Detection of contaminated samples using a two-way compositing scheme

Compositing of sediments or water samples provides an opportunity to screen numerous samples economically if contamination is a relatively rare occurrence. However, standard compositing procedures simply identify that contamination exists among one or more constituent samples of the composite. Using a two--way compositing strategy, detected contamination in composited samples can be attributed directly to constituent samples without further analyses. Procedure is illustrated using benthic sediment samples contaminated with crude oil following an oil spill. The proposed compositing scheme has a relative efficiency of n/2 compared to the analysis of individual samples when n2 is the number of samples screened (e.g., n2 = 16 samples, relative efficiency is 4/2 = 2)