Dominic M. DiToro

Application of the biotic ligand model to predicting zinc toxicity to rainbow trout, fathead minnow, and Daphnia magna

The Biotic Ligand Model has been previously developed to explain and predict the effects of water chemistry on the toxicity of copper, silver, and cadmium. In this paper, we describe the development and application of a biotic ligand model for zinc (Zn BLM). The data used in the development of the Zn BLM includes acute zinc LC50 data for several aquatic organisms including rainbow trout, fathead minnow, and Daphnia magna. Important chemical effects were observed that influenced the measured zinc toxicity for these organisms including the effects of hardness and pH. A significant amount of the historical toxicity data for zinc includes concentrations that exceeded zinc solubility. These data exhibited very different responses to chemical adjustment than data that were within solubility limits. Toxicity data that were within solubility limits showed evidence of both zinc complexation, and zinc-proton competition and could be well described by a chemical equilibrium approach such as that used by the Zn BLM.

The Challenges of Hazard Identification and Classification of Insoluble Metals and Metal Substances for the Aquatic Environment

The OECD is currently harmonizing procedures for aquatic hazard identification of substances. Such a system already exists in Europe where it is recognized that special consideration must be given to sparingly soluble metals and metal compounds (SSMMCs) because standard hazard testing procedures designed for organic chemicals do not accommodate the characteristics of SSMMCs. Current aquatic hazard identification procedures are based on persistence, bioaccumulation, and toxicity (PBT) measurements. Persistence measurements typically used for organic substances (biodegradation) do not apply to metals. Alternative measurements such as complexation and precipitation are more appropriate. Metal bioaccumulation is important in terms of nutritional sufficiency and potential food chain transfer and toxicity. Unlike organic substances, metal bioaccumulation potential cannot be estimated using log octanol-water partition coefficients. Further, bioaccumulation and bioconcentration factors are often inversely related to exposure concentration for most metals and organisms, and hence are not reliable predictors of chronic toxicity or food chain accumulation. Metal toxicity is due predominately to the free metal ion in solution. In order to assess the toxicity of SSMMCs, the rate and extent of transformation to a soluble form must be measured.

A food chain model of cadmium in western lake Erie

Abstract The simple food chain model illustrated here could prove useful in large scale planning applications provided additional data are collected on the various trophic levels. The model demonstrates the increase in concentration of potentially toxic substances, such as cadmium, as one proceeds up the food chain. The food chain model also illustrates how interactive modeling between complex non-linear and linear compartment model can be accomplished. The problem of verification and data availability are highlighted by the model: estimates of transfer rates and biomass of different trophic levels must be on hand. This model therefore is an example of a modeling structure that is still in an early stage of development; hence the reliance on linear kinetics rather than possibly more realistic non-linear mechanisms. Nevertheless, the spatial-trophic level structure of the model indicates the general behavior of a toxicant such as cadmium when released into the water environment.

Anomalous binding of organic contaminants may be artifactual due to radiochemical impurities

Abstract A potential artifact is described that could lead to erroneous estimates of the partition coefficients for binding of contaminants to sorbents such as soil, sediment, or dissolved humic material. The artifact can arise if sorbants are radiolabeled but contain even relatively small amounts of radiolabeled impurities. The following types of errors could result from data affected by this artifact: partition coefficients for sorption could be underestimated; systems in which binding was fully reversible could appear to be at least partially nonreversible and partition coefficients could appear to decrease as the sorbent concentration increased. Several criteria are suggested to assure that experimental results are not affected by this artifact.

A Three-Dimensional Model for Cohesive Sediment Dynamics in Shallow Bays

The fate and transport of pollutants in aquatic systems is strongly influenced by cohesive sediment dynamics. This paper describes the development and validation of a high-resolution, three-dimensional, time-variable, cohesive sediment transport model of Green Bay. The model incorporates state-of-the-art cohesive sediment resuspension and deposition methodology, including bed armoring and flocculation. Resuspension and deposition are functions of bed shear stress due to wave-current interaction. To compute shear stresses and water column transport, hydrodynamic and wind-wave models of the bay were integrated with the sediment transport model. Boundary conditions at the Green Bay-Lake Michigan interface were derived from a coarser resolution hydrodynamic model of Lake Michigan. The model accounts for all significant sources of solids into the system including major tributaries, direct runoff, shoreline erosion and internal solids (i.e., algae) production. The model was simulated for a period of 516 days. Results indicated that the model was capable of reproducing the temporal variation of observed inorganic suspended sediment concentrations at 25 locations and annual sedimentation rates at 49 other locations.

Sediment Toxicity and Equilibrium Partitioning Development of Sediment Quality Criteria for Toxic Substances

The toxicity of chemicals in sediments is strongly influenced by the extent to which the chemicals bind to the sediment. This modifies the chemical potential to which the organisms are subjected. As a consequence, different sediments will exhibit different degrees of toxicity for the same total quantity of chemical. These differences have been reconciled by relating organism response to the chemical concentration in the interstitial water of the sediments (Adams et al., 1985; Swartz, et al., 1985; Muir et al., 1985; Adams, 1987; Kemp and Swartz, 1988; Nebeker and Schuytema, 1988). The relevant sediment properties, therefore, are those which influence the distribution of chemical between the solid and aqueous phases.