42 Urban Geochemistry I

Monday, 21 March 2011
1:30 PM - 5:30 PM
Monongahela

PRELIMINARY STUDY ON CHEMICAL AND MINERALOGICAL CHARACTERISTICS OF URBAN SOILS IN JERSEY CITY, NEW JERSEY

Paper number: 42-10
Program: Theme Sessions
Time: 3:40 PM – 3:55 PM

Authors

Abstract

In this study, 11 surface soil samples (top 10 cm) from 7 different urban parks and one GeoProbe soil core (247 cm) were collected from a 5km radius of New Jersey City University, Jersey City where at least 10 known smelters, metal works and foundries were located in the early 20th century. Silt and clay size fractions (<63µm) of the samples were analyzed for their Pb and Pb-isotopic compositions as well as mineralogical characteristics by utilizing ICP-MS and XRD, respectively. Lead concentrations in surface soils ranged from 131 to 1120 mg/kg (361 ± 269 mg/kg). The soils having the highest and the lowest Pb concentrations were from the same park. Lead concentrations in the core also varied significantly from the top (265 mg/kg) to the subsurface (22 mg/kg). The second highest Pb concentration in the core (258 mg/kg) was found in a sample containing numerous fragments of coal ash and bricks which are typical for fill material. The other subsurface samples have low Pb concentrations (25 ± 3 mg/kg). It is evident that both spatial and vertical variations of Pb concentrations in the urban soils are site specific depending on current and historical anthropogenic activities.

Lead isotope compositions of the surface soil samples displayed a narrow range of variation (206/207Pbmean: 1.194 and 208/207Pbmean: 2.472) and fall within the modern environmental range of 206/207Pb (1.185 and 1.215). Compared to the surface soil samples, the subsurface soil samples displayed relatively wide range of Pb-isotopic compositions (206/207Pbmin-max: 1.185 - 1.227 and 208/207Pbmin-max: 2.474 - 2.513). The diagrams based on Pb-isotope ratios 206/204Pb versus 207/204Pb or 208/204Pb revealed linear trends which may indicate potential mixing of two end members. Nevertheless, Pb-ore used in the industries as well as natural background level and their Pb-isotope signatures in Jersey City are yet to be identified. The mineralogy of the soil samples were dominated by quartz, K-feldspar, plagioclase (albite) with trace amount of clays (illite), micas (chloritoids) and heavy minerals including rutile. In addition, trace amount of organic materials (naphta) and arsenic oxides were identified in some samples typically containing fill materials. Overall, the relative abundance of major and trace minerals vary noticeably in these urban soils.