Heavy metals in soil and plants after long-term sewage irrigation at Tianjin China: A case study assessment

•A case study in China was undertaken to understand the long-term effect of sewage irrigation on heavy metal concentrations in soil and plants.•Significant heavy metal (Cd, Zn and Hg) pollution has occurred in soils of areas using untreated waste water irrigation in Tianjin, China.•Based on the soil to plant transfer factor of heavy metals, there is a strong accumulation effect of Cd in vegetables.•Mean Cd, Pb and As concentrations in vegetables were higher than national safety limits, whereas mean concentrations of Cu, Zn and Cr were safety.