Essay On Toxicity Test

1.1.2.2.2 The performed toxicity test principle:

The preformed test in this experiment is a modified method of the limit test OECD TG 203, and is more adapted for marbled crayfishes. The principle of the test is to show that the LC50 is greater than 100 mg /l. In this test, the marbled crayfishes were exposed to the different test substances dissolved in water and observed for 120 hours. Ever 24 h the mortality, the growth, color and the movement of the crayfishes were recorded. When 1 crayfishes of the test group dies, the test should be terminated and a complete OECD TG 203 should be performed. This test has the advantage of using only one concentration, and thus fewer crayfishes, thus it is more ethical and more practical.

In this test

The newly deposited eggs have a spherical shape of about 1.3 to 1.5 mm in diameter, enclosed by two chorions, and are attached to the pleopods for brooding. [7] [8]. Developmental stages of Marbled crayfishes’ embryogenesis can be easily monitored due to the embryo`s development at the surface of the egg. 1.1.2.3.2 Toxicity test on eggs

The test was designed to test different groups of eggs with the chosen test substance and an extra group of eggs as a control group. The eggs should be laid in a flask filled with water and dissolved test substance, and the development stages of the eggs should be controlled. Any change in the egg development should be recorded. A distributed egg appears in orange color and it should be thrown away immediately. The test should be carried out in many concentrations. The Growth and the development of the eggs were controlled under stereomicroscope.

1.1.2.3.3 Stereo microscope:

The stereo microscope is a variant design of the optical microscope, the light is reflected from the surface of an object rather than transmitting through it. The use of reflected light from the object allows examination of the eggs which are black colored and too thick and opaque for the other