Summary
This study reveals a significant methodological problem in UK contaminated land risk assessment: standard laboratory methods for measuring soil organic carbon cannot differentiate between natural organic matter and petroleum hydrocarbons, resulting in artificially elevated SOC values. Analysis of 2,377 brownfield samples showed that a 1,000 mg/kg increase in TPH correlates with a 0.46 percentage point increase in reported SOC (or 0.79 percentage points when converted to SOM using the Van Bemmelen factor), which can shift soils into less stringent assessment bands and mask genuine human health risks by overestimating the sorptive capacity of soils.
Regional applicability
This study is directly applicable to United Kingdom contaminated land practice and policy. The findings have immediate implications for how the Environment Agency, local authorities and contaminated land consultants conduct risk assessments under Part IIA Environmental Protection Act 1990 and the CLEA model. The work suggests that current generic assessment criteria may be inadequately stringent for petroleum-impacted brownfield sites.
Key measures
Total petroleum hydrocarbons (TPH, mg/kg), soil organic carbon (SOC, %), total organic carbon (TOC), soil organic matter (SOM, %), loss on ignition (LOI), correlation coefficients, generic assessment criteria (GAC) band assignments
Outcomes reported
The study quantified the positive correlation between total petroleum hydrocarbons (TPHs) and soil organic carbon (SOC) measurements in 2,377 brownfield soil samples, demonstrating that TPH concentrations artificially inflate reported SOC values and lead to underestimation of human health risks in contaminated land assessments.
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