Dust collected from streets, parks and schools in seven US cities has revealed distinct chemical signatures reflecting decades of industrial activity, traffic and pesticide use, according to a new study
Researchers led by the University of Virginia analysed road dust from seven mid-sized cities in the eastern US for 11 potentially toxic elements, including lead, arsenic, cadmium, copper, zinc and nickel.
The results suggest that urban dust can act as a repository for both contemporary pollution and contaminants released decades ago, with differences in its composition reflecting the industrial history and development of individual cities.
“Our lab specializes in analyzing the elemental profile of environmental samples, which can tell you about the history of a city,” said lead author Minh Tri “Robin” Truong, a doctoral student in environmental sciences at the University of Virginia.
“Richmond, for example, is an older city with coal-fired power plants and a waste incineration plant, which explains the trace levels of lead found in road dust.”
Researchers collected samples from Trenton, New Jersey; Wilmington, Delaware; Richmond, Virginia; Raleigh and Greensboro, North Carolina; Charleston, South Carolina; and Augusta, Georgia.
Importantly for assessing possible human exposure, sampling was not confined to heavily trafficked roads.
“These dust samples are not from the middle of the highway,” said co-author Justin Richardson, professor of environmental sciences at the university. “They were collected at public spaces, such as parks, schools and downtown areas where residents are likely to be exposed.”
Municipal fingerprint
Statistical analysis revealed distinct regional patterns. Trenton and Wilmington, both northeastern cities with long histories of industrial activity, recorded higher metal concentrations than the other locations. In Charleston and Augusta, meanwhile, historical pesticide use and port activity had a stronger influence on the dust’s composition.
Copper, zinc, molybdenum and nickel were enriched above levels expected from natural sources, indicating contributions from activities including industry and non-exhaust traffic emissions.
Lead, arsenic and cadmium were associated more strongly with historical sources including coal combustion, waste incineration and insecticide use.
Source-apportionment analysis attributed around 31% of the potentially toxic element contribution to a group of hazardous metals associated with sources including coal combustion and insecticides. The remaining 69% was associated with other urban sources, including vehicle emissions, industry, waste incineration and maritime activity.
The study also found hotspots where concentrations of potentially toxic elements exceeded some US Environmental Protection Agency and World Health Organization soil guidelines. Lead concentrations above the EPA guideline of 200mg/kg occurred in hotspots associated with lower-income downtown communities.
The question of exposure
Particle size was another concern. In Trenton, Raleigh and Greensboro, up to 10% of the dust was in the respirable fraction below 10 micrometres, which the researchers said could increase potential inhalation risks.
A health-risk assessment indicated that calculated hazard index values were up to 4.5 times higher for children than adults. Augusta produced an index above one when maximum concentrations of five metals were considered, indicating the possibility of adverse effects. However, the researchers emphasised that average concentrations across the study did not exceed health recommendations.
Road dust itself is not directly monitored by the US EPA, although particulate matter and lead are among the pollutants regulated under the Clean Air Act. The researchers suggest their geochemical approach could help identify sources of road-dust contamination in other understudied urban areas.
“Tracing spatial mid-size Eastern US cities road dust pollution: insights from source apportionment and health risk assessment”, is published in Environmental Science and Pollution Research.
