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Local Geochemical Baselines Reduce Variation Caused by the Use of Different Conservative Elements in Predicting Cu and Zn Enrichment in Agricultural Soils, Kenya

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Abstract

This study illustrates the inconsistencies that may result from using different background values and conservative elements in the calculation of enrichment factors. By using 75 soil samples collected from agricultural lands adjacent to Mau and Aberdare forests, Zn and Cu enrichments was assessed using enrichment factor. The geochemical background values used for this study were concentrations of the upper continental crust (UCC), logarithmized UCC concentrations and concentrations of elements in soils from the forested lands as the local background values. Calcium, Mn, and Fe were used as the conservative elements. In addition, Cu and Zn geoaccumulation index was determined for comparison purpose. When UCC values were applied, the average Cu enrichment was 0.24, 1.42 and 15.3 when Mn, Ca and Fe were used as the conservative elements, respectively. The average Zn enrichment was 0.6 when Mn was used, and increased to 4.53 and 31.3 Ca and Fe was used, respectively. Compared to Mn and Ca, Fe resulted to higher enrichments. Application of local background values significantly reduced variation in Zn and Cu enrichments, as the average Zn and Cu enrichments were relatively similar regardless of the conservative element used. Based on this, Zn enrichment ranged from minimal to extreme while Cu enrichment ranged from minimal to high. Cu Igeo ranged from − 1.96 to 2.49 while Zn Igeo ranged from − 2.74 to 2.11, implying that the soils ranged from not polluted to moderately polluted. Zn and Cu contamination levels in the agricultural soils was best evaluated using local geochemical baselines.

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Acknowledgements

This work was supported by Sino-Africa Joint Research Center (number: SAJC202102), Chinese Academy of Sciences and National Natural Sciences of China, (number: NSFC 31361140360) and the Chinese Academy of Science—The World Academy of Science (CAS-TWAS) presidential fellowship.

Funding

This work was supported by Sino-Africa Joint Research Center (Number: SAJC202102), Chinese Academy of Sciences and National Natural Sciences of China, (Number: NSFC 31361140360) and the Chinese Academy of Science—The World Academy of Science (CAS-TWAS) presidential fellowship.

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  1. Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan, 430074, China

    Kelvin Babu Githaiga, Samwel Maina Njuguna & Xue Yan

  2. Sino-Africa Joint Research Center, Chinese Academy of Sciences, Wuhan, 430074, China

    Kelvin Babu Githaiga, Samwel Maina Njuguna & Xue Yan

  3. University of Chinese Academy of Sciences, Beijing, 100049, China

    Kelvin Babu Githaiga & Samwel Maina Njuguna

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Project idea and proposal writing by KBG and XY; project approval and funds acquisition by XY; fieldwork and data collection by KBG and SMN; data analysis by KBG and SMN; manuscript writing by KBG; manuscript review and correction by all the authors.

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Correspondence to Xue Yan.

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Githaiga, K.B., Njuguna, S.M. & Yan, X. Local Geochemical Baselines Reduce Variation Caused by the Use of Different Conservative Elements in Predicting Cu and Zn Enrichment in Agricultural Soils, Kenya. Chemistry Africa 4, 869–880 (2021). https://doi.org/10.1007/s42250-021-00256-6

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