Investigating ingestion risks from soils and vegetables grown in urban lead-contaminated soil, and mitigation by soil amendments

Community gardens and allotments are being trialled as a nature-based solution to mitigate multiple health and social, economic, and environmental/climate issues in Belfast. However, working in close proximity to urban lead-contaminated soils and ingestion of site-grown produce may pose significant health risks to community members unless remediating action is undertaken. Current research indicates that organic soil amendments adsorb common urban metal contaminants, particularly lead, and thus may limit plant/crop uptake and consequent human health risks after ingestion. This research seeks to investigate health risks associated with ingesting soils and vegetables grown in lead-contaminated and biochar-remediated soils in Lower Botanic Gardens, Belfast, using controlled pot experiments and concurrent field plots. Pots and plots will comprise combinations of high and low lead concentrations in soil, high and low lead concentrations in soil amended with 5%w/w biochar, and seeded with leaf (lettuce), bulb (garlic), and root (carrot) vegetables. Following a standard growth period, the pre- and post-growth soils, and vegetables will be tested using the Unified BARGE Method in vitro bioaccessibility methodology to determine the bioaccessible fraction for lead derived from soils and vegetables with and without biochar remediation. This will then give an indication of ingestion risk associated with biochar-amended and non-amended lead-contaminated soils, and different soil-grown vegetables. It is anticipated that there may be a mild-moderate risk of lead absorption in the gut after ingestion of non-amended contaminated soils; followed by a reduced risk posed by ingestion of site-grown vegetables with a risk hierarchy of carrot > garlic > lettuce; and a further reduced risk from produce grown in biochar-amended soils. These results would support the use of soil amendments to improve the scope of greening nature-based solutions on typically unfeasible contaminated sites, with the ultimate goal of enhancing health and social, economic, and environmental/climate conditions in urban areas.