"Ecological Risk Assessment of Heavy Metals to Freshwater Benthic Macroinvertebrate Assemblages Based on Field Survey in the Hasama River Basin, Miyagi, Japan" 

Yuichi Iwasaki¹, Takashi Kagaya², Kenichi Miyamoto³, Hiroyuki Matuda¹

¹Yokohama National University
²the University of Tokyo
³National Institute of Advanced Industrial Science and Technology

SETAC North America 27th Annual Meeting 2006 (Montreal 2006/11/9)

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Abstract

Environmental standards in Japan for water quality of zinc on aquatic organisms were set in November, 2003. The standard zinc concentration in the freshwater environment is 30μg/L determined by the chronic toxicity of a mayfly Epeorus latifolium. In order to examine the validity of this standard concentration, we assessed ecological risks of heavy metals to riverine benthic macroinvertebrate assemblages by a field survey. We measured physicochemical characteristics, heavy-metal concentrations, and benthic macroinvertebrate assemblage structures at 9 riffle sites in the Hasama river basin in which the Hosokura mine (closed in 1987) was located. The range of zinc concentrations in these sites was 2-921 μg/L. Taxon richness, abundance and biomass of dominant benthic macroinvertebrate taxa were analyzed using two statistical analyses: analyses of variance and multiple linear regressions. By these analyses, we evaluated the effects of the heavy metal pollution on macroinvertebrates. Ephemeroptera and Trichoptera richness, and abundance of many taxa (29-48%) significantly decreased due to the existence of the heavy metal pollution and with increasing heavy-metal concentrations. The effects on mayflies were particularly remarkable, suggesting that Ephemeroptera contains more species sensitive to heavy metals than any other orders. On the other hand, some Diptera taxa significantly increased with heavy-metal concentrations. The results suggest that typical benthic macroinvertebrate assemblages appeared at the station where the zinc concentrations were approximately twice as much as the standard concentration.

Keywords

生態リスク，重金属