Volatile toxicants, continuous flow toxicity

Microcosms are laboratory systems generally consisting of tanks such as fish aquaria containing natural sediment and water, or soil. In those which have been most extensively evaluated for aquatic systems, continuous-flow systems are used. In all of them, continuous measurement of 14C02 evolved from 14C-labeled substrates may be incorporated, and recovery of both volatile and nonvolatile metabolites is possible so that a material balance may be constructed (Huckins et al. 1984). It should be pointed out that the term microcosm has also been used to cover much smaller scale experiments that have been carried out in flasks under anaerobic conditions (Edwards et al. 1992), and to systems for evaluating the effect of toxicants on biota (Section 7.4.2). Some examples are given to illustrate different facets of the application of microcosms to study various aspects of biodegradation. 

The environmentally acceptable nature of supercritical carbon dioxide has already been discussed in this chapter, but another type of solvent which is generating great interest as a possible replacement for volatile organic compoimds is ionic hquids. A detailed account of ionic liquids and their application for catalyst immobilization is the subject of Chapter 5, edited by H. Olivier, in this handbook. In essence, ionic Hquids are involatile, of low toxicity, and very stable, and are therefore seen as having a low environmental impact. The very different properties of supercritical carbon dioxide and ionic liquids makes them ideally suited for use in combination to provide an environmentally acceptable form of two-phase catalysis, which might be carried out as a continuous-flow process. 

Fig. 1, Continuous-flow embryo-larval test system. Dilution water and toxicant were supplied to the mixing chamber using peristaltic and syringe pumps. Insoluble toxicants were suspended in test water by mechanical homogenization, and a magnetic stirrer was used to provide additional agitation in the stirring compartment of the test chamber. To minimize loss of volatile toxicants, the test chamber was designed to preclude an air-water interface. (Copyright ASTM, 1916 Race Street, Philadelphia, PA 19103. Reprinted with permission.)...

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