BIOACCUMULATION DYNAMICS OF HEAVY METALS IN Oreochromis nilotycus: PREDICTED THROUGH A BIOACCUMULATION MODEL CONSTRUCTED BASED ON BIOTIC LIGAND MODEL (BLM)
ABSTRACT: In estuarine
ecosystem, sediments are not only functioning as heavy metal scavenger, but
also as one of potential sources for heavy metals to the ecosystem. Due the
capability of aquatic organisms to accumulate heavy metals, there is
possibility of heavy metals to exert their toxic effect towards the organisms
and other organisms positioned in higher trophic level, such as fish, and
further to human beings. To understand the different processes of heavy metal
bioaccumulation in a dynamic manner, a bioaccumulation model is required. Since
bioaccumulation starts with the uptake of chemical across a biological
membrane, the bioaccumulation model was constructed based on Biotic Ligand
Model (BLM). The input for the model was determined from laboratory scale
simulated estuarine ecosystem of sediment-brackish water (seawater:Aqua 1:1) for determining the heavy metal fractions in sediments;
simulated Oreochromis nilotycus – brackish water (fish-water) ecosystem for
determining the rate constants; simulated fish-water-sediment ecosystem for
evaluating the closeness between model-predicted and measured concentration,
routes and distribution within specific internal organs. From these
bioaccumulation studies, it was confirmed that the internalization of metals
into the cells of gills and internal epithelias follows similar mechanisms, and
governed mostly by the waterborne or hydrophilic heavy metals. The level of
hydrophilic heavy metals are determined by desorption equilibrium coefficients,
1/K D , and influenced by salinity. Physiologically, the essential Cu and Zn
body burden in O. nilotycus are tightly homeostasis regulated, shown as
decreasing uptake efficiency factor, E W , at higher exposure concentrations,
while non essential Cd and Hg were less or not regulated. From the distribution
within specific internal organs, it was revealed that carcass was more relevant
in describing the bioaccumulation condition than liver. It is clear that every
heavy metal has its own bioaccumulation dynamics, depend to the metal studied
and environmental conditions, however the obtained parameters are applicable to
bioaccumulation of Cd and Hg in natural estuarine ecosystem of Segara Anakan,
Central Java.
Author: Sri Noegrohati
Journal Code: jpkimiagg060013
