Title

Dislodgeable and leachable arsenic from in-service and recycled CCA-treated wood that potentially impacts humans

Date of Award

2006

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Civil and Architectural Engineering

First Committee Member

Helena Solo-Grabriele, Committee Chair

Abstract

Since the 1970's, chromated copper arsenate (CCA) had been the most common preservative used in the U.S. to treat wood intended for residential outdoor structures, such as playsets, decks, fences, utilities poles, and marine docks. Many in-service CCA-treated structures currently exist due to the long service life although as of January 1, 2004, CCA-treated wood was no longer manufactured for residential uses in the U.S. Arsenic has been documented to be removed from CCA-treated wood by hand contact or rainfall. Such forms of removal arsenic are called "dislodgeable arsenic" and "leachable arsenic" respectively. The objectives of this dissertation were to evaluate dislodgeable and leachable arsenic from in-service and recycled CCA-treated wood that potentially impacts humans. In order to achieve this goal, three subtopics were discussed.The first study focused on dislodgeable arsenic from in-service CCA-treated wood. In this study, a standard synthetic wipe method, which is very useful to collect large numbers of samples without causing any unnecessary arsenic exposures to testing personnel, was proposed based on earlier studies. The study showed that the levels of dislodgeable arsenic can be affected by many environmental factors, e.g. CCA retentions, distribution of arsenic within in-service structures, age of wood, frequency of usage or rubbing, climate, and sealants/coatings.The second study focused on leachable arsenic from in-service CCA-treated wood. In this study, 2 large field scale decks; one was made from CCA-treated wood and the other was made from untreated wood, were constructed to monitor deck runoff water, soil; and infiltrated water for 3 years. The runoff water concentrations decreased with time but continuously exceeded guideline levels based on an empirical model. The soil concentrations exceeded the residential guideline within six months of the CCA-treated deck installation and increased with time. The infiltrated water concentrations through 0.7 m of sandy soil under the CCA-treated deck exceeded guideline levels in less than one year and increased with time.The third study focused on leachable arsenic from recycled CCA-treated wood. In this study 6 different mulches, pairs (iron-oxide colored and non-colored) of three different treated wood fractions (0, 5, and 100%), were prepared and evaluated in the field for 1 year and also subjected to the synthetic precipitation leaching procedure (SPLP) before and after 1 year weathering. The study showed that iron-oxide colorant reduced leaching of arsenic. An empirical model showed that arsenic concentrations in the field leachate would be controlled by pH of rainfall and weathering time. Lower pH of rainfall would increase the concentrations during the first 3 months. Overall the concentrations decreased with time. The study showed that both the arsenic concentrations in the field and SPLP leachate from mulch containing a small fraction of CCA-treated wood exceeded guideline levels consistently for 1 year. Overall this dissertation suggests that humans can be exposed to arsenic directly through in-service and recycled CCA-treated wood or indirectly via environments contaminated with arsenic leached from the wood product.

Keywords

Engineering, Environmental

Link to Full Text

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