Small but different effect of fouling on the uptake rates of semipermeable membrane devices and polar organic chemical integrative samplers.

Semipermeable membrane devices (SPMD) and polar organic chemical integrative samplers (POCIS) were exposed to a cocktail of organic chemicals using a flow-through system. Samplers were removed and analyzed every 7 d over a four-week period in order to determine sampling rates (Rs) for individual compounds. Prior to laboratory exposure, half of the samplers were allowed to foul naturally for six weeks, in order to examine differences in uptake due to fouling. The amount of fouling ranged from 0.2 to 2.8 g dry weight/dm2 for POCIS and 0.1 to 1.4 g dry weight/dm2 for SPMDs, and the pattern of accumulation was also different between them. The Rs values were determined by fitting curves to time course uptake data and also by using performance reference compounds (PRCs) for SPMDs. Sampling rates ranged from 2.7 to 14.2 L/d for SPMDs and 0.01 to 0.27 L/d for POCIS. Fouled SPMDs showed a reduction in Rs (<20%) for all but one compound, and there was a similar reduction in the release of PRCs. However, PRC-predicted R, values were overall somewhat higher than those from fitted curves. Uptake of alkylated phenols in POCIS was generally higher (up to 55%) in fouled samplers. The reason for this is not known, but is possibly due to some reduction in interactions with the membrane in fouled samplers. There was no overall pattern in the relationship of sampling rate differences with log Kow or over time for either sampler. Release of compounds from POCIS after a drop in exposure water concentrations provides some encouragement for the application of a PRC approach to polar passive samplers.