Enhancement of mercury depuration from cockles (Anadara Granosa) utilizing catalytic chelation technique

Abstract

Cockles, Anadara Granosa is one of the common shellfish consumed as a source of protein by the Indo-Pacific Asians including Malaysia. This bivalve is a filter-feeding mollusk and can be easily contaminated by different types of pollutants. Since the cockle’s habitat is in the estuarine sediment, its soft tissue usually accumulated with a high concentration of toxic and heavy metals such as mercury. Cockles themselves have the ability to remove toxic metals out from their soft tissues, which is called a depuration process. However, the natural depuration process is very slow and needs to be enhanced. Developing a method that can safely enhance the depuration process and remove mercury from cockles is the main concern, thus the depuration of mercury from cockles was enhanced through this study utilizing the sodium acetate (CH3COONa) as the chelating agent, and catalyzed by the heterogeneous alumina supported calcium oxide catalyst. The treatment optimization was performed by applying the response surface methodology (RSM) combining the pH ranging from 7 to 10, the dosage of the chelating agent from 400 ppm to 600 ppm, temperature from 29.5 to 37.5 °C, and time of reaction between 1, 3 and 5 hours. The cockle’s soft tissues were prepared using the nitric acid digestion method adopted from AOAC 999.10 for the analysis of mercury content using Flow Injection Mercury System (FIMS) based on cold vapor atomic absorption spectroscopy (CVAAS). The LOD and LOQ of the method were 0.028 mg/kg and 0.090 mg/kg respectively. The results obtained as statistically analyzed and it has been found that the maximum depuration achieved at ±99% of mercury removal and the mercury content in the cockle’s soft tissue could comply with the standard regulations for mercury content in food.