Toxicity identification evaluation of metal-contaminated sediments using an artificial pore water containing dissolved organic carbons

Recent investigations of sediment-associated pollutants in Lake Champlain i ndicated significant contamination with As, Mn, and Ni in Outer Malletts Ba y, Vermont, USA. Ceriodaphnia dubia exposed to sediment pore water from sev eral sites in Outer Malletts Bay showed repeatable, acute mortality at only one site. A toxicity identification evaluation (TIE) was conducted on pore water to determine the contaminants causing mortality at this site. Unlike most TIE applications, the dilution water used in these tests was formulat ed to match the hardness, alkalinity, pH, conductivity, and dissolved organ ic carbon content of the pore water. Results from phase I of the TIE indica ted that divalent metals may be responsible for toxicity. Phase II results revealed levels of Mn above LC50 values. Spiking experiments employed in ph ase III confirmed Mn as the principal toxicant in sediment pore water. The formulated pore water worked well and helped ensure that toxicant behavior was influenced primarily by each TIE manipulation and not by physical and c hemical differences between the dilution and site water. Although the Mn to xicity at this site may be the result of its unique geomorphology, this sit uation underscores the need to look broadly for potential toxicants when ev aluating contaminated sites.