Brownfield land and emergency hospital admissions in England: a small-area ecological study using contamination hazard score as an exposure proxy

Background: Empirical evidence on the health impacts of brownfield land (previously developed land that may be contaminated) remains limited, mainly due to poorly defined exposures and pathways. Here we assessed associations between an area-level contamination hazard score and emergency hospital admissions across England, using the score as a proxy for the potential contamination associated with brownfield land. Methods: We used Lower-layer Super Output Area (LSOA)-level population-weighted contamination hazard scores in Bayesian hierarchical models to examine the risk of emergency hospital admission (age-sex standardised, 2010-2019) with a primary diagnosis of i) all-cause (excluding external causes), ii) respiratory diseases, and iii) cardiovascular diseases (CVD). Models were adjusted for deprivation, population density, tobacco expenditure, greenspace, urbanicity, and ethnicity, and included spatially structured and unstructured random effects to account for residual spatial autocorrelation between neighbouring areas. Stratified analyses assessed potential effect modification by deprivation, urban/rural classification, and region. Results: We included 42,875,231 admissions for all natural causes, 6,657,050 for respiratory diseases, and 4,393,461 for CVD across 32,844 LSOAs in England. LSOAs with higher contamination hazard scores showed a non-linear decreasing trend in relative risk (RR) for all health outcomes. Spatial variation was evident, with stronger negative associations in urban and the least deprived LSOAs, while rural and more deprived LSOAs showed weaker associations or greater uncertainty. Region-specific analyses demonstrated inverse associations for all outcomes in London and for all natural causes and respiratory admissions in the North West and East of England. Other regions showed no consistent pattern across outcomes. Conclusion: Higher contamination hazard scores were associated with lower emergency hospital admission risks. This suggests that areas with a greater legacy of potentially contaminating land uses do not necessarily experience poorer contemporary population health. The inverse associations may partly reflect subsequent remediation and urban regeneration, although the underlying mechanisms require further investigation.