Constructed soils for mitigating lead (Pb) exposure and promoting urban community gardening: The New York City Clean Soil Bank pilot study

Gardening provides a wide range of benefits to urban residents but may also increase risks of exposure to contaminants in soils. Here we evaluate the use of clean excavated glacial sediments and locally produced compost, to create soils for urban gardens in New York City, NY, USA. The objectives of this study are to examine contaminants in compost and manufactured soil, assess safety of produce, and evaluate the agronomic value of soil mixes with different ratios of sediment and compost. Methods of analysis include quantifying metal/metalloid concentrations in sediments, composts, and plant tissues, soil agronomic parameters (pH, salinity, organic matter, total nitrogen, total carbon), and crop yield. Contaminant levels in sediments from the New York City Clean Soil Bank (CSB) (<10 mg Pb kg−1) were far below background levels of soils in two selected gardens (66 and 1025 mg Pb kg−1), while available composts had highly variable levels of contamination (10-232 mg Pb kg−1). A relatively clean compost was used for this study (19 mg Pb kg−1). Metal/metalloid levels did not increase in constructed soils during the 1-year pilot study period, and crops were well below EU safety standards of 0.1 and 0.3 mg Pb kg−1 for fruits and leafy greens, even when surrounded by contaminated soils. Sediment/compost mixtures produced yields comparable to control plots. Results suggest that CSB sediments have high potential to serve as manufactured topsoil. Creating these soil mixtures diverts materials from expensive waste disposal, reduces contamination risks for urban residents, and promotes the myriad benefits of urban agriculture and community gardening.