drinkingwateranalysis_methodinfo

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Drinking water analyses

Overview of tests and assessments

Total alpha- and beta-radioactivity Tritium

Radon-222

Radium-226 and radium-228

Uranium

Gamma-emitting nuclides

Dose assessment

Total alpha- and beta-radioactivityISO 17025: This test is included within the scope of the laboratorys accreditation.

Introduction

Radionuclides likely to be encountered in drinking water emit alpha- or beta-radiation, and anindication of the significance of radioactivity levels can be obtained by the fairly simplemeasurement of the total amounts of these emissions without the need for complicatedanalyses of individual contaminants. Such total radioactivity measurements can beperformed rapidly and cost-effectively.

Method

An aliquot of water is evaporated to a small volume and transferred to a glass vial in which it isevaporated to dryness. The residue is dissolved in a dilute mineral acid and a small volume ofscintillator solution added. The radioactivity level is determined by liquid scintillation counting(LSC) which discriminates between alpha- and beta-particle emissions. This method does notinclude gaseous radon or its immediate decay products, and a separate method is requiredfor these.

Minimum detectable concentration

Analytical results are expressed as becquerels (Bq) per litre for each of the emission types(1 Bq = 1 nuclear transformation per second). The minimum detectable concentrations for totalalpha- and beta-radioactivity concentrations are 0.03 Bq/L

and 0.2 Bq/L,

respectively.

Sampling requirementsSample volume 200 mL.

Turnaround time

Turnaround time is 5 working days from receipt of sample.

NRL Client information sheetPO Box 25099 Page 1/6CHRISTCHURCH Drinking water methods March 2008


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Tritium

Introduction

Tritium is a radioactive isotope of hydrogen (H-3) which decays with a half-life of 12.3 yearswith the emission of beta radiation. Small amounts are produced naturally in the environmentby cosmic radiation. It is also produced in nuclear reactors and weapon detonations. Mosttritium found in the environment results from nuclear weapons testing before 1980. In water,tritium forms part of the water molecule in place of a hydrogen atom (tritiated water) and it istherefore readily assimilated by biological organisms.

Method

An aliquot of the water is mixed with a liquid scintillator in a glass vial and the tritium betaemissions are counted by LSC together with those of a second sample spiked with a knownamount of tritium. The method may suffer from interferences from other beta-emittingradionuclides but the regulatory limits for tritium are usually much higher than those of otherradionuclides (around 1 kBq/L) and any interferences are therefore insignificant.


The minimum detectable concentration is 100 Bq/L.

Sampling requirements

Sample volume 100 mL.

Turnaround time




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Radon-222ISO 17025: This test is included within the scope of the laboratorys accreditation.

IntroductionRadon-222 (

222Rn) is a chemically inert noble gas which is the decay product of radium-226

(itself part of the natural uranium-238 radioactive decay series), decaying by alpha-particleemission with a half-life of 3.8 days. As all rocks and soils contain

238U, artesian waters

inevitably contain222

Rn which dissolves in the water during its passage through subterraneanmaterials. Radon-222 itself decays through a series of short-lived radioactive isotopes ofpolonium, lead and bismuth:

26.8 min 19.9 min3.05 min3.8 days 214Po214Pb218Po222Rn 214Bi

The measurement of

222Rn involves the detection of the combined alpha-particle emissions

from the three alpha-emitters in this series (222

Rn,218

Po and214

Po).

Method

An aliquot of the water sample is mixed with a liquid scintillator and alpha emissions countedby LSC. The contribution of interfering alpha-emitting radionuclides is determined byanalysing a blank sample.


A water sampling kit comprising a one-litre polyethylene sampling bottle, tubing for fillingbottle and sampling instructions is supplied by NRL on request. A one-litre water samplerepresentative of the source should be collected. To minimise

222Rn loss, the sampling bottle

must be gently filled to the top, without agitation or aeration of the source water. The samplemust be shipped back to the NRL within 48 hours after sampling.


The minimum detectable concentration for222

Rn is 2 Bq L-1

assuming delivery of the samplewithin 48 hours. Resampling may be requested if there are delays in shipping to NRL.


Sample volume 100 mL. Samples must be transported in radon-proof sampling bottles. Thesecan be obtained from NRL.

Turnaround time




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Radium-226 and Radium-228

Introduction

The radium isotopes radium-226 and radium-228 are members of the naturally occurringuranium and thorium decay series. Radium is partially soluble in water and may therefore bepresent in drinking waters from underground sources.

Method

The analytical method relies on the decay of the radium isotopes to their respective decayproducts which emit gamma radiation. The radium is coprecipitated from the water withbarium sulphate and the collected precipitate is embedded in epoxy resin to trap the

222Rn

gas emanating from the226

Ra. After a resting period of thirty days, when the radon hasreached equilibrium with the

226Ra, the sample is analysed by detection of gamma-emitting

species, particularly214

Pb and214

Bi, by gamma spectrometry. Radium-228 concentrationsare determined in the same samples through detection of gamma emissions associated with

its decay product actinium-228.


The minimum detectable concentration of each isotope is 0.05 Bq/L.



Turnaround time

Turnaround time is 35 working days after receipt of sample.



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Uranium

Introduction

Three natural isotopes of uranium exist in the environment: 238U (half-life 4.47109 a), 235U(7.0410

8a) and

234U (2.4510

5a). These uranium isotopes are found in varying

concentrations throughout the Earths crust. Uranium is partially soluble in water, formingstrong complexes with carbonate ions, and is therefore rather mobile in the environment.

Method

The separation of the uranium isotopes from other radionuclides is performed by calciumphosphate coprecipitation followed by extraction chromatography. Analysis of the recovereduranium is performed by alpha spectrometry which distinguishes between alpha emissionsfrom the three isotopes.

Minimum detectable concentrationThe minimum detectable concentration for each isotope is 0.01 Bq/L.



Turnaround time




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Gamma emitting nuclidesISO 17025: This test is included within the scope of the laboratorys accreditation.

IntroductionMany radionuclides emit gamma radiation during decay. The radiation is characteristic ofeach radionuclide and may therefore be used for identification and quantification of nuclides.

Method

A 500 mL aliquot of the sample is analysed by high-resolution gamma spectrometry, withoutany pretreatment.


The minimum detectable concentration is radionuclide dependent.



Turnaround time


Dose assessment

Introduction

The ultimate purpose of drinking water regulations is protection from the harmful effects ofcontaminants. Most regulations stipulate maximum allowable concentrations for a selectionof radionuclides and total alpha- and beta-radioactivity to allow fast decision making. Othersrequire a full dose assessment based on measured or estimated radionuclide concentrations.Such an assessment clarifies whether the water is fit for human consumption.

Turnaround time

Turnaround time is 2 working days from completion of the necessary analyses.


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