As the most recognizable natural secondary carotenoid astaxanthin producer, the green microalga Haematococcus pluvialis cultivation is performed via a two-stage process. The first is dedicated to biomass accumulation under growth-favoring conditions (green stage), and the second stage is for astaxanthin evolution under various stress conditions (red stage). This mini-review discusses the further improvement made on astaxanthin production by providing an overview of recent works on H. pluvialis, including the valuable ideas for bioprocess optimization on cell growth, and the current stress-exerting strategies for astaxanthin pigment production. The effects of nutrient constituents, especially nitrogen and carbon sources, and illumination intensity are emphasized during the green stage. On the other hand, the significance of the nitrogen depletion strategy and other exogenous factors comprising salinity, illumination, and temperature are considered for the astaxanthin inducement during the red stage. In short, any factor that interferes with the cellular processes that limit the growth or photosynthesis in the green stage could trigger the encystment process and astaxanthin formation during the red stage. This review provides an insight regarding the parameters involved in bioprocess optimization for high-value astaxanthin biosynthesis from H. pluvialis.

Several rivers around Gua Musang had been suspected as polluted area due to waste discharge from ore mining and palm oil factories located near the rivers. However, more evidence is needed to support the statement. Therefore, this study had been carried out to determine the water quality of Aring, Lebir and Relai Rivers at Gua Musang, Kelantan via its physiochemical parameters. Elemental concentrations of Fe, Al, Mn, Zn and Pb were determined in both water samples and sediment cores collected from Aring, Lebir and Relai Rivers to evaluate the accumulation trend of the heavy metal. The pollution level of heavy metals in Aring, Lebir and Relai Rivers were then investigated by using geo-accumulation index. The heavy metals of sediment were analysed by Atomic Absorption Spectrometer (AAS) after being digested by an acid mixture of HNO3/HCL (1:3; v/v). This study shows that Aring, Lebir and Relai Rivers need to treated before direct consumption. The horizontal spatial distribution of heavy metals in water and sediment suggests that the rivers were contaminated with Mn, Fe, Al and Zn. Although Aring Rivers shows the highest concentration of Mn in both water and surface sediment, the inconsistent trend of vertical profiling of heavy metals through sediment cores shows Lebir River has the highest Fe, Pb, Zn and Al geoaccumulation while Relai River has the highest Mn geoaccumulation.

Industrial and sand mining activities have severely degraded the water quality of the Kelantan River, as well as the river ecosystem. However, there have been inadequate studies on the effect of industrial and sand mining on organisms in the Kelantan River. Therefore, this study assessed the concentrations of Pb, Cd, Zn and Cu in the bivalves of genus (Polymesoda expansa) marsh clams from the Kelantan River tributaries, namely the Geting River and the Semarak River, which are located near to an industrial and a sand mining area, respectively. More than 50 marsh clams were collected at these sites. Heavy metals in marsh clams were extracted using aqua regia methods and analyzed using a Flame Atomic Absorption Spectrometer (FAAS). The mean concentrations of Pb, Cd, Zn and Cu at the Semarak River were 4.61, 2.16, 194 and 6.20 mg/kg, respectively. Accordingly, the concentrations at the Geting River were 4.43, 2.50, 196 and 7.90 mg/kg, respectively. The pattern of metal concentrations within the whole tissue of marsh clams from the Geting River and the Semarak River were in the following order: Zn > Cu > Pb > Cd (concentration in mg/kg). The mean concentration of selected metals (Zn, Cd, Pb) in the studied samples exceeded the permissible limit set by the Malaysia Food Safety and Food Regulation 1985, the Food and Agricultural Organization, the World Health Organization, the Ministry of Health Thailand, and the Food and Drug Administration of United States (USFDA). Therefore, continuous monitoring of these bioindicators is essential to minimize the increasing health risk for aquatic life, as well as in food sources for human consumption, in the Kelantan River Basin. HIGHLIGHTS Heavy metals in Marsh Clam (Polymesoda expansa) tissues shows higher concentration in  the small and medium sizes compare to big size The concentration of heavy metals (Zn, Cd and Pb) in Marsh Clam (Polymesoda expansa) tissues have exceeded the permissible limit set by  Food and Drug Administration of United States (USFDA) and Malaysia Food Safety and Food Regulation Monitoring of heavy metals in aquatic organisms especially near to industrial and sand mining areas should be conducted regularly to reduce the risk to human health GRAPHICAL ABSTRACT

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