A sediment toxicity evaluation of the upper Mississippi River system

As part of the Environmental Monitoring and Assessment Program for Great River Ecosystems (EMAP-GRE), 530 sediment samples were collected from 447 randomly-selected shoreline sites along the main channels of the Ohio, Missouri, and Upper Mississippi Rivers between 2004 and 2006. Toxicity in these sediment samples was measured using a 7-day Hyalella azteca survival and growth test. Based on the results of testing, 65 sites (14.5%) exhibited acute toxicity and 130 sites (29.1%) exhibited chronic toxicity. Overall, one-hundred eighty-two (182) sites (40.7%) were characterized as either acutely toxic (52; 28.6%), chronically toxic (117; 64.3%), or both (13; 7.1%). Probability estimates indicate that of the 4721.4 river km sampled, sediment from 15.9±3.0% of the river segments (752.2±49.6 km) were acutely toxic, 27.4±3.5% (1289.2±57.2 km) were chronically toxic, and 40.0±3.65% (1887.0±67.5 km) exhibited either acute or chronic toxicity. Select toxic samples were analyzed for 21 pesticides, 20 polychlorinated biphenyl (PCB) congeners, and 6 polybrominated diphenyl ether (PBDE) congeners. For all samples tested, the concentration levels of these analytes were below known toxicity thresholds and neither unionized ammonia concentration, nor osmotic stress (as measured by conductivity) could account for the toxicity found in the sediments. These results demonstrate the potential utility of an amphipod-based toxicity test as an indicator of stress (e.g., from polluted runoff and contaminated river sediments) that might otherwise not be detected from sediment chemical analysis or other methods.