Characteristics of Concentration and Composition of Heavy Metals in Seawater, Sediment and Macroalgae, Ulva sp., in Yatsu Tidal Flat in Tokyo Bay, Japan

Macroalgae, Ulva sp., seawater and sediments in Yatsu tidal flat, Japan were examined to clarify the characteristic distributions of heavy metals and their interactions within these compartments of the ecosystem. The heavy metal concentrations were higher in fall than summer for Fe, Cu and Zn, but were constant with respect to season for Pb and Cd. The distribution of heavy metals in Ulva sp. harvested from Yatsu tidal flat was close to in Ulva sp. grown in other parts of the world with the following decreasing order of concentration of Fe>>Zn>Cu≥Pb>>Cd, but differed from that of other. Ulva spp. was considered to have an inherent characteristic ratio of heavy metals. In the sediments, heavy metal content was higher in the muddy area of the tidal flat than sandy area, while the compositions were similar for the two areas. The difference in heavy metal content would be attributed to the difference in organic matter and sediment particle size. The major heavy metal in the suspended particulate matter (SPM) in seawater was determined to be Fe followed by Zn, Pb, Cu and Cd, which exhibited a similar composition as those in the sediments. SPM was considered to be derived by tidal shear forces. Absorption of heavy metals into Ulva sp. did not depend on the seawater concentrations, but on the absorbability inherent in Ulva sp. In comparisons of Concentration Factors for heavy metals in Ulva sp., essential elements as Fe, Cu and Zn were preferentially absorbed compared to nonessential metals as Pb or Cd.