Blooming of blue-green algae (Microcystis sp.) that produce toxic substances,microcystins, in the reservoir of the reclaimed land in Isahaya Bay (Kyushu Japan) and accumulation of the toxic substance in the sediment and aquatic animals II.-- Deposition, d

摘要

An artificial reservoir was completed in Isahaya Bay (Kyushu, Japan) in April 1997, when reclamation construction started by blocking the head of Isahaya Bay with a 7-km dike. This enclosed 3550 ha, including a 2900-ha tidal flat. In the 2600-ha 2-m-deep reservoir, Microcystis sp. blooms have occurred almost every summer/autumn. During a bloom, the concentration of microcystins (MCs) in the lake water sometimes exceeds 10 parts per billion (ppb), and that of the pore water in the sediments is roughly one order of magnitude greater than that of the lake water. These MCs in the pore water remain throughout the non-bloom season, and when the lake water is drained, they are dredged up with the sediments and discharged into the sea. A level of 2.4 μg MCs/g-ww was detected in the livers of mullet living in the reservoir. Oysters collected near the outlet of the drain gate contained about 0.5 μg MCs/g-ww. If these MCs are MC-LR, these concentrations are one to several grams greater than the tolerable daily intake (TDI) of MC-LR for a 60-kg human. In addition, low MC concentrations are detected in the pore water of sediments over a wide range of the Ariake Bay. The only way to avoid the risk of MCs is to introduce seawater via the drain gate, to raise the salinity of the reservoir. (222 words)