**5. Acknowledgement**

The study of Cd indexes was supported by Grant-in-Aid no. 20580344 from the Ministry of Education, Science, Sports, and Culture, Japan. The study of the index for multiple elements was supported by River Fund in charge of the Foundation of River and Watershed Environment Management (FOREM), Japan (Nr. 22-1215-016). The pilot study of factor analysis was presented at the 35th Annual Meeting of Japanese Avian Endocrinology in Okayama Prefecture. The attendance of students at this meeting was supported by Lion Trading Co., Ltd., Tokyo, Japan.
