A Microscale Approach for the Quantitative Detection of PCBs and PAHs in Small Tissue Masses

PURPOSE: This technical note outlines an analytical approach for the detection of PCBs and PAHs in very small amounts (c. 100 mg wet weight) of invertebrate tissue, including a brief synopsis of the methodology and comparison with traditional techniques. The intent is to show the abilities and limitations of these techniques, how they compare to recommended target detection limits, and how they might be used to support Corps investigations into contaminant bioavailability. While the PAH microscale method is fairly comparable to the traditional method in terms of both method detection limits and mean absolute recoveries, the PCB microscale method did not perform as well with respect to recoveries. However, the PCB microscale method was technically viable with comparable detection limits, and acceptable inter-replicate variability. Ultimately, the choice of whether a laboratory might apply these microscale methods is dependent upon the specific data quality objectives for a particular project (U.S. Environmental Protection Agency (USEPA) 1995). For bioaccumulation and toxicity testing protocols, the microscale method would in many cases offer adequate analytical sensitivity, precision, and accuracy. BACKGROUND: Organic contaminants, including polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), are ubiquitous in urban river, estuarine, and coastal sediments, and can pose significant risks to human health, the environment and the nation's economy (National Research Council (NRC) 1997). Quantifying ecological risk requires assessment of contaminant bioavailability, which is determined by various physical, chemical, and biological processes that control uptake into exposed organisms (NRC 2003). Bioavailability of PAHs, PCBs, and other organic contaminants is assessed using bioaccumulation tests, which have been developed and standardized for use with a varied battery of sediment biota (USEPA/U.S. Army Corps of Engineers (USACE) 1998). Bioaccumulation tests typically require well-replicated factorial exposures of small invertebrates, and often result in samples of very small wet weight (c. 50-500 mg) for tissue concentration analyses. However, traditional analytical methods are designed to address trace levels of contaminants in significantly larger sample sizes (as much as 20-25 g of tissue sample, USEPA 1996), while the Environmental Chemistry Branch at ERDC generally requests 3- to 4-g tissue samples for such methods. Clearly, there is a need for validated analytical methods capable of analyzing contaminants in much smaller tissue masses. The microscale methods discussed herein were developed from standard EPA analytical methods (EPA 1996), compensating for a lower initial tissue mass by additional concentration of the final extract volume. Working with lower sample masses or extract volumes is challenging due to difficulties in monitoring final extract volume, the concomitant concentration of compounds that