We published an article (Elston et al. 2005) in Volume 24 of the Journal of Shellfish Research demonstrating substantial contamination of St. Louis Bay, Mississippi with dioxins and heavy metals, including chromium, nickel and arsenic that occurred in close proximity to a large titanium dioxide plant that has operated near the Bay since the early 1980s. We conducted an exhaustive evaluation of potential sources of contamination and concluded that the plant was the most likely source of contaminants. We were aided in this analysis by a variety of data including a preplant baseline study (Lytle & Lytle 1982) and a study of dioxin contamination in oysters harvested from Southern Mississippi conducted in 1997 (Fiedler et al. 1997). In this addendum we publish new information that further implicates the plant as the source of dioxin contamination, corrects minor underestimates from our original report in some of the WHO-TEQ (World Health Organization Toxic Equivalencies) for dioxins in St. Louis Bay and Mississippi Sound shellfish and also corrects the estimated magnitude of increase of dioxins in Southern Mississippi since 1997. These corrections do not change the conclusions of our original study. In fact, the increases in WHO-TEQs for shellfish and the new data obtained since publication of that article provide additional and substantial support for our conclusion that the plant is the primary source of dioxin contamination. In addition, these new data call into question the reliability and utility of data reported by the plant to the United States Environmental Protection Agency Toxic Release Inventory for use in assessing the public health risk of releases from the plant. This new information demonstrates 2,3,7,8 TCDD, the most toxic dioxin congener and one recognized as a carcinogen by the International Agency for Research on Cancer, is in fact present on the plant site, a fact previously unknown and unreported, although we reported this congener in the two sediment samples adjacent to the plant outfall in our original report.