Accumulation and partitioning of heavy metals in mangroves: A synthesis of field-based studies

Abstract

We report the findings of a comparative analysis examining patterns of accumulation and partitioning of the heavy metals copper (Cu), lead (Pb) and zinc (Zn) in mangroves from available field-based studies to date, employing both species level analyses and a phylogenetic approach. Despite mangroves being a taxonomically diverse group, metal accumulation and partitioning for all metals examined were broadly similar across genera and families. Patterns of metal accumulation were also similar regardless of whether species were classified as salt secreting or non-secreting. Metals were accumulated in roots to concentrations similar to those of adjacent sediments with root bio-concentration factors (BCF; ratio of root metal to sediment metal concentration) of 1< or =. Root BCFs were constant across the exposure range for all metals. Metal concentrations in leaves were half that of roots or lower. Essential metals (Cu and Zn; translocation factors (TF; ratio of leaf metal to root metal concentration) of 0.52 and 0.53, and leaf BCFs of 0.47 and 0.51, respectively) showed greater mobility than non-essential metals (Pb; TF of 0.31 and leaf BCF of 0.11). Leaf BCFs for the essential metals Cu and Zn decreased as environmental concentrations increased. The non-essential metal Pb was excluded from leaf tissue regardless of environmental concentrations. Thus mangroves as a group tend to operate as excluder species for non-essential metals and regulators of essential metals. For phytoremediation initiatives, mangrove ecosystems are perhaps best employed as phytostabilisers, potentially aiding in the retention of toxic metals and thereby reducing transport to adjacent estuarine and marine systems.

Spatial and temporal variation of the nutrients in the sediment and leaves of two Brazilian mangrove species and their role in the retention of environmental heavy metals

“…For other forests, such as dry tropical forests and savannas, seasonal variation of nutrients is related to mechanisms of uptake and retranslocation (villela and Lacerda, 1992). This has also been reported for mangrove forests (Wang et al 2003;Macfarlane et al, 2007).…”

“…Mangroves tend to show little accumulation of heavy metals, with higher concentration of these elements in root tissue than in leaves (Silva et al, 1990;Macfarlane et al, 2007). In general, the concentration factors for heavy metals in mangrove leaves are lower than 1.0 and there was no correlation between the concentration in leaves and sediments Thomas and Fernandez, 1997).…”

Heterogeneity of elemental composition and natural abundance of stables isotopes of C and N in soils and leaves of mangroves at their southernmost West Atlantic range

“…In general the concentrations of the heavy metals (Fe, Mn, Cu, and Zn) appear to be within the lower range of concentrations reported for other mangrove sites in Brazil (Machado et al, 2002;Bernini et al, 2010) and elsewhere (Alongi et al, 2003;MacFarlane et al, 2007). The δ 13 C values separated S. densiflora from the rest because of its C4 photosynthesis.…”

Influence of chromium in Laguncularia racemosa (L). Gaertn f. physiology

“…A number of studies have found metals to be accumulated predominantly in root tissue, rather than in foliage (Peters et al, 1997;MacFarlene, Koller and Blomberg, 2007). The data seem to suggest that concentrations of translocated metals are low with bioconcentration factors (BCF; ratio of leaf metal to corresponding sediment metal concentration) ranging from <0.01 to 0.06 for mangrove trees (Lacerda, 1997).…”