Abstract
High concentrations of cadmium in brown crab are an issue of food safety, and large variations between different areas have been found. To investigate the relative importance of dietary and aqueous uptake regarding the overall accumulation in brown crab, we used stable isotopes to trace the uptake from both routes simultaneously in the same animals. We demonstrated that the analytical challenges regarding background concentrations of natural isotope distribution and polyatomic interferences in the different matrices can be overcome with an appropriate analytical setup and modern mathematical corrections using a computer software. Cadmium was accumulated via both routes and was found in all measured organs at the end of the exposure phase. The obtained data were used to establish accumulation curves for both uptake routes and estimate accumulation parameters for hepatopancreas, as the most important organ in crab regarding total cadmium body burden. Using the estimated parameters in combination with naturally relevant cadmium concentrations in seawater and diet in a model, allowed us to predict the relative importance of the aqueous and dietary uptake route to the total hepatopancreas burden. According to the prediction, the dietary route is the main route of uptake in brown crab with a minimum of 98% of the accumulated cadmium in hepatopancreas originating from diet. Future studies addressing the source and accumulation of cadmium in crab should therefore focus on the uptake from feed and factors connected to foraging.
Highlights
The brown crab (Cancer pagurus) is an appreciated seafood species with an increasing value and a global catch of about 50 000 t (FAO, 2018) with about 5 000 tons harvested in Norway in 2016 (Søvik et al, 2017)
As the binding capacity for Cd ions in MT is limited, expression is induced at a certain exposure level (Pedersen et al, 2014) and overload could lead to an interaction of the different uptake routes
Low and environmentally relevant concentrations were used in seawater (0.5 μg 106Cd/L) and feed (1 mg 108Cd/kg wet weight) and the background Cd concentrations in the wild-caught crabs were high and strongly varying, it was possible to reliably detect and quantify even low contributions of Cd from both uptake routes in all measured tissues except claw meat (Fig. 2)
Summary
The brown crab (Cancer pagurus) is an appreciated seafood species with an increasing value and a global catch of about 50 000 t (FAO, 2018) with about 5 000 tons harvested in Norway in 2016 (Søvik et al, 2017). The uptake of metals in crab can occur via two different routes: from water over the gills, or via the dietary route from ingested diet. The importance of these routes regarding the overall metal concentration at steady-state can be determined using a kinetic model when assimilation efficiency, ingestion rate, and unidirectional uptake and elimination rate constants are known for the species in question (Luoma & Rainbow, 2005; Wang et al, 1996). Strady et al (2011) have further shown the potential of using stable isotopes to simultaneously trace aqueous and dietary uptake in the same animals in the case of oysters. As the binding capacity for Cd ions in MT is limited, expression is induced at a certain exposure level (Pedersen et al, 2014) and overload could lead to an interaction of the different uptake routes
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