SEDIMENT EFFECT CONCENTRATIONS DEVELOPED
Procedures are described in USEPA (1996) for calculating and evaluating sediment effect concentrations (SECs) using laboratory data on the toxicity of contaminants associated with field- collected sediment to the amphipod, Hyalella azteca, and the midge, Chironomus riparius. SECs are defined as the concentrations of individual contaminants in sediment below which toxicity is rarely observed and above which toxicity is frequently observed. These SECs were used to classify toxicity data for Great Lake sediment samples tested as part of the USEPA Great Lakes National Program Office (GLNPO) Assessment and Remediation of Contaminated Sediments (ARCS) Program (Fox and Tuchman 1996; Ingersoll et al. 1996).
Three types of SECs were calculated for Hyalella azteca and for Chironomus riparius: (1) Effect Range Low (ERL) and Effect Range Median (ERM), (2) Threshold Effect Level (TEL) and Probable Effect Level (PEL), and (3) No Effect Concentration (NEC; analogous to Apparent Effect Thresholds). The SECs were calculated using: (1) dry-weight concentrations, (2) dry-weight concentrations normalized to total organic carbon concentrations (for non-ionic organics), or (3) dry- weight concentrations normalized to acid volatile sulfide concentrations (for divalent metals). SECs were calculated primarily for total metals, simultaneously extracted metals, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons. The ranges of concentrations in sediment were too narrow in the database to adequately evaluate SECs for butyltins, methyl mercury, polychlorinated dioxins and furans, or chlorinated pesticides.
About 60 to 80% of the sediment samples in the database are correctly classified as toxic or not toxic depending on type of SEC evaluated. ERMs and ERLs are generally as reliable as paired PELs and TELs at classifying both toxic and non-toxic samples in the database. Reliability of the SECs in terms of correctly classifying sediment samples is similar between ERMs and NECs; however, ERMs minimize Type I error (false positives) relative to ERLs and minimize Type II error (false negatives) relative to NECs. Correct classification of samples can be improved by using only the most reliable individual SECs for chemicals (i.e., those with a higher percentage of correct classification).
Calculating SECs using dry-weight concentrations vs SECs calculated using sediment concentrations normalized to TOC concentrations for PAHs and total PCBs resulted in similar correct classification of toxicity and similar Type I and Type II error. The range of TOC concentrations in the database was relatively narrow compared to the ranges of contaminant concentrations. Therefore, normalizing dry-weight concentrations to a relatively narrow range of TOC concentrations had little influence on relative concentrations of contaminants among samples.
The SECs were calculated from toxicity tests with field-collected samples. If a chemical concentration exceeds an SEC generated using data from these tests with field-collected samples, it does not necessarily mean the chemical caused the observed effect. Rather, the SEC is the concentration of a chemical that is associated with the effect. Field-collected sediments typically contain complex mixtures of contaminants. Additional information is needed to identify the specific contaminants that were actually responsible for the toxicity. Confirmation of sediment toxicity due to individual or groups of contaminants can be determined by using Toxicity Identification Evaluation procedures or by conducting toxicity tests with spiked sediments. Once the probable cause(s) of sediment toxicity has been identified, better decisions can be made regarding remediation options. Although the sediment effect concentrations (SECs) can be used as guidance for evaluating contaminated sediment, there is no intent expressed or implied that these SECs represent USEPA or USGS criteria.
Fox, R.G., and M. Tuchman. 1996. The assessment and remediation of contaminated sediments (ARCS) program. J. Great Lakes Res. 22:493-494.
Ingersoll, C.G., P.S. Haverland, E.L. Brunson, T.J. Canfield, F.J. Dwyer, C.E. Henke, and N.E. Kemble. 1996. Calculation and evaluation of sediment effect concentrations for the amphipod Hyalella azteca and the midge Chironomus riparius. J. Great Lakes Res. 22:602-623..
U.S. Environmental Protection Agency. 1996. Calculation and evaluation of sediment effect concentrations for the amphipod Hyalella azteca and the midge Chironomus riparius. EPA 905-R96- 008, Chicago, IL.
A copy of USEPA (1996) including the database on disk is available through Callie Ballatino, USEPA, GLNPO, 77 W. Jackson, Chicago, IL (312/353-3490, fax -2018; email firstname.lastname@example.org). An electronic copy of USEPA (1996) including the database is also available through the CERC home page.