Supercritical fluid extraction of polycyclic aromatic hydrocarbons from white pine (Pinus strobus) needles and its implications

A supercritical fluid extraction (SFE) method was developed for the extract ion of polycyclic aromatic hydrocarbons (PAHs) from fresh and fallen pine n eedles. Toluene-modified CO2 was used as the extracting fluid, and the extr acted PAHs were analyzed by GC-MS. Using a two-stage extraction procedure, a static extraction at 180 degreesC and a dynamic extraction at 60 degreesC , and an in-cell silica gel plug plus a post-oven silica gel column, the ex traction and fractionation of PAHs can be accomplished in one step. Over a seven month period, a significant variation was observed for PAHs in urban samples, while PAHs in mountain samples were at much lower levels (by a fac tor of similar to8) and showed little seasonal change. Although dry fallen needles and fresh needles contained similar amounts of PAHs, in the fallen needles the lower molecular weight PAHs were partially lost while the highe r molecular weight PAHs were slightly enriched. Pollution in urban areas wa s found to be highly localized, and buildings and trees are believed to be important factors in the restriction of atmospheric PAHs.