The health benefits and risks of growing-your-own produce in an urban environment

The practice of gardening and growing-your-own (GYO) produce in urban areas, has been associated with many potential benefits to health from increased fruit and vegetable consumption and exercise, but also health risks arising from exposure to potentially toxic elements (such as cadmium: Cd, and lead: Pb) in urban soils. However, the potential health benefits of gardening are currently overlooked by authorities during assessments of contaminated land, which may result in access to urban gardens and allotments being incorrectly restricted or removed because of concerns over the impact to human health. The trade-off between health benefits and risks is investigated in this thesis through: the sampling and analysis of the properties of allotment soils (chapter 2); a comparison of plant uptake models (chapter 3) verified using a pot experiment (chapter 4), and a questionnaire survey investigating the effect of gardeners’ routines on benefits and risks (chapter 5). The different areas of study are combined in the creation of a model framework developed to estimate health benefits and risks attributable to urban gardening (chapter 6). A total of 149 allotment plots were sampled across the city of Nottingham and analysed in the laboratory for trace element concentrations by ICP MS. Concentrations of lead (Pb) in top-soils exceeded the category 4 screening level of 84 mg Pb kg-1 dw in most plots (n=129), with a median concentration across all plots of 214 mg Pb kg-1 dw. However, other elemental concentrations (As, Cd, Cr) were below the respective C4SLs for an allotment land-use and unlikely to pose health risks. In comparison, analysis of the results of a questionnaire survey of 120 gardeners’ routines, suggested that gardening more regularly in autumn and winter was positively correlated with categories of increased fruit and vegetable consumption and exercise (one-way ANOVA; p < 0.05). Furthermore, gardeners over the age of 45 scored significantly better in the physical health (but not the mental health) categories of the SF 36 v 2 questionnaire compared to standardised scores when results were adjusted for age and gender (Table 5.9). Health benefits and risks were combined using a prototype Bayesian Network (BN) model developed according to the principles of CLEA (Contaminated Land Exposure Assessment model). Health outcomes from benefits (e.g. fruit and vegetable consumption) and risks (e.g. lead toxicity) were derived using a sub-model; requiring odds and hazard ratio’s for the outcomes of disease. The model predictions suggested that for the study population, whilst there were some benefits attributable to urban gardening, these appeared to be outweighed by health risks from potential exposure to Pb. Further work is required to confirm or refute this finding and to validate and improve the BN model. The study also highlights the importance of considering health benefits of gardening in risk assessment in future for urban gardeners. Future work should also consider weaknesses highlighted in the use of the CLEA model to predict health risks for gardeners, especially in the prediction of plant uptake of toxic elements, and the limited data availability describing the toxic effects of chemicals exceeding a threshold value which may or may not result in SPOSH