Aquatic modeling

For an aquatic model of chemical fate and transport, the input loadings associated with both point and nonpoint sources must be considered. Point loads from industrial or municipal discharges can show significant daily, weekly, or seasonal fluctuations. Nonpoint loads determined either from data or nonpoint loading models are so highly variable that significant errors are likely. In all these cases, errors in input to a model (in conjunction with output errors, discussed below) must be considered in order to provide a valid assessment of model capabilities through the validation process. 

Regnell, O. 1990. Conversion and partitioning of radio-labelled mercury chloride in aquatic model systems. Canad. Jour. Fish. Aquat. Sci. 47 548.553. 

Isensee, A.R. and G.E. Jones. 1975. Distribution of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in aquatic model ecosystem. Environ. Sci. Technol. 9 668-672. 

Ohkawa, H., R. Kikuchi, and J.S. Miyamoto. 1980. Bioaccumulation and biodegradation of the (S)-acid isomer of fenvalerate (Sumicidin ) in an aquatic model ecosystem. Jour. Pestic. Sci. 5 11-22. 

Isensee, A.R., G.E. Jones, J.A. McCann, and F.G. Pitcher. 1979. Toxicity and fate of nine toxaphene fractions in an aquatic model ecosystem. Jour. Agric. Food Chem. 27 1041-1046. 

The methodology for conducting aquatic model ecosystem studies was well established by the late 1990s. However, the use of the data in risk assessments raised a number of uncertainties regarding their interpretation and implementation [32]. Four of the uncertainties that were identified were the extent to which aquatic model ecosystem data generated in one location could be applied to another situation, the potential influence of mixtures of chemicals or stressors, whether the timing (season) of application would influence the outcome of the study, and whether differences in ecosystem properties (e.g., trophic status) might influence the results. 

Figure 3. Aquatic model ecosystem. Aquarium (90 X 35 X 45 cm) divided by a glass barrier with holes. Components 50 L of Freemans standard reference water and 7 kg Katano sandy loam soil.

Table IV. Bioaccumulation of DDT and its metabolites in aquatic model ecosystem...

Figure 4. Concentration of 14C and fenitrothion in water of aquatic model ecosystem (a) fenitrothion added once to the model ecosystem (b) fenitrothion added to the model ecosystem 2 more times at 7th and 14th day.

Table V. Distribution of C, fenitrothion and its degradation products in individual components of aquatic model ecosystem Water and soil.

Table VIII. Bioaccumulation ratio of total C and fenitrothion in aquatic model ecosystem.

A Terrestrial-Aquatic Model Ecosystem for Evaluating the Environmental Fate of Drugs and Related Residues in Animal Excreta... 

When farm animals are treated with drugs both as a prophylactic or curative measure, majority of the drug or drug related residues are eliminated in the excreta. Poultry as well as farm animal excreta is allowed to compost into manure and the manure is used on the farm land. The objective of the present study was to design a terrestrial-aquatic model ecosystem for evaluating the environmental fate of drugs and related residues in the animal excreta used as manure. 

The modified terrestrial-aquatic model ecosystem described here has been found to be a useful tool in studying the environmental fate of drugs and related residues present in animal excreta used as manure. The operation of the ecosystem is relatively simple and yet it allows one to study the complex metabolic transformations of a drug or related residues in its various components. Especially interesting is the study of the degradation of a compound in the soil in the presence of microorganisms found in the animal excreta. This information is important since it eventually determines whether a compound and/ or its metabolites will bioaccumulate in the various elements of the environment. 

The primary purpose of this project was to demonstrate that aquatic model ecosystems could be further scaled up in size to provide greater amounts of the components (biomass, soil and water) to satisfactorily study metabolism kinetics. We used trifluralin, a dinitroaniline herbicide, since its metabolic pathways are well known and the metabolites were readily available. 

Only one other study has been conducted to evaluate the fate of trifluralin in an aquatic model ecosystem (10). In their system, trifluralin persisted much longer in water than in our study (probably due to less photodegradation through the use of artificial light). As a result, they reported much higher concentrations of trifluralin in snails and fish than we found, but no residues in daphinds. They also reported the presence of Compound 7 plus several other known and unknown metabolites. 

Yockim RS, Isensee Ar, Jones GE. 1978. Distribution and toxicity of TCDD and 2,4,5,-T in an aquatic model ecosystem. Chemosphere 3 215-220. 

Surface water biodegradation t,/2 < 20 d in water and sediment with flooded soils and terrestrial-aquatic model ecosystems (Muir 1991). 

Isensee, A.R. (1976) Variability of aquatic model ecosystem-derived data. Inst. J. Environ. Studies 10, 35. 

Yockim, R.S., Isensee, A.R., Walker, E.A. (1980) Behavior of trifluralin in aquatic model ecosystems. Bull. Environ. Contamin. Toxicol. 24, 134-141. 

The time schedule of aquatic model ecosystem experiments and the size of the system itself favor population growth of small organisms with short generation times... 

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