Micro-scale toxicity tests

Because of the pressing contemporary need to assess an ever-growing number of chemicals and complex environmental samples, the development and use of small-scale toxicity tests (also called micro-scale toxicity tests or microbiotests ) have increased because of their attractive features. Simply defined as a test involving the exposure of a unicellular or small multicellular organism to a liquid or solid sample in order to measure a specific effect , small-scale tests are generally simple to execute and characterized by traits which can include small sample volume requirements, rapid turnaround time to results, enhanced sample throughput and hence cost-effectiveness (Blaise et al., 1998a). 

In undertaking our search of the literature linked to bioanalytical assessment of solid waste leachates (Tab. 2), we circumscribed it to small-scale toxicity testing performed on leachates. Furthermore, we did not exclude marine bioassays, but we exclusively selected literature references involving test battery approaches (TBAs) on solid wastes (or their elutriates). As defined previously in the first chapter of this book, a TBA represents a study conducted with two or more tests representing at least two biotic levels. As also pointed out in Section 2 of this chapter, TBAs are suitable to assess hazard at different levels so as not to underestimate ecotoxicity. Nevertheless, we have not excluded from this review publications describing other types of bioassays (e.g., terrestrial bioassays, sub-cellular bioassays or those carried out with recombinant DNA (micro)organisms and biosensors), when those were part of the TBA. 

Bermingham, N., Costan, G., Blaise, C. and Patenaude, L. (1996) Use of micro-scale aquatic toxicity tests in ecolabelling guidelines for general purpose cleaners, in M. Richardson (ed.), Environmental Xenobiotics, Taylor Francis Books Ltd, London, England, pp. 195-212. 

Requiring low-sample volume micro-scale tests for its cost-effective application, the PEEP index has thus far employed bioassays with bacteria, algae and microinvertebrates. While well-standardized toxicity tests using freshwater fish existed at the time of the PEEP s conception in the early 1990 s (e.g., the Environment Canada fingerling rainbow trout 96-h lethality test to assess industrial wastewaters), they were excluded because of their large sample volume needs (e.g., close to 400 L of effluent sample required to undertake a multiple dilution 96-h LC50 bioassay in the case of the trout test). In addition to effluent sample volume, the cost of carrying out salmonid fish acute lethality bioassays for the 50 priority industrial effluents identified under SLAP I (the first 1988-93 Saint-Lawrence River Action Plan) was prohibitive. 

The first study was designed to assess the suitability of various microscale bioassays and recommend an appropriate testing strategy for sediment toxicity assessment (Cote et al., 1998a,b). The recommended test batteries included seven micro-scale laboratory assays conducted on bacteria (Vibrio fischeri), cnidarians (Hydra attenuata), micro-crustaceans (Thamnocephalus platyurus), and benthic macroinvertebrates (Hyalella azteca and Chironomus riparius), and involved two phases of exposure (pore water and whole sediment). A total of 16 stations were included in the toxicity assessment scheme. 

The RDE detoxification concept was validated for both environmental and therapeutic applications. While the environmental detoxification is a relatively known topic that has been tested at a micro-pilot scale, the therapeutic applications are more novel. The wide range of pollutants/toxics investigated contain very different types of molecules, so the potential for applying this innovative technology is high. 

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