Polycyclic aromatic hydrocarbons (PAHs) are by-products from the incomplete combustion or pyrolysis of organic materials. Many PAHs and their derivatives are strongly potent carcinogens and/or mutagens, and belong to a chemical class targeted by the US Environmental Protection Agency (EPA). PAHs have been found with high concentrations in soil and water environment, posing great threats to human health all over the world.
Uptake by plants from the surrounding soil and water is an important step for the transfer of organic toxic contaminants into food chain and web. Clearly, understanding of how plants take up organic contaminants such as PAHs from the environment will have considerable benefits for risk assessment purposes. However, there is still limited information available on plant uptake of PAHs from soil and water in the last decades. As a result, the distribution of PAHs in soil/water-plant systems heretofore needs to be elucidated.
In this work, the uptake of phenanthrene and pyrene, as representatives of PAHs, by ryegrass (Lolium multiflorum Lam) from culture solution was investigated using a greenhouse study. The initial concentrations of phennathrene and pyrene in aqueous solution were 1.00 and 0.12 mg/L. It was observed that the concentrations of these PAHs in ryegrass firstly increased and decreased thereafter in the uptake duration of 0288 h. While the accumulated amounts of tested PAHs by ryegrass roots and shoots increased straightly, and root and shoot concentration factors of phenanthrene and pyrene initially increased sharply and a steady state was observed thereafter in 0288 h. It was notable that shoot concentrations, accumulated amounts, and shoot concentration factors of phenanthrene or pyrene were generally much lower than root. In addition, root concentration factors of pyrene were generally 85%179% higher than those of phenanthrene. By contrast, shoot concentration factors of pyrene were smaller than those of phenanthrene. The translocation of phenanthrene and pyrene from root to shoot was observed in that duration. The translocation factors (TF) were calculated. TF values increased firstly and kept approximately steady thereafter in 0288 h. However, TF values of phenanthrene and pyrene were small (less than 0.031 and 0.009, respectively), indicating that the translocation of these compounds from root to shoot in ryegrass was dramatically restricted. In addition, since the Kow value of pyrene was bigger than that of phenanthrene, a larger portion of pyrene would be partitioned into plant tissues particularly plant lipid parts, resulting in the smaller TF values of pyrene than those of phenanthrene. Results of this greenhouse study would provide some insight into the uptake of hydrophobic organic chemicals by plants, and would be valuable for food security and environment protection.