A 892 VOLUME 111 | NUMBER 16 | December 2003 • Environmental Health Perspectives

Environews Innovations

Environmental Health Perspectives • VOLUME 111 | NUMBER 16 | December 2003 A 893

Innovations | Down with Road Dust

DOWNWITH

T here are more than 3.9 mil-lion miles of roadway in theUnited States, according to

the Federal Highway Administration,and, depending on the area of thecountry you’re in, as much as 70% ofthat road mileage is unpaved. The1997 U.S. Environmental ProtectionAgency (EPA) National Air Qualityand Emissions Trends Report statesthat those unpaved roads—whichcan cover a wide range of composi-t ions, from compacted dir t toshale/slate to gravel—are responsiblefor more than 10 million tons of par-ticulate matter emissions each year.Economic, logistical, and even aes-thetic realities indicate the impossi-bi l i ty of paving every mile ofunpaved roadway in America. Thegoal, then, is to minimize the genera-tion and spread of dust particles.

To help control dust , roadbuilders can either mix somethinginto the roadway as it’s built or theycan apply something after the fact,but many traditional dust suppres-sants have serious flaws. One new

approach is Dust Stop, a proprietaryformulation of natural starches pro-duced by the Canadian firm CypherInternational that may prove bothhealthier and more effective than tra-ditional suppressants.

The Trouble with DustA 1993 U.S. Department of Trans-portation study by civil engineeringprofessor Thomas Sanders andthen–graduate student Jonathan Addoof the Colorado State University cites a1983 Forest Service estimate that forevery vehicle traveling one mile ofunpaved roadway once a day, every dayfor a year, one ton of dust is depositedalong a corridor extending 500 feet outon either side of the median. In the 1December 1999 issue of EnvironmentalScience & Technology, Ann Miguel andGlen Cass, environmental engineeringprofessors at the California Institute ofTechnology, identified at least 20 differ-ent human allergens, including moldsand pollen, in dust stirred up frompaved roads. Miguel says results wouldbe similar, if not worse, on unpaved

roads, especially if it’s a frequently trav-eled unpaved road in an agriculturalarea, where pollens and other plantmatter would be prevalent on road-ways. Other substances found in lesseramounts include rubber breakdownparticles from tires and asbestos parti-cles from brakes.

“Particles of the roadway itself willbe continually ground smaller, untilthey approach the ten- to fifteen-micron danger size where they canmore easily penetrate deep into thelungs,” says Miguel. This is also theideal size range for particles to stay air-borne for longer periods of time—largerthan this, they tend to settle more quick-ly and are less of an immediate hazard,although they are still subject to thesame grinding/regrinding phenomenon.

Particles larger than 2.5 microns canlodge in the upper respiratory area,where they may cause severe irritation.Effects may be especially pronounced ininfants, the elderly, and those with pre-existing conditions such as asthma.Particles this size may also be linked tosome respiratory cancers.

ROAD DUST

Back

grou

nd, t

ire: P

hoto

disc

; tru

ck in

set:

Jul

ie R

eini

tz/I

owa

Was

te R

educ

tion

Cen

ter

Particles smaller than 2.5 microns godeeper into the lungs, where they can dam-age epithelial cells and even pass into thebloodstream. “Small dust particles, some ofwhich may derive from . . . dust as well ascombustion sources, have even been foundin the heart material of some subject ani-mals,” says John Watson, a research profes-sor in the division of atmospheric sciences atNevada’s Desert Research Institute. Dustparticles this small can elude all but themost specialized of filters. So those who livenear unpaved roads aren’t the only people atrisk from these particles—vehicle passengersalso are exposed, even if they ride with theirwindows rolled up.

Some studies indicate that humanhealth isn’t the only thing that suffers inthe dispersion of road dust. Watson pointsout that near unsurfaced roads, plants aretypically dusty, and anecdotal evidence sug-gests that crop yields can be reduced.According to a 1996 technical report by theU.S. Army titled Dust Control MaterialPerformance on Unsurfaced Roadways andTank Trails, dust on leaf surfaces increasesleaf temperatures and water loss, anddecreases carbon dioxide uptake. This maymake vegetation susceptible to chronicdecreases in photosynthesis and growth,eventually leading to accelerated erosion inareas such as roadsides from lack of ade-quate stabilizing vegetation.

And the dust impacts not only the air,but the water as well, as it settles into near-by streams and rivers. In February 2000,researchers led by biology professor Dennis

Murphy of the University of Nevada,Reno, released an assessment of California’sLake Tahoe citing a 30-year decline in clar-ity from 102 feet to 66 feet. Much of theproblem was attributed to increased algalgrowth triggered by atmospheric depositionof phosphorus compounds associated inpart with road dust.

Further, as Sanders and Addo pointout, “the generation of dust means the lossof [fine aggregate material], which act asroad surface binders. This represents a sig-nificant material and economic loss.”According to their report, Iowa’s 99 coun-ty secondary road departments spent morethan $32 million for aggregate replacementin 1978 alone. Tim Trumbull, an environ-mental specialist with the Iowa WasteReduction Center at the University ofNorthern Iowa, further points out thatdust can cause low visibility on unpavedroads, abrades mechanical equipment, anddamages electronic components such ascomputers.

Traditional Dust Suppressants: AMixed BlessingTraditional dust suppressants generally fallinto one of six generic categories: surfactants,

which are short-term wetting agents requir-ing frequent application; adhesives such aslignin sulfonate (tree sap), which act asbinders to form a seal over the surface; elec-trochemical stabilizers derived from sul-fonated petroleum, which expel water fromthe soil and increase compaction; petroleumproducts, which bind fine particles togeth-er; chloride salts, which both attract mois-ture from the atmosphere and retard itsevaporation; and miscellaneous other prod-ucts including microbiological binders andpolymers.

But some of these products pose envi-ronmental hazards that are worse than thedust itself, and the effects of others areunknown. Thomas Piechota, an assistantprofessor of civil and environmental engi-neering at the University of Nevada, LasVegas, is part of a task force looking atroad dust suppressants and their use andregulation. Piechota and colleagues recent-ly completed a water quality impact studyin Clark County, Nevada. The researcherstested 11 different substances (represent-ing the major suppressant categories) byapplying them to unpaved roads, thensimulating sufficient rainfall to createrunoff. Then they analyzed the runoff for

organics, inorganics, metals, andother substances.

“The summary of that studyindicates that no matter what sup-pressant was used, you would seesome sort of water quality impact,”says Piechota. “Some compounds,like the petroleum compounds,contributed more metals, volatileorganic compounds, and the like,while others, like magnesium chlo-ride, had a less noticeable environ-mental impact.” Another point thathe says doesn’t get raised often isthe fact that any suppressant isgoing to create a more or lessimpervious surface. “So when youdo get rainfall,” he says, “you’ll getincreased runoff, which has a

hydrologic impact of its own.”Human health effects also are a con-

cern. According to the 2000 handbookUnsealed Roads Manual: Guidelines toGood Practice, published by Australia’sARRB Transport Research, “petroleum-based products present the greatest envi-ronmental risk with potential hydrocarboncontamination of vegetation, water cours-es, or groundwater if applied excessively orwashed from the roadway before curing.”

Aside from the environmental andhuman health effects, many traditional dustsuppressants simply aren’t that effective.Trumbull conducted a year-long test in2000 in which he looked at the effectiveness

A 894 VOLUME 111 | NUMBER 16 | December 2003 • Environmental Health Perspectives

Innovations | Down with Road Dust

It’s a dusty job, but somebody has to do it. University of Northern Iowa researchers samplethe effectiveness of dust suppressants in keeping road runoff from entering nearby water sources.

Julie

Rei

nitz

/Iow

a W

aste

Red

uctio

n C

ente

r

of a number of dust sup-pressants. He applied sixdifferent suppressantsalong an unpaved road-way—magnesium chlo-ride, calcium chloride,lignin sulfonate, asphaltmillings, new soybean oil,and used fryer oil (which,unlike the other five, isnot as commonly used as adust suppressant).

Trumbull’s tests indi-cated that the lignin sul-fonate was effective, yettended to adhere to pass-ing vehicles and was diffi-cult to remove frompainted surfaces. Thechlorides worked less welland tended to breakdown more quickly, whilethe oils also worked wellbut lost their effectivenessquickly when the road surface was bladedduring maintenance.

“One of the things that strikes meabout dust suppressants as a whole,” saysWatson, “is the lack of detailed studies ontheir effectiveness and their impact on boththe environment and human health. Wehaven’t really looked at how they impactsoil and water, and the mechanisms bywhich they move through soil into subsur-face and nearby water supplies.” Watsonalso points out that many suppressants areproprietary materials, so there’s not a lot ofpublicly available information about them.“Most of the statements I’ve seen don’tconstitute rigorous proof. There is very lit-tle rigorous verification of effectiveness, lack

of toxicity, et cetera,” he says. “The generalposition seems to be ‘Well, it’s not on any-one’s toxics list, so it must be okay.’”

The Starch SolutionAccording to Cypher spokesperson ToddBurns, the need for a new type of dust sup-pressant was obvious from the logisticaland environmental problems rife amongtraditional suppressants. Then, he says,Cypher discovered starch derivatives as atackifier for hydroseeding applications—mixing mulch, seed, fertilizer, and waterinto a slurry that is sprayed on the ground.“The basic ideas are the same: spraying asubstance over the top of a surface andhaving it stay there for a designated period

of time,” says Burns. “Sowe figured if the starchcould bond to the soilsurface, it should be ableto do so on a road surfaceas well.”

Burns says Dust Stopcan be used on gravel,limestone, dirt, sand, orany other unpaved road-bed. According to Burns,the liquified starch formsa chemical bond with theparticles on the surface ofthe road, and the largerthe particle size, the moreefficiently the productwill function. “Smallerparticles will allow DustStop to leach a little far-ther from the surface,” hesays, “while material withlarger particle sizes willhelp contain Dust Stop

closer to the surface and help it form athicker layer of binding protection onthe top.”

Dust Stop promotional materials saythe product has been designed for high-,moderate-, and low-temperature applica-tions, and that it is available in a citronellascent, which the company claims repelsrodents, small animals, and insects, signifi-cantly lowering roadkill incidents anddeterring disease-carrying insects aroundtreated roads.

Dust Stop is made entirely with naturalstarches that are completely biodegradable.While the exact composition of Dust Stop(as well as its cost information) is propri-etary, the company’s material safety datasheet identifies it as a “modified polysaccha-ride,” a “somewhat alkaline” substance (pH10.8–11.5) that is a mild skin and respira-tory irritant. The firm PSC AnalyticalServices performed the rainbow trout 96-hour pass/fail toxicity test (a test that mea-sures the effect of exposure to a test sampleon the survival of young rainbow trout overa 96-hour period) on Dust Stop, and testresults showed 0% mortality after 96 hours.

Dust Stop has been tested on unpavedroadways in China, Canada, and othercountries, and is currently being tested ona heavily traveled dirt road outside ofPrescott, Arizona. While only time will tellif Dust Stop is indeed a viable alternativeto traditional dust suppressants, prelimi-nary results suggest that the starch solu-tion may bring about a healthy resolutionto the problem of dusty unpaved roads.

Lance Frazer

Environmental Health Perspectives • VOLUME 111 | NUMBER 16 | December 2003 A 895

Innovations | Down with Road Dust

Sugge s t ed Read ingDust Stop: Multiple-Use Environmentally Friendly Dust Suppressant [company website].

Winnipeg, Manitoba: Cypher International. Available: http://www.cypherltd.com/duststop.php [accessed 17 November 2003].

Gebhart DL, Hale TA, Michaels-Busch K. 1996. Dust Control Material Performance onUnsurfaced Roadways and Tank Trails. USAEC/USACERL Technical Report SFIM-AEC-ET-CR-96196. Aberdeen Proving Ground, MD: U.S. Army EnvironmentalCenter. Available: http://aec.army.mil/usaec/technology/dustcontrol.pdf [accessed 17November 2003].

Sanders TG, Addo JQ. 1993. Effectiveness and Environmental Impact of Road DustSuppressants. MPC-94-28. Fargo, ND: Mountain Plains Consortium [for the U.S.Department of Transportation]. Available: http://www.ndsu.nodak.edu/ndsu/ugpti/MPC_Pubs/html/MPC94-28.htm [accessed 17 November 2003].

Watson JG, Chow JC, Pace TG. Fugitive dust emissions. In: Air Pollution EngineeringManual, Second Edition (Davis WT, ed). New York, NY: John Wiley & Sons,2000:117–135.

Stopping dust safely. A sprayer is used to apply the starch-based Dust Stop suppres-sant to a rural roadway.

Cyp

her

Inte

rnat

iona

l