Abstract
The bottom sediment in the Seto Inland Sea taken in the period 1981-1985 and 1991-1994 was investigated to evaluate the change of heavy metal concentrations of the elements, Cd, Pb, Cu, Zn, and Mn. The sea area which had higher concentrations of heavy metals in the 1980's showed a decrease in some area in the 1990's. The test of the difference on average values for Cd, Pb, Zn, and Mn indicated that it was significant at the 1% or 5% level in the entire Seto Inland Sea as well as for the concentration of Cu in the Sea of Hiuchi and Osaka Bay. These results suggest that the regulation of waste water and the decrease in pollutant loadings conducted since 1970's was related to the decline of the heavy metal concentrations in the bottom sediment of the entire Seto Inland Sea. In some sea areas, however, the concentrations of heavy metals in the bottom sediments were maintained at the same level, or became worse than in the 1980's. This shows that it is necessary to make more of an effort to rehabilitate the condition of the bottom sediment
