| The difficulties associated with monitoring the transport and fate of contaminants in the aquatic environment have inspired several researchers to design membrane-based passive samplers that can provide a time-integrated measure of dissolved concentrations of persistent organic pollutants (POPs). These designs include triolein-filled polyethylene membranes--now commonly referred to as the semipermeable membrane device or SPMD. The purpose of this dissertation research is to examine the performance and kinetics of passive sampling devices such as SPMDs in the field as well as in the lab.; We compare SPMDs with an in situ bioassay using the mussel Mytilus edulis. A good correlation was observed between the SPMDs and the caged mussels, with R{dollar}sp2{dollar} values ranging from 0.57 to 0.85 for individual pesticides (N = 16) and from 0.81 to 0.96 for individual PCB congeners (N = 20). In addition, a mathematical consideration of SPMDs reveals that equilibrium status can be easily manipulated to suit one's needs by changing SPMD design parameters such as membrane thickness, surface area and substrate volume. We also use a computer model to determine the effect of fluctuating water concentrations on two different configurations of SPMD. This model shows that a rapidly equilibrating SPMD will lose sequestered contaminants if the concentration in the surrounding water drops. However, the effect on the predictive ability of the equilibrium model is generally not more than a factor of two, and this is only in a few extreme scenarios. We then report on the results of a six-month laboratory study to compare the uptake kinetics of SPMDs, as well as low density polyethylene (LDPE) tubing used in their construction, using an inexpensive static exposure system. Calculated sampling rates for SPMDs, when normalized to a standard SPMD configuration, compared favorably with those derived from flow-through exposure studies. We also conclude that, although uptake into LDPE is much slower than SPMDs, the LDPE accumulates substantial amounts of contaminants, and provides an inexpensive alternative to SPMDs. Finally, we examine the utility of LDPE strips as an economical screening tool in a large-scale ecological hazard assessment in the Lower Mississippi River region. |
