Evaluating toxicity risk in sediments after remediation at a Superfund megasite using a Triad approach.

The Pine River downstream of the Velsicol Superfund site has been contaminated with various hydrophobic organic pollutants for more than 50 years. Remediation and sediment dredging near the site began in spring of 1999, and was completed in 2006. In 2011, the Michigan Department of Environmental Quality completed a baseline assessment report long-term monitoring plan for the Pine River. However, there has been limited assessment of the benthic community since this evaluation. The objective of this research was to evaluate the risk of Pine River sediment to aquatic macroinvertebrates downstream from the Superfund site after decades of degradation and dredging using the Triad approach. Three sites were selected downstream from the Superfund site, and an upstream reference site was used. At each site, macroinvertebrates surveys were conducted and sediments were collected for chemical analysis of DDT (1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane) and its degradation products and for laboratory toxicity testing for mortality and sublethal effects using Hyalella azteca and Chironomus dilutus. Sediment concentrations of DDT, DDD, and DDE were below levels expected to cause toxicity, and there was no observed toxicity in laboratory tests. Additionally, there were no statistically significant differences in richness, richness of Ephemeroptera, Plecoptera, and Trichoptera (EPT) species, total EPT abundance, percent EPT, or percent dominant taxa between the reference site and the downstream sites. There was an observed decrease in abundance of macroinvertebrate taxa at all downstream sites and a shift in macroinvertebrate structure when comparing the reference with most impaired sites. Although the sites downstream of the Superfund site remain different than the upstream control, there are improvements in species composition and abundance. However, more research is needed to evaluate the potential effects on ecosystem function.