Handbook of Solvents - George Wypych - ChemTech - Ventech!

15.2.2 A simple test to determine toxicity using bacteria 1095
15.2.2 A SIMPLE TEST TO DETERMINE TOXICITY USING BACTERIA
James L. Botsford
Department of Biology, New Mexico State University, Las Cruces, NM, USA
15.2.2.1 Introduction
The author has developed a simple, inexpensive and rapid method to measure toxicity using
a bacterial indicator. This paper describes this test in detail. It also reviews the field of alternative
tests for toxicity, tests not involving viable animals.
15.2.2.2 Toxicity defined
In toxicology, a compound is defined to be toxic if it damages living organisms. There is no
chemical definition of toxicity. Classically, toxicity is determined from the LD50 for animals,
the amount of the compound that kills 50% of the test animals (Rodericks, 1992).
Typically varying concentrations of the toxin are given to groups of 10 animals and a single
test can take 80 to 100 animals. Tests can take several weeks. Animal tests are expensive.
The animals must be cared for and trained personnel are required. The animals are force fed
the toxin so it passes through the acidic stomach or the toxins are introduced by
intraperitoneal injection. This can alter the activity of the toxin. The results from animal
tests are difficult to interpret since animals can die of causes other than the toxic chemical
and analysis of the data usually requires sophisticated statistical analysis. In the United
States it is estimated that 30 million animals die each year testing for toxic chemicals. Many
question the value of animal tests (Ruelius, 1987). Results vary dramatically between
strains of animals. Results with closely related species, rats and mice, often don’t agree
well. The drug Thalidomide many years ago was tested in animals and was found to be
harmless. The drug had tragic effects on humans. And, of course, animal tests do not note if
the animal becomes ill from the toxin. They only note if the toxin kills the animal.
Often it is not known why the chemical is toxic. It is simply observed that animals
coming in contact with the toxin die at abnormally high rates. Obviously the first step in a
study of a toxic chemical, is simply to determine if it is toxic.
Most animal tests are run with rats and mice, the usual laboratory animals. Rats and
mice are rodents and they have a caecum, a chamber that opens off the small intestine. The
caecum contains many microorganisms. It is not known what the role of the aecum could be
in handling toxic chemicals. This may influence results with rats and mice.
Alternatives to animal tests are sought. The sand flea Daphnia magna is used extensively.
Tests are inexpensive, most the animal rights advocates are not offended. Daphnia
tests are difficult to perform and require highly skilled personnel. The tests typically take
two days (Stephenson, 1990). Once it has been determined that the toxin kills the juvenile
cells, it can be determined if the toxin interferes with maturation of the juveniles, with reproduction
in the adults, or if the toxin simply inhibits growth. However, nearly all reports
simply deal with death of the animals. Ceriodaphnia dubia offers another approach to this
sort of test (Jung and Bitton,1997). There is a version of this test called Ceriofast TM that
takes only one hour. Daphnia testing requires laboratory skills that typically lab workers do
not develop. The juvenile insects must be isolated using a dissecting microscope. The animals
must be monitored to determine if they are living. It is necessary to watch the culture to
know when to isolate the juveniles.