View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Columbia University Academic Commons 76905_ch81 p1236-1246.qxd 10/4/06 9:32 PM Page 1236 MARKED SET 81 Polycyclic Aromatic Hydrocarbons and Petroleum Industry Steven Stellman, PhD, MPH Tee L. Guidotti, MD, MPH, DABT CHEMISTRY AND STRUCTURES chrysene, dibenz(a,h)anthracene, fluoranthene, fluo- rene, indeno(1,2,3-cd)pyrene, naphthalene, phenan- The term polycyclic aromatic hydrocarbons (PAHs) threne, pyrene) that includes a group of seven PAHs (in generally refers to a group of chemical compounds bold) that are probable human carcinogens. Figure 81.1 consisting of carbon and hydrogen atoms arranged as illustrates structures of key PAHs. The best-known PAH is planar compounds whose principal structural feature benzo(a)pyrene (BaP), due to its early identification in is fused rings. Their nomenclature has evolved over coal tar and later use as a model compound for investigat- many decades and is complex. A comprehensive listing, ing the carcinogenic properties of tobacco smoke. including traditional synonyms and chemical struc- tures, is given by Sander and Wise (1). PAHs are produced during the incomplete combustion SOURCES OF POLYCYCLIC of organic material and are among the most ubiquitous AROMATIC HYDROCARBONS environmental pollutants. The combustion processes that IN THE ENVIRONMENT release PAHs invariably produce a variety of compounds, and in fact, it is difficult or impossible to ascribe health PAHs enter the environment through both natural and effects in humans to particular members of the PAH manmade processes. The principal natural sources of family. Hence, PAHs are usually treated as a group for the environmental PAH are forest fires and volcanic activity purpose of risk assessment. However, the relative amounts (3,4). Forest fire emissions are particularly severe in of individual PAHs released vary from one source to Indonesia, where they are often lit to clear forests in another. The PAH “fingerprint” of diesel exhaust, for preparation for agricultural activities. During the 1997 example, is markedly different from that of mainstream Indonesian haze disaster, concentrations of PAH were tobacco smoke (2). Thus, environmental concentrations 6 to 14 times higher than in unaffected areas (5). of PAHs reported in the literature often consist of lists Malaysia, relatively unaffected until recently, has had with varying numbers of compounds. Polycyclic organic severe haze problems. Fires in peat forests in Malaysia matter is defined as a group of 16 individual PAH are thought to contribute 25% to 35% of atmospheric species (acenaphthene, acenaphthylene, anthracene, PAH (6). Burning of wood for heating and cooking has benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluo- always been an important manmade source of atmos- ranthene, benzo(ghi)perylene, benzo(k)fluoranthene, pheric PAH. Since the Industrial Revolution there have 76905_ch81 p1236-1246.qxd 10/4/06 9:32 PM Page 1237 MARKED SET Polycyclic Aromatic Hydrocarbons and Petroleum Industry 1237 Residential heating, including wood burning Boström et al. (10) note that “residential burning of wood is regarded as the largest source of PAHs” in both the United States and Sweden. In Sweden, between 1990 and 1995, domestic heating sources including dis- trict heating contributed up to one third of total emis- sions of PAHs to air (101 out of 153 total tons per year in 1995). In the United States there has been considerable progress in improving the efficiency of outdoor wood- burning furnaces for heating homes and hot water. The U.S. Environmental Protection Agency (EPA) reported in 1998 that two different wood furnace designs emit- ted 0.2 g to 0.4 g PAH per kg wood fuel under various conditions. Emissions in relation to energy output were less than 17 mg per MJ input, which was less than a cer- tified wood stove but several orders of magnitude greater than a natural gas furnace (11). Measurements of PAH in domestic wood emissions were dominated by Figure 81.1 PAHs. phenanthrene (690 ␮g per MJ), followed by fluoran- thene (148 ␮g per MJ), pyrene (114 ␮g per MJ), and anthracene (97 ␮g per MJ). BaP content was minor (10 ␮g per MJ) (12). Burning of heating oil for home heating is a minor source of PAH, especially compared been important stationary sources, such as manufacturing with wood burning (13). and power generation, and since the early 20th century, mobile sources in the form of gasoline and, later, diesel- Power Generation fueled engines also became important contributors to Coal-fired power plants have represented a source of total environmental PAHs. environmental PAH, at least in the past. In a 1982 study, high concentrations of PAH were reported in sed- Stationary Anthropogenic Sources of iments taken in southwestern Lake Erie near a large Polycyclic Aromatic Hydrocarbons Emissions coal-fired power plant (14). However, increasingly strin- gent regulations over the years have reduced their Stationary sources of anthropogenic PAH emissions importance (15,16). arise from industrial and household activities and account for about 80% of total annual PAH emissions in Municipal Incinerators the United States (7). Industrial sources include power Municipal incinerators are a troublesome source of PAH generation, municipal incinerators, and industrial man- emissions, in part because it is difficult for municipal ufacturing processes. authorities to exercise stringent control over the content It is difficult to estimate precisely the contribution to and composition of the refuse that they must collect total atmospheric PAH from its many different sources, for legal and public health reasons. PAH measured and few such estimates are available. A 1982 report by in fly ash from municipal waste incinerators usually Ramdahl et al. (8) put the proportion of PAH emissions includes phenanthrene, benzo(g,h,i)perylene, fluoran- in the United States from industrial sources at 41%; res- thene, benzo(a)fluoranthene, indeno(1,2,3-c,d)pyrene, idential heating 16%; mobile sources 25%; open burn- and chrysene (17–19). The relative abundance of spe- ing 13%; and power generation and incineration 5% cific PAH has been reported to differ considerably be- and 1%, respectively. Total PAH emissions were esti- tween incinerators operated in the United States and in mated at about 11,000 metric tons. Boström et al. (10) the United Kingdom: Shane et al. (20) reported phe- cite tabulations from the European Environmental nanthrene to be the most abundant and frequently Agency that break down an estimated 1,900 tons of detected PAHs in samples of fly ash and bottom ash col- PAH emissions in 1992 according to emission source: leted from 18 U.S. sites, whereas British data favored 60% (1,120 tons) was attributed to nonindustrial com- benzo(g,h,i)perylene. bustion plants, including domestic wood burning; 20% (383 tons) was from road transport; and lesser amounts Industrial Manufacturing were from production processes and combustion in Several manufacturing activities have been responsi- manufacturing industries (9). ble for large environmental emissions. These include 76905_ch81 p1236-1246.qxd 10/4/06 9:32 PM Page 1238 MARKED SET 1238 Chapter 81 manufacture or processing of coal tar, coke, asphalt, and including smoking (30,31), and for three-ringed PAH petroleum catalysts/cracking operations. Coal tars are compounds (32). Indoor air concentrations of PAH gen- byproducts of destructive distillation (carbonization) of erally reflect both indoor and outdoor sources. Data coal to produce coke or gas and may contain hundreds from the Total Human Environmental Exposure Study, to thousands of individually identifiable chemicals which examined human exposure to BaP via inhalation (21,22). Coal tars are used in the manufacture of indus- and food pathways for 13 households in Philipsburg, trial products, including pesticides and pharmaceuti- New Jersey, suggested that up to 50% of the outdoor cals, and have been used as auxiliary blast-furnace fuels particulate concentration of BaP could penetrate indoors in the production of steel (23). Coal tars result from the (33). Studies by Sheldon et al. (34,35) also found cooling and purification of manufactured gas, a process outdoor BaP highly correlated with indoor levels in that can also produce waste products known as “purifier California, contributing more than 50% on average to waste,” which could contain sulfur and cyanide impuri- indoor levels. Studies done elsewhere have found similar ties, and may persist in the environment for many years results: the contribution of outdoor sources to the heav- (24). Coal-tar pitches, which are formed as residues ier PAHs was 63% to 80% for five- to seven-ringed com- during distillation of coal tars, are used as a binder in pounds in U.S. cities and 76% for BaP in Japanese cities preparing anodes used in the smelting of aluminum. It (36). In one study, homes with gas heating systems were has been noted that in the United Kingdom, aluminum found to have higher average indoor PAH than homes production and anode baking (part of the anode manu- with electric heating systems (37). facture process) were the largest sources of PAH emissions until 1996, contributing about half of all emissions. However, as a result of the 1990 Environmental Pro- HUMAN EXPOSURES tection Act, which led to heavy investment in abatement equipment, emissions were eventually reduced to about Environmental 5% of the total (25). Individuals are exposed to complex mixtures of pollu- tants that may have arisen from a multitude of sources. Mobile Sources of Polycyclic Aromatic It is rarely possible to track down specific atmospheric Hydrocarbon Emissions sources, especially in urban environments. Attempts Automotive exhaust from cars and trucks is a major con- have been made to characterize the relative abundance tributor to atmospheric PAH, particularly in urban envi- or “fingerprints” of atmospheric PAH in a variety of set- ronments (26).