## 4 Research Focus and Trend
According to the thesis published by [PERSON] [10] that examined the chemical behaviour, composition and toxicity of WAF, SAB has the highest magnitude of acute toxicity on marine organisms, whereas MGO and IFO 180 are generally more toxic than SAB upon longer exposure due to their higher proportion of high molecular weight PAHs. Aromatic hydrocarbons are more water-soluble than saturated alkanes of similar molecular weight, hence are regarded as major toxicity agents. Monocyclic aromatic hydrocarbons including benzene, toluene, ethyl benzene and xylene (BTEX) are the most water-soluble, therefore easing the migration and dispersion in the environment and cells [24]. In temperate regions, BTEX is highly volatile but the low Antarctic temperature exacerbates surface evaporation in polluted sites. The molecular diffusion of BTEX is greatly reduced, causing the contact time with water to be relatively longer. Ultimately, the ratio of dissolved to evaporated hydrocarbons increases, which \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Keyword** & **No. of** & **Co-Word** & **No. of** \\  & **Article** & & **Article** \\ \hline Soil pollution & 98 & hydrocarbons & 66 \\ Biodegradation & 92 & soil pollution & 60 \\ Bioremediation & 87 & bioremediation & 56 \\ Hydrocarbon & 81 & oil spill & 50 \\ Environmental monitoring & 63 & biodegradation & 44 \\ Oil spill & 62 & environmental monitoring & 42 \\ Toxicity & 36 & controlled study & 34 \\ Bacterium & 34 & bacteria (microorganism) & 32 \\ Controlled study & 34 & chemistry & 30 \\ Soil & 34 & toxicity & 27 \\ Polycyclic aromatic hydrocarbon & 31 & concentration (composition) & 26 \\ (PAH) & 31 & sediment & 26 \\ Water pollutant & 31 & sediment & 26 \\ Chemistry & 30 & water pollutants, chemical & 26 \\ Sediment & 29 & PAH & 24 \\ Concentration (composition) & 26 & animals & 22 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Descriptive analysis: top 15 most frequent keywords and co-words in descending order. imposes a huge threat to the Antarctic aquatic life [10]. Meanwhile, PAHs of higher molecular weight have lesser acute toxicity due to their lower solubility, but their persistence is much greater than that of lighter fractions. PAHs are lipophilic, which enhances the adsorption to organic matter and they tend to bio-accumulate in lipid tissue of organism leading to chronic effects [25]. The study of [PERSON] and [PERSON] [26] reported the narcosis effect of PAHs in which toxicity could be photoenhanced upon ultraviolet radiation on cellular tissues. Environmental monitoring in Antarctic research covers a diverse range of toxicology studies on marine organisms, invertebrates, birds and plants. Local mortality of intertidal marine invertebrates and long-term impact on bird population have been reported on most oil spill incidents. The acute and chronic exposure and sublethal effect on mortality, growth and reproduction of meirofauna communities have been investigated in field [27; 28] and laboratory tests [29]. Toxicity responses of these organisms towards hydrocarbon compounds are species-specific, which can also correspond to their life stages. [PERSON] et al. [28] reported on the differences in Antarctic nematodes and copepods abundance upon diesel treatment in a five-year field experiment at Casey Station, East Antarctica. Nematodes were seen to be more sensitive to hydrocarbons compared to copepods, showing a sharp decline in abundance in the early stage. Nevertheless, both meirofaunal organisms were negatively impacted by the effect of hydrocarbon and were likely to persist for more than five years or show little recovery in community structure. The toxicity of hydrocarbon on plants can be observed through morphological characteristics such as germination, root and shoot growth, photosynthetic efficiency and chlorophyll content. Hydrocarbon contamination induces inhibitory effect on plant early life cycle that results in delayed germination as well as slow root and shoot growth rate [27; 21].