放射性核素^(95)Zr在水生态系中的输运

Migration and distribution of radioactive nuclide Zirconium-95 in the aquatic ecosystem

采用模拟污染物的同位素示踪技术研究了95Zr在水生态系中的迁移、消长和分配动态,并应用库室模型确定了各体系的拟合方程。结果表明:95Zr进入水中后,在水生态系中发生沉淀或与其他离子进行络合或被水生生物吸收或被吸附等形式在系统中迁移和转化,从而在系统各部分中分配和积累。在引入后的很短时间内,池水中95Zr的比活度迅速降至一定值后缓慢下降;底泥通过与95Zr进行离子交换,富集了大量的95Zr;水葫芦(凤眼莲)也可在短期内吸附大量的95Zr;螺蛳(环棱螺)和鲫鱼(鲫)对95Zr的吸附能力较弱,螺蛳肉中95Zr的富集率大于在壳中的富集率,95Zr在鱼体内的分布主要集中在内脏中。95Zr在系统各部分的量均受时间的影响。

The dynamics of transportation, accumulation, diminishing and distribution of 95^Zr in a simulated aquatic ecosystem was studied by isotope-tracer technique, and the fitting equation was established by application of a closed fivecompartment model. The results showed that when 95^Zr was introduced into aquatic system, it was transported and transformed via depositing, complex with other ions, adsorption and absorption by aquatic living organisms, resulted in redistribution and accumulation in part of the organisms. After introduction, the specific activity of 95^Zr in the water decreased sharply to a certain value in a short time and then decreased slowly. The sediment accumulated a large amount of 95^Zr by ion exchange. The water hyacinth （Eichhornia crassipes） could also adsorb a large amount of 95^Zr in a short period of time. Snail （BeUamya purificata） and fish （ Carassius Auratus） had a poor capacity of adsorbing 95^Zr. The amount of 95^Zr in the snail flesh was greater than that in the shell, and the distribution of 95^Zr in the fish was found mainly in the viscera. The amount of 95^Zr in individual compartment of the system was affected with time. Three glass tanks with dimensions of 60cm 40cm 50cm were constructed. 8kg of paddy soil on powdery loam was filled into each pool. The tanks were flooded with 601 water. 10 ml of 95^ZrF4 with a specific activity of 4.32 × 10^5 Bq/ml was introduced into the water after one week. The water was stirred gently to get a homogeneous distribution of radionuclide. The radionuclide specific activity in water was 72.00Bq/ml. Fifteen water hyacinth （Eichhorma corssipes （Mart） Solms）, and 30 snails （Bellamya purificata ） and 15 fish （Carassius anratus ）were put into each tank. Water was added with intervals of 3 days in order to maintain a constant height of water. The samples were collected at time interval of 1,2, random collected from each pool, and disposable plastic 4, 6, 9, 15, 22, 29 and 34 days. Four 5ml aliquots of water were cups were filled with them （20ml） for activity measurements. A fish was taken from each tank. The fish was divided into fin, viscera, liver, gill, skin, flesh, bone, head and roe, and each part was weighed. They were then cut into smaller pieces. Twenty gram samples from each part were put into the disposable plastic cups for measurements. In the meantime column was sectioned samples were put into , two sediment columns were collected from each tank using a sediment sampler. Each sediment into two equal parts, and each part was smashed and mixed thoroughly. Afterwards 20g of sediment plastic cups for measurements. Every sample had 3 replications. The 95^Zr emits 13 and γparticles when it decays. Those were measured with a multi-channel γspectrometer （ model BH 1224, Beijing Nuclear Instrumentation Factory）. The counting error was controlled to be lower than 5%. The counts was calibrated with counting efficiency, diminish time, disintegration and other factors. The resuhs showed that the specific activity of 95^Zr in water decreased rapidly with time due to precipitation, adsorption to sediment and uptake by water calabashes, and snails and fishes. Most of 95 Zr in sediment was found concentrated in the surface layer. It was indicated that 95^Zr in water could not readily move downwards with percolating water before remained in surface sediment. The specific activity of 95^Zr in different parts of organisms in orders of root 〉 leaf in water hyacinth and flesh 〉 shell in the snails. The organ uptaking and adsorbing 95^Zr was mainly of intestines and stomach （viscera）. 95^Zr absorbed by gill and fin was though a direct contact with water. The specific activity of 95^Zr in flesh, bone, liver and eggs was relatively lower, which were only a little higher than the background level. It was indicated that 95^Zr remained in intestines, stomach, gill and fin could not readily transport to inner organ such as flesh, bone, liver and eggs. The specific activity of 95^Zr in different parts of fish was arranged in order of viscera 〉 gill 〉 fin 〉 skin, fish scale 〉 bone, head, eggs 〉 flesh. A closed five-compartment system model was applied to imitate the experimental data. For dynamics of specific activity in whole water, sediment, water hyacinth, snails, and fishes, it could be described with the following exponential regression equations respectively, the specific activity of water C1 = 654. 3447e^-2. 2147t ＋ 0. 3285e^-006690t ＋ 0. 1119e^-0.0129t ＋ 0. 1099e^-0.1845t, ＋ 0. 0006e^-0.3378t, and sediment C2 = 85. 7971e^-2.2147t ＋ 1. 6024e^-006690t ＋ 91. 8122e^-0.0129t ＋ 2. 9428e^-0.1848t ＋ 0. 3845e^-0.3378t, and water hyacinth C3 = （118995. 7705e^-2.2147t ＋ 119516. 3543e^-0.66904 ＋ 682. 5725e^-0.129t ＋ 656. 1561e^-0.1348t ＋ 5. 3418e^-0.3378t）/m3（t）, and snail C4 = （10198. 6263e^-22147t ＋ 304. 2514e^-0.6690t ＋ 679. 3532e^-0.0129t ＋ 155. 6352e^-0. 1848, ＋ 9201. 0370e^-0. 3378t）/m4（t） , and fishC5 = （213794. 5841e^-2 2147t ＋ 4717. 3065e^-0.6690t ＋ 6210. 0565e^-0.0129t ＋212256. 7591e^-0.1848t ＋ 23. 4206e^-0.3378t）/m5（t） were gained. The ANOVA showed that each regression equation can described the dynamics of accumulation and diminishment of 95^Zr in the aquatic ecosystem preferably.