RADIOLOGICAL IMPACT OF FERTILIZERS: PRODUCTION AND USE - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 282

respectively (UNSCEAR, 2000). The most heavily contaminated areas (>3700 kBq·m -2 of
137 Cs) were located mostly within the 30 km radius around Chernobyl. However, it also
seriously affected other countries such as Finland, Sweden, Norway, Germany, and Austria,
where there were areas in which about 40-185 kBq·m -2 of 137 Cs were deposited (UNSCEAR,
2000). The importance of the Fukushima deposition in Europe was lower than the Chernobyl
one (Masson et al., 2011).

I NDUSTRIAL P RODUCTION OF F ERTILIZERS

Radioactivity in Raw Material
The industrial production of fertilizers is mainly based on the processing of phosphate
rock in order to produce phosphate based fertilizers. The phosphate rock reserves are located
in different countries worldwide. Table 1 shows the content of some naturally occurring
radionuclides from the uranium ( 238 U, 234 U, 230 Th, 226 Ra, 210 Pb, and 210 Po) and thorium series
( 232 Th and 228 Ra), and 40 K in phosphate rocks in different countries. The 238 U content in
phosphate rock presents the highest activity level and a great variation range, within 10 -
13745 Bq·kg -1 . The 232 Th content in phosphate rocks was usually lower than that of 238 U,
within a range 0.8 - 753 Bq·kg -1 . The 40 K content was the lowest, within the range 1.4 - 360
Bq·kg -1 . The radionuclides immediately following 238 U ( 234 U and 230 Th) usually show similar
activity levels than 238 U, suggesting that they are close to secular equilibrium in the phosphate
rock. The 226 Ra was not necessarily in secular equilibrium with its predecessor, 238 U, in all
phosphate rocks, being the ratio 226 Ra/ 238 U within the range 0.6-2.0 (Papastefanou et al.,
2001). The 210 Pb and 210 Pb were usually in secular equilibrium with 226 Ra. Table 1 does not
fully show the degree of equilibrium because not all descendants are systematically
determined in every paper.
The great worldwide range of uranium in phosphate rocks, about four orders of
magnitude, can be attributed to the different origin of phosphate rocks used, which can be
classified in: i) volcanic/igneous origin; ii) sedimentary origin; and iii) biological origin, the
accumulated droppings of marine birds, which generated deposits of guano. The uranium
content in sedimentary phosphate rocks are higher than those of volcanic/igneous origin
(Papastefanou et al., 2001; IAEA, 2003; Righi et al., 2005; Falk et al., 2006). Table 2 shows
the range of 238 U, 226 Ra, and 232 Th reported for phosphate rocks in which their origin was
specified. The 226 Ra in sedimentary phosphate was higher than in volcanic ones due to the
higher content of 238 U. The content of 232 Th in sedimentary rocks was also higher in volcanic
phosphate rock. The enhanced uranium content in sedimentary ores can be attributed to the
ionic substitution of calcium by uranium into carbonate and apatite crystals -

Ca 5 (PO 4 ) 3 (F,Cl,OH)-, or by its direct absorption (Rutherford et al., 1994; IAEA 2003).
Other raw materials also used as fertilizers are known as potash. The term potash
comprises various salts containing potassium in water-soluble form: KCl, K 2 SO 4 , K 2 CO 3 , and
other potassium compounds. Due to their high potassium content, the main naturally
occurring radionuclide is 40 K, which is 0.012% of stable potassium content.