An in situ toxicity identification evaluation method Part II: Field validation

When sediments are found to be toxic usually there is a mixture of chemicals present. Often it is important to establish which chemicals contribute to the toxicity. Establishing causality can be difficult and often requires fractionation with subsequent toxicity testing. The sample collection and manipulation process can alter chemical bioavailability and toxicity. An in situ toxicity identification evaluation (iTIE) chamber is described that was placed in sediments and fractionated pore-water chemicals into nonpolar chemicals, metals, and ammonia-type groups. This method was field tested and compared to the laboratory-based, U.S. Environmental Protection Agency (U.S. EPA) toxicity identification evaluation (TIE) method. Field studies were performed at three sites contaminated primarily with polycyclic aromatic hydrocarbons (PAHs) (Little Scioto River, OH, USA), polychlorinated biphenyls (PCBs) (Dicks Creek, OH, USA), and chlorobenzenes (Sebasticook River, ME, USA). Both the iTIE and the U.S. EPA TIE methods used Daphnia magna in 24-h exposures. Although the iTIE and TIE were conducted on sediments from the same location, there was significantly more toxicity observed in the iTIE testing. The dominant chemical classes were separated by the iTIE method and revealed which fractions contributed to toxicity. The loss of toxicity in the TIE approach did not allow for subsequent fractionation and stressor identification. Advantages of the iTIE over the TIE method were greater sensitivity and ability to detect causative toxic chemical fractions; lack of sediment collection and subsequent manipulation; and, thus, reduction in potential artifacts, more realistic exposure with slow, continual pore-water renewal in situ, ability to evaluate pore waters in sandy or rocky substrates where pore waters are difficult to collect, and a quicker phase I evaluation. Limitations of the iTIE method as compared to the TIE methods were extensive pretest assembly process, fewer phase I fractionation possibilities, and restriction to shallow waters. The results of these studies suggest that the iTIE method provides a more accurate and sensitive evaluation of pore water toxicity than the laboratory TIE method.