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the phosphogypsum stacks was within the range (0.082-2.5) mSv/y (Rutherford et al., 1994;
Mas et al., 2006; Al-Altar et al., 2011). This range of variation reflects the range of
226
Ra in
phosphogypsum, 9.1-3219 Bq·kg
-1
(see Table 3). The external exposition exposures reported
can surpass the limit of 1 mSv·yr
-1
for general population (EC, 1996), and therefore they are
usually monitored, and changes in the working conditions are introduced, such as the
reduction time allowed to remain in a given location. The external exposure can also be
minimized by the construction of protection zones around the stacks, and the use of trees
around to form wind barriers (Mas et al., 2006; Al-Altar et al., 2011). The effective dose in a
Spanish fertilizer industry, corrected by occupational factor, was 1.6 mSv·yr
-1
, lower than
previously found (2.15-2.5 mSv/y) due to the additional shielding of the water circulation
system (Mas et al., 2006).
The dust generated by wind erosion of the stacks was not supposed to be a serious
problem in temperate environments, because a crust is usually developed on top of them
(Rutherford et al., 1994). However, in other dryer climates with high wind speeds, with
maximums over 100 km/h, the surface soil (0-20 cm) surrounding the phosphogypsum stacks
presented higher content of naturally occurring radionuclides in the predominant wind
direction than in deeper soil (20-40 cm) (Al-Altar et al., 2011), implying that phosphogypsum
particles were resuspended and deposited on surface soil.
The presence of enhanced
226
Ra content in phosphogypsum turns it into a source of
radon, which is it decay product. The radon exhalation rates from <0.004-3.6 Bq·m
-2
·s
-1
(Rutherford et al., 1994; Dueñas et al., 2007). The exhalation coefficient depends on the
porosity, density, moisture level, temperature, and
226
Ra content of the phosphogypsum stack
(Dueñas et al., 2007; Lee et al., 2012). Cracks on the phosphogypsum crust also enhance the
radon exhalation (Rutherford et al., 1994). As the phosphogypsum stacks are usually located
outdoors, the radon accumulation close to them would not probably be high, about 1.1-15
Bq·m
-3
while in open ground was about 3.7-5 Bq·m
-3
(Rutherford et al., 1994). However, it
can pose a risk when houses or other closed buildings are built on reclaimed phosphogypsum
stacks, so radon can accumulate indoors (Papastefanou et al., 2006). The exhalation rate can
be reduced by the soil covering used for the stack restoration. Using a soil layer of 25 cm
decreased the exhalation from the range 0.042-0.500 Bq·m
-2
·s
-1
for unrestored sites to 0.011-
0.339 Bq·m
-2
·s
-1
for restored ones (Dueñas et al., 2007). Structures built on reclaimed
phosphate land presented a radon concentration within the range 4-500 Bq·m
-3
, with a
weighted average of 40 Bq·m
-3
(UNSCEAR, 1988). About 5% of the phosphogypsum
production is used a building material in the manufacture of cement, wallboards and plaster
(UNSCEAR, 1998). Due to its high
226
Ra content, it can be a source of indoor radon, and is
banned (IAEA, 2003).
Before the banning of direct offshore discharges (OSPAR, 1996), about 20% of the
phosphogypsum generated in a Spanish fertilizers industry (Absi et al., 2004) and about 2 ton
per year in the Netherlands (Köster et al., 1995) were discharged in aquatic ecosystems.
However, there is a high degree of uncertainty about the quantity of NORM discharges
because they were not always reported (Betti et al., 2004). These discharges had a significant
radiological impact on the ecosystems. They increased the naturally occurring radionulide
content in water and sediments close to the evacuation points (Köster et al., 1985; Martínez-
Aguirre et al., 1994; Köster et al., 1995). The particulate matter in suspension in water also
contained fine particles of phosphogypsum, enriched in
226
Ra and
210
Po, within the ranges
830-2460 Bq·kg
-1
and 1048-1524 Bq·kg
-1
respectively (Bolívar et al., 1996). The impact was
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