The following points highlight the five tests conducted for determining the effect of toxicity on organisms. The tests are: 1. Full Life Cycle Tests 2. Partial Life Cycle Toxicity Tests 3. Most Sensitive Early Life Stage Toxicity Tests 4. Functional Tests 5. Bioassay in Toxicity Testing.
Test # 1. Full Life Cycle Tests:
These are typical chronic toxicity tests conducted on test organisms, that measure the effects of chronic exposure to a chemical on reproduction, growth, survival and other parameters extending over one or more generations.
Full life cycle toxicity test is an important tool for understanding and evaluating the potential hazard of toxicants that will interfere with normal growth, development and attainment of reproductive potential of an organism.
In this full life cycle test, exposure is initiated with viable gametes, newly fertilized ova, early stages of developing embryos, growth and development of the young organism, attainment of sexual maturity and production of a second generation organism. All test populations, except controls, are exposed continuously (for at least five concentration) to the chemical for a period sufficient for the control to grow and produce F1 offspring.
ADVERTISEMENTS:
Each population is exposed to a different chemical concentration and assessment of mortality, normal growth and development to sexual maturity and fecundity is done in comparison to the control populations. The changes observed in the case of the exposed populations in comparison to the control are then identified and statistical analyses are made.
Chronic toxicity tests are performed on vertebrates such as fathead minnow, sheepshead minnow and several fish species. It is also conducted on invertebrates such as water flea, shrimp, several crustaceans etc.
Test # 2. Partial Life Cycle Toxicity Tests:
Here groups of individuals of one species are exposed to different concentration of a toxicant only to a part of its life cycle. Such tests conducted on fishes (brook trout or blue gills) can be completed in less than 15 months.
Test # 3. Most Sensitive Early Life Stage Toxicity Tests:
The life cycles of vertebrates and invertebrates have some developmental stages which are more sensitive than other stages. These most sensitive stages are used to predict chronic toxicity of chemicals to organisms. Early life stage (ELS) tests measure the effect of chronic exposure on survival and growth of the most sensitive life stages such as eggs and larva of fishes.
ADVERTISEMENTS:
A relatively short exposure of the early sensitive life stages of fish to a toxicant can be used to estimate maximum acceptable toxicant concentration (MATC) without a complete life cycle test. Major toxic effects measured are on survival and growth.
Test # 4. Functional Tests:
Functional tests measure the chronic toxicity of chemicals in various physiological functions or functional response of organisms, which include changes in blood chemistry, histology, swimming performance, avoidance respiration, enzyme activities, sensory perception and disease resistance.
Functional tests have been used in studies on bioaccumulation and biotransformation processes. Functional responses are often sensitive indicators of sub-lethal toxic effects.
Test # 5. Bioassay in Toxicity Testing:
Bioassay is a test to evaluate the relative potency of a chemical by comparing its effect on a living organism with that of a standard preparation. Bioassays are performed to assess the strength of the chemical from the degree of response shown by the test organisms and not by the estimate of the concentration of the chemical that is toxic to those organisms.
ADVERTISEMENTS:
Bioassays are used extensively by the pharmaceutical industry to evaluate the potency of vitamins and other pharmacologically active compounds.