TY - JOUR
T1 - The protective role of dietary calcium against cadmium uptake and toxicity in freshwater fish
T2 - An Important role for the stomach
AU - Wood, Chris M.
AU - Franklin, Natasha M.
AU - Niyogi, Som
N1 - Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2006
Y1 - 2006
N2 - Waterborne cadmium causes toxicity in freshwater fish by inducing hypocalcaemia. Research on the rainbow trout (Oncorhynchus mykiss), a sensitive model species, has demonstrated that this occurs because Cd2+ ions compete with waterborne Ca2+ ions for the active branchial uptake pathway which normally ensures internal homeostasis of calcium levels. Therefore, increases in waterborne calcium concentrations (?hardness') protect against waterborne cadmium uptake and toxicity in both acute and chronic exposures. Increases in dietary calcium concentration also protect against waterborne exposure, because elevated gastrointestinal calcium uptake down-regulates the Ca2+ uptake pathway at the gills, thereby simultaneously reducing Cd2+ entry. Furthermore, dietary calcium also protects against dietborne cadmium exposure, although the physiological mechanisms appear to differ from those at the gills. Surprisingly, the principal site of this inhibitory action of dietary calcium on gastrointestinal cadmium uptake appears to be the stomach, which is also the major site of gastrointestinal calcium uptake, rather than the intestine as in mammals. These results underline the importance of considering not only water chemistry but also dietary chemistry in the environmental regulation of cadmium, and suggest that fish in the wild under chronic cadmium stress would benefit by switching to a more calcium-rich diet. While diet switching has been seen in the wild in fish under metal stress, its etiology remains unknown; to date, laboratory experiments have not been able to show that voluntary diet-switching of an adaptive nature actually occurs.
AB - Waterborne cadmium causes toxicity in freshwater fish by inducing hypocalcaemia. Research on the rainbow trout (Oncorhynchus mykiss), a sensitive model species, has demonstrated that this occurs because Cd2+ ions compete with waterborne Ca2+ ions for the active branchial uptake pathway which normally ensures internal homeostasis of calcium levels. Therefore, increases in waterborne calcium concentrations (?hardness') protect against waterborne cadmium uptake and toxicity in both acute and chronic exposures. Increases in dietary calcium concentration also protect against waterborne exposure, because elevated gastrointestinal calcium uptake down-regulates the Ca2+ uptake pathway at the gills, thereby simultaneously reducing Cd2+ entry. Furthermore, dietary calcium also protects against dietborne cadmium exposure, although the physiological mechanisms appear to differ from those at the gills. Surprisingly, the principal site of this inhibitory action of dietary calcium on gastrointestinal cadmium uptake appears to be the stomach, which is also the major site of gastrointestinal calcium uptake, rather than the intestine as in mammals. These results underline the importance of considering not only water chemistry but also dietary chemistry in the environmental regulation of cadmium, and suggest that fish in the wild under chronic cadmium stress would benefit by switching to a more calcium-rich diet. While diet switching has been seen in the wild in fish under metal stress, its etiology remains unknown; to date, laboratory experiments have not been able to show that voluntary diet-switching of an adaptive nature actually occurs.
KW - Aquatic chemistry
KW - Cadmium
KW - Calcium
KW - Fish
KW - Hardness
KW - Metal uptake
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U2 - 10.1071/EN06056
DO - 10.1071/EN06056
M3 - Article
AN - SCOPUS:33845643530
VL - 3
SP - 389
EP - 394
JO - Environmental Chemistry
JF - Environmental Chemistry
SN - 1448-2517
IS - 6
ER -