radioactivity in environmental samples: calibration standards measurement methods, quality...

Environment International, Vol. 10, pp. 109-116, 1984 0160-4120/84 $3.00 + .00 Printed in the USA. All rights reserved. Copyright © 1984 Pergamon Press Ltd.

RADIOACTIVITY IN ENVIRONMENTAL SAMPLES: CALIBRATION STANDARDS MEASUREMENT METHODS, QUALITY ASSURANCE, AND DATA ANALYSIS a

C. Richard Cothern Office of Drinking Water, U.S. Environmental Protection Agency, Washington, D.C. 20460, USA

Arthur N. Jarvis and Earl L. Whittaker Environmental Monitoring System Laboratory, U.S. Environmental Protection Agency, Las Vegas, Nevada 89114, USA

Lewis Battist Office of Radiation Programs, U.S. Environmental Protection Agency, Washington, D.C. 20460, USA

(Received 9 December 1983; Accepted 9 April 1984)

The numerous environmental radioactivity measurements made by and for the U.S. Environmental Pro- tection Agency (U.S. EPA) include measurements on samples of water, urine, food, milk, and air filters. Calibration standards are listed which are available in the form of water solutions and soils for a wide range of radionudides. Method validation procedures for U.S. EPA approval include protocol development and single-laboratory and multiple-laboratory evaluation for precision and accuracy. Inter- laboratory comparison studies are conducted for both cross-check and performance evaluation samples and involve 295 federal, state, and local laboratories. For water samples, 80%-90% of the participating laboratories are within the control limits for most of the radionuclides measured; however, some problem areas exist, especially for radium-228 and strontium-89 and -90. For milk and food samples, more than 90% of the laboratories are within control limits for cobalt-60 and cesium-137 but some problems exist for the measurement of strontium-90, iodine- 131, and potassium-40. For tritium, 91% of the laboratories are within the control limit for water samples and 87% are within the control limits for the urine samples. The laboratory performance for air filter samples shows some problems for gross beta, strontium-90 and cesium-137 measurements.

Int roduct ion

M e a s u r e m e n t o f the concen t r a t i on o f r ad ioac t iv i ty in env i ronmen ta l samples p e r f o r m e d by the U.S. En- v i ronmen ta l P ro t ec t i on A g e n c y (U.S. E P A ) is requ i red by var ious regu la t ions o f the U.S . E P A a n d for the Nuc lea r Regu l a to ry C o m m i s s i o n (NRC) and the De- p a r t m e n t o f Energy . E n v i r o n m e n t a l r ad ioac t iv i ty m easu remen t s a re c o n d u c t e d regu la r ly by m a n y different federa l , s ta te , local , a n d p r iva te l abo ra to r i e s .

aThis report has been reviewed by the Office of Drinking Water, U.S. Environmental Protection Agency, and approved for publication. Ap- proval does not signify that the content necessarily reflects the views and policies of the U.S. Environmental Protection Agency.

These d a t a a re used for a wide var ie ty o f purposes , in- c luding assessment o f hea l th effects , e s tab l i shment o f s t anda rds and guidel ines , a n d compl i ance m o n i t o r i n g for en fo rcemen t act ivi t ies .

The e nv i ronme n ta l survei l lance act ivi t ies wi th in U.S. E P A inc lude suppo r t for the Off ice o f R a d i a t i o n P ro - g ram ' s test well mon i to r i ng as requ i red by the Resource Conse rva t i on a n d Recovery A c t ( R C R A , 1976), gross a lpha -pa r t i c l e ac t iv i ty a n d gross be ta -pa r t i c l e act ivi ty me a su re me n t s requ i red by the N a t i o n a l P o l l u t a n t Dis- charge E l i m i n a t i o n Sys tem ( N P D E S , 1976), a n d moni - to r ing act ivi t ies requ i red by the Safe Dr ink ing W a t e r Ac t ( S D W A , 1974). The r a n g e . o f samples for all the var ious p r o g r a m s are col lec ted and ana lyzed for different m e d i a inc luding ur ine , mi lk , food , water , and air fi l ters.

109

110 C.R. Cothern, A. N. Jarvis, E. L. Whittaker, and L. Battist

The measurements required by the SDWA for radionuclides are listed in the National Interim Primary Drinking Water Regulations (NIPDWR; U.S. EPA, 1981). Monitoring required by these regulations include gross alpha-particle activity, gross beta-particle activity, radium-226, radium-228, and fission fragments and ac- tivation products (some of the radionuclides of interest are strontium-89 and -90, chromium-51, cobalt-60, zinc-65, cesium-134, cesium-137, and ruthenium-106). Uranium and radon are specifically excluded from the gross alpha-particle activity (defined as measured activity minus uranium and radon activity), but to subtract them out, their concentration must be determined.

The NIPDWR specifies the radiochemical methods to be used for these measurements. Some of the procedures contained in the NIPDWR have been updated and improved (see, for example, U.S. EPA, 1980). Some of the procedures are undergoing validation to allow their use in U.S. EPA-approved laboratories. A more complete discussion of the current state of methods for the determination of concentration of radionuclides in drinking water is provided by U.S. EPA (1983b).

Methods Development, Validation, and U.S. EPA Approval

New and improved methods are continually being developed. Those of primary interest to U.S. EPA are the ones that are less expensive to perform, quicker, or, in some cases, more precise than those presently being used. Also, as new requirements emerge, new methods will be needed or existing ones will need to be validated.

As an example of these needs, the NIPDWR requires a single sequence of radiochemical measurements for natural radioactivity, with each succeeding measurement dependent on the previous one (see general discussion of the flow chart in U.S. EPA, 1981, p. 51). In this sequence radium-228 measurements are required only if radium-226 exceeds 3 pCi/L. This requirement was included because of the expense of monitoring for radium-228. Since radium-228 is a beta emitter (beta- gamma as opposed to alpha-gamma), methods are being investigated which could either screen for only gross beta-particle activity or provide a less expensive method for assaying radium-228 activity. In addition, some con- sideration is being given for a possible future standard for uranium and radon. These and other potential drinking water contaminants such as polonium-210, lead-210, and thorium will require validated methods if they are regulated.

Several steps are required to validate a method for use by U.S. EPA in its environmental monitoring program. The first step is to develop a detailed protocol. The protocol or written analytical procedure must include a complete, step-by-step procedure specifying technique, reagents and equipment, and methods to be used.

Next, the procedure is tested by one laboratory to evaluate the precision and accuracy. The method is then submitted to a collaborative test by six or more laboratories, with protocol revisions made if necessary. A final protocol specifying precision and accuracy is then prepared. Examples of the resulting methods used in the measurement of concentrations o f radioactivity in drinking water are listed in U.S. EPA (1980).

Some laboratories use methods different from the listed U.S. EPA-approved methods for specific pollut- ants. However, in order to be acceptable to U.S. EPA, these must be shown to be equivalent to the validated U.S. EPA methods in the following way:

For limited use (one laboratory): (a) collect a minimum of three representative

samples from different sites; (b) analyze each sample four times with the pro-

posed method and four times with the U.S. EPA method;

(c) compare data. For nationwide use:

(a) collect six representative samples from five separate sources;

(b) analyze four times with the proposed method and four times with the EPA method;

(c) compare data.

Thus, a total of 240 measurements are needed to validate a method for nationwide use.

Laboratory Certification For a laboratory to be certified to perform analysis of

drinking water samples for radioactivity for compliance purposes, several specific requirements must be met. Among the requirements are the following (for more detail concerning the requirements, see U.S. EPA, 1982a.):

A laboratory must participate at least twice each year in those U.S. EPA laboratory intercomparison cross-check studies that include each of the analyses for which the laboratory is, or wants to he, certified. Analytical results must be within control limits described in U.S. EPA (1978).

A laboratory must also participate once each year in an appropriate water supply performance evaluation (blind sample) study ad- ministered by U.S. EPA. Analytical results must he within control limits established by U.S. EPA for each analysis for which the laboratory is, or wants to be, certified.

The quality assurance program of the U.S. EPA, of which the drinking water laboratory certification program is a part, is designated to encourage the development and implementation of quality control procedures at all levels of sample collection, analysis, data han- dling, and reporting.

Radioactivi ty in environmental samples 111

Calibration Standards The major objective of this program is to encourage

the development of intralaboratory and interlaboratory quality control procedures and thus help ensure that environmental radiation data are valid. Accurately calibrated samples (known as standard solutions), furnished by U.S. EPA through its laboratory in Las Vegas [En- vironmental Monitoring Systems Laboratory (EMSL- LV)] are used by laboratories in calibrating new instruments, implementing and maintaining routine instrument calibration programs, evaluating analytical procedures, and developing and revising data processing programs.

The radionuclides used in preparing standard solutions are obtained from the National Bureau of Stan- dards (NBS), Laboratoire de Metrologie des Rayon- nements Ionisants (Paris, France), or from commercial sources. The uncertainty in the known activity of those supplied radionuclide solutions ranges from 0.5% to 5%. The activity of radionuclide impurities, excluding daughters, is documented and typically is less than 1 °7o of the activity of the principal radionuclide at the time of sample preparation.

Upon receipt of a radionuclide solution by EMSL- LV, the radionuclide activity is checked for impurities and for the activity specified by the supplier. Following purity and activity verification, the solution is diluted to

the desired concentration, using acid preservative and carrier of the same chemical composition as was used by the supplier. The diluted solution is aliquoted into 5-mL glass ampuls which are then flame-sealed and added to the EMSL-LV inventory of standard radionuclide solutions.

To assure further the precision and accuracy of the prepared standard solutions, the Quality Assurance Division of EMSL-LV participates in ongoing traceabil- ity studies (Cavallo et al., 1973) with the NBS. In general, the U.S. EPA and NBS values are within 10/0- 2% of each other (see U.S. EPA, 1982b).

The inventory of standard solutions consists of a number of calibrated radionuclide solutions as shown in Table 1. Except for 1311, every effort is made to maintain this inventory so that samples can be shipped in a timely manner. The " q is prepared bimonthly and distributed to requestors on record.

Throughout the year, the additional radionuclide solutions listed in Table 2 are calibrated and made available for distribution. The U.S. EPA will obtain, calibrate, and distribute any of these radionuclides as time and resources permit, after 10 or more requests have been received.

Table 1. Inventory of standard solutions.

Type Major Gamma a °70 Gamma Isotope Emission Half-Life Peak (MeV) Abundance d p m / g b

3H b e t a - 12.35 yr - - 10,000 ~4C beta - 5730 yr - - 10,000

~4Mn gamma 312.5 day 0.835 99.978 40,000

sTCo gamma 270.9 day 0.122 85.6 80,000 6°Co b e t a - , gamma 5.271 yr 1.333 100 40,000

63Ni b e t a - 92 yr - - 10,000 65Zn b e t a + , gamma 244.1 day 1.115 50.75 160,000

89Sr beta - 50.6 day - - 160,000

9°Sr b e t a - 28 yr - - 10,000

'°6Ru beta - , gamma 369 day 0.512 20.6 160,000

1°9Cd gamma 435 day 0.088 3.72 0.2 #Ci/g "°mAg b e t a - , gamma 250.8 day 0.658 94.6 80,000

'2~Sb b e t a - , gamma 2.77 yr 0.428 29.6 320,000 '3'I b e t a - , gamma 8.04 day 0.364 81.2 0 .4/zCi /g

'33Ba gamma 10.5 yr 0.356 62.4 160,000

'~Cs b e t a - , gamma 2.062 yr 0.605 97.6 40,000

'37Cs b e t a - , gamma 30.17 yr 0.662 85.0 20,000 ~*4Ce b e t a - , gamma 284.3 day 0.134 10.8 320,000 226Ra alpha 1600 yr -- -- 10,000

22~RaC b e t a - 5.75 yr - - 30,000 23°The alpha 7.7 x 104 yr - - 10,000

232THC alpha 1.4 x l01° yr -- - 10,000

232U alpha 72 yr -- - 25,000

23sU alpha 4.5 x 109 yr -- -- 2,500 2~gPuc alpha 2.4 x 10" yr -- - 6,000 24~puC b e t a - 14.4 yr - - 10,000 24~Am alpha 433 yr - - 10,000

aAnd/or gamma used to calibrate solution activity. bApproximate activity (dmp/g) of the radionuclide on the date calibrated. Cprepared and calibrated by the National Bureau of Standards.


Table 2. Standard solutions supplied as needed.

Type Major Gamma a % Gamma Isotope Emission Half-Life Peak (MeV) Abundance dpm/g b

7Be gamma 53.3 day 0.477 10.3 640,000 22Na beta + , gamma 2.602 yr 1.274 99.9 20,000 46Sc b e t a - , gamma 82.80 day 1.120 100 160,000 51Cr gamma 27.704 day 0.320 9.80 0.2 #Ci/g ssCo be ta+, gamma 70.8 day 0.811 99.45 160,000 SgFe beta - , gamma 44.6 day 1.099 56.1 320,000 75Se gamma 120 day 0.265 59.5 320,000 8sSr gamma 64.85 day 0.514 98.0 160,000 88y beta+, gamma 107 day 1.836 99.35 160,000 95Zr b e t a - , gamma 63.98 day 0.757 54.3 320,000

t°3Ru gamma 39.35 day 0.497 86.4 320,000 12'Sb b e t a - , gamma 60.20 day 0.603 97.9 160,000 la9Ce gamma 137.65 day 0.165 80.0 160,000 '41Ce b e t a - , gamma 32.50 day 0.145 48.0 320,000 23°Hg b e t a - , gamma 46.59 day 0.279 81.5 160,000 2°'Bi gamma 38 yr 0.570 97.8 20,000

aAnd/or gamma used to calibrate solution activity. bApproximate activity (dprn/g) of the radionuclide on the date calibrated.

Calibrated soil samples for use as reference materials are also available. These samples have been dried, ground to pass a 170-mesh or a 200-mesh screen, and carefully blended. Reports of calibration accompany the samples. The samples are packaged in glass con- tainers which contain approximately 10 g of soil (some are available in 100-g packages). Soils available are as follows: pitchblende, monazite, uranium mill tailings, shale, fly ash, and mixed soils.

Intercomparison Study and Performance Evaluation Studies

Unlike standard solutions, sample activities provided for these studies are not given to participants. By analyzing the samples provided by U.S. EPA, each participating laboratory may determine the validity of its environmental radiation measurements, identify instrument and procedural problems, and compare its performance with that of other laboratories. These studies also enable U.S. EPA to access the precision and accuracy of radioactivity measurements and to judge the capability of radioanallytical laboratories to analyze environmental samples.

Simulated environmental samples containing one or more radionuclides are prepared in homogenous batches. Aliquots of each batch are distributed to each participating laboratory. Both intercomparison and performance evaluation ("blind") samples are used in the studies. Intercomparison samples contain one or two radionuclides whose activities are unknown to participants. The performance evaluation or "blind" studies use a complex mixture of alpha, beta, and photon emitters, where neither the radionuclides nor the activities are known to participants. The participants perform triplicate analyses of each sample and return their

results to U.S. EPA for statistical evaluation. Upon completion of each study, participants receive a letter containing the correct concentrations of the radionuclides which were present in the sample. Approx- imately two weeks later, each participant receives a final computer report containing the results of the study. A complete description of the program, including the types of samples available, the activity levels, acceptable performance limits, a distribution schedule, an example of a final report, and the calculations used in preparing the report, is published every two years (e.g., see U.S. EPA, 1983a).

Currently there are 295 federal, state, and local nuclear facility, university, and private radioanalytical laboratories participating in some phase of the intercomparison studies program. Any laboratory involved in environmental radiation monitoring may participate in any study and receive samples according to the established distribution schedule. The number of participants in the studies generally varies from 45 laboratories for the tritium in urine study to about 195 laboratories in the gross alpha and gross beta activities in water studies.

For each radionuclide measured, a laboratory sub- mits three analytical results. The mean of these three results is considered to be the reported value.

Outliers, statistically rejected by Chauvenet's Cri- teria, are not used in the statistical calculations of the experimental grand average and standard deviations (Rabinowitz, 1967). The expected laboratory precision for a single determination is actually a specification limit (o) based on both collaborative studies and ex- perience with laboratories which are consistently within the control limits. Most of these limits, as listed in Table 3, were established prior to 1973 and have not been changed since that time.

Radioactivity in environmental samples 113

Table 3. Control limits for each type of analysis.

Activity Analysis pCi/L

Photon Emitters 5-100 >100

Strontium-89 5-100 >100

Strontium-90 2-30 >30

Gross Alpha _< 20 >20

Gross Beta _<_ 100 >100

Tritium _< 4000 >4000

Radium-226 and >0.1

Radium-228 Iodine- 131 < 55

>55 Uranium _< 35

>35 Plutonium-239 > 0.1

One Standard Deviation for a Single Determination

(pCi/L) Control Limits

± 3~/,,/~

5 # ±8.7 5°7o of known # ±0.087(#)

5 /z ±8.7 5070 of known # ±0.087(#)

1.5 ~ ±2.6 5070 of known ~ ±0.087(#)

5 /~ ±8.7 25070 of known /~ ±0.043(#)

5 /z ±8.7 5070 of known ~ ±0.087(#)

(169.85) (known) 0.0933 /~ ±294(#) 0.0933 10070 of known ~ ±000.17(#)

15070 of known /~ ±0.26(#)

6 ~ ± 10.4 10070 of known /~ ±00.17(#)

6 /z ± 10.4 15% of known /z ±00.26(#) 10% of known /z ±0.17(#)

The value of the "specification limit" (17) is used for determining the warning level and the control limits for each study. Since each participating laboratory reports the results of three analyses, the warning levels and control limits are calculated as follows:

warning level = # ±

control limits = # ±

217

317

where # = known value of the radionuclide in the sample; 17 = specification limit (1 standard deviation of a

single determination); N = number of analyses reported (In all cases

N = 3).

The performance of a laboratory is judged by com- paring the mean of the three results reported by the laboratory with the known value. This is accomplished by calculating the normalized deviation of the mean, defined below, of each set of three analyses f rom the known value. The procedures used for these calculations are described below:

Definitions X = mean measured value; # = known value; D = deviation of mean from known value; 17 = expected laboratory precision;

17,, = standard error of the mean; N = number of measured results.

D = X - t z

and the standard error of the mean is

o . = 1 7 /x /N ,

and thus the normalized deviation of the laboratory's mean is

D ~ 17,n •

Whenever the normalized deviation of a laboratory's mean value from the known value for three determina- tions is _< 3, the performance of the laboratory for that radionuclide is acceptable. I f the absolute value of the normalized deviation from the known value is > 3, performance is unacceptable.

Table 4 indicates the percent of laboratories whose results were within the control limits for water studies, and Table 5 contains similar percentages for the other types of studies. The following is a discussion of the results shown in these tables (for more detail, see U.S. EPA, 1983a).

Water Studies An examination of the water intercomparison studies

data reveals that over 90O7o of the participating laboratories have been within the control limits for cesium-134 and tritium. Between 80°7o and 90o70 of the laboratories have demonstrated acceptable performance for cobalt-60,


Table 4. Summary of laboratory performance in water studies.

Study (Water Samples)

Percent of Laboratories Within CL

Gross alpha and beta activities Gross alpha 86 Gross beta 81

Radium-226 and radium-228 Radium-226 80 Radium-228 76

Strontium-89 and strontium-90 Strontium-89 81 Strontium-90 65

Mixed photon emitters Chromium-51 54 Cobalt-60 89 Zinc-65 84 Cesium- 134 92 Cesium-137 87 Ruthenium- 106 55

Blind (mixture of alpha, beta, and photon emitters) Gross alpha 88 Gross beta 53 Radium-226 52 Radium-228 79 Strontium-89 77 Strontium-90 59 Cesium- 134 94 Cesium- 137 94 Uranium 88

Tritium 91 Iodine- 131 80 Plutonium-239 67 Uranium 82

Table 5. Summary of laboratory performance in milk, food, urine, and air filter studies.

Study (Matrices Other than Water)

Percent of Laboratories Within CL

Milk Strontium-89 87.0 Strontium-90 66.2 Iodine- 131 78.5 Cesium-137 95.0 Cobalt-60 93.0 Potassium 72.3

Food Strontium-89 57.3 Strontium-90 48.3 Iodine- 131 80.5 Cesium- 137 86.7 Potassium 48.3

Urine Tritium 87.0

Air Filter Gross alpha 85.5 Gross beta 53.8 Strontium-90 64.0 Cesium-137 77.5

cesium-137, gross alpha and gross beta activities, zinc-65, uranium, strontium-89, and iodine-131.

The blind performance evaluation (PE) data indicates that more than 90°7o of the reporting laboratories had acceptable results for cesium-134 and cesium-137. Be- tween 8007o and 9007o of the laboratories were within the control limits for uranium and gross alpha activity measurements.

From a comparison between the performance data for the measurement of these radionuclides which were common to both the blind and intercomparison studies the percentages within the control limit are shown in Table 6 (see U.S. EPA, 1983a, for more detail).

Performance (i.e., the percent of laboratories within the control limits) should be better for the intercomparison samples, which contain only one or two radionuclides, than for the blind samples, which contain a complex mixture of alpha-, beta-, and photon-emitting radionuclides that are more difficult to analyze. An examination of the data indicates that this is generally true.

There is need for considerable improvement in the measurement of gross beta activity, as shown in Table 6, especially when several different beta-emitting radionuclides are present in the same sample. Some improvement can be accomplished by: (1) requiring all laboratories to calibrate their counting instruments with the same standard; (2) preparation of the detailed protocol for the calibration of proportional counters and the determination of beta efficiency; and (3) training of analysts in proper procedures.

The data also indicate a need for improvement in the measurement of radium-226. This can be accomplished by: (1) requiring all laboratories to use the radon emanation procedure which is specific for radium-226; (2) improving the precipitation method; or (3) by developing alternate methodology. The most promising approach is to require the use of the radon emanation procedure (U.S. EPA, 1975). The instrumentation, glassware, and counting cells are relatively inexpensive and simple to operate. There appears to be little hope in improving the currently approved precipitation procedures (U.S. EPA, 1975). However, alternate test procedures (e.g., alpha/gamma coincidence counting of radium-226) are technically promising.

The measurement of radium-228 in the presence of other beta-emitting radionuclides is a significant problem, as evidenced by the fact that 48070 of the laboratories were outside the control limits for this measurement in the three blind PE studies. Since the measurement problems may be due to inherent deficiencies in the currently approved methodology, studies are being conducted by U.S. EPA to access the validity and reliability of several of the measurement methods for radium-228 (Noyce, 1981).

Approximately 35°70 to 4007o of the laboratories participating in the strontium-89 and strontium-90 studies have been consistently outside the acceptable limit in the

Radioactivity in environmental samples

Table 6. Performance of laboratories participating in water studies.

115

Blind Sample Studies Intercomparison Studies

Number of Number of Labs Percent of Number of Number of Labs Percent of Difference Study Studies Per Study Labs in CL Studies Per Study Labs in CL (%)

Gross alpha 3 75 88 7 98 86 2 Gross beta 3 73 53 7 98 81 28 Radium-226 3 55 79 5 67 80 l Radium-228 3 43 52 5 49 76 24 Strontium-89 3 46 77 4 47 81 4 Strontium-90 3 47 59 4 49 65 6 Uranium 3 40 88 2 53 82 6 Cesium- 134 3 52 94 3 76 92 2 Cesium- 137 3 54 94 3 77 87 7

analysis of strontium-90. This is due to deficiencies discovered in the current approved methodology, which is technique-dependent. The method for the measurement of both strontium-89 and strontium-90 has been collaboratively tested and published (U.S. EPA, 1980), but has not yet been published as the new approved method.

The approved method for the measurement of uranium in drinking water is a fluorometric method (ASTM-D9097) which, although dependent on the re- producibility of the technique used in the preparation of samples, appears to be adequate for the measurement of total uranium, since 8207o to 8807o of the laboratories have had acceptable performance. However, it is not possible to relate the fluorometrically determined total uranium activity to gross alpha activity measurements without making assumptions concerning the equilib- rium of the various isotopes of uranium which may be present in the sample. During the past few years, there has been increased interest in the promulgation of a uranium standard for water. As a result of this growing interest in uranium measurements, an alternate test procedure that can be used to measure total uranium alpha activity has been validated by collaborative testing (U.S. EPA, 1980).

Radionuclides in Milk, Food, Urine, and Air Filters For measurements of radionuclides in milk, food,

urine, and air filters there is no U.S. EPA procedure for approving methods as there is for drinking water measurements. For these media the methods used are the state-of-the-art methods commonly used in laboratories.

During the period between March 1981 and May 1982, four intercomparison studies for radionuclides in milk were completed. The samples, using homogenized milk purchased from a local dairy are spiked with strontium-89, strontium-90, and cesium-137. Occa- sionally, iodine-131 and cobalt-60 are also included. In addition to these isotopes, the laboratories are also expected to analyze for the naturally occuring isotope potassium-40.

The percent of laboratories within the control limits for the analysis of each radionuclide in milk is sum-

marized in Table 7. The results indicate that the laboratories have little difficulty measuring either cobalt-60 (93070 within the control limits) or cesium-137 (95070 within the control limits). There appears to be few, if any, problems in the measurement of strontiumo89 (8707o within control limits). However, there appear to be problems in the measurement of strontium-90 (66070 satisfactory), iodine-131 (78070 satisfactory)and potassium-40 (72.3070 satisfactory). For more details, see U.S. EPA (1983a).

The food sample, which contains protein, carbohy- drates, fat and water, is designed to simulate the dietary intake of a "standard man." After mixing the basic con- stituents, with formalin added as a preservative, the sample is spiked with strontium-89, strontium-90, iodine-131, and cesium-137. It is then packaged in 1-gal cubitainers. Each participating laboratory is provided

Table 7. Comparison of laboratory performance in water, milk, and food studies.

Analysis

Average Number Percent of Number of of Participants Laboratories

Studies per Study Within CL

Water Strontium-89 4 47 81 Strontium-90 4 49 65 Iodine- 131 4 53 80 Cesium-137 3 77 87 Potassium-40 NA - - Cobalt-60 3 76 89

Milk Strontium-89 4 33 87.0 Strontium-90 4 38 66.2 Iodine- 131 2 46 78.5 Cesium-137 4 52 95.0 Potassium-40 4 51 72.3 Cobalt-60 1 60 93.0

Food Strontium-89 3 17 57.3 Strontium-90 3 18 48.3 Iodine- 131 3 27 80.5 Cesium- 137 3 28 86.7 Potassium-40 3 28 48.3 Cobalt-60 NA -- -

116

with two samples and requested to analyze them for the nuclides of interest. The laboratories are also requested to measure potassium-40, a naturally occurring radionuclide present in foods. Each laboratory is expected to perform three analyses of each sample. The performance of the laboratories is summarized in Table 7.

There appear to be few, if any, difficulties with the measurement of either cesium-137 (86.7°7o within control limits) or iodine-131 (80.5O7o within control limits). However, significant problems exist with the measurement of strontium-89 (57.3% within control limits), strontium-90 (48.3% within control limits), and potassium-40 (48.3% within control limits) in food. The higher levels of potassium present in food should, in fact, yield better data than can be expected from a milk sample of the same size.

Four studies with tritium in urine, having concentrations of tritium varying from 1330 to 2700 pCi/L, have been completed. The samples consisted of human urine to which a known concentration of tritium had been added. Each laboratory participating in the study received one 50-ml sample containing tritium plus a 50-ml blank sample for background measurements. Each laboratory did three analyses of the spiked sample. Laboratory performance for the tritium in urine studies are summarized and compared with that of the tritium in water studies in Table 8. A more detailed assessment of these results are provided by U.S. EPA (1983a).

Four studies with radionuclides on air filters have been conducted during the reporting period. In these studies, air filters are distributed to the participating laboratories for gross alpha, gross beta, cesium-137, and strontium-90 analyses. Each participating laboratory receives three spiked air filters containing the radionuclides of interest, and they are expected to return the results of three independent measurements. The performance of the laboratories is summarized in Table 9. A more detailed assessment of these results is provided by U.S. EPA (1983a).

Conclusion

The measurement of radioactivity in environmental samples is an evolving process. With the improvement of existing methods and the development of new methods, validation will continue to be an important

Table 8. Comparison of laboratory performance in tritium in water and tritium in urine studies.


Analysis Studies per Study Within CL

Water Tritium 7 77 91

Urine Tritium 4 28 87

C. R. Cothern, A. N. Jarvis, E. L. Whittaker, and L. Battist

Table 9. Performance of laboratories in air filter studies.


Analysis Studies per Study Within CL

Gross Alpha 4 79 85.5 Gross Beta 4 78 53.8 Strontium-90 4 33 64.0 Cesium-137 4 54 77.5

step. The U.S. EPA produces a wide variety of calibration standards for use in environmental monitoring. Although most standards and laboratories are perform- ing satisfactorily, some problem areas have been iden- tified and are being examined. The continuing quality assurance program will reveal problem areas that must be addressed. With this constant vigilance, U.S. EPA requires that all environmental measurements be of the highest quality.

References

Cavallo, L. M., Coursey, B. M., Garfinkel, S. B., Hutchinson, J. M. R., and Mann, W. B. (1973) Needs for radioactivity standards and measurements, Nucl. Instrum. Methods 112, 5-18.

National Interim Primary Drinking Water Regulations (1976) Fed. Reg. 41, 28402.

National Pollutant Discharge Elimination System (1976) 33 USC 466 et seq.

Noyce, J. R. (1981) Evaluation of methods for the assay of radium-228 in water. NBS Technical Note 1137, National Bureau of Standards, Washington, DC.

Rabinowitz, J. (1967) Principles of Radioisotope Methodology. Burgess Publishing, Minneapolis, MN.

Resource Conservation and Recovery Act (1976) 42 USC 6901 et seq. Safe Drinking Water Act (1974) 42 USC 300 et seq. U.S. Environmental Protection Agency (1975) Interim radiochemical

methodology for drinking water. EPA-600/4-75-008 (Revised), Environmental Monitoring and Support Laboratory, Cincinnati, OH.

U.S. Environmental Protection Agency (1978) Environmental radioactivity laboratory intercomparison studies program, FY-1978-1979. EPA-600/4-78-032, Environmental Monitoring Systems Laboratory, Las Vegas, NV.

U.S. Environmental Protection Agency (1980) Prescribed procedures for measurement of radioactivity in drinking water. EPA-600/ 4-80-032, Environmental Monitoring Systems Laboratory, Cincin- nati, OH.

U.S. Environmental Protection Agency (1981) Radioactivity in drinking water. EPA 570/9-81-002, Office of Drinking Water (WH-550), Washington, DC.

U.S. Environmental Protection Agency (1982a) Manual for the certification of laboratories analyzing drinking water. EPA 570/9-82-002, Office of Drinking Water (WH-550), Washington, DC.

U.S. Environmental Protection Agency (1982b) Environmental Pro- tection Agency, radioactivity standards inventory and distribution program's annual status report (June 1981 to June 1982). EPA 600/X-82-017, Environmental Monitoring Systems Laboratory, Las Vegas, NV.

U.S. Environmental Protection Agency (1983a) Intercomparison program for radiation quality assurances: Annual Report. EPA 600/X-83-010, Environmental Monitoring Systems Laboratory, Las Vegas, NV.

U.S. Environmental Protection Agency (1983b) Proceedings of the National Workshop on Radioactivity in Drinking Water, Tidewater Inn, Easton, MD, May 24-29, 1983. Office of Drinking Water (WH-550), Washington, DC.

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