Current extent

The goal of this paper Is to present the current status of model validation and field testing of chemical fate and transport models other papers in this symposium discuss the state-of-the-art of modeling specific processes, environments, and multimedia problems. The process of model validation, and its various components, is described considerations in field testing, where model results are compared to field observations, are discussedp an assessment of the current extent of field testing for various processes and media is presented and future field testing and data needs are enumerated. 

Working groups were organized with specific responsibility to assess the utility and limits of four different methods (or tools) currently used by EPA and industry for evaluating hazards posed by toxic chemicals (1) laboratory toxicity data, (2) microcosm test data, (3) site-specific data, and (4) chemical fate and exposure model results. The Exposure Modeling Committee (3.) report presented an assessment of the current extent of field model testing and recommendations for future testing efforts. 

Table I. CURRENT EXTENT OF FIELD TESTING FOR SCREENING LEVEL MODELS (3) 100 = Model thoroughly field tested 0 = Model not tested...

Schade, G., Heinzow, B., 1998. Organochlorine pesticides and polychlorinated biphenyls in human milk of mothers living in northern Germany Current extent of contamination, time trend from 1986 to 1997 and factors that influence the levels of contamination. Sci. Total Environ. 215, 31-39. 

Researchers have mixed responses on the current extent of the air pollution problem in relation to its impact on vegetation. We know that injury occurs in many sensitive native and domestic plant species throughout the country. We do not know how severe the long term pollution effects will be on domestic species, on the frequency or distribution of native species, or on the complex interactions between native species and the effects of these interactions on plant communities. Much research is needed in this area before we can adequately speculate on the future of agricultural production. 

Fig. 1 A diorama of a Phaeocystis ecosystem, in which physical, chemical, geological, and biological components interact to varying degrees to influence food web structure, biogeochemical flows, and ecosystem function. For simplicity, only well-documented components are illustrated. Current extent of our knowledge base is qualitatively related to font size. Arrow magnitude and direction indicate major known flows increasingly smaller and more numerous arrows imply unknown connections, the importance of indirect flows among ecosystem compartments, and overall system complexity...

During the approval of new active substances, usage data may provide a clear indication of the likely uptake of a new pesticide, knowing what pesticide(s) it is likely to replace and the current extent of its use. 

Until the early 1980s, only a few countries were known to be affected by iodine deficiency, but over the last two decades, knowledge of the global magnitude of iodine deficiency has improved considerably. The surveillance of iodine deficiency worldwide and the current extent of the problem is the focus of this chapter. 

Why should systematists as a group be self-conscious, apologetic, or defensive Notwithstanding the current extent of antagonism toward systematics, the fact remains that such antagonisms, when expressed, are more a measure of a man s breadth as a biologist than an indictment of systematics. Whatever traumata any one of us individually may have experienced, our prestige and stature will be the... 

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