Abstract:
Whole effluent toxicity (WET) testing is a method used to evaluate the adverse
effects on aquatic organisms in receiving water. It is used to protect ecological systems
and to fill in data gaps created by using only data from physical and chemical analysis.
The objectives of this study are to determine the effects of organism’s age, water
temperature range, type of dilution water and varrying exposure durations to the
toxicity of industrial whole effluent of Giant Freshwater Prawn, Macrobrachium
rosenbergii. The toxicity tests were performed by using a static non-renewal design.
The results demonstrated firstly that the prawns were sensitive to the toxicity of
the industrial effluent. Second, organism age significantly affected the LC50 (p<0.01).
Younger prawn (25 days) were more sensitive to the toxicity of the industrial effluent.
Test conditions also had a significant effect on the 48 and 96 hour LC50 (p<0.05).
Exposure duration significantly affect lethality of the effluent (p<0.01). The LC50’s
were lower in 96 hour tests than they were in 24, 48 and 72 hour test. However, water
temperature range did not have a significant effect on lethality of the effluent. LC50’s
could not be calculated for tests using receiving water as the diluent as there was
100% mortality at 24 hours exposure. The LC50’s for test using synthetic seawater as
the diluent ranged from 18% to 69% in 25-day-old prawn, and 31% to 76% in 35-dayold
prawn. The optimum test conditions for testing the toxicity effect of industrial
whole effluent on Giant Freshwater Prawn, M. rosenbergii, were found to be organism
age of 25 days, a temperature of 25±1°C or room temperature (23.0-27.6°C), an
exposure duration of 96 hours and a salinity of between 13-15 ppt using synthetic
seawater as the diluent.
From these findings, it is recommended that further research be carried out using
other types of effluent, as well as different endpoints for acute and short-term chronic
tests in M. rosenbergii. Other species of organisms should also be studied both
freshwater and marine system.