Trace metal contamination and bioaccessibility in two Ulster County Urban Community Gardens, New York State (USA)

In this short communication, soil trace element mobility factors are compared to the bioconcentration factor (BCF; plant tissue to soil total concentration) and evaluated for their effectiveness in estimating contamination pathways between soil and cultivated vegetables. These mobility factors are bioaccessibility (BAF, the ratio of exchangeable to total soil trace metal concentrations) and translocation (TF, the ratio of leaf to root trace metal total concentrations).

Kale was grown in two urban gardens in Ulster County, New York. Soil pH tests were carried out alongside analyses by ICP-OES on soil samples for total and exchangeable trace element concentrations and on kale roots and leaves for total metal concentrations (29 paired soil-kale samples), namely Al, Ba, Cd, Cr, Co, Cu, Pb, Sr, and Zn.

Total soil Cd, Pb, and Zn were above permissible levels in weakly alkaline soil, and kale was contaminated with Ba, Cu, and Sr. It was found that BAF explains kale contamination by Ba, Cu, Sr, and Zn more than the other indicators.

The exchangeable fraction should be included in assessing trace metal contamination. This comparison of mobility indicators is a novel way of examining contamination problems in urban food production and improves the understanding of how evaluating soil dynamics helps identify ways to develop health-protective ecologically sustainable practices in cities.