Assessing Soil Contamination Risks Near Urban Railway Lines Through Field Sampling

Thesis Abstract

Urban railway infrastructure, while vital for sustainable transportation, has been increasingly associated with environmental concerns pertaining to soil contamination, especially in densely populated settings. The proximity of railway lines to residential and commercial areas heightens the potential exposure to hazardous substances such as heavy metals, hydrocarbons, and other pollutants originating from rolling stock emissions, brake pad wear, locomotive maintenance, and ballast materials. Despite ongoing debates regarding the extent of contamination and its health implications, systematic empirical assessments remain limited, particularly within metropolitan environments where industrial activity and transport emissions intersect. This study aims to evaluate soil contamination risks in areas adjacent to urban railway lines through comprehensive field sampling, with specific objectives to quantify pollutant concentrations, identify spatial variation patterns, assess potential sources, and evaluate associated health risks based on established standards. Employing a quantitative cross-sectional research design, the study will analyze soil samples collected at 100 predetermined sites along and near selected railway corridors within the metropolitan region. Stratified random sampling will ensure representative coverage of areas at varying distances from the railway infrastructure. The primary population comprises soils from zones within a 50-meter radius of railway tracks, with sampling points distinguished based on proximity (0-10m, 10-30m, and 30-50m) to analyze gradient effects. Data collection instruments include geographically referenced soil sample containers, portable X-ray fluorescence (XRF) analyzers for in-situ preliminary screening, and laboratory-based analytical techniques such as inductively coupled plasma mass spectrometry (ICP-MS) for precise quantification of heavy metals (e.g., lead, cadmium, chromium, zinc, and nickel), hydrocarbons, and other organic pollutants. Data analysis adopts statistical methods including descriptive statistics to summarize pollutant levels, Analysis of Variance (ANOVA) to determine significant differences between distance zones, and multiple regression analysis to elucidate relationships between pollutant concentrations and potential predictors such as train frequency, maintenance activities, and traffic volume. Theoretical underpinning is anchored on the Pollution-Hazard Model, which postulates that pollutant spread and concentration are contingent upon both emission sources and environmental factors influencing dispersion and accumulation. Additionally, the Environmental Risk Assessment framework will be employed to evaluate potential health threats based on pollutant concentrations relative to international safety standards (e.g., WHO and EPA guidelines). The anticipated findings include high concentrations of selected heavy metals and hydrocarbons in soils closer to railway lines, with a clear gradient decreasing with increased distance. The study expects to identify key pollution sources, delineate spatial contamination patterns, and quantify associated health risks. Results will reveal statistically significant correlations between train traffic density and soil pollutant levels, suggesting anthropogenic influence. These findings will contribute empirical evidence to fill the existing literature gaps concerning soil pollution dynamics in urban railway contexts, emphasizing the need for targeted remediation strategies and policy interventions. This research concludes that soils in proximity to urban railway lines pose potential environmental health risks, especially for communities residing near heavily trafficked corridors. It advocates for continuous monitoring using standardized sampling protocols, implementation of pollution mitigation measures (such as ballast stabilization and emission controls), and development of regulatory frameworks for soil quality management in railway zones. The study further recommends expanding investigations to include bioaccumulation assessments and longitudinal monitoring to elucidate temporal trends. Overall, this research advances understanding of urban soil contamination pathways and informs sustainable transportation infrastructure planning, ultimately contributing to public health protection and environmental sustainability.