SORPTION-DESORPTION CHARACTERISTICS OF HEAVY METALS AND THEIR AVAILABILITY FROM THE SEDIMENT OF SEGARA ANAKAN ESTUARY
ABSTRACT: Estuarine sediments
are increasingly recognized as both a carrier and a possible source of heavy metals
in pollution of aquatic ecosystems. The bioavailability of heavy metal from
sediments, however, is a long-standing impediment of questions in determining
the metal effects in ecosystems. The fraction considered as available heavy
metal are both the dissolved heavy metal and the exchangable cations. The main
objective of this study is to understand the extent of heavy metal availability
from sediments in estuarine ecosystem. It was found that the availability of
heavy metals, i.e. copper, zinc, cadmium, and mercury in the estuarine
ecosystem investigated, are governed by the relative strength of the
electrostatic attraction of their complexation to the ligands present both in
the sediment and the overlaying waters. Under simulated estuarine ecosystem, it
was observed that Cu and Zn prefer to form organo-complex through ligand
exchange, while Cd and Hg tend to form chloro-complex through electrostatic
interaction. Therefore, the availability of Hg and Cd is higher in more saline
overlaying water. On the contrary, the availability of Cu and Zn is lower in
more saline overlaying waters, as indicated by their respective water-sediment
distribution coefficient, KD. Similar behaviour of heavy metal was observed in
natural field conditions of Segara Anakan estuary. Due to the higher salinity
of the overlaying water, the availability of Cd and Hg in dry season was higher
than in wet season, while Zn was more available in wet season due to the higher
input of organic matters from the inland. The patterns of heavy metal release
from the sediment are consistent to that obtained in experiments of the
undisturbed simulation, where highest release was obtained for Cd. Surprisingly,
it was found that even though Cd was not detected in the sediment, higher level
of Cd in water medium was observed in dry season, and Cu seems to retain in the
sediment in both dry and wet seasons. Compared to the unextractable fraction,
the extractable was very low, therefore Geloina sp. was used as biomonitor for
dissolved Cd and Hg, and Zn in sediment. Generally, the heavy metal
concentration in Geloina sp. was higher in dry season than in wet season, but
no Cu uptake was detected. Therefore, the establishment of limit values of
heavy metals in sediment is highly recommended.
Author: Sri Noegrohati
Journal Code: jpkimiagg050019
