Article pubs.acs.org/est
Emissions of Polycyclic Aromatic Hydrocarbons, Polychlorinated Dibenzo‑p‑Dioxins, and Dibenzofurans from Incineration of Nanomaterials Eric P. Vejerano, Amara L. Holder, and Linsey C. Marr* Department of Civil and Environmental Engineering, Virginia Tech, 418 Durham Hall, Blacksburg, Virginia 24061, United States S Supporting Information *
ABSTRACT: Disposal of some nanomaterial-laden waste through incineration is inevitable, and nanomaterials’ influence on combustion byproduct formation under high-temperature, oxidative conditions is not well understood. This work reports the formation of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated-dibenzo-p-dioxins and dibenzofurans (PCDD/ Fs) from incineration of paper and plastic waste containing various nanomaterials, including titania, nickel oxide, silver, ceria, iron oxide, quantum dots, and C60-fullerene, in a laboratory-scale furnace. The presence of nanomaterials in the waste stream resulted in higher emissions of some PAH species and lower emissions of others, depending on the type of waste. The major PAH species formed were phenanthrene and anthracene, and emissions were sensitive to the amount of nanomaterials in the waste. Generally, there were no significant differences in emission factors for the larger PAH species when nanomaterials were added to the waste. The total PAH emission factors were on average ∼6 times higher for waste spiked with nanomaterials v. their bulk counterparts. Emissions of chlorinated dioxins from poly(vinyl chloride) (PVC) waste were not detected; however, chlorinated furans were formed at elevated concentrations with wastes containing silver and titania nanomaterials, and toxicity was attributable mainly to 2,3,4,7,8-pentachlorodibenzofuran. The combination of high specific surface area and catalytic, including electrocatalytic, properties of nanomaterials might be responsible for affecting the formation of toxic pollutants during incineration.
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INTRODUCTION Nanomaterials are incorporated into a wide variety of products, including food, cosmetics, appliances, electronics, coatings, and medical drugs and devices. The Project on Emerging Nanotechnologies has catalogued more than 1300 consumer products containing or claiming to contain nanomaterials or employing nanotechnology in their manufacture.1 Nanotechnology and nanoscience are expected to contribute ∼$2.6 trillion to the global economy by the year 2014.2 While the economic impact of nanotechnology is certain, its environmental and health implications are not well understood.3 There have been studies of nanomaterials that are released into the environment during the production4,5 and use phases of the life cycle,6,7 but the disposal phase has received scant attention.8,9 As the use of nanotechnology continues to grow, it is inevitable that nanomaterials will enter the waste stream. In the United States, at least 13% of municipal solid waste is incinerated,10 and this percentage is much higher in some European countries.11 Incineration is known to produce hazardous combustion byproducts, including polycyclic aromatic hydrocarbons (PAHs),12 polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans (PCDD/Fs).13−20 Chlorine-containing solids such as poly(vinyl chloride) (PVC) in plastics, which make up as much as 7 wt % of municipal solid waste,21 are © XXXX American Chemical Society
precursors to PCDD/F formation. Depending on the type of air pollution control system on an incinerator, some combustion byproducts may be emitted into the atmosphere in the gaseous and/or particulate phase.22 PCDD/Fs are known to persist and bioaccumulate in both terrestrial and aquatic systems.13,17 The focus of this study is to investigate the influence of nanomaterials on PAH and PCDD/F formation in waste that is incinerated. To our knowledge, there have been only two publications about the role of nanomaterials in the formation of hazardous combustion byproducts. One study showed that thermal decomposition of PVC containing zerovalent iron nanoparticles resulted in elevation of PCDD/F emissions by a factor of 104.23 However, it has also been demonstrated that nanomaterials incorporated into plastics can reduce the formation of dioxins during combustion.24 Many of the nanomaterials found in consumer products are metals and metal oxides, and certain metals are known to catalyze and enhance the formation of dioxins and furans during combustion.25−27 Nanomaterials’ large specific surface area may also Received: November 29, 2012 Revised: March 20, 2013 Accepted: March 25, 2013
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dx.doi.org/10.1021/es304895z | Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Environmental Science & Technology
Article
detached and blasted with compressed air for 30 s to remove deposited particles, and the entire system was flushed with clean air at 1 L min−1 for 10 min. Analysis of blank samples after a burn found no detectable PAHs. Extraction and Analyses of PAH and PCDD/Fs. Filters and XAD-2 resins were extracted via sonication in dichloromethane. The extracts were analyzed by GC-MS according to EPA Method TO-13A for the 16 priority PAH compounds: naphthalene (NAP), acenaphthylene (ACN), acenaphthene (ACP), fluorene (FLR), phenanthrene (PHE), anthracene (ANT), fluoranthene (FLN), pyrene (PYR), chrysene (CHR), benz[a]anthracene (BAA), benzo[b]fluoranthene (BBF), benzo[a]pyrene (BAP), benzo[k]fluoranthene (BKF), indeno[1,2,3-c,d]pyrene (I1P), dibenz[a,h]anthracene (DAA), and benzo[g,h,i]perylene (BGP). For PCDD/F analysis, PVC samples spiked with 1 wt % metal-containing nanomaterials and controls (no nanomaterials) were incinerated. Gaseous and particulate emissions were collected and sent to a commercial laboratory for analysis. The details of the extraction and analytical procedures, including quality assurance and quality control, are described in greater detail in the Supporting Information. Repeatability. Duplicate analyses of PAP, 0.1 wt % Ag/PVC, 0.1 wt % ceria/PVC, 10 wt % Ag/CB, and 10 wt % NiO/CB samples were performed. Results showed that the variation in total PAH emission factors was
