Accumulation properties of inorganic mercury and organic mercuryin the red-crownedcrane Grus japonensis in east Hokkaido, Japan

Abstract

The red-crowned (Japanese) crane Grus japonensis is native to east Hokkaido, Japan, in contrast to the East Asia mainland. Previously, we reported that red-crowned cranes in Hokkaido were highly contaminated with mercury in the 1990s and that the contamination rapidly decreased to a moderate level in the 2000s. In the present study, we determined levels of organic mercury (O–Hg) in the liver and kidney of cranes in east Hokkaido in comparison with levels of total mercury (T–Hg). T–Hg levels in the kidneys were higher than those in the livers in adults but not in subadults and juveniles; however, the reverse was the case for O–Hg even for adults. The ratio of O–Hg to T–Hg in both the liver and kidney decreased as T–Hg increased in the three developmental stages. While the ratios of O–Hg to T–Hg in the liver and kidney of adults were significantly lower than those of juveniles, the ratios were similar for adults and juveniles in a lower range of T–Hg. The ratio of selenium (Se) to T–Hg decreased as T–Hg increased in both the liver and kidney, irrespective of stages. Mercury burdens in feathers were about 59% and 67% of the total body burdens for juveniles and adults, respectively. Furthermore, ratios of carbon and nitrogen stable isotopes to T–Hg varied greatly, with no relation to mercury level in the liver. The results suggest slow accumulation of inorganic mercury in the kidney of red-crowned cranes in east Hokkaido, Japan