Environmental Protection
Agency
Office of Pesticide Programi
Washington, DC 20460
(TS-766C)
&EPA
Pesticide
Fact Sheet
Name of Chemical:
Reason for Issuance:
Date Issued:
Fact Sheet Number:
Tributyltin
Preliminary Determination
October 1, 1987
143
1. Description of chemicals
Chemical Name
bis(tri butyl tin)
adipate
bis(tributyltin)
dodecenyl succinate
bis(tributyltin)
oxide
bis(tributyl,tin)
sulf ide
tributyltin acetate
tributyltin acrylate
tributyltin fluoride
tributyltin meth-
acrylate and
copolymer
tributyltin resinate
Common
Name
none
none
TBTO
none
none
none
TBTF
TBTM
TBTM
none
Chemical Abstract
Service Number
7437-35-6
12379-54-3
56-35-9
4804-30-4
56-36-0
13331-52-7
1983-10-4
2155-70-6,
26345-187
none assigned
EPA
Shaughnessy
Code
083117
083101
083001
083113
083105
083121
083112
083120
083119
083114
Chemical family: Organotins
Pesticide type: biocide, antifoulant, and disinfectant. The
Special Review is being conducted for the use of these chemicals
in antifoulant paint registrations. Twenty TBT compounds are
registered as pesticidal active ingredients and nine of the
compounds are registered for use in antifouling paints. The
major TBT pesticide is tributyltin oxide.
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Registrations: nt.ifoulant paints containing tributyltin (TBT)
compounds were initially registered in the early 1960’s. At
the initiation of the 3pecial Review there were 364 TBT anti—
fouling paint formulations and 20 formulating intermediates
with a total of 61 manufacturers. Since January, 1986, 162
products have been voluntarily cancelled and some companies have
merged such that there are now 210 registered antifouling
paint formulations and 12 formulating intermediates with
34 manufacturers, although nearly half of the paint formulations
have been suspended for non—compliance with a Data Call In
Notice issued in July, 1986.
2. Use patterns and formulations
Application sites: TBT’s are used in antifoulant paints
applied to ship and boat hulls as well as buoys, crab pots,
fish nets, etc. TBT’s are also registered as wood preserva-
tives, disinfectants, and biocides for use in cooling towers,
pulp and paper mills, breweries, leather processing facilities,
and textile mills.
Paint formulations: TBT antifouling paints may be classified
into three categories according to the way the TBT moiety is
incorporated into the paint coating and subsequently released.
o Free association paints: In these conventional
coatings the TBT is physically incorporated into
the paint matrix (which contains the pigment, water—
soluble resins, and inert substances). The TBT
leaches from the paint surface by diffusion. Gradually,
the paint matrix becomes clogged with insoluble materials
trapping some of the toxicant while leaving the surface
unprotected.
o Copolymer paints: In this category the TBT moiety
is chemically bonded to a polymer matrix. The
biocide is released only by chemical hydrolysis
of the TBT itself. These paints are characterized
by slow dissolution from ship hulls and thus achieve
a constant but prolonged, release of antifoulant
tox icant.
o Ablative paint: These paints have characteristics of
both of the other two types of paint. The TBT is not
bound to a polymer, but is incorporated into the paint
matrix. Ablative paints are soft paint films with the
rosin portion of the paint slightly water soluble so
that the surface slowly sloughs or ablates away as the
painted vessel moves through the water. This allows
new toxicant layers to be exposed and prevents the
buildup of insoluble materials.
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A TBT antifouling paint formulation can have a single TBT
active ingredient, can be combined with one or more of the
other eight TBT antifoulants, can be combined alone with
copper compounds (especially cuprous oxide), can be combined
with triphenyltin fl.ioride (another organotin antifoulant), or
can be combined with copper and other organotin compounds.
Products are formulated with 0.5 to 4 percent active ingredient
TBT. Application rates are commonly from 150 to 400 square
feet per gallon of paint.
3. Science Findings
Chemical characteristics. Tributyltin compounds are chemically
characterized by a tin Sn) atom covalently bonded to three
butyl (C 4 H 9 —) moieties. When released from the paint matrix or
polymer into the aqueous environment, TBT exists mainly as a
mixture of TBT hydroxide, TBT chloride, and TBT carbonate
species from reaction with carbonates in seawater.
Environmental fate: The environmental chemistry and fate of
tributyltin in aquatic environments are complex and not com-
pletely understood. Studies indicate that photolysis and
microbial action are potential mechanisms of degradation from
tn— to di— to monobutyltin and finally to inorganic tin.
Studies indicate the halt—life of TBT may be 116 days in aerobic
soils, 815 days in anaerobic soils, 6 to 12 days in sea water,
and up to 238 days in fresh water. TBT accumulates in sediment
at levels that are one to four orders of magnitude greater than
the concentration found in the respective water column. This
amassing of toxicant can have serious consequences for organisms
living and feeding in the benthos.
Low concentrations of elemental or inorganic forms of tin
appear to cause negligible toxicological effects in man or wild-
life. However, when carbon groups, such as butyl units, are
added to the tin, there is an increase in fat solubility,
ability to penetrate biological membranes, and consequently,
toxicity. As the number of butyl groups is increased from one
to three, there is a corresponding increase in lipophilicity
and toxicity to aquatic organisms. However, the addition of a
fourth butyl group decreases the toxicity of the molecule.
Ecological characteristics: The TBT compounds are toxic
to aquatic organisms at the low parts per billion (ppb) level.
A summary of aquatic TBT toxicity values are presented below:
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° Fish
Acute Toxicity:
Chronic Toxicity:
Bioaccumulation:
Behavioral Toxicity:
0 Bivalves
Acute Toxicity:
Chronic Toxicity:
Bloaccumulat ion:
Bioavailable:
Gastropods
Acute Toxicity:
Chronic Toxicity:
Bioavailable:
° Crustaceans
Acute Toxicity:
Chronic Toxicity:
Bioaccumulation:
Bioavai lable:
Behavioral Toxicity:
Algae
Acute and Chronic
Toxicity:
Bioaccumulation:
B ioavai lable:
0.96 — 24.0 ppb
> 0.2 ppb
200— to 4300—fold
Avoidance occurred at 1.0
to 24.0 ppb. Fish may not
detect harmful sublethal
levels.
0.9 to 2.3 ppb
0.02 to 0.05 ppb
2000— to 6000—fold
Yes, even with high silt
loads.
> 0.01 ppb
0.002 to 0.02 ppb
Yes, was promoted as a
molluscicide against schisto—
somiasis because it readily
adsorbed to organic matter;
snails preferentially ingest
organic matter. (Lowest
value is an extrapolation.)
0.42 to 2.2 ppb
> 0.09 ppb
4400—fold
Yes, more from food than
from water.
0.5 ppb caused positive photo-
taxis in daphnids.
growth inhibition at 0.1 to
0.35 ppb
800— to 30,000—fold
Yes, since filter feeders
readily consume algae it can
be assumed that phytoplankton
laden with TBT can be con—
summed by aquatic organisms.
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TBT concentrations are reported to be highest in areas of heavy
boating and shipping activity. Before recoating, old paint
containing the remaining TBT residue is scraped from the vessel
hull ani sometimes the scrapings are washed into the water
adjacent the boat or shipyard (despite TBT labels prohibiting
this practice). TBT has been measured in marine and fresh
water environments at levels indicated below. Note that ND
means non—detectable or below the level of detection of the
analytical method used.
Chesapeake Bay: ND to 0.8 ppb
San Diego Bay: ND to 1.0 ppb
San Francisco Bay: ND to 0.16 ppb
Honolulu Harbor 0.045 to 0.27 ppb
Los Angeles!
Long Beach Harbor: ND to 0.12 ppb
Narragansett Bay: ND to 0.13 ppb
Thames River (CT): ND to 0.009 ppb
Mayport Florida: ND to 0.016 ppb
Lake Superior: 0.02 ppb
Lake Ontario: 0.05 to 0.84 ppb
Population Effects: In France, a correlation has been found
between TBT in the water column of certain estuaries and gross
malformations in Pacific oysters grown in commercial oyster
beds in and around areas of heavy boating activity. Following
a ban on TBT antifouling paints on vessels less than 25 meters
in length, the degree of shell deformities has decreased and
the regeneration rate of juvenile oysters (spat) has improved.
In England TBT has been reported causing similar shell
deformities in Pacific oysters and reproductive abnormalities
(imposex) in dogwelk snails. The Department of Fish and
Wildlife of Oregon recently have found shell deformities in
commercial Pacific oyster beds in Coos Bay which are near a
small shipyard applying and removing TBT antifouling paints.
4. TBT Release Rates
The Tributyltin Data Call In Notice (TBT DCI) required all
registrants of TBT antifouling paints to measure TBT release
from registered paints following a test method developed in
cooperation with the American Society for Testing and Materials
(ASTM). In addition, each laboratory conducting the TBT release
test was required to test a standard copolymer test paint.
Release rate data were submitted for 96 TBT antifouling paint
products by July 1, 1987. From a review of these data, it was
determined that at least 57 of the tests were conducted satis-
factorily and all data were normalized according to adjustments
made using the standard test paint results. Two release rate
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values were determined for each product: 1) a short tern
cumulative release measured over t e first 14 days of the test
period a d 2) an av. cage daily release rate (average of the
dall/ release over seeks 3 to 5 of t’ie test). Details of
release rate data are available in the Tributyltin Technical
Support Document.
Generally, the release rates start high (short term cumulative
release ranged from 1 to 1128 ug/cm 2 ) and gradually decrease
over the course of the test period (average daily release rate
ranged from 0.02 to 21.53 ug/cm 2 /day). Some paints with a high
percentage of TBT have a miich higher short term cumulative
release than do other paints tested. It was concluded that
while there was a strong statistical correlation between the
percent active ingredient and the average daily release rate,
the data points were too scattered for the percent active
ingredient alone to be useful for regulating TBT paints. The
scattered data points indicated that other factors, such as the
type and quality of the inert ingredients (resins, rosins,
binders, etc.) may be important in determining the release rate
of a paint and that regulating on percent active ingredient
would not necessarily reduce environmental loading.
Results of the release rate tests also showed that some TBT
ablative and free association paints have lower release rates
than many copolymer paints. The free association paints with
release rates lower than copolymer paints generally had a low
percentage of TBT in their formulations.
5. summary of regulatory position and rationale
The Agency initiated a Special Review of TBT products used as
antifoulants in January, 1986, based on concern of possible
adverse effects of TBT to nontarget aquatic organisms. The
Agency recognized that additional data were required and issued
a Data Call In Notice (DCI) for TBT products registered for use
as antifoulants or registered as formulating intermediates used
to produce antifoulant products. The DCI required information
on product chemistry data, TBT release rate data, usage data,
worker exposure data, ecological effects data, and environmental
fate data. The DCI also required submission of any available
efficacy data. For many products, product chemistry data, TBT
release rate data, and usage data have been received. Although
the Agency will not have the ecological and environmental fate
data from the DCI for another one to four years, the Agency
believes sufficient data are available to propose a set of
regulatory actions. In 1985, the Agency issued a DCI on
tributyltin oxide requiring data on chronic toxicity to mammals.
These data are not due into the Agency until 1990.
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The Agency examine.:3 a range of regulatory options to reduce TBT
loading into the environment. The Agency considered: 1) can—
ceiling all TBT antifouling paint registrations, 2) proposing
a restriction on the maximum permitted percent TBT active
ingredient in registered products, 3) regulating the type of
paint formulation, 4) regulating the release rate, 5) restrict-
ing the size of vessel treated, and 6) classifying TBT antifou].—
ing paints as restricted use pesticides and requiring additional
wording on the label giving directions concerning application,
removal, and disposal of TBT paints to reduce the amount of TBT
entering the aquatic environment from these activities.
The Agency is proposing continued registration of TBT antifouling
paint products with certain regulatory restrictions: 1) limir
the maximum organotin release rate from paint formulations,
2) prohibit use of TBT on non—aluminum vessels under 65 feet in
length, and 3) classify TBT antifouling paints as restricted
use pesticides and require additional wording on the label
regarding application, removal, and disposal of TBT paints to
prevent introduction of TBT paint wastes into the aquatic
environment. Specifically, the Agency is proposing a maximum
short term cumulative release (days 1 to 14 of test period) of
168 ug organotin (calculated as TBT cation )/cm 2 and an average
daily release rate (averaged over weeks 3 to 5 of the test) of
4.0 ug organotin (calculated as TBT cation)/cm 2 /day. The
Agency believes that the proposed release rate restrictions would
reduce 1oading ’five—fold from its estimated average daily
release rate of 20 ug/cm 2 /day before initiation of the Special
Review (calculated for all TBT paint formulations from the
submitted release rate data). The prohibition of use on vessels
under 65 feet should reduce by 37 percent (the estimated volume
of TBT paint used on this size class by a boat and shipyard
survey) the total amount of TBT antifoulant currently used and
potentially available for environmental contamination. This
limitation in use will result in a reduction in TBT concentration
primarily in estuarine and fresh water areas where these small
vessels are used and moored and where the risk from TBT effects
is the greatest. The restricted use classification and additional
wording on the label regarding size restriction and directions for
applying, removing, and disposing of TBT paints without introducing
paint wastes into the water will help ensure that TBT paints
are not used on vessels under 65 feet and that TBT paints will
be applied and disposed in a manner which will reduce the risk
of inadvertent aquatic contamination. Monitoring and efficacy
data will be required separately which will be used to evaluate
the effectiveness of these proposals.
Upon receipt and evaluation of additional data, the Agency
may determine that further regulatory action is warranted.
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6. Contact person at EPA
Dr. Janet L. Andersen
Environmental Protection Agency
Office of Pesticide Programs
Registration Division (TS—767C)
40]. M Street, S.W.
Washington, D.C. 20460
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