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MTI Registration Review Team

Human Health & Environmental Effects

Pat Jennings 

Jim Breithaupt 

Bill Erickson

Jonathan Leshin 

Timothy Dole 

Sumitra Biswas 

Risk Management

Donna Kamarei

Rose Kyprianou 

Office of General Counsel

Philip Ross 
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TERMS, ABBREVIATIONS AND SYMBOLS

A.I. or a.i. active ingredient

ASRI activated sludge respiration inhibition

CAS Chemical Abstracts Service 

CFR Code of Federal Regulations 

COC concentration-of-concern

EC50 median (or 50 percent) effect concentration

EDSP Endocrine Disruptor Screening Program 

EPA Environmental Protection Agency

FDA Food and Drug Administration 

FFDCA Federal Food, Drug, and Cosmetic Act

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act

FQPA Food Quality Protection Act 

Kow octanol-water partition coefficient

LC50 median (or 50 percent) lethal concentration

LD50 median (or 50 percent) lethal dose

Log Kow logarithm of the octanol-water partition coefficient

μg microgram

mg/kg milligram per kilogram

mg/kg/day milligram per kilogram per day 

mg/L milligram per liter

mm Hg millimeter of mercury

MRID Master Record Identification Number

N/A not applicable 

nm nanometers

OCSPP Office of Chemical Safety and Pollution Prevention

OPP Office of Pesticide Programs

% percent

PC Code Pesticide Chemical Code

pH power of hydrogen or power of the concentration of the hydrogen ion

ppm parts per million

PWP Preliminary Work Plan

RED Reregistration Eligibility Decision

SAR structure activity relationship

TGAI technical grade active ingredient

TMDL total maximum daily loads

U.S. EPA United States Environmental Protection Agency 

UV/VIS ultraviolet/visible light absorption

WWTPs wastewater treatment plants
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Table of Contents

1 Introduction............................................................................................................................. 6

1.1 Statutory and Regulatory Authority ................................................................................. 6

1.2 Case Overview ................................................................................................................. 6

1.3 Chemical Identification and Properties............................................................................ 7

1.4 Use/Usage Description..................................................................................................... 8

1.4.1 Registrations ............................................................................................................. 8

1.4.2 Summary of Registered Uses.................................................................................... 9

1.4.3 Usage Information .................................................................................................... 9

1.5 Regulatory History ........................................................................................................... 9

1.5.1 Tolerance Information .............................................................................................. 9

1.6 Incidents........................................................................................................................... 9

1.6.1 Human Health ........................................................................................................... 9

1.6.2 Ecological ................................................................................................................. 9

2 Anticipated Data Needs ........................................................................................................ 10

3 Human Health Risk Assessment........................................................................................... 10

3.1 Existing Toxicological Endpoints.................................................................................. 10

3.2 Dietary Exposure............................................................................................................ 10

3.2.1 Food and Drinking Water ....................................................................................... 10

3.3 Occupational and Residential Exposures....................................................................... 10

3.3.1 Occupational Exposures.......................................................................................... 10

3.3.2 Residential Exposures............................................................................................. 10

3.4 Aggregate and Cumulative Exposure............................................................................. 11

3.4.1 Aggregate Exposures.............................................................................................. 11

3.4.2 Cumulative Exposures............................................................................................ 11

4 Environmental Risk Assessment........................................................................................... 11

4.1 Threatened and Endangered Species.............................................................................. 11

4.2 Environmental Fate Assessment .................................................................................... 11

4.2.1 Water Quality.......................................................................................................... 12

4.3 Ecological Effects Assessment....................................................................................... 12

4.3.1 Ecotoxicology Endpoints........................................................................................ 12

4.4 Exposure Analysis Plan.................................................................................................. 12

4.4.1 Aquatic and Terrestrial Wildlife Exposure Estimates ............................................ 12

4.4.2 Screening Level Down-the-Drain Analysis............................................................ 12

5 Endocrine Disruptor Screening Program (EDSP)................................................................. 13

6 Optional Label Changes........................................................................................................ 14

7 Combined Preliminary Work Plan and Proposed Interim Registration Review Decision ... 14

8 Next Steps............................................................................................................................. 14

9 References............................................................................................................................. 15

Appendix A Toxicology Profile............................................................................................... 17

Appendix B Environmental Fate ............................................................................................. 21

List of Tables

Table 1 – Summary of Anticipated Risk Assessments and Data Needs for Registration Review: 

MTI ................................................................................................................................................. 7
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Table 2 – Anticipated Registration Review Schedule .................................................................... 7

Table 3 – Chemical Identification of MTI...................................................................................... 7

Table 4 – Physical-Chemical Properties for MTI........................................................................... 8

Table 5 – Summary of MTI Registered Uses ................................................................................. 9

Table 6 – Acute Toxicity Studies for MTI.................................................................................... 17
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1 Introduction

This document is the Environmental Protection Agency’s (EPA or “the Agency”) combined 

Preliminary Work Plan (PWP) and Proposed Interim Registration Review Decision for 2HCyclopent(d)isothiazol-3(4H)-one, 5,6-dihydro-2-methyl-, herein referred to as MTI, and is 

being issued pursuant to 40 CFR Sections 155.50, 155.56 and 155.58. This document explains 

what EPA’s Office of Pesticide Programs knows about MTI, noting that no additional data nor 

further assessments are required, and provides an anticipated timeline for completing MTI’s

review. It also includes the Agency’s Proposed Interim Registration Review Decision for MTI.

A registration review decision is the Agency's determination whether a pesticide meets, or does 

not meet, the standard for registration in the Federal Insecticide, Fungicide, and Rodenticide Act 

(FIFRA). The Agency may issue, when it determines it to be appropriate, a proposed interim 

registration review decision before completing a registration review. Among other things, the 

proposed interim registration review decision may require new risk mitigation measures, impose 

interim risk mitigation measures, identify data or information required to complete the review, 

and include schedules for submitting the required data, conducting the new risk assessment and 

completing the registration review.

1.1 Statutory and Regulatory Authority

The Food Quality Protection Act (FQPA) of 1996 mandated a registration review program. All 

pesticides distributed or sold in the United States generally must be registered by the U.S. EPA 

based on scientific data showing that they will not cause unreasonable risks to human health or 

the environment when used as directed on product labeling. The registration review program is 

intended to make sure that, as the ability to assess risk evolves and as policies and practices 

change, all registered pesticides continue to meet the statutory standard of no unreasonable 

adverse effects to human health or the environment. Changes in science, public policy, and 

pesticide use practices will occur over time. Through the registration review program, the 

Agency periodically reevaluates pesticides to make sure that as change occurs, products in the 

marketplace can be used safely. Information on this program is provided at 

http://www2.epa.gov/pesticide-reevaluation.

The Agency is implementing the registration review program pursuant to Section 3(g) of FIFRA 

and will review each registered pesticide every 15 years to determine whether it continues to 

meet the FIFRA standard for registration. The regulations governing registration review begin at 

40 CFR 155.40. The Agency will consider benefits information and data as required by FIFRA. 

The public phase of registration review begins when the initial docket is opened for each case. 

The docket is the Agency’s opportunity to state what it knows about the pesticide and what 

additional risk analyses and data or information it believes are needed to make a registration 

review decision.

1.2 Case Overview

The docket for MTI (case 5018) has been established at http://www.regulations.gov in docket 

number EPA-HQ-OPP-2015-0266. Documents associated with this registration review can be 
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viewed in this docket. Tables 1-2 below summarize the issues relevant to this registration review 

case and the anticipated registration review schedule.

Table 1 – Summary of Anticipated Risk Assessments and Data Needs for Registration 

Review: MTI

Risk Assessment 

Assessment 

Necessary to 

Support 

Registration Review

Date of Most 

Recent Assessment

Type of Assessment 

Required 

(New/Updated)

Data Anticipated 

as Needed

Dietary (food/ drinking 

water) No N/A None None

Occupational & 

Residential Handler / 

Post Application

No N/A None None

Aggregate No N/A None None

Cumulative No N/A None None

Tolerance Review No N/A None None

Ecological No N/A None None

N/A = Not applicable

Table 2 – Anticipated Registration Review Schedule

Anticipated Activity Target 

Date*

Completion 

Date

Combined Preliminary Work Plan and Interim Registration Review Decision and Implementation 

Open 60-Day Public Comment Period for Combined Preliminary Work Plan and 

Proposed Interim Decision 2015-09 2015-09

Close Public Comment Period 2015-11

Issue Interim Decision 2016-03

Begin Post-Decision Followup 2016

Total (years) 1

*The anticipated schedule will be revised as necessary (e.g., need arising under the Endocrine Disruptor Screening Program with 

respect to the active ingredients in this case).

1.3 Chemical Identification and Properties

Table 3 presents the active ingredient to be assessed in case 5018: MTI (PC Code 107107). 

Table 3 – Chemical Identification of MTI

Chemical Name MTI

Chemical

Classification Isothiazolone

PC Code 107107

CAS Number 82633-79-2

Molecular Formula C7H9NOS
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Molecular Weight 

(grams/mole) 155.22

Molecular Structure

The MTI physical chemistry information is summarized in Table 4. 

Table 4 – Physical-Chemical Properties for MTI

Guideline

Numbers MTI Source

830.6303

Physical State

Straw-colored 

liquid 43678303

830.7000

pH at 25 °C 4.8 43678303

830.7050

UV/Visible Absorption

Limited light 

absorption between 

290-800 nm

43138707

830.7300

Density (g/cm3)

1.016 43678303

830.7370

Dissociation Constant pKa and pKb

5.7 (pKa)

8.3 (pKb) 43138706

830.7550

Log Kow 0.64 EPIWEB 4.11

830.7840

Solubility in water (mg/L) at 25 oC

20,400 EPIWEB 4.11

830.7950

Vapor pressure (mm Hg) at 25 °C 6.62 x 10-4 EPIWEB 4.11

Henry’s law (atm m3 mol-1) 6.62 x 10-9 Calculated

1.4 Use/Usage Description

1.4.1 Registrations

There is one EPA registered product containing MTI as an active ingredient.1 The product 

contains five percent MTI and is a liquid formulation. 

 

1 Promexal X-50 Preservative, EPA Reg. No. 59441-5
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1.4.2 Summary of Registered Uses

Table 5 presents a summary of the registered use of MTI that will be assessed in this registration 

review. 

Table 5 – Summary of MTI Registered Uses

Use - Material Preservation Application Method Application Rate

Aqueous composition used in the manufacture of 

imaging products Open Pour 100 ppm

1.4.3 Usage Information

The amount of MTI used per year is very low. The exact amount is provided in a confidential 

report (MRID 49677601).

1.5 Regulatory History

The first product containing MTI was registered on July 23, 1996 for material preservation of 

imaging products. A Reregistration Eligibility Decision (RED) was not completed for MTI 

because it was registered after November 1, 1984. 

1.5.1 Recent/Pending Regulatory Actions 

There are no recent or pending regulatory actions for MTI.

1.5.1 Tolerance Information

EPA has not established tolerances or tolerance exemptions for residues of MTI in or on raw 

agricultural commodities or processed food and feed products under the Federal Food, Drug, and 

Cosmetic Act (FFDCA) Section 408. MTI has not been cleared as a food additive by the U.S.

Food and Drug Administration (US FDA) under FFDCA Section 409.

1.6 Incidents

1.6.1 Human Health 

There are no human health incidents in the OPP Incident Data System for the time period from 

8/06/2001, when the product was transferred from Zeneca to Kodak, to the present (search 

conducted on July 27, 2015). There is one incident listed for when the product was registered to 

Zeneca. This incident was included in the first quarter aggregate report for 2000 and was rated as 

grade D (minor). No other information was provided in the aggregate report. 

1.6.2 Ecological

There are no ecological incidents in the OPP Incident Data System as of July 21, 2015.
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2 Anticipated Data Needs

The Agency does not anticipate requiring any additional data to support this registration review.

3 Human Health Risk Assessment

The Agency does not anticipate the need to conduct a human health risk assessment for MTI.

3.1 Existing Toxicological Endpoints

Based on the required personal protective equipment (PPE) and engineering controls, there are 

no toxicological endpoints of concern and no points of departure are set. The requirement for a 

subchronic inhalation study, 90-day dermal toxicity study, rabbit developmental study, 

reproduction and fertility study, dominant lethal mutation assay and immunotoxicty assay were 

reviewed by the Hazard and Science Policy Council (HASPOC) on July 23, 2015 and waived 

(TXR# 0057278) based on limited usage, PPE, and engineering controls used.

3.2 Dietary Exposure

The Agency does not anticipate the need to conduct a dietary exposure assessment to support this

registration review. 

3.2.1 Food and Drinking Water 

A dietary (food and drinking water) exposure assessment is not anticipated to be required for MTI at 

this time. MTI is used as a preservative for the manufacture of aqueous compositions used in the 

manufacture of imaging products and is not expected to result in dietary exposures. Therefore, a 

dietary exposure assessment is not required.

3.3 Occupational and Residential Exposures

3.3.1 Occupational Exposures

Occupational handler exposures could occur during the open pouring of the MTI product from 

the original containers into smaller containers and from the smaller containers into batches of 

film emulsion. The label indicates, however, that all handling of the MTI product must be done 

under local exhaust ventilation and thus inhalation exposures are anticipated to be negligible. In 

addition, dermal exposures are also expected to be negligible given the small amounts handled 

and the use of PPE including rubber gloves and goggles or a faceshield.

Occupational post application exposures to MTI residues on the film during color film 

developing are also not anticipated because color film developing is an automated process that 

involves immersion in several chemical solutions followed by a water wash and drying. 

3.3.2 Residential Exposures

Residential exposures are not anticipated because MTI is used only in an industrial process to 

manufacture imaging products (i.e. film) which is then developed using an automated process. 
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3.4 Aggregate and Cumulative Exposure

3.4.1 Aggregate Exposures 

Aggregate exposures normally include dietary, drinking water and residential exposures. Since 

these exposures are not anticipated for MTI, a risk assessment of aggregate MTI exposures is not 

needed. 

3.4.2 Cumulative Exposures 

Dietary, drinking water and residential exposures are not anticipated for MTI, thus a risk 

assessment of cumulative exposures to MTI and toxicologically similar chemicals is not needed. 

4 Environmental Risk Assessment

The Agency does not anticipate the need to require data or to conduct an environmental risk 

assessment for MTI. The Agency has not previously conducted a risk assessment that supports a 

complete endangered species determination for MTI; further, no assessment is needed at this 

time due to lack of potential exposure. Waste materials that are generated following the use of 

MTI as an imaging preservative undergo incineration. Consequently, disposal of waste materials 

is expected to be negligible and the potential for ecological organisms to be exposed to MTI is 

expected to be negligible. 

4.1 Threatened and Endangered Species

There is no reasonable expectation for the registered use of MTI to cause direct or indirect 

adverse effects to threatened and endangered species. Usage is low and waste materials are 

recycled. No environmental exposure is expected. No adverse modification of any designated 

critical habitat for such species is expected from the use of MTI. EPA has made a “no effect” 

determination for MTI under the Endangered Species Act (ESA) for all listed species and 

designated critical habitat for such species and has therefore concluded that consultation with the 

Fish and Wildlife Service and the National Marine Fisheries Service under ESA section 7(a)(2)

is not required.

4.2 Environmental Fate Assessment

MTI is an isothiazolone microbiocide which is stable to hydrolysis at pH 5, 7, and 9 and 25 oC 

(MRID 43138732). Although no guideline study on photodegradation in water was performed, 

MTI is expected to be relatively stable to photodegradation in water based on results from a UVvisible absorption study. Only 7 % of MTI degraded within 24 hours of the onset of a UVvisible absorption study (MRID 43138707, Guideline 830.6313), which indicated that 

photodegradation is expected to be negligible. No other fate data have been submitted, but no 

data are expected to be necessary based on use pattern and industry practices.
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4.2.1 Water Quality

MTI is not identified as a cause of impairment for any water bodies listed as impaired under 

section 303(d) of the Clean Water Act2. In addition, no Total Maximum Daily Loads (TMDL) 

have been developed for MTI3. More information on impaired water bodies and TMDLs can be 

found at EPA’s website4.

4.3 Ecological Effects Assessment

4.3.1 Ecotoxicology Endpoints

Acute and chronic toxicity data from registrant-submitted studies (850 OCSPP Harmonized Test 

Guidelines) are used to evaluate the potential effects to aquatic and terrestrial nontarget 

organisms. The available data indicate that technical-grade MTI is moderately to highly toxic to 

freshwater organisms and moderately to practically nontoxic to birds (Table 10). No additional 

ecotoxicity data are expected to be needed.

Table 10. Available Ecological Effects Endpoints

Receptor 

Group

Test 

Material Scenario Toxicity Endpoint(μg/L) Reference

Freshwater fish TGAI Acute LC50 = 0.89 mg ai/L 43138712

Freshwater 

invertebrates TGAI Acute EC50 = 1.3 mg ai/L 43138713

Birds TGAI

Acute LD50 = 152 mg/kg-bw 43138708

Dietary LC50 >5620 ppm 43138709,

43138710

4.4 Exposure Analysis Plan

4.4.1 Aquatic and Terrestrial Wildlife Exposure Estimates

Aquatic and terrestrial exposures are not anticipated from the use of MTI as an imaging 

preservative. Consequently, no aquatic and terrestrial assessments of exposure are anticipated to 

be performed. 

4.4.2 Screening Level Down-the-Drain Analysis

No Down-the-Drain (DtD) releases to wastewater treatment plants (WWTP) from the use of MTI 

as an imaging preservative are expected. Consequently, no DtD assessment is anticipated to be 

conducted for MTI.

 

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

3http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id=885&p_pollutant_

group_name=PESTICIDES

4 http://www.epa.gov/owow/tmdl/
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5 Endocrine Disruptor Screening Program (EDSP)

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential adverse 

outcomes from exposure to chemicals. Collectively, these studies include acute, subchronic and 

chronic toxicity, including assessments of carcinogenicity, neurotoxicity, developmental, 

reproductive, and general or systemic toxicity. These studies include endpoints which may be 

susceptible to endocrine influence, including effects on endocrine target organ histopathology, 

organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, reproductive loss, 

and sex ratios in offspring. For ecological hazard assessments, EPA evaluates acute tests and 

chronic studies that assess growth, developmental and reproductive effects in different 

taxonomic groups. As part of its most recent registration decision, for MTI, EPA reviewed these 

data and selected the most sensitive endpoints for relevant risk assessment scenarios from the 

existing hazard database. However, as required by FFDCA section 408(p), MTI is subject to the 

endocrine screening part of the Endocrine Disruptor Screening Program (EDSP). 

EPA has developed the EDSP to determine whether certain substances (including pesticide 

active and other ingredients) may have an effect in humans or wildlife similar to an effect 

produced by a “naturally occurring estrogen, or other such endocrine effects as the Administrator 

may designate.” The EDSP employs a two-tiered approach to making the statutorily required 

determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a 

chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal 

systems. Chemicals that go through Tier 1 screening and are found to have the potential to 

interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA 

will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 

testing is designed to identify any adverse endocrine-related effects caused by the substance, and 

establish a dose-response relationship between the dose and the E, A, or T effect. 

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between October 

2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 chemicals, 

which contains 58 pesticide active ingredients and 9 inert ingredients. A second list of chemicals 

identified for EDSP screening was published on June 14, 20135and includes some pesticides 

scheduled for registration review and chemicals found in water. Neither of these lists should be 

construed as a list of known or likely endocrine disruptors.

For further information on the status of the EDSP, the policies and procedures, the lists of 

chemicals, future lists, the test guidelines and the Tier 1 screening battery, please visit our 

website.6

 

5 See http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0477-0074 for the final second list of 

chemicals.

6 http://www.epa.gov/endo/
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6 Optional Label Changes

The Agency invites comment on any label amendments that could be considered to improve 

label clarity. 

7 Combined Preliminary Work Plan and Proposed Interim 

Registration Review Decision

In accordance with 40 CFR Sections 1550.50, 155.56 and 155.58, the Agency is issuing this 

combined Preliminary Work Plan and Proposed Interim Registration Review Decision. Based on 

the assumption of no exposure to humans and non-target organisms, no additional data are 

anticipated to be needed and no risk assessments are planned. The Agency has made a “no 

effect” finding based on lack of potential exposure for endangered species (see Section 4). 

Except for the EDSP component of the MTI registration review case, the Agency has made the 

proposed decision that no additional data and no further risk assessments are required.

8 Next Steps

A Federal Register Notice will announce the availability of this combined Preliminary Work 

Plan and Proposed Interim Registration Review Decision for MTI and allow a 60-day comment 

period. If there are no significant comments or additional information submitted to the docket 

during the comment period that leads the Agency to change its proposed decision, EPA may 

issue an interim decision. The final decision on the registration review for MTI (case 5018) will 

occur after an EDSP FFDCA section 408(p) determination is made. See the estimated timeline 

for the completion of MTI registration review in Table 2. 
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9 References 

43138718 McCall, J. (1990) 2-Methyl-4,5-Trimethylene-4-Isothiazolin-3-One: Acute Oral 

Toxicity to the Rat: Lab Project Number: CTL/P/2791. Unpublished study prepared by ICI 

Central Toxicology Lab. 49 p. 

43138719 McCall, J.; Leah, A. (1990) 2-Methyl-4,5-Trimethylene-4-Isothiazolin-3-One: Acute 

Dermal Toxicity to the Rat: Lab Project Number: CTL/P/2946. Unpublished study prepared by 

ICI Central Toxicology Lab. 37 p. 

43138720 Barlow, A.; Leah, A. (1990) 2-Methyl-4,5-Trimethylene-4-Isothiazolin-3-One (MTI): 

Eye Irritation to the Rabbit: Lab Project Number: CTL/P/2811. Unpublished study prepared by 

ICI Central Toxicology Lab. 21 p. 

43138721 Barlow, A.; Leah, A. (1990) 2-Methyl-4,5-Trimethylene-4-Isothiazolin-3-One (MTI): 

Skin Irritation to the Rabbit: Lab Project Number: CTL/P/2810. Unpublished study prepared by 

ICI Central Toxicology Lab. 18 p. 

43138722 Lees, D. (1990) 2-Methyl-4,5-Trimethylene-4-Isothiazolin-3-One (MTI): Skin 

Sensitization to the Guinea Pig: Lab Project Number: CTL/P/2960. Unpublished study prepared 

by ICI Central Toxicology Lab. 31 p. 

43138724 Rattray, N. (1993) 2-Methyl-4,5-trimethylene-4-isothiazolin-3-one (MTI): 90 Day 

Feeding Study in Rats: Lab Project Nos. CTL/P/3858: PR0903. Unpublished study prepared by 

Zeneca Central Toxicology Lab. 537 p. 

43138726 Rattray, N. (1993) 2-Methyl-4,5-Trimethylene-4-Isothiazolin-3-One (MTI): 90 Day 

Toxicity Study in Dogs: Lab Project Number: CTL/P/3972: PD0931. Unpublished study 

prepared by Zeneca Central Toxicology Lab. 342 p. 

43138727 Pinto, P. (1993) 2-Methyl-4,5-trimethylene-4-isothiazolin-3-one (MTI): 

Developmental Toxicity Study in the Rat: Lab Project Number: CTL/P/3921: RR0603. 

Unpublished study prepared by Zeneca Central Toxicology Lab. 375 p. 

43138728 Calander, R.; Priestley K. (1990) 2-Methyl-4,5-Trimethylene-4-Isothiazolin-3-One: 

An Evaluation of Mutagenic Potential Using S. typhimurium and E. coli: Lab Project Number: 

CTL/P/2844. Unpublished study prepared by ICI Central Toxicology Lab. 40 p. 

43138729 Jones, K.; Mackay, J. (1990) 2-Methyl-4,5-trimethylene-4- isothiazolin-3-one (MTI): 

An Evaluation in the Mouse Micronucleus Test: Lab Project Number: CTL/P/3132. Unpublished 

study prepared by ICI Central Toxicology Lab. 40 p. 

43138730 Jones, K.; Mackay, J. (1990) 2-Methyl-4,5-Trimethylene-4-Isothiazolin-3-One (MTI): 

An Evaluation in the In Vitro Cytogenetic Assay in Human Lymphocytes: Lab Project Number: 

CTL/P/3035. Unpublished study prepared by ICI Central Toxicology Lab. 34 p. 
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43138731 Kennelly, J. (1990) 2-Methyl-4,5-Trimethylene-4-Isothiazilin-3-One (MTI): 

Assessment for the Induction of Unscheduled DNA Synthesis in Rat Hepatocytes In Vivo: Lab 

Project Number: CTL/P/3134. Unpublished study prepared by ICI Central Toxicology Lab. 43 p

49677601 Occupational Exposure Assessment of the Use of Promexal X50 as a Biocide in 

Kodak Color Negative Film Products, John H. Heyer, Eastman Kodak Company, June 10, 2015.
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Appendix A Toxicology Profile

Acute Toxicity for Product Labeling 

Table 6 – Acute Toxicity Studies for MTI

Guideline No./ Study 

Type MRID No. Results Toxicity Category

870.1100/ 

Acute oral toxicity 43138718 LD50 = 224 (M) and 168 (F) mg/kg for males and females II

870.1200/ 

Acute dermal toxicity 43138719 Animals sacrificed due to severity of skin irritation I

870.1300/ 

Acute inhalation toxicity N/A No data performed I

870.2400/ 

Acute eye irritation 43138720 Animals sacrificed due to severity of eye irritation I

870.2500/ 

Acute dermal irritation 43138721 No erythema or edema seen at 72 hours IV

870.2600/ 

Skin sensitization 43138722 Sensitizer Not applicable 

N/A=Not available 

Subchronic Toxicity 

There are two subchronic toxicity studies, 1 in rat and 1 in dogs, both are considered acceptable.

90-day feeding study rat – MRID 43138724

MTI was administered to AlpK:APfsd (Wistar derived) rats of both sexes for a period of 90 days 

in the diet at dose levels of 0, 50, 250, or 1000 ppm corresponding to mean MTI intakes of 0, 4.1, 

20.7 or 83 mg/kg/day (M) or 0, 4.6, 23.2, or 93 mg/kg/day (F). Statistically significantly 

decreased body weights were observed at 1000 ppm in males throughout the treatment period 

(e.g. to 84.8% of controls at 14 weeks). Mean body weight gains at 250 and 1000 ppm in males 

were reduced to 95.2 and 79.3% of controls for weeks 1-14. Mean food efficiency values for 

high dose males were statistically significantly decreased for weeks 1-13 (to 89.7% of controls). 

Statistically significantly decreased body weights were observed at 250 and 1000 ppm in females 

throughout the treatment period (e.g. to 94.5 and 87.8% of controls at 14 weeks for 250 and 1000 

ppm, respectively). Likewise, mean body weight gains decreased in dose related fashion to 

89.1% and 68.7% of controls at 250 and 1000 ppm, respectively, for weeks 1-14. Mean food 

efficiency values for weeks 1-4 decreased with increasing dose, reaching statistical significance 

at 250 and 1000 ppm, at 91.3 and 75.6% of controls, respectively. There were no apparent 

toxicologically significant findings in clinical chemistry, hematology, or macroscopic and 

microscopic pathology.

LOEL: 250 ppm, based on dose related and statistically significant decreases in food efficiency 

for females coupled to dose related decreases in body weight gain.
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NOEL: 50 ppm.

90-day feeding – dogs – MRID 43138726

In a 13-week subchronic feeding study (MRID# 431387-26) MTI was administered to beagle 

dogs of both sexes for a period of 90 days in the diet at dose levels of 0, 100, 300, or 1000 ppm, 

corresponding to mean MTI intake of 0, 3.1, 9.3 or 31.5 mg/kg/day in males and 0, 3.2, 10.1, or 

33.4 mg/kg/day in females. There were no effects on body weight or body weight gain for either

sex. This is in contrast with effects observed in the pilot study (MRID 43138725): body weight 

gain in females at 928 and 464 ppm in the pilot study were 36.4% and 54.5% of controls, 

respectively. Changes in hematology and clinical chemistry parameters did not follow a clear 

dose related trend and appeared to be incidental to the treatment. No clear-cut, dose-related 

effects were observed upon macroscopic examination of the dogs. Although clear macroscopic 

signs of irritation of the tongue were seen in 1392 and 928 ppm females in the pilot study, no 

signs of tongue irritation were seen in this study. There were no apparent treatment-related 

histological findings. This study does not define a LOEL due to the absence of clear-cut, doserelated effects. The NOEL is 1000 ppm, the highest dose tested 

Developmental Toxicity 

There is one developmental toxicity study in rats. The developmental toxicity study in rabbits 

was waived by HASPOC (TXR# 0057278).

Developmental toxicity study – rat – MRID 431387-27

A developmental toxicity study (MRID# 431387-27) was conducted with Wistar-derived rats 

(Alpk:APfsD)(SPF) to assess the developmental toxicity potential of MTI in mated female rats 

(groups of 24/dose) gavaged during gestation days (gds) 7-16 (inclusive) at dose levels of 0, 5, 

15 or 40 mg/kg/day. Maternal toxicity was established for the highest dose tested (HDT) by: 1)

the observation of 2 deaths on gds 12 and 13 (1 in extremis, 1 found dead), 2) Clinical signs of 

toxicity in 4 dams (including the two which died) related to the respiratory system (abnormal 

noise, labored breathing, gasping, reduced breathing rate), 3) statistically significant depressions 

in mean body weight of 4-6.5% (gds 8-16 inclusive) which remained decreased following 

cessation of dosing, 4) a 62 % decrement in mean body weight gain during the dosing period, 

and 5) statistically significant depressions in mean food consumption on gds 7-10, 10-13 and 13-

16. There were no apparent dose-related effects upon mean implantations/dam, live fetuses/dam, 

resorptions/dam (early, late), postimplantation losses, the sex ratios, mean fetal weights or 

external/ visceral/skeletal anomalies. The Maternal toxicity NOEL is equal to 15 mg/kg/day 

while the LOEL is equal to 40 mg/kg/day. (HOT). This is based upon increased mortality and 

clinical signs (respiratory system), depressed mean body weight and weight gain and decreased 

food consumption. The Developmental NOEL is equal to 40 mg/kg/day (HOT) while the LOEL 

could not be determined.

Reproductive Toxicity

This requirement was waived by HASPOC (TXR# 0057278).
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Chronic Toxicity 

This study is not required for this use pattern.

Carcinogenicity 

This study is not required for this use pattern.

Mutagenicity 

The database for mutagenicity is considered adequate. Four mutagenicity studies were conducted 

and an additional dominant lethal assay was waived.

In an initial microbial/mammalian microsome plate incorporation assay (MRID No. 43138731) 

Salmonella typhimurium strains TA 1535, TA 1537, TA 1538, TA98, and TA 100, and 

Escherichia coli strain WP2uvrA pKM101 were exposed to 0, 0.32, 1.6, 8.0, 40, 100, or 200 

μg/plate of MTI in the presence or absence of SS activation derived from Arochlor 1 254 

induced rat liver. For the repeat trial, nonactivated levels of 0, 0.16, 0.8, 4.0, 20, 50, or 100 

μg/plate were assayed with the Salmonella strains and 0, 0.064, 0.32, 1.6, 8.0, 20, or 50 pg/plate 

were assayed with E. coli Doses evaluated under SS-activated conditions were similar to those 

used in the initial trial. Dimethyl sulfoxide was used as the solvent. Although slight but 

significant and dose-related increases in revertant colonies of strain TA 1 535 were seen in the 

SS-activated phase of the initial assay, the effect was not reproducible and, therefore, did not 

provide sufficient evidence of a mutagenic response. MTI was cytotoxic (~ 100 μg/plate -SS; 

~200 pg/plate + S9) in all strains but failed to induce a mutagenic effect. All strains responded to 

the mutagenic action of the appropriate positive control.

In an in vivo/in vitro unscheduled DNA synthesis (UDS) study (MRID No. 43138731), groups of 

five male rats were administered a single oral gavage dose of 0, 76, 117, or 180 mg/kg MTI 

prepared in deionized water. The high dose was estimated to be 80% of the male rat oral LD50. 

Animals were sacrificed at 4 and 1 2 hours post-treatment and recovered hepatocytes were 

scored for UDS. Two independent trials were performed. Clinical signs of toxicity noted 

immediately after dosing included salivation, difficulty in breathing, and staining and fluid 

around the nose. Treatment with MTI produced no evidence of cytotoxicity for the target cells. 

There was also no evidence of a genotoxic response at any dose or sacrifice time. 

In an in vitro cytogenetic assay (MRID No. 43138730), cultured human lymphocytes, obtained 

from one male and one female donor were exposed to MTI doses of 0, 2, 10, or 20 pg/ml -S9 

(male donor); 0, 1, 5, or 10 μg/ml -S9 (female donor) or 0, 2, 10, or 20 μg/ml + S9 (both donors) 

(MRID No. 431387-30, HED Doc. No. 011613) . The test material was delivered to the test 

system in dimethyl sulfoxide, and the S9 was derived from Aroclor 1254 induced rat liver. 

Significant (p < 0.01) clastogenic effects were seen at 10 and 20 pg/ml without S9 activation and 

at 20 μg/ml with S9 activation in lymphocytes derived from the male donor and at 10 and 20 

pg/ml + S9 in cells derived from the female donor. Higher levels with or without S9 activation 

were severely cytotoxic. MTI is considered positive for the induction of structural chromosomal 

aberrations in cultured human lymphocytes. Cultured human lymphocytes tested positive for 
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structural chromosomal aberrations in the presence and absence of metabolic activation at 

concentrations as low as 10 microgram/ml. The response was much more pronounced in the 

presence of metabolic activation.

In the mouse micronucleus assay (MRID No. 43138729) MTI tested weakly positive at a dose 

level up to 136 mg/kg. In this assay, groups of five male and five female C57BL/6 mice received 

single oral gavage administrations of 0, 85 or 136 mg/kg (males) or 0, 103 or 164 mg/kg 

(females) MTI delivered in physiological saline. At 24, 48 or 72 hours postexposure, high dose 

animals were sacrificed and bone marrow cells were examined for micronucleated polychromatic 

erythrocytes (MPEs). Bone marrow cells were harvested from animals in the low-dose groups 

only at 24 hours after treatment. Unscheduled deaths occurred in five high-dose males and four 

high-dose females; dead animals were replaced with mice from a secondary group. A significant 

(p < 0.05) decrease in the ratio of normochromatic to polychromatic erythrocytes (PCEs), 

indicating cytotoxic effects on the target organ, was seen in the high-dose groups (both sexes) at 

the 24-hour sacrifice. A significant (p<0.01) increase in mean MPEs for males administered 136 

mg/kg at 24 hours prompted the study investigators to evaluate an additional 2000 PCEs/male 

from the 24- and 48-hour sacrifice groups for the high dose and from the 24-hour sacrifice group 

for the low dose. Based on this expanded analysis, the data showed nonsignificant increases in 

MPEs for high-dose males at both sacrifice times. A similar response was present in high-dose 

females at 48 hours. The study authors attributed the increase in males (48 hr.) to a single animal 

having high MPE counts (14/1000--initial count; 13/1000 and 12/1000 –subsequent extended 

counts). However, increases in the number of micronuclei were seen in individual animals as 

follows: 

2 high-dose males (24 hrs)--4.3 or 4.0 MPEs/1000 PCEs vs. 2.1 MPEs/1000 PCEs (controls)

2 high-dose males (48 hrs)--3 .3 or 13.0 MPEs/1000 PC Es vs. 1. 7 MPEs/1000 PCEs (control)

1 low-dose male (24 hrs)--4. 7 MPEs/PCEs vs. 2. 1 MPEs/1000 PC Es (controls)

1 high-dose female (48 hrs)--10 MPEs/1000 PCEs vs. 1 .8 MPEs/1000 PCEs.

Although the statistical significance of the results was lost owing to the wide variability in the 

data, the increased sample size (3000 PCEs/males at all doses and sacrifice times) increases our 

confidence in the test system's ability to predict a doubling over background as a true biological 

effect. It is also of note that MTI induced an unambiguous clastogenic response in cultured 

human lymphocytes (see MRID No.431387-30). It is concluded, therefore, that the results in this 

mouse micronucleus assay are consistent with a weak clastogenic and/or aneugenic response.

Other Toxicological Effects 

Immunotoxicity study was waived by HASPOC (TXR# 0057278). Acute and subchronic 

neurotoxicty studies are not required for this use pattern.
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Appendix B Environmental Fate

Environmental Fate and Transport Properties of MTI

MTI is an isothiazolone microbiocide. The guideline environmental fate data that have been 

submitted for hydrolysis indicates stability at pH 5, 7, and 9 and 25 oC (MRID 43138732). 

Although no guideline study on photodegradation in water was performed, MTI is expected to be 

relatively stable to photodegradation in water based on results from a UV-visible absorption 

study. Only 7 % of MTI degraded within 24 hours of the onset of a UV-visible absorption study 

(MRID 43138707, Guideline 830.6313), which indicated that photodegradation is negligible. 

No additional environmental fate data have been submitted for MTI, but no data are needed 

because of the lack of environmental exposure.

Environmental Fate References for Appendix B

MRID 43138707. Comber, M.; Roberts, G.; Woods, C. (1993) MTI: Photostability: Lab Project 

Number: BL4892/B. Unpublished study prepared by Brixham Environmental Labs., Zeneca Ltd. 

16 p.

MRID 43138732. Brown, D.; Stanley, R. (1992) 2-Methyl-4,5-Trimethylene-4-Isothiazolin-3-

One (MTI): Determination of Hydrolysis as a Function of pH: Lab Project Number: BL4450/B. 

Unpublished study prepared by Imperial Chemical Industries PLC, Brixham Lab. 11 p.