Environmental risks of heavy metals in railway soils: Challenges to ecosystem management

Abstract

Heavy metal contamination near high-traffic railways presents serious risks to food safety, particularly in agricultural regions adjacent to rail transport corridors. This study investigated heavy metal in soils and wheat plants along the Arak-Tehran railway in Iran, focusing on how distance from the railway and soil depth influence contamination levels. Soil and plant samples were collected at intervals from 0 to 300 m away from the railway to assess the concentrations of nickel (Ni), cadmium (Cd), lead (Pb), and zinc (Zn). The findings indicated that heavy metal concentrations decreased with increasing distance from the railway, with surface soils showing higher contamination than subsurface soils. Soil parameters like Organic matter, calcium carbonate, and cation exchange capacity were positively correlated with the absorption of heavy metals. The Geoaccumulation Index (Igeo) classified the area as highly polluted, particularly by cadmium (Igeo = 6.39), nickel (Igeo = 6.72), and lead (Igeo = 4.01). Contamination factor (Cf) values for nickel (158.47), cadmium (125.67), and lead (24.23) along with the average Pollution Load Index (PLI) of 31.5, confirm severe soil contamination. The translocation factor analysis revealed that cadmium had the highest translocation rate from roots to shoots, followed by zinc, nickel, and lead. Both the aerial and root parts of wheat contained heavy metal concentrations exceeding FAO/WHO safety limits, posing a potential health risk to populations consuming crops from this area. Despite high soil contamination, heavy metals were efficiently transferred to the aerial parts of the wheat, particularly cadmium and lead. These findings underscore the health risks posed populations consuming wheat and other crops grown in agricultural zones near the Arak-Tehran railway, where heavy metal contamination from the railway infrastructure can impact food safety.