Bioaccumulation and depuration of zinc in the tissues of Heterobranchus longifilis exposed to zinc oxide nano-particles
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Date
2022
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Abstract
Industries use zinc oxide nano-particles (ZnO-NPs) to produce most commercial and
medicinal goods, but indiscriminate discharge of their effluents into the aquatic
environment may accumulate in the tissues of the fish. The ability of these metal oxides
to accumulate in the tissue of fish due to their nano size could lead to a reduction in the
nutritional value of the fish. Therefore, this study aimed to evaluate the rate of zinc
bioaccumulation in tissues of Heterobranchus longifilis. Juveniles of H. longifilis were
exposed to sub-lethal concentrations (0.0, 6.00, 8.00, 10.00, 12.00 mg/l) of ZnO-NPs for
60 d and depurated for 30 d. At the end of each experiment, fish were sacrificed and
analyzed for bioaccumulation. The increasing order of concentration of zinc was as
follow: bone< muscle < blood < skin < kidney < liver < GIT < gills having 0.068mg/g to
0.263 mg/g from muscle to gills. That was above the permissible limits (0.050 mg/g) in
fish tissues, except in the bone with 0.054 mg/g, which was still within the acceptable
limits. Gills accumulated the highest (0.263 mg/g) content of zinc, and bone had the
lowest (0.054 mg/g). After the depuration period, the content of zinc in the tissues
decreased in all the tissues but still remained above the maximum permissible limits in
gills, GIT, kidney, liver and skin (0.175 mg/g, 0.162 mg/g, 0.066 mg/g, 0.071 mg/g and
0.073 mg/g respectively). However, the bone, blood and muscle were able to depurate
the zinc content to values (0.031 mg/g, 0.034 mg/g, and 0.044 mg/g, respectively) below
the acceptable limits of Zn in fish tissues. The results indicated that zinc from ZnO-NPs
bioaccumulated in H. longifilis tissues, but the fish could depurate the metal naturally.
However, the ability to depurate the bioaccumulated metal is time-dependent