The effects of three heavy metals Copper (Cu), lead (Pb) and zinc (Zn), and the interaction
of an essential (Zn) and non-essential (Pb) metal on germination, growth, and accumulation
of metals in the grey mangrove, Avicennia marina (Forsk.) Vierh var. australasica
(Walp.) Moldenke, were studied under laboratory conditions. Avicennia marina was found
to be highly tolerant to the metals applied. Copper was accumulated in root tissue
in a linear relationship at lower sediment concentrations, but at concentrations of
200 microg/g and higher, no further increases in root Cu levels occurred. Translocation
of Cu from the root to leaf tissue was low, yet revealed similar accumulation patterns
as root tissue. Significant reductions in seedling height leaf number and area were
found with significant increases in Cu concentrations in tissues at 100 microg/g sediment
Cu. At Cu sediment levels of 400 microg/g, a decrease in total biomass and root growth
inhibition was observed. Emergence was retarded with increasing copper concentration,
with 800 microg/g sediment Cu resulting in a total inhibition of emergence. The LC50
for emergence and EC50 for biomass was 566 and 380 microg/g Cu respectively. Lead
accumulation in root tissue was lower that other metals, yet increased in a dose dependant
fashion across the sediment Pb concentration range examined. Lead was excluded from
leaf tissue at Pb sediment concentrations up to 400 microg/g, above which limited
transport of Pb occurred. Little negative effects on growth were observed due to the
low accumulation of Pb. Zinc uptake was high, and was accumulated in a linear fashion
in root tissue across the sediment Zn concentration range applied. Zinc translocation
to leaf tissue exhibited a dose dependant relationship with both root and sediment
Zn levels. Emergence decreased with increasing sediment Zn concentrations, with 1000
microg/g sediment Zn showing 100% mortality. Significant reductions in seedling height,
leaf number, area, biomass and root growth inhibition were found at concentrations
of 500 microg/g sediment Zn. The LC50 for emergence and EC50 for biomass was 580 and
392 microg/g Zn respectively. Lead and Zn in combination resulted in an increased
accumulation of both metals in leaf tissue and increased toxicity than individual
metals alone, and is the first noted occurrence of a Pb and Zn additive response in
angiosperms. Possible mechanisms of accumulation and toxicity are discussed.