105
performed, even though it’s well known that the cultivation of organic soils is an
important human exposure pathway of trace elements and radionuclides (Saetre
et al. 2013). It’s essential and necessary thus to understand the differences on the
accumulation of U by the different plants, especially considering the edible portions
of the vegetables, since data on the element concentrations might be very useful for
radiological risk assessments (Staven et al. 2003) and for predicting the fate of the
contaminants in the environment and in the food chain (Willey 2014). Thus, mechanisms controlling the TF of U in tropical regions are of a great concern, considering
that these areas are large producers of food worldwide (Fig. 5).
4 Conclusions
The evaluation of radionuclides in tropical areas is important for the assessment of
human exposure to the natural radioactivity, especially in those areas affected by
agricultural, industrial, or mining activities. Geochemical and environmental factors
may affect U availability for both aquatic and terrestrial organisms (discussed in
previous sections).
In the aquatic environment, the risk of the presence of bioavailable forms of U is
well known. Uranium can be partitioned among dissolved and particulate phase
before being uptaken by organisms, and the chemistry of the natural waters presents
a huge effect on U mobility and availability. Many analytical techniques have been
employed to perform the U speciation in natural aquatic systems and to determine
the so-called bioavailable forms of U. However, inconsistencies in the definition of
which U fraction/species is the one bioavailable are observed. Even though studies
employing biological and chemical approaches improved the knowledge about the
mechanisms involved in the U uptake by organisms and the U bioavailability in
natural aquatic systems, some gaps still need to be filled (e.g., considering the characteristics of tropical waters, sediments, and soils), and more studies are necessary
to comprehend the whole mechanism of U uptake and the environmental and biological conditions that are involved in the U bioavailability and toxicity to aquatic
organisms.
With respect to the terrestrial environments, climate strongly influences soil
types, thus controlling U mobility and availability. For each soil, differences in the
solubility and mobility of U as well as translocation within the plants are dominated
by specific and nonspecific adsorption as well as different complexation affinities
for inorganic and organic ligands, which depend mainly on the soil pH. Considering
that the bioavailable fraction depends on the physicochemical characteristics of the
soils, it’s important to take into account soil properties, bioavailable U concentrations measured by different methods, and U accumulation in plants, when attempting to determine how soil properties influence the prediction of the bioavailable
portions of U. Novel knowledge into the mechanisms controlling U mobility in
tropical terrestrial systems and the prediction of U availability in soils could improve
Biogeochemistry of Uranium in Tropical Environments
performed, even though it’s well known that the cultivation of organic soils is an
important human exposure pathway of trace elements and radionuclides (Saetre
et al. 2013). It’s essential and necessary thus to understand the differences on the
accumulation of U by the different plants, especially considering the edible portions
of the vegetables, since data on the element concentrations might be very useful for
radiological risk assessments (Staven et al. 2003) and for predicting the fate of the
contaminants in the environment and in the food chain (Willey 2014). Thus, mechanisms controlling the TF of U in tropical regions are of a great concern, considering
that these areas are large producers of food worldwide (Fig. 5).
4 Conclusions
The evaluation of radionuclides in tropical areas is important for the assessment of
human exposure to the natural radioactivity, especially in those areas affected by
agricultural, industrial, or mining activities. Geochemical and environmental factors
may affect U availability for both aquatic and terrestrial organisms (discussed in
previous sections).
In the aquatic environment, the risk of the presence of bioavailable forms of U is
well known. Uranium can be partitioned among dissolved and particulate phase
before being uptaken by organisms, and the chemistry of the natural waters presents
a huge effect on U mobility and availability. Many analytical techniques have been
employed to perform the U speciation in natural aquatic systems and to determine
the so-called bioavailable forms of U. However, inconsistencies in the definition of
which U fraction/species is the one bioavailable are observed. Even though studies
employing biological and chemical approaches improved the knowledge about the
mechanisms involved in the U uptake by organisms and the U bioavailability in
natural aquatic systems, some gaps still need to be filled (e.g., considering the characteristics of tropical waters, sediments, and soils), and more studies are necessary
to comprehend the whole mechanism of U uptake and the environmental and biological conditions that are involved in the U bioavailability and toxicity to aquatic
organisms.
With respect to the terrestrial environments, climate strongly influences soil
types, thus controlling U mobility and availability. For each soil, differences in the
solubility and mobility of U as well as translocation within the plants are dominated
by specific and nonspecific adsorption as well as different complexation affinities
for inorganic and organic ligands, which depend mainly on the soil pH. Considering
that the bioavailable fraction depends on the physicochemical characteristics of the
soils, it’s important to take into account soil properties, bioavailable U concentrations measured by different methods, and U accumulation in plants, when attempting to determine how soil properties influence the prediction of the bioavailable
portions of U. Novel knowledge into the mechanisms controlling U mobility in
tropical terrestrial systems and the prediction of U availability in soils could improve
Biogeochemistry of Uranium in Tropical Environments