The excessive enrichment of trace elements in migratory and breeding red-crowned cranes (Grus japonensis) in China

Abstract

The excessive enrichment of trace elements, such as Pb and Cd, from food may contribute to the decline of migratory red-crowned cranes (Grus japonensis) in China. To test this prediction, we determined the concentrations of Pb and Cd, as well as further macro and trace elements (Ca, Mg, Cu, Zn) in the target species and their prey (sediment, reed root, mollusk, arthropods, and common fish species) in both the wintering (Yancheng wetland) and breeding sites (Zhalong wetland) of cranes in China. The maximum concentrations of Pb (130 mg kg⁻¹ dry weight (dw)) and Cd (10.60 mg kg⁻¹ dw) in the sediments of breeding site and the maximum concentration of Cd (4.50 mg kg⁻¹ dw) in the sediments of wintering site exceeded the probable effect level values (91.30 mg kg⁻¹ for Pb and 3.53 mg kg⁻¹for Cd), suggesting the potential exposure risk of the examined species. Indeed, Pb and Cd contents of essential foods, i.e., aquatic animals, sampled in two sites were above the limit of allowable concentration recommended by the Joint Food and Agriculture Organization of the United Nations/World Health Organization food standards program. Approximately 80, 31.4, and 60.3 mg kg⁻¹ dw of Pb were detected in the eggshells, liver, and kidney, respectively, of the target species, and the values are above the levels of concern (1.7 mg kg⁻¹ for eggshell and 30 mg kg⁻¹ for liver and kidney) in common birds. Nevertheless, the increased Pb and Cd levels in the prey and bodies of the red-crowned cranes did not induce the levels of Ca and Mg depletion. Average contents of the macronutrients, Ca (1.38 g kg⁻¹ dw) and Mg (1.32 g kg⁻¹ dw), in the liver of the examined species exceeded the background concentrations (0.2–0.4 g kg⁻¹ for Ca and 0.4–0.8 g kg⁻¹ for Mg) in the liver of birds. Consumption of Ca-rich foods, e.g., grits and exoskeleton species, may aid in compensating the possible loss caused by the increased Pb and Cd concentrations in the bodies of the cranes.