Why are fertilizers with polonium 210 used when growing tobacco?
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.