Role of light and heavy minerals on natural radioactivity level of high background radiation area, Kerala, India

Applied Radiation and Isotopes 85 (2014) 1–10

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Role of light and heavy minerals on natural radioactivity level of high background radiation area, Kerala, India V. Ramasamy a,n, M. Sundarrajan b,c, G. Suresh d, K. Paramasivam a, V. Meenakshisundaram e a

Department of Physics, Annamalai University, Tamilnadu, India Department of Physics, Sri Chandrasekharendra Saraswathi Viswa Mahavidyalaya, Enathur, Kanchipuram, Tamilnadu, India c Department of Physics, Manonmaniam Sundaranar University, Tirunelveli, Tamilnadu, India d Department of Physics, Arulmigu Meenakshi Amman College of Engineering, Vadamavandal (Near Kanchipuram), Tamilnadu, India e Former Head, Health and Safety Division, IGCAR, Kalpakkam, Tamilnadu, India b

H I G H L I G H T S








Due to the higher activity concentrations, the present sediments pose significant radiological threat to the peoples. Light mineral characterization shows the presence of eight light minerals. Heavy mineral separation analysis revealed the presence of nine heavy minerals. Multivariate statistical analysis gives an idea about the role of mineralogy on radionuclide concentrations. Along with clay content, the heavy minerals induce the 238U and 232Th concentrations and light mineral calcite controls the

40

K concentration.

art ic l e i nf o

a b s t r a c t

Article history: Received 19 June 2013 Received in revised form 18 October 2013 Accepted 28 November 2013 Available online 6 December 2013

Natural radionuclides (238U, 232Th and 40K) concentrations and eight different radiological parameters have been analyzed for the beach sediments of Kerala with an aim of evaluating the radiation hazards. Activity concentrations (238U and 232Th) and all the radiological parameters in most of the sites have higher values than recommended values. The Kerala beach sediments pose significant radiological threat to the people living in the area and tourists going to the beaches for recreation or to the sailors and fishermen involved in their activities in the study area. In order to know the light mineral characterization of the present sediments, mineralogical analysis has been carried out using Fourier transform infrared (FTIR) spectroscopic technique. The eight different minerals are identified and they are characterized. Among the various observed minerals, the minerals such as quartz, microcline feldspar, kaolinite and calcite are major minerals. The relative distribution of major minerals is determined by calculating extinction co-efficient and the values show that the amount of quartz is higher than calcite and much higher than microcline feldspar. Crystallinity index is calculated to know the crystalline nature of quartz present in the sediments. Heavy mineral separation analysis has been carried out to know the total heavy mineral (THM) percentage. This analysis revealed the presence of nine heavy minerals. The minerals such as monazite, zircon, magnetite and illmenite are predominant. Due to the rapid and extreme changes occur in highly dynamic environments of sandy beaches, quantities of major light and heavy minerals are widely varied from site to site. Granulometric analysis shows that the sand is major content. Multivariate statistical (Pearson correlation, cluster and factor) analysis has been carried out to know the effect of mineralogy on radionuclide concentrations. The present study concluded that heavy minerals induce the 238 U and 232Th concentrations. Whereas, light mineral (calcite) controls the 40K concentration. In addition to the heavy minerals, clay content also induces the important radioactive variables. & 2013 Elsevier Ltd. All rights reserved.

Keywords: Beach sediments Natural radionuclides Minerals Statistical analysis

1. Introduction Minerals are the composite of different elements and occur naturally as crystalline inorganic substances in sediments. Mineral

n

Corresponding author. Tel.: þ 4144 222488. E-mail addresses: [email protected], [email protected] (V. Ramasamy). 0969-8043/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apradiso.2013.11.119

sediments, sands and mud are weathered from mountain belts, transported by rivers, glaciers or wind and deposited at the coast. Minerals are classified into two types on the basis of its density such as light minerals (specific density less than 2.9  103 kg m  3) and heavy minerals (specific density greater than 2.9  103 kg m  3) (de Meijer et al., 2001). The distribution and characterization of light minerals in beach sediments have persuaded by many geoscientists and studied them with respect to depositional environment and provenance (Cherian et al., 2004). Extensive beach sand deposits are

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located along the coastal lines of the eastern and the western parts of India. Out of the total world deposit of about 2500 million ton, India has a share of about 10–11% i.e. about 275 million ton (Siddiqui et al., 2000). Beach sand deposits are the major source of beach sand minerals, commonly known as Heavy Minerals. Mineralogical characterization comprises two main parameters namely mineral assemblage and chemical composition of mineral groups or even individual mineral grains. The composition of mineral assemblages is related to the mineralogical composition of the source region and also related several other processes such as physical sorting, mechanical abrasion and dissolution. Physical sorting is a result of hydrodynamic conditions during transport and depositional stages. It controls both absolute and relative abundance of minerals. Mechanical abrasion takes place during transport and cause grains to diminish in size by a combination of fracturing and rounding. Dissolution causes partial and complete loss of minerals in a variety of geochemical conditions at several stages in the sedimentation cycle. Mineralogical properties of beach sand reflect the geological history of the original rock formation (Carvalho et al., 2011). Many areas in the world such as Australia, Brazil, China, India, Iran, Japan, etc., possess high levels of natural radiation. In the recent years, studies on the high background radiation areas in the world have been of prime importance for risk estimation due to long-term lowlevel whole body exposures to the public. Southwest coast of India is known since long as one of the high level background radiation areas in the world. Natural radiation levels in the region are higher than normal which are believed to be emitted from the rich deposits of the monazite bearing beach sand. The mineral monazite contains radioactive elements, which is the main cause for natural radiation in the southwest coast belt (Singh et al., 2007). In the process of mineral formations, the radionuclides are incorporated as trace elements in their crystal lattice. Later on and through erosive processes, these minerals are transported and can reach the coast becoming part of the sediments (Ligero et al., 2001). According to Carvalho et al. (2011), most of the uranium and thorium atoms are bound in dark colored accessory minerals known as heavy minerals. However, thorium (by adsorption) and potassium (chemical composition) are associated with clay minerals. They also stated that the light minerals such as quartz and feldspar may contain relatively high concentrations of 40K. Hence, based on the above discussions, accumulation and distribution of radionuclides depend mostly on the characteristics (types and abundance) of the light and heavy minerals. Kerala is the most densely populated state in India and about 80% of peoples are living in the coastal zone. The state Kerala has the coastal length about 560 km which covers about 15% of the state's total area of 38,863 sq km. The major renewable resources available along this coastal zone are water, agriculture and fisheries and nonrenewable resource such as placer minerals, soils, sub fossil deposits, etc. Kerala is endowed with a rich diversity of marine fishes with a numerical strength of more than 300. The Chavara coast of Kerala is well known place for rich heavy mineral deposits. Most of the industrial and commercial establishments in Kerala have been concentrated in the coastal zone (Ramasamy et al., 2013). Therefore, radioactivity level of the coastal region of Kerala (beaches) in relation to light and heavy minerals are essential to know the mineralogical effect on natural radiation level. We have published the spatial distribution of radionuclides and their radiological hazardous nature of the Kerala beach sediments in our Applied Radiation and Isotopes journal (Ramasamy et al., 2013). In that article, it is concluded that the light and heavy minerals may be played a role in different sampling sites and hence the present study. In the present study, role of light and heavy minerals on natural radiation level of the beach sediments is focused. For this, core radioactivity data and their discussion were taken from Ramasamy et al. (2013) to correlate them with the mineralogical data. Hence, the

main goal of this study is to: (i) analyze the mineralogical (light and heavy) characterization of the beach sediments of Kerala, India, (ii) calculate extinction coefficient and crystallinity index in order to know the relative distribution of major minerals and crystalline nature of quartz respectively, (iii) know the percentage of sand, silt and clay by granulometric analysis and finally (iv) assess the role of mineralogy on natural radiation level of the beach sediment using multivariate statistical analysis.

2. Materials and methods 2.1. Study area Kerala has ten coastal districts. The present study area covers four coastal districts such as Ernakulam, Alappuzha, Kollam and Trivandrum (91 57′ 49″; 761 14′ 16″–81 34′ 21″; 761 50′ 9″). Nearly 45% of coastal region was covered by the present study. The surficial sediments of the continental shelf and slope of Kerala can be divided into terrigenous, biogenous and chemogenous sediments. In the shelf and slope of Kerala, terrigenous sediments mostly occur as sands in the near shore (up to 10–12 m water depth) followed by a zone of silty clays on the inner shelf. An admixture of abundant terrigenous and biogenic constituents carpets the outer shelf. Around 1.33 crores peoples are living in the present study area. Other importances of study area were presented in Ramasamy et al. (2013). 2.2. Sample collection The present study area covers a total length of about 200 km, from which 39 successive locations were selected and numbered as S1-S39 (Fig. 1). The sample locations were recorded in terms of degree – minute – second (latitudinal and longitudinal position) using a hand-held global positioning system (GPS) (Model: GARMIN GPS-12) unit. Each location is separated by a distance of approximately 4–5 km. The samples were collected from 5–10 m away from the high tide at the depth of 0–5 cm, when it makes towards the road side. Samples were collected by plastic spade during summer period of 2011 and collected samples were packed in polyethylene bags. Each sample has the weight of about 3 kg. The collected samples were air dried at room temperature in open air. 2.3. Radioactivity measurements Details of sample preparation, and instrument used and procedure for radioactivity measurement (gamma ray spectrometer) were clearly presented in Ramasamy et al. (2013). The below detectable limit (BDL) of the each radionuclide is 5.5 Bq/kg for 238U and 232Th and 21.5 Bq/kg for 40K. 2.4. Mineralogical study 2.4.1. Characterization of light minerals 2.4.1.1. Sample preparation and instrument used. Wet grinding was carried out by placing 30–50 mg of the sample in an agate mortar along with 20–25 drops of ethanol. The ground samples were dried in an hot air oven at 110 1C to remove the moisture content and sieved to 53 μm grain size. Using the KBr pellet technique, the sample was mixed with KBr at various ratios viz., 1:10, 1:20, 1:30, 1:40 and 1:50. The mixture was then pressed into a transparent disc in dye at sufficiently high pressure. The samples in the ratio 1:30 was taken for further analysis, since it gives rise to maximum transmittance and observable peaks (Ramasamy et al., 2011). Using the Perkin-Elmer RX1 FTIR spectrometer, the infrared spectra for all sediment samples were

V. Ramasamy et al. / Applied Radiation and Isotopes 85 (2014) 1–10

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Fig. 1. Location of Kerala beaches with their experimental sites.

recorded in the region 4000–400 cm  1. The resolution of the instruments is 0.001 cm  1 and the accuracy is 74 cm  1.

2.4.2. Characterization of heavy minerals Preparation and preliminary analysis of sediment samples were carried out as per the procedure given in Carver (1971) and Solai et al. (2009). Heavy mineral separation was carried out in three fractions (coarse, medium and fine) using heavy liquid bromoform of 2.89 specific gravity as per the standard procedures outlined by Milner (1962). Separated heavies were washed and then mounted on the glass slide using Canada balsam (Solai et al., 2009). The total heavy mineral percentages (THM) were calculated. The heavy fractions were mounted on glass slides and counted under polarized light using a Leica Petrological microscope by the line counting method. Using a hand magnet, magnetic minerals (magnetite) were separated from the heavy mineral fractions and the weight percentage was estimated. Further, the samples were subjected into Frantz Isodynamic separator to separate illmenite and other nonmagnetic fractions (Nallusamy et al., 2013).

2.5. Granulometric analysis The samples were also examined to measure their granulometric fractions such as contents of sand, silt and clay. Using an ASTM sieve, about 100 g of sediment was taken for separation of sand, silt and clay fractions by sieving.

3. Results and discussion 3.1. Radiological characterization of beach sediments Statistics of the activity concentrations of the radionuclides U, 232Th and 40K in present beach sediment samples are presented in Table 1. The activity concentration ranges for 238U, 232 Th and 40K are BDL – 1187.16 721.79 Bq/kg with an average 170.4 78. 4 Bq/kg, BDL – 5328.17 23.3 Bq/kg with an average 547.3710.9 Bq/kg and BDL – 693.5 731.2 Bq/kg with an average 117.2716.0 Bq/kg respectively. Measured activities of the radionuclides differed widely because activity levels in the beach environment mainly depend on their physical, chemical and 238

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Table 1 Statistics of the radionuclides concentrations and radiological parameters (Ramasamy et al., 2013).

Concentration of 238U (Bq/kg) Concentration of 232Th (Bq/kg) Concentration of 40K (Bq/kg) Absorbed dose rate (nGy/h) AEDE (μSv/y) AGDE (μSv/y) Raeq (Bq/kg) H Iγ I ELCR (  10  3) n

Average

Maximum

Minimum

World average*

170.47 8.4 547.3 7 10.9 117.2 7 16.0 414.17 20.3 507.8 7 13.3 2850 7 30.4 961.8 7 25.3 2.6 7 0.01 3.3 7 0.09 9.59 7 0.09 1.7 7 0.05

1187.17 21.7 5328.17 23.3 693.5 7 31.2 3767.5 7 38.4 4620.5 7 34.6 25946 7 45.7 8806.17 55.1 23.7 7 0.14 30.6 7 0.19 94.5 7 9.8 16.2 7 0.1

BDL BDL BDL 6.98 72.1 8.56 73.13 48.217 10.5 15.5 7 5.5 0.047 0.01 0.05 70.02 0.117 0.06 0.03 70.01

33 45 420 57 70 1000 370 1 0.5 2 0.29

UNSCEAR (2000).

Table 2 The observed absorption wave numbers and corresponding minerals from FTIR spectra of all samples. Sl. no.

Name of the minerals

Site number

Observed wave number (cm  1)

1

Quartz

S1-S39 S1-S39 S1-S39 S1-S39 S1-S39 S1-S39 S1-S39 S1-S39

460–464 512–516 693–694 777–778 796–799 1080–1084 1161–1165 1870–1874

2

Microcline feldspar

S1-S39

582–586

3

Orthoclase feldspar

S2, S3, S5, S11, S13-S24, S26, S32, S34- S37 S1, S2, S4-S7, S11, S13, S15, S24-S26, S28-S35

532–536 643–647

4

Kaolinite

S1-S39 S1, S2, S3, S7, S10, S12, S14, S21, S22- S28, S30 S28, S32, S33

1015–1018 3398–3410 3689–3691

5

Gibbsite

S1-S39

666–670

6

Calcite

S2, S17, S21, S23, S25 S2, S11, S21, S28 S1-39 S32, S33 S1, S2, S15, S21, S28

712–713 875–878 1466–1477 1636 2517–2521

7

Montmorillonite

S1, S3, S13, S15-S23, S25, S26, S28, S34

886–888

8

Organic carbon

S1-S39 S1-S39

2850–2853 2923–2926

geo-chemical properties (Abdi et al., 2009). The combined effect of weathering, rivers, streams, morphological features of the river basins and their interaction with the sea influenced the distribution of the radioactive heavy minerals in the beach sectors along the coastal zone (Singh et al., 2007). Mean activity concentration is in the order 40K o 238U o 232Th. Actually, concentration of both 238U and 232Th is much higher than the 40K (Table 1). Only in 18 locations (46%), the activity concentration of 238U is lower than the world average value (33 Bq/kg). The 62% of sampling sites is having higher concentration of 232Th when compared with world average value (45 Bq/kg). The activity concentration of 40K is lower than the world average value (420 Bq/kg) (UNSCEAR, 2000) in all sampling locations except S24. The mean activity concentration of 238U is 5 times higher than the world average value (33 Bq/kg) and 6 times higher than the Indian average value (28.67 Bq/kg). The mean concentration of 232 Th is 12 and 8.5 times higher than the world (45 Bq/kg) and Indian average values (63.83 Bq/kg), respectively. The mean concentration of 40K is lower than the world average (420 Bq/kg) and Indian average value (400 Bq/kg), respectively (UNSCEAR, 2000).

3.2. Radiological parameters To assess the statistical information about cancers, average lifetime of people, typical health diseases, etc. for the present study area, the different radiological indices were calculated and details of calculations are presented in Ramasamy et al. (2013). Statistics of the all calculated radiological parameters and their recommended levels are given in Table 1. Averages of all the calculated radiological parameters are higher than recommended values. Also, all the radiological parameters in most of the sites are having higher values than recommended values. Very high values are observed in site number S23 (Chavara beach) due to the presence of rich deposits of black sand. The obtained results show that the harmful radiation effects are pose to the public and tourists going to the beaches for recreation or to the sailors and fishermen involved in their activities in the area. 3.3. Light mineral characterization – FTIR All the samples were subjected into FTIR analysis and observed wave numbers (cm  1) are tabulated with corresponding minerals (Table 2). A selected representative FTIR spectrum (site number S2) is

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shown in Fig. 2. From the Table 2, the minerals such as quartz, microcline feldspar, orthoclase feldspar, kaolinite, calcite, gibbsite, montmorillonite and organic carbon are identified by comparing the observed wave numbers with available literature (Russell, 1987; Ramasamy et al., 2009, 2004). Among the various observed minerals, the minerals such as quartz, microcline feldspar, kaolinite and calcite are major and others are trace on the basis of their presence and intensities of corresponding peaks. Quartz is one of the non-clay minerals and invariably present in all samples. Generally, white sand beaches are typically composed of quartz-rich sediments. Due to its hardness and chemical structure, quartz is a very durable mineral that is difficult to weather and erode. Therefore, quartz is often the most prevalent mineral found in beach sediments. According to Hlavay et al. (1978), the presence of quartz in the samples can be confirmed by the characteristic peaks at around 778 and 796 cm  1 with Si–O symmetrical stretching vibrations. In the presence study, the above mentioned characteristic peaks are observed with well intensity in all the samples. Also, the presence of quartz is explained by Si–O asymmetrical bending vibration at around 462 cm  1 and Si–O symmetrical bending vibrations around 694 cm  1. The 1082 and 1162 cm  1 absorption region arising from Si–O asymmetrical stretching vibration due to low Al for Si substitution are also indications of the presence of quartz. The sharp visible peaks at around 514 and 1872 cm  1 are also the characteristic peaks of quartz. Feldspar is the also principal constituent in natural sediments. Even there are so many types of feldspars such as orthoclase, microcline, sanidine (K – feldspar), albite (Na – feldspar) and anorthite (Ca – feldspar), mostly it is existed in three important compositions such as orthoclase, microcline and sanidine (Kodama, 1985). Though three feldspars (orthoclase, microcline and sanidine) have the same chemical formula (KAlSi3O8), they have different structures (orthoclase – monoclinic, microcline – triclinic and sanidine – tetrahedral). The peak corresponding to the range 582–586 cm  1 is due to the O–Si–(Al)–O bending vibration. This peak shows that the presence of microcline feldspar and it is observed in all the sites. The peaks in the range 643–647 and 532– 536 cm  1 are due to the Al–O coordination vibrations indicating the presence of orthoclase feldspar (Ramasamy et al., 2011). Kaolinite is the clay mineral with the chemical composition Al2Si2O5(OH)4. It is layered silicate mineral, with one tetrahedral sheet linked through oxygen molecules to one octahedral sheet of alumina 100

%Transmittance

80

60

40

20 4000

3500

3000

2500

2000

1500

1000

500

Wave number (cm-1) Fig. 2. FTIR spectrum of sediment sample of site number S2. [Q – quartz, O.F. – orthoclase feldspar, M.F – microcline feldspar, K – kaolinite, C – calcite, G – gibbsite, and O.C. – organic carbon].

5

octahedral. It is produced by chemical weathering of feldspars. Due to extremely fine nature (finer than silt), it is mixed with water and easily transported as a liquid slurry. The presence of an absorption band at or around 3690, 3400 and 1016 cm  1 indicate the presence of clay mineral constituents as kaolinite (Ramasamy et al., 2011, 2004). Kaolinite shows a characteristic IR absorption sequence in the range of 3700–3600 cm  1. The absorption peak corresponds to stretching vibrations of inner surface OHs (3696 cm  1). Absorbance at 1016 cm  1 is attributed to stretching of an O atom bound to both Si and tetrahedral Al (Summer, 1995). According to Russell (1987) and Ramasamy et al. (2005), if four peaks are observed in the region 3697– 3620 cm  1, the mineral is said to be in an ordered state. However, in the present study only one peak is observed at around 3690 cm  1 in some sites. This suggests that the present kaolinite mineral may be in a disordered state. Calcite is the most common carbonate mineral in sediments. Carbonates are commonly deposited in marine settings when the shells of dead planktonic life settle and accumulate on the sea floor. The mid infrared region (1400–1500 cm  1) of the spectra is dominated by the vibrational modes of carbonate ions (Ramasamy et al., 2011). From the Table 2, it can be observed that the absorption peak in the range 1466–1477 cm  1 is presented in all the samples. This is easily recognized by the presence of calcite in all the samples. Also, the presence of some other major peaks in the range 875–878 cm  1 and 712–713 cm  1 and some minor peaks in the range 1636 cm  1 and 2517–2521 cm  1 shows that the existence of calcite in some samples (Table 2). The absence of some peaks from sample to sample may be due to the interference of silicate minerals or due to the particle size of the minerals (Ramasamy et al., 2009). The frequency assignments reported by Herzberg (1945) for carbonate minerals are a symmetric stretching, ν1; an out of – plane bending, ν2; a doubly degenerate asymmetric stretching, ν3 and a doubly degenerate planer bending ν4. But the symmetric oscillation represented by ν1 is reported to be infrared inactive, hence only three fundamentals are ordinarily encountered. These have been recorded for various calcite group minerals in the regions of absorption at approximately 1430 cm–1 (ν3), 909– 833 cm–1 (ν2) and 769–666 cm–1 (ν4). These combinational modes of vibration are matched with present investigation. Gibbsite is an aluminum hydroxide mineral. It is a secondary mineral which is commonly found in lateritic formations, highlyweathered soils and clay deposits of tropical and subtropical region. It is an alteration product of many aluminous and alumino-silicate minerals under intense weathering conditions. The appearance of a peak in the range 666–670 cm  1 shows the presence of the Al bearing mineral gibbsite (Russell, 1987). Though it is observed in all sites, it has in weak intensity. Appearing peaks in the region 2850–2853 and 2923– 2926 cm  1 in all the samples show the presence of organic carbon (Song et al., 2001). Montmorillonite contains both tetrahedral and octahedral isomorphous substitution, Al (and occasionally Fe3 þ ) for Si in the former case, and Fe3 þ and Mg for Al in the latter (Russell, 1987). As a result of these substitutions, crystalline order is reduced and structural imperfections arise, which lead to considerable broadening of IR absorption bands. The presence of the OH deformation band of the AlFe3 þ OH grouping in the range 886–888 cm  1 is observed in some of the sites which may be due to the presence of montmorillonite.

3.3.1. Relative distribution of quartz, microcline feldspar, kaolinite and calcite The extinction coefficient is the parameter defining how a particular mineral is distributed among the others in the sediments (Suresh et al., 2012). With reference to the number of peaks

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and intensity, the minerals such as quartz, microcline feldspar, kaolinite and calcite are considered as major minerals and other minerals are accessory. Therefore, it is interesting to study the relative distribution of quartz, microcline feldspar, kaolinite and calcite in present sediments. The relative distribution of major minerals can be quantified by calculating the extinction co-efficient for the characteristic peaks of quartz, microcline feldspar, kaolinite and calcite at around 778, 585, 1015 and 1470 cm  1 respectively for all sites using the formula used by Ramasamy and Ponnusamy (2009). Calculated values are shown in Fig. 3. From this figure, amount of above major minerals in the sediments decreases in the order of quartz 4calcite4microcline feldspar 4kaolinite. The distributions of major minerals in the sediments are not uniform. This may be due to the wind, waves and currents constantly move and redistribute coastal sediments along the shorelines. The ranges of extinction coefficient values for quartz, microcline feldspar, kaolinite and calcite are 10.93 (S3) – 560.33 (S35), 1.00 (S39) – 55.90 (S16), 2.97 (S15) – 28.39 (S16) and 1.00 (S39) – 278.87 (S24). With the maximum and minimum limits of the above said minerals, the other sites may be arranged for the containment of the same mineral quantitatively in an order. This shows the erratic distribution of major minerals in the present sediments due to the rapid and extreme changes occur in highly dynamic environments of sandy beaches. 3.3.2. Crystallinity index of quartz Crystalline nature of the minerals present in the sediments can be assessed by calculation of crystallinity index. Though, it is

EC

300 200

important to calculate for the present sediments, method, purpose and details of calculation have already been established in Hlavay et al. (1978) and Ramasamy et al. (2011, 2009, 2003). The crystallinity index of quartz has been calculated by taking the ratio of the intensity of the absorption band at 777 cm  1 (I777) due to the vibrations in tetrahedral site symmetry and at 695 cm  1 (I695) due to the vibrations in octahedral site symmetry by constructing the tangent base line for these bands (Hlavay et al., 1978). The tetrahedral symmetry is stronger than the octahedral. If the structural changes take place, the damage occurs first in octahedral than tetrahedral (Ramasamy et al., 2003). Therefore the intensity of the bands due to the vibration in the two symmetries will supply the information about the crystallinity. If the crystallinity is minimum, the minerals are said to be in disordered state. If it is maximum, the minerals are considered to be in ordered state. The crystallinity of quartz may give clear indication on the crystalline forms of other minerals because quartz is the mineral which crystallizes last. If this crystallinity of quartz is maximum, the other minerals may also be expected to be equally in well crystallized state. Hence, it is useful to find out the crystallinity index of quartz rather than the other minerals. Crystallinity index of quartz is calculated and calculated values are shown in Fig. 4. From this figure, calculated values are ranged from 0.21 to 0.99. According to Ramasamy et al. (2011), if the crystallinity index values are below 0.75, then it is said to be ordered crystalline quartz. The intermediate crystalline quartz is represented by values in between 0.75 and 1.00. If the values are greater than 1.00, then it is said to be disordered. Sixteen sites which are mostly presented in central part of the study area are having values in between 0.75 and 1.00. This shows that the presence of intermediate crystalline quartz in the above sites. Ordered crystalline quartz is presented in remaining sites since the calculated values are below 0.75. Very low values (0.21–0.30) are observed in site numbers S12, S34, S35, S37–S39. This may be due to the presence of well ordered crystalline quartz.

100

3.4. Heavy mineral separation analysis

0 30

The heavy mineral separation analysis has been carried out to know the total heavy mineral (THM) weight percentage in the present samples. Weight percentage of separated heavy minerals is varied from 0.03% to 99.71% (Fig. 4). The THM percentage is varied greatly from site to site. It is minimum in S1 and it is

EK

25 20 15 10 5

Total Heavy mineral (%)

0 60

EMF

50 40 30 20 10 0 600

100 80 60 40 20 0

EQ

S4

S9

S14

S4

S9

S14

S19

S24

S29

S34

S39

S19

S24

S29

S34

S39

400 300 200 100 S5

S10

S15

S20

S25

S30

S35

Site Number Fig. 3. Relative distribution of major minerals such as quartz, microcline feldspar, kaolinite and calcite in the sediments. The figure shows that EQ 4EC 4EMF 4EK (Note: EQ, EMF, EK and EC respectively represents relative distribution of quartz, microcline feldspar, kaolinite and calcite).

Crystallinity Index

500

1.0 0.8 0.6 0.4 0.2

Site Number Fig. 4. Crystallinity index of quartz and total heavy mineral percentage in all sites.

V. Ramasamy et al. / Applied Radiation and Isotopes 85 (2014) 1–10

maximum in S23 (Chavara beach). Other sites are having intermediate values. Very high THM percentage (96% to 99.71%) is observed in only three sites S22, S23 and S24. Next higher percentage (30.12%) is observed in S27. Only four sites (S3, S20, S25 and S28) have THM percentage in the range of 12% to 18%. All other sites are having low (within 10%) THM percentage. The actual sorting and concentration of heavy minerals takes place due to the actions of two principal agents i.e. action of waves and wind. Ocean waves and surfs play predominant role in the concentration of the heavy minerals. A breaking wave takes all the fore-shore minerals to the beach but the back wash carries only the lighter minerals back to the sea. Repeated action of waves results in sorting and the concentration of heavy minerals in beach sediments (Siddiqui et al., 2000). The heavy mineral analysis revealed the presence of nine heavy minerals such as monazite, zircon, magnetite, illmenite, rutile, garnet, tourmaline, silimanite and chlorite. The basic statistics of individual heavy minerals is presented in Table 3. From the table, the minerals such as monazite, zircon, magnetite and illmenite are considered as predominant and other minerals are taken as minor minerals. The quantity range of monazite is higher which is ranged from 6.32% to 36%. Monazite is a primary ore of several rare earth metals, most notably thorium, cerium and lantdhanum. It forms in phosphatic pegmatites but it is actually a standard trace constituent in many ordinary igneous, metamorphic and vein filling rocks. It can be weathered out from their host rocks and carried downstream great distances and deposited in beaches. It is commonly presented in reddish-brown color. The quantities of zircon, magnetite and illmenite are almost equal and they are next abundant heavy minerals to monazite in the sediments. Shape of zircon is mechanically altered (commonly euhedral to subherdal) due to their stability and lack of good cleavage. It appears commonly colorless (Joshua and Oyebanjo, 2009). Magnetite is the most magnetic of all the naturally occurring minerals on Earth. It is sometimes found in large quantities as black sand in beaches. It is carried to the beach through rivers from erosion and is concentrated through wave action and currents. Illmenite is a weak magnetic minerals and it is commonly recognized in metamorphic and igneous rocks. Quantitatively rutile and tourmaline are almost same. They are next abundant set of minerals to the zircon, magnetite and illmenite. Rutile is commonly presented in red in color. It is a common accessory mineral in high temperature and high pressure metamorphic and igneous rocks. Tourmaline occurs on granite pegmatites. It is usually brown in color (sometimes greenish) or brownish yellow. Its shape is commonly euhedral (Joshua and Oyebanjo, 2009). Other three minerals such as garnet, silimanite and chlorite are least in quantity.

7

3.5. Granulometric analysis Granulometric analysis has been carried out to know the content of sand, silt and clay (%) in the present sediments. Percentage of sand, silt and clay (%) content of the sediment samples are presented in Fig. 5. This table shows that sand is the main constituent in all the sampling locations, which is varied from 56.12% to 97.73%. Silt content is the second most constituent which is varied from 2.22% to 43.58%. The least constituent is clay which is varied from 0.01% to 4.12%. The average sand, silt and clay content in the sediment is 75.85%, 23.34% and 0.57% respectively. Among the all sites, comparatively clay content is higher in the sites such as S3, S23, S24 and S26. 3.6. Multivariate statistical analysis Multivariate statistical analysis was employed to assess the relationship and interdependency among the sediment characteristics because of its usefulness as a tool to reduce and organize large data sets into groups with similar characteristics without losing much information. It is widely accepted and effectively used in radioactive analysis. In the present study, multivariate statistical analysis (Pearson's correlation, cluster and principal component analysis) is used to draw a valid conclusion regarding the interrelation among the variables. The parameters such as concentration of 238U, 232Th and 40K, absorbed dose rate (quantity to represent the level of radioactivity), extinction coefficient of major minerals such as quartz, microcline feldspar, kaolinite and calcite, percentage of total heavy minerals and granulometric contents such as percentage of sand, silt and clay are taken for this multivariate analysis. 3.6.1. Pearson's correlation analysis Pearson's correlation analysis is performed by SPSS 16 software to establish relationships among the variables. It gives linear correlation matrix and the matrix is presented in Table 4. According to the values of Pearson correlation coefficients (Table 4), the radioactive variables such as 238U and 232Th concentrations and absorbed dose rate are correlated among themselves with high positive correlation coefficients. Natural radioactivity level of another high background radiation area, Orissa, India had analyzed effectively by Mohanty et al. (2004). They got better positive correlation (r ¼ 0.98) between the concentrations of 238U and 232 Th. They inferred that the existing better positive correlation clearly indicates the presence of significant amounts of monazite and zircon in the beach samples. In the present study, rich 100

0

75

%

)

25

Monazite Zircon Magnetite Illmenite Rutile Tourmaline Garnet Silimanite Chlorite

Minimum

Maximum

6.32 9.02 11.02 0.00 0.67 0.00 0.30 0.00 0.00

36.00 31.21 29.00 29.21 15.13 19.21 8.21 8.21 7.63

50

50

Weight % of the heavy minerals

)

1 2 3 4 5 6 7 8 9

Name of the minerals

%

Sl. no.

t(

Cl

Sil

ay (

Table 3 Basic information (N¼ 39) of the individual heavy minerals.

25

75

0

100 0

25

50

75

100

Sand (%) Fig. 5. Distribution of sand, silt and clay (%) content in sediments.

8

V. Ramasamy et al. / Applied Radiation and Isotopes 85 (2014) 1–10

Table 4 Pearson correlation matrix among the variables. Bold and italic values in the table represent the better and moderate positive correlation between the variables. U

U Th K DOSE EQ EMF EK EC THM Sand Silt Clay

1.000 0.974 0.411 0.982  0.334  0.074  0.079 0.455 0.865 0.094  0.156 0.695

Th

1.000 0.383 0.999  0.289  0.148  0.106 0.425 0.845 0.158  0.222 0.744

K

1.000 0.395  0.166 0.226  0.155 0.731 0.350  0.195 0.150 0.464

DOSE

1.000  0.297  0.134  0.103 0.436 0.851 0.146  0.210 0.740

EQ

1.000  0.315  0.008  0.068  0.311 0.504  0.469  0.226

EMF

1.000 0.442 0.058  0.143  0.532 0.526  0.092

EK

EC

THM

1.000  0.111  0.110  0.035 0.038  0.077

1.000 0.632  0.118 0.080 0.416

Sand

1.000 0.008  0.053 0.508

Silt

1.000  0.996 0.225

Clay

1.000  0.306

1.000

Note: U, Th and K represent concentration of 238U, 232Th and 40 K (Bq/kg) respectively, DOSE – absorbed dose rate (nGy/h), EQ, EMF, EK and EC respectively represent relative distribution of quartz, microcline feldspar, kaolinite and calcite, THM – weight percentage of total heavy mineral, sand, silt and clay represents percentage of sand, silt and clay (%).

33.41

Cluster - III

Similarity (%)

presence of heavy minerals such as monazite, zircon, etc. in the present beach can also be confirmed by the obtained better positive correlation between the 238U and 232Th. Also, from the high positive correlations between the 238U and 232Th concentrations and absorbed dose rate show that total level of radioactivity is mainly depends upon both 238U and 232Th concentrations. Weak correlations between the above said radionuclides and 40K concentration explain that 40K concentration may not be related to the 238 U and 232Th bearing heavy minerals (Mohanty et al., 2004). By the presence of weak correlation between the 40K and absorbed dose rate, it can be confirmed that the individual contribution of 40 K to the total dose rate is lower. Also from the Table 4, an interesting core subject of the present study i.e. effect of mineralogy on radionuclide concentrations can be assessed. Among the four major light minerals, only calcite is well correlated with 40K concentration and moderately correlated with other radioactive variables. Interestingly, the percentage of total heavy mineral is well correlated with radioactive variables except 40K concentration. Total heavy mineral is poorly correlated with 40K concentration. Thus, any one light mineral/heavy mineral/more than one light/heavy minerals can fix the one or more natural radionuclide concentrations in sediments. Because of both 238U and 232Th concentrations are positively correlated with total heavy minerals, it is expected that the actinides (238U and 232 Th) could be incorporated in heavy minerals (monazite) crystal lattices. Beach sands are mainly composed of two principal types namely carbonate sands and quartz dominant sands (El-Gamal et al., 2007). Sorption characteristics of radionuclides with carbonate mineral sands such as calcite, aragonite and limestone are little explored. Breban et al. (2004) had stated that activity concentration of radionuclides in the sediments depends on the amount of calcium carbonate in the sediments. In the present study, it is true. Finally, from the Table 4, another relation can be found. Among the granulometric contents, content of clay is well correlated with radioactive variables (except 40K) and moderately correlated with 40 K concentration. This correlation indicates that in addition to the heavy minerals, clay content is also act as a second factor to boost up the level of radioactivity in the present sediments. Generally, lower grain sized particles induce the level of radioactivity. In clay sized fractions, organic matter, clay minerals and other contaminants are rich. These things which are presented in clay fractions can enhance the sorption characteristics of the sediments (Shetty and Narayana, 2010). Content of clay, heavy mineral percentage and amount of calcite are moderately correlated among themselves and correlated with radioactive variables. The above contents have common mechanism which controls the radionuclides

55.60

Cluster - II

Cluster - I

77.80

100.00 EQ EMF Sand Silt

EK

EC

K

U

Th Dose HM % Clay

Variables Fig. 6. Dendrogram shows cluster of variables. Note: U, Th and K – concentration of 238 U, 232Th and 40K (Bq/kg), dose – absorbed dose rate (nGy/h), sand, silt and clay represents percentage of sand, silt and clay (%) respectively, EQ, EMF, EK and EC respectively represents relative distribution of quartz, microcline feldspar, kaolinite and calcite, HM (%) – weight percentage of total heavy mineral.

concentrations. Thus, the above contents could be the characteristic parameters which are having a great effect on radionuclides concentrations in sediment.

3.6.2. Cluster analysis (CA) Cluster analysis is a technique which is used to provide important information about the grouping of variables on the basis of similarity. CA is carried out by MINITAB 15 software to confirm the obtained relation between the variables through correlation analysis. Details and purpose of CA are presented in Ramasamy et al. (2013). It gives dendrogram and derived dendrogram is shown in Fig. 6. In this dendrogram, all the variables are grouped into three statistically significant clusters based on the similarity of the variables. Cluster I consists of five variables such as 238U and 232Th concentrations, absorbed dose rate, total heavy mineral percentage and clay content. In this cluster, heavy mineral percentage is grouped with above said radioactive variables with high similarity. However, clay content is grouped with radioactive variables with comparatively low similarity. Cluster I confirms that the radioactivity variables except 40K mainly depend upon the heavy mineral percentage and depend upon the clay content. Cluster II consists of amount of calcite and 40K. Cluster II is also linked with cluster I variables with low similarity. This indicates that 40K concentration depends upon light mineral calcite. However, calcite has less similarity with other radioactive variables.

V. Ramasamy et al. / Applied Radiation and Isotopes 85 (2014) 1–10

The variables such as amount of quartz, microcline feldspar and kaolinite, and content of sand and silt are grouped in cluster III. This cluster is also linked with cluster I with very low similarity. This grouping can be formed on the basis of low similarities with main radioactive variables. Thus, the above cluster III parameters should be a least factor to induce the level of radioactivity. 3.6.3. Factor analysis (FA) Factor analysis is performed to identify the factors influencing the level of radioactivity in the present sediments. Obtained total variance and rotated factor loadings of the variables are given in Tables 5 and 6. FA revealed four factors with eigen value 41, explaining 86.45% of the total variance (Table 5). The first factor accounted for 42.23% of the total variance and mainly characterized by high positive (4 0.7) loading of variables (cluster I variables) such as concentrations of 238U, 232Th, absorbed dose rate, heavy mineral percentage and clay content. Also, factor 1 consists of variables (cluster II variables) such as amount of calcite and 40K concentration with moderate positive (40.5– o0.7) loading. Factor 1 proves that main influence factor is percentage of HM and next influence factor is content of clay to increase the total level of radioactivity. Factor 2 accounted for 24.04% which mainly consists of content of silt and microcline feldspar with high positive loading and content of sand with high negative loading. It indicates that the silt and microcline feldspar is second factor to induce the level of radioactivity. Sand content is acted as a negative factor to induce the radioactivity. Factor 3 accounted for 10.57% which consists of kaolinite content with Table 5 Total variance explained for radioactive variables and other sediment properties. Component

1 2 3 4 5 6 7 8 9 10 11

Initial eigen values Total

% of variance

Cumulative %

5.068 2.886 1.268 1.153 0.649 0.382 0.312 0.216 0.044 0.022 0.000

42.234 24.048 10.571 09.607 05.410 03.181 02.597 01.800 00.365 00.185 00.002

42.23 66.28 76.85 86.45 91.86 95.05 97.64 99.44 99.81 99.99 100.00

Table 6 Rotated factor loading of the variables.

9

moderate positive loading. It shows that the kaolinite content may be acted as a least factor. Factor 4 accounted for 9.60% and it consists of 40K concentration and major light minerals with low positive loading. The last factor gives an idea about light mineral associations with 40K. However, these variables do not influence the total radioactivity.

4. Conclusion Natural radiation level, mineralogical (light and heavy) and granulometric characteristics of Kerala beach sediments have analyzed successfully. Average concentrations of natural radionuclides (238U and 232Th) and all calculated radiological parameters are higher than the recommended level. All the radiological parameters in most of the sites are having higher values than recommended values. Therefore, the sediments of Kerala beach pose significant radiological threat to the people living in the area and tourists going to the beaches for recreation or to the sailors and fishermen involved in their activities in the study area. The FTIR analysis confirms the presence of various light minerals. Among the various observed minerals, quartz, microcline feldspar, kaolinite and calcite are major and others are trace on the basis of their presence and intensities of corresponding peaks. The amount of above major minerals in the sediments decreases in the order of quartz 4calcite4 microcline feldspar 4kaolinite. Crystallinity index values indicate the presence of well ordered, ordered and intermediate crystalline quartz in present study area. Heavy mineral separation analysis authenticates that THM percentage is varied greatly from site to site and the presence of nine heavy minerals. Among the nine heavy minerals, monazite, zircon, magnetite and illmenite are considered as predominant and other minerals are minor minerals. Due to the rapid and extreme changes occur in beaches, erratic distribution of light and heavy minerals is observed. Granulometric analysis shows that sand is the main and clay is least constituent in all the sampling locations. Presence of heavy minerals such as monazite and zircon are also confirmed by correlation analysis. Multivariate statistical analysis provides information about the effect of mineralogy on radionuclide concentrations. The present study concluded that heavy minerals induce the 238U and 232Th concentrations. Whereas, light mineral calcite is control the 40K concentration. In addition to the heavy minerals, clay content also induces the important radioactive variables.

Acknowledgment

Variables

Factor 1

Factor 2

Factor 3

Factor 4

U Th K DOSE EQ EMF EK EC THM Sand Silt Clay

0.954 0.958 0.559 0.962  0.315  0.126  0.161 0.630 0.884 0.119  0.188 0.796

0.011  0.070 0.352  0.055  0.622 0.726 0.173 0.241 0.071  0.937 0.925  0.117

0.185 0.180  0.474 0.177  0.275 0.301 0.721  0.478 0.019 0.105  0.114 0.080

 0.095  0.110 0.440  0.104 0.415 0.413 0.549 0.408  0.121 0.199  0.206 0.138

Note: U, Th and K represent concentration of 238U, 232Th and 40K (Bq/kg) respectively, DOSE – absorbed dose rate (nGy/h), EQ, EMF, EK and EC respectively represent relative distribution of quartz, microcline feldspar, kaolinite and calcite, THM – Weight percentage of total heavy mineral, sand, silt and clay represents percentage of sand, silt and clay (%).

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