Theme: 11. Advanced Diagnostic Tools

Topic Area: 11a. Environmental Forensics: Site Characterization and Source Determinations

Formatted Title:

Evaluating Anthropogenic Cd Sources in Surface Soils Using Cd, Zn, Pb Concentrations and Stable Isotope Data

Background/Objectives:

Soils adjacent to a former industrial site located in the northeastern USA were found to have cadmium (Cd) concentrations that exceeded regulatory screening criteria. There were two potential anthropogenic sources of atmospherically deposited Cd to the area of interest, a lead smelting facility and a chemical manufacturing facility with a cadmium oxidizer unit. The primary objective of this work was to distinguish sources of atmospherically deposited Cd in shallow soils. The objective of this presentation is to introduce Cd, zinc (Zn) and lead (Pb) concentrations and stable isotope data from surface soil sample extractions and apply these data to evaluate background characteristics, distributions, and identify site soils with anthropogenic Cd characteristics to understand the contribution of atmospheric Cd to site soils.

Approach/Activities:

Distinguishing sources of Cd to shallow soils using Cd, Pb and Zn concentrations and stable isotope data is addressed with the assumption that these metals were primarily transported to the soils through atmospheric deposition, which was controlled by output from historical known potential anthropogenic sources and annual variation in the wind direction. We quantified the following isotope ratios: ¹¹⁴Cd/¹¹⁰Cd (d¹¹⁴Cd), ²⁰⁸Pb/²⁰⁶Pb, and ⁶⁶Zn/⁶⁴Zn (d⁶⁶Zn) for labile (surface adsorbed) sample extracts. Sample processing included soil extractions, total digestions, and resin column purifications prior to analyses. All analyses were performed in a class-10,000 ultra clean instrument room containing a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). Cadmium concentrations and stable isotopes were measured in 16 samples from 10 locations. Additionally, historical seasonal wind data were included in the Cd source assessment.

Results/Lessons Learned:

A review of variation in labile concentrations indicates locations with co-variations in Cd, Zn and Pb concentrations. The lower Cd concentrations ranged from 1,222 ng/g to 10,508 ng/g with associated d¹¹⁴Cd values ranging from 0.26‰ to – 1.6‰. Higher Cd concentrations ranged from 189,317 ng/g to 480,051 ng/g with associated d¹¹⁴Cd values ranging from - 2.1 ‰ to - 1.9 ‰. The strongly depleted d¹¹⁴Cd values associated with the high concentration Cd samples were collected from one area of the site containing soil piles or directly adjacent to soil piles. The trend in Cd concentration and stable isotope data indicate one source of Cd to the site that covaries with Zn and Pb at locations indicative of anthropogenic source (e.g., strongly depleted stable isotope signature). Concentrations and stable isotope signatures indicate a mixing trend to background concentrations and stable isotope signatures (slightly depleted to slightly enriched) in both directions away from the soil piles. These distributions indicate that there was one source of Cd to the area of interest and that it covaries with Zn and Pb. This presentation will discuss general site background, site conditions, samples collected, analytical procedures and combine data from metal concentrations and stable isotope characteristics to evaluate Cd sources to the site.

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Richard Coffin