Evaluation of discrimination factor in crab (Scyalla serrata) for 90Sr, in the ambient environment of Mumbai Harbour bay

Understanding the mechanisms by which radionuclides are cycled in marine foodchain is essential for predicting concentrations in harvestable seafood, evaluating the role of organisms in redistributing radionuclides, and assessing radiation dose to population. In the present study the discrimination factor (DF) of 90Sr, in various size groups of crab were evaluated. The DF directly relates the impact of 40Ca(stable), which is a chemical analogue of 90Sr (radioactive) and 88Sr (stable) on the bio-accumulation of 90Sr in edible and non-edible parts of crab. Around 96 crabs were harvested from Mumbai Harbour Bay. These crabs were grouped into five groups according to their carapace widths (5.0-5.5 cm, 6.5-7.5 cm, 8.0 cm, 8.5-9.0 cm and 9.5-10.0 cm). Samples were dissected and edible and non edible portions were segregated and analysed for 90Sr and stable 40Ca and 88Sr. The measurement of 90Sr was done on low background gas flow counting system after radiochemical separation. The measurement of stable Sr and Ca was done by Atomic Absorption Spectrometer (AAS) after complete destruction of matrix (Flesh and shell) by wet digestion. The concentration of 90Sr, 88Sr (stable) and 40Ca(stable) is always higher in case of shell compared to flesh. The shell to flesh ratio in all size groups except 9.1-10.0 cm.(largest) of crab shows similar trend for 90Sr, 88Sr and 40Ca. The discrimination factor (DF) for 90Sr and stable strontium (88Sr) were computed w.r.t. stable calcium (40Ca). The DF for 90Sr varies between 93-428 in flesh while in shell 4.67-15.16 whereas for stable 88Sr DF varies between 1.75-7.74 and 0.34-0.59 for flesh and shell respectively. (author)