{"id":1378,"date":"2011-05-17T06:37:46","date_gmt":"2011-05-17T11:37:46","guid":{"rendered":"http:\/\/blogs.edf.org\/nanotechnology\/?p=1378"},"modified":"2026-03-14T13:02:09","modified_gmt":"2026-03-14T18:02:09","slug":"they-paved-paradise-all-right-and-with-a-potent-human-carcinogen-to-boot","status":"publish","type":"post","link":"https:\/\/blogs.edf.org\/health\/2011\/05\/17\/they-paved-paradise-all-right-and-with-a-potent-human-carcinogen-to-boot\/","title":{"rendered":"They paved paradise, all right, and with a potent human carcinogen to boot"},"content":{"rendered":"

Richard Denison, Ph.D.<\/em>, is a Senior Scientist.<\/em><\/p>\n

Imagine if someone spread a human carcinogen across millions of acres of land.\u00a0 Then imagine that the carcinogen was found to be entering surface waters due to runoff from the treated acreage.\u00a0 And then that the carcinogen was found to be accumulating in the dust in homes located near the treated acres.<\/p>\n

Far-fetched?\u00a0 Hardly.\u00a0 Welcome to the good ol\u2019 US of A.\u00a0\u00a0 <\/p>\n

An estimated 1% of the area of the lower 48 states is covered with impervious surfaces<\/a>.\u00a0 That\u2019s more than 32,000 square miles \u2013 the size of South Carolina or Austria.\u00a0 About 25% of that area \u2013 approximately 5.2 million acres \u2013 is comprised of parking lots, just slightly less than the area taken up by roads and by buildings, 28% and 29% respectively.\u00a0 Most of those parking lots, as well as many driveways, are paved with asphalt.<\/p>\n

It is exceedingly common for asphalt-paved parking lots and driveways to be \u201csealed\u201d to make them more impervious and hence last longer (interestingly, roads paved with asphalt are only rarely sealed).\u00a0 The sealant of choice in most of the U.S.<\/a> is made with coal tar pitch (in the Western U.S., asphalt-based sealants are typically used).\u00a0 One estimate suggests some 85 million gallons of coal tar-based sealants are sold each year<\/a> in the U.S.<\/p>\n

So what\u2019s not to like about coal tar and coal tar pitch?<\/strong><\/p>\n

Coal tar pitch is the residue left over from distillation of coal tar, which is in turn a by-product of the process used to transform coal into coke for use in making steel.\u00a0 Both coal tar and coal tar pitch are produced in huge volumes every year in the U.S.\u00a0 According to the most recent EPA data, more than one billion pounds of coal tar were produced in 2005, and from that material more than 500 million pounds of coal tar pitch were derived.<\/p>\n

Coal tar and coal tar pitch have both been shown to cause cancer in people<\/a>, including cancers of the skin, scrotum, lung, bladder and renal pelvis and possibly leukemia as well.<\/p>\n

The likely culprit?\u00a0 Polycyclic aromatic hydrocarbons (PAHs), a complex mix of individual chemicals many of which have been linked to a whole range of cancers.\u00a0 Coal tar pitch is comprised of 50 percent or more of PAHs, and coal tar-based sealants typically are 20 to 35 percent coal-tar pitch<\/a>. That amounts to a lot of carcinogens being spread around willy-nilly.<\/p>\n

PAHs are also linked to a broad array of environmental impacts.\u00a0 Among other effects, some PAHs are toxic, carcinogenic, mutagenic or teratogenic (i.e., cause birth defects) to aquatic life.<\/p>\n

But who licks their driveway?<\/strong><\/p>\n

Now, many of you are probably still saying, what\u2019s the big deal?\u00a0 No one\u2019s going to be exposed to stuff spread on parking lots, right?<\/p>\n

Wrong.<\/p>\n

Enter the real heroes of this story: researchers at the National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey<\/a>.\u00a0 In monitoring urban lakes and streams, the researchers began noticing elevated levels of PAHs; core samples of sediments taken from urban lakes across the country showed that the increases began in the 1960s and coincided with regions having increased use of coal tar-derived sealants.<\/p>\n

Now, PAHs come from a host of sources.\u00a0 In addition to their presence in coal tar, they\u2019re a product of incomplete combustion generated by sources such as motor vehicles, wood fires and smoking cigarettes.\u00a0 But each source of PAHs has its own \u201cfingerprint,\u201d and the USGS researchers were able to show that the predominant source of PAHs in the urban lakes was coal tar-based sealants.<\/p>\n

Sealants erode and break down over time, of course.\u00a0 Indeed, sealant manufacturers recommend reapplication every 2-4 years.\u00a0 One can simply sweep up dust from a sealed parking lot or driveway and analyze it for the PAH fingerprint. \u00a0When the USGS researchers did so in 9 cities across the country, here\u2019s what they found:<\/p>\n

\"PAH<\/p>\n

Remember I said that a different type of sealant derived from asphalt is used in the Western U.S.?\u00a0 Now look again at the map above \u2013 striking, no?\u00a0 Coal-tar-based sealants (used in cities shown in blue) contain about 1,000 times more PAHs than do sealants with an asphalt base (used in cities shown in yellow).<\/p>\n

Running off with the lot<\/strong><\/p>\n

Studies of surface runoff from sealed and unsealed asphalt parking lots are equally striking.\u00a0 PAH levels are ten-fold higher in runoff from asphalt-sealed lots than from unsealed lots \u2013 and 65 times higher from lots treated with coal tar-based sealants.<\/p>\n

And when that runoff enters surface waters?\u00a0 A USGS factsheet<\/a> describes the results:<\/p>\n

Scientific studies have shown a relation between coal-tar-based pavement sealcoat and harmful effects on aquatic life.<\/p>\n