Monitoring and mitigation of toxic heavy metals and arsenic accumulation in food crops: A case study of an urban community garden

Urban community gardens have increased in prevalence as a means to generate fresh fruits and vegetables, including in areas lacking access to healthy food options. However, urban soils may have high levels of toxic heavy metals, including lead and cadmium and the metalloid arsenic, which can lead to severe health risks. In this study, fruit and vegetable samples grown at an urban community garden in southeastern San Diego, the Ocean View Growing Grounds, were sampled repeatedly over a four-year time period in order to measure potential contamination of toxic heavy metals and metalloids and to develop solutions for this problem. Metal nutrient, heavy metal, and metalloid concentrations were monitored in the leaf and fruit tissues of fruit trees over the sampling period. Several of the fruit trees showed uptake of lead in the leaf samples, with Black Mission fig measuring 0.843-1.531 mg/kg dry weight and Mexican Lime measuring 1.103-1.522 mg/kg dry weight over the sampling period. Vegetables that were grown directly in the ground at this community garden and surrounding areas showed arsenic, 0.80 + 0.073 mg/kg dry weight for Swiss chard, and lead, 0.84 +/- 0.404 mg/kg dry weight for strawberries, in their edible tissues. The subsequent introduction of raised beds with uncontaminated soil is described, which eliminated any detectable heavy metal or metalloid contamination in these crops during the monitoring period. Recommendations for facilitating the monitoring of edible tissues and for reducing risk are discussed, including introduction of raised beds and collaborations with local universities and research groups.