INTERNATIONAL TOPICAL CONFERENCE ON Po AND RADIOACTIVE LEAD ISOTOPES

Description

Polonium-210 and Lead-210 in the Terrestrial environment: A historical review. Polonium-210 occurs widely in the terrestrial environment, and is as -emitter an important component of man's natural radiation background. It´s presence in deep soils and minerals may be traced to the decay of radionuclides of the 238U decay chain 234Th>234Pa>234U>230Th>226Ra> 222Rn(3.82 d) >218Po>214Po>214Bi>214Po> 210Pb(22.3 a)>210Bi(5 d) > 210Po(140d) >206Po(stable). Thus 210Pb and 210Po are present in soil and groud water and their reference maximum concentration in drinking water are 0.2 and 0.1 Bq/l respectiely. Radon-222 diffuse from soil to the athmosphere where it´s decay products attach to airborne particles. Since late 1950th observations of 210Bi/210Pb and 210Po/210Pb activity ratios have been widely used to determine the mean residence time of natural aerosols in the throposphere. The annual and seasonal variation of 210Po and 210Pb concentrations in air will be reviewed. The fallout of airborne particles results in the contamination of plants or the top soil with 210Pb, 210Bi and 210Po. Most of the natural radioactivity content in plant is 210Po as the result of the direct deposition of 222Rn daughters from atmospheric precipitation. In 1964 it was pointed out that appreciable concentration of polonium-210 occurs in tobacco that is inhaled by smoking. Since then, several investigators have studied both the sources and behavior of 210Po and 210Pb in relation to smoking, and the biological effects of these on lung tissues and other organs. The reults of those studies will be reviewed and related to other terrestrial contamination pathways. In the studies of the fallout from the athmospheric nuclear weapons tests during 1950th and 60th high activities of 137Cs was found in lichens. In the Nordic countries lichens of the cladonia family are grazed by reindeer which are consumed by man to whom by this way the radioactive fallout was transferred. Evidently the same would apply for the natural occuring 210Po and 210Pb. Mesurement of 210Po in communities of lichen (Cladonia alpestris) in central Sweden during the past 40 years seems to indicate a quite constant level of about 560  70 Bq.m-2 and a 210Pb / 210Po activity ratio of 1.0  0.1. During this period the specific actvity of 210Pb was 232 Bq/kg of stable lead but in the past, before the use of lead in petrol, it was much higher. The value recorded in Sweden in 1970 agrees very well with values recorded in Norway in 2001. Thus during the past 40 years there seems to have been a quite constant level of 210Po fallout. The food-chain: lichen-reindeer man has served as a model a terrestrial food-chain for human uptake of 210Pb / 210Po and for studying the specific activity ratio of 210Pb/Pb which will be reviewed in a historical perspective. Various terrestrial food chans contribute to various extent of 210Po intake. Western diet includes from 40 to 400 mBq of polonium-210 per day corresponding to an annual intake of about 10-100 Bq , while in Nordic populations who consune a lot of reindeer it is about 10 times higher. Uranium mining, milling and processing of ores give rise to environmental release of radionuclides belonging mainly to the uranium decay series, and originate a large amount of residues accumulated in spoil heaps and tailings piles. Mining, milling, transporting of phosphate ores, manufacturing of phosphate fertilizers and using phosphate fertilizers containing uranium are other ways in which the workers, public and the environment are exposed to enhanced natural radioactivity. In the environmental monitoring program around such mines and processing plants , uranium, radium isotopes, 210Po and 210Pb are monitored in air particulates, soil, sediment, plants, and water and biota samples. These data gives valuable informaion about seasonal and annual variations of 210Po and 210Pb fallout. The author suggest that an analysis of long term studies of the variations of 210Po/210Pb activity in the terrestrial environment ratio might be used as an indicator for the effect of climat changes.

Period	2009 Oct 25 → 2009 Oct 28
Event title	INTERNATIONAL TOPICAL CONFERENCE ON Po AND RADIOACTIVE LEAD ISOTOPES
Event type	Conference
Location	Seville, SpainShow on map