抄録
Arsenic concentration exceeding Japanese water quality standard of 0. 01mg·l-1 was observed in the Ina-gawa river probably due to the 1995 South Hyogo earthquake. The Kinki Regional Construction Bureau performed the intensive survey for a year to ascertain the extent of this abnormal pollution shortly after the earthquake. We discussed the distribution and the increasing of arsenic on the basis of the data from this survey. Much higher concentrations of arsenic were noticed in the tributaries such as Shio-kawa and Yato-gawa rivers, and followed by the points, which directly received these inputs, in Ina-gawa river. The arsenic concentration commenced to increase around at a time of the earthquake, and reached the maximum 1 or 2 months later. Then arsenic gradually decreased in concentration with time and the tendency apparently followed first order- kinetic model. Though the Ina-gawa river showed the decrease in concentration to below the standard level 4 months later the earthquake, most observed data in the tributaries were still continued to be above 0.01mg·l-1 over the survey period. However, arsenic concentrations at each site during the latter half of the survey appeared to be the “background level” in the Ina-gawa river basin because of slower but rather constant in the decreasing rates.
