![](media/image1.png){width="1.5833333333333333in"
height="1.5416666666666667in"}**UNITED STATES ENVIRONMENTAL PROTECTION
AGENCY**

WASHINGTON, D.C. 20460

OFFICE OF

PREVENTION, PESTICIDES AND

TOXIC SUBSTANCES

> April 13, 2006

**[MEMORANDUM]{.underline}**

**SUBJECT:** Environmental Fate Assessment of Didecyl dimethyl ammonium
chloride (DDAC) for the Reregistration Eligibility Decision (RED)
Document

> **Case No.**: 3003 **DP Barcode:** 323303

**FROM:** Srinivas Gowda, Microbiologist/Chemist

Risk Assessment and Science Support Branch (RASSB)

Antimicrobials Division (7510C)

**TO:** Mark Hartman, Branch Chief

Benjamin Chambliss, Team Leader

Najm Shamim, Risk Assessor

Regulatory Management Branch II

Antimicrobials Division (7510C)

Tracy Lantz, Chemical Review Manager

Regulatory Management Branch I

> Antimicrobials Division (7510C)

**THRU:** Siroos Mostaghimi, Acting Team Leader, Team one

Risk Assessment and Science Support Branch (RASSB)

Antimicrobials Division (7510C)

Norman Cook, Branch Chief

Risk Assessment and Science Support Branch (RASSB)

> Antimicrobials Division (7510C)

**[Chemical Name]{.underline}** **[PC Code]{.underline}**
[**CAS#**]{.underline} **[Common Name]{.underline}**

Didecyl dimethyl ammonium chloride 069149 7173-51-5 DDAC

Environmental Fate Science Chapter and Fate Assessment on DDAC is
submitted for Reregistration Eligibility Decision (RED).

**1-DECANAMINIUM, N-DECYL-N,N-DIMETHYL-, CHLORIDE (DDAC)**

**ENVIRONMENTAL FATE SCIENCE CHAPTER**

**EXECUTIVE SUMMARY**

DDAC is used primarily as a disinfectant, sanitizer, or as a
microbiocide/microbiostat. It also serves as an algaecide,
bacteriocide/bacteriostat, fungicide/fungistat, insecticide, miticide,
virucide, and tuberculocide. Use sites for DDAC include agricultural
premises and equipment, food handling, commercial, industrial and
institutional settings, residential areas or areas of public access,
pets and kennels, medical facilities, swimming pools, aquatic areas, and
industrial water systems. DDAC is also used as a wood preservative. As
an agricultural pesticide, DDAC is used for ornamental plants, shrubs,
and vines. Some of the required guideline studies for an environmental
fate assessment have been submitted. The Agency is using these
environmental fate studies for fate assessment of DDAC to fulfill the
reregistration requirements. However, field dissipation and aquatic
field dissipation studies as well as a long-term study on accumulation
on soils are still needed.

DDAC has been shown to be hydrolytically stable under abiotic and
buffered conditions over the pH 5-9 range. DDAC is stable to
photodegradation in pH 7 buffered aqueous solutions; even in the
presence of a photosensitizer (acetone), degradation is minimal. DDAC is
not subject to photodegradation in soil.

Aquatic metabolism studies under aerobic and anaerobic conditions
indicate that DDAC is stable to microbial degradation. The calculated
aerobic and anaerobic half-lives of ^14^C-DDAC in flooded river water
are 180 days and 261 days, respectively. Similarly, DDAC was found to be
stable with very little degradation in aerobic soils during a year-long
metabolism study. However, a report on the biodegradability of DDAC
prepared by the Registrant concluded that the degree of DDAC
biodegradability is variable and is influenced by the chemical
concentration, alkyl chain length, the presence of anionic moieties and
the quantity and characteristics of the microbial population. According
to this report, DDAC is biodegradable and environmentally acceptable.
This report was based on information from the open literature,
unpublished sources, and meeting proceedings and has not been reviewed
by the Agency.

DDAC is immobile in soil. A soil mobility study reviewed by the Agency
shows that DDAC has a strong tendency to bind to sediment/soil with
Freundlich K~ads~ values of 1,095, 8,179, 32,791, and 30,851 in sand,
sandy loam, silty clay loam, and silt loam soils, respectively. Because
of its strong adsorption to soils, DDAC is not expected to contaminate
surface and ground waters.

Bioaccumulation of DDAC in freshwater fish is not likely to occur. Mean
steady state bioconcentration factors for DDAC were determined to be
38X, 140X, and 81X in the edible, nonedible, and whole body fish tissue,
respectively. DDAC is not expected to pose a concern for
bioconcentration in aquatic organisms.

Information on the aqueous availability of DDAC from wood indicates that
the use of DDAC as a wood preservative may result in minimal releases to
the environment.

**I. [Environmental Fate Assessment]{.underline}**

A.  Abiotic

In a hydrolysis study conducted under abiotic and buffered conditions,
methyl-labeled ^14^C-didecyl dimethyl ammonium chloride (DDAC), at
concentrations of 8.47 to 8.69 μg/ml, was stable in sterile aqueous
buffer solutions adjusted to pH 5 (0.2 M acetate), pH 7
\[tris(hydroxymethyl)aminomethane- (TRIS)\], pH 7
\[N-2-hydroxyethyl-piperazine-N'-2-ethanesulfonic acid (HEPES)\], and pH
9 (0.2 M borate) that were incubated in darkness at 25C ± 1C for 30
days. Of the recovered radioactivity throughout the 30-day monitoring
period, DDAC residues comprised 92.0 to 95.9% (pH 5), 89.9 to 94.5% (pH
7, HEPES), 93.1 to 97.9% (pH 7, TRIS), and 92.0 to 96.7% (pH 9). The
calculated half-lives for DDAC (extrapolated beyond the experimental
timeframe) were 368 days at pH 5, 194 days at pH 7 (TRIS), 175 days at
pH 7 (HEPES), and 506 days at pH 9. The hydrolysis guideline
requirements (OPP 161-1) have been fulfilled by this study (MRID No.
411758-01).

The photodegradation potential of DDAC was investigated in sensitized
and nonsensitized buffer solutions adjusted to pH 7 (0.2 M TRIS).
Methyl-labeled ^14^C-didecyl dimethyl ammonium chloride (DDAC), at a
concentration of 8.58 μg/ml, was relatively stable in nonsensitized
sterile aqueous buffer solutions that were continuously irradiated with
a xenon light source at 25C ± 1C for 30 days. DDAC concentrations
ranged from 91.2 to 103% of the applied radioactivity with no
discernible pattern of decline. In the dark controls, DDAC
concentrations ranged from 93.5 to 100% of the applied radioactivity
throughout the 30-day monitoring period. In a similar experiment using
acetone-sensitized buffer solutions, DDAC was also found to be
relatively stable. DDAC declined from 100% of the applied radioactivity
immediately post treatment to 93.1% at the end of 30-day monitoring
period. DDAC concentrations ranged from 96.2 to 102 percent of the
applied radioactivity with no discernible pattern of decline in the dark
sensitized controls. The calculated half-life of DDAC (extrapolated
beyond the experimental timeframe) was 227 days based on results for the
sensitized irradiated solutions. The photodegradation in water guideline
requirements (OPP 161-2) have been fulfilled by this study (MRID
411758-02).

B. Biotic

The aerobic aquatic biotransformation of DDAC was studied in a pond
water/sediment system (water - pH of 8.7, sediment - pH of 8, sandy loam
texture, organic carbon content of 1.6%) from Northwood, North Dakota
treated with methyl-labeled \[^14^C\]DDAC at a nominal concentration of
10 parts per million (ppm). The treated water/sediment system was
incubated in the dark for 365 days at 25C. The calculated half-lives of
^14^C-DDAC in water, sediment, and in the entire system were 180 days,
22,706 days (60.5 years), and 8,366 days (22.9 years), respectively. At
test termination, 101% of the applied radioactivity was partitioned from
water to sediment. Transformation products were not present in any
significant amounts in the water or sediment. The aerobic aquatic
metabolism guideline requirements (OPP 162-4) have been fulfilled by
this study (MRID 422538-03).

A study of the anaerobic aquatic metabolism of DDAC in lake water and
sediment was also conducted. Samples of lake water and sediment were
incubated at 25 C in a dark environment for 365 days. In this study,
DDAC was shown to be stable to microbial degradation. The calculated
half-lives, based on first-order degradations of ^14^C-DDAC in anaerobic
water, sediment and in the entire system were 261, 4,594, and 6,217
days, respectively. Transformation products were not present in any
significant amounts in the water or sediment. This study satisfies the
anaerobic aquatic metabolism guideline requirements (OPP 162-3) (MRID
No. 422538-02).

The aerobic soil metabolism of DDAC was investigated in a sandy loam
soil, which is a representative agricultural soil. The soil was treated
with \[^14^C\]DDAC to achieve a concentration of 10 ppm and incubated in
darkness at 25C for up to 365 days. DDAC was found to be stable with
very little degradation during the year-long study. Transformation
products were not present in any significant amounts. The calculated
half-life for degradation was 1,048 days. This study is acceptable and
satisfies guidelines (OPP 162-1) for aerobic soil metabolism (MRID No
422538-01).

A review of information from the open literature, unpublished sources
and meeting proceedings prepared by the Registrant indicates that DDAC
is aerobically biodegradable. The report author noted that the aerobic
and anaerobic aquatic metabolism studies conducted on DDAC were designed
to assess the environmental fate of DDAC based on outdoor applications
of agricultural chemicals but not the direct biodegradability potential
of DDAC as a result of its use as an antimicrobial. Other limitations of
the tests were noted such as loss of microbial activity during air
drying of soil material, limited gas exchange in the aerobic test, and
the use of unacclimated microbial systems. According to this report, the
degree of DDAC's biodegradability is variable and is influenced by the
chemical concentration, alkyl chain length, the presence of anionic
moieties and the quantity and characteristics of the microbial
population.

A mechanism of biodegradation for DDAC in which several bacterial
species are needed for ultimate biodegradation of this compound is also
described.

In an adsorption/desorption study reviewed by the Agency, DDAC was found
to be immobile in four representative agricultural soils (sand, sandy
loam, silt clay loam, and silt loam). Freundlich K~ads~ values were
1,095 for the sand, 8,179 for the sandy loam, 32,791 for the silty clay
loam, and 30,851 for the silt loam soils. Respective K~oc~ values were
437,805, 908,757, 1,599,564, and 1,469,081. Freundlich K~des~ values
were 591 for the sand soil, 2,074 for the sandy loam soil, 8,309 for the
silty clay loam soil, and 7,714 for the silt loam soil. Respective K~oc~
values were 236,473, 230,498, 405,328, and 367334. This study (MRID No.
413853-01) partially fulfills the adsorption/desorption data
requirements for DDAC (OPP 163-1) by providing information on the
mobility (batch equilibrium) of unaged ^14^C-DDAC in sodium
azide-sterilized sand, sandy loam, silty clay loam, and silt loam soils.
However, additional data are required on the mobility of aged ^14^C-DDAC
residues in soil.

A 46-day study (28-day bioconcentration and 18-day depuration period)
was conducted to evaluate the bioconcentration of DDAC in bluegill
sunfish under flow-through aquarium conditions (MRID No. 458341-01). In
this study, the levels of ^14^C residues in the edible, nonedible and
whole body fish tissue reached steady state by day 10 of exposure. Mean
steady state bioconcentration factors for DDAC were 38X, 81X, and 140X
in the edible tissue, whole body fish tissue, and nonedible tissue,
respectively. These bioconcentration factors are considered relatively
low and indicate that DDAC would not be expected to bioaccumulate in
fish tissue. By day 14 of the depuration period, 57%, 67%, and 71% of
the ^14^C residues present on the last day of exposure in the edible,
whole body, and nonedible tissue, respectively, had been eliminated.
DDAC was found to bind significantly to the non-edible segments of the
bluegill, especially the skin and scales. ^14^C residue levels were
approximately 2 to 6 times higher in skin tissue than those observed for
the corresponding edible tissue. The half-life of DDAC was determined to
be between 7 and 14 days of depuration. Study results also indicated
that the half-life of DDAC in edible tissue is significantly shorter
than that of the nonedible segments. The Agency noted that the
concentration of DDAC in the treatment aquarium was continuously above
nominal and was not consistently maintained within ± 20% of the mean
measured value. In addition, the temperatures ranged between 17-18 °C,
which is below the recommended temperature of 20-25 °C. However, the
study was found by the Agency to be acceptable and provided useful
information on the bioaccumulation of DDAC residues in bluegill sunfish.
It satisfies the bioaccumulation in fish data requirements for DDAC (OPP
165-4/850.1730).

A photolysis study was conducted with DDAC on soil treated at a nominal
concentration of 10 ppm. The study consisted of two test systems: an
exposed test system that was continuously irradiated with a xenon arc
light source for 30 days and a non-exposed test system. In the exposed
system, the photolysis rate constant and half-life of DDAC were reported
as 5.26 x 10^-3^ days^-1^ and 132 days, respectively. The photolysis
rate constant and half-life of DDAC in the non-exposed system were
determined to be 4.11 x 10^-3^ days^-1^ and 169 days, respectively. This
study is acceptable and meets guidelines for the fulfillment of data
requirements for DDAC on photodegradation on soil (OPP 161-3) (MRID No.
424807-01).

An aqueous availability study (MRID No. 455243-05), performed according
to the American Wood Preservers' Association Standard, Method E11-97,
evaluated the leachability of didecylmethyl ammonium carbonate
(DDACarb), a related compound, from treated wood. Wood samples were
vacuum-treated with 0.85 percent (0.5X retention level), 1.7 percent
(1X), and 3.4 percent (2X) of DDACarb, and placed in deionized water for
14 days. Leachate was collected from the sampling unit at intervals of
6, 24, and 48 hours, and 4, 6, 8, 10, 12, and 14 days following the
start of the leaching period. The corrected amount of DDACarb recovered
from the leachate ranged from 186.1 µg to 764.7 µg (0.5X retention
level), from 218.9 µg to 1152.9 µg (1X), and from 446.2 µg to 2101.1 µg
(2X). The total recovery from the leachate over the 14-day period was
3464.7 µg, 4483.0 µg and 7444.7 µg for the 0.5X, 1X and 2X retention
levels, respectively.

**APPENDIX**

**Environmental Fate Data for DDAC**

**A. [Environmental Fate Guideline Studies]{.underline}**

**1. Hydrolysis (OPP Guideline Number 161-1, MRID No. 411758-01)**

This hydrolysis study was reviewed by the Agency and was found
acceptable. The hydrolysis data requirements for DDAC have been
fulfilled.

In this study, methyl-labeled \[^14^C\]DDAC (didecyldimethylammonium
chloride, radiochemical purity 99.2%, specific activity 9.01 mCi/mmol),
in deionized, sterile-filtered water, was added to sterile pH 5
(acetate), pH 7 (TRIS), pH 7 (HEPES) and pH 9 (borate) aqueous buffer
solutions at concentrations of 8.47-8.69 μg/ml. Aliquots of the treated
buffer solutions were added to sterile, foil-covered culture tubes and
incubated in the dark at 25 ± 1C for 30 days. Samples were removed for
analysis at 0, 4, 7, 14, 22, and 30 days post treatment.

At each sampling interval, duplicate aliquots of the buffer solutions
were analyzed for total radioactivity by liquid scintillation counting
(LSC). An additional aliquot of the test solution was analyzed by
one-dimensional TLC on silica gel plates developed in
chloroform:methanol:formic acid (60:40:2, v:v:v). Radioscanning was used
to locate and quantify radioactive areas. TLC plates from the 0- and
30-day sampling intervals were analyzed by autoradiography.

Study results indicate that methyl-labeled \[^14^C\]DDAC was relatively
stable in sterile pH 5, pH 7 (TRIS and HEPES), and pH 9 buffer solutions
incubated in the dark at 25 ± 1C for 30 days. In the pH 5 buffer
solution, the parent was present at 92.0% of the recovered radioactivity
at 30 days posttreatment (range during the study: 92.0 - 95.9% of the
recovered radioactivity); total \[^14^C\]DDAC residues during the study
ranged from 8.22 μg/mL to 8.95 μg /ml with no discernible pattern. The
parent comprised 89.9 - 94.5% and 93.1 - 97.9% of the recovered
radioactivity in the pH 7(HEPES) and pH 7 (TRIS) buffer solutions,
respectively. Total \[^14^C\]DDAC residues during the study ranged from
7.93 μg /ml to 9.02 μg /ml in the pH 7 (HEPES) buffer solution and from
7.83 μg /ml to 8.90 μg /ml in the pH 7 (TRIS) buffer solution . In the
pH 9 buffer solution, total \[^14^C\]DDAC residues ranged from 8.00 μg
/ml to 8.67 μg /ml with no discernible pattern; parent \[^14^C\]DDAC
comprised 92.0 - 96.7% of the recovered radioactivity. The material
balances were 95.6 - 104% for the pH 5 solution, 93.6 - 106% for the pH
7 (HEPES) solution, 90.1 - 102% for the pH 7 (TRIS) solution, and 92.3 -
100% for the pH 9 solution.

The calculated half-lives for \[^14^C\]DDAC were 368 days at pH 5, 194
days at pH 7 (TRIS), 175 days at pH 7 (HEPES), and 506 days at pH 9. It
was noted that these statistical estimates are of limited value because
the calculations involve extrapolation considerably beyond the
experimental time limits of the study.

TLC analysis of the pH 7 (HEPES) solution at day 30 indicated a slight
decrease (approximately 10%) in the size of the parent peak; the
material appeared to form a shoulder on the parent peak. However, given
the apparent half-life of 175 days and a low correlation coefficient (r2
= 0.575), the authors concluded that this observation did not indicate
significant degradation.

**2. Photodegradation in Water (OPP Guideline No. 161-2, MRID No.
411758-02)**

This photodegradation study was reviewed by the Agency and was found to
be acceptable. The photodegradation in water data requirements for DDAC
have been satisfied.

In this study, methyl-labeled \[^14^C\]DDAC (didecyldimethylammonium
chloride, radiochemical purity ≥ 98.5%, specific activity 9.01
mCi/mmol), in deionized water, was added to sterile pH 7 (TRIS) buffer
solution at a concentration of 8.58 µg/ml. \[^14^C\]DDAC was also added
at a concentration of 8.59 µg /ml to a sterile pH 7 (TRIS) buffer
solution that had been photosensitized with 1% acetone. Aliquots of the
treated solutions were transferred to borosilicate glass culture tubes
with Teflon-lined screw tops. Some of the vials containing the test
solutions were covered with aluminum foil and stored inside a closed box
(dark control samples). The box was placed along with unwrapped tubes
(12) in a photolysis apparatus. A xenon lamp was used to continuously
irradiate the samples for 30 days. The temperature in the photolysis
chamber was maintained at 25 ± 1C.

Aliquots of the test solutions were analyzed immediately post treatment
and duplicate samples of irradiated and dark control solutions were
removed for analysis at 1.03, 2.02, 7.03, 14.0, 21.0, and 29.9 days post
treatment. At each sampling interval, duplicate aliquots of irradiated
and dark control solutions were analyzed for total radioactivity by
liquid scintillation counting (LSC). Additional aliquots of each test
solution were analyzed by one-dimensional TLC on silica gel plates
developed in chloroform:methanol:formic acid (60:40:2, v:v:v).
Radioactive areas were located and quantified by radioscanning. In
addition, TLC plates from the 0- and 30-day sampling intervals were
autoradiographed. The volatilization of \[^14^C\] residues from the
irradiated and dark control samples was also measured.

Methyl-labeled \[^14^C\]DDAC, at a concentration of 8.58 µg/ml, was
relatively stable in nonsensitized aqueous buffer solution (pH 7) that
was continuously irradiated with a xenon light source at 25C ± 1C for
30 days. In the irradiated samples, \[^14^C\]DDAC was present at 100% of
the applied radioactivity immediately post treatment and ranged from
91.2 to 103% of the applied radioactivity throughout the study period
(1.03 -- 29.9 days). \[^14^C\]DDAC was 93.5-98.9% of the applied
radioactivity from 1.03 -- 29.9 days and was present at 100% of the
applied radioactivity immediately post treatment in the dark control
samples.

In the irradiated sensitized samples, \[^14^C\]DDAC was present at 100%
of the applied radioactivity immediately post treatment and declined to
93.1% at 29.9 days. An unidentified degradate was detected, but not
quantified. In the dark controls, \[^14^C\]DDAC was 100% of the applied
radioactivity immediately post treatment and 96.2-102% of the applied
radioactivity from 1.03 -- 29.9 days. The calculated photolytic
half-life was 227 days.

Material balance ranged from 90.4 to 102%. Results of the volatility
experiments indicated little or no volatilization of \[^14^C\]DDAC from
the test solutions.

**3. Aerobic Soil Metabolism (OPP Guideline No. 162-1, MRID No.
422538‑01)**

This aerobic soil metabolism study was reviewed by the Agency and found
to be acceptable. The study meets guidelines for the fulfillment of data
requirements for DDAC on aerobic soil metabolism. However, the Agency
stated that the Registrant must provide evidence that aerobic conditions
were maintained throughout the experiment.

In this study, samples of sandy loam soil (collected from Northwood,
North Dakota, 78% sand, 10% silt, 12% clay, 1.8% organic carbon, pH 6.3,
CEC 0.7 meq/100 g) were treated with methyl-labeled \[^14^C\]DDAC
(didecyldimethylammonium chloride, radiochemical purity 90%, specific
activity 9.01 mCi/mmol), at a nominal concentration of 10 parts per
million (ppm).

The treated soil samples were incubated in darkness at 24-26C for up to
365 days; soil moisture levels were maintained between 70% and 75% of
field moisture capacity by the addition of water as needed. The test
system consisted of a standard tall form 3,000 ml resin-pot as the
incubation vessel and included an ethylene glycol trap, a sulfuric acid
trap and two potassium hydroxide traps vessels for trapping CO~2~ and
volatile organics. Samples were analysed at 0, 1, 3, 7, 14, 31, 61, 92,
123, 182, 273, and 365 days of incubation. The soil samples were
extracted with 30 ml of 80:20 (v:v) dimethylformamide:acetic acid and
then shaken for 1 hour, followed by centrifugation for 10 minutes. Total
radioactivity in the samples was determined by liquid scintillation
counting (LSC). Quantification and identification of the ^14^C-DDAC
residues was performed using TLC and/or HPLC.

Material balance averaged 100.5 ± 4.1% of the applied amount. The
concentration of the parent compound decreased from a mean of 93.7% of
the applied amount at day 0, to a mean of 72.85% of the applied amount
at the end of the study period. However, no biotransformation of the
parent compound was reported. The calculated half-life of ^14^C-DDAC in
aerobic soil was 1,048 days.

Extractable ^14^C-residues decreased from a mean of 98.55% of the
applied amount at day 0 to a mean of 74.87% of the applied amount at the
end of study period. Non-extractable ^14^C-residues increased from a
mean of 1.45% of the applied amount at day 0 to a mean of 17.74% of the
applied at the end of the incubation period. At study termination, an
average of 1.95% of the applied radioactivity was present as volatile
organics. CO~2~ was not present in any significant amount.
Transformation products were not present in any significant amounts in
the water or sediment.

**4. Anaerobic Aquatic Metabolism (OPP Guideline No. 162-3, MRID No.
422538-02)**

This anaerobic aquatic metabolism study was reviewed by the Agency and
was found acceptable. It fulfills the anaerobic aquatic metabolism data
requirement for DDAC; however the Agency noted that the Registrant must
submit information describing how anaerobic conditions were assured and
maintained.

The anaerobic aquatic metabolism of DDAC was studied using subsamples
(10 g dry weight) of sieved (2 mm) sandy loam sediment from Northwood,
ND (62% sand, 22% silt, 16% clay, pH 8, CEC 16.3 meq/100g, organic
carbon 1.6%) flooded with 20 ml of lake water from the same site (pH
8.1). The sediment water samples were treated with a sufficient amount
of methyl-labeled \[^14^C\]DDAC (didecyldimethylammonium chloride,
radiochemical purity 90%, specific activity 9.01 mCi/mmol), to achieve a
nominal concentration of 10 parts per million (ppm). The test tubes were
incubated in the dark at a temperature of 25 °C for 365 days; the test
system consisted of a standard tall form 3000-ml resin-pot as the
metabolism vessel. An ethylene glycol trap, a sulfuric acid trap and two
potassium hydroxide traps were attached for the collection of carbon
dioxide (CO~2~) and volatile organic compounds. Sediment, water and
volatile traps were sampled at 0, 1, 3, 7, 14, 31, 61, 92, 123, 182,
273, and 365 days of incubation. Volatile traps were also sampled at
151, 212, 243, 304 and 335 days of incubation.

At each sampling interval, sediment:water samples were centrifuged and
the aqueous phase decanted. The water samples were extracted via mixing
with an equal volume of 80:20 (v:v) dimethylformamide:acetic acid and
then run through a 0.2- filter to remove any suspended solids. The
sediment samples were extracted with 30 ml of 80:20 (v:v)
dimethylformamide:acetic acid and then shaken for 1 hour, followed by
centrifugation for 10 minutes. Quantification and identification of the
^14^C-DDAC residues was performed using TLC and/or HLPC.

Material balance averaged 103.1 ± 3.5 % of the applied amount for the
year-long study. The test conditions outlined in the study protocol were
maintained throughout the study. Extractable \[^14^C\]residues in
sediment increased from a mean of 84.87 % at day 0, to a mean of 92.22 %
of the applied amount, at study termination. Non-extractable
\[^14^C\]residues in sediment decreased from a mean of 12.21 % at day 0,
to a mean of 10.39 % of the applied amount, at study termination. At the
end of the study, 0.30 % of the applied radioactivity was present as
volatile compounds, and this activity was later confirmed to be
^14^C-carbon dioxide via precipitation with barium chloride.

The concentration of ^14^C-DDAC in water decreased from a mean of 100 %
at day 0 to a mean of 68.65 % of the applied amount, at study
termination. The concentration of ^14^C-DDAC in the sediment increased
from a mean of 93.85 % at day 0 to a mean of 97.45 % of the applied
amount, at the end of the study period. The study authors noted that
transformation products were not present in any significant amounts in
the water or sediment.

The calculated half-life of ^14^C-DDAC (for the entire system), based on
a first-order degradation, was 6,218 days. The Agency's calculated
half-lives, based on first-order degradations of ^14^C-DDAC in anaerobic
water, sediment and in the entire system were 261, 4,594, and 6,217
days, respectively. No biotransformation of the parent compound was
reported.

**5. Aerobic Aquatic Metabolism (OPP Guideline No. 162-4, MRID No.
422538-03)**

This aerobic aquatic metabolism study was reviewed by the Agency and was
found to be acceptable. It satisfies the aerobic aquatic metabolism data
requirements for DDAC. However, the Agency noted that the Registrant
must submit information describing how aerobic conditions were assured
and maintained.

In this study, subsamples (10 g dry weight) of sieved (2 mm) sandy loam
sediment from Northwood, ND (62% sand, 22% silt, 16% clay, pH 8, CEC
16.3 meq/100g, organic carbon 1.6%) were weighed into culture tubes and
flooded with 20 ml of lake water from the same site (pH 8.7). The
sediment was treated with a sufficient amount of methyl-labeled
\[^14^C\]DDAC (didecyldimethylammonium chloride, radiochemical purity
98.5 ± 0.04%, specific activity 9.01 mCi/mmol), to achieve a nominal
concentration of 10 parts per million (ppm). The test tubes were
incubated in the dark at 25C for 365 days; the test system consisted of
a standard tall form 3000-ml resin-pot as the metabolism vessel. An
ethylene glycol trap, a sulfuric acid trap and two potassium hydroxide
traps were attached for the collection of carbon dioxide (CO~2~) and
volatile organic compounds. Sediment, water and volatile traps were
sampled for analysis at 0, 1, 3, 7, 14, 31, 61, 92, 123, 182, 273, and
365 days of incubation. Volatile traps were also sampled at 151, 212,
243, 304 and 335 days of incubation.

At each sampling interval, sediment:water samples were centrifuged and
the aqueous phase decanted. Before analysis by thin layer chromatography
(TLC), the 6-, 9-, and 12-month water samples were concentrated by
evaporating aliquots to dryness and redissolving in methanol. The other
water samples were not concentrated prior to analysis. The sediment
samples were extracted with 30 ml of 80:20 (v:v) dimethylfomamide
(DMF):acetic acid and then shaken for 1 hour, followed by centrifugation
for 10 minutes. Quantification and identification of the ^14^C-DDAC
residues was performed using TLC and/or high performance liquid
chromatography (HLPC).

The material balance averaged 105 ± 2.8 % of the applied amount for the
year long study. The mean total recovery of the radiolabelled material
applied was 1.5 ± 0.9% for water and 101.9 % for sediment (93.0 ± 4.4%
for extractable residues and 8.9 ± 3.3% non-extractable residues). The
concentration of ^14^C-DDAC in water decreased from 2.20 % at day 0, to
0.83% of the applied at study termination. The concentration of
^14^C-DDAC in the sediment increased from 86.0% at day 0 to 87.8% of the
applied, at the end of the study period. At test termination, 101% of
the applied radioactivity was partitioned from water to sediment.
Transformation products were not present in any significant amounts in
the water or sediment.

Extractable \[^14^C\]residues in sediment decreased from an average of
90.0 % at day 0, to 89.9 % of the applied amount at the end of
incubation period. Non-extractable \[^14^C\]residues in sediment
increased from 7.8% at day 0, to 11.3% of the applied amount, at study
termination. At the end of the study, 4.5 % of the recovered
radioactivity was present as volatiles. The volatiles were determined to
be ^14^C-carbon dioxide via precipitation with barium chloride.

As determined by the Agency, the half-lives of ^14^C-DDAC in water,
sediment, and in the entire system were 180 days, 22,706 days (60.5
years), and 8,366 days (22.9 years), respectively. The Registrant
calculated a half-life of 8,365 days for ^14^C-DDAC in the entire
system. The pathway of aerobic biotransformation of ^14^C-DDAC in
water-sediment system was not described.

**6. Adsorption/Desorption (OPP Guideline No. 163-1, MRID No.
413853-01)**

This adsorption/desorption study was reviewed by the Agency and found
scientifically valid. This study partially fulfills the
adsorption/desorption data requirements for DDAC by providing
information on the mobility (batch equilibrium) of unaged ^14^C-DDAC in
sodium azide-sterilized sand, sandy loam, silty clay loam, and silt loam
soils. Additional data are required on the mobility of aged ^14^C-DDAC
residues in soil.

Based on the results of preliminary batch equilibrium studies, an
equilibration period of 24 hours and a soil:solution ratio of 1:200
(w:v) were chosen for this study. For the adsorption phase of the study,
aliquots (200 ml) of 0.1 N CaCl~2~ solution containing methyl-labeled
\[^14^C\]DDAC (didecyldimethylammonium chloride, radiochemical purity
97.5%, specific activity 9.01 mCi/mmol), at nominal concentrations of
0.70, 3.50, 5.25, and 7.0 µg/ml, were added to sterile Nalgene screw-cap
bottles containing subsamples (1 g) of sand, sandy loam, silty clay
loam, or silt loam soils. The soil samples had been air-dried, sieved (2
mm) and sterilized by addition of 1% sodium azide (w:w) prior to the
experiment. Triplicate tubes were prepared for each soil type/treatment
rate combination. After the adsorption equilibration period of 24 hours
in a dark environmentally controlled chamber at approximately 25 ± 1C,
the soil:solution slurries were centrifuged and triplicate aliquots of
the supernatant were analyzed for total radioactivity by liquid
scintillation counting (LSC).

For the desorption phase of the study, pesticide-free 0.01N CaCl~2~
solution (equal to the volume removed in the adsorption phase) was added
to the soil pellets from the adsorption phase of the study. The
soil:solution slurries were again equilibrated for 24 hours at
approximately 25 ± 1C in the dark. Following equilibration, the
soil:solution slurries were centrifuged and triplicate aliquots of the
supernatant were analyzed for total radioactivity by LSC.

The sandy loam, silty clay, and silt loam samples were dried and
analyzed for total radioactivity by LSC following combustion. The sand
soil samples were extracted three times with dimethylformamide:acetic
acid (80:20). Following extraction, the samples were centrifuged and
aliquots of the supernatant were analyzed by LSC. Subsamples of the
extracted soil were analyzed by LSC following combustion.

^14^C-didecyl dimethyl ammonium chloride (DDAC), at nominal
concentrations of 0.70-7.0 µg/ml, was determined to be immobile in
sodium azide-sterilized sand, sandy loam, silty clay loam, and silt loam
soil:solution slurries (1:200) that were equilibrated in darkness at
25C ± 1C for 24 hours. Freundlich K~ads~ values were 1,095 for sand,
8,179 for the sandy loam, 32,791 for the silty clay loam, and 30,851 for
the silt loam soils. Respective K~oc~ values were 437,805, 908,757,
1,599,564, and 1469081.

Study results for the desorption phase indicate that 16.26 to 39.33% of
the absorbed radioactivity was desorbed from the sand soil, 2.20 to
12.60% was desorbed from the sandy loam soil, 0.20 to 1.40% was desorbed
from the silty clay loam soil, and 0.20 to 1.66% was desorbed from the
silt loam soil. Freundlich K~des~ values were 591 for the sand soil,
2,074 for the sandy loam soil, 8,309 for the silty clay loam soil, and
7,714 for the silt loam soil. Respective K~oc~ values were 236,473,
230,498, 405,328, and 367334.

Material balances were 88.5 - 108.1% for the sand soil, 91.6 - 108.5%
for the sandy loam soil, 78.3 - 106.5% for the silty clay loam soil, and
80.8 - 118.0% for the silt loam soil.

**7. Field dissipation study on soil (OPP Guideline No. 164-1)**

> A field dissipation study on soil is required for DDAC. No data have
> been submitted to the Agency.

[]{.mark}

8.  **Aquatic field dissipation study (OPP Guideline No. 164-2)**

> An aquatic field dissipation study is required for DDAC. No data have
> been submitted to the Agency.
>
> **9. Long-term study on accumulation on soil (OPP Guideline No.
> 164-5).**
>
> A long-term study on accumulation on soil is required for DDAC if
> pesticide residues do not readily dissipate in soil. No data have been
> submitted to the Agency.
>
> .

**10. Bioaccumulation in Fish (OPP Guideline No. 165-4, MRID No.
458341‑01)**

This bioaccumulation study was reviewed by the Agency and found
scientifically valid. It satisfies the bioaccumulation in fish data
requirements for DDAC.

In this study, Bluegill (220) were continuously exposed to a nominal
concentration of 59 μg/L of DDAC for 28 days in an exposure aquarium. A
control aquarium was also used which had the same conditions as the
treatment aquarium. Water samples were collected from a central point in
the treatment aquarium on days 0, 3, 4, 10, 11, 17, and 24 of exposure.
Five fish were collected for tissue analysis from the treatment aquarium
on days 4, 10, 17, 24, and 28 of exposure. Water samples and fish were
collected from the control aquarium for ^14^C-residues on days 0 and 28
of exposure.

Following a 28-day exposure period, 40 of the fish remaining in the
exposure aquarium were transferred to an aquarium containing untreated
dilution water for an 18-day depuration period. Water samples were
collected during the depuration period on days 3, 7, 12, and 18. Five
fish were collected on days 3, 7, 14, and 18 of the depuration phase.
Water samples and fish were collected from the control aquarium on day
18 of depuration for ^14^C-residues.

The aqueous ^14^C-residues measured in the exposure system during the 28
days were consistently above nominal, at a mean measured concentration
of 93 μg/L (± 32) DDAC. Concentrations of ^14^C-residues present in the
depuration aquarium remained at \<11 μg /L throughout the 18 days. The
levels of ^14^C-residues in the edible, non-edible, and whole tissue of
bluegill exposed to DDAC reached steady state by day 10. The mean steady
state bioconcentration factor for DDAC in the edible, nonedible and
whole body tissue of the bluegill were determined by the authors to be
38X, 140X and 81X, respectively. The half-life of the ^14^C-residues
present in all tissue portions of the bluegill were found to be between
7 and 14 days. The elimination of ^14^C-residues for edible, nonedible
and whole body tissue was 38%, 66% and 56%, respectively. Of the
accumulated ^14^C-residues in the edible tissue of bluegill exposed 28
days to DDAC, 65.5% was extractable with a polar solvent (methanol),
8.1% was extractable with a non-polar solvent (hexane), and 25.9% was
not extractable with either solvent. Analysis of skin tissue after 28
days of exposure displayed that ^14^C-residue levels were approximately
2 to 6 times higher than those observed for the corresponding edible
tissue. Analytical results for QA samples analyzed concurrently with
water samples during the exposure and depuration period resulted in a
mean recovery (standard deviation) of 91 ± 5.93 percent. Analyses of the
QA samples analyzed with the tissue samples during exposure and
depuration resulted in a mean recovery (standard deviation) of 88.7 ±
6.29 percent.

The concentration of DDAC in the treatment aquarium was continuously
above nominal concentration and was not consistently maintained within ±
20 percent of the mean of the measured values (93 μg /L). The
temperature recommended for testing bluegill is 20-25 °C. In this study,
the temperatures ranged between 17-18 °C.

The study authors concluded that ^14^C-residues reached steady state by
day 10 of exposure. They found that the bioconcentration factor of
^14^C-residues in edible tissue of bluegill was much lower (38X) than
that of the nonedible tissues (140X) and also found that DDAC binds
significantly to the non-edible segments of bluegill, and especially to
the skin and scales. The study results indicated that the half-life of
DDAC in the edible tissue of the bluegill is significantly shorter than
that of the nonedible segments.

**11. Photolysis Rate on Surface of Soil (OPP Guideline No. 161-3, MRID
No. 424807‑01)**

This study was reviewed by the Agency and was found to be scientifically
valid and acceptable. The study meets guidelines for the fulfillment of
data requirements for DDAC on photodegradation on soil.

In this study, aliquots (1 g dry weight) of sandy loam soil were placed
in silanized glass vials and treated with \[^14^C\]DDAC at a nominal
concentration of 10 ppm. Half of the vials were placed in a photolysis
chamber where they were exposed to a xenon arc light source for 30 days
in an environmentally controlled chamber at 25 ± 1C. The rest of the
vials were not exposed to the xenon arc light source. One exposed and
one non-exposed test sample were removed from the photolysis chamber on
days 1, 3, 7, 14, 21, and 30. Each vial was extracted with aliquots of
80:20 (v:v) dimethylformamide:acetic acid. Thin layer chromatography
(TLC)/autoradiography/liquid scintillation counting (LSC) were used to
measure 14C-DDAC and potential photolysis products.

For both exposed and non-exposed test systems, the mean ^14^C-mass
balance was 104%. The parent compound was the only radioactive component
obtained in the test samples when analyzed by TLC and HPLC. In the
exposed system, the photolysis rate constant and half-life of DDAC were
reported by the study authors as 5.26 x 10^-3^ days^-1^ and 132 days,
respectively. The photolysis rate constant and half-life of DDAC in the
non-exposed system were determined to be 4.11 x 10^-3^ days^-1^ and 169
days, respectively.

Soil bound residues increased from 9.48% of the dose at day 0 to 25.5
and 20.9% in the exposed and non-exposed test systems, respectively. The
nature of these bound residues was investigated by HPLC analysis of the
extracts from composites of reserve day 30 soil samples from both
systems. The analytical results indicated the presence of the parent
compound and no significant degradation products.

**12. Biodegradability of DDAC (No MRID Number)**

This report is an assessment of the biodegradability of DDAC based on
the review of information from the open literature, unpublished sources
and meeting proceedings. It also provides a summary of the current
information available on the environmental fate of DDAC. The report was
submitted by the Registrant to EPA, but has not been reviewed by the
Agency.

Based on the review of the studies in the report, Lee (1992) concluded
that:

"Results of studies published in the open literature, literature
reviews, conference proceedings and information obtained from
unpublished sources indicate that ADBAC and DDAC are biodegradable with
the rate and extent of degradation influenced by quat concentration,
alkyl chain length, the presence of anionic moieties, and the type of
microbes. These factors and the design of the test system are important
in interpreting the reliability of biodegradability test results.

After release of ADBAC and DDAC to domestic waste streams or in the open
environment, a combination of physical and chemical properties, in
addition to biodegradability, influence their fate through the
environmental compartments of air, water, soil/sediment and biota.
Important properties for evaluating the environmental fate of these
materials include solubility, vapor pressure, surface activity and
adsorptive properties."

**13. Aqueous Availability (Leachability) (American Wood-Preservers'
Association Standard Method E11-97 "Standard Method for Determining the
Leachability of Wood Preservatives, MRID No. 455243-05)**

This study was reviewed by the Agency based on the standards specified
by the American Wood-Preservers' Association Standard Method E11-97 and
found to be acceptable. The study was submitted by Lonza Inc. to fulfill
the requirements for registration of the product, Bardac 22C50, EPA File
Symbol 6836-EGA. Bardac 22C50 consists of two active ingredients:
didecylmethyl ammonium carbonate (DDACarb) and didecyl ammonium
bicarbonate, both of which are similar in structure to DDAC.

The test material used in the study was Bardac 22C, which contained
51.7% of the active ingredient DDACarb. The purpose of this study was to
determine the leach rate of DDACarb from a sample of treated wood in
deionized water using high performance liquid chromatography (HPLC).

Southern pine wood blocks (19.0 ± 0.2 mm) were vacuum treated with 0.85
percent, 1.7 percent, and 3.4 percent of Bardac 22C (based on the active
ingredient DDACarb). After treatment, the blocks were subjected to a
post-treatment fixation for 7 days followed by conditioning for 28 days
in an environment producing a moisture content of 9 to 10 percent. After
conditioning, the blocks were vacuum-treated with deionized water and
placed in additional deionized water for 14 days.

Leach rates of DDACarb from wood blocks were determined by removing the
leachate from the sampling unit at intervals of 6, 24, and 48 hours, and
4, 6, 8, 10, 12, and 14 days following the start of the leaching period.
The leachate was extracted with aqueous tetramethylammonium chloride
(TMAC) and methylene chloride and analyzed by HPLC. After 14 days of
leaching, the wooden blocks were extracted with acetonitrile and aqueous
TMAC and analyzed by HPLC.

The corrected amount of DDACarb recovered from the leachate ranged from
186.1 µg to 764.7 µg (0.5X retention level), from 218.9 µg to 1152.9 µg
(1X), and from 446.2 µg to 2101.1 µg (2X). The total recovery from the
leachate over the 14-day period was 3464.7 µg, 4483.0 µg and 7444.7 µg
for the 0.5X, 1X and 2X retention levels, respectively. For all three
retention levels, the leachability of DDACarb declined continuously over
the 14-day period with the exception of the leaching rate of the 2X
retention level, which began lower than the other two retention levels
(160.4 µg), significantly increased at Day 1 (2101.1 µg), and decline
gradually through Day 14 (496.8 µg). The total amount of DDACarb
recovered from the leachate and the wood blocks combined were 176,983.0
µg (101.8%), 286,606.6 µg (99.5%), and 542,370.3 µg (104.9%) for the
0.5X, 1X and 2X retention levels, respectively.

American Wood Preservers' Association Standard, Method E11-97: "Standard
Method of Determining the Leachability of Wood Preservatives was
generally followed; however, an issue of concern was that the study did
not report running spike samples along with the test samples during HPLC
analysis. Rather, the samples were corrected using average validated
extraction recoveries of 92.1 percent from three different fortification
levels with seven replicates per level.

**BIBLIOGRAPHY**

**[MRID]{.underline} [Citation]{.underline}**

411758-01 Dykes, J. and M. Fennessy. 1989. Hydrolysis of
Didecyldimethylammonium chloride (DDAC) as a function of pH at 25 °C.
Final Report #37004. Unpublished study prepared by Analytical
Bio-chemistry Laboratories, Inc.

411758-02 Dykes, J. and M. Fennessy. 1989. Determination of the
Photolysis Rate of Didecyldimethylammonium chloride (DDAC) in pH 7
Buffered solution at 25 °C. Final Report #37005. Unpublished study
prepared by Analytical Bio-chemistry Laboratories, Inc.

413853-01 Daly, D. 1989. Soil/Sediment Adsorption-desorption of
\[^14^C\]Didecyldimethylammonium chloride (^14^C-DDAC). Lab Project
Number 37009. Unpublished study prepared by Analytical Bio-Chemistry
Laboratories.

422538-01 Cranor, W. 1991. Aerobic Soil Metabolism of
\[^14^C\]Didecyldimethylammonium chloride (^14^C-DDAC). Final Report.
Lab Project Number 37006. Unpublished study prepared by ABC
Laboratories.

422538-02 Cranor, W. 1991. Anaerobic Aquatic Metabolism of
\[^14^C\]Didecyldimethylammonium chloride (^14^C-DDAC). Final Report.
Lab Project Number 37007. Unpublished study prepared by ABC
Laboratories.

422538-03 Cranor, W. 1991. Aerobic Aquatic Metabolism of
\[^14^C\]Didecyldimethylammonium chloride (^14^C-DDAC). Final Report.
Lab Project Number 37008. Unpublished study prepared by ABC
Laboratories.

424807‑01 1992. Schmidt, J. Determination of the Photolysis Rate of
Didecyldimethylammoniumchloride on the Surface of the Soil. Final Report
\# 39505. Unpublished study prepared by ABC Laboratories.

455243-05 2001. Bestari, K. Determination of the Leachability of Bardac
22C from Treated Wood. Centre for Toxicology, University of Guelph,
Guelph, Ontario N1G 2W1, Canada.

458341‑01 1990. Fackler, P.H., E. Dionne, D.A. Hartley, and S.P.
Shepherd. Bioconcentration and Elimination of ^14^C- Residues by
Bluegill (*Lepomis macrochirus*) Exposed to Didecyldimethylammonium
Chloride (DDAC). Final Report. Study No. 11696.0887.6104.140.
Unpublished study prepared by Springborn Laboratories, Inc.

Lee, C. 1992. Assessment of the Biodegradability of ADBAC and DDAC.
Unpublished report prepared by Roy F. Weston, Inc. Contractor's Fate
Summary