Terrestrial-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. 

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

Sanborn JR, Metcalf RL, Bruce WN, et al. 1976. The fate of chlordane and toxaphene in a terrestrial-aquatic model ecosystem. Environ Entomology 5 533- 538. 

Application of radiolabeled mirex to plants grown in a terrestrial/aquatic laboratory model ecosystem indicated that when the plant leaves were eaten by caterpillars, the aquatic system became contaminated. Mirex was detected in all segments of two aquatic food chains (alga > snail and plankton > daphnia > mosquito > fish) within 33 days. Undegraded mirex contributed to over 98.6, 99.4, 99.6, and 97.9% of the radiolabel in fish, snails, mosquitoes, and algae, respectively. No metabolites of mirex were found in any of the organisms (Francis and Metcalf 1984 Metcalf et al. 1973). 

Francis BM, Metcalf RL. 1984. Evaluation of mirex, photomirex and chlordecone in the terrestrial aquatic laboratory model ecosystem. Environ Health Perspect 54 341-346. 

Figure 2. Schematic of the modified model ecosystem detailing a complete terrestrial/aquatic environment for the study of drug biodegradability and ecological...

An ecosystem can be thought of as a representative segment or model of the environment in which one is interested. Three such model ecosystems will be discussed (Figures 1 and 2). A terrestrial model, a model pond, and a model ecosystem, which combines the first two models, are described in terms of equilibrium schemes and compartmental parameters. The selection of a particular model will depend on the questions asked regarding the chemical. For example, if one is interested in the partitioning behavior of a soil-applied pesticide the terrestrial model would be employed. The model pond would be selected for aquatic partitioning questions and the model ecosystem would be employed if overall environmental distribution is considered. 

Figure 3. General model of bio geo chemical cycles in the Earth s ecosystems. The left part is bio geochemical cycling in terrestrial ecosystems, the right part is aquatic ecosystems and the central part is connected with the atmosphere. The fine solid lines show the biogeochemical food webs (the Latin numbers I-XXI) and directed and reverse relationships between these...

Calculation Methods for Critical Loads of Heavy Metals The selection of a computation method or model is the third step in the flowchart for calculating critical loads of heavy metals (Figure 4). There are different models that can be used to calculate critical loads for terrestrial and aquatic ecosystems, based on receptor properties and on certain critical limits. Relevant aspects in relation to the selection of a calculation method are... 

De Vries, W., Schutze, G., Romkens, P., Hettelingh, J-P., et al. (2002). Guidance for the Calculation of Critical Loads for Lead and Cadmium in Terrestrial and Aquatic Ecosystems. Preliminary Modelling and Mapping of Critical Loads for Cadmium and Lead in Europe. RIVM. Report 259101011/2002, pp. 17-35. 

Virtanen, M., Hattula, M.L., Arstila, A.U. (1979) Behavior and fate of 4-chloro-2-methylphenoxyacetic acid (MCPA) and 2,6-dichloro-o-cresol as studied in an aquatic-terrestrial model ecosystem. Chemosphere 8, 431. 

Semifield tests, sensu stricto, are experimental ecosystems that run under fieldlike outdoor conditions. Aquatic micro- and mesocosms have been widely used in assessing effects of substances under semilield conditions (Stephenson et al. 1986 Arnold et al. 1991 Hill et al. 1994 van den Brink et al. 1996 Kennedy et al. 1999 van den Brink and Ter Braak 1999 Culp et al. 2000a, 2000b Sibley et al. 2001a, 2001b, and many others). Also, terrestrial model ecosystems (TMEs) have been developed that are, in contrast to the use of field plots, separated from their source site and run under laboratory conditions (Knacker et al. 2004). Because experience is limited, they will be considered here only marginally. 

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