Robert V. Thomann

Model of PCB in the Lake Michigan lake trout food chain.

An age-dependent food chain model that considers species bioenergetics and toxicant exposure through water and food is developed. The model is successfully calibrated to 1971 PCB concentrations of Lake Michigan alewife and lake trout by using a dissolved PCB concentration in the water of 5-10 ng/L. The model indicates that for the top predator lake trout, PCB exposure through the food chain can account for greater than 99% of the observed concentration. An octanol-water partitioning calculation using a coefficient of 10/sup 6.72/ and lake trout lipid concentrations failed to reproduce the observed data by a factor of about 4. It is estimated that a criterion specifying that PCB concentrations of all ages of lake trout be at or below 5 ..mu..g/g (wet weight) in the edible portion would require that dissolved PCB concentrations be reduced to somewhere between 0.5 and 2.5 ng/L.

Physico-Chemical Model of Toxic Substances in the Great Lakes

A physico-chemical model of the fate of toxic substances in the Great Lakes is constructed from mass balance principles, incorporating principal mechanisms of paniculate sorption-desorption, sediment-water and atmosphere-water interactions, and chemical and biochemical decay. The steady state mass balance model of the suspended solids in the open lake water yields net solids loss rates from 0.02 mjdfor Saginaw Bay to 1.22 m/dfor Lake Ontario. Calibration of the toxic model is through comparison to plutonium-239 data collected in the 1970s using a 23-year time variable calculation. The results indicate that, in general, the sediments are interactive with the water column in the Great Lakes through resuspension and horizontal transport. Fifty percent response times of 239Pu following a cessation of load extend beyond 10 years with sediment resuspension. The calibrated model was also applied to polychlorinated biphenyl (PCB) using a high and low estimate of contemporary external load and with and without volatilization. The lower load level (lake range 640 to 1,390 kg/yr) with volatilization (at an exchange rate of 0.1 m/d) appears to be more representative of observed surface sediment data for the open lake waters. Calculated water column concentrations for the lower load level with and without volatilization ranged from 0.25 to 0.90 ng/Lfor open lake waters. Fifty percent response times for PCB following cessation of load varied from less than 5 years when volatilization was included to 10 to 20 years without volatilization. Comparison of these response times to decline of concentrations of PCB in Lake Michigan bloaters indicates that, at least for that lake, volatilization is occurring at an exchange rate of about 0.1 m/d.

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.

Physio-chemical and ecological modeling the fate of toxic substances in natural water systems

ABSTRACT Thomann, R.V., 1984. Physio-chemical and ecological modeling the fate of toxic substances in natural water systems. Ecol. Modelling, 22: 145–170. A basic framework for the modeling of the fate of chemicals in natural water systems is presented. Both the physical/chemical and ecological fate of the substance are considered. The fully time variable equations do not present any significant insight into the general behavior of chemical fate. However, under a steady state assumption and including bottom sediment interactions, relatively simple formulations result that permit rapid calculation of the maximum concentrations that might be expected. It is shown that for a completely mixed lake the ratio of the areal loading rate of the toxicant to the water column concentration is determined by the hydraulic overflow rate and the net loss rate of the toxicant from the water column. Thus, c T = W Ta /q + w T for c T as the total toxicant concentration, W Ta as the areal loading rate of the chemical, q as the hydraulic overflow rate, and w T the net loss of the chemical. The net loss rate w T is a function of all water column and sediment decay rates and interactions. The steady state food chain model of the accumulation of a toxic chemical from both water and food sources is shown to be a means for estimating the parameters of loss and sediment interaction for a lake. The steady state case of the discharge of a chemical into a stream provides a simple means for estimating net loss rates under some reasonable assumptions. Also coupling the food chain model to the physio-chemical model permits the use of chemical concentrations in the fish to estimate the net loss of toxicant in a stream. Application is made to metals concentrations in Lakes Ontario and Michigan and to 1,4 dichlorobenzene in Lake Zurich. The theory indicates that under zero decay of the chemical in the sediment and equal partition coefficients in the sediment and the water column that the chemical in particulate form in the sediment should equal that in the water column. Metals data for Lake Ontario appears to confirm this result at least to order of magnitude. For streams, application is made to a) cadmium in the Sajo River in Hungary where a net loss rate of about 0.12 m/d is estimated, and b) PCBs in the fish and sediment of the South Branch of the Shiawassee River in Michigan where net loss rates of about 3/day are estimated.

Estimated Responses of Lake Ontario Phytoplankton Biomass to Varying Nutrient Levels

Abstract A series of simulations of the response of the open lake region of Lake Ontario to various levels of nutrient input is described using a simplified dynamic model of phytoplankton-nutrient interactions in a vertically segmented lake. The analysis of the simulations indicates the importance of the overall loss rates of nutrient. Under an hypothesized, but reasonable, set of model parameters, the simulations indicate that the present observed open lake phytoplankton biomass of Lake Ontario does not appear to be in equilibrium with the present input nutrient load. For an assumed equilibrium condition, the simulations indicate that reductions in phosphorus load will be accompanied by reductions in biomass. A “pastoral” simulation using load estimates consistent with the conditions prior to mans intensive activity indicates that spring phytoplankton levels were 30%-70% of present levels depending upon the kinetic assumptions. Analysis of lake response to the U.S.-Canada Water Quality Agreement loads using three kinetic assumptions (optimistic, reasonable, pessimistic) indicates a range from 25% decrease to 80% increase in peak phytoplankton over present levels. For an implementation period of 10 years, a load reduction rate of about 1-1.5 metric tons phosphorus/day per year appears to be a sound objective to maintain or reduce present phytoplankton levels.

Deterministic and Statistical Models of Chemical Fate in Aquatic Systems

This paper has several purposes: (a) to summarize the basic models of the steady state transport and fate of chemicals in aquatic systems including uptake and distribution in the aquatic food chain, (b) to illustrate the deterministic time variable behavior of chemical fate models with several applications to the Great Lakes and (c) to develop some statistical models of chemical variability in aquatic organisms, specifically, the fish.

THE FATE OF PCBs IN THE HUDSON RIVER ECOSYSTEM

The focus of this paper is the description of the distribution and fate of polychlorinated biphenyls (PCBs) in the Hudson River with particular emphasis on the aquatic ecosystem. A settlement between the New York State Department of Environmental Conservation (NYSDEC) and the General Electric Company (GE) concerning the contamination of the Hudson River by PCBs discharged from GE’s facilities at Fort Edward, New York, called for an overall study of the Hudson. The direction of the work reported on herein is to provide input into the decision making process of estimating the effects of remedial actions on PCB levels in the general biota and the larger migratory fish. This paper considers only briefly the transport of PCBs in the abiotic sector (e.g., bottom sediment, suspended particulate matter and water column); a more complete treatment is given in reference I . FIGURE I is a schematic of the Hudson River that indicates the mile points (MP) of key locations and also shows the divisions of the Hudson into reaches for the physical transport analysis and reaches for the biologic analysis. From the Federal Dam at Troy to the Ocean, the Lower Hudson is tidal and depending on the average freshwater flow, the end of the salt water intrusion oscillates approximately between the Tnppan Zee Bridge ( M P 25) and Poughkeepsie ( M P 75) and under severe drought conditions, it may reach as far north as MP 80. The long term monthly average discharge and the 1976 monthly average discharge from the Upper Hudson to the Lower Hudson are 13,270 cfs and 22,100 cfs respectively. The major interactions that lead to the PCB distribution i n the biotic and abiotic sectors of a given aquatic environment are shown in FIGURE 2. Although the detailed dynamics of these interactions are not known at the present time, a qualitative overview is possible. PCBs exist i n a body of water in two main components, the dissolved and the particulate phases. The dissolved component includes PCBs that exist in solution and the particulate component includes PCBs that are adsorbed on various forms of particulate (suspended) matter. The formation of these two components results from the characteristic low solubility and high adsorption of the PCBs. The particulate component may settle and contaminate the bottom sediment. On the other hand, the bottom sediment can be resuspended through the shearing action of the overlying water and through the actions of organisms that inhabit the upper layers of the bottom sediment. The existence of contaminated bottom sediment gives rise to dissolved PCBs in the interstitial water, which diffuses dispersively into the overlying water. At the air-water interface. there are evaporative PCB losses from

Calculated Contribution of Surface Microlayer PCB to Contamination of Lake Michigan Lake Trout

The possible significance of PCB concentration in the surface microlayer of Lake Michigan to contamination of lake trout was examined using a modification of a previously developed food chain model. Vertically migrating zooplankton were assumed to spend a fraction of each day exposed to a surface microlayer with dissolved and phytoplankton PCB concentrations at values that resulted in an average exposure concentration 2.1 times greater than subsurface levels. Considering a worst case scenario, the model indicated that approximately 12% (3 μg/g) of the PCB concentration in adult lake trout could be contributed from the microlayer.