過去利用『210Pb和210Po』的放射性活度不平衡，在水體自然淨化與環境間生地化循環的探討皆著重在海洋方面，關於河流的研究可謂寥寥可數。有鑑於此，本研究利用河水中210Pb和210Po放射性活度的不平衡，推演出微量元素或汙染物於自然水體中的停留時間，清除速率和清除時間等生地化傳輸、溶解及循環機制，藉以了解其對環境研究的影響及意義。

本研究由三部份組成。(1)210Pb和210Po在雨水中放射性活度的不平衡(2)210Pb和210Po在河水中的地球化學行為(3)以210Po為示蹤劑探討顆粒活性汙染物在河水中的遷移機制。

實驗結果顯示雨水中210Po的活度介於3.5~42.0 dpm/100kg，平均10.4 dpm/100kg，210Po的活度較不受季節因素影響。比較而言210Pb的活度則呈較大時序變化，其變化範圍介於10.0~1181.0 dpm/100kg，平均192.0 dmp/100kg，並且210Pb活度在颱風期間隨降雨量增加而增加，而使210Po/210Pb比值隨颱風降雨量增加而減小。本研究顯示210Po/210Pb比值介於0.04~0.48之間，經計算在大氣中顆粒活性汙染物停留時間約為12~200 天，而210Po/210Pb比值大小與活性汙染物在大氣停留時間成正相關。

河水研究結果表明二仁溪河水中溶解相210Po的活度平均1.53 dpm/100kg，其活度遠小於雨水，說明210Po很快地被顆粒物吸附並從河水中清除。二仁溪河水中顆粒相210Po的活度是溶解相210Po活度的3~90倍，而顆粒相的210Po含量約佔總210Po含量77%，顆粒相210Pb活度是溶解相210Pb活度2.2 ~102.3倍，平均佔總210Pb含量68 %。顯然，二仁溪中210Pb和210Po是以顆粒相為主，與大洋210Pb和210Po以溶解相為主的情形正好相反(Nozaki et al.,1976)。反映了顆粒物在二仁溪中對活性汙染物遷移具決定性作用。研究還表明二仁溪溶解相210Po/210Pb的比值，介於0.45~4.87，平均1.44，證明二仁溪河水有大量過剩210Po存在。由於雨水210Po/210Pb比值大部分介於0.04~0.48之間，顯然大氣不是二仁溪河水中大量過剩210Po的主要來源。我們推測這未知來源210Po可能與二仁溪有機物汙染有關。

在雨季(春夏)時，二仁溪河水中溶解相與顆粒相均以210Po過剩為主。在乾季(秋冬)時只有接近出海口地方其210Po/210Pb比值會小於1，這是由於在乾季時缺少雨水造成河水流量顯著降低，而海水又向河水方向混合，導致所測210Po/210Pb比值與表層海水相似(即210Po/210Pb比值小於1)。利用水中固、液兩相放射性活度，我們求得顆粒活性汙染物210Po的分配係數Kd值為2.4×10^4~6.03×10^5，而210Pb的Kd值為 4×10^3~4.52×10^5。這些計算結果顯示210Pb與210Po Kd值均與總懸浮顆粒物濃度SPM(mg/kg)成反相關關係，表明顆粒活性汙染物可能以膠態形式進入河水溶解相中，使顆粒汙染物停留在水中的時間加長，即分配係數小停留時間長。

本文根據二仁溪河水溶解相與顆粒相210Pb和210Po不平衡，第一次提出河水210Po清除模型，模型計算表明二仁溪流域水體的停留時間為0.26~28.8年，平均12.8 年，同時210Po被顆粒物清除的常數介於0.003~
0.067，平均0.025，清除時間為14.8~345.7 天平均84.6天。除乾季時受海水影響的站位，或南雄橋上游的某些站位，由於210Po/210Pb比值小於或接近於平衡值，則該模型不可適用外，我們的清除模型可以合理解釋顆粒活性汙染物在河流中清除和遷移行為。

In the past, researches on the natural purification and biogeochemical cycling of contaminants in the environment that have been carried out based on 210Pb-210Po radioactive disequilibrium, all stressed on the ocean. Relatively few have been done on rivers. In this study, I investigated the 210Pb-210Po radioactive disequilibrium in river waters and based on this disequilibrium, to deduce the biogeochemical transport, dissolution, and cycling parameters of trace elements or contaminants such as residence time, scavenging rate and time, etc. The results helped understand the impacts and implications of 210Pb-210Po radioactive disequilibrium on the environmental studies.

This research is composed of three parts: (1) the 210Pb-210Po disequilibrium in rain water, (2) the geochemical behavior of 210Pb and 210Po in river water, and (3) the use of 210Po as a tracer to study the migration mechanisms of the particle-reactive pollutants in rivers.

Results showed that the activity of 210Po in rainwater ranges from 3.5~42.0 dpm/100kg, averaging ~10.4 dpm/100kg and showing insignificant seasonal variability. In contrast, the activity of 210Pb shows greater temporal changes, ranging from 10.0~1181.0 dpm/100kg, with an average of ~192.0 dmp/100kg. The activity of 210Pb increases progressively during the period of typhoon, causing the 210Po/210Pb ratio to decrease as the typhoon progresses. This research shows that the 210Po/210Pb ratio varies from 0.04~0.48. It is estimated that the residence time of particle-reactive pollutants in the atmosphere is about 12~200 days, positively correlated with the 210Po/210Pb ratios in rain water.

The measurements on river waters indicated that the activity of dissolved 210Po in Erren River averages 1.53 dpm/100kg, much smaller than in rainwater. It is suggested that 210Po was easily absorbed and removed from the solution by the riverine particles. The activity of particulate 210Po in Erren River was 3~90 times that of dissolved one, or averaging about 77% of total 210Po activity in river water. In comparison, the activity of particulate 210Pb was 2.2 ~102.3 times that of dissolved 210Pb, or ~68 % of the total 210Pb. Obviously, 210Pb and 210Po in Erren river waters were mainly carried by particulates, in contrast with those in the open oceans (Nozaki et al., 1976).
This reflected that the particulates exert an important control on the transport of the particle-active pollutants. The research also indicated that the ratio of 210Po to 210Pb in the dissolved phases ranges from 0.45~4.87, averaging 1.44, proving that a significant excess of 210Po existed in Erren River waters. Because the 210Po/210Pb ratio in rainwater is in the range of 0.04~0.48, the atomsphere is obviously not the main source of the excess 210Po in Erren River. It is inferred that this unknown source of 210Po may be related to the organic pollution in Erren River.

During the rainy season (spring and summer), the dissolved and particulate phases in the Erren river waters both contain excess 210Po. However, In the dry season (fall and winter), their 210Po/210Pb ratio in stations adjacent to the estuary changes to < 1, a ratio close to that in seawater. It is likely that during the dry season, seawater may flow into the river and mix with river waters, causing the 210Po/210Pb ratio to decrease. It is estimated from the measured 210Po and 210Pb activities in the particulate and dissolved phases that the distribution coefficient (Kd) of particle-reactive pollutant is about 2.4×10^4 ~6.03×10^5 for 210Po and 4×10^3~4.52×10^5 for 210Pb. The calculated Kd values of 210Pb and 210Po both show negative correlations with the concentration of suspended particulate matter (SPM, mg/kg). This indicated that a significant amount of particle-active pollutant may exist in river waters in the form of colloid, decreasing the Kd values and increasing the residence time of pollutants in river waters.

This study proposed for the first time a scavenging model based on the observed 210Po-210Pb disequilibria of the dissolved and particulate phases in Erren river waters. Model calculations indicated that the water resident time in the Erren River basin varies temporally, ranging from 0.26~28.8 years and averaging 12.8. The scavenging rate constant of 210Po particles was between 0.003~ 0.067 day-1, averaging 0.025 day-1 and the scavenging time were 14.8~345.7 days, averaging 84.6 days. Except for stations influenced by seawater intrusion during the dry season or some stations upstream of the Namyung Bridge, where this model is not applicable because the 210Po/210Pb ratio is smaller than or approaches to the equilibrium value, our scavenging model can reasonably explain the scavenging and transport behavior of particle-reactive pollutants in the rivers.

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