| Macroporous polystyrene-divinylbenzene resins such as XAD-2 have been widely used to sample hydrophobic organic constituents (HOCs) in ambient waters since the early 1970s. However, there has been little critical evaluation of their efficacy.; In field studies, the efficiency for PCBs was evaluated using tandem columns. The amount of PCB retained on the second column ranged from negligible to greater than the amount retained on the first column. Moreover, as the hydrophobicity of PCB congeners increased, the ability of the resin to retain them decreased.; It is hypothesized that dissolved organic matter (DOM) binds the PCBs, thereby making them inaccessible to the resin surface. Laboratory testing was conducted with 14C-labeled 2,2',5,5'-tetrachlorobiphenyl (log Kow = 5.84), in commercial humic acid (HA) solutions (0-12 mg/L). Breakthrough, measured as effluent/influent concentration, increased from 1 to 12% as DOM increased. In comparison, the more hydrophobic pesticide mirex (log Kow = 7.19) in 6 mg DOC/L HA solutions broke through at ∼40%.; The performance of XAD-2 was further tested using filtered waters from the St. Lawrence River, Hudson River, and Onondaga Lake amended with a 14C-labeled mirex. Breakthrough ranged from 18% to 85%. Using Hudson River water, the performance of XAD and an anion exchange resin was examined at two flow rates. 40-60% of the mirex broke through both XAD-2 and anion exchange resins when operated between 1.5 and 4 bed volumes per minute (min -1). When operated at 0.4 min-1, however, the breakthrough rate reduced to about 10% for ion exchange, and 30% for XAD-2. Acidification of water containing commercial HA did not improve recovery of the mirex. In summary, XAD does not fully capture HOCs in filtrate. Both anion exchange and XAD resins require that the sample volume, flow rate, and DOM interactions with the HOCs be considered to assure adequate capture of hydrophobic contaminants. |
