http://reply.papertrans.cn/1/87/8640/8640-31.png
Submitted on: 02 October 2005.
Revised on: 14 January 2006.
Accepted on: 06 March 2006.
___________________Environmental Health---BMC
http://reply.papertrans.cn/1/87/8640/8640-33.png
http://reply.papertrans.cn/1/87/8640/8640-34.png
http://reply.papertrans.cn/1/87/8640/8640-35.png
http://reply.papertrans.cn/1/87/8640/8640-36.png