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学術研究成果リスト

Detail of Grant Awarded Academic Researches

Project

Mapping of Hazardous Heavy-metal Elements in River Sediments and River Water throughout the entire Tama River system

Academic
Research
No.300
Principal
Investigator
Yasuhiro Kato
Affiliation Graduate School of Engineering, The University of Tokyo
Research
Summary

As a follow up to the Academic Research No. 283, we have carried out a field survey of the Tama River downstream from the Hamura Weir starting in July 2010, and collected 137 samples of river sediments and river water from 76 sites at the Aki River, Kita-aki River, Yozawa River, and Asa River, and the main stream of the Tama River, making the total number of samples 313 from 169 sites, counting the ones collected the previous year. We used ICP-MS and XRF to conduct chemical analyses of these samples, and have found that among the toxic heavy metal elements (Cu, Zn, As, Cd, and Pb) in river sediment samples from the entire Tama River system excluding the estuary area, the Cu and Zn in some samples exceeded the standard values for concentration in soil while the concentrations of other elements were substantially less than their standard values. However, the concentrations of most of the toxic heavy-metal elements in the river sediments were statistically significantly higher than the average values found at the upper continental crust (UCC). There is a high possibility of hydrothermal ore deposit not yet found in this area, and abnormal values of heavy-metal elements may be due to this geological environment. The Zn and As in the river water were below the water quality standard values, leading to the conclusion that there is almost no pollution by toxic heavy-metal elements in all the river streams of the Tama River. In the meantime, we have found a substantial increase in the concentrations of toxic heavy-metal elements in the estuary area. In addition to the increase in the environmental burden caused by human activities, this trend is perhaps due to agglomeration of heavy-metal elements prompted by smaller particle sizes.


 


With our academic research No. 283, we now have completed our collection and analyses of samples of river sediments and river water from 169 sites in the entire Tama River system (Taba River, Kosuge River, Okutama Lake, Nippara River, Ohtaba River, Aki River, Kita-aki River, Yozawa River, Asa River, and main stream of the Tama River). We came to know the distribution of 54 elements in river sediments and 11 elements in river water. This is an exclusive geochemical mapping with extremely high accuracy unlike any other. This highly accurate accumulation of data will make specific recommendations for environmental cleanup possible. Also, by combining data gained from our research and data on river flow rate, it would be possible to estimate the flux of 54 elements from the Tama River system to the ocean. Moreover, it is hoped that by estimating the flux of toxic heavy-metal elements caused by human activities going into the ocean, it would be possible to assess their effects on the ocean environment.

Collaborators

Koichiro Fujinaga (Graduate School of Engineering, The University of Tokyo)

Kentaro Nakamura (Japan Agency for Marine-Earth Science and Technology)

Yayoi Itabashi (Graduate School of Engineering, The University of Tokyo)

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