hydrolyzed more slowly, or was stable to hydrolysis. 

Hydrolytic products were more readily formed at an alkaline pH than at neutral and acidic pH. It 

has been hypothesized that omadine disulfide is formed by oxidation at all pH's, and at alkaline 

conditions omadine disulfide reacts with hydroxide ions to form omadine sulfinic acid (MRID 

40383001).

There is no record of receipt of acceptable data on photodegradation in water, and the 

registrant should submit these data to support the continued use of this product. However, the 

RED dated January 1996 concluded that photolysis is probably a more important route of 

dissipation than hydrolysis, based on photolytic half-lives of 40-126 minutes at a concentration 

of 100 mg/l and irradiation by natural sunlight. Raw data were allegedly provided to the Agency 

by Olin Corporation, but the methodology was not documented in sufficient detail and decline of 

specific degradates was not addressed. Therefore, an additional study will need to be submitted.

The Agency did not conduct an environmental fate assessment for sodium omadine 

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

assessment for material preservatives (including sodium omadine) 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 15 of this document.

Information and data from other omadine (pyrithione) complexes will also be used to 

provide a complete characterization of the fate of sodium omadine in the environment. Sodium 

omadine would dissociate into sodium and omadine ions. The omadine ions would be expected 

to possible form metal complexes like zinc and copper omadine (also referred to as zinc or 

copper pyrthione). Degradates that are expected are those common to zinc and copper 

pyrthiones which are non-chelated pyrithione and pyridine degradates:

• Pyrithione disulfide

• Pyrithione sulfinic acid

• Pyrithione sulfonic acid

• Pyrithione thiosulfonic acid

• Pyridine disulfide

• Pyridine sulfinic acid

• Pyridine sulfonic acid

• 2-mercaptopyridine/2-mercaptopyrine-N-oxide (mixed disulfides)
Page 11 of 27

Water Quality

Sodium omadine 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 sodium omadine,

based on information provided at the Agency’s National Pesticide TMDL web site (searched 

April 7, 2011)3

. 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.

C. Ecological Effects Summary

No ecological risk assessment was performed for sodium omadine at the time of the 

registration. Available ecotoxicity guideline studies for sodium omadine and the results are 

summarized in Table 2. Potential data which may be used in the assessment includes 

information from metal omadine complexes and degradates; these data are summarized in Tables 

3 and 4, respectively. Before use in the assessment this information will be normalized to the 

number of moles of omadine present. For evaluating effects to the estuarine environment, the 

metal complex data will be used to estimate toxicity from discharge of sodium omadine. The 

Agency's conclusions for the terrestrial and aquatic effects studies for sodium omadine are as 

follows.

a. Toxicity to Terrestrial Animals

Birds, Acute and Subacute

Sodium omadine is moderately toxic to avian species on an acute oral basis and 

slightly toxic to avian species on subacute dietary basis.

b. Toxicity to Mammals

Acute Oral: Sodium omadine is slightly toxic to mammals on an acute oral basis.

2-generation rat reproduction study: Slightly decreased number of pups per litter 

born in both generations (possibly a consequence of reduced mating success due 

to hind limb atrophy), delayed development in pups from both generations 

 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_pollutant_

group_name=PESTICIDES
Page 12 of 27

(including open ears and eyes and startle response), and decreased pup body 

weight and weight gain in both sexes.

c. Toxicity to Aquatic Animals

Freshwater Fish and Invertebrates

Sodium omadine was found to be very highly toxic to rainbow trout, bluegill 

sunfish and daphnia. From the information available coldwater rainbow trout are 

more acutely sensitive to sodium omadine than bluegill sunfish and daphnia, but 

the degree is unknown because the study did not provide a definitive LC50 value 

for the rainbow trout (i.e, 96-h LC50 < 7.3 ppb sodium omadine).

d. 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 13 of this document.

Table 2. Ecotoxicity Data Summary for Sodium omadine

MRID

No.

GUIDE 

LINE

COMMON 

NAME

TAXONOMIC 

NAME

TEST 

TYPE

%

AI

STUDY 

TIME DOSE TYPE TOXICITY TOX LEVEL NOEL STUDY 

STATUS

TOX 

CATEGORY

00103228 850.1010

(72-2)

Water flea Daphnia

magna

S 40.0 48 hr EC50 0.022

(9.2 μg ai/l)

ppm 0.011 Acceptable Very highly 

toxic

40494501

Lot No. 

F113C

850.1075

(72-1d)

Rainbow 

trout

Oncorhynchus 

mykiss

S 41.9 96 hr LC50 <0.076

(< 7.3μg

ai/l)

ppm N.R. Supplemental Very highly 

toxic

40358501 850.1075

(72-1b)

Bluegill 

sunfish

Lepomis 

macrochirus

S 41.9 96 hr LC50 8.1

(8100 μg

ai/l)

ppm 0.89 Acceptable Very highly 

toxic

40363401 850.2100

(71-1)

Bobwhite 

quail

Colinus

virginianus

O 41.9 14 D LD50 441

(185 mg/kg 

ai)

mg/kgbw<150 Acceptable Moderately

toxic

00073656 850.2200

(71-2a)

Bobwhite 

quail

Colinus

virginianus

D 40.0 8 D LC50 3246

(1300 mg ai/l)

ppmdiet1000 Acceptable Slightly toxic

00073657 850.2200

(71-2b)

Mallard

duck

Anas

platyrhynchos

D 40.0 8 D LC50 9119

(3650 mg ai/l)

ppmdiet1000 Acceptable Slightly toxic

40247801 81-1 Rat --------- ----- 40.0 ----- LD50 1500 (M+F) mg/kgbw------ Acceptable III

Slightly toxic
Page 13 of 27

MRID

No.

GUIDE 

LINE

COMMON 

NAME

TAXONOMIC 

NAME

TEST 

TYPE

%

AI

STUDY 

TIME DOSE TYPE TOXICITY TOX LEVEL NOEL STUDY 

STATUS

TOX 

CATEGORY

41097201 83-4 Rat -------- ----- 40.2 ----- Parental 

LOEL

Reproductive 

LEL

1.5

3.5

mg/kgbw/day

mg/kgbw/day

0.5

1.5

Acceptable

Based on increased incidence of 

histologic atrophy in the upper 

hindlimb skeletal muscles 

(reduction in fiber diameter) in 

F1 females (3/25), F0 males 

(7/23), and F1 males (9/25). 

Additional parental effects seen 

at 3.5 mg/kg/day included 

increased histologic atrophy in 

the upper hindlimb skeletal 

muscles in F0 females (19/24), 

and F1 females (20/23); and 

significantly decreased body 

weight in F0 and F1 females.

Based on slightly decreased 

number of pups per litter born 

in both generations (possibly a 

consequence of reduced mating 

success due to hind limb 

atrophy), delayed development 

in pups from both generations 

(including open ears and eyes 

and startle response), and 

decreased pup body weight and 

weight gain in both sexes.

Test Type—O: oral; D: dietary; F: flow-through; S: Static; 

Tox Level—mg/kg-bw: milligrams per kilogram-body weight; 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)

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.

Table 3. Aquatic Ecotoxicity Data Summary for Zinc and Copper Omadine

Test

Species

Test material

(% ai)

96-h LC50

(μg ai/L)

(95% CI)

Toxicity

Category

MRID No./

Study Status

Rainbow trout zinc pyrithione 

(97.8)

3.6

(3.0-4.3)

very highly

toxic

438646-13/

Acceptable

Fathead minnow zinc pyrithione 

(97.8)

2.6

(2.1-3.2)

very highly

toxic

438646-06/

Acceptable

copper pyrithione 

(94.7)

4.3

(3.7-5.0)

very highly

toxic

457743-18/

Acceptable

Waterflea copper pyrithione 

(94.7)

10.1

(7.9-13)

very highly toxic 457743-16/

Acceptable

zinc pyrithione 

(97.8)

8.2

(5.2-25.8)

very highly toxic 438646-04/

Acceptable
Page 14 of 27

Sheepshead

minnow

zinc pyrithione 

(97.8)

400

(200-590)

highly toxic 438646-05/

Acceptable

Mysid shrimp zinc pyrithione 

(97.8)

4.7

(4.0-5.5)

very highly

toxic

438646-07/

Acceptable

Eastern oyster copper pyrithione

(94.7)

9.2

(0-∞)

very highly

toxic

457743-17/

Acceptable

zinc pyrithione 

(97.8)

22.0

(18.9-27.3)

very highly

toxic

438646-08/

Acceptable

Table 4. Acute Toxicity of Two Pyrithione Degradates to Fish and Aquatic Invertebrates 

Exposed in the Water Column

Test

Species

Test material

(% a.i.)

96-h LC50

(μg a.i./L)

(95% CI)

Toxicity

Category

MRID No./

Study Status

Rainbow

trout

pyridine sulfonic acid (98) 57,100

(48,300-69,800)

slightly toxic 438646-27/

Acceptable

pyrithione sulfonic acid 

(98.5)

92,300

(73,600-124,000)

slightly toxic 438646-16/

Acceptable

pyridine sulfonic acid (98) 68,500

(55,200-85,000)

slightly toxic 438646-21/

Acceptable

pyrithione sulfonic acid 

(98.5)

58,800

(48,700-71,000)

slightly toxic 438646-18/

Acceptable

Waterflea pyridine sulfonic acid (98) >122,000 practically 

nontoxic

438646-22/

Acceptable

pyrithione sulfonic acid 

(98.5)

>127,000 practically 

nontoxic

438646-19/

Acceptable

Sheepshead 

minnow

pyridine sulfonic acid (98) >127,000 practically 

nontoxic

438646-23/

Acceptable

pyrithione sulfonic acid 

(98.5)

>137,000 practically 

nontoxic

438646-17/

Acceptable

Mysid 

shrimp

pyridine sulfonic acid (98) 71,000

(62,800-81,100)

slightly toxic 438646-26/

Acceptable

pyrithione sulfonic acid 

(98.5)

70,300

(61,600-81,600)

slightly toxic 438646-20/

Acceptable
Page 15 of 27

Eastern 

oyster

pyridine sulfonic acid (98) 85.600

(73,300-102,500)

slightly toxic 438646-24/

Acceptable

pyrithione sulfonic acid 

(98.5)

96,200

(89,313-104,560)

slightly toxic 438646-15/

Acceptable

Adverse Ecological Incidents

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

(EIIS) regarding sodium omadine. 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 sodium omadine’s use patterns 

described in this document. Sodium omadine uses that have potential for environmental 

exposure are material preservatives discharges. The Agency needs to conduct environmental 

fate and ecological risk assessments for material preservatives 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 a rainbow trout acute toxicity study, algal toxicity 

data, a freshwater fish early life stage study, an invertebrate life cycle study outlined on page 16

of this document. 

The Agency has not conducted a risk assessment for sodium omadine that supports a 

complete endangered species effects determination. The ecological risk assessment planned 

during registration review will allow the Agency to determine whether sodium omadine’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.

Environmental Fate and Ecotoxicity Data Gaps and Anticipated Work

Environmental fate and ecological risk assessments have not been conducted for sodium 

omadine. The Agency needs to conduct environmental fate and ecological risk assessments for 

material preservatives that 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 sodium omadine and/or any of 

its major degradation products that are of potential concern for all registered uses of sodium 

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

environmental fate and ecological risk assessment:
Page 16 of 27

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

environmental fate assessment for material preservative uses:

o Activated Sludge Sorption Isotherm (GLN 835.1110);

o Photodegradation in water (GLN 835.2240); and

o Ready biodegradability (OCSPP 835.3110), Porous Pot Test (OCSPP 835.3220), 

or Simulation Tests to Assess the Biodegradability of Chemicals Discharged to 

Wastewater (OCSPP 835.3280), or Simulation Test – Aerobic Sewage Treatment: 

A. Activated Sludge Units (OCSPP 835.3240) 4

.

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

complete ecological risk assessment, including an endangered species assessment:

o Rainbow trout acute toxicity test (GLN 850.1075);

o Algal toxicity (Tier II) using freshwater green alga, Selenastrum capricornutum

(GLN 850.5400) (If the IC50 is equal to or less than 1000 ppb, data for three 

additional algal species and an aquatic non-vascular plant test would also be 

required);

o Freshwater invertebrate life cycle study (GLN 850.1300);

o Fish early life stage test with rainbow trout (the most sensitive fish species) (GLN 

850.1400);

o Activated Sludge Respiration Inhibition (GLN 850.6800 or OECD 209);

Facility Emissions to WWTP Modeling

For assessing the fate of sodium omadine and its major toxic degradates, emitted to 

receiving waters from antimicrobial uses of sodium omadine such as metalworking cutting 

fluids, photographic industry the Agency anticipates using the available environmental fate 

information from guideline studies for sodium omadine and information for other omadine 

complexes and the following emission scenarios.

• Potential environmental releases and associated exposures of concern for antimicrobial 

uses related to metalworking fuids will be those identified in "Emission Scenario 

Documents on the Use of Metalworking Fluids", Number 28 of OECD Series on 

Emission Scenario Documents dated July 6, 2011;

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

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

Biodegradation in Activated Sludge Study or (ii) Simulation Test – Aerobic Sewage Treatment: A. Activated Sludge 

Units or the (iii) 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 (iii) Simulation Test –

Aerobic Sewage Treatment: A. Activated Sludge Units or (iv) 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 (i) Biodegradation in Activated Sludge or (ii) Simulation Test – Aerobic Sewage 

Treatment A. Activated Sludge Units, or (iii) the Porous Pot study is required.
Page 17 of 27

• Potential environmental releases and associated exposures of concern for antimicrobial 

uses related to adhesive preservatives will be those identified in "Emission Scenario 

Document on Adhesive Formulation", Number 20 of OECD Series on Emission Scenario 

Documents dated April 24, 2009;

• Potential environmental releases and associated exposures of concern for antimicrobial 

uses related to paints and coating preservatives will be those identified in "Emission 

Scenario Document on Coating Industry (Paints, Laquers and Varnishes)", Number 22 of 

OECD Series on Emission Scenario Documents dated April 24, 2009;

• To estimate exposure related to releases of sodium omadine to domestic wastewater 

treatment plants from uses such as sodium omadine in detergents, laundry rinses, and 

cleaners the Agency will rely on the Office of Chemical Safety and Pollution Prevention 

(OCSPP) model, Exposure and Fate Assessment Screening Tool (E-FAST, version 2.0, 

2007, or EFAST2). From this model, the Agency will use the “Down-the-Drain” (DtD) 

module, which is designed to evaluate releases to domestic wastewater treatment plants. 

It is suitable for all the indoor sources of d-phenothrin that could potentially be exposed 

through a “down-the-drain” scenario. The model provides screening level estimate 

concentrations of chemicals in surface water that may result from household uses and the 

disposal of consumer products into wastewater using a few simple input parameters 

(production volume and fraction of the chemical removed during wastewater treatment).

Facility information needed to estimate aquatic exposures from emissions to WWTP 

for each emission scenario include the following:

• The number of metalworking fluid sites using sodium omadine or the maximum annual 

production volume of sodium omadine used for metalworking fluids in the United States 

and its territories;

• The number of adhesive industrial or manufacturing sites using sodium omadine or the 

maximum annual production volume of sodium omadine used in the adhesive 

formulation industry in the United States and its territories; 

• How many of each of these facilities has on-site and/or off-site wastewater treatment.

• The production volume used in detergents and cleaners.

In the absence of information on the number of these facilities that use sodium 

omadine and how many of these facilities have on-site and/or off-site wastewater treatment, the 

Agency will assume that all such facilities in the United States have the potential to use sodium 

omadine.

In the absence of appropriate test data on biodegradation during wastewater 

treatment, the Agency will assume that there is no removal of sodium omadine and its major 

toxic degradates during wastewater treatment and that the amount of sodium omadine and its 

major toxic degradates released with the effluent from a wastewater treatment facility will be the 

same as the amount entering the wastewater treatment facility.
Page 18 of 27
Page 19 of 27

Appendix A. Environmental Fate Guideline Study Justifications

Study Title: Activated Sludge Sorption Isotherm

Guideline Number: 835.1110

Test Substance: TGAI

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). No data is 

currently available. 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 non-target 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 removal of the antimicrobial as a result of sorption to activated sludge. 

Percent removal via sorption to activated sludge and percent removal via biodegradation are used to 

determine overall removal of the antimicrobial during wastewater treatment. Overall removal during 

wastewater treatment 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 nontarget 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 and that the chemical does not biodegrade to an appreciable extent then the chemical has 

the potential to pass through the WWTP and therefore could be discharged to the aquatic environment. 

This determination could trigger further data requirements to assess the chemical’s impact upon release. 

If the data indicates relatively high potential to sorb to sludge, a screening assessment of potential 

exposure to ecological organimsm as a result of biosolids use and disposal would be performed.

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

If the data show that removal of the chemical during wastewater treatment is negligible, then the risk 

assessments for this chemical would reflect the magnitude of potential risk derived from this chemical’s 

negligible removal. 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 
Page 20 of 27

could result in use restrictions which are unnecessarily severe. 

Study Title: Photodegradation in water

Guideline Number: 835.2240

Test Substance: TGAI

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 sodium omadine

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 sodium omadine 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 sodium omadine 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.

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 sodium omadine.
Page 21 of 27

Study Titles: Ready Biodegradability; Porous Pot Test; or Simulation Test – Aerobic Sewage 

Treatment: A. Activated Sludge Units; or Simulation Tests to Assess the Biodegradability of 

Chemicals Discharged to Wastewater (particularly Biodegradation in Activated Sludge)

Guideline Numbers: 835.3110; 835.3220; 835.3240; or 835.3280, respectively

Test Substance: TGAI

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. These 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 

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

the (i) Biodegradation in Activated Sludge Study or (ii) Simulation Test – Aerobic Sewage Treatment: A. 

Activated Sludge Units or the (iii) 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 (iii) Simulation Test – Aerobic Sewage Treatment: A. Activated Sludge Units or (iv) 

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 (i) 

Biodegradation in Activated Sludge or (ii) Simulation Test – Aerobic Sewage Treatment: A. Activated 

Sludge Units, or (iii) 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 nontarget 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, 
Page 22 of 27

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).

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 23 of 27

Appendix B: Ecological Guideline Study Justifications

Study Title: Fish acute toxicity test using rainbow trout, the most sensitive species

Guideline Number: 850.1075

Test Substance: TGAI

Rationale for Requiring the Data

The available study for this species indicates it is the more sensitive species tested, however, while the 

value itself is the lowest fish acute value it is a nondefinitive value (i.e., 96-hr LC50 <7.3 ppb). The use of 

the bluegill definitive value (8100 ppb) available to assess risk would underestimate acute toxicity. 

Alternatively, use of the existing rainbow trout data would also underestimate risk. Scientifically sound

freshwater fish data for sodium omadine is necessary because freshwater fish may be exposed based on 

the antimicrobial use patterns of sodium omadine. The requested data would allow EPA to soundly 

estimate risks to freshwater fish, including defining an action area for endangered species. Without these 

data, the Agency would use the supplemental data which would underestimate risk to an unknown 

degree.

Practical Utility of the Data

1. How will the data be used?

These data are needed for a registration review decision and for an endangered species assessment, which 

will be conducted as part of that decision. The freshwater fish acute study data would allow the Agency 

to analyze acute lethal effects to freshwater fish from acute exposures due to sodium omadine use. The 

effects data would be used to determine the likelihood that the acute risks can potentially impact aquatic 

communities, either by direct effects on fish or by indirect effects by reducing food resources to species 

that rely on fish as a food resource.

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

Risk estimates (i.e., risk quotients or concentration of concern values) cannot be evaluated without these 

data. In the absence of data, acute risks to freshwater fish would use the supplemental data but this 

would lead to an underestimation of risk, and the degree of underestimation would be unknown. The 

lack of these data will limit the flexibility the Agency and registrants have in addressing risks or having 

confidence in declaring no affects to non-listed and listed species and in coming into compliance with the 

Endangered Species Act, and could result in use restrictions or withdrawal of uses for sodium omadine

which may otherwise be avoided, or which are unnecessarily severe.

Study Title: Aquatic Invertebrate Life-Cycle (freshwater species)

Guideline Number: 850.1300

Test Substance: TGAI

Rationale for Requiring the Data

No chronic life cycle toxicity data for a freshwater invertebrate species has been submitted for sodium 

omadine. Chronic aquatic invertebrate data for sodium omadine is necessary because based on sodium 

omadine’s use pattern and fate information freshwater invertebrates may be repeatedly exposed to sodium 

omadine and its major degradates. The requested data would allow the Agency to estimate chronic risks to 

freshwater invertebrates from exposure to sodium omadine, including defining an action area for 

endangered species. Without these data, the Agency is unable to evaluate the potential chronic risks to 

freshwater invertebrates associated with chronic exposure to sodium omadine. The Agency would have to 

presume chronic risk to listed and non-listed freshwater invertebrates, but would not be able to quantify the 
Page 24 of 27

risk.

Practical Utility of the Data

1. How will the data be used? 

These data are needed for a registration review decision and for an endangered species assessment, which 

will be conducted as part of that decision. The aquatic invertebrate life-cycle study would allow the 

Agency to analyze chronic effects, including effects on reproductive success, survival and growth, to 

freshwater invertebrates due to exposure to sodium omadine. The effects data would be used to determine 

the likelihood that the chronic risks can potentially impact aquatic communities, either by direct effects on 

invertebrates or by indirect effects on fish by reducing their food sources. 

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

In the absence of data, chronic risks would be presumed to freshwater invertebrates under chronic exposure 

conditions. The lack of these data will limit the flexibility the Agency and registrants have in addressing 

risks to non-listed and listed species and in coming into compliance with the Endangered Species Act, and 

could result in use restrictions or withdrawal of uses for sodium omadine which may otherwise be avoided, 

or which are unnecessarily severe.

Study Title: Fish Early-life Stage Toxicity Test (freshwater species) using the most sensitive species 

Rainbow trout

Guideline Number: 850.1400

Test Substance: TGAI

Rationale for Requiring the Data

No fish early-life stage toxicity test for sodium omadine has been submitted. The fish early-life stage 

toxicity test provides the lethal and sublethal effects of a test substance on fish species. The study is 

necessary for sodium omadine because the antimicrobial use patterns and environmental fate 

characteristics are expected to result in repeated exposure of freshwater organisms. The requested data 

would allow the Agency to estimate chronic risks to freshwater fish from exposure to sodium omadine, 

including defining an action area for endangered species. Without these data, the Agency is unable to 

evaluate the potential risks to freshwater fish and aquatic-phase amphibians (for which fish serve as 

surrogates) associated with chronic exposure to sodium omadine. If the test is not conducted with the 

most acutely sensitive species, an acute toxicity test for the species used in the early life stage test needs 

to be conducted to allow calculation of an acute-to-chronic ratio for use in predicting an early life stage 

result for the most acutely sensitive species.

Practical Utility of the Data

1. How will the data be used? 

The data from the fish early life stage test will be used to estimate the chronic risks to freshwater fish and 

amphibians associated with chronic exposures to sodium omadine. The data will reduce uncertainties 

associated with potential risks to freshwater fish and amphibians thereby facilitating sound environmental 

management of natural resources, particularly, freshwater fisheries. 

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

In the absence of data, chronic risks would be presumed to freshwater fish/amphibians under chronic 

exposure conditions. The lack of these data will limit the flexibility the Agency and registrants have in 

addressing risks to non-listed and listed species and in coming into compliance with the Endangered 

Species Act, and could result in use restrictions or withdrawal of uses for sodium omadine which may 
Page 25 of 27

otherwise be avoided, or which are unnecessarily severe.

Guideline Number: 850.5400

Study Title: Algal toxicity (Tier II)

Test Species: green alga, Selenastrum capricornutum (if IC50 < 1000 ppb three additional 

species are required: one freshwater diatom species, one estuarine/marine species, and one 

cyanobacterium species)

Test substance: TGAI

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 sodium omadine as toxic or non-toxic to plants. If toxic (IC50, <

1000 ppb) additional species (one freshwater diatom species, one estuarine/marine species, and one 

cyanobacterium species) 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 sodium omadine 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.

Study Title: Aquatic plant growth, floating vascular species (Lemna sp.), Tier II

Guideline Number: 850.4400

Test Substance: TGAI

Rationale for Requiring the Data

No non-rooted vascular aquatic plant toxicity data has been submitted for sodium omadine. Based on its 

use patterns discharge of sodium omadine and its major degradates will be discharged to surface waters. 

If the algal toxicity study with Selenastrum capricornutum indicates that sodium omadine is toxic to 

aquatic plants data with a nonvascular aquatic plant is needed to characterize risk to higher tier plants. 

The requested data would allow the Agency to estimate risks to aquatic plants from exposure to sodium 

omadine, including defining an action area for endangered species. 

Practical Utility of the Data

1. How will the data be used?

These data are needed for a registration review decision and for an endangered species assessment, which 

will be conducted as part of that decision. Mats of floating non-rooted aquatic plants provide habitat for 

small invertebrates, food and shelter for fish and amphibians, and food for waterfowl and marsh birds. 
Page 26 of 27

The floating vascular aquatic plant study would allow the Agency to evaluate effects to a critical 

component of the structure and function of the aquatic plant community. A toxicity study on a non-rooted 

vascular aquatic plant species is used to establish a dose response relationship of sodium omadine with 

effects to non-rooted aquatic plants in terms of yield, growth rate, and area under the growth curve. The 

effects data would be used to determine the likelihood that losses to non-rooted aquatic vascular plants 

will occur and that such losses would indirectly lead to loss of other aquatic organisms through impacts 

such as loss of a food resource, habitat, or habitat quality. 

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

If the algal toxicity study with Selenastrum capricornutum indicates that sodium omadine is toxic to 

algae, in the absence of sodium omadine data with a vascular aquatic plant sodium omadine would be 

assumed to be toxic. The lack of these data will limit the flexibility the Agency and registrants have in 

addressing risks to non-listed and listed species and in coming into compliance with the Endangered 

Species Act, and could result in use restrictions or withdrawal of uses for sodium omadine which may 

otherwise be avoided, or which are unnecessarily severe.

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

Chemicals or Activated Sludge Respiration Inhibition Test

Guideline Number: 850.6800 or OECD 209, respectively

Test Substance: TGAI

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.
Page 27 of 27

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.