Uptake and accumulation of polycyclic aromatic hydrocarbons in the mangroves Avicennia marina and Rhizophora mucronata

This study investigated the uptake and accumulation of polycyclic aromatic hydrocarbons (PAHs) in two mangrove species, Avicennia marina and Rhizophora mucronata. We tested the hypothesis that A. marina would absorb and accumulate more PAHs than R. mucronata. One-year old seedlings of both species were subjected to Bunker Fuel Oil 180 for 3weeks, and the concentration of PAHs was analyzed by gas chromatography-mass spectrometry (GC/MS). The concentration of PAHs was significantly higher in A. marina than in R. mucronata. The major portion of the PAH pool was in roots (96% in A. marina, 98% in R. mucronata) compared to leaves. The dominant PAHs in roots of both species possessed two to three rings and included phenanthrene, anthracene, fluorene, and acenaphthene. In shoots, PAHs in A. marina included phenanthrene, chrysene, anthracene, acenaphthene, benzo[k+b]fluoranthene, pyrene, benzo[a] anthracene, and benzo[a] pyrene, while those in R. mucronata included phenanthrene, naphthalene, fluoranthene, fluorene, and acenaphthene. Phenanthrene was the dominant PAH in roots and shoots of both species. The greater susceptibility of A. marina appears to be due to its greater root length and specific root length, which permit more exposure to oil than R. mucronata. Other contributory factors include root anatomical characteristics such as larger air spaces, lower suberization of root epidermal cells, lower concentrations of polyphenols, tannins, lignin, and a less efficient antioxidative system. This study provides novel information on differences in the uptake and accumulation of PAHs in two contrasting mangrove species.