Citation:

Otter, R., D. Walters, Jim Lazorchak, K. Fritz, AND M. Mills. Impact of dredging on river sediment, water, aquatic macroinvertebrate, and riparian spider PCB concentrations. 2023 International Conference on the Remediation and Management of Contaminated Sediments, Austin, TX, January 09 - 12, 2023.

Impact/Purpose:

Contaminated sediments in freshwater ecosystems is a global environmental problem that affects have risks to aquatic and nearby terrestrial food webs. U.S. EPA Office of Research and Development and the U.S. EPA Great Lakes National Program Office conducted an extensive evaluation of the remedial project at the lower Ottawa River, where ~183,500 cubic meters of sediment contaminated with polychloronated biphenyls (PCBs) were removed. Sediment, water, aquatic macroinvertebrates, and riparian spiders were monitored before (2009) and after (2011, 2012, 2013, and 2015) sediment removal at 18 stations along the river. This findings from this 7-year study compares the response of different remediation endpoints varied over time and highlights key findings to apply in monitoring remediation effectiveness at other contaminated sites.

Description:

Background/Objectives.  Recent studies have shown that polychlorinated biphenyls (PCBs) can be exported from aquatic to terrestrial food webs via insect-mediated contaminant flux, therefore extending the potential risk from contaminated sediments beyond aquatic biota to riparian predators (e.g., spiders). In 2010, a remedy of hydraulic dredging occurred at the Lower Ottawa River (Maumee AOC) that removed ~250,000 cubic yards of sediments contaminated with PCBs, polycyclic aromatic hydrocarbons, and lead. Prior to dredging, a remedy effectiveness plan was designed to investigate the impacts this remedy on contaminant exposure across multiple organisms inhabiting the river and the surrounding riparian environment. Measurement endpoints included PCB concentrations in bulk sediment, surface water, macroinvertebrates, and riparian spiders. There were two study objectives for this presentation: 1) determine if significant and consistent relationships existed between bulk sediment, water, macroinvertebrates, and spiders; and 2) assess the remedy effectiveness using bulk sediment, water, macroinvertebrates, and spiders.   Approach/Activities. Eighteen interspersed sampling locations were included in this study design; 10 from dredged area and eight from non-dredged areas. Nearly identical sampling took place at each sampling location beginning in 2009, a year prior to dredging and  in post-dredging dredging years: 2011, 2012, 2013, and 2015. At each sampling location and during each year bulk sediment, water, aquatic macroinvertebrates (mainly Chironomidae using modified Hester-Dendy multi-plate samplers), and riparian spiders (Tetragnathidae hand-collected from webs at night) were sampled. Analysis of PCBs was performed via USEPA Method 8270D (gas chromatorgraphy-mass spectrometry in selective ion monitoring mode).    Results/Lessons Learned. Objective 1 – Overall, site-specfic total PCB concentrations were significantly and positively correlated among all matrices across all years, except for sediment. Sediment concentrations were highly variable throughout the study period. PCB concentrations in aquatic macroinvertebrates were highly correlated with concentrations measured in water, and in turn, were strongly predictive of concentrations in riparian spiders that are specialized predators of adult aquatic insects. Objective 2 – By 2015, PCB concentrations in aquatic macroinvertebrates and riparian spiders were at, or below, their respective 2009 (pre-dredged) concentrations.  Bulk sediment concentrations varied throughout the study.   Overall, bulk sediment was a very poor predictor of PCB bioavailbility across this seven year study. However, site-specfic fate and transport of PCBs was evident using concentrations in water, aquatic macroinvertebrates, and spiders. In addition, this work has filled a critical knowledge gap in the utilization of Tetragnathidae spiders as bio-sentinels of aquatic pollution by showing that despite year-to-year changes in PCB concentrations, consistent relationships existed between spiders and other biotic (aquatic macroinvertebrate) and abiotic (water and sediment) endpoints.

Record Details: