Page 2 of 7

Table 1. Registered Active Product of Dimethoxane

Registration # Registration Name Company 

Name

Formulation 

Type

% of Active 

Ingredient

464-682 BIOBAN DXN 

Antimicrobial

The Dow 

Chemical Co.

Ready-to-use

solution 87

Science Findings

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

fate, and ecotoxicity data for dimethoxane. The findings are summarized below.

Product Chemistry Summary

Common Name: Dimethoxane

Chemical Name: 2, 6-dimethyl-m-dioxan-4-ol acetate

CAS Registry Number: 828-00-2

OPP Chemical Code: 001001

Case: 3064

Molecular Formula: C8O4H14

Trade and Other Names: Dimethoxane, Acetomethoxane

Molecular weight: 174.2 g/mol

Molecular Structure:

Color: Clear yellow to light amber.

Physical State: Liquid

Odor: Strong odor - Characteristic halide odor. Mustard-like odor.

Stability: Stable after exposure to Zinc foil (a reducing agent). Not

stable at:

(a) low temperatures (-2 to 9 oC) after 48 hours

(b) high temp. (53-54 oC) for 2 weeks.

(c) simulated sunlight (Xenon lamp) for 24 hours.

Oxidation/Reduction: N/A

Flammability-Flash Point: 87oC/189oF (Tag Closed Cup)

Explodability: N/A
Page 3 of 7

Storage Stability: Stable during the storage period of 17.72 months at ambient temp.

Miscibility: N/A

Corrosion Characteristics: Corrosion rate of zinc coupons - 3.06 mm ± 0.266 per year

Dielectric breakdown voltage: N/A

pH: 5.8 at 25 oC

UV/Visible absorption: NR

Viscosity: 8.5 cPs at 25 oC

Melting point: N/A

Freezing Point: Below 25oC/77oF

Boiling Point: 66-68 oC at 3 mm Hg

Density: 1.060 - 1.075 g/ml at 25 oC

Specific Gravity: 1.0704 (25 oC/25 oC)

Dissociation Constant: N/A. Hydrolyses in aqueous solution to produce acetic acid and the 

corresponding free alcohol.

log P (octanol-water): N/A. Hydrolyzes in water.

Solubility: > 2 gm/ml @ 25 oC in Methanol, Hexane & Water. Not stable

in water. The approximate saturation point of test sample:

Methanol: 3.11 x 103

Hexane: 2.25 x 103

Water: 2.38 x 103

Vapor Pressure: 0.111 mm Hg at 23 oC

Henry's Law Constant: 1.24E-07 atm-m3/mole 25oC EST (EPI Suite)

Enf. Analytical Method: Gas Chromatograph

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

dimethoxane.
Page 4 of 7

Environmental Fate Summary

The Agency could not conduct a meaningful fate assessment because of limited data. 

The hydrolysis study was not adequate because it was not in compliance with OPPTS guideline 

835.2120 and no data were available on the activated sludge sorption isotherm or the ready 

biodegradability.

For hydrolysis (MRID Nos. 43326901 & 43797301) the available data indicate that the 

major route of degradation is abiotic hydrolysis aided by microbial mediated degradation. 

Furthermore, the data indicate that dimethoxane is highly unstable in water with over 50% of the 

compound hydrolyzed in 2 hours. Dimethoxane is appearing to react with water to form acetic 

acid and a transient intermediate, dioxinol. The dioxinol then breaks down into acetaldehyde and 

aldol (aldehyde + alcohol dimer). The breakdown into acetic acid and dioxinol is completed in 

14 hours. The study is classified as supplemental and provides useful information for risk 

assessment. A new study is not required.

In an acceptable Activated Sludge Respiration Inhibition study (OECD 209; MRID 

45560901) dimethoxane was shown to be essentially non-toxic to activated sludge respiration 

inhibition with an EC50 value of 1,060 mg/l. The study is acceptable.

The Agency did not conduct an environmental fate assessment for dimethoxane because 

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

material preservatives (including dimethoxane) that may potentially pass through waste water 

treatment plants (WWTPs) and may be discharged into terrestrial and aquatic environments. For 

this assessment the Agency anticipates needing those data outlined on page 6 of this document.

Water Quality

Dimethoxane 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 

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

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

based on information provided at 

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

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

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

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

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

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

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

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

assessments.
Page 5 of 7

Ecological Effects Summary

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

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

appropriate label precautions, and may be seen in Table 2 below.

a. Toxicity to Terrestrial Animals

(1) Birds, Acute and Subacute

Dimethoxane is slightly toxic to practically nontoxic to avian species on an acute 

oral and subacute dietary basis.

b. Toxicity to Aquatic Animals

(1) Freshwater Fish

Dimethoxane is not more than slightly toxic to both cold and warm water fish.

(2) Freshwater Invertebrates

Dimethoxane is not more than slightly toxic to aquatic invertebrates.

c. Toxicity to Plants (Algae)

Dimethoxane was toxic to freshwater alga at 3.4 ppm.

Table 2. Ecotoxicity Data Summary for Dimethoxane

GUIDE

LINE

COMMON

NAME

TAXONOMIC 

NAME

TEST

TYPE

%

AI

STUDY

TIME

DOSE

TYPE

TOXI

CITY

TOX

LEVEL NOEL STUDY STATUS

TOX 

CATEGORY MRID

Avian Acute Oral Toxicity

71-1

850.2100

Bobwhite 

quail

Colinus 

virginianus

O 92 14 D LD50 1585 MGK 810 Acceptable Slightly 

toxic

41962502

Avian Subacute Dietary Toxicity

71-2b

850.2200

Mallard 

duck

Anas 

platyrhynchos

D 92 8 D LC50 >5620 PPM 5260 Acceptable Practically 

nontoxic

41962503

71-2a

850.2200

Bobwhite 

quail

Colinus 

virginianus

D 92 8D LC50 >5620 PPM >5620 Acceptable Practically 

nontoxic

41962504

Freshwater Fish Acute Toxicity

72-1c

850.1075

Rainbow 

trout

Oncorhynchus 

mykiss

F 88.5 96 hr LC50 >37 PPM 10 Suppl Slightly 

toxic

41936701

Freshwater Invertebrate Acute Toxicity

72-2

850.1010

Water 

flea

Daphnia 

magna

F 88.5 48 hr EC50 >24 PPM 13 Suppl Slightly 

toxic

41962501

Algal Toxicity (Aquatic (Algal) Plant Growth Tier II)

123-2

850.5400

Green 

algae

Selenastrum 

capricornutum

S 94.3 96 hr EC50 3.4 PPM 2.39 Suppl Toxic 45664601

45828001
Page 6 of 7

Ecological Effects Risk Assessment

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

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

allow the Agency to determine whether dimethoxane’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 

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

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

be discharged into terrestrial and aquatic environments. Therefore, the Agency anticipates needing 

the proposed environmental fate data for dimethoxane and/or any of its major degradation products 

that are of potential concern for all registered uses of dimethoxane. The following environmental 

fate data are needed to conduct an environmental fate and ecological risk assessment:

The Agency anticipates needing the following data to conduct a complete 

environmental fate assessment for material preservative uses:

o (GLN 835.1110) Activated Sludge Sorption Isotherm; and

o (GLN 835.3110) Ready Biodegradability.
Page 7 of 7

Appendix A. Environmental Fate Guideline Study Justifications

Guideline Number: 835.1110

Study Title: Activated Sludge Sorption Isotherm

Practical Utility of the Data

1) What is the value of the study?

The results from activated sludge sorption study would allow EPA to assess the distribution of the 

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

those chemicals which sorb to sludge biomass.

2) How would the data be used?

The data would be used to determine the sorption potential of dimethoxane to activated sludge biomass 

and in biological wastewater treatment systems.

3) How could the data affect the risk assessment?

If dimethoxane is not sorbed or biodegraded then, it would pass through a biological treatment system 

unaffected and it may contaminate surface and drinking waters and also may have potential adverse 

effects to nontarget organisms.

4) What is triggering the need for this data?

Studies are needed to conduct environmental fate assessment and to determine the sorption potential of 

activated sludge for the removal of specific chemical compounds in biological wastewater treatment 

systems.

Guideline Number: 835.3110

Study Title: Ready Biodegradability

Practical Utility of the Data

1) What is the value of the study?

The ready biodegradability study would enable the Agency to determine the likelihood that the 

antimicrobial pesticide of biodegrading in aquatic environments under aerobic conditions.

2) How would the data be used?

The results from the data would be used to determine the rate and extent of aerobic biodegradation of 

dimethoxane when it is released into aquatic environments and would help establish if dimethoxane is 

stable or not stable under real environmental conditions.

3) How could the data affect the risk assessment?

If the result shows low biodegradability then, dimethoxane would occur in significant quantities in 

WWTP effluents (water and biosolids) and in environmental compartments (e.g., surface waters) such 

that potential adverse effects to nontarget organisms, found in such environmental compartments, may 

occur.

4) What is triggering the need for this data?

Data are needed to conduct environmental fate assessment and to determine the ready biodegradability of 

dimethoxane.

Sign-off Date: 11/23/10 DP Barcode No.: D382303