GEOCHEMICAL FINGERPRINTS AND FUGATIVE CONTAMINANTS OF RESIDENTIAL AND NON-RESIDENTIAL COMPOST MATRICES IN SUBURBAN BOSTON, MA TO SUPPORT LOCAL AGRICULTURE

Childhood lead (Pb) exposure is a leading environmental justice issue globally. Pb in soils has been identified as a common pathway for Pb exposure, particularly for children. Soil remediation efforts in the Boston area, where Pb in soil has been documented to average 950 µg/g, primarily aim to cover, or “cap,” contaminated soil with low-concentration Pb compost. However, Boston municipal compost has exhibited a mean concentration of 207 ug/g over the past two decades, which is over 2 times the 80 µg/g limit set by the City of San Francisco. This community-based study analyzes geochemical distinctions between residential and non-residential compost samples in the suburbs of Boston, MA to supplement existing studies on heavy metal contaminants in the area’s municipal compost.

We reached out to community members with backyard composters and local farms to provide them with both trace element and nutrient analyses of their compost, with a goal of reporting back a range of quality parameters (including Pb, K, Ca, N, C, and C/N). We reported back quality parameters in an accessible format, educating participants on best practices for backyard composting. A liter of finished compost was collected from each participant before being oven-dried at 40°C and homogenized into powders in a tungsten carbide mixer mill. Powders were prepared for pED-XRF (Spectro XEPOS-He) in triplicate and flash combustion (Elementar CHNS Vario Micro Cube). Results validate Fitzstevens et al.’s 2017 biogeochemical characterization of municipal compost matrices and confirm the model’s applicability in suburban settings. Plotting [Si/Ca] [Pb/Ti] concentrations permits a relatively inexpensive, effective method to identify fugitive Pb sources in the Boston area. Suburban residential compost has an average concentration of 69 μg/g Pb while the non-residential samples average 89 μg/g Pb. This demonstrates suburban compost feedstocks have lower mean Pb levels compared to Boston municipal compost, and are excellent candidates for a locally sourced material to cap more contaminated urban soils to minimize lead exposure. In-situ residential and farm compost produced in the suburban areas surrounding Boston can support both private and commercial agriculture as well as sustainability efforts.