Funding for this research was provided by:
Research on Migration/Transformation and Safety Threshold of Heavy Metals in Farmland Systems (2016YFD0800400)
Text and Data Mining valid from 2019-12-02
Received: 27 June 2019
Accepted: 16 October 2019
First Online: 2 December 2019
Compliance with ethical standards
: The authors declare that they have no conflict of interest.