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$' U UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

S @ WASHINGTON D.C., 20460 

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MEMORANDUM 

SUBJECT: 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

December 21 , 2011 

Product Chemistry, Environmental Fate, and Ecological Effects Scoping 

Document in Support of Registration Review of Methylene 

bis( thiocyanate) 

PC Code: 068102 DP Barcode: 394334 

Decision No.: 455140 Registration Nos.: See Table 1 

Petition No(s).: NA Regulatory Action: Ecological 

Environmental Scoping Document 

for Registration Review 

Risk Assessment Type: Single Case No.: 2415 

chemical 

TXRNo.:NA CAS No.: 6317-18-6 

MRID Nos.:See Tables 2, 3 & 4 and 40 CFR: None 

Pg.no.5 

FROM: 1r=srinivas Gowda, Microbiolo 

THRU: 

TO: 

William Erickson, Biologist ~~:::::::~vv.. ..... ~~~,Jj/.l)J~ 

Najm Shamim, Chemist 

Risk Assessment and Science Support Branch (RASSB) 

Antimicrobials Division (751 OP) -<.. ~ 

Nader Elkassabany, Branch ~ ~ ~ , _ n 

Donna Randall, Peer Reviewer 'V\...~ 1'l-/2...I/t( 

Risk Assessment and Science Support Branch (RASSB) 

Antimicrobials Division (751 OP) 

Mark Hartman, Branch Chief 

Lance Wormell, Team Leader 

Rebecca von dem Hagen, Chemical Review Manager 

Regulatory Management Branch II 

Antimicrobials Division (751 OP) 

Page 1 of28 
Page 2 of 28

Executive Summary

Methylene bis(thiocyanate) (MBT) an organothiocyanate compound is registered for use 

as a material preservative, wood preservative and as a microbiocide/microbiostat in industrial 

process and water systems. MBT was first registered in the United States in 1949 as an active 

ingredient. A Reregistration Eligibility Decision (RED) was issued by EPA for methylene 

bis(thiocyanate) in 1997. Currently there are fifteen companies with a total of 40 active 

registrations. Six of the products are registered as a technical with an active ingredient 

declaration of 98.95 to 99%. The remaining 34 products are registered end-use products with 

active ingredient declarations ranging from 2.5 to 10%; these products consist of soluble readyto-use solutions, flowable soluble concentrates, solid soluble concentrates, wettable powders, and 

emulsifiable concentrates. 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 MBT products require that discharges to aquatic environments comply with a National 

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

process, risk assessments for the material preservative, wood preservative and industrial process 

and water systems will be conducted. 

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

fate and transport of MBT is incomplete. The environmental fate data gaps for this antimicrobial

include aqueous photolysis at pH 5, soil adsorption/desorption study, aerobic and anaerobic 

aquatic metabolism studies, activated sludge respiration inhibition, and one of four waste 

biodegradability tests (ready biodegradability, porous pot test, or one of two simulation tests). 

The purpose of these tests is to address discharge of fluids from industrial process and water

systems, cooling water systems (recirculating), pulp and paper mills, oil and gas well production 

systems, metal working fluids and wood preservatives. In terms of what is known about the 

environmental fate of MBT it is hydrolytically stable at pH 5, but degrades easily at pH 7 and 9.

It is not likely to bioaccumulate as its Log Kow is around 2. Through the hydrolysis and 

photolysis from the wood surfaces, the common degradates formed are: thiocyanate, formic acid, 

and carbon dioxide. Under environmental conditions formation of cyanide from the thiocyanate 

moiety is not known to occur. 

MBT is highly to very highly toxic to freshwater and estuarine/marine animals and is 

highly toxic to birds on an acute oral basis. In order to perform an ecological risk assessment, 

including an endangered species determination for all uses, the Agency anticipates needing a 

freshwater fish early-life stage study, a vascular aquatic plant (Tier II) toxicity study, aquatic 

plant (Tier II) toxicity tests with 4 algae species, a honeybee acute contact study, a residue 

toxicity to honeybee study and a freshwater invertebrate sediment study.
Page 3 of 28

Introduction

MBT was first registered in the United States in 1949 as an active ingredient. Currently, 

40 products are registered which are listed in Table 1 (Appendix C) for incorporation into

products such as adhesives, coatings, fuels, metalworking cutting fluids, textiles, plastic 

products, resin emulsions, paints, paper products and various other products as a material 

preservative; and as a microbiocide in pulp/paper mills, cooling water systems (recirculating), oil 

field operations, air washer systems, brewery pateurizers, hydrotesting, leather processing and 

industrial water supply systems. MBT is also used for wood sapstain control and mold on freshly 

cut hardwood and softwood lumber, logs, poles, posts and timbers. A Reregistration Eligibility 

Decision (RED) was issued by EPA for methylene bis(thiocyanate) in 19971

.

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

fate, and ecotoxicity data for methylene bis(thiocyanate). The primary source of information for 

this assessment was the 1997 methylene bis(thiocyanate) RED. The findings are summarized 

below.

A. Product Chemistry Summary of Methylene bis(thiocyanate) (98% Min. TGAI)

Common Name: Methylene bis(thiocyanate) (MBT)

Methylene dithiocyanate

Thiocyanic acid, methylene ester

Chemical Name: Methylene bis(thiocyanate)

Trade and Other Names: Slimicide MC

Busan 110

Nalco D-1994

Antiblu 3737

Cytox

OPP Chemical Code: 068102

CAS Registry Number: 6317-18-6

Molecular Formula: C3H2N2S2

CH2(SCN)2

Molecular weight: 130.2 g/mole

Molecular Structure: N≡C-―S―CH2―S―C≡N

Color: Yellow to light orange solid.

 1 http://www.epa.gov/oppsrrd1/REDs/2415red.pdf
Page 4 of 28

Physical State: Solid, granular.

Odor: Sulfur like smell.

Stability: Stable when stored for 14 days exposed to the following 

conditions: ambient temperature, broad-spectrum light, 

stainless steel, galvanized steel, aluminum, copper, iron 

(III) oxide, aluminum tartrate, and copper acetate. Loss of 

active ingredient was observed when stored for 14 days

with zinc acetate.

MBT is stable as a bulk chemical for 2 weeks at 

temperatures up to 60° C when stored capped with a 

nitrogen headspace and protected from light.

Oxidation/Reduction: No reaction observed under ambient conditions when 

mixed with tap water, hexane, monoammonium phosphate, 

or zinc; mild reaction with potassium permanganate 

solution.

Flammability: Not applicable for products which do not contain 

combustible liquids.

Explodability: Contains no explosive ingredients.

Storage Stability: No evidence of degradation or decomposition was observed 

during the GC analysis of the stability samples. Visual 

inspection of the samples at the end of the 12-month 

storage period detected no evidence of physical change, 

such as clumping or discoloration. The amount of MBT 

determination for each analysis indicated that MBT was 

stable for one year under the conditions of the study.

Storage stability at room temperature (18 months) and at 

55°C (8 wks.): Stable.

Miscibility: Not applicable to products not intended to be diluted with 

petroleum solvents.

Corrosion Characteristics: After storage in contact with the technical grade MBT at 

54°C for 30 days, a color change was observed for the 

sample; however, no signs of corrosion were evident in the 

packaging material.

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

electrical equipment.
Page 5 of 28

pH: Not applicable to solids.

UV/Visible absorption: Not Reported.

Viscosity: Not applicable to solid products.

Melting point: Sample melted over a range of 105.4 to 106.8°C with no 

observed decomposition. (105-107 °C).

Boiling Point: N/A, MBT is a solid at room temperature.

Density: 0.820 g/mL

Dissociation Constant: It is non-ionic. Not determined because MBT was found to 

be unstable at pH levels higher than nine or lower than 

three, a spectrometric determination is not possible.

Log Ko/w: Ko/w (~0.01M solution) 2.2 ± 0.4 (s)

Ko/w (~0.001M solution) 2.1 ± 0.3 (d)

Solubilities: Its solubilities are 0.28, 0.35 and 5.1 g/100mL in water, 

octanol and methanol, respectively at 25°C.

Soluble in water.

Vapor Pressure: 1.22 x 10-4mmHg at 26 ± 1°C

Henry's Law Constant: 2.61E-008 atm-m3/mole (Source: EPI Suite)

Enforcement Analytical

Method: Gas Chromatography;

High Pressure Liquid Chromatography (HPLC).

All product chemistry data requirements have been satisfied for the active ingredient MBT.

(Source: MRIDs 41648001, 41607701, 41611902, 41611901, 40518601, 42739201, 41611901, 

42739202, 41607702, 41648002, 40518602, 40518602, 41648003, 41982101, and 43328601).

B. Environmental Fate Summary

No environmental fate assessment was performed for MBT at the time of the registration. 

Available environmental fate guideline studies and the results are summarized in Table 2.

The Agency's conclusions for the degradation and aqueous availability or leaching 

studies are summarized in Table 2 below.
Page 6 of 28

Table 2. Environmental Fate Data Summary for MBT

Guide line No. Data Type Summary MRID No.

161-1 Hydrolysis Stable at pH 5; half life at pH 7 = 6.18 days; 

half life at pH 9 = 2.22 hours; major 

degradates: thiocyanate, formic acid, and 

carbon dioxide

43092101

NonGuideline 

Study

Photolysis on 

treated Wood 

pieces

Treated Wood pieces irradiated with artificial 

light for 360 hours.

MBT-treated pine wood surfaces: half life: 61 

days; MBT-treated oak wood: half life: 48 

days; MBT treated.

Degradate identified: thiocyanate

43511101

NonGuideline 

Study

Aqueous 

Availability 

or Leaching 

Study

Wood pieces were dipped in MBT solution 

(1000-2000 ppm range), and were air dried for 

30 minutes or 30 days. The leachates were 

obtained in buffered medium as well as in 

artificial sweat solution either on a 30 minute 

sampling or 21 day sampling. MBT leached > 

70% between 3 days to 7 days duration.

The most common degradates were: 

thiocyanate and carbon dioxide, at pH 7, and 9

43545601

In summary, the registrants have submitted an acceptable hydrolysis study (MRID # 

430921-01), and information on photolysis of MBT on treated wood pieces (MRID # 435111-

01), and a wood leaching study (MRID # 435456-01). MBT is hydrolytically stable at pH 5, but 

degrades easily at pH 7 and 9. Through the hydrolysis and photolysis from the wood surfaces, 

the common degradates formed are: thiocyanate, formic acid, and carbon dioxide. The identified 

degradates of MBT are: formic acid, thiocyanate ions and carbon dioxide which are the ultimate 

degradation product (mineralization) of MBT. The Agency had speculated the formation of 

cyanide ion as a degradate in the RED document; however, additional data has indicated that the 

formation of cyanide ion from thiocyanate is not possible under environmental relevant 

conditions. Both formic acid which mineralizes into carbon dioxide under the environmental 

conditions, and carbon dioxide is itself the mineralized product, the Agency does not intend to 

ask for data on these degradates.

MBT is not likely to bioaccumulate as its Log Kow is around 2. 

The Agency needs to conduct an environmental fate assessment for material 

preservatives (including MBT) and industrial slimicides used in recirculating water cooling 

towers, pulp and paper mills, oil and gas well development, metal working fluids and wood 

preservatives that may potentially pass through waste water treatment plants (WWTPs) and may 

be discharged into terrestrial and aquatic environments. For this assessment the Agency 
Page 7 of 28

anticipates needing those data outlined on page 10 of this document. In addition, the Agency 

needs to conduct an environmental fate assessment for MBT used in wood preservatives. 

Water Quality

MBT 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 MBT, based on 

information provided at the Agency’s National Pesticide TMDL web site (searched April 7, 

2011)3

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

. More information on impaired water bodies and TMDLs can be found at 

. The Agency invites submission of water quality data for this 

pesticide. To the extent possible, data should conform to the quality standards in Appendix A of 

the OPP Standard Operating Procedure: Inclusion of Impaired Water Body and Other Water 

Quality Data in OPP’s Registration Review Risk Assessment and Management Process (see: 

http://www.epa.gov/oppfead1/cb/ppdc/2006/november06/session1-sop.pdf ), in order to ensure 

they can be used quantitatively or qualitatively in pesticide risk assessments.

C. Ecological Effects Summary

No quantitative ecological risk assessment was performed for MBT at the time of the 

RED. Available ecotoxicity guideline studies are summarized in Tables 3 and 4. The Agency's 

conclusions for the terrestrial and aquatic effects studies are as follows.

a. Toxicity to Terrestrial Organisms

MBT is highly toxic to birds on an acute-oral basis (LD50s = 45-50 mg/kg-bw/day) but is 

practically nontoxic on a dietary basis (LC50s >5000 ppm). A summary of the avian toxicity 

data endpoints from registrant-submitted studies is provided in Table 3. Insect pollinator data 

are required but not available. Mammalian toxicity data are not required, but acute and chronic 

data are available in the human health scoping document. 

Table 3. Summary of the Endpoints from Submitted Terrestrial Toxicity Studies for MBT

Study Type Species Toxicity Value Toxicity 

Classification MRID & Status

Acute – Avian 

Oral

850.2100

Northern Bobwhite 

(Colinus 

virginianus)

LD50: 50 mg/kg-bw/day Highly toxic 150232

Acceptable

Acute – Avian 

Oral

850.2100

Mallard

(Anas 

platyrhynchos)

LD50: 45 mg/kg-bw/day Highly toxic 150231

Acceptable

 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 8 of 28

Table 3. Summary of the Endpoints from Submitted Terrestrial Toxicity Studies for MBT

Study Type Species Toxicity Value Toxicity 

Classification MRID & Status

Acute – Avian 

Dietary

850.2200

Northern Bobwhite 

(Colinus 

virginianus)

LC50: >5000 mg/kg-diet Practically nontoxic 150233

Acceptable

Acute – Avian 

Dietary

850.2200

Mallard

(Anas 

platyrhynchos)

LC50: >5000 mg/kg-diet Practically nontoxic 150232

Acceptable

b. Toxicity to Aquatic Organisms

A summary of acute and chronic aquatic ecotoxicity data endpoints from registrantsubmitted studies is provided in Table 4. MBT is highly to very highly acutely toxic to 

freshwater and estuarine/marine fish (LC50s = 89 to 606 μg/L) and very highly toxic to aquatic 

invertebrates (EC50 and LC50s = 3 to 61 μg/L). Chronic data are available for a freshwater 

invertebrate but not for fish. Reproduction and growth of water fleas were adversely affected at 

16 μg/L (NOAEC = 5.8 μg/L) chronic exposure. Acute and chronic data for sediment-dwelling 

organisms are not available.

Table 4. Summary of the Endpoints from Submitted Aquatic Toxicity Studies for MBT

Study Type Species Toxicity Value Toxicity 

Classification MRID & Status

Acute –

Freshwater Fish

850.1075

Rainbow trout 

(Oncorhynchus 

mykiss)

96-hr LC50: 89 μg/L Very highly toxic 405186-09

Acceptable

Acute –

Freshwater Fish

850.1075

Bluegill sunfish 

(Lepomis 

macrochirus)

96-hr LC50: 250 μg/L Highly toxic 405186-08

Acceptable

Acute –

Estuarine/Marine 

Fish

850.1075

Sheepshead minnow 

(Cyprinodon 

variegatus)

96-hr LC50: 606 μg/L Highly toxic 425134-02

Acceptable

Acute –

Freshwater 

Invertebrate

850.1010

Water flea (Daphnia 

magna) 48-hr EC50: 61 μg/L Very highly toxic

405186-01

Acceptable

Acute –

Estuarine/Marine 

Invertebrate

850.1025

Eastern oyster 

(Crassostrea 

virginica)

96-hr LC50: 3 μg/L Very highly toxic 424416-01

Acceptable

Acute –

Estuarine/Marine 

Invertebrate

850.1035

Mysid shrimp 

(Americamysis 

bahia)

96-hr LC50: 36 μg/L Very highly toxic 425134-02

Acceptable

Chronic –

Freshwater 

Invertebrate

850.1300

Water flea (Daphnia 

magna)

NOAEC: 5.8 μg/L

LOAEC: 16 μg/L

(reproduction, growth)

NA 425170-01

Acceptable
Page 9 of 28

c. Toxicity to Aquatic Plants

Aquatic plant data (vascular and non-vascular species) are required for the risk 

assessment. No data are available.

Adverse Ecological Incidents

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

(EIIS) regarding MBT. 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 MBT’s use patterns described in 

this document. MBT uses that have potential for environmental exposure are material 

preservatives, wood preservatives, and industrial slimicides used in recirculating water cooling 

towers and pulp and paper mills discharges. The Agency needs to conduct environmental fate 

and ecological risk assessments for material preservatives and industrial slimicides used in 

recirculating water cooling towers and pulp and paper mills that potentially pass through waste 

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

environments. In addition, the Agency needs to conduct an ecological risk assessment for MBT 

used in wood preservatives. For this ecological risk assessment, including an endangered species 

assessment for all uses, the Agency anticipates needing the ecotoxicity data outlined on page 9 of 

this document.

The Agency has not conducted a risk assessment for MBT that supports a complete 

endangered species effects determination. The ecological risk assessment planned during 

registration review will allow the Agency to determine whether MBT’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 MBT. 

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

preservatives and industrial slimicides used in recirculating water cooling towers and pulp and 

paper mills that potentially pass through waste water treatment plants (WWTPs) and may be 

discharged into terrestrial and aquatic environments. In addition, the Agency needs to conduct 

an environmental fate and ecological risk assessment for MBT used in wood preservatives. 

Therefore, the Agency anticipates needing the proposed environmental fate and ecotoxicity data 

for MBT and/or any of its major degradation products that are of potential concern for all 

registered uses of MBT. The following environmental fate and ecotoxicity data are needed to 

conduct an environmental fate and ecological risk assessment:
Page 10 of 28

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

environmental fate assessment for material preservative use, and industrial slimicides 

used in recirculating water cooling towers and paper mills:

o Activated Sludge Sorption Isotherm (GLN 835.1110);

o Adsorption/Desorption Study (GLN 835.1230);

o Aqueous Photolysis (at pH 5) (GLN 835.2240);

o Aerobic Aquatic Metabolism Study (GLN 835.4300);

o Anaerobic Aquatic Metabolism Study (GLN 835.4400);

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

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

Simulation Tests to Assess the Biodegradability of Chemicals Discharged to 

Wastewater (GLN 835.3280), or Simulation Test-Aerobic Sewage Treatment: A. 

Activated Sludge Units (GLN 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 for 

material preservatives and industrial slimicides used in industrial process and water 

systems and wood preservative uses of MBT:

o Fish early-life stage toxicity test, freshwater species (GLN 850.1400);

o Aquatic plant toxicity test, vascular species (GLN 850.4400);

o Aquatic plant toxicity test, non-vascular (4 species) (GLN 850.5400);

o Honeybee acute contact (GLN 850.3020);

o Toxicity of residues to honeybees (GLN 850.3030);

o Sediment acute toxicity test, freshwater invertebrate (GLN 850.1735);

o Sediment acute toxicity test, marine invertebrate (GLN 850.1740); and

o Sediment chronic toxicity test, freshwater invertebrate (no guideline number).

The sediment toxicity tests will be waived if acceptable environmental fate data 

are provided to demonstrate that the half-life of the pesticide in the sediment is <

10 days and if all of the following conditions are met: 1) Kd <50, 2) Koc <1000, 

and 3) Kow <3.

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

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

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

Units or (iii) 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) a) Biodegradation in Activated Sludge or b) Simulation Test –

Aerobic Sewage Treatment: A. Activated Sludge Units or c) the Porous Pot Test. If the Ready Biodegradability 

study is conducted and the test substance passes, then no further testing is required. If, however, the test substance

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 11 of 28

Facility Emissions to WWTP Modeling

For assessing the fate of MBT and its major degradates, emitted to receiving waters from 

industrial process water uses of MBT such as at pulp and paper mills, for recirculating cooling 

towers, and oil and gas well development, metal working fluids and wood preservatives the 

Agency anticipates using the available environmental fate information from guideline studies for 

MBT and its major degradates, and the following emission scenarios.

• Potential environmental releases and associated exposures of concern for antimicrobial 

uses related to the Pulp, Paper, and Board Industry will be those identified in "Emission 

Scenario Documents on Pulp, Paper, and Board Industry", Number 23 of OECD Series 

on Emission Scenario Documents dated July 8, 2009.

• Potential environmental releases and associated exposures of concern for antimicrobial 

uses related to the Oil and Gas Well Production Industry will be those identified in the 

latest version of the OECD Emission Scenario Document for the Oil Well Production 

Industry or those identified in the latest version of Generic Scenarios developed by the 

Chemical Engineering Branch of EPA/OCSPP/OPPT/CEB (Chemical Engineering 

Branch). On-shore operations assume potential for disposal of drilling fluids and produce 

water to public or industrial waste treatment facilities and off-shore operations assume 

emissions directly to the surrounding water, post-treatment for removal of oil.

• Potential environmental releases and associated exposures of concern for uses of 

antimicrobial uses related to recirculating cooling towers will be assessed using the 

Generic Scenarios for recirculating cooling towers developed by the Chemical 

Engineering Branch of EPA/OCSPP/OPPT/CEB and modified for use for antimicrobials 

by the Antimicrobial Division.

Facility information needed to estimate aquatic exposures from emissions to WWTP for each 

emission scenario and directly to water from the oil and gas well development sites include the 

following:

• The number of pulp and paper mill sites using MBT or the maximum annual production 

volume of MBT used in pulp and paper mills in the United States and its territories;

• The number of recirculating cooling tower sites using MBT or the maximum annual 

production volume of MBT used in cooling towers in the United States and its territories; 

• The number of oil and gas well development sites using MBT or the maximum annual 

production volume of MBT used in oil and gas well development in the United States and 

its territories; 

• The number of metalworking fluid sites using MBT or the maximum annual production 

volume of MBT used in metalworking fluid preservatives in the United States and its 

territories; 

• How many of each of these facilities has on-site and/or off-site wastewater treatment.
Page 12 of 28

Facility information needed to estimate aquatic exposures from emissions to WWTP from the 

industrial wood preservative process include the following:

• The number of facilities that pressure treat wood products with thiamethoxam; and

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

In the absence of information on the number of these facilities that use MBT 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 MBT.

In the absence of appropriate test data on biodegradation during wastewater 

treatment, the Agency will assume that there is no removal of MBT and its major toxic 

degradates during wastewater treatment and that the amount of MBT and its major degradate 

released with the effluent from a wastewater treatment facility will be the same as the amount 

entering the wastewater treatment facility. In the absence of data on the percent removal of 

MBT and its major degradate during drinking water treatment the Agency will assume there is 

no removal of MBT or its major toxic degradates.
Page 13 of 28

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 non-target 

endangered and non-endangered species. Exposure data are integral parts of the risk equation for 

determining the impact of pesticides to beneficial nontarget organisms through direct exposure from their 

food sources and habitat.

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

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

water 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 in 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 organisms 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 could result in 
Page 14 of 28

use restrictions which are unnecessarily severe. 

Study Title: Sediment and Soil Adsorption/Desorption

Guideline Number 835.1230

Test Substance: TGAI

Rationale for Requiring the Data

A partition (or distribution) coefficient, Kd, is needed to conduct the environmental fate 

assessment to support the MBT uses in pulp and papermill process water systems, recirculating 

water cooling systems, and oil and gas well production development process systems, 

metalworking fluid and wood preservatives. The data is not currently available. The Agency has 

a limited understanding of the potential for MBT to partition and disperse in the aquatic 

environment by means of sorption to geological materials (e.g., soil, sediments, organic or 

biological matter). A leaching adsorption/desorption study is needed in order to determine the 

Kd, which will allow the Agency to determine whether it will be tightly bound to sediments, 

which in turn will allow the Agency to understand the magnitude of MBT exposure to sediment 

dwelling organisms. 

Controlled environmental fate and transport laboratory studies are used to determine the 

persistence, mobility, and bioconcentration potential of a pesticide active ingredient and its major 

degradates. The studies offer information on how, or by what mechanism, the pesticide degrades 

or dissipates, the rate at which it degrades or dissipates, where it goes, and what transformation 

products are formed. 

Practical Utility of the Data

1. How will the data be used?

The data would establish the significance of partitioning of MBT and its major degradates to 

sediment as a route of transport and dispersion. The data would also help establish the Kd, the 

partitioning of MBT between soil and water in water/sediment systems. The Kd data from the 

adsorption/desorption study are used as inputs to exposure models. These models estimate the 

expected environmental concentrations of the pesticide and it’s degradates under various 

environmental and use conditions for drinking water and ecological risk assessments. The 

requested data will result in better characterization of MBT mobility and will allow refined 

exposure estimates for drinking water and ecological risk assessments. 

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

In the absence of acceptable quantitative partitioning data, conservative assumptions about the 

pesticide’s sorption will be used. For the purposes of aquatic water column exposure modeling, 

MBT will be assumed to be highly mobile, which will lead to conservative aquatic exposure 

estimates that may result in unnecessary mitigation. For sediment exposure modeling, MBT will 

be assumed to partition primarily to sediment, which will lead to conservative sediment exposure 

estimates. If a direct measure of the partition coefficient were available, it would be used as an 

input for aquatic/sediment modeling which would provide refined aquatic/sediment exposure 

estimates, allowing for more accurate assessments of potential risks in drinking water and to 

ecological receptors, including endangered species.

Guideline Number: 835.2240

Study Title: Photodegradation in water

Practical Utility of the Data

1) What is the value of the study?
Page 15 of 28

Guideline Number: 835.2240

Study Title: Photodegradation in water

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 MBT 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 MBT 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 MBT 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 environmental fate assessment to support 

material preservative and industrial slimicide uses in pulp and papermill process water systems and 

recirculating water cooling tower systems for MBT. Also data are needed in order to conduct an 

environmental fate assessment for outdoor wood preservative use pattern of MBT.

Study Title: Aerobic Aquatic Metabolism

Guideline Number: 835.4300

Test Substance: TGAI

Rationale for Requiring the Data

Aerobic aquatic metabolism data is needed to conduct the environmental fate assessment to support the 

MBT uses in pulp and papermill process water systems, recirculating water cooling systems, and oil and 

gas well production development process systems, metalworking and wood preservatives. Acceptable data 

on the aerobic aquatic metabolism of MBT in two-sediment systems are required. The data is not currently 

available. The Agency has limited understanding of how MBT behaves in aerobic aquatic environments 

after discharge to receiving water. The purpose of aerobic aquatic metabolism study is to determine the 

nature and extent of microbial degradation under aerobic conditions in receiving water/sediment systems 

during the dispersal of the biocide throughout the aquatic environment, and to characterize the formation 

and decline of degradates. This information will determine the persistence and concentrations of MBT and 

potential degradates over the time in representative aerobic water/sediment systems. The results of the 

study will indicate the potential for MBT to contaminate the aquatic environment since biocide residues 

may be taken up by the sediment biota and passed on to other parts of the aquatic food web. Data are 

needed for two sediment-water systems conducted (one each) at neutral and acidic pHs.
Page 16 of 28

Practical Utility of the Data

1. How will the data be used?

The data would establish the significance of aerobic aquatic microbial degradation of MBT as a route of 

degradation and identify, if possible, the degradation products formed that may adversely affect non-target 

organisms and may contaminate water and food sources of aquatic organisms. The data would also help 

establish the aerobic aquatic aerobic half-life of MBT in water/sediment systems, and possibly it’s 

degradates, and assist in developing a degradation pathway.

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

The results of this study would indicate the nature and extent of formation and decline under aerobic 

aquatic conditions of MBT and it’s degradates that may be taken up by sediment biota and passed on to 

other parts of the aquatic food web, and facilitates assessment of potential disposal problems. The study 

helps to determine the degradation rate (half-life) of MBT in the presence of microorganisms in different 

natural water/sediment systems and establishes what metabolites (degradates) are formed under aerobic 

(oxygen-rich) conditions in the laboratory. If we do not receive this data MBT would be assumed to be 

stable to aerobic metabolism and we would not know if the chemical breaks down leading to reduced risk 

to human health or the environment or we would not know if more toxic degradates are formed leading to 

increased risk to human health or the environment. 
Page 17 of 28

Study Title: Anaerobic Aquatic Metabolism

Guideline Number: 835.4400

Test Substance: TGAI

Rationale for Requiring the Data

Anaerobic aquatic metabolism data is needed to conduct the environmental fate assessment to support the 

MBT uses in pulp and papermill process water systems, recirculating water cooling systems, and oil and 

gas well production development process systems, metalworking fluids and wood preservatives systems. 

Acceptable data on the anaerobic aquatic metabolism of MBT in two-sediment systems are required. The 

data is not currently available. The Agency has limited understanding of how MBT behaves in anaerobic 

aquatic environments after discharge to receiving water. The purpose of an anaerobic aquatic metabolism 

study is to determine the nature and extent of microbial degradation under anaerobic conditions in 

water/sediment systems during the dispersal of the biocide throughout the aquatic environment, and to 

characterize the formation and decline of degradates. This information will determine the persistence and 

concentrations of MBT and potential degradates over time in representative anaerobic water/sediment 

systems. The results of the study will indicate the potential for MBT to contaminate the aquatic 

environment since biocide residues may be taken up by the sediment biota and passed on to other parts of 

the aquatic food web. Additionally, anaerobic conditions are more likely to prevail where biocides are 

found in aquatic environments than in strictly terrestrial environments. Data are needed for two sedimentwater systems conducted (one each) at neutral and acidic pHs.

Practical Utility of the Data

1. How will the data be used?

Anaerobic aquatic metabolism data will facilitate a better understanding of the fate of MBT residues in 

water and sediment. The data would establish the significance of anaerobic aquatic microbial degradation 

of MBT as a route of degradation and identify, if possible, the degradation products formed that may 

adversely affect non-target organisms and may contaminate water and food sources of aquatic organisms. 

The data would also help establish the anaerobic aquatic microbial half-life of MBT in water/sediment 

systems, and possibly it’s degradates, and assist in developing a degradation pathway.

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

The results of this study would indicate the nature and extent of formation and decline under anaerobic 

aquatic conditions of MBT and it’s degradates that may be taken up by sediment biota and passed on to 

other parts of the aquatic food web, and would facilitate assessment of potential disposal problems. The 

study helps to determine the degradation rate (half-life) of MBT in the presence of microorganisms in 

different natural water/sediment systems and establishes what metabolites (degradates) are formed under 

anaerobic (oxygen-poor) conditions in the laboratory. If the data indicate that degradation in anaerobic 

conditions occurs rapidly in acidic and or neutral aquatic systems and produces nontoxic transformations 

products, then the Agency could potentially determine that MBT residues of concerns do not persist in 

these systems. If data indicate that degradation is not appreciable in aquatic systems or that transformation 

products are similar or higher toxicity than the parent compound, then the Agency could conclude that 

MBT residues of concern persist in aquatic systems under anaerobic conditions. In the absence of the 

requested data, MBT anaerobic aquatic metabolism half-lives will be conservatively assumed to be stable 

across the environmental pH range. 
Page 18 of 28

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 19 of 28

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 20 of 28

Appendix B: Ecological Guideline Study Justifications

Study Title: Fish Early-life Stage Toxicity Test (freshwater species)

Guideline Number: 850.1400

Test Substance: TGAI

Rationale for Requiring the Data

No fish early-life stage toxicity test for MBT 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 

MBT because the pesticide use patterns and environmental fate characteristics are expected to result in 

repeated exposure of freshwater organisms. 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 MBT. 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 MBT. 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 withdrawl of uses for MBT which may otherwise be 

avoided, or which are unnecessarily severe.

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 MBT. Uses of MBT in 

industrial process and water systems and discharges from oil and gas well development are expected to 

lead to exposure of aquatic organisms due to the repeated release and transport of MBT from use sites 

into aquatic ecosystems, and the persistence of MBT. Without these data, the Agency is unable to 

evaluate the potential risks to non-rooted vascular aquatic plants associated with exposure to MBT. 

Practical Utility of the Data

1. How will the data be used?

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. 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 MBT with effects to non-rooted aquatic plants in terms of yield, growth 
Page 21 of 28

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?

Because this is the only member of the quaternary phosphonium class of antimicrobials currently 

registered in the U.S., there is no possibility of using submitted toxicity data from closely-related 

surrogate chemicals to fill in potential data gaps. Therefore, until additional data become available, risks 

to non-rooted vascular plants (both Federally-listed and non-listed species) will be assumed in future 

MBT risk assessments. 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 withdrawl of uses for MBT which may otherwise be 

avoided, or which are unnecessarily severe.

Study Title: Aquatic plant growth, non-vascular species (one freshwater green alga species, one 

freshwater diatom species, one estuarine/marine species, and one cyanobacterium species), Tier II

Guideline Number: 850.5400

Test Substance: TGAI

Rationale for Requiring the Data

No nonvascular aquatic plant toxicity data has been submitted for MBT. A battery of four species, 

representing different morphological characteristics and environmental habitats are required for use 

patterns resulting in emissions to surface waters. Uses of MBT in industrial process and water systems 

and discharges from oil and gas well development, recirculating cooling tower, metalworking and wood 

preservatives are expected to lead to exposure of aquatic organisms due to the repeated release and 

transport of MBT from use sites into aquatic ecosystems, and the persistence of MBT. For MBT, there is 

evidence in the open literature that effects to algal species may occur at or below levels resulting on 

impacts to microbes. Without these data, the Agency is unable to evaluate the potential risks to nonvascular aquatic plants associated with exposure to MBT. The Agency would have to presume risk to 

federally listed and non-listed non-vascular plants, but would not be able to quantify the risk.

Practical Utility of the Data

1. How will the data be used?

The four aquatic nonvascular plant studies would allow the Agency to analyze effects on primary 

production. A toxicity study on non-vascular aquatic plant species is used to establish a dose response 

relationship of MBT with primary productivity 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 primary production 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?

Because this is the only member of the quaternary phosphonium class of antimicrobials currently 

registered in the U.S., there is no possibility of using submitted toxicity data from closely-related 

surrogate chemicals to fill in potential data gaps. Therefore, until additional data become available, risks 

to aquatic non-vascular plants (both Federally-listed and non-listed species) will be assumed in future 

MBT risk assessments. 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 withdrawl of uses for MBT which may otherwise be 

avoided, or which are unnecessarily severe.
Page 22 of 28

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.

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.

Guideline Number: 850.1735

Study Title: Sediment acute toxicity test, freshwater invertebrate

Practical Utility of the Data

1) What is the value of the study?

MBT may tend to accumulate in sediments over time and pose risks to sediment-dwelling organisms in 

freshwater environments.

2) How would the data be used?

Reported endpoints such as survival, growth, and/or emergence are compared to estimated sediment 

concentrations to determine the potential for risk.

3) How could the data affect the risk assessment?
Page 23 of 28

Guideline Number: 850.1735

Study Title: Sediment acute toxicity test, freshwater invertebrate

Practical Utility of the Data

Exceedance of the LOC indicates a potential for risk to sediment-dwelling organisms that may warrant 

regulatory action to mitigate risk.

4) What is triggering the need for this data?

Uses of MBT as a wood preservative and in industrial processes and water systems may lead to acute 

exposure of aquatic organisms due to transport of the active ingredient into aquatic sediments.

Guideline Number: 850.1740

Study Title: Sediment acute toxicity test, marine invertebrate

Practical Utility of the Data

1) What is the value of the study?

MBT may tend to accumulate in sediments over time and pose risks to sediment-dwelling organisms in 

estuarine/marine environments.

2) How would the data be used?

Reported endpoints such as survival, growth, and/or emergence are compared to estimated sediment 

concentrations to determine the potential for risk.

3) How could the data affect the risk assessment?

Exceedance of the LOC indicates a potential for risk to sediment-dwelling organisms that may warrant 

regulatory action to mitigate risk.

4) What is triggering the need for this data?

Uses of MBT as a wood preservative and in industrial processes and water systems may lead to acute 

exposure of aquatic organisms due to transport of the active ingredient into aquatic sediments.

Study Title: Test Method: 100.5 Life-cycle Test for Measuring the Effects of Sediment-associated 

Contaminants on Chironomus dilutus (formerly known as C. tentans) 

Guideline Number: Agency-wide guideline USEPA 2000b; Non-850 guideline, Special Study

Exposure Method: Spiked whole sediment

Test Substance: TGAI

Rationale for Requiring the Data

No chronic spiked-sediment toxicity test for a freshwater benthic emergent insect has been submitted for 

MBT. Use of MBT in industrial processes and water systems and oil and gas well production systems, 

recirculating cooling towers, metalworking fluids and wood preservatives may result in the active 

ingredient reaching aquatic sediments. Sediment benthos may be exposed to sediment associated 

chemicals via pathways not accounted for in water only studies, such as ingestion of sediment. Chemicals 

that partition to sediment and are persistent in the sediment have the potential to pose a chronic risk to 

sediment benthos. MBT or its degradates are assumed to partition to sediment and be persistent in aquatic 

environments.

For freshwater sediment studies, chronic tests on a benthic emergent insect (Chironomus dilutes, formerly 

Chironomus tentans) and an amphipod (Hyalella azteca) are requested. Although both are freshwater 

species, Hyalella and Chironomus differ substantially in their ecological niche (i.e., infaunal species 

versus epibenthic), physiology, and potential sensitivities to MBT exposure. Prior to conduct of the 
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study, the test design and protocol must be submitted for Agency review and approval. If the half-life is 

found to be <10 days in both aerobic and anaerobic aquatic sediment metabolism studies a 10-day 

survival and growth study for this species using public draft 850.1735 Whole Sediment Acute Toxicity 

Invertebrates, Freshwater. Prior to conduct of the study, the test design and protocol must be submitted 

for Agency review and approval as the there are changes in recommended testing guidance from that 

provided in the public draft.

Practical Utility of the Data

1. How will the data be used? 

Data from sediment toxicity studies will be used to estimate potential risks to benthic organisms 

associated with uses of MBT. Data from sediment toxicity studies will be compared to estimated 

sediment chronic exposure concentrations to evaluate the potential for MBT to adversely impact survival, 

emergence, reproduction, and growth of sediment invertebrates.

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

If the data indicates that registered MBT usage may pose a risk of adverse effects to non-target benthic 

organisms above the Agency Level of Concern, the Agency may explore decision options to mitigate this 

risk. The lack of these data will limit the flexibility the Agency and registrants have in coming into 

compliance with the Endangered Species Act, and could result in use restrictions for MBT which may 

otherwise be avoided, or which are unnecessarily severe.

Study Title: Methods for Assessing the Chronic Toxicity of Marine and Estuarine SedimentAssociated Contaminants with the Amphipod Leptocheirus plumulosus

Guideline Number: Agency-wide guideline USEPA 2001c; Non-850 guideline, Special Study

Exposure Method: Spiked whole sediment

Test Substance: Pure active ingredient

Rationale for Requiring the Data

No chronic spiked-sediment toxicity test for an estuarine/marine benthic amphipod has been submitted for 

MBT. Use of MBT in industrial processes and water systems and oil and gas well production systems 

may result in the active ingredient reaching aquatic estuarine/marine sediments. Sediment benthos may 

be exposed to sediment associated chemicals via pathways not accounted for in water only studies, such 

as ingestion of sediment. Chemicals that partition to sediment and are persistent in the sediment have the 

potential to pose a chronic risk to sediment benthos. MBT and its degradates are assumed to partition to 

sediment and be persistent given the lack of aquatic fate information.

Prior to conduct of the study, the test design and protocol must be submitted for Agency review and 

approval. If the half-life is found to be <10 days in both aerobic and anaerobic aquatic sediment 

metabolism studies a 10-day survival and growth study for this species using public draft 850.1740 

Whole Sediment Acute Toxicity Invertebrates, Freshwater. Prior to conduct of the study, the test design 

and protocol must be submitted for Agency review and approval as the there are changes in recommended 

testing guidance from that provided in the public draft.

Practical Utility of the Data

1. How will the data be used? 

Data from sediment toxicity studies will be used to estimate potential risks to benthic organisms 

associated with uses of MBT. Data from sediment toxicity studies will be compared to estimated 

sediment chronic exposure concentrations to evaluate the potential for MBT to adversely impact survival, 

emergence, reproduction, and growth of sediment invertebrates.

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

If the data indicates that registered MBT usage may pose a risk of adverse effects to non-target benthic 
Page 25 of 28

organisms above the Agency Level of Concern, the Agency may explore decision options to mitigate this 

risk. The lack of these data will limit the flexibility the Agency and registrants have in coming into 

compliance with the Endangered Species Act, and could result in use restrictions for MBT which may 

otherwise be avoided, or which are unnecessarily severe.

Guideline Number: 850.3020

Study Title: Honeybee acute contact

Practical Utility of the Data

1) What is the value of the study?

This study will be used to determine lethal effects to honeybees from acute exposure to MBT. 

2) How would the data be used?

 The LD50 is used to categorize acute toxicity of MBT to insect pollinators.

3) How could the data affect the risk assessment?

Categorization of the toxicity level indicates the need for product labels to bear a precautionary 

statement for insect pollinators.

4) What is triggering the need for this data?

Uses of MBT as a wood preservative may lead to acute exposure of honeybees that contact wood 

treated with MBT.

Guideline Number: 850.3030

Study Title: Toxicity of residues to honeybees

Practical Utility of the Data

1) What is the value of the study?

This study will be used to assess honeybee mortality from exposure to wood treated with MBT. 

2) How would the data be used?

 Measurement endpoints for lethality are compared to exposure estimates to evaluate the potential for 

risk.

3) How could the data affect the risk assessment?

Mortality of honeybees from exposure to wood treated with MBT may warrant regulatory action to 

mitigate risk to insect pollinators.

4) What is triggering the need for this data?

Uses of MBT as a wood preservative may lead to acute exposure of honeybees that contact wood 

treated with MBT.
Page 26 of 28

Appendix C:

Table 1. Registered Products of MBT

Registration

No.

Registration

Name

Company 

Name

Formulation 

Type

% of Active 

Ingredient

1022-583 NEXGEN

IBC 

Manufacturing 

Co.

Emulsifiable 

Concentrate 14.7

1448-34 MTC-10 Buckman 

Laboratories Inc.

Ready-to-Use 

Solution 10

1448-80 METHYLENE 

BIS(THIOCYANATE)

Buckman 

Laboratories Inc.

Technical 

Chemical 99

1448-81 BUSAN 1009 Buckman 

Laboratories Inc.

Ready-to-Use 

Solution 10

1448-102 BUSAN 1071 Buckman 

Laboratories Inc.

Soluble 

Concentrate 2.5

1448-147 M-20-1 Buckman 

Laboratories Inc.

Ready-to-Use 

Solution 10

1448-148 M-20-2 Buckman 

Laboratories Inc.

Soluble 

Concentrate 10

1448-171 M-5-1 Buckman 

Laboratories Inc.

Ready-to-Use 

Solution 2.5

1448-172 M-5-2 Buckman 

Laboratories Inc.

Soluble 

Concentrate 2.5

1448-357 MTC-10-SR Buckman 

Laboratories Inc.

Ready-to-Use 

Solution 10

1448-358 MTC-10-CT Buckman 

Laboratories Inc.

Ready-to-Use 

Solution 10

1448-359 MTC-10WB-CT Buckman 

Laboratories Inc.

Ready-to-Use 

Solution 10

1448-360 MTC-10WB-SR Buckman 

Laboratories Inc.

Ready-to-Use 

Solution 10

1448-375 MECT-F Buckman 

Laboratories Inc.

Formulation 

Intermediate 10

1448-376 BUSAN 1071WB Buckman 

Laboratories Inc.

Wettable 

Powder 2.5

1448-377 BUSAN 1009 WB Buckman 

Laboratories Inc.

Ready-to-Use 

Solution 10
Page 27 of 28

Registration

No.

Registration

Name

Company 

Name

Formulation 

Type

% of Active 

Ingredient

1448-408 BUSAN 1350 Buckman 

Laboratories Inc.

Wettable 

Powder 8

1448-435 BUSAN 1265WB Buckman 

Laboratories Inc.

Soluble 

Concentrate/

Solid

10

1448-438 BUSAN 1223 Buckman 

Laboratories Inc.

Emulsifiable 

Concentrate 10

1448-439 BUSAN 1234 Buckman 

Laboratories Inc.

Soluble 

Concentrate 10

1706-112 NALCON 7619 Nalco Company Ready-to-Use 

Solution 10

1706-200 NALCON 10WB Nalco Company Ready-to-Use 

Solution 10

3876-121 GE BETZ SLIMICIDE C31 GE Betz, Inc. Ready-to-Use 

Solution 5

8622-42 METHYLENE BIS 

(THIOCYANATE)

ICL-IP America, 

Inc.

Technical 

Chemical 99

9386-4 AMA-10 Kemira 

Chemicals, Inc.

Ready-to-Use 

Solution 10

9386-12 THIONATE Kemira 

Chemicals, Inc.

Technical 

Chemical 99

9386-26 AMA-10S Kemira 

Chemicals, Inc.

Ready-to-Use 

Solution 10

9386-31 AMA-10W Kemira 

Chemicals, Inc.

Ready-to-Use 

Solution 10

33677-1 TOLCIDE(R) MBT Rhodia UK 

Limited

Technical 

Chemical 99

47091-12 SM-10P INDUSTRIAL 

MICROBIOCIDE

Aurora Specialty 

Chemistries

Ready-to-Use 

Solution 10

56156-1 X-100 NATURAL SEAL 

WOOD PRESERVATIVE

American 

Building 

Restoration 

Products Inc

Ready-to-Use 

Solution .5

62190-30 ANTIBLU MC-30 Arch Wood 

Protection, Inc.

Emulsifiable 

Concentrate 14.7

64715-1 VEDEXIL-DM/K Lamirsa Technical 98.95
Page 28 of 28

Registration

No.

Registration

Name

Company 

Name

Formulation 

Type

% of Active 

Ingredient

Laboratories 

Miret S.A.

Chemical

67869-17 N-948 TECHNICAL Verichem, Inc. Technical 

Chemical 99

67869-31 N-948 WB Verichem, Inc.

Soluble 

Concentrate/

Solid

10

73612-1 SENTRY

Chemcolour 

Industries (NZ) 

Ltd.

Soluble 

Concentrate 6.42

74655-4 SPECTRUM RX-32 Hercules 

Incorporated

Ready-to-Use 

Solution 7

74655-6 SPECTRUM RX-38 Hercules 

Incorporated

Ready-to-Use 

Solution 5

74655-7 SPECTRUM RX-31 Hercules 

Incorporated

Ready-to-Use 

Solution 5

84377-1 BELLICIDE Bell Performance 

Inc

Flowable 

Concentrate 2.5