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DETAILS OF THE PROPOSED PROJECT TO BE UNDERTAKEN
Topic: Remediation and Bioremediation of Uranium contaminated soils of Andhra
Pradesh, India
ORIGIN OF PROPOSAL:
Uranium is a naturally occurring element that can be found in low levels within all rock, soil,
and water. Uranium is also the highest-numbered element to be found naturally in significant
quantities on earth and is always found combined with other elements. Along with all
elements having atomic weights higher than that of iron, it is only naturally formed in
supernovas. The decay of uranium, thorium, and potassium-40 in the Earth's mantle is
thought to be the main source of heat that keeps the outer core liquid and drives mantle
convection, which in turn drives plate tectonics. Uranium's average concentration in the
Earth's crust is (depending on the reference) 2 to 4 parts per million, or about 40 times as
abundant as silver. The Earth's crust from the surface to 25 km (15 mi) down is calculated to
contain 1017 kg (2×1017 lb) of uranium while the oceans may contain 1013 kg (2×1013 lb). The
concentration of uranium in soil ranges from 0.7 to 11 parts per million (up to 15 parts per
million in farmland soil due to use of phosphate fertilizers), and its concentration in sea water
is 3 parts per billion.
Uranium is a silvery-white metallic chemical element in the actinide series of the
periodic table, with atomic number 92. In nature, uranium is found as uranium-238
(99.2742%), uranium-235 (0.7204%), and a very small amount of uranium-234 (0.0054%).
Uranium decays slowly by emitting an alpha particle. The half-life of uranium-238 is about
4.47 billion years and that of uranium-235 is 704 million years, making them useful in dating
the age of the Earth. The potential risk of uranium soil contamination is a global problem.
Depleted, enriched and natural uranium contamination in soil and water has been identified at
many sites worldwide, so that measures for preventing should be considered as a preliminary
step towards the remediation of contaminated areas. Contamination of the environment can
occur from a variety of different sources of radionuclides, including
•
military tests;
•
radiation accidents;
•
various nuclear fuel cycle activities (uranium mining, processing of ore, fuel
fabrication and reprocessing of nuclear fuel);
•
electricity generation;
•
mining and
•
processing of some other natural resources such as gas, oil, tin and phosphate;
•
application of radionuclides in industry,
•
research and medicine; and
•
loss of nuclear weapons.
Radioactive contamination of the environment can cover surface regions of hundreds
of square kilometers, including agricultural areas, forested or other semi-natural regions.
Contamination of the soil can occur either from deposition of uranium originally discharged
into the atmosphere, or from waste products discharged directly into or on the ground (e.g.,
water containing uranium from either underground or open-pit mines). Some specific
characteristics of uranium contamination of the environment determine the need for
restoration measures. The physicochemical forms of uranium, which depend on the release
scenario and the density of radioactive fallout during dispersion and deposition, may
influence the behaviour and availability of this radionuclide in its transfer along food chains.
The mobility of uranium along the agricultural food chain, and initially within the soil,
depends mainly on two factors, the soil properties and the physical and chemical properties of
uranium compounds. The impacts on ecosystems and potential land use depend on the
vulnerability of the ecosystem in question and the specific features governing radionuclide
transfer in these environments.
Contaminated sites can be classified according to different criteria. Assuming that
similar environmental behaviour and contamination patterns of radionuclides can be expected
for similar contamination scenarios, the origin and contamination scenarios can be utilised to
classify such sites. On the other hand, contaminated sites can also be classified based on the
preliminary assessed potential radiation risk to the population.
OBJECTIVES OF THE PROPOSED PROJECT:
The main objective of this project proposal is to assess the recent advances in uranium
removal from contaminated soils, using either Chemical and/or biological techniques (such as
hyperaccumulator plants, or high biomass crop species after soil treatment with chelating
compounds).And screening of the technologies applicable to a contaminated site which is
depend on the cleanup goals, the form of pollutants present and the volume and
physical/chemical properties of the polluted soils and the concentration of pollutants.
Review of R & D in the proposed area (National & International Status, Importance,
patents etc.):
Clean up of contaminated aquifers is a difficult and expensive problem because of the
inaccessibility of the subsurface and the volume of soil requiring treatment. Current
approaches in India and other countries to bioremediation of uranium are based upon the
complexation, oxidation-reduction (redox), and alkylation reactions introduction. Microdial
leaching,
microbial
surfactants
(biosurfactants),
volatilization,
and
bioaccumulation/complexation are all strategies that have been suggested for removal of
uranium from contaminated environments. Unfortunately, the number of accompanying fieldbased studies has, thus far, been small.
STUDY AREA:
•
Scientists have found massive uranium deposits at the mines in Tummalapalle in
Andhra Pradesh, a site that has the potential to emerge as the largest reserve of the
key nuclear fuel in the world.
•
Cuddapah basin, Andhra Pradesh, endowed with rich mineral wealth, is one of the
important and fairly well studied geological units in peninsular India. Uranium
exploration in the Cuddapah basin was initiated in the late 1950’s to search the quartzpebble-conglomerate type uranium mineralisation which had dominated the world
uranium supply at that time.
•
Lambapur-Peddagattu region, 130km south-west of Hyderabad where uranium project
in progress and a uranium processing plant at Seripalli, 54 km from mine site.
WORK PLAN (INCLUDING DETAILED METHODOLOGY AND TIME
SCHEDULE)
I Year:
Soil washing and in situ flushing involve the addition of water with or without additives
including organic and inorganic acids, sodium hydroxide which can dissolve soil organic
matter, water soluble solvents such as methanol, nontoxic cations complexing agents such as
ethylene-diamine-tetraacetic acid (EDTA), acids in combination with complexation agents or
oxidizing/reducing agents(1). Bio-surfactants, biologically produced surfactants may be
promising agents for enhancing removal of metals from contaminated soils and sediments.
Virtually all soil-washing or soil-flushing systems are designed to treat soils where the
majority of the contaminants are concentrated in the finer-grained materials or on the surfaces
of the larger soil particles(1). Many soil-washing processes are simply screening processes
that separate the fine, contaminated particles from the bulk of the soil. The large particle
fraction, which constitutes the bulk of many soils, is then clean and does not need further
treatment before it can be placed back onsite.
II Year:
CHARACTERIZATION: Characterization and solubility measurements of uraniumcontaminated soils to support risk assessment is to be assessed as per the method described
by Elless et al (2) (1997)
SOLIDIFICATION/STABILIZATION: The purpose of solidification and stabilization is to
treat contaminated soils so that the contaminants are suitably immobilized from potential
leaching into the environment. Solidification is the binding of a waste/soil into a solid mass to
reduce its contaminant leaching potential, whereas stabilization is the reduction of the
solubility and/or chemical reactivity of a waste/soil. These technologies are applicable to a
wide range of wastes / soils, but are particularly well suited for metals and are typically
limited to soils containing less than 1% organics(3).
IN SITU IMMOBILIZATION: Contaminated soils can be treated in situ or ex situ to
immobilize the pollutants. In situ treatment has the advantage of minimizing the exposure of
site works and local residents to airborne pollutants. It is also has the potential for minimizing
disruption to or demolition of existing structures. Mobility is strongly related to the
physicochemical state and the location of pollutants(2,3).
CHEMICAL REDUCTION TREATMENTS: As with immobilization, contaminated soils
can be treated in situ or ex situ to reduce the pollutants and thereby their toxicity and
mobility. The redox potential (Eh) depends on the availability of oxygen in soils, water and
sediments, and upon biochemical reactions by which microorganisms extract oxygen for
respiration. Redox conditions influence the mobility of metals in two different ways. Firstly,
the valence of certain metals changes. For instance, under reducing conditions, Fe3+ is
transformed to
Fe2+
and, similarly, the valence of manganese and arsenic is subject to direct
changes. Since the reduced ions are more soluble, increased concentrations of these metals
have been observed in reducing environments such as groundwaters and sediment solutions.
Under reducing conditions, sulfate reduction will take place: for example, in sediments, lead
sulfide with a low solubility if formed. On the other hand, an increase in the redox potential
will cause lead sulfide to become unstable, with a subsequent rise in dissolved lead
concentrations (3).
III Year
BIOREMEDIATION: The objective of bioremediation is to exploit the naturally occurring
biodegradative processes to clean up contaminated sites. There are several types of
bioremediation: in situ bioremediation is the in-place treatment of a contaminated site; ex situ
bioremediation is the treatment of contaminated soil or water that is removed from a
contaminated site; and intrinsic bioremediation is the indigenous level of condition
biodegradation that occurs without any stimulation or treatment. The following three methods
will be screened and assessed.
(1) Enzymatic dissimilatory metal bioreduction of soluble U(VI) in sparingly soluble
U(IV)(4,5),
(2) Chemical reduction by microbially-generated by-products (6), and
(3) Biosorption on cell surface, biopolymers or dead organisms(6)
Finally aim is to assess the advantages and disadvantages with above remediation
technologies and to measures the applicability and the circumstances of applicability uranium
remediation technologies.
Potential Impacts of the Proposed Studies:
The results of these data will be useful to determine the initial need for site
remediation, plans for further remediation and implementation of remedial actions as well as
to ensure that there is compliance regarding the residual concentrations of radionuclides in
the environment post-remediation.
¾ Assists mining communities in making scientifically sound and environmentally
informed decisions about extracting Uranium resources.
¾ Provides new data about speciation, partitioning to common soil phases, and toxicity
of uranium that will assist regulatory agencies in determining appropriate bonds for
mining these elements.
¾ Places MRP at the forefront of proactive research assessing potential environmental
impacts of uranium, thereby raising the visibility of the program within the
organization and broader scientific community.
References:
1. Martyushov-VV; Bazylev-VV. (1992) Behavior of heavy natural radionuclides in
irrigated soils. Soviet-Journal-of-Ecology. 23: 1, 12-16; translated from Ekologia 1:
16-20.
2. Elless MP, Armstrong AQ, Lee SY. (1997) Characterization and solubility
measurements of uranium-contaminated soils to support risk assessment. Health Phys.
72(5):716-26.
3. Hazardous Waste Consultant “HWC” (1996): Remediating Soil and Sediment
contaminated with Heavy Metals, 14 (6): 41 - 47. New York, Elsevier Science.
4. Freethey G. F., Naftz D. L., Rowland R. C., and Davis J. A. (2002) Deep Aquifer
Remediation Tools: Theory, Design, and Performance Modeling. In Handbook of
Groundwater Remediation Using Permeable Reactive Barriers (ed. D. L. Naftz, S. J.
Morrison, J. A. Davis, and C. C. Fuller), pp. 133-163. Academic Press.
5. Al Kaddissi S, Legeay A, Gonzalez P, Floriani M, Camilleri V, Gilbin R, Simon O.
(2011) Effects of uranium uptake on transcriptional responses, histological structures
and survival rate of the crayfish Procambarus clarkii. Ecotoxicol Environ Saf. (In
press)
6. Grégoire Seyrig (2010) uranium bioremediation: current knowledge and trends. Basic
Biotech eJournal 3:3.