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The biogeochemistry of selenium in Sunan grassland, Gansu, Northwest China, casts doubt on the belief that Marco Polo reported selenosis for the first time in history


In order to clarify the historic academic problem of whether or not livestock poisoning in ancient Suzhou of Northwest China, recorded by Marco Polo in 1295, was selenosis, this study deals with the biogeochemistry of selenium in Sunan County in the Hexi Corridor, which is part of ancient Suzhou in China. It was found that quite a number of farm animals had suffered from intoxication and died as a result of grazing poisonous grasses, mostly Oxytropis DC, Stellera chamaejasme, and Achnatheru inebrians. Toxic symptoms of livestock grazing on Oxytropis DC are similar to those of selenium toxicity, for instance, hair loss and hoof lesions as described by Marco Polo. Therefore, we thought that toxic grass, probably Oxytropis DC, led to the intoxication of livestock recorded by Marco Polo. Average Se concentrations in two members of this species were 0.112 ± 0.038 mg/kg for the root of Oxytropis glabra, 0.102 ± 0.027 mg/kg for the stem and leaf of Oxytropis glabra, and 0.066 ± 0.009 mg/kg for Oxytropis ochrocephala. The average soil selenium concentration was 0.205 ± 0.127 mg/kg on grassland producing Oxytropis glabra and 0.152 ± 0.024 mg/kg on grassland producing Oxytropis ochrocephala. The average Se concentration in other plants was 0.076 mg/kg in the root of Ephedra monosperma Mey, 0.029 mg/kg in the root of Rheum palmatum, 0.031 mg/kg in the root of Stellera chamaejasme, 0.037 mg/kg in Achnatherum inebrians, and 0.067 mg/kg in forage grass (Achnatherum splendens ohwi). Selenium concentrations in soils and plants in Sunan County are far less than the thresholds causing selenium toxicity in livestock. As a result, this study concludes that the livestock poisoning recorded by Marco Polo in 1295 might not have been selenosis.

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This project was supported by The National Natural Science Foundation of China (Grant No. 40473048) and The National Key Natural Science Foundation of China (Grant No. 40133010). The authors wish to thank Dr Zhao Chengzhang, Mrs Ying Cuiqin, Mr Lang Yongbin, Mrs Zhang Ailing, and the Pasturage Bureau of Sunan Yugur Autonomous County, Gansu Province, P.R.C., for excellent assistance during the fieldwork. Great thanks are due to chemical engineer Lin Hongwen at the Institute of Geochemistry, Chinese Academy of Sciences, Guiyang City, P.R.C., for his help with sample analysis. Dr Olle Selinus, Geological Survey of Sweden, is also acknowledged for helping to edit the manuscript.

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Correspondence to Baoshan Zheng.

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Shao, S., Zheng, B. The biogeochemistry of selenium in Sunan grassland, Gansu, Northwest China, casts doubt on the belief that Marco Polo reported selenosis for the first time in history. Environ Geochem Health 30, 307–314 (2008).

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  • Marco Polo
  • Sunan County
  • Selenium toxicity
  • Oxytropis DC
  • Livestock