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Year : 2013  |  Volume : 36  |  Issue : 3  |  Page : 128-132  

Laser flourimetric analysis of uranium in water from Vishakhapatnam and estimation of health risk

Environmental Monitoring and Assessment Section, Health Safety and Environment Group, Bhabha Atomic Research Centre, Trombay, Mumbai, Maharashtra, India

Date of Web Publication28-Jul-2014

Correspondence Address:
G G Pandit
Environmental Monitoring and Assessment Section, Health Safety and Environment Group, Bhabha Atomic Research Centre, Trombay, Mumbai, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0972-0464.137478

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Uranium is a naturally occurring radioactive element that is both radiologically and chemically toxic. The presence of uranium in the aquatic environment is due to the leaching from natural deposits, release in mill tailings, the combustion of coal and other fuels, and the use of phosphate fertilizers that contain uranium. Intake of uranium through air and water is normally low, but in circumstances in which uranium is present in a drinking water source, the majority of intake can be through drinking water route. The uranium concentrations in ground water samples from Vishakhapatnam, India were estimated using laser fluorimetric technique and were observed to range from 0.6 to 12.3 ppb. The laser fluorimetry technique was found to be an excellent tool for direct measurement of uranium concentration in water samples at ultra-trace levels. The annual effective dose, cumulative dose for 70 years and the lifetime excess cancer risk from drinking of this water were calculated. The risks were low averaging only 10.6 × 10 -6 as none of the samples were observed to exceed the WHO recommended uranium concentration limit of 30 ppb.

Keywords: Cancer risk, dose, drinking water, hexavalent uranium, Iaser fluorimetry

How to cite this article:
Bhangare R C, Tiwari M, Ajmal P Y, Sahu S K, Pandit G G. Laser flourimetric analysis of uranium in water from Vishakhapatnam and estimation of health risk. Radiat Prot Environ 2013;36:128-32

How to cite this URL:
Bhangare R C, Tiwari M, Ajmal P Y, Sahu S K, Pandit G G. Laser flourimetric analysis of uranium in water from Vishakhapatnam and estimation of health risk. Radiat Prot Environ [serial online] 2013 [cited 2021 Apr 15];36:128-32. Available from: https://www.rpe.org.in/text.asp?2013/36/3/128/137478

  Introduction Top

In recent years, there have been many incidences of presence of uranium in ground water. [1],[2] The major concern about contamination of uranium in drinking water is that uranium is a naturally occurring radioactive element that is both radiologically as well as chemically toxic. Uranium has both natural and anthropogenic sources that could lead it to the ground aquifers. These sources include leaching from natural deposits, release in mill tailings, emissions from the nuclear industry, combustion of coal and other fuels, and the use of phosphate fertilizers that contains uranium and contribute to ground water pollution. [1],[2],[3],[4] Uranium exists in various oxidation states, but the most dominant states of uranium are the hexavalent and tetravalent. The hexavalent state of uranium is particularly important in water because the tetravalent compounds are almost all insoluble. In nature, the hexavalent form of uranium is commonly obtained in the form of uranyl ion UO 2 2+ . Although ubiquitous in the environment, uranium has no known metabolic function in animals and is currently regarded as non-essential. [5] Uranium enters into human tissues mainly through drinking water, food, air and other occupational and accidental exposures. Intake of uranium through air and water is normally low, but in circumstances in which uranium is present in a drinking water source, the majority of intake can be through drinking water. Water with uranium concentration above the recommended maximum acceptable concentration of 30 ppb [6],[7] is not safe for drinking purposes as it can cause damage to internal organs, on continuous intake.

A comprehensive explanation of natural environmental uranium concentration ranges, forms of ingestion and inhalation, body absorption and excretion, and other radiological and chemical aspects of uranium are well explained and presented in the literature. [8] Elevated uranium concentrations in drinking water have been associated with many epidemiological studies such as leukemia, stomach and urinary track cancer as well as kidney toxicity, renal, bone damage and increased diastolic and systolic blood pressure, yet a clear understanding of the human toxicity from uranium elevated drinking waters has not been achieved nor associated. [9],[10],[11],[12] A recent study, [13] found a strong correlation between uranium concentration in drinking water and uranium in bone, suggesting that bones are good indicators of uranium exposed via ingestion of drinking water. Therefore, such studies trigger further assessment of uranium's adverse health effects on humans and/or the environment for countries where elevated uranium concentration in drinking water has been observed.

The World Health Organization (WHO) guidelines ensure an exposure lower than 0.1 mSv y -1 assuming a water consumption rate of 2 L per day. A TDI (tolerable daily intake) of 0.6 g kg -1 of body weight per day was derived using the LOAEL (lowest-observed-adverse-effect level) of 60 g kg -1 of body weight per day and an uncertainty factor of 100 (for intra and interspecies variation). [6] An exposure of about 0.1 mg kg -1 of body weight of soluble natural uranium results in transient chemical damage to the kidneys. [14] Hence, it becomes important to study the level of uranium in drinking water for health risk assessment. This study has been undertaken for the estimation of uranium concentration in drinking water collected from Vishakhapatnam, India, using laser induced fluorimetry. The estimated concentrations were further used for calculation of health risk due to drinking of this water.

  Materials and methods Top

Laser induced fluorimetry

In Laser induced fluorimetric analysis technique, U (VI) can be efficiently excited by using a laser light source in the near UV region (350-300 nm). All fluorescence measurements were performed with the Quantalase Uranium analyser (Model QL/LEDF/01)   fabricated by Laser Applications and Electronics Division, Centre for Advanced Technology (CAT), Department of Atomic Energy, Indore, India. in which a compact sealed-off nitrogen laser emitting very intense but short lived (7 ns) pulses of 337.1 nm which selectively excites the fluorescence of the uranyl ions in the solution. Under UV excitation uranyl salts emit green luminescence, which is detected by a photomultiplier tube (PMT). Sodium pyrophosphate (Na 4 P 2 O 7 .10H2 O) solution (5%) was prepared in distilled water and a pH value of 7.0 was adjusted by adding dilute (10% vol/vol) phosphoric acid solution drop wise. This solution acts as fluorescence enhancing reagent. [15] Also, it effectively complexes U (VI) and buffers the solutions to ensure a defined state of U (VI) in the analyzed sample. Due to the insolubility of tetravalent uranium in aqueous solutions it is absent in the water samples. Thus the uranium in water is entirely in the hexavalent state. Most of the organic species present in natural water fluoresce when excited by nitrogen laser. But

the fluorescence is mostly in the blue region. A long-pass filter mounted in front of the PMT cuts off the fluorescence of the other organic compounds present. Organic compounds derived from break down of plant materials generally have very short fluorescence lifetime (a few ns) whereas uranyl fluorescence is few tens of microseconds. Hence, the detector is time gated such that the fluorescence is measured only after reducing the background substantially.

Sampling and analysis

Water samples were collected from bore-wells and open wells at different locations in and around Vishakhapatnam, Andhra Pradesh, India. The samples were filtered before analysis. The instrument was calibrated with standard samples containing 1, 2, 5, 10, 15, 20 and 30 ppb of uranium. To overcome the effect of interfering materials that would be present in the sample, internal standard addition method was used during analysis. The limit of detection obtained using this method was as low as 0.2 ppb. Each sample was collected in duplicates and also was analysed in duplicates. Thus each water sample was effectively analyes 4 times (n = 4). Statistical analyses included calculations of the mean value and the standard deviation which were calculated using Microsoft excel software.

  Results and discussion Top

Uranium concentration in water

The uranium concentrations in ground water alongwith the total dissolved solids (TDS) and P H of the samples from different places around Vishakhapatnam are shown in [Table 1].
Table 1: Concentrations of U in ground water at different locations in Vishakhapatnam

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The concentrations of uranium in the collected samples varied from 0.6 ppb to 12.3 ppb. The water from Nutulagontipalem showed minimum uranium concentration whereas the water from Gobburu showed maximum. The average uranium concentration in all the water samples was 5.1 ppb. Only 3 locations showed concentration above 10 ppb, and none of the samples was exceeding the WHO limit of 30 ppb. There was no correlation found between the uranium concentration and TDS or P H of the samples.

Comparison of uranium concentration with world values

The values of the uranium concentration in drinking ground water obtained in this study were compared with other studies worldwide. The results are shown in [Table 2].
Table 2: Range of uranium concentration in drinking water worldwide

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Uranium concentration in drinking water worldwide shows large variations. The amount of uranium present in the waters mainly depends upon geology of the area. The water from Jordan had largest range of uranium concentration varying from 0.04 ppb to 1400 ppb. In most of the countries, the maximum uranium concentration is exceeding the WHO limit of 30 ppb. South Greenland had the minimum uranium concentration range of 0.5 to 1 ppb only. Even in some of the studies on the drinking waters from India the range of uranium concentration is alarming and extends from 0.03 to 1442.9 ppb. The concentration of Uranium in ground waters raised alarms in the country after the contamination levels in drinking water from Punjab were found to be reasonably high. As shown in [Table 2], the drinking water concentrations of uranium in Punjab and Aligarh, UP are far higher than the WHO limit of 30 ppb. However the concentration of uranium in ground water from Jaduguda which is well known for uranium mining are much lower than the WHO limit. In comparison with other studies worldwide, and within India it can be seen that the uranium concentrations in Vishakhapatnam were on very lower side.

Dose and risk from uranium in drinking water

The probable effective dose and corresponding lifetime excess cancer risks due to consumption of the uranium contaminated ground water were calculated from the uranium concentration in ground water from all sampling locations. The results are depicted in [Table 3]. The dose was calculated by

D = AC x F x Intake (1)
Table 3: Dose and lifetime risk estimation from uranium concentration in ground water

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where, D is the annual effective dose (μSv y -1 ), AC is activity concentration of uranium (Bq L -1 ), and F is effective dose per unit intake via ingestion (4.5 × 10 -8 μSv y -1 /Bq L -1 ) and I is the average water intake (2L per Day = 730 liters per year). The calculations for dose rate, cumulative dose, and average lifetime excess cancer risk were made by using the conversion factor given by ICRP 72 [38] and WHO [6] for public exposed to natural uranium. Cumulative dose was calculated for an average life of 70 y (Annual Effective dose × 70 years) and cancer risk has been predicted by using risk factor of 7.3 × 10 -2 per Sv [6, 39].

LR = CD x RF (2)

Where LR is the Lifetime excess cancer risk, CD is the Cumulative dose and RF is the risk factor. Annual effective dose from the collected drinking waters was found to vary from 0.25 μSv y -1 to 5.03 μSv y -1 , which is well below the recommended limit of 0.1 mSv y -1.6 Cumulative doses calculated from these water samples were found in the range of 17.8-352 μSv. The corresponding life time excess cancer risk was found to vary from 1.3 × 10 -6 to 25.7 × 10 -6 with a mean value of 10.6 × 10 -6 in water samples. The risk was calculated by multiplying the risk factor of 7.3 × 10 -2 per Sv with reference dose level (RDL) equal to 0.l mSv annual exposure via drinking water. [6]

  Conclusion Top

The laser fluorimetric technique was observed to be very efficient for the analysis of trace level uranium concentrations in water. Detection limits as low as 0.2 ppb were achieved using this technique for direct analysis of the ground water. The standard addition method effectively removes matrix interference if any producing accurate results. The uranium concentration in none of the ground water samples in this study were exceeding the WHO guidelines of 30 ppb. Hence, the waters can be considered to be safe for consumption. The calculated doses from possible intake of uranium through these ground waters were very low and the life time excess cancer risk had a mean value of 10.6 × 10 -6 which is quite low when compared with uranium concentrations in drinking waters from other countries worldwide.

  References Top

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  [Table 1], [Table 2], [Table 3]

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