Treated Wood: Evaluating Toxicity During Disposal

A Research Pre-Proposal Submitted to

The Florida Center for Solid and Hazardous Waste Management (FCSHWM)

August 25, 2000

Principal Investigator: Helena Solo-Gabriele, Ph.D., P.E.

University of Miami, Dept. of Civil, Arch., and Environ. Engineering

Co-Principal Investigator: Timothy Townsend, Ph.D.

Univ. of Florida, Dept. of Environmental Engineering Sciences

ABSTRACT

The quantities of wood disposed that are treated with chromated copper arsenate (CCA) are forecasted to increase by a factor of 7 within the next 15 years. Current disposal pathways for the wood, through C&D landfills or through reuse as mulch or wood fuel, should be evaluated from a toxicity perspective so that risks to human and ecological health can be evaluated. A notable toxin within CCA is arsenic. The toxicity of the arsenic is largely a function of the particular form (or species) of the arsenic. Some species are generally non-toxic (e.g. the type of arsenic found in marine shellfish) and others are very toxic (e.g. As(III)). The objective of the first phase of this project is to quantify the arsenic species (As(III), As(V), DMA, MMA) in leachates (as per TCLP and SPLP protocols) from CCA-treated wood. Furthermore, leachates will be analyzed from a series of lysimeters designed to simulate C&D landfill conditions. Once the arsenic species are quantified, the existing disposal pathways for CCA-treated wood will be evaluated from a relative toxicity perspective. Scaling computations will be performed to put the relative toxicity values into a tangible perspective.

An alternative to disposal-end management of CCA-treated wood is to promote methods which minimize the quantities of CCA-treated wood ultimately disposed. Several non-arsenical wood treatment preservatives have been identified as promising substitutes for CCA-treated wood (e.g. ACQ-, CBA-, CC-, and CDDC-treated wood). During the second phase of this study, the toxicity of alternative-chemical treated wood as well as untreated and CCA-treated controls will be experimentally determined through a set of 5 tests including MetPLATE^TM, Microtox^TM, an invertebrate test, an algal assay, and a test designed to measure hormonally active agents. These different tests will be used collectively to evaluate the relative toxicity of CCA-treated wood versus that of its alternatives.

BACKGROUND, MOTIVATION, AND OBJECTIVES

Wood is a particularly good building material given that it is characterized by a high strength to weight ratio, it is generally cost effective, and is generally aesthetically pleasing in appearance. If wood is used in the outdoor environment, especially in Florida’s warm humid climate, it should be treated to protect it against insect and fungal attack. The most common wood preservative used in the U.S. and in Florida is chromated copper arsenate (CCA). CCA-treated wood maintains its structural integrity for 25 to 40 years.

One of the drawbacks associated with CCA-treated wood is the disposal of the chemical that it contains. Roughly 6300 tons of CCA chemical are imported into the State on a yearly basis. As of the year 2000, the cumulative amount of CCA chemical imported into the state is estimated at 130,000 tons of which 28,000 tons is in the form of arsenic. If this quantity of arsenic were assumed to impact the upper 1 inch of Florida soils (using the entire surface area of the State) the arsenic concentration in this soil would increase by 5 mg/kg. This value indicates that the potential impacts of CCA-treated wood can be significant, especially given the low natural background levels for arsenic in Florida’s soils (0.42 mg/kg geometric average) (Ma et al. 1997) and the low risk-based guidance concentrations that have been established by the Florida Department of Environmental Protection (FDEP) for residential (0.8 mg/kg) and industrial (3.7 mg/kg) land uses (FAC, Chapter 62-777).

It has been estimated that only a fraction of the CCA imported into the State has been ultimately disposed (9% or 2500 tons arsenic or 11,000 tons of CCA). There is a 5 to 25 year “window of opportunity” to recapture a majority of this arsenic if it is found, with certainty, that currrent disposal pathways are unacceptable. Current pathways for the disposal of CCA-treated wood include landfilling within C&D landfills (which are generally unlined) and reuse as wood fuel or mulch. The impacts of current disposal methods, specifically with respect to arsenic, should be evaluated further. Since different forms (or species) of arsenic result in different levels of toxicity, evaluating the impacts of arsenic disposal will require an analysis method that can measure different species. Furthermore, long-term efforts (greater than 25 years) should focus on minimizing the amount of arsenic that will ultimately require disposal. One option for waste minimization is the use of non-arsenical wood treatment preservatives.

The first objective of this research project is to evaluate the arsenic concentrations (total and individual species) associated with leachates from CCA-treated wood. This objective will be met through “Phase I” of this research project by utilizing a series of lysimeters to simulate landfill conditions, by subjecting CCA-treated wood to standard leaching tests (TCLP and SPLP) and analyzing for arsenic concentrations within the leachate. The second objective of this study is to evaluate the toxicity of alternative-chemical treated wood (wood treated with ACQ, CBA, CC, or CDDC). Toxicity will be evaluated experimentally as part of “Phase II” of this study through a set of 5 standardized toxicity tests.

METHODOLOGY - Scientific Approach

Phase II: Arsenic Speciation of CCA-Treated Wood Leachates

Task a: Method Development. Many arsenic species exist. Those found in the environment, in order of increasing toxicity, include dimethylarsinic acid (DAA), monomethylarsonic acid (MAA), arsenate [As(V)], and arsenite [As(III)]. During the year 2000 portion of this study, methods have been developed for analyzing As(V) and As(III) in environmental samples. The objective of this task during the upcoming year, year 2001, will be to develop methods for analyzing DAA and MAA in addition to As(V) and As(III). Two methods are available for such analysis. These methods include: 1) use of an HPLC (High Pressure Liquid Chromatograph) coupled with an ICP-MS (Inductively Coupled Plasma-Mass Spectrometer) and 2) use of an atomic fluorescence spectrometer (AFS) system coupled with an HPLC and a arsine hydride generator (HG). Currently as part of the year 2000 project, the research team is also exploring appropriate methods for sample preservation. There is one particular technique (Le et al. 2000) that uses an online filter and a set of cartridges that are capable of separating the different arsenic species upon sample collection, thereby avoiding sample preservation problems. It is likely that this sample collection system will be used, especially if samples must be transported across large distances.

Task b: Lysimeter Installation. In order to simulate the leachate from a C&D landfill, a set of lysimeters will be established. These lysimeters will contain simulated C&D waste, CCA-treated wood, and untreated wood.

Task c: Leachate Analyses. Leachates from the lysimeters will be analyzed (on a pre-determined time schedule) for arsenic species. Furthermore, samples CCA-treated wood and untreated wood will be subjected to leaching tests such as the standard TCLP (simulated landfill) and SPLP (simulated rainfall). Leachates from these tests will be analyzed for arsenic species as well.

Scaling Computations. Different disposal options for CCA-treated wood will be evaluated from a “relative toxicity” perspective. These relative toxicities will then be scaled against tangible quantities so that individuals can get a better understanding for the magnitude of the arsenic releases.

Note: Complimentary Study on Chromium Speciation. There is currently a complimentary study on chromium speciation that has been funded directly through the Florida Department of Environmental Protection. Dr. Tim Townsend is the PI on that project. Efforts will be coordinated between the two studies assuming that both studies obtain funding.

Phase II: Toxicity of the Alternatives to CCA-Treated Wood

Chemical alternatives investigated during this phase of study are those which contain no arsenic and maintain the positive aesthetic characteristics of CCA-treated wood (e.g. non-oily, paintable, etc..). During the1999 portion of this study, four chemicals which met these criteria were identified as the most promising alternatives to CCA. These alternatives included:

· ACQ: alkaline copper quaternary, produced by Chemical Specialties Inc.

· CBA: Copper Boron Azole, produced by Hickson.

· CC: Copper Citrate, produced by Osmose Wood Preserving.

· CDDC: copper dimethydithiocarbamate, produced by Kodiak Inc.

All of these alternatives contain copper and organic co-biocides. Five standardized toxicity tests will be conducted on these four alternative-chemical treated wood products as well as on a series of controls. The controls include untreated wood and two CCA-treated wood samples provided by two different facilities. As part of the year 2000 study, these samples were collected and analyzed through TCLP and SPLP and are therefore well characterized. The focus of the year 2001 study will be to run five toxicity tests on these treated wood samples. Multiple tests were chosen because each method has its strengths and therefore a combination of tests will be performed to assess the overall toxicity of the contaminants. Toxicity tests that will be run on these samples include the following.

Microtox ^TM: Microtox ^TM is the most common toxicity test used to evaluate wastewater effluents. This test is sensitive to organic contaminants, but does not perform well when evaluating heavy metal toxicity (Bitton 1994). This test will be useful for evaluating the toxicity of the organic co-biocides without large interference from the metals portion of the alternative wood treatment preservatives.

MetPLATE ^TM: MetPLATE ^TM is a rapid enzymatic assay specific for the detection of heavy metal toxicity. The test is sensitive to copper and chromium but not sensitive to arsenic (Bitton et al. 1994).

Invertebrate Test: This toxicity test involves the exposure of Daphnia (Ceriodaphnia dubia < 24 hours old) to the leachates.

Algal Assay: This toxicity test evaluates the growth inhibition of algae (Selenastrum capricornutum) following a 96 hour exposure to the sample and its dilutions (USEPA 1994). This assay provides a measure of chronic toxicity associated with bioavailable metals and herbicides (Blaise 1991; Hickey et al. 1991; St. Laurent et al. 1992).

Hormonally Active Agents: Hormonally active agents (HAA) are compounds which disrupt chemical pathways within a cell. Many pesticides are HAA. This test is based on the interaction of HAA in the leachate with an integrated human estrogen receptor that ultimately causes a color change in proportion to its concentration.

TIMELINE

Project Duration: 1.3 years

Project Start Date: January 1, 2001, Project End Date: April 30, 2002

Description

2001

2002

Phase I: Arsenic Species in Leachates

Phase II: Tox. Tests, Alternative Chemicals

Progress Reports

TAG Meetings

Draft & Final Project Report

Both research tasks will be completed by the end of 2001. A draft of the final report will be available in February 2002. The report will be finalized by April 2002, after comments are received from the Center and from the TAG.

DELIVERABLES

A technical advisory group (TAG) will be established for the project and will likely include the 20 members that participated during the year 2000 project. A minimum of two TAG meetings will be held per year. TAG meetings have been very successful in the past. The last three TAG meetings held on the CCA-treated wood research had between 50 to 60 attendees. A final report will be prepared which documents the methods and results from both phases of the research. Essential information will be included in the main body of the final report and less essential information will be included in an appendix. The current web site, will continue to be maintained and updated throughout the duration of the project. Quarterly progress reports, minutes of the technical advisory group meetings, technology transfer plan, etc.. will be submitted to the Center as required.

PRACTICAL BENEFITS FOR END USERS

Results of the research are practical. Quantifiying the arsenic concentrations (total and individual species) leached from CCA-treated wood (Phase I) will be used to determine whether current disposal pathways for CCA-treated wood are acceptable. If it is found that significant amounts of arsenic are leached as As(III) (the more toxic form of arsenic), for example, the disposal pathway corresponding to that leachate should not be encouraged. Furthermore, the results from the arsenic leachate study can also be used with FDEP risk models for establishing arsenic regulatory limits associated with different disposal pathways. Results from the toxicity tests on alternative-chemical treated wood will be used to determine whether the alternatives should be promoted as potential substitutes to CCA. Currently it appears as though the alternatives are more desirable given that the disposal standards for the copper and the organic co-biocides are more lax (or non-existent) than those for arsenic. However, before these alternatives are promoted as a means of waste minimization is must be known whether or not they present a risk from a toxicity perspective. The alternative-chemical treated wood should be promoted for use within Florida only if it is found to be less toxic than CCA.

SEPARATION OF WORK AMONG THE UNIVERSITIES

Helena Solo-Gabriele will be responsible for all administrative activities required by the Center, for coordinating TAG meetings, and for all deliverables. She will also be responsible for directly supervising Phase I of the project. Tim Townsend will be responsible for supervising Phase II and for preparing an internal report on this Phase of work that will be used in the final report for the project. Although both PIs have separate work phases, they plan to coordinate their research efforts in the most effective manner possible. For example, Dr. Timothy Townsend is the PI on a current research project evaluating chromium speciation. Samples that are needed for this project for arsenic speciation analysis (e.g. samples of CCA-treated wood run through TCLP and SPLP) will be split and analyzed by the respective Universities.

PERTINENT LITERATURE AND REFERENCES

Bitton, G. 1994. Wastewater Microbiology. Wiley-Liss, Inc. New York.

Bitton, G., K. Jung and B. Koopman. 1994. Evaluation of a microplate assay specific for heavy metal toxicity.

Archives of Environmental Contamination and Toxicology 27: 25-28.

Blaise, C. 1991. Microbiotests in aquatic ecotoxicology: characteristics, utility, and prospects. Environmental

Toxicological Water Quality. 6:145-155.

Florida Administrative Code, 2000. Chapter 62-777, Contaminant Cleanup Target Levels.

Florida Department of Environmental Protection, Tallahassee, Florida.

Hickey, C.W., C. Blaise, and G. Costan. 1991. Microtesting appraisal of ATP and cell recovery toxicity end points

after acute exposure of Selanastrum capricornutum to selected chemicals. Environmental Toxicological Water Quality. 6:383-403.

Le, X.C., S. Yalcin, and M. Ma, 2000. Speciation of submicrogram per liter levels of arsenic in water: on-site

species separation integrated with sample collection. Environmental Science & Technology, 34, 2342-2347.

Ma, L.Q., Harris, W., and Hornsby, A., 1997. Background Concentrations of Trace Metals in Florida Surface Soils,

Report #97-4. Florida Center for Solid and Hazardous Waste Management, Gainesville, FL.

Solo-Gabriele, H.M., and Townsend, T., 1999. Disposal Practices and Management Alternatives

for CCA-Treated Wood Waste. Waste Management Research, 17: 378-389.

Solo-Gabriele, H.M., Townsend, T., Kormienko, M., Stook, K., Tolaymat, T., and Gary, K., 2000.

Alternative Chemicals and Improved Disposal-End Management Practices for CCA-Treated Wood, Report# 00-03. Florida Center for Solid and Hazardous Waste Management, Gainesville, FL.

St. Laurent, D., C. Blaise, P. Macquarrie, R. Scroggins, and R. Trottier. 1992. Comparative assessment of

herbicide phytotoxicity to Selenastrum capricornutum. Using microplate and flask bioassay procedures. Environmental Toxicological Water Quality. 7:35-48.

Tolaymat, T.M., Townsend, T.G., and Solo-Gabriele, H., 1999. Chromated copper arsenate treated wood in

recovered construction and demolition waste recycling facilities. Environmental Engineering Science, 17(1): 19-28.

USEPA. 1994. Methods for measuring the acute toxicity of effluents in receiving waters to freshwater and marine

organisms. 4^th ed. EPA/600/4-90/027.