Toxicity effects of trace metals on Zebra fish (Danio rerio) embryo
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Date
2015
Journal Title
Journal ISSN
Volume Title
Publisher
Uva Wellassa University of Sri Lanka
Abstract
Water quality deterioration is a major problem in the most of the countries, due to organic and
inorganic contaminants. Among all the toxicant trace metals are threaten to the aquatic ecosystem
and organisms. Metals are natural component of aquatic ecosystem. Trace metals such as Copper
(Cu), Zinc (Zn) and Chromium (Cr) are important for the metabolic and other biological activities of
lives whereas Mercury (Hg), Lead (Pb), Cadmium(Cd) are biologically non-essential metal that can
be toxic to biota even at very low concentration. High concentration of some essential trace metals
can be toxic when it exceeds the limits(Ebrahimi and Taherianfard, 2011).High accumulation of trace
metal in both biotic and abiotic components causes serious health consequences. Thus, assessment
of their toxicity has become an important component of water pollution monitoring. Now in most of
the toxicity studies Zebra fish (Danio rerio) embryo used as an alternative model for the fish acute
toxicity to determine the toxicity of pollutants. Therefore this study was focused on determination of
the acute toxicity of Cu, Zn, Cd, As, Pb and Hg that produce lethal effect on zebra fish embryos
during four day period.
Materials and Methodology
Zebra fish breeding was carried out and eggs were collected using a small pipette. The stock solution
of 1000 ppm of selected Cu, Zn, Pb, Cd, As and Hg were prepared a day before the test by dissolving
Copper sulfate (CuSO4.5H2O), Zinc sulfate (ZnSO4. 7H2O), Lead nitrate (Pb(NO3)2, Arsenic
pentoxide (As2O5), Cadmium chloride (CdCl2. ½ H2O) and Mercury chloride (HgCl2) in deionized
water. The working treatment solution was prepared daily by serial dilution of the stock solution.
Initially a range finding test was carried out in the nominal concentrations of (1000, 100, 10, 1 and
) for 96 hours. Ten eggs per concentrations were used. Deionized water was used as a
negative control. Each treatment had three replicates. Acute Cu, Zn, Pb, As, Cd and Hg toxicity
experiments were performed for a 4-day period using Danio rerio embryo. Ten test concentrations
of Cu, Cd (0.025, 0.05, 0.1, 0.2, 0.4, 0.8, 1.6, 3.2, 6.4 and 10.0 mgL⁻ ), Zn, Pb, As (2.0, 4.0, 8.0, 16.0,
32.0,64.0, 125.0,250.0, 500.0 and 1000.0 mgL⁻ ) and Hg (0.002, 0.004, 0.008, 0.016, 0.032, 0.064,
0.125, 0.250, 0.500 and 1.0 mgL⁻ ) were prepared by diluting the stock solution in deionized water.
Deionized water was used as negative control and as internal plate control. As a positive control
concentration of 15% ethanol(Hassan et al., 2008) was used with each embryo batch for testing.
Fertilized zebra fish embryos were immersed in the test solutions before cleavage, by the 16 cell-
stage. At least twice the number of eggs needed per treatment group (40 eggs) was randomly selected
and transferred into the respective concentrations and controls within the 90 minutes of post
fertilization. 24-well plates were filled with 2 mL per well freshly prepared test solutions. In each
plate twenty wells were used for test concentrations and four were used as internal plate control.
Another plate was used as positive control. The eggs in standard 24- well plate were covered by shelf
adhesive foil and maintain at a temperature to 26 ± 1 °C. The mortality of the fish eggs were recorded
at 24, 48, 72 and 96 hours of exposure using a stereo microscope with the indicator of lethality;
coagulation of fertilized egg, lack of somite formation, lack of detachment of the tail and lack of heart
beat as described in OECD/ OCDE 236, 2013; guideline for the test of chemical, Fish Embryo Acute
Toxicity (FET) tests. Dead eggs were removed immediately. Three replicates were performed
individually. In this study the acute toxic effect of each metal on the Danio rerio embryo was
determined by Probit Analysis LC50 determination method. Data analysis was performed by using
statistical software SPSS15.
Description
Keywords
Animal Sciences, Export Agriculture, Aquaculture and Fisheries, Aquatic Resources, Fish