Takayuki Shiozawa

Sedimentation rates and heavy metal pollution of sediments in the Seto Inland Sea

In the Suo-Nada area of the Seto Inland Sea, Japan, sedimentation rates and the sedimentary record of anthropogenic metal loads were determined by combining the Pb-210 dating technique with heavy metal analysis of the sediments. The sedimentation rates vary from 0.11 to 0.27 g cm−2 yr−1. Lower sedimentation rates were observed in the eastern part of the basin which is characterized by a bottom with sand and gravel, and fast tidal currents.Anthropogenic and natural loads of copper and zinc into the sediments are 34 and 326, and 65 and 375 ton yr−1, respectively. The anthropogenic loads are fairly low compared with those of the other main areas of sediment accumulation in the Seto Inland Sea. The highest level of zinc and copper pollution was observed in the western part of the basin because of waste discharge from an old and big ironworks outside basin since the early 1900s.

Heavy metals and accumulation rates of sediments in Osaka Bay, the Seto Inland Sea, Japan

The metal load into sediments and the change in the sedimentary environment of Osaka Bay in the Seto Inland Sea have been studied through geochemical analysis of core sediments, using both Pb-210 dating and a selective chemical leaching technique. Analytical results from a 6-m core of sediment show that copper and zinc pollution started in the late 1800s and the present enrichment ratios of copper and zinc, relative to background levels (20 mg kg−1 for Cu and 94 mg kg−1 for Zn), are 2.8 and 4.1, respectively. The present anthropogenic copper and zinc loads into Osaka Bay sediments, are 47 and 368 ton yr−1, while natural copper and zinc loads are 40 and 186 ton yr−1, respectively. Osaka Bay sediment at the present day is considered to be seriously polluted by zinc, now. The vertical profiles of copper and zinc in four successively separated fractions (10% acetic acid soluble fraction: F-HAC, 0.1M hydrochloric acid-soluble fraction: F-HCl, hydrogen peroxide-soluble fraction: F-H2O2 and hydrofluoric acid-soluble fraction: F-HF) from the core sediments indicate that enrichments of copper and zinc in the upper layer of the sediment are dependent on increases in the metal contents of the F-HAC, F-HCl and F-H2O2 fractions. Copper in F-HAC, and zinc in F-HAC and F-HCl, seem to be of anthropogenic origin.Results of sequential studies of the whole Seto Inland Sea can be summarized as follows: At the present time, the sedimentary loads of copper and zinc over the whole Seto Inland Sea area are 630 and 3,500 ton yr−1, respectively, while the natural and anthropogenic loads are 320 and 310 ton yr−1 for copper and 1,800 and 1,700 ton yr−1 for zinc, respectively.

Heavy metal pollution in sediment from the Seto Inland Sea, Japan

Abstract To discuss the geochemical and environmental behaviors of heavy metals in the Seto Inland Sea which is the largest semi-closed coastal sea in Japan, (1) distributions of heavy metals concerning pollution were examined and (2) mass balances of Zn and Cu were studied by applying a simple box model. Increase in heavy metal contents of core sediments already started in the late 1800s and is considered to be due to human activities. Recently, the pollution of sediment in Osaka Bay which is most contaminated sea area in the Sea, seems to have tended to decrease. In 1980, total sedimentary loads of Cu and Zn over the whole area of the Sea were estimated to be 630 and 3,500 tons/yr, respectively. Further, the sedimentary loads without and with human activities were estimated separately to be, respectively, 320 and 310 tons/yr for Cu and 1,800 and 1,700 tons/yr for Zn. Total inputs of Cu and Zn into the Sea were estimated to be 870 and 4,250 tons/yr and about one half of this being the results of human activities. 70% of the Cu input and 80% of the Zn input are accumulated into the sediments.

Sedimentation rate and heavy metal pollution in sediments in Harima Nada (Harima Sound), Seto Inland Sea

Sedimentation rates were determined with the210Pb technique in six sediment cores from Harima Nada (Harima Sound), Seto Inland Sea. The rate of deposition varies from 0.11 g cm−2y−1 in the northern part to 0.33 g cm−2 y−1 in the southern part of the basin. A marked increase in copper and zinc content was observed above a depth in the core corresponding to about 1900 A.D. as a result of increasing human activities. Anthropogenic input of copper and zinc decreased slightly after 1970. Natural background levels of copper and zinc in the sediment in this sound are 11–16 ppm and 100–120 ppm, respectively. The total amounts of anthropogenic copper and zinc in the sediments were estimated to be 110–180μg cm−2 and 610–1,280μg cm−2, respectively. These values constitute 40–50% of the total sedimentary input of copper and zinc in the sediments since about 1900 A.D.

Vertical distribution of particulate manganese and iron in the Beppu Bay

Around the thermocline, difference in the depth of the maximum concentration between particulate manganese and iron was observed above the basin located at the south-western corner of the Beppu Bay, along with the remarkable difference in pH and Eh.

Vertical distribution of heavy metals and its seasonal variations in Beppu Bay

From July to November, the thermocline which has strong temperature gradient (0.7‡C m−1) is formed in the bottom water of Beppu Bay, and it prevents the downward mixing of surface water. This has caused the bottom water of the basin to become depleted in oxygen, and in November the bottom water below about 60 m depth becomes anoxic. Accordingly manganese and iron are reduced and more soluble under the anoxic condition, those concentrations are high relative to surface water, and the maximums are 1,240Μg l−1 and 80Μg l−1. Under the anoxic condition, the flux of dissolved manganese from the sediment is about 10Μg cm−2 day−1.

Mass balance of heavy metals in the seto inland sea, Japan

Abstract To discuss the geochemical and environmental behavior of heavy metals in the Seto Inland Sea, the largest semi-enclosed coastal sea in Japan, mass balances of Cu and Zn were studied by application of a simple box model using sedimentation rates and heavy metal contents of core sediments. In 1980, total sedimentary loads of Cu and Zn over the whole area of the Sea were estimated to be 630 and 3500 tons year −1 , respectively. Further, the sedimentary loads without (natural) and with human activities were estimated separately to be, respectively, 320 and 310 tons year −1 for Cu and 1800 and 1700 tons year −1 for Zn. Total inputs of Cu and Zn into the Sea, in 1980 were estimated to be 870 and 4250 tons year −1 about one half of this being the result of human activities. 70% of the Cu input and 80% of the Zn input are taken into the sediments. Mean residence times of Cu and Zn in the Sea are calculated to be ≈0.3 and 0.2 years, respectively. Since these values are relatively small compared to the mean residence time of the seawater (0.9 years), Cu and Zn supplied to the Sea are considered to be accumulated rapidly in the sediments.

Seasonal cycle of manganese in seawater in Harima Sound

Vertical and horizontal distributions of manganese in Harima Sound (Harima Nada, Seto Inland Sea) were measured in August and December 1979. High concentrations of dissolved and particulate manganese were found in bottom waters in August, suggesting that the bottom enrichment is probably due to the diffusion of dissolved manganese out of the sediment.From measured distributions, we estimate the annual flux of manganese at the sediment-water interface to be more than 800 tons per year, if Harima Sound is a closed system for manganese.

Behavior of manganese in aqua-benthic environment in the Hiro Bay

The horizontal and vertical distributions of manganese in sea water, interstitial water and sediments in the Hiro Bay, Seto Inland Sea, Japan, have been investigated. The outflow from a pulp mill is the primary source of manganese in this bay. The industrial waste water contained 0.19 mg l−1 of manganese, mostly in a dissolved form. This manganese diffused out both horizontally and vertically into the surrounding sea water. The content of manganese in the liquid and solid phases in the sediments, however, are inverse with that in the sea water; namely the lowest concentration of manganese in the sediments was observed at the station near the outfall and manganese concentration increased with the distance from the outfall.

Determination of cadmium, lead and copper in interstitial water by anodic stripping voltammetry

This paper gives the results of determination of cadmium, lead and copper in interstitial water of the coastal sediment, Seto Inland Sea, Japan by using anodic stripping voltammetry.An aliquot of 4–5 ml interstitial water separated from 30–70 ml of sediment is used for the simultaneous determination of ionic cadmium, lead and copper. No significant differences were observed on the content of trace metals between surface water and interstitial water of the top of the sediment.