## 5 Remediation Techniques: Physical, Chemical and Biological Approaches  
Following an oil spill, natural attenuation is the first approach to control the worsening of the situation. Natural attenuation is the reduction of contaminant mass, volume, concentration, mobility and toxicity through a variety of physical, chemical and biological processes under favourable conditions without human intervention [31]. This process eliminates most of the lighter chain hydrocarbons, which is however inadequate for PAHs [32]. A long timeframe is required to remove significant level of contaminants for no external force involved to expedite the process. With very low rates of degradation achieved in the cold Antarctic environment, a broad spectrum of remediation techniques was introduced classified into physical, chemical and biological methods.  
Physical treatment effectively controls oil spills in a water environment through two main steps: containment and recovery. Equipment such as oil boomer and skimmer serve as a barrier to trap the oil and prevent it from spreading. After skimmer operation, oleophilic adsorbents are used to remove the remaining oil that can soak as much as 70 times their weight in oil depending on their material [33]. In situ burning is another method that is able to remove up to 98% of the oil spill. The oil slick on the sea surface has to be above a threshold of thickness (around 3 mm) to be possibly ignited into flame and kept under control within the polluted site. These applications are still limited to rough sea wave and high wind velocity [34].  
A chemical remediation method is more applicable as an emergency response when the sea condition is too rough for mechanical methods. Chemicals such as dispersant are sprayed over the sea surface by aircraft to enhance the mixing of oil and water into smaller oil droplets. This dispersant contains surfactant accountable for breaking up the oil slick, and aims to reduce the immediate risk to marine life. However, the chemical clean-up attempt is still controversial as it may impose a huge negative impact on benthic organisms. [PERSON] et al. [35] reported that the combination of dispersant Corexit 9500A and oil magnified the toxicity on _B. manjavacas_ by 52-fold. The research by [PERSON] et al. [36] concluded that the application of dispersants alone showed a toxic effect on copepods and nematodes and, meanwhile, the chemically dispersed oil did not impose a greater harm.  
Environmental-friendliness and cost savings are the major concerns for all remediation techniques. Bioremediation, which relies on biological mechanism to reduce (degrade,  
Figure 2: Co-occurrence network in the research field. Co-words are mapped into two major clusters implying the research themes (red: environmental monitoring; green: remediation mechanism).  
detoxify, mineralise or transform) the concentration of pollutants to an innocuous state, is adopted in the field to manage the Antarctic spill sites like Casey Station [37]. As the Antarctic Treaty forbids the importation of foreign organisms into the Antarctic, indigenous organisms proven with hydrocarbon-degrading ability play a major role in ecosystem recovery. Effective bioremediation is dependent on the features of the treatment site such as soil texture, climate variables, water availability as well as existing vegetation and terrain topology [38]. In general, bioremediation can be carried out ex situ and in situ depending on the resource availability.