台灣西南海域底棲魚體內釙-210與鉛-210活度探討

Abstract

Po-210和Pb-210皆為U-238系列中的親顆粒性放射元素，然因兩者化性不同而顯現不同生地化行為，Pb-210較親無機性顆粒，Po-210則較易與生物性顆粒結合，常被運用於海洋顆粒清除作用研究，由於Po-210可被浮游植物與浮游動物吸收並隨食物鏈傳遞而富集於高階之魚鮮中，為人類食物主要的天然輻射源。魚類位於海洋食物鏈終端，且為人類重要蛋白質來源，本研究為了探討底棲魚體Po-210及Pb-210關係，於台灣西南海域採集不同深度(67、124、255、308、391、910 m) 地點之底棲魚類樣品，計17科33種底棲魚，並測量其全魚與各器官之Po-210和Pb-210活度。 本研究結果顯示，全魚Po-210活度範圍介於2.8到94.7 dpm/g之間、Pb-210活度範圍介於0.3-8.5 dpm/g、Po-210/Pb-210比值則介於5.4至24.7之間，不同科之間Po-210與Pb-210活度皆有差異，可能與魚類生活型態相關，而不同科魚種間Pb-210活度差異和Po-210相似，但活度遠低Po-210，可見生物相較於Pb-210更傾向富集Po-210。魚體不同器官Po-210活度介於0.8到172 dpm/g之間、Pb-210活度介於ND至9.9 dpm/g，而Po-210/Pb-210比值則介於 2.5 - 52.3，其中以內臟活度最高，肌肉次之，骨骼最低。但軟骨魚的骨骼Po-210與Pb-210的活度都較肌肉為高，此差異可能是硬骨魚與軟骨魚骨骼成分差異所造成。與文獻報告浮游生物數據相比，Po-210濃縮係數(CF)於浮游動物有最大值，營養階層較高的魚類Po-210濃縮係數反而下降，可看出Po-210活度並未隨營養階層上升而變高，Pb-210濃縮係數則隨著營養階層上升而下降，於浮游植物有最大值，而各生物Po-210/Pb-210比值則有隨營養階層上升而上升的趨勢。 台灣底棲魚貢獻放射性攝取劑量約 380 mSv/year，與他國相比較高，可能是台灣每人漁獲消耗量較高，且魚體活度亦較其他地區為高所致。

Belonging to the 238U-series, Po-210 and Pb-210 are well known for their particle-reactive characteristics in marine environments. Po-210 contributes a dominant fraction of the radiation dose received by humans, which originated from the accumulation effect of ingested seafood. Fish is the final chain of aquatic food web and provides important protein source for the human being of the world. In this thesis, demersal fishes were collected from the sea off southwestern Taiwan for the determination of Pb-210 and Po-210 activities. Po-210 activity in fish samples were found to vary from 2.8 to 94.7 dpm/g dry weight and Pb-210 activity were found to vary from 0.3 to 8.5 dpm/g dry weight. The Po-210/Pb-210 ratios in the whole fish ranges from 2.5 to 52.3 and is generally greater than unity, which indicates that Po-210 is preferentially taken up by organisms compared to its progenitor Pb-210. Po-210 and Pb-210 are non-uniformly distributed within these fishes, the highest levels being found in the digestive organs whereas the lowest levels being found in the muscle and bones. Po-210 activity is higher than Pb-210 activity in both of muscle and viscera. Owing to the different component, Po-210 and Pb-210 activities in bones of chondrichthyes are higher than that in osteichthyes. There is no systemic variation found for Po-210 activity in different trophic level, however, Po-210/Pb-210 ratios tend to increase along with the food chain. The annual ingestion dose of 380 mSv/year due to Po-210 in demersal fish is estimated. The annual ingestion dose in Taiwan is higher than other studies, which may be caused by the higher consumption of fish in Taiwan and the higher Po-210 activities in demersal fishes collected from the sea off southwestern Taiwan.