Using Tenax Extractable Concentrations to Determine the Bioavailable Contaminant Fraction in Sediments

It is well understood that bioavailability-based estimates of exposure are more accurate than traditionally used techniques. One method is the use of Tenax extractable concentrations. This technique uses Tenax, a porous polymer resin, to quantify the amount of hydrophobic organic contaminant that desorbs from sediment. This labile fraction is representative of exposure to benthic organisms and correlates with bioaccumulation and toxicity for several compounds and species. There are two general ways to compare Tenax extractable concentrations to exposure: determining the rapidly desorbing fractions using sequential extractions and using a fixed time single-point extraction. These extractions can be conducted by mixing small masses of sediments (typically <3 g) in overlying water with small masses of Tenax (~0.5 g) and mixing this matrix for fixed periods. The amount of sediment and Tenax can be altered to account for differences in organic carbon and contaminant concentrations. Since the Tenax floats, it can easily be removed from the matrix, and the compounds of interest can be extracted from the beads. These values are normalized for the proportion of organic carbon and compared to lipid-normalized tissue concentration or toxicity values. While there are some limitations to the method, it provides a rapid, accurate, cost-effective means of comparing and evaluating risk of hydrophobic organic contaminants in sediments.