The Leaden Road (To Unforeseen Devastation)
New research shows that roadway grit is a source of elevated lead levels in the five boroughs.
Published April 10, 2006
By Adrienne J. Burke
Ever since the sale of lead-based paint for residential use was banned in 1978, efforts to protect children from the dangers of lead exposure have focused on removing chipping paint from homes. But a team of New York scientists now suggests that, at least in the five boroughs, another insidious source of household lead contamination is being overlooked: city grit.
Jack Caravanos, assistant professor of environmental and occupational health science in the School of Health Sciences at Hunter College, oversaw a series of experiments that uncovered six lead “hotspots” in New York and indicated that the rest of the city isn’t exactly unleaded either.
Results of three studies, two of which were published February in the scientific journal Environmental Research, and another that’s forthcoming in the journal Chemosphere, could lead city-dwellers to become obsessive about housekeeping.
And Caravanos and his colleagues say their research might help explain why, after a quarter century of efforts to regulate lead in paint, gasoline, drinking water, and consumer products, blood lead levels are down nationally, but have not been reduced in urban areas at the same rate as elsewhere.
PhD Street Cleaners
One experiment examined dust at city intersections. For four weeks, on lightly trafficked Sunday mornings, Caravanos’ graduate students surreptitiously spread out over the five boroughs with 8-foot ladders taking swipes from the tops of crosswalk signals along nearly 50 miles of roadway.
A second study looked at 255 samples of grit scooped up from the ground under elevated subways and steel trestles along major city thoroughfares.
And a third tested grime as it accumulated every week for two-years on glass plates set on sawhorses on a Hunter College rooftop and in an unused stairwell.
All turned up dangerous levels of lead.
In more than 80 percent of the samples gathered from atop crosswalk signals, lead levels far exceeded the 40 micrograms per-square-foot deemed safe by EPA for indoor floors (no safety standard exists for outdoor dust). The citywide median lead dust level came in at greater than six times that number.
In Brooklyn, the city’s most leaded borough, the median level detected was 18 times the EPA limit. Staten Island ranked next highest, followed by the Bronx, and then Queens. Lead levels were lowest in Manhattan, and surprisingly lowest of all in lower Manhattan, which the researchers guess is due to extensive and repeated cleanup efforts undertaken there since 9/11.
In roadway grit collected at street level, more than 20 percent of samples exceeded the EPA limit of 400 parts per million for lead in outdoor soil. Under elevated subway trestles or highway overpasses, lead levels reached more than 1,000 parts per million.
Dangerous Dirt
Why should New Yorkers be concerned about the toxins lurking in street dirt in dark corners or on traffic signal surfaces that no one can reach? Says Arlene Weiss, consulting toxicologist on the studies, “If they’re small enough particles, they get resuspended and transported to different places. When weather is dryer and warmer, the dust gets resuspended and wafted around.”
Weiss, who is on the faculty of the NYU School of Medicine, says the glass plate experiments show one way lead-loaded street grit can wind up in the home. On an otherwise clean surface near a cracked-open window, she and her colleagues were “startled to find that the interior lead dust standards may be exceeded after only three weeks of accumulation.” Not good news for those not in the habit of wiping down their windowsills.
How problematic is exterior dust compared to other sources of lead? While careful to acknowledge that ingested lead-based paint chips are more hazardous to children, who can suffer learning disabilities, mental impairment, or even coma as a result of lead poisoning, Caravanos says, “there is some contribution to blood lead levels from outside the house.”
Indeed, a 2002 Childhood Lead Poisoning Prevention Program Report from the NYC Department of Health and Mental Hygiene identified nearly 500 children in Brooklyn’s Bedford Stuyvesant-Crown Heights and East Flatbush neighborhoods with elevated blood lead levels. “The fact that the three sites with the highest lead dust levels found in this study were part of East Flatbush area raises questions as to whether there is a correlation between areas with high background lead dust loadings and high rates of childhood lead poisoning,” the study authors write. (Samples were not collected in Bed Stuy-Crown Heights.)
Shoes, Strollers, Skateboards, (and Pets)
But lead dust isn’t just blowing in the wind. It’s tracked into homes on supposedly benign objects like shoes, strollers, skateboards, and pets. “Parents wheel their strollers through the street, it gets on their feet, and gets tracked into the residence. Carpeting is a haven for leaded dust, and kids who have mouthing behavior will bite anything,” says Weiss.
The news is most disconcerting for residents near the so-called “hotspots.” In Manhattan, lead levels on crosswalk signal surfaces near the George Washington Bridge were 40 times higher than the EPA indoor standard. And the scientists suspect that airflow directions may in part explain the 20-times-EPA-limit levels on surfaces due east in the Bronx. In Queens, areas with levels 30 times the EPA limit were detected adjacent to the Queensboro Bridge and Queens Plaza and in central Queens along Queens Boulevard. The area of Flatbush Ave. and Avenue D in Brooklyn was deemed a hotspot, and one on Staten Island is adjacent to a large municipal sanitary landfill that contains uncapped soil and debris taken from Ground Zero.
Because no EPA standard exists for outdoor lead dust levels, and because it’s not clear whether roadway grit qualifies as soil and would therefore be regulated by EPA soil limits, Caravanos and his team acknowledge that their results aren’t going to induce any immediate cleanup action. Says Weiss, “We don’t think it’s about cleaning up [the outdoors].” The lead dust is ubiquitous, she says. The challenge is to eliminate the source.
Getting the Lead Out
So just how did the lead get into the grit? The studies didn’t seek to identify the sources, but Caravanos and his colleagues have some educated guesses about what they are.
Yellow paint used on streets and signage contain lead chromate (as does paint used on crosswalk signals, so the researchers were careful to take swipes only from surfaces where paint was intact.) As it deteriorates, Caravanos hypothesizes that particles join the road grit.
Another surprising culprit could be the tire balance weights that fly off car and truck wheels, or get knocked off during sloppy parallel parking maneuvers, and get ground up in the street. Rudolph Jaeger, another study author and a retired professor at the NYU School of Medicine, points out: “Every car has four tires, every tire needs to be in balance. All trucks have balanced tires, and because they’re bigger and heavier with more wheels, the amount of lead used there is greater.”
And the researchers say steel trestles that are constantly under maintenance are another source, evidenced by the fact that lead levels in road grit are highest under trestles.
“Ultimately,” the researchers say, “the development of an outdoor lead dust standard, one on which to base risk assessment procedures, would be beneficial to the public in urban areas. Background levels of contamination must be known in order to apply appropriate cleanup standards.”
Meantime, New Yorkers can protect themselves and their children from lead-contaminated dust by keeping a hygienic home. Caravanos recommends doing away with carpeting in favor of floors that can be wet-mopped frequently, wiping down windowsills and areas near open windows weekly, and keeping an eye on what gets tracked into your home on wheels, shoes, and paws.
Also read: The Academy’s Role in Asbestos Abatement and How Does New York City Prepare for Flooding?
