Promoted dissipation of phenanthrene and pyrene in soils by amaranth (Amaranthus tricolor L.)

A study was conducted to investigate the performance of amaranth, a known hyperaccumulator of cesium, on the promotion of the dissipation of soil phenanthrene and pyrene, which are PAHs (polycyclic aromatic hydrocarbons). Amaranthus tricolorL. 'een choi' was the cultivar used. The presence of Amaranthus tricolor L. evidently enhanced the dissipation of these PAHs in soils with initial phenanthrene concentrations of 7.450-456.5 mg/kg dw (dw, dry weight) and pyrene of 8.010-488.7 mg/kg dw. At the end of the experiment (45 days), the residual concentrations of phenanthrene and pyrene in spiked soils with plants were generally higher than those with no plants. The loss of phenanthrene and pyrene in vegetated soils was 87.85-94.03% and 46.89-76.57% of the soil with these chemicals, which was 2.55-13,66% and 11.12-56.55% larger than the loss in non-vegetated soils, respectively. The accumulation of phenanthrene and pyrene by the plant was evident. Root and shoot concentrations of these chemicals monotonically increased with increasing soil PAH concentrations. Bioconcentration factors (BCFs), defined as the ratio of chemical concentrations in plants and in the soils (on a dry weight basis), of phenanthrene and pyrene by roots were 0.136-0.776 and 0.603-1.425, while by shoots were 0.116-0.951 and 0.082-0.517, respectively. BCFs of phenanthrene and pyrene tended to decrease with the increasing concentrations of soil phenanthrene and pyrene. Plant accumulation only accounted for less than 0.32% (for phenanthrene) and 0.33% (for pyrene) of the total amount enhancement of the dissipated PAHs in vegetated vs. non-vegetated soils. In contrast, plant-promoted microbial biodegradation was the predominant contribution to the plant-enhanced dissipation of soil phenanthrene and pyrene. These results suggested the feasibility of the radionuclide hyperaccumulator in phytoremediating the soil PAH contaminants.