Uptake of lead (pb) and cadmium (cd) by two species of mangrove (rhizophora apiculata and avicennia alba) grown hydroponically and in field conditions

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Date
2006
Authors
Irnasari
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Abstract
Mangrove ecosystems act as buffer zones for heavy metal mobilization before these reach the off shore areas. Therefore, evaluation of the uptake of some heavy metals by mangrove species is important. In natural conditions, uptake of metals by mangrove plants is controlled by physicochemical conditions in mangrove sediments that are rich in organic matter. Thus, to exclude these physicochemical effects, a hydroponic method was applied. An assessment of Pb and Cd uptake by mangrove species was carried out both in laboratory experiments and field cultivation. The effect of salinity on Pb and Cd uptake by R. apiculata and A. alba as well as the influence of heavy metals and salinity stress on the growth of both species have been investigated using hydroponic cultivation in the laboratory. After 3 months exposure to various levels of Pb (0.03; 0.3 and 3mg/l) and Cd (0.005; 0.05 and 0.5mg/l) under various salinity regimes (0 °/oo. 15 °/oo and 30 °/00), Pb and Cd were significantly accumulated in the roots of both mangrove species. A. alba showed higher uptake of Pb and Cd compared to R. apiculata, especially in their leaves reaching two fold. The laboratory study also showed that salinity was found to significantly inhibit the Cd uptake by R. apiculata and A. alba. The total concentration of Cd in R. apiculata at salinity 30°/00 reduced around 34% and around 22% for A. alba from Cd concentration at 0 °/00 salinity. However, both species showed the best growth at salinity 15°/00. Salinity was also suggested to reduce the toxic effects of Pb and Cd on mangrove plants. The assessment of metal uptake by mangrove species under natural conditions was conducted at two mangrove areas, Merbok mangrove forest and Juru. The metal uptake from mangrove sediments by R. apiculata under field experiment was lower than under hydroponic cultivation. However, the translocation of metals from the roots to the shoots (stems and leaves) were quite similar. Finally, lower metal uptake by mangrove species under natural conditions may be related to the metal behaviour in mangrove sediments where they can be immobilized by the physicochemical properties of the sediments, such as their organic content.
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Lead (pb) , Two species , Grown hydroponically , Mangrove (rhizophora apiculata) , Avicennia alba
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