Fate model aquatic systems

Fate of Chemicals in Aquatic Systems Process Models and Computer Codes... 

From these data, aquatic fate models construct outputs delineating exposure, fate, and persistence of the compound. In general, exposure can be determined as a time-course of chemical concentrations, as ultimate (steady-state) concentration distributions, or as statistical summaries of computed time-series. Fate of chemicals may mean either the distribution of the chemical among subsystems (e.g., fraction captured by benthic sediments), or a fractionation among transformation processes. The latter data can be used in sensitivity analyses to determine relative needs for accuracy and precision in chemical measurements. Persistence of the compound can be estimated from the time constants of the response of the system to chemical loadings. 

The characteristics of the applied models have been described in detail in the chapters Environmental Fate Models [50] and A Revision of Current Models for Environmental and Human Health Impact and Risk Assessment for Application to Emerging Chemicals [49] and only a brief overview is given here. Since each model has its own approach (i.e., QWASI is focused on the aquatic system), the combined results are expected to give a wider view with in-depth analyses for different aspects compared to just one model with its special characteristics. 

QWASI, the Quantitative Water, Air Sediment Interaction model by Mackay et al. [14] is a fugacity III model (Version 3.10, 2007) and it describes the fate of chemicals in aquatic systems, depending on direct discharge, inflow in rivers, and atmospheric deposition. Hence, this model addresses the local scale, as does the 2-FUN Tool. 

Hudson, R. J. M. (1998). Modeling the fate of metals in aquatic systems the mechanistic basis of particle-water partitioning models, Crit. Rev. Anal. Chem., 28, 19-26. 

In this paper, the volatilization of five organophosphorus pesticides from model soil pits and evaporation ponds is measured and predicted. A simple environmental chamber is used to obtain volatilization measurements. The use of the two-film model for predicting volatilization rates of organics from water is illustrated, and agreement between experimental and predicted rate constants is evaluated. Comparative volatilization studies are described using model water, soil-water, and soil disposal systems, and the results are compared to predictions of EXAMS, a popular computer code for predicting the fate of organics in aquatic systems. Finally, the experimental effect of Triton X-100, an emulsifier, on pesticide volatilization from water is presented. 

EXAMS (Exposure alysis Modeling stem) is an elaborate computer program that predicts the fate of organic chemicals in aquatic systems (24). Most input data can be easily measured, calculated, or obtained from literature sources. For this reason, the program is readily accessible to chemists for use as a predictive tool. 

Bartell SM, Gardner RM, O Neill RV. 1988. An integrated fates and effects model for estimation of risks in aquatic systems. In Adams WJ, Chapman GA, Landis WG, editors. Aquatic toxicology and hazard assessment. Volume ASTM STP 971. Philadelphia (PA) American Society for Testing and Materials, p 261-274. 

De Vries DJ. IMPAQT, a physico-chemical model for simulation of the fate and distribution of micro pollutants in aquatic systems.The Netherlands and TOW-IW T250, Delft Hydraulics, 1987. 

Lake, J.L., Rubinstein, N. Pavignano, S. (1987) Predicting bioaccumu-lation Development of a simple partitioning model for use as a screening tool for regulating ocean disposal of wastes. Fate and Effects of Sediment-Bound Chemicals in Aquatic Systems, eds. K.L. Dickson, A.W. Maki W.A. Brungs, pp. 151-166. New York Pergamon Press. 

SCHEME 4 The two-compartment system of the aquatic fate model EXWAT. 

The models described in Section 10.3 are whole system models that include all processes involved in the transport and fate of contaminants in aquatic systems. Application of these models therefore demonstrates how particle deposition and resuspension affect the transport and fate of contaminants associated with those particles. The case study presented in Section 10.4 for the Lower Fox River is an example of how research knowledge and appropriate field data collection on sediment deposition and resuspension processes (reviewed in Section 10.2) have been incorporated into conceptual and numeric models (reviewed in Section 10.3) that support assessment and remediation of contaminated sediment sites. 

In a continuous model river test system it can be shown that after passage through a sewage treatment plant ester sulfonates have no significant influence on the qualitative and quantitative composition of the biocenosis of a receiving water [113]. All the investigations into the environmental fate of a-sulfo fatty acid esters demonstrate that aquatic toxicity is alleviated by their fast ultimate biodegradability, which allows them to be classified as environmentally compatible. 

Data Structures. Inspection of the unit simulation equation (Equation 7) indicates the kinds of input data required by aquatic fate codes. These data can be classified as chemical, environmental, and loading data sets. The chemical data set , which are composed of the chemical reactivity and speciation data, can be developed from laboratory investigations. The environmental data, representing the driving forces that constrain the expression of chemical properties in real systems, can be obtained from site-specific limnological field investigations or as summary data sets developed from literature surveys. Allochthonous chemical loadings can be developed as worst-case estimates, via the outputs of terrestrial models, or, when appropriate, via direct field measurement. 

Crockett, A.B. Hern, S.C. Kinney, W.L. Flatman, G.T. "Guidelines for Field Testing Aquatic Fate and Transport Models Interim Report" U.S. Environ. Prot. Agency, Environ. Monitoring Systems Lab. Las Vegas, Nevada, 1982 p. 174 + Appendices. 

Model ecosystems have been used for about 8 years to measure the distribution and fate of pesticides in the aquatic environment. Over that period of time numerous design changes have evolved that have increased the versatility of the ecosystem and improved simulation of environmental conditions. In our laboratory, we have used the static model ecosystem primarily to model the pond or small lake environment, and to simulate the likely rates and modes of pesticide entry (1). More recently, we have developed larger systems capable of providing sufficient biomass for accumulation and dissipation rate determinations (2) and for metabolic studies (3). 

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. 

Kwint RLJ, Kramer KJM (1996) The annual cycle of the production and fate of DMS and DMSP in a marine coastal system. Mar Ecol Prog Ser 134 217-224 Laroche D, Vezina AF, Levasseur M, Gosselin M, Stefels J, Keller MD, Matrai PA, Kwint RLJ (1999) DMSP synthesis and exudation in phytoplankton a modeling approach. Mar Ecol Prog Ser 180 37 19 Lee PA, de Mora SJ (1999a) A review of dimethylsulfoxide in aquatic environments. Atmosphere-Ocean 37 439-456... 

An available aquatic fate computer model, EXAMS (Exposure Assessment Modelling System, 19), provided predictions for comparison with the field-measured volatilization flux. EXAMS inputs include ... 

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