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Article History

Received: 8 February 2018

Accepted: 4 September 2018

First Online: 10 September 2018

Compliance with ethical standards

:

: The authors declare that they have no competing interests, and neither the principal investigators nor the co-investigators have actual or potential conflict of interest.

: Ethical approval for the research was obtained from the joint research and ethics review committee of Catholic University of Health and Allied Sciences and Bugando Medical Centre (<i>CREC# 126/2016</i>). Permission to collect soil samples was sought and obtained from the respective regional, district, and village authorities according to where the sample was obtained. A written informed consent was obtained from the <i>pemba</i> vendors. For those who were illiterate, a consent form was read aloud by a member of the research team and <i>pemba</i> vendors were asked to provide a thumb print if they agreed to participate in the study.

: Not applicable.

: The data sets used and/or analyzed during the current study are available from the corresponding author on reasonable request.