Emissions of Chromium, Copper, Arsenic, and PCDDs/Fs from Open Burning of CCA-Treated Wood

Abstract

Aged and weathered chromated copper arsenate (CCA) treated wood was burned in an open burn research facility to characterize the air emissions and residual ash. The objectives were to simulate, to the extent possible, the combustion of such waste wood as might occur in an open field or someone's backyard; to characterize the composition and particle size distribution (PSD) of the emitted fly ash; to determine the partitioning of arsenic, chromium, and copper between the fly ash and residual ash; and to examine the speciation of the CCA elements. This work reports preliminary air emission concentrations and estimated emission factors for total particulate matter, arsenic (As), chromium (Cr), copper (Cu), and polychlorinated dibenzodioxins/dibenzofurans (PCDD/F) totals and toxic equivalents (TEQs). The partitioning of As, Cr, and Cu between the emitted fly ash and residual ash is examined and thermochemical predictions from the literature are used to explain the observed behavior. Results indicate a unimodal fly ash PSD between 0.1 and 1.0 microm diameter. In addition to a large carbonaceous component, between 11 and 14% of the As present in the burned CCA treated wood was emitted with the air emissions, with the remainder present in the residual ash. In contrast, less than 1% of both the Cr and Cu present in the wood was emitted with the air emissions. PCDD/F levels were unremarkable, averaging 1.7 ng TEQ/kg of treated wood burned, a value typical for wood combustion. Scanning electron microscopy (SEM) was unable to resolve inorganic particles consisting of Cu, Cr, or As in the wood samples, but X-ray absorption fine structure (XAFS) spectroscopy confirmed that the oxidation states of the CCA elements in the wood were Cu2+, Cr3+, and As5+. SEM examination of the fly ash samples revealed some inorganic microcrystals within the mostly carbonaceous fly ash, while XAFS spectroscopy of the same samples showed that the oxidation states after combustion were mixed Cu+ and Cu2+, Cr3+, and mixed As3+ and As5+. Estimates of the ratios of the mixed oxidation states based on the XAFS spectra were As3+/(total As) = 0.8-0.9 and Cu+/(total Cu) = 0.65-0.7. The Cu and Cr present in the fly ash were determined to coexist predominantly in the two oxide phases CuCrO2 and CuCr2O4. These results indicate that the open burning of CCA-treated wood can lead to significant air emissions of the more toxic trivalent form of As in particle sizes that are most respirable.

Arsenic Chemistry

“…Arsine along with As 0 , As 4 , As 2 , and AsO may also result from the production of methane and other combustible gases during coal gasification ((Diaz-Somoano, López-Antón and Martínez-Tarazona, 2004), 1241(López-Antón et al, 2007); Chapter 5). Once in the atmosphere, arsine oxidizes to As 4 O 6 , which subsequently deposits on atmospheric particles (Chein et al, 2006(Chein et al, ), 1901(Chein et al, -1902 Other human activities that release arsenic include: herbicide use, automobile traffic, marine vessels, glass manufacturing, steel production, waste incineration, Portland cement manufacturing, and the combustion of CCA-preserved wood ( (Shih, 2005), 88; (Matschullat, 2000), 302; (Chein et al, 2006;Wasson et al, 2005;Frey and Zhao, 2004); Chapter 7). Total anthropogenic emissions of arsenic to the atmosphere are about 18 800-25 800 t per year (Shih, 2005), 88.…”

Arsenic in Human History and Modern Societies

“…In 1998, the production of CCA wood preservatives accounted for more than 90 % of the As 2 O 3 used in the United States (Leist, Casey and Caridi, 2000), 126. However, as previously discussed in this chapter, the voluntary agreement between the US EPA and wood preservative manufacturers discontinued the use of CCA in virtually all American consumer products after 2003 (Wasson et al, 2005), 8865; (Townsend et al, 2003), 781. Except for the use of highly pure arsenic in the production of semiconductors, the utilization of arsenic in American commercial products declined during the second half of the twentieth century (Leist, Casey and Caridi, 2000), 126.…”

“…If spills occur at CCA manufacturing sites, arsenic would tend to collect on organic matter in the A horizons of soils and on iron and other (oxy)(hydr)oxides in the B and C horizons (Chapter 3; (Lund and Fobian, 1991)). Toxic arsenic fumes may be released from the burning of CCA-treated wood ( (Wasson et al, 2005); Chapter 7). In one case, arsenic from the burning of treated plywood in a poorly ventilated cabin poisoned a Wisconsin, US family (Gorby, 1994), 3.…”

“…Under a voluntary agreement between the US EPA and manufacturers, CCA was discontinued in virtually all consumer products in the United States after 2003 (Wasson et al, 2005), 8865; (Townsend et al, 2003), 781. Additionally, CCA wood preservatives have been banned in Norway and Denmark , 296.…”

Arsenic in Natural Environments

“…They are estimated at 12 800 and 6240 t As/year, respectively (Matschullat, 2000), 301. Other human activities that release arsenic include herbicide use, semiconductor manufacturing, automobile traffic, marine vessels, glass manufacturing, steel production, waste incineration, Portland cement manufacturing, and the combustion of CCA-preserved wood ( (Shih, 2005), 88; (Matschullat, 2000;Chein et al, 2006), 302; (Wasson et al, 2005;Frey and Zhao, 2004); Chapter 7). Total anthropogenic emissions of arsenic to the atmosphere are about 18 800-25 800 t year −1 (Shih, 2005), 88.…”