Linear relationships of the median lethal concentrations of several hundreds of chemicals for a variety of organisms with Vibrio fischeri median effective concentrations are investigated. Significant correlations can be developed for many aquatic species including the fishes fathead minnow, bluegill, catfish, goldfish, goldorfe, guppy, killifish, rainbow trout, sheepshead minnow, and zebrafish; the water flea Daphnia sp.; such crustaceans as Artemia sp. and Crangon sp.; the ciliate Tetrahymena pyriformis; and algae, such as Chlorella sp. These interspecies relationships can be used to estimate order-of-magnitude type toxic effects of many substances for these aquatic organisms. Highly significant relationships can be obtained when selecting compounds on a chemical basis, such as alcohols, ketones, aromatics, etc., which allow the calculation of the compounds' toxicities to the corresponding aquatic species with increased accuracy and confidence. Analogous correlations with mammalian (rat and mouse) oral, intraperitoneal, and intravenous median lethal dose (LD50) data are much weaker than those for most aquatic species. However, there are significant differences between these three routes of administration and the intravenous LD50 data show the best relationship with the Vibrio data.
The rising interest in finding alternatives to using large scale, expensive, and time-consuming aquatic and terrestrial species tests for chemicals and commercial products has led to the investigation of several alternatives. One promising alternative is the use of bacteria for this purpose, especially Vibrio fischeri, formerly known as Photobacterium phosphoreum and commonly referred to as the Microtox test (Azur Environmental, Carlsbad, CA).
The photoluminescent bioassay uses a suspension of V. fischeri bacteria in saline water (to protect this marine bacterium from osmotic damage) and measures the reduction in light output of its natural luminescence on exposure to the toxicant of interest. In contrast to most aquatic bioassays, in which acute toxicities are usually measured over a period of 96 hr, the bacteria test can be performed in a matter of minutes. Furthermore, dormant bacteria concentrates can be kept frozen and ready for use for a prolonged period. Therefore, this test has generated widespread interest and has been adopted as a standardized test in several jurisdictions. It can be performed on demand in the laboratory without the need for keeping fish or mammals in larger scale facilities for extended periods. This convenience is obviously accompanied by savings in cost and time. Materials and specialized spectrophotometers are readily available from several commercial suppliers of the luminescence bioassay test systems, which are marketed under the
names Microtox (Azur Environmental), Lumistox (Dr. Lange GmbH, Berlin, Germany), and Biotox (BioOrbit, Turku, Finland).
Considerable toxicity data for V. fischeri/P. phosphoreum are available in the form of monographs (1,2) covering over 1200 chemicals. More recently, interactive databases have become available on CD-ROM. These CD-ROMs are marketed under the names Computox (Environment Canada, Ottawa, Ontario), which covers 1500 substances (3), and TerraTox (TerraBase Inc., Burlington, Ontario), which covers over 1700 substances (4), as well as specialized software for data analysis and toxicity estimation (4) available under the name TerraFit (TerraBase Inc.) Furthermore, symposium proceedings dealing with the use of photoluminescent bacteria for ecotoxicologic monitoring have been published (5). It is not surprising then that the V. fischeri/P. phosphoreum data have become the largest published toxicity test data set for a single aquatic species.
The biochemical mechanisms by which compounds exert a toxic or bioluminescence-reducing effect on the bacterium are only partly understood. In principle, the enzyme luciferase catalyzes the oxidation of reduced riboflavin phosphate, which is accompanied by emission of light. This process is linked with the microbial metabolism, and hence is directly linked to the toxic effect of a substance on the bacterium (6). Although different toxic mechanisms may exist in other organisms, substances highly toxic in one organism often also produce effects on quite different organisms. Isenberg, one of the original developers of the photoluminescent bacterial bioassay, describes this as testimony to the unity of life and shows that the median effective concentration (EC50) values for a variety of anesthetic gases are very similar for bacteria, mouse, dog, cat, and human (6).
Several studies have dealt with the relative sensitivity and comparability of the luminescent bacteria test with other, mostly aquatic, bioassays. Because this bioassay can be performed with relative ease and speed and at a limited cost, it is of particular interest as a test vehicle for routine monitoring once good correlations with local species have been established. A growing number of publications also use it for the ecotoxicologic assessment of contaminated soils and sediments and as a monitoring tool for site remediation. In research and product development studies, this test allows the rapid screening of novel compounds or a series of related compounds for their relative biologic activity. Given the large number of available data and the simplicity and robustness of the test, it is of much interest to undertake qualitative and quantitative comparisons of the Microtox test data with those of other bioassays, particularly aquatic species. A variety of earlier studies on this subject include the works by Kaiser et al. (7), Zhao (8), Kaiser (9), Fort (10), Munkittrick et al. (11), Bulich et al. (12), Xu et al. (13), Dutka and Kwan (14), Maas-Diepeveen and van Leeuwen (15), Nacci et al. (16), Tarkpea et al. (17), Greene et al. (18), DeZwart and Slooff (19), Ribo and Kaiser (20), Qureshi (21), and Curtis (22). Given the multitude of species, bioassays, and chemical substances, this study emphasizes those species and bioassays where larger numbers of data are in common, perusing the largest available data compilation (4).