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Physiological stress
response of Macrobrachium vollenhoevenii (Herklots
1857) to interacting effects of binary mixtures of
industrial effluents
L. O. Chukwu* and O. F. Lawson
Aquatic
Toxicology and Ecophysiology Laboratory, Department of
Marine Sciences, University of Lagos, Akoka, Lagos.
*Corresponding author. E-mail:
obinnalcunilag@yahoo.com
Accepted 20
February, 2009 |
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The toxicities of effluents from paint and textile industrial
establishments in Lagos State, Nigeria and their binary
mixtures based on predetermined (1:1) and equitoxic (4:3)
ratios were evaluated against the juvenile stage of prawn,
Macrobrachium vollenhoevenii in laboratory bioassays. On
the basis of derived toxicity indices, the paint effluent
with 96 h LC50= 54.73 ml/L was found to be 1.33
times less toxic than the textile effluent (96 h LC50=
40.99 ml/L) when acting alone against M. vollenhoevenii.
In the joint toxicity tests, the binary mixtures in a
predetermined ratio (1:1) with 96 h LC50= 49.45
ml/L was 1.16 times more toxic than the equitoxic mixtures
(4:3) with 96 h LC50= 57.7 ml/L. The interactions
between binary mixtures showed significant departures from
the action of individual constituent effluent when acting
singly, and depended largely upon the proportions of
additions of the mixture components. On the basis of
synergistic (Synergistic Ratio, SR) and
concentration-addition models (Relative Toxicity Unit, RTU),
the relationship between binary mixtures (1:1) of paint and
textile effluents against M. vollenhoevenii were in
conformity with models of synergism and antagonism (SR=
1.11, 0.83; RTU= 0.97) while equitoxic mixtures (4:3)
conformed to antagonism (S.R =0.94, 0.71, RTU =0.84) model.
Furthermore, the isobologram model showed that both binary
mixtures conformed to sub-additive action. Symptoms of
toxicosis observed in the test organisms include loss of
equilibrium, agitated swimming, spiral movement, followed by
weakness, periods of quiescence and death. It is concluded
that the incorporation of joint action toxicity evaluation
with bio-monitoring tools are clearly relevant in setting
effective and realistic environmentally safe limits of
pollutants or verifying ecological significance of existing
water criteria meant to protect aquatic biota.
Key
words:
Toxicity, effluent, synergism, antagonism, interactions,
M. vollenhoevenii. |
