Background: Bioaccumulation tests are a critical component of regulatory dredging evaluations. Standard bioaccumulation tests conducted in accordance with procedures outlined in the Ocean Testing Manual (OTM) and the Inland Testing Manual (ITM) typically utilize the clam Macoma nasuta and the polychaete worm Alitta virens (formerly Nereis) for marine evaluations and the oligochaete Lumbriculus variegatus for freshwater evaluations. Bioaccumulation tests are designed to detect statistical differences in tissue residues of dredged and reference sediment exposed test organisms. However simple statistical differences may not equate to biologically relevant differences, therefore it is important to understand the role of variability associated with test design (laboratory exposure and tissue chemistry) and provide guidance to ensure appropriate expenditure of resources for additional analysis only when biologically relevant differences have been established. While many labs have demonstrated capability to conduct bioaccumulation tests and many labs have demonstrated capability to quantify tissue residues, the inter-laboratory variability associated with conducting exposures and quantifying resulting tissue residues in 28-day bioaccumulation tests has never been addressed.
Methods: To quantify variability of laboratory bioaccumulation tests, the USACE-ERDC, the USGS-CERC and the commercial bioassay laboratories EA Engineering and EcoAnalysts participated in an inter-laboratory evaluation (i.e., ring test). Test organisms were exposed in standard 28-day bioaccumulation tests to diluted New Bedford Harbor (MA) sediment containing PCBs (2 ppm) and PAHs (0.7 ppm). At test termination all participating labs provided resulting tissues to ERDC for analysis of the NOAA’s 18 congener list (analyzed by GC-ECD; EPA Method 8082) and EPA’s 16 high priority PAHs (analyzed by GC/MS Selective Ion Monitoring, EPA 8370C) to enable quantification of variability associated with conducting bioaccumulation tests.
Results: The concentration of PCBs in the sediments used by the labs ranged narrowly from 0.290 to 0.301 ppm thus ensuring homogeneous exposure concentration across labs. Mean total lipids at experiment termination ranged from 0.8 to 1.2% for Alitta and 0.25 to 0.26% for Macoma. PCBs body residues ranged narrowly across replicates, with coefficient of variation ranging from 9 to 15% across the four bioassay labs. Mean Sum PCBs in tissues varied by less a factor of two across labs, ranging from 50 to 67 ppb for Allita and 98 to 157 ppb for Macoma. Normalization of PCB body residues by total lipids increased variability, but means still varied by less a factor of two across labs. PAHs were mostly below detection in Alitta but pyrene was detected in all Macoma samples with means ranging by less than a factor of two across labs (3.6 to 6.0 ppb).
Conclusion: Using the same analytical laboratory for all tissue analysis, variability of bioaccumulation results across bioassays labs was low. PCBs and PAH bioaccumulation across replicates for a given lab and means across labs varied by less than a factor of two.
Path-forward: The ring test for Lumbriculus was successful but analytical results are not yet available. To evaluate the variability across analytical labs, separate, parallel 28-day Macoma and Alitta bioaccumulation tests utilizing the same marine sediment and exposure conditions was conducted at ERDC. Splits of the resulting tissue composite sample for each species will be analyzed at ERDC and in-house and by three commercial analytical laboratories.
If you have further questions, please contact Dr. David Moore: david.w.moore@usace.army.mil