# Harnessing Biotechnology for the Remediation of Organic Pollutants in Coastal Marine Ecosystems
## 4 Biotechnological Methods for Remediation
### Phytoremediation Approaches
Mangrove species like _Avicennia marina_ and terrestrial plants such as _Veiteria zizanioides_ (vetiver grass) have been shown to degrade hydrocarbons, pesticides and phenolic compounds in coastal zones through this mechanism [73], while plants such as _Tegetes patula_, _Ipomea balsamina_, and _Mirabilis jalapa_ have been widely used for their ability to degrade chlorinated solvents and hydrocarbons, transforming them into non-toxic chemicals in groundwater and soil environments [72]. The presence of rhizospheric microbes further enhances degradation through synergistic interactions. Phytostabilization  
Phytostabilization involves the immobilization of contaminants, especially heavy metals within the soil matrix or plant root systems. This mechanism is crucial in preventing the spread of contaminants in sediments [74]. This process operates through mechanisms such as adsorption, precipitation and complexation within the rhizosphere [72; 75]. For instance, plants like _Arabidopsis arenasa_, _Deschampsia cespitosa_, _Silene vulgaris_, _Zea mays_, and _Brassica napus_[76; 77] have demonstrated efficacy in reducing the bioavailability of heavy metals like lead (Pb), zinc (Zn), and cadmium (Cd) by forming stable complexes in the root zone [67]. Enhancement of phytostabilization can be achieved through soil amendments, including organic matter, biochar, and microbial inoculants [78]. These amendments improve soil structure, pH, and microbial activity, which further help in immobilizing contaminants. For example, the addition of spent mushroom compost and attapulge has been shown to improve soil pH and fertility [79; 80], enhancing the phytostabilization capacity of plants like _Koelreuteria paniculata_, which also modulates the rhizospheric microbial community to favor beneficial fungi [81]. Phytovolatilization  
Phytovolatilization involves the uptake of contaminants by plants, their transformation into volatile forms, and subsequent release into the atmosphere. This mechanism involves various steps: the plants first absorb the contaminants from the soil, transform the volatile or semi-volatile chemicals into more volatile forms, and then release the contaminants to the atmosphere through plant transpiration via the leaves [67; 72]. This method is particularly applicable to elements like selenium (Se), mercury (Hg) and arsenic (As) [81]. Plants such as _Brassica juncea_ and _Brassica oleraca_ have been used for the volatilization of selenium [82; 83], while _Polypogon nonspeliensis_ has been employed for arsenic [72]. Phytovoltailization can occur through direct pathways, where contaminants are absorbed and volatilized via transpiration, or indirect pathways, where root activity enhances the volatilization of subsurface contaminants [79]. Factors influencing this process include plant species, contaminant properties, and environmental conditions. For example, poplar trees (_Populus_ spp.) have been used to volatilize trichloroethylene (TCE), a common groundwater contaminant, by absorbing it through roots and releasing it as a less toxic vapor [84]. Phytofiltration  
Phytofiltration is the use of plant roots (rhizofiltration), shoots (caulofiltration), or seedlings (blastofiltration) to remove contaminants from aqueous environments [67]. In rhizofiltration, plants absorb, adsorb, and precipitate pollutants like heavy metals from water through their root systems [72; 85]. Aquatic plants such as _Eichhornia crassipes_ (water hyacinth), _Typha assuifolia_ (narrowleaf cattail) and _Salvinia natans_ have shown significant potential in removing metals like cadmium (Cd), lead (Pb) and mercury (Hg) from contaminated water bodies [86; 87]. Terrestrial plants such as _B. Juncea_ and _H. Annus_ are also popularly used for rhizofiltration due to their longer and hairy root systems. After these plants are saturated with the pollutants, they are harvested and disposed of [67].