Conventional Assessment of Toxicity of Effluents and Novel Low-Cost Toxicity Evaluations for Aquatic and Terrestrial Environments

K. Wadhia and K. Clive Thompson

ALcontrol Laboratories,


The failure of biological treatment processes in industrial and municipal wastewater treatment plants is one of the major causes of toxic throughput and non-compliance with discharge permit limits.  Both operators and the regulatory agency are placing increased emphasis on controlling toxic or inhibitory discharges.  Since the early 1900s various methods to determine the respiration rate of bacteria have been used to assess the ability of a bacterial population to remove substances from wastewater (treatability or biodegradability) and to determine the effects of the substances on the bacteria (inhibition or toxicity).  The test developed at ALcontrol Laboratories utilises innovative technology to examine the potential deleterious effects of toxicants on microbial flora in activated sludge.  Respiration rate measurements are obtained using MERIT 20 channel respirometers.  The microprocessor-based respirometers have fully automated environmental control and data collection systems.

In sewage treatment, the removal of ammonia is carried out by biological processes including percolating filter beds and activated sludge plants.  Nitrosomonas bacteria oxidize ammonia to nitrite and Nitrobacter further oxidises this to nitrate.  The nitrification inhibition test, developed at ALcontrol Laboratories with an ingenious buffering system, allows the measurement of a culture of Nitrosomonas to remove ammonia.  A measure of nitrification inhibition in samples is determined by comparison with a non-inhibitory control.

Conventional aquatic bioassays, like the fish or Cladoceran tests, are impractical for routine environmental screening.  Culturing and testing is very expensive and laborious, as well as time and space consuming.  Local differences in stock culture increases the variation in the test results, and test organisms may not always be available.  This has led to the development of small-volume tests with small organisms, so-called Microbiotests.  Toxkit™ microbiotests are commercially available kits featuring polycellular organisms.  These tests overcome the need to maintain continuous cultures by employing biological material in dormant (cryptobiotic) or immobilised form.  The Toxkits™ represent an important development in the use of battery of test species.  The utilisation of bioassays with different representative species of different trophic levels in the ecosystem is necessary because of significant ‘interspecies sensitivity differences’ to toxicants.  For testing terrestrial samples (e.g. soils; sediments and sludges) some novel tests will also be described.  These include a direct contact test (Ostracodtoxkit F™) for zootoxic assessment, and a seed germination/root elongation test (Phytotoxkit F™) designed to provide a rapid low-cost phytotoxic evaluation.

The aforementioned tests will be described and salient features and evaluations will be conveyed.


Bioassays; Biological Assessment; Ecotoxicity; Leachates; Microbiotests; Phytotoxicity; Sediments; Soil Extracts

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