3 Water Toxicity Monitoring using Optical Oxygen Sensing and Respirometry

Approximately one third of available freshwater is currently used for agricultural, industrial or domestic purposes. This results in contamination of the water with a wide range of pollutants originating from ~300 million tons of compounds used in industrial and consumer products, ~140 million tons of fertilizers, several million tons of pesticides, 0.4 million tons from oil and gasoline spillages (1). To tackle the emerging threat of contamination and depletion of freshwater stocks, large initiatives such as the EU Water Framework Directive (WFD) (2) have been established. The WFD is concerned with “scope of water protection to include all waters, to set clear objectives in order that a “good status” be achieved.” Successful realization of such projects, and of the other environmental monitoring tasks, is linked to the availability of techniques for detailed toxicological assessment, screening and monitoring of large number of chemical and environmental samples, plus validation and wide deployment of such techniques. Conventional toxicity tests with higher animal models such as rodents or primates based on the determination of lethal doses of toxicants (3) have limited use, due to their ethical constrains, low speed and high costs. Other systems include bioluminescent test for the presence of toxic compounds using freeze dried luminescent bacteria Vibrio fischeri (formerly called Photobacterium phosphoreum (4)) found in the marine environments (5) and functioning via an endogenous flavin monooxygenase enzyme luciferase. V. fischeri provided the basis for several commercial kits such as Microtox® (Azur Environmental, Carlsbad, CA), Mutatox® (with dark mutant of V.fischeri) (6), Deltatox® (portable, without temperature control), which have been extensively validated (7, 8) and accepted as a standard method by International Standard Organization (ISO) (9). Although providing good sensitivity, short assay time and simplicity, these tests are limited to just one strain of simple prokaryotic test organism and to samples that do not interfere with luminescent measurements. Samples that are turbid, absorb light or quench luminescent reaction can interfere the assay and cause measurement problems and invalid results. The need to find alternatives to expensive, space, time and labour consuming toxicity tests using aquatic and terrestrial species has led to the development of alternative methods. Thus, ethical (10) and regulatory issues (11) are favouring the use of animal models such as bacteria (12), small vertebrates (zebrafish Danio rerio) (13), invertebrates (the fruit fly Drosophila melanogaster (14), and brine shrimp Artemia salina (15). Daphnids, particularly D.