FACT SHEET

Summary of the Risk Assessment and Regulatory Decision 

for 

Acid Copper Chromate (ACC)

Action

	On May 30, 2006, the Environmental Protection Agency (EPA, or the
Agency) approved a new ACC wood preservative product in response to a
registration application submitted by Forest Products Research
Laboratory (FPRL).  This is one of several ACC registration applications
that have been submitted to the Agency.  At the time of this approval,
Osmose, Inc. was the only company with a current registration for ACC
but had not produced or sold the product in the United States for many
years. 

	In January 2004, EPA sent letters to the applicants clarifying that the
existing data were not sufficient to support a favorable regulatory
decision.  The letter identified the additional studies that would be
needed to enable the Agency to fully assess whether or not the increase
in exposure resulting from a new ACC registration would lead to a
“significant” increase in the likelihood of unreasonable adverse
effects. 

	In response to the Agency’s January 2004 letter, Osmose submitted a
wipe study and FPRL submitted a worker inhalation study.  With these two
studies the database is sufficient to assess the risks associated with
occupational and residential exposures expected from the use of ACC.

Risk Assessment Summary

	The risk assessment conducted by the Agency focused on the potential
exposures to the most toxic constituent of ACC-treated wood, hexavalent
chromium.  Hexavalent chromium converts over time to a less toxic
substance, trivalent chromium.  Therefore, the amount of time between
treatment and exposure affects the risk estimates.  The Agency
identified both cancer and non-cancer toxicological effects for use in
the assessment.  Hexavalent chromium is a known human carcinogen when
exposure occurs via the inhalation route.  Based on this exposure
pathway, cancer risk estimates were developed for workers in treatment
plants and other occupational groups that could be expected to be
exposed to hexavalent chromium in the air.  Residents are not expected
to be exposed via this pathway.  

	

	Residents and workers may, however, be exposed to hexavalent chromium
by making dermal contact with treated wood surfaces.  The toxicological
effect of concern for the dermal exposure is dermal sensitization.  

	In 2004, the Agency sought technical guidance from the FIFRA Scientific
Advisory Panel (SAP) on quantifying risks when the toxicological effect
of concern is dermal sensitization.  Hexavalent chromium was used as a
case study.  In its final report, the SAP recommended using the
methodology and results from the Nethercott et al. study to quantify
dermal sensitization risk from exposure to hexavalent chromium.  The
Agency followed the SAP’s recommendation for use of the critical dose
identified in the Nethercott et al. study but did not use uncertainty
factors of less than 1 for deriving the total uncertainty factor applied
to the critical dose identified in the Nethercott et al. study.  The
Nethercott et al. study was subsequently reviewed by the Human Studies
Review Board on May 2, 2006, and determined to be appropriate for risk
assessment.

	The National Toxicology Program (NTP) is currently conducting a study
to determine whether hexavalent chromium is a carcinogen via the oral
route of exposure.  Preliminary results may not be available until 2007.
 The Agency intends to review these data when they become available.  

Residential Exposure and Risk

	Based on the Agency’s risk assessment, residential risks are of
concern for ACC.  The estimated levels of hexavalent chromium present on
treated wood exceeded the Agency’s level of concern for dermal
exposure from 36 to 197 days after treatment.  The range of risks
reflects different retention levels (0.25 pcf for above ground
applications and 0.5 pcf for ground contact applications) and wood types
(southern yellow pine and Douglas fir).  EPA anticipates that the most
common retention/wood type combination for residential use patterns
would be 0.5 pcf retention in southern yellow pine.  Under this scenario
hexavalent chromium levels exceed the Agency’s level of concern for
100 days after treatment.

	Incidental oral exposures are not expected to pose risks above the
Agency’s level of concern.  Inhalation exposure to hexavalent chromium
is not expected to occur in the residential setting, so a residential
cancer assessment was not conducted.

Occupational Exposure and Risk

	Occupational cancer and non-cancer risks are of concern for most
scenarios.  Risk estimates were calculated for general use and
industrial uses only, because non-cancer residential risks were already
found to be of concern.  The amount of wood typically treated in a day
is significantly higher when wood to be used in residential applications
is included.  

	Risks for ACC industrial uses are very similar (slightly less risky) to
those for chromated copper arsenate (CCA) industrial uses, which is the
predominant treatment alternative currently in use.  The CCA risks are
driven primarily by the arsenic in the wood preservative.  CCA is not
registered for treatment of wood for residential uses.

Regulatory Decision

The Agency has completed its review of an application to register ACC
for use in treating wood intended for industrial and residential
applications.  Following an extensive review of the scientific
information, EPA approved the limited use of ACC for treated wood used
only in commercial and industrial applications.  These limited
applications are not expected to result in significant exposures to the
general public. The potential risks to workers in treatment plants are
similar to those found for workers in plants using the registered wood
preservative, CCA.  Thus, labels will provide for the use of personal
protective equipment in order to mitigate risks.   

For residential uses (decks, playsets, etc.), EPA has found that surface
residues of hexavalent chromium can persist and potentially elicit
dermal sensitization up to 100 days following treatment.  Based on
existing information, the Agency does not believe that it is feasible to
mitigate this risk adequately through label restrictions, given the
rapid turnover of treated wood in the marketplace (often much less than
30 days during peak use times) and difficulties in establishing an
enforceable method for ensuring that wood would not be available to
consumers during the time required for hexavalent chromium to convert to
the less-toxic trivalent chromium.

ACC products may only be used for preservative treatment of the
following categories of forest products and in accordance with the
respective cited standard (noted  parenthetically) of the 2001 edition
of the American Wood-Preservers’ Association (AWPA) Standards: 

Timber for mine ties and bridge ties only (C2) 

Lumber and timber for salt water use only (C2) 

Piles (C3)

Poles (C4)

Wood for highway construction (C14)

Round, half-round, and quarter-round fence posts (C16) 

Poles, piles, and posts used as structural members on farms (C16) 

Wood for marine construction for salt water use (C18)  

Lumber for permanent wood foundations (C22) 

Round poles and posts used in building construction (C23) 

Sawn timber to support residential and commercial structures (C24) 

Sawn cross arms (C25) 

Structural glued laminated members and laminations before gluing (C28)

Structural composite lumber (C33) 

Shakes and shingles (C34)

Lumber and timbers for Cooling Towers (C30) in accordance with the
respective cited standard of the 2002 edition of the AWPA Standards

 

To minimize occupational exposures, the Agency is requiring use of
certain personal protective equipment (PPE).  Specifically, dermal
exposure to workers will be mitigated by the use of coveralls, socks,
chemical-resistant footwear, goggles or face shields, and
chemical-resistant gloves and aprons. Inhalation exposure to workers
will be mitigated by requiring the use of respirators for workers in
areas where the concentration of hexavalent chromium exceeds the
Occupational Safety and Health Administration Permissible Exposure Limit
or in areas where the concentrations are not known.  Additionally,
ACC-treated wood will bear Consumer Information Tags or “end-tags.” 
These required end-tags will include specific precautionary statements
for carpenters and others who may come into contact with ACC-treated
wood products.

In response to the risk assessment, Osmose voluntarily submitted an
amendment to its ACC label deleting residential uses.  The FIFRA 6(f)
notice deleting all residential uses from the Osmose label was published
on July 18, 2006, in the Federal Register.  The comment period on this
action closed on August 17, 2006, and all residential uses were removed
from the Osmose label on August 18, 2006.  As a result, ACC may not be
used to treat wood intended for use in residential settings, such as
decking and playsets, where significant exposures are likely to occur.  

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