Strontium (Sr) and Molybdenum (Mo)
The contents of strontium in the surface and subsurface horizons are
125.9 mg·kg–1 (Table 3). The mean worldwide
background concentration for Sr in soil is 147.9
mg·kg–1 (Kabata-Pendias 2011) and in Castilla-La
Mancha it is 380.0 mg·kg–1, although in this
Community values of up to 3384.9 mg·kg–1 have been
found in soils on gypsum or gypsum marls (Conde et al. 2008). Alcubillas
is an active agricultural area and therefore the levels determined
cannot be attributed to the use of soil amendments (e.g., phosphorus
fertilizers). Various anthropogenic activities, including the
application of fertilizers, the generation of nuclear power, and the
burning of coal to generate power, have led to increased levels of
strontium (Sr) in soil (Burger and Lichtscheidl 2019). The great
potential for the accumulation of Sr in plants and animals can pose
serious environmental and human health hazards, which include cancers
and disorders of the nervous system (Burger and Lichtscheidl 2019). The
average Sr contents in some materials commonly used in agriculture
include 80.9 mg·kg–1 in manure, 75.9
mg·kg–1 in sewage sludge, and 270.9
mg·kg–1 in industrial sludge (Munthali et al. 2015).
Phosphate fertilizers can also act as a local source of Sr contamination
in soil (Abdi et al. 2015). It is worth highlighting that all Sr
concentrations for all soil types in this study were below the
background value, thus indicating that there is no Sr pollution in the
study area.
Molybdenum is involved as a micronutrient anion in various physiological
and enzymatic processes in plants (Mishra et al. 2006) and humans
(Schwarz and Belaidi 2013). Sr is able to affect the health of plants
and animals because in high concentrations it is a potentially toxic
metal (Evans and Barabash 2010). The average Mo content in the surface
soils of Alcubillas was 0.9 mg·kg–1 and in the
subsurface soils it was 1.0 mg·kg–1 (Table 3), with a
maximum level of 1.3 mg·kg–1. In comparison to the
pedogechemical references for Castilla-La Mancha these values are lower
or similar and they are also lower than the mean background content of
Mo in surface soils as a worldwide average (1.1
mg·kg–1, Kabata-Pendias 2011).