Remobilization of Heavy Metals by Mangrove Leaves

Abstract

Several studies have been carried out on heavy metal pollution in mangrove ecosystems. However, the role of mangroves in heavy metal remobilization is still relatively unknown. On one side, mangrove woody organs and soils sequester heavy metals for long time periods, but on the other hand, senescence of mangrove leaves may return these metals collected by roots to the upper layers of the soil. Here, we analyzed the concentration of chemical elements (Al, As, Cd, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sr, V, and Zn) as a function of age in mangrove leaves to understand heavy metals retention by the plant and to quantify the amounts shed with senescing leaves. In addition, we estimated metal concentrations and stocks in mangrove soils. Our results revealed that the concentration of most metals increased with leaf age, resulting in the remobilization of metals stored in soil, thereby returning metals to the upper layers of the soil during senescence of mangrove leaves. Only Cu was reabsorbed prior to shedding of leaves, a mechanism similar to that described for nutrients in mangroves globally. These results provide key data to understand mangroves role in the dynamics of heavy metals.

Sediment Metal Contamination, Bioavailability, and Oxidative Stress Response in Mangrove Avicennia marina in Central Red Sea

“…However, sediments were extremely enriched with Sr (Abrahim and Parker, 2008). Similar concentrations of heavy metals to the concentrations in this present study except V were also reported from other locations in central Red Sea and northern and southern parts of the Red Sea (Hanna, 1992;Fowler et al, 1993;Badr et al, 2009;Soliman et al, 2015;Abu-Zied and Hariri, 2016;Youssef and El-Sorogy, 2016;Ruiz-Compean et al, 2017;Almahasheer et al, 2018). This suggests that the six mangrove ecosystems investigated in this study might not be under severe heavy metal pollution despite the different anthropogenic activities going on in these ecosystems and their catchment.…”

“…The plant-sediment interaction based on metal accumulation is better estimated using the BCF. However, the BCFs for all the 13 metals were <1, suggesting an effective mechanism of detoxification or exclusion by A. marina (Almahasheer et al, 2018;Aljahdali and Alhassan, 2020a). In addition, it should be noted that some heavy metals determined in this study such as Fe, Cu, Mn, and Mo are essential for plant growth, if not in excess or above a limit where they become toxic (Appenroth, 2010).…”

“…However, the threat to mangrove ecosystems has been on the increase due to anthropogenic chemicals from the ever-increasing industrialization and urbanization centered on population growth (Polidoro et al, 2010;Chaudhuri et al, 2014). Mangrove plants such as Avicennia marina can be used to remove contaminants from the sediment; this is known as green remediation used widely in most developing parts of the world (Nouri et al, 2017;Almahasheer et al, 2018). Mangroves play a vital role in removing contaminants from sediments, leading to improved sediment quality in coastal ecosystems due to their ability to grow in chemical-polluted coastal environments (Chai et al, 2019).…”

Human proximity suppresses fish recruitment by altering mangrove-associated odour cues

“…As mangroves naturally accumulate compounds from their environments, many pollutants are incorporated into the plant’s tissues 46 . These then have the potential to be subsequently remobilized when those tissues degrade, with greater bioavailability than those held in sediments 47 . The presence of pollutants will also alter the microbial community associated with the water column, sediment, and plant material 44 , 48 , which could further impact litter decomposition and associated chemical cues.…”

Remobilization of zinc in sediments by mangrove and its associated species in Blanakan River, West Java, Indonesia

“…The BCF of Cu in Pluchea indica was > 1 (Soraya et al 2019). Despite considered as heavy metal, Zn is one of the essential micronutrients for plant growth and nontoxic (Appenroth 2010;Almahasheer et al 2018). However, the Zn can be toxic for plant if the Zn exceeds the plant toxicity threshold which is 300-600 mg/kg (Long et al 2003).…”