Elevated lead concentrations in surface soils and cores from New York City

Urban soil can be highly contaminated from past and present sources of lead (Pb) and poses a health hazard to children who might ingest contaminated dust or soil through hand-to-mouth behavior. In New York City, Pb concentrations in 370 surface soils from the backyards of 76 homes in Brooklyn and Manhattan (mean 1,200±1,000 mg/kg Pb, ±1SD) far exceed the New York Soil Cleanup Objective of 400 mg/kg. In addition, backyard soil contained more Pb than publicly accessible parks and street tree pits (mean: 250±290 mg/kg Pb). This information was shared with local residents to provide them with important information about their soils so they could decide where to allow their children to play.

To document the depth distribution of Pb and try to understand the source of contamination, 49 soil cores were collected from a subset of 27 homes, and 12 of these were analyzed for ²¹⁰Pb and ¹³⁷Cs. Inventories of ²¹⁰Pb (3.5±0.9 kBq/m2) and ¹³⁷Cs (0.9±0.6 kBq/m2) correspond to 71% and 50% of the radionuclide inventory based on fallout, respectively. Concentrations of Pb generally decrease with depth in 30 cores (60%) but remain elevated relative to background. In only 3 cores (6%) do Pb concentrations drop <100 mg/kg Pb by 20 cm and in only 10 (20%) by 40 cm. Mean uncorrected Pb inventories of 340±210 g/m² Pb (mean±1SD, n=12) increase by a factor of 1.5 to 2.5 if normalized to whole-core ²¹⁰Pb or ¹³⁷Cs inventories. Most soil core Pb inventories are well above the fallout of Pb previously calculated from a well-constrained core collected in the Central Park lake. The origin of this additional Pb input is unclear, however elevated Pb concentrations in the size fraction above 1 mm, radionuclides, Pb/Sn ratios, and individual grains picked from the cores containing 1000 mg/kg to 6% Pb suggest an additional local non-atmospheric source.

Regardless of the source of Pb, concentrations in backyard surface soils and with depth remain elevated and are not suitable for child play areas. Widespread testing is needed to identify hazards as testing only in publicly accessible areas would underestimate health risk. Collaboration with community organizations and local universities was crucial to collecting these samples and can provide a useful model for generating and providing the environmental health hazard data to local residents.