Agriculture Reference
In-Depth Information
(Zielinski et al., 1997; Badruzzaman et al., 2012). Increases in the uranium content by factors
1.4-5.3 have been observed in a river receiving the run-off water of farming lands using
fertilizers (Baeza et al., 2011). In that case, the uranium contribution of run-off was higher
than other NORM industry (coal-fired power plant) located upstreams. It was also correlated
with the Mg
2+
, Ca
2+
, SO
4
2-
, and NO
3
-
content in water, which origin was the fertilizer used,
mainly NPK S (MgS) 6-10-18 S(3-36) with potassium from sulfates. The uranium association
with the run-off water can be due to its higher water-soluble fraction, about 10%, than other
naturally occurring radionuclides in that fertilizer (Baeza et al., 2011).
Another exposure pathway from the naturally occurring radionuclides is their transfer to
foodstuff, which can be consumed by humans. The uranium, radium, and thorium content in
corn, leaves, grain and wheat grown in lands using NPK fertilizer for years have been
reported similar to those grown in non-fertilized (IAEA, 2003). Phosphogypsum can also be
used as agricultural amendments of soils (about 1-2% of production), which also increased
their radioactivity content, mainly
226
Ra, from 37-54 Bq·kg
-1
to 50-479 Bq·kg
-1
of
226
Ra
(Papastafanou et al., 2006). Rice grown on soil amended with phosphogypsum and not
amended presented similar
226
Ra content, within the range 0.36-1.98 Bq·kg
-1
, leading to an
annual effective dose by ingestion about 0.86 μSv·yr
-1
(Papastafanou et al., 2006).
Fertilizers As Countermeasures for Anthropogenic Radionuclides
Fertilizers have been used as agricultural countermeasures to inhibit or at least decrease
the transfer of anthropogenic radionuclides into produces. Their use is based on the saturation
of the soil solution with the additional supply of nutrients chemically analogues to the
released radionuclides from the fertilizers (Nisbet et al., 1993). The most important
anthropogenic long-lived radionuclide released into the environment is radiocaesium (see Fig.
2), which is chemically analogue to potassium, being both alkaline elements. Radiostrontium
is the following anthropogenic radionuclide mostly released into the environment, and
chemically analogue to calcium, both alkaline earth elements.
The application of potassium based fertilizers was able to reduce the transfer of
radiocaesium to plants about 40-60% (Jacob et al., 2009; Rosén et al., 2011). There are a
great variety of fertilizers used: potash either as K
2
SO
4
(Whicker et al., 1999; Zhu et al.,
2000b) or KCl (Mocanu et al., 2001; Salt et al., 2001); and NPK type fertilizers in different
ratios (Kaunisto et al., 2002; Camps et al., 2004; Jacob et al., 2009). The application rate was
within the range 100-200 kg K·ha
-1
(Zhu et al., 2000b; Mocanu et al., 2001). Higher
application rates, 2000-2500 kg K·ha
-1
, were used in soils with low potassium content (Salt et
al., 2001; Robison et al., 2009). Regarding NPK fertilizers, maximum reduction was reported
for the NPK ratio 1:1.5:2 (Jacob et al., 2009). The reduction of the radiocaesium transfer to
plant was observed during long periods of time, 10-34 yr after fertilization (Kaunisto et al.,
2002; Robison et al., 2009; Rosén et al., 2011). These fertilizers supply additional potassium
which decreases the
137
Cs:K ratio in the soil solution (Nisbet et al., 1993; Zhu et al., 2000b).
At lower concentrations of potassium in soil solution (<10
-2
-10
-1
µM), the root uptake
mechanism is unable to distinguish between Cs
+
, Rb
+
, and K
+
(Nisbet et al., 1993; Shaw et al.,
1993; Zhu et al., 2000a). However, at higher concentrations a critical threshold was observed,
above which the root uptakes K
+
preferentially to Cs
+
. In the case of wheat, it occurred
around 20 μM (Shaw et al., 1993). The addition of potassium also had effect on other
Search WWH ::
Custom Search