漂着 ごみ量の測定に必要な海浜ごみの砂浜からの流出による消失半減期

The amount of marine litter released from each country is reflected in the amount of beached litter originating from each corresponding country. Therefore, the monitoring results are instrumental in improving the measures to prevent the outflow of waste. However, the actual quantity washed ashore minus the quantity of outflow is the change of accumulated quantity on beach. Therefore, we measured the elimination half-life of litter items on eight beaches facing the Sea of Japan, and classified the items the beached quantity of which are possible to be measured. Consequently, it is impossible to measure the beached quantities of debris of polystyrene foam and plastic bags because of their instant transport even by weak wind. The elimination half-life of PET bottles from the beaches is about one month, because some of them contain residues or sand. Therefore the beached quantities of most of plastic bottles are considered possible to be measured by monthly monitoring. Disposable lighters and glass bottles are not affected by wind transport, and their elimination half-lives are around three months. However, it is difficult to measure the beached quantity of plate-like debris thinner than disposable lighters, because they are buried and exposed by blown sand.