Siygeza Systems

THE WEAVER TEST

This new test for the determination of the toxicity of any water and/or effluent has many advantages over the existing systems:

The test measures toxicity related to the human being, as it tests the effect of the toxins on human cells.

The results are full repeatable and are obtained within 24 hours.

Tests done so far confirm that the Weaver test is extremely accurate and gives the user a fast effective and less expensive method to determine the toxicity of water used or effluent produced. It also allows a producer of water-based products to confirm that his products are non-toxic to the human being.

The applications are wide and far:

- Identify polluted waters allowing for better and cheaper treatment.
- Protect the environment and the communities living from natural waters.
- Suitable for rivers, waters, underground water, wells and effluents.
- Can be part of quality control system to ensure water used or produced is within specifications.

In South Africa, water and wastewater are coming under tough scrutiny as new legislation is being prepared by government to assess our most valuable and scarce resource, not only in terms of chemical pollution but also in terms of biological impact on the environment.

Until recently, the assays developed and commonly used were based on biological sensors like fish, daphnia, bacteria and algae. After many years of research, Dr Mike Whitcutt of HBA, a Section 21 Company in Gauteng, South Africa has developed a toxicity test that makes use of human cells in vitro as a bio-sensor system. This new test is called the "Weaver Test" - it is capable of assessing the overall toxicity of water from any origin (industrial, recreational and source water for drinking) on an environment that is closer to the human environment than any other assay system presently in use worldwide.

Ideally, a biological test for assessing toxicity in water and sediments should be sensitive, reproducible, robust and available at low cost. It is also important that such a test system should allow a large number of specimens to be processed and the volume of material should be small and manageable in terms of transport. The biosensor must be readily available and its biological characteristics should be fully understood.

The new development of HBA, which is the first test of this kind, involves an in vitro system, based on the response of human cells to the toxic effect of the test sample over 24 hours. The toxic stress elicits responses of general biochemical pathways that are markers of viability and are found in all mammalian cells as well as in other, lower forms of life. Further developments of the "Weaver Test" system are anticipated.

USE OF A MODIFIED MTT TEST FOR WATER QUALITY ASSESSMENT

J.M. Whitcutt, PhDHighveld
Biological Association (HBA), Sandringham, Johannesburg

ABSTRACT (Submitted to the 35th Convention of the South African Chemical Institute Potchefstroom, RSA, September 24 to 29, 2000)

MTT, [3-(4,5-dimethyl-thiazolyl-2)-2,5-diphenyltetrazolium bromide] has been used to measure the activity of the oxidative pathways in many different systems and situations since it was first introduced by Pearse in 1957, and there is an extensive literature available on its many applications, including much on toxicity testing.

In collaboration with other groups looking at problems of water toxicity in South Africa, we have modified the standard MTT toxicity assay and adapted it for the rapid mass testing of water samples.

Assays are carried out in 96-well microtitre plates containing 20 000 to 30 000 K-562 human leukemia cells per well. Allowing for the necessary positive and negative controls, standards and statistical controls, hundreds of unknown samples can be processed in duplicate per day. Colorimetric readings are fed directly to a computer and printed out as numerical units of toxicity between 0 (positive control standard) and 100 (negative control standard). Tests are done following a double blind procedure.

THESE ARE SOME INTERESTING FEATURES OF THE WEAVER TEST