Passive Analysis of PAHs in Waterways Using LDPE films
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Low-density polyethylene (LDPE) is a nonpolar hydrocarbon polymer which has adsorptive properties for other nonpolar compounds and can be used to passively monitor organic pollutants in waterways. The Concho River has a relatively constant flow but based on environmental conditions the concentration of PAHs can vary dramatically. A sampling apparatus was designed to rest on the river bottom holding LDPE films suspended in the water for up to several days. Neutral organic compounds in the river, including PAHs, accumulate on the films and are later extracted – potentially enhancing detection limits. This study uses a variety of methods to enhance the detection, identification and quantification of environmental PAHs. The ability of the LDPE films to absorb PAHs was tested in vitro by submerging them in water spiked with four PAHs (40 ppb) for 24 hours. The extract was analyzed using GC-FID and the observed signal to noise ratios suggest that detection limits as low as 0.03 ppb may be possible. The spiked water was analyzed before and after sampling indicating a 95% decrease in PAH levels. This suggests a 51% recovery. Further work is being done to understand the factors limiting absorption and recovery. Attempts to enhance detection limits by using multiple films and extending absorption time are ongoing. Three trials of the sampling system in the Concho river suggest the presence of several PAHS at very low levels. The enhancements being developed should allow us to confirm their presence and estimate concentrations which are probably well under 1 ppb.