Phytoextraction of Pb and Cd by Catalpa bignonioides in Crude Oil-Contaminated Soil

Soil contamination by heavy metals and petroleum hydrocarbons has become a serious issue threatening the environment and human health, necessitating effective remediation approaches. This study investigated the phytoextraction potential of Catalpa bignonioides seedlings (1- and 2-years-old) for lead (Pb) and cadmium (Cd) in soils contaminated with 1% and 2% crude oil. The aim was to assess the capability of plants in extracting these heavy metals from polluted soils. Results showed that both crude oil concentrations significantly eliminated both biomass and chlorophyll of plants compared to the control. Pb and Cd concentrations in contaminated soils were higher than in oil-free soils but remained within the acceptable limits set by WHO/FAO (2007). In the control soil, Pb concentrations were 2.290 (mg·kg⁻¹ in roots) and 1.957 (mg·kg⁻¹ in shoots), while in the 2% crude oil soil, they increased to 2.493 (mg·kg⁻¹ in roots) and 2.467 (mg·kg⁻¹ in shoots). The highest Cd concentrations 6.535 (mg·kg⁻¹ in roots), 2.904 (mg·kg⁻¹ in shoots) were found in 2% crude oil-treated plants. TF values for Pb approached or reached 1 in 2-year-old seedlings, while for Cd were consistently below 1. Pb exhibited higher BAF values overall (3.601–4.400), whereas the bioaccumulation factor (BAF) for Cd exceeded 1 only in 2-year-old plants. Overall, older plants removed significantly greater amounts of Pb and Cd, suggesting Catalpa bignonioides is promising for remediating crude oil-polluted soils.