Human-health probabilistic risk assessment: the role of exposure factors in an urban garden scenario

Despite the environmental, economic and social benefits of urban gardening, there are also potential threats to human health due to the possible enrichment of urban soils in anthropic contaminants. As of today, our knowledge about the influence of population characteristics and local habits of garden use on risk estimates is incomplete. This work studies the effect of the variability of local exposure factors on the output of a risk assessment in an urban garden scenario through a probabilistic risk assessment (PRA) and an uncertainty analysis. A total of 24 soil samples and 23 samples of lettuce were collected in six urban gardens. Trace element concentration were analysed in both matrices with an atomic absorption spectrometer. Relevant exposure factors were characterized by onsite and online surveys. The results showed that the use of widely accepted, default exposure values overestimate the risk when compared with the result of an assessment with local information. In this study, the 95th percentile of the risk distribution did not exceed human health unacceptability thresholds. Exposure frequency and vegetable consumption rates were the variables to which the risk outcome was most sensitive. This study highlights the importance of characterizing urban gardeners' local activity patterns when assessing the acceptability of urban agriculture in terms of human health.