Why are fertilizers with polonium 210 used when growing tobacco?
I'm thinking of pursuing a science fair in which I create my own fertilizer for tobacco that doesn't contain polonium or lead. However, I need more background research. Does anyone know why these fertilizers are used?
According to RADIOACTIVITY IN CHEMICAL FERTILIZERS by Milica M. Rajačić, Nataša B. Sarap, Marija M. Janković, Jelena D. Nikolić, Dragana J. Todorović and Gordana K. Pantelić at the Institute for Nuclear Sciences "Vinča", University of Belgrade, Belgrade, Serbia, and the relatively short half-life of polonium, it appears that primordial metals are the only hazard in fertilizers:
Natural radioactivity results mainly from primordial radionuclides, such as 40K and the radionuclides from the 232Th, 238U and 235U series and their decay products. Terrestrial radioactivity and exposure due to gamma radiation depend primarily on the geological conditions and appear in different quantities in the soils of each region in the world. 1 [...]
Fertilizers usually employed in the agriculture contain traces of heavy metals and relatively high concentrations of naturally occurring radionuclides. Phosphate containing fertilizers have been used worldwide to increase the quantities of the micronutrients, which are being continuously taken off from the soil due to farming activities. At the same time, the use of such fertilizers is the main anthropogenic source of the uranium input in the environment (about 73 % of the total input of uranium) 2. [...]
A total of 140 samples of different types of fertilizers were measured for their radioactivity content using gamma spectrometry technique in order to assess the implications of extended use of fertilizers on the concentrations of natural radionuclides in cultivated soil. The obtained data show that the activity concentration of naturally occurring radionuclides in fertilizer samples were 87 Bq/kg, 4860 Bq/kg and 220 Bq/kg for 226Ra, 40K and 238U, respectively, which exceeds the activity concentration in soil by an order of magnitude. As it was shown in the paper, the use of fertilizers has a negligible effect on Raeq and D in soil due to dilution of fertilizer used on the large amounts of cultivated soil. However, the long term application of these fertilizers can have the effect of an accumulation of radioactivity in soils that can be harmful for the health of farmers and consumers of the products. [...]
1: Akhtar N. Radionuclide pollution due to fertilizer use in some saline soils of the Punjab and their potential risk assessment on human health. Department of Physics Bahauddin Zakariya University Multan, Pakistan, 2006. 2: Stojanović M, Stevanović D, Milojković J, Mihajlović M, Lopičić Z, Šoštarić T. Influence of soil type and physical–chemical properties on uranium sorption and bioavailability. Water Air Soil Pollut 2012;223:135- 144.
Artificial fertilizer is cheaper than regular fertilizer that also contains long-term nutrients, but also contains Po-210:
Among all carcinogenic substances contained in tobacco smoke, Polonium 210 (Po-210), with a half-life of 138 days, is one of the most dangerous, by exerting a devastating, chronic, slow and progressive carcinogenesis activity. The main source of Po-210 in tobacco is represented by fertilizers (polyphosphates) containing radium-226 (Ra-222) which decades to plumb 210 (Pb-210). Through the thricomes Pb-210 is concentrated in the tobacco leaves, where it turns to Po-210, which at the cigarette combustion temperature (800-900 degrees C) reaches the gaseous state and it is absorbed by the micro particles released into tobacco smoke. Thus, smoke becomes radioactive in both its gaseous and corpuscular components and reaches the airways, where, particularly at the branches level and together with other substances, it exerts its carcinogenic activity, especially in those subjects with impaired respiratory mucosal clearance. The carcinogenic risk/one year lifetime of a smoker of 20 cigarettes per day is equivalent to that of undertaking 300 chest x-rays. It is calculated that Po-210 may be independently responsible of 4 lung cancers every 10,000 smokers. During cigarette's combustion, tobacco smoke is also released in the air, contributing to serious health risks for those exposed to passive smoke.
