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Geographic distribution of the sampling sites in Henan province, central China used in this study. A: Henan province (HN, shadowed areas) is located in the central part of mainland China. B: Shadowed areas are the sampling locations for the present survey. AY: Anyang; SMX: Sanmenxia; LY: Luoyang; XC: Xuchang; ZK: Zhoukou; ZMD: Zhumadian; XY: Xinyang.

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