Geochemical fractionation study in combination with equilibrium based chemical speciation modelling of Cd in finer sediments provide a better description of Cd bioavailability in tropical estuarine systems

Geochemical fractionation study of cadmium (Cd) in combination with equilibrium based chemical speciation modelling (visual MINTEQ) in finer sediment samples (silt and clay portion), provided a better description of Cd bioavailability for sessile organisms (like oysters) in the Zuari estuary, west coast of India. A substantial fraction of total Cd in the finer sediment samples was present as water soluble, exchangeable and carbonate/bicarbonate forms and showed a strong positive relationship with Cd-bioaccumulation in oysters (Magallana sp.) from the study area. Cadmium bioaccumulation (ranged from 2.4-7.9 mg.kg(-1)) in soft tissues of the edible oyster was high (higher than the maximum permissible limit for human consumption) throughout the study period of one year. Equilibrium based speciation modelling suggest that sedimentary CdCl2, CdCl+ and Cd2+ were responsible for Cd bioaccumulation in the oysters. This study describes that combination of geochemical fractionation study of metals in finer sediments and equilibrium based speciation modelling can be very useful in comprehending link between sedimentary metal speciation and its bioaccumulation in sessile organisms. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The geochemical fractionation study of cadmium in finer sediment samples in the Zuari estuary on the west coast of India, combined with equilibrium-based chemical speciation modelling, provided a better understanding of cadmium bioavailability for sessile organisms like oysters. The study found a strong positive relationship between the forms of cadmium in sediment samples and cadmium bioaccumulation in oysters, suggesting a potential risk of cadmium bioaccumulation exceeding permissible limits in oysters. The results highlight the importance of combining geochemical fractionation study and equilibrium-based speciation modelling for comprehending the linkage between sedimentary metal speciation and bioaccumulation in sessile organisms.