CCA: Regulatory History and Current Status
Dr. Raj Sharma, Arch Chemicals, Inc., Norwalk, CT  

EXAFS Investigation of Cr and As in CCA Treated Materials
Dr. Peter Nico, California State University, Stanislaus,Turlock, CA

Arsenic and Speciated Chromium Levels in Soil Surfaces Near Treated Wood Playscapes
John H. Butala, M.S., Toxicology Consultants, Inc., Gibsonia, PA

Does Disposed CCA-Treated Wood Influence Arsenic or Chromium Concentrations in Subsurface Drinking Water Supplies? 
Dr. Jennifer K. Saxe, Gradient Corporation, Cambridge,  MA

Hand-Wipe Sampling of CCA-Treated Wood with Comparison to CPSC Hand-Wipe Study
Dr. William F. Gutknecht, Research Triangle Institute, Research Triangle Park, NC

Relative Bioavailability of Arsenic from Soil Affected by CCA-treated Wood and Dislodgeable Arsenic from CCA-treated Wood Collected from Residential Structures 
Stan W. Casteel, Tim J. Evans, Margaret A. Miller, Sue E. Turnquist, University of Missouri, Columbia, MO

Dermal Absorption of Arsenic from Residues on CCA-Treated Wood 
Yvette Lowney and Mike Ruby, Exponent, Boulder, CO
Ronald Wester, University of California, San Francisco, CA
Stewart Holm and Xiaoying Hui, Georgia-Pacific, Atlanta, GA

CCA: Regulatory History and Current Status

R.K. Sharma, PhD, Arch Chemicals, Inc, PO Box 5204, 501 Merritt 7, Norwalk, CT 06856, Tel: 203-229-2606, Fax: 203-229-2613

Chromated Copper Arsenate (CCA) has had a safe history of use as a wood preservative for the last 75 years. CCA is a mixture of the oxides of arsenic, chromium and copper which, following vacuum pressure treatment, form a relatively insoluble “complex” with wood.  In the US, CCA formulations are one of three types that conform to the American Wood-Preservers’ Association (AWPA) standards.  CCA Type C, the principal formulation used to treat timbers, utility poles, piling, plywood and lumber, is a dilute aqueous solution (2% CCA) of arsenic pentoxide, chromium trioxide and copper oxide.

Studies on the CCA complex indicate that the arsenic and chromium are both bound to constituents in the wood matrix.  Recent studies on the bioavailability of dislodgeable CCA complex, obtained from the surface of treated wood, indicate that it is poorly absorbed via the oral and dermal routes.  This is in contrast to inorganic arsenic alone which is more readily absorbed.  The US Environmental Protection Agency (EPA) regulates the sale, distribution and use of CCA under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA).  As part of its “reregistration program” for all pesticides, EPA is currently reviewing CCA.

In February 2002, wood preservative manufacturers amended their respective registrations with the EPA to transition to a new generation of wood preservatives for use in non-industrial treated wood products by December 31, 2003.  This step was taken in light of current interest and anticipated market demand for alternative products. EPA is currently reviewing CCA under two separate risk assessments. One risk assessment is specifically considering children's exposure at residential sites, playground settings and public parks. The other risk assessment, being conducted under the Agency's reregistration program, focuses on the industrial uses of CCA that will continue. 

The U.S. Consumer Product Safety Commission (CPSC) held a Commission Briefing on March 17/18, 2003 to consider a petition filed by two environmental groups to ban the use of CCA pressure-treated wood in playground equipment. The staff presented a report to the Commissioners that contained a risk assessment which purports to show an increased risk of bladder and lung cancer for children who play on play sets made with CCA treated wood.  The CPSC staff recommended that the Commissioners defer action on the petition, pending finalization of EPA review.  The CPSC Commissioners have yet to vote on the petition. 

EXAFS Investigation of Cr and As in CCA Treated Materials

Dr. Peter S. Nico, Department of Chemistry, California State University, Stanislaus, 801 West Monte Vista Ave, Turlock, CA 95382
Dr. Scott E. Fendorf, Geological and Environmental Sciences, Stanford University, Stanford, CA 94301

The forms of Chromium and Arsenic in Chromated Copper Arsenate (CCA) treated materials were examined through bulk Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy.  The sample set consisted of new CCA treated wood, aged CCA treated wood, and the dislodgable residue from aged CCA treated wood.  No significant differences between the three samples were observed in either the Cr or As EXAFS.  Based on edge position and lack of pre-edge features, it was concluded that the Cr was present in the Cr(III) oxidation state whereas the As was present as As(V).

The As EXAFS indicated the presence of an oxygen shell containing approximately 4 atoms at a distance of 1.68 A, which is indicative of As(V).  There was also a second shell Cr backscatter at approximately 3.28 A.  The Cr EXAFS was more complex indicating not only a nearest neighbor oxygen shell at approximately 1.99 A, but also three different second shell backscatters: As at 3.28 A, Cr at 3.50 A, and C at 2.99 A.

The presence of a Cr backscatter in the Cr EXAFS suggests that the Cr is present as a dimer.  This dimer appears to be bound to As and simultaneously bound to some carbon containing ligand.  Presumably this ligand is part of the wood structure.

A micro-EXAFS map of the Cr, Cu, and As distribution in the aged wood sample was also obtained. This map showed a very uniform distribution of the three elements through out the wood samples confirming the absence of any Cr-As crystallites.

Arsenic and Speciated Chromium Levels in Soil Surfaces Near Treated Wood Playscapes

John H. Butala, MS DABT, Toxicology Consultants, Inc., Gibsonia, PA

Four playgrounds in eastern and western United States were sampled to characterize soil surface around CCA pressure treated wood play structures.  Soil surface samples were evaluated for the metal components of CCA as well as hexavalent chromium and water-soluble arsenic. Site-wide concentrations and site-specific background levels of the analytes were determined.

Samples of the playscape base material (soil or wood chips) at the base of playground equipment were collected at each playground.  Sixteen samples were collected per playground in a grid pattern to assess site-wide concentrations; 12 samples were collected per playground in a linear pattern in the general direction of water runoff from CCA pressure treated wood support structures to assess impacts from leaching; and 4 background samples were collected per playground at locations outside the areas considered to be affected by the CCA pressure treated wood structures.

All samples were analyzed for total metals (As, Cr, Cu) using Inductively Coupled Plasma spectroscopy (ICP).  A minimum of ten percent of the samples were subjected to the Synthetic Precipitation Leaching Procedure (SPLP) extraction method and analyzed by USEPA Method 6010A analysis to estimate the water-soluble fraction of arsenic in the base material.

Total arsenic and copper concentrations were elevated above site background at two sites, total chromium was elevated above site background at three sites but the concentrations of all CCA metals were well within naturally occurring regional background levels for arsenic, chromium and copper.     

No relationship was evident in metal concentrations verses distance from treated wood structures.  

No detectable CrVI was found at three of the sites (limit of detection for CrVI in these matrices was 0.39-2.0 ppm), and at the fourth site where the ground cover was wood chips, 8 of 32 samples contained CrVI but only one was above site background levels.

The calculated percent of arsenic in the form of water-soluble arsenic varied at each playground.  For background levels, the range was from zero to 104%, and for soil surfaces at playscape equipment the range was zero to 15%, indicating a reduced arsenic bioavailability.

Does Disposed CCA-Treated Wood Influence Arsenic or Chromium Concentrations in Subsurface Drinking Water Supplies?

Jennifer K. Saxe and Eric J. Wannamaker, Gradient Corporation, 238 Main Street, Cambridge, MA 02142, Tel: 617-395-5000, Fax: 617-395-5001

The recent decrease in the arsenic drinking water maximum contaminant level (MCL) has heightened scrutiny of natural and anthropogenic arsenic contributions to subsurface drinking water supplies.  Chromium is another element for which potential human health concerns have been raised when it is detected at sufficient levels in drinking water.  Wood preserved with chromated copper arsenate (CCA) is widely used in Florida and commonly disposed of in unlined landfills.  We examined regulatory groundwater monitoring data for evidence of arsenic and chromium migration from unlined construction and demolition (C&D) debris landfills in Florida.  Florida was chosen because soil, groundwater, landfill design, weather, and levels of CCA-treated wood use make the state a uniquely sensitive indicator for observing arsenic and chromium migration from CCA-treated wood disposal sites, should it occur.  We developed and quality-checked a CCA-treated wood disposal model to estimate the amount of wood and associated arsenic and chromium disposed in unlined landfills.  The model indicates that by 2000, an estimated 13 million kg of arsenic and 30 million kg of chromium in CCA-treated wood were disposed in Florida.  However, groundwater monitoring data do not indicate that arsenic or chromium is migrating from unlined C&D landfills.  This suggests that even under conditions conducive to observing CCA-treated wood influences to arsenic and chromium concentrations in groundwater, groundwater impacts are not observed, for reasons that may include the stability of these elements in the wood matrix and the assimilatory capacity of other landfilled wastes and underlying soil. 

Hand-Wipe Sampling of CCA-Treated Wood with Comparison to CPSC Hand-Wipe Study

W. F. Gutknecht, Ph.D., W. C. Eaton, Ph.D., J. F. Nichol, B.S., C. A. Salmons, B.S., M.S.P.H., C. V. Wall, B.S., F. X. Weber, B.S., W. G. Winstead, Jr., B.S., Research Triangle Institute (RTI) Research Triangle Park, NC  27709

A potential for exposure (i.e., incidental ingestion and dermal contact) to dislodgeable metal complex exists because most of the outdoor wooden decks and play structures in the U.S. are constructed from CCA-preserved wood.  This study was performed to provide a reliable estimate of the amounts of metal complex removed via hand contact with treated deck wood surfaces.  In addition to studies of direct hand exposure, cloth wipe procedures were performed to derive a reliable transfer reduction factor (TRF) to more accurately relate the amount of metals dislodged using commonly employed wipe procedures to the amount removed by the adult hand.

A pilot study was first performed to:  (1) develop methods for collection of deck boards from the field; (2) optimize and standardize block wipe and hand rub sampling techniques based on those used by the Consumer Product Safety Commission (CPSC) in a similar study; and (3) develop sample digestion and chemical analysis methods for total CCA and for Cr(VI).  A mini-study was conducted using the techniques developed in the pilot study to test the efficacy of these procedures.  The mini-study included eight volunteers for hand sampling and approximately 120 board samples (coupons) cut from five decks.  Using the methods found acceptable in the mini-study, a full study was performed that included 21 volunteers and approximately 750 coupons cut from recently-treated wood and 20 decks.  

The CPSC conducted several studies using very similar techniques; for example, the block used by RTI was square while block used by CPSC was round, but both weighed 1,100 g.  Also, hand rubbing was performed by both groups with a 1,100-g weight placed on the back of the hand.

RTI and CPSC obtained similar results for block wipe and hand loading.  For example, the block wipe loading for arsenic (As) for the RTI mini- and full studies combined (720 samples) ranged from 23 µg/wipe to 695 µg/wipe, whereas the range for the CPSC Phase IV study  (108 samples) ranged from 30 µg/wipe to 496 µg/wipe; the hand loading found by RTI ranged from about 0.27 µg/hand to 306 µg/hand while CPSC reported a range of 1.0 µg/hand to 20.9 µg/hand in their Phase III study (32 samples); the mean As value for the RTI combined studies was 8.5 µg/hand compared to 7.7 µg/hand for the CPSC Phase III study.  As noted, there is wide variation in the ranges for the hand results.  This is considered due to the wide variation in available dislodgeable material between decks and from board to board within a given deck.  TRF values have been calculated and statistical analyses performed.

In summary, reliable estimates of the amounts of CCA material transferred from board to hand have been determined in a large scale study, along with estimates of the amounts transferred to a wipe and the relationship between these two types of sampling.  

Relative Bioavailability of Arsenic from Soil Affected by CCA-treated Wood and Dislodgeable Arsenic from CCA-treated Wood Collected from Residential Structures

Stan W. Casteel, Tim J. Evans, Margaret A. Miller, Sue E. Turnquist

A juvenile swine model was used to measure the enteric absorption of arsenic from soil adjacent to chromated-copper-arsenate (CCA)-treated wood utility poles placed in service in 1988. In a second study the swine model was used to measure the enteric absorption of arsenic from dislodgeable material obtained from the surface of weathered (1-3 years) residential structures constructed with CCA-treated wood.  The relative bioavailability of arsenic was assessed by comparing the absorption of arsenic from the test material (utility pole soil and dislodgeable material) to that of a reference material (sodium arsenate).  The study was performed within the spirit and guidelines of Good Laboratory Practices and followed a protocol reviewed by the USEPA.

The arsenic concentrations in the test materials were 320 μg/g in the utility pole soil and 3500 ug/g in the dislodgeable material (dislodgeable material was a composite obtained from several boards, as individual boards only produce minute quantities).  In each dosing trial, groups of five semi-fasted swine were orally dosed with sodium arsenate (0, 30, or 60 ug/kg/day) or test material (30, 60, or 120 ug/kg/day) twice a day for either 12 (dislodgeable material) or 15 (soil) days.  The amount of arsenic absorbed by each pig was evaluated by measuring the amount of arsenic excreted in the urine (as measured on days 6 to 7, 8 to 9 and 10 to 11) during 48 hour collections.  The urinary excretion fraction (UEF) (the ratio of the amount excreted in 48 hours divided by the dose administered in 48 hours) was calculated for sodium arsenate and the test material using linear regression analysis.  The relative bioavailability (RBA) of arsenic in the test material compared to that in sodium arsenate was calculated as:

The results are summarized below:

           SEM = Standard error of the mean

           N = Number of data points used in curve fitting

           CI = Confidence interval

Using sodium arsenate as a soluble reference form of arsenic in each independent study, the RBA estimates for both test materials (49% for soil and 29% for dislodgeable material) are significantly lower than the default value of 80%-100% that is employed when reliable site-specific data are lacking.  This demonstrates that the absorption of arsenic from the test materials is significantly less than soluble forms of arsenic.  Use of these data will improve the accuracy of risk estimates for humans who may incidentally ingest soil adjacent to CCA-treated wood or dislodgeable material from CCA-treated wood structures.

Dermal Absorption of Arsenic from Residues on CCA-Treated Wood 

Yvette Lowney and Mike Ruby, Exponent, Boulder, CO
Ronald Wester, University of California, San Francisco, CA
Stewart Holm and Xiaoying Hui, Georgia-Pacific, Atlanta, GA

In their December 2001 final report, the Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel (SAP) that evaluated U.S. EPA’s assessment for children’s exposure from contact with CCA-treated wood and soil recommended:  “In view of the limitations of the research on which this (the dermal absorption value for arsenic) evaluation was based, the Panel considered that there was an urgent need for further research on skin absorption of CCA residues, employing the form of the arsenic found in dislodgeable residues and soil from CCA-treated installations.”  The research reported herein evaluated the dermal absorption of arsenic from residues present on the surface of CCA-treated wood.

In the absence of any data specific to CCA, assumptions for dermal absorption of arsenic from CCA-treated wood were based on data from Wester (1993).  The Wester study was based on dermal application of radiolabeled, soluble arsenic, and soluble arsenic mixed with soil.  The use of radiolabeled arsenic eliminated the potential for background urinary arsenic levels o mask low-level absorption from the dermal applications.  However, the primary limitation of the 1993 study for evaluating absorption of arsenic from dislodgeable residues on CCA-treated wood is the use of soluble arsenic—the study did not address absorption from complex environmental matrices.  The research reported herein used methods developed for soil bioavailability studies that are planned to evaluate arsenic absorption following environmental exposure.  The methods parallel those of Wester (1993), with modifications in the surface area of application and dietary intake of arsenic.  These modifications maximize the potential for detection of dermally absorbed arsenic in exposed animals above background levels.

Two forms of arsenic were administered in this work.  The first, arsenic in solution, was applied to the skin of monkeys to calibrate the model against prior absorption research and to serve as the basis of comparison for absorption of arsenic from CCA residues (i.e., identify the absorption relative to soluble arsenic).  The second research substrate was residue collected from the surface of CCA-treated wood.  This paper describes the research methods, test materials, and results, expressed as dermal absorption of arsenic from CCA residues relative to dermal absorption of soluble arsenic.

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