Distribution of Heavy Metals in the Tissues of Saunders’s Gulls in the Yellow River Delta

Abstract

Avian species, as part of the higher-order vertebrates and situated at the upper trophic levels of the food chain, are particularly vulnerable to environmental pollutants owing to their potential for bioenrichment. This physiological characteristic renders birds as sensitive indicators of ecosystem health and contaminant exposure. In this study, sampling was done in the Saunders’s Gulls nesting grounds and feeding regions in the Lijin Field of the Yellow River Delta Nature Reserve in May 2018 and April 2019. Deceased individuals of Saunders’s Gulls were collected, totaling 15 nestlings (8 females and 7 males) and 3 adult female Saunders’s Gulls. We determined the concentrations of cadmium (Cd), iron (Fe), nickel (Ni), manganese (Mn), copper (Cu), chromium (Cr), and lead (Pb) in various tissues—including the heart, sternum, muscles, kidneys, lungs, intestines, and liver—of Saunders’s Gulls across different age and sex groups. Tissues were processed by drying and grinding, hydrogen peroxide digestion, and metal concentrations in different tissues were compared using atomic absorption spectrometry. Pearson correlation analysis and principal component analysis were used to understand the effects of different metals on gulls of different ages and sexes. Our findings indicated that, on average, Fe was the most abundant metal in all tissues of Saunders’s Gulls. The content of Fe in all tissues of female Saunders’s Gull nestlings ranged from 625.919 to 1,352.175 mg/kg, and in female adult Saunders’s Gulls, the content of Fe in the tissues confined 1,167.484–2,969.771 mg/kg. Notably, Ni was the least abundant in the intestines of adult birds, ranging from 0.926 to 1.572 mg/kg. We observed higher Fe concentrations in adult birds compared with nestlings, with the liver being the primary site of Fe accumulation in both female nestlings and adults. The study revealed that different tissues of Saunders’s Gulls have varying capacities for metal accumulation, with the liver, kidneys, and muscles showing the highest levels. Additionally, we found that different age and sex groups exhibit distinct metal concentration profiles in their tissues. Juvenile gulls were more likely to accumulate metals such as Mn, Cu, and Fe, whereas adult gulls were more affected by Cr and Pb. This research contributes valuable insights into metal pollution assessment in the Yellow River Delta wetlands, aiding in the ecological monitoring and management of metal pollution in this region.