# Harnessing Biotechnology for the Remediation of Organic Pollutants in Coastal Marine Ecosystems
## 4 Biotechnological Methods for Remediation
### Limitations and Challenges of Bioremediation and Phytoremediation in Marine Environments  
Environmental Constraints  
Marine environments are highly dynamic and often present extreme conditions that can hinder the process of biological remediation. The outcomes of the bioremediation can be dependent on physical variables at the site which include pH, temperature, oxygen and availability of nutrients [89]. High salinity levels can inhibit microbial metabolic activity, especially for non-halotolerant species, hence reducing the efficiency of biodegradation [90]. Likewise, changes in temperature and pH can affect the enzymatic activity of both microorganisms and plants, which in turn disrupts key metabolic pathways [91]. Furthermore, reduced oxygen levels, especially in eutrophic or hypoxic zones, create hypoxic or anoxic conditions and impact the composition and activity of microbes, limiting aerobic degradation processes, which compels the use of anaerobic or facultative microbial strains [92] that may be less efficient or slower-acting.  
Chemical factors like the quantity and type of contaminants, the presence of surfactants, and the accessibility of sources of carbon and nitrogen influence bioremediation [93]. Many organic pollutants, especially hydrophobic compounds like PAHs and PCBs, bind tightly to sediment particles due to their low water solubility and hydrophobic nature; pollutants like PAHs tightly adhere to sediments, which leads to accumulation in coastal and deep sediments [33], or are sequestered in microenvironments where microbial and plant access is restricted. This limited bioavailability severely reduces the rate and extent of degradation, even in the presence of highly capable degrading organisms. Innovative delivery systems or surfactants may be required to improve pollutant solubility and accessibility, but these additions may alter the ecosystem or require further remediation themselves.  
Potential Formation of Toxic Intermediates  
One of the under-explored risks of biological remediation is the in complete degradation of complex pollutants, which leads to the formation of toxic intermediates [94]. For example, during the microbial breakdown of PAHs or PCBs, partially oxidized products (e.g., chlorobenzates, quinones) may exhibit greater toxicity or persistence than the parent compounds. If these intermediates accumulate due to metabolic bottlenecks or unfavorable environmental conditions, they may pose additional risks to marine organisms and human health.  
Compatibility with Native Species and Ecological Balance  
The introduction of non-native microbial strains or engineered organisms through bioaugmentation or genetic modification raises concerns about potential ecological disruptions, such as the outcompeting of native microbial communities or horizontal gene transfer [95]. Similarly, the use of fast-growing plants in phytoremediation, especially invasive species like _Eichlornia cassipes_ (water hyacinth), may alter the natural balance of coastal vegetation and disrupt local biodiversity [96]. While these plants can effectively remove pollutants, they can also displace native vegetation, alter water flow, and negatively impact wildlife due to their rapid growth and spread.  
Economic and Regulatory Constraints  
Deploying biotechnological solutions in marine environments often involves significant upfront costs, especially when incorporating advanced technologies such as bioelectrochemical systems, genetically engineered microbes, or nanomaterials. Moreover, infrastructure limitations, especially in low- and middle-income coastal nations, impede long-term implementation and environmental monitoring. The regulatory frameworks for releasing GMOs or engineered systems into open marine settings remain unclear or restrictive in many regions; this poses challenges for the research and development of marine genetic engineering, limiting practical adoption despite scientific feasibility [97].