Urban Natural Resources Stewardship

Heavy Metals

Research Issue

[graph:] Mean (S.E.) concentrations of soil metals in residential lawns by age of structure (pre- and post-1940 structures). Different letters represent significant differences for a metal between structure age at alpha = 0.05. Data were log transformedElevated heavy metal concentrations are almost universally reported in urban soils, though often with high variances.  Most of the heavy metal sources in urban landscapes have been associated with roadside environments, interior and exterior paint, stack emissions, management inputs, and industrial waste.  As these heavy metals are emitted into urban environments, they may accumulate in the soil.

Soil acts as a sink for heavy metals through sorption, complexation, and precipitation reactions.  These retention mechanisms are regulated by organic matter, pH, cation exchange capacity, and oxides of a soil.  Therefore, the heavy metals that reach a soil will vary in their availability to plants, soil fauna, and humans based on how these characteristics spatially vary in the urban landscape.  Soils with relatively high amounts of organic matter and oxides, and neutral to alkaline pH, will generally have both a lowered availability to plants and animals and a lowered leaching rate to groundwater of heavy metals.  However, as is the case with most urban environments, soils are physically disturbed and experience a loss of organic matter and a possible change in oxygen level, which weaken the capacity to bind metals, resulting in an increase in availability and mobility of metals which, ultimately, may affect human health.

Our Research

We have collected soils throughout the Baltimore-Washington metropolitan area in different land uses, in riparian zones, and along urban-rural gradients and digested them to extract various metals.  Results have shown that soil levels of metals are associated with traffic volume, parent material, and housing age.  Lead (Pb), nickel, copper, and zinc are ubiquitous in urban environments and are related to roads and cars.  In addition, Pb levels are also related to the distance to structures, particularly houses.  In riparian zones, there are higher concentrations of metals near the outflow where there is greater urbanization than the headwaters of the Gwynns Falls watershed.  This trend is also found in urban-rural gradients.  We continue to investigate heavy metals at various scales from landscape down to parcel level.

Expected Outcomes

Our research results on metals, which at high levels of soil contamination can pose a risk to human health, has helped to inform local health agencies and policy decisions.  Furthermore, our data helps the City of Baltimore and local community groups to better predict where elevated soil metal, especially Pb, levels occur and thus guide remediation efforts.  Of course, a comprehensive approach including level of contamination, desired land use, and community preferences along with accounting for other organic and inorganic pollutants must be taken into consideration.

Research Products

Pouyat, R.; Szlavecz, K.; Yesilonis, Ian D.; Wong, C.; Murawski, L.; Marra, P.; Casey, R.; Lev, S. 2015. Multi-scale assessment of metal contamination in residential soil and soil fauna: A case study in the Baltimore–Washington metropolitan region, USA. Landscape and Urban Planning 142 (2015) 7–17.  

Bain, Daniel J.; Yesilonis, Ian D.; Pouyat, Richard V. 2012. Metal conentrations in urban riparian sediments along an urbanization gradient. Biogeochemistry. 107: 67-79.

Pouyat, Richard V.; Szlavecz, Katalin; Yesilonis, Ian D.; Groffman, Peter M.; Schwarz, Kirsten. 2010. Chemical, physical and biological characteristics of urban soils. Chapter 7. In: Aitkenhead-Peterson, Jacqueline; Volder, Astrid, eds. Urban Ecosystem Ecology. Agronomy Monograph 55. Madison, WI: American Society of Agronomy, Crop Science Society of America, Soil Science Society of America: 119-152.

Yesilonis, I.D.; Pouyat, R.V.; Neerchal, N.K. 2008. Spatial distribution of metals in soils in Baltimore, Maryland: role of native parent material, proximity to major roads, housing age and screening guidelines. Environmental Pollution. 156: 723-731.

Yesilonis, Ian D.; James, Bruce R.; Pouyat, Richard V.; Momen, Bahram . 2008. Lead forms in urban turfgrass and forest soils as related to organic matter content and pH. Environmental Monitoring and Assessment. 146: 1-17.

Pouyat, Richard V.; Yesilonis, Ian D.; Szlavecz, Katalin; Csuzdi, Csaba; Hornung, Elizabeth; Korsós, Zoltan; Russell-Anelli, Jonathan; Giorgio, Vincent . 2008. Response of forest soil properties to urbanization gradients in three metropolitan areas. Landscape Ecology. 23: 1187-1203.

Research Participants

Last Modified: November 10, 2015