Radiochemical Methods and Data Evaluation Wm. Kirk Nemeth New Jersey Department of Health & Senior Services, Environmental Chemical and Laboratory Services, Radioanalytical Services

WHAT WE’LL COVER TODAY The analytical process: sample collection to data reporting and uncertainties Methods for sample preparation for drinking water samples QA data: what to look for

SOURCES OF DATA VARIABILITY This list provides a broad sense to some of the sources of imprecision affecting environmental measurements. Definitions of precision and accuracy. Precision is the extent to which a given set of measurements of the same sample agree with their mean. Accuracy is the extent to which a given measurement agrees with the standard value for that measurement.

UNCERTAINTIES RANDOM: Includes the radioactive decay process itself, random timing uncertainties, variations in collection, sample preparation, positioning of the sample at the detector, etc. The list is nearly endless. SYSTEMATIC: can be considered to be conceivable sources of inaccuracy which are biased and not subject to random fluctuations and those which may be due to random cause but cannot be or are not assessed by statistical methods.

PROPOGATION OF ERRORS The total error for any analytical scheme involves errors in all steps: sampling, preparation and measurement. If sampling uncertainty is  50%, and the analysis only has a 2% error; your total error is still very large

DATA QUALITY OBJECTIVES (DQOs) A statement of the overall level of uncertainty that a decision-maker is willing to accept in results derived from environmental data The level of uncertainty can be defined through defining the uncertainty in each step of the analytical process. QA data are key in defining the level of uncertainty Often many clients will request analyses to be performed on aqueous samples and not comprehend what it is they hope to achieve from the data we provide. We attempt to resolve this situation by discussing the circumstances surrounding the sample and our capabilities.

STEPS TO BE DISCUSSED Sample Collection and Preservation Methods Quality Assurance

SAMPLE COLLECTION & PRESERVATION IN THE FIELD Consult DEP Field Sampling Manual and Laboratory SOP manual Collection of radiological samples - typically 1 gallon plastic for all but Radon-222 and Tritium Preservation (Where and How?) HNO3 to pH < 2 is ideal Filtration before or after H+ Holding Times within 48 hours for gross alpha/beta (includes collection, transport, preparation and counting) Analyze within 6 months These manuals will detail the collection of the proper collection technique, the proper container and preservation (if appropriate). Collection: Normally 1 gallon is sufficient for the analyses of alpha/beta, radium 226, radium 228, and Uranium. This will allow for laboratory duplicates, if necessary. Radon and tritium samples are collected separately. Radon-222 and tritium must be collected in glass containers; radon samples are collected in glass liquid scintillation vials (containing mineral oil) without preservation and tritium samples are collected in 50 ml or 100 ml glass bottles without preservation. We require that radon samples be collected in duplicate to observe sampling technique. The preservation should ideally be performed at collection but can be accomplished upon delivery to the laboratory (if delivered the same day), the 16 hour hold is observed if not preserved at collection) The timing can become a difficult issue if the sample is delivered by mail, when considering the analysis must be performed within 48 hours from collection.

SAMPLE PREPARATION METHODS CAVEATS NJDEP/OQA only certifies for certain preparation methods You must match the method of preparation to the method of analysis SDWA samples must use Federally approved methods

Analytical Methods Approved by EPA for Radionuclide Monitoring

NJDHSS PREPARATION METHODS FOR DRINKING WATER EPA 900.0: Gross Alpha/Beta (evaporation) EPA 900.1: Gross Alpha (co-precipitation) EPA 903.0: Radium 226 NJ Method: Radium 228 EPA 00-07: Uranium EPA 913: Radon

Required Detection Limits

DETECTION LIMIT DEFINITIONS Instrument Detection Limit (IDL) Lowest observable value above instrument background in the absence of sample matrix Method Detection Limit (MDL) Minimum detectable concentration that has 99% confidence of being greater than 0.

ISSUES AFFECTING MEASUREMENT CHOICE Regulatory implications/limitations Detection limit needs Potential analytical interferences Cost Time Experience/skill needed to conduct analyses

QA/QC COMPONENTS Instrument Calibration Blanks Duplicates Spikes Calibration Verification Reference Materials Instruments to be used are indicated in each method listed. As an example, a proportional counter (capable of discriminating an alpha particle from a beta) such a as thin window, gas flow counter should be used for alpha/beta counting. It can be used in the analysis of radium 226, radium 228, strontium 89 & 90, iodine 131. Several instruments can be used for the variety of uranium methods listed. Instrument calibration: Attenuation calibration nuclides for alpha are thorium 230 and natural uranium. Amercium 241 is approved for use with gross alpha co-precipitation methods Attenuation calibration nuclide for beta is Cs-137 or Sr-90/Y-90. Blanks: In the laboratory, methods blanks are run with every batch. Typically blank samples represent 5 to 10% of the sample workload. Blank samples use the same glassware, reagents, hotplates, heating lamps, etc. as that of actual samples and are created and analyzed with samples. Deionized water (or representative water) is used in the creation of blanks. precipitation

CALIBRATION EPA approves the use of particular isotopes to create attenuation curves. Typically 20 or more planchets of varying weight. Attenuation standards are typically laboratory created using NIST traceable materials. They should mimic actual samples. Some methods use internal tracers for calibration. Samples must be within the weight range dictated by the method. Instruments to be used are indicated in each method listed. As an example, a proportional counter (capable of discriminating an alpha particle from a beta) such a as thin window, gas flow counter should be used for alpha/beta counting. It can be used in the analysis of radium 226, radium 228, strontium 89 & 90, iodine 131. Several instruments can be used for the variety of uranium methods listed. The instrument used for our isotopic uranium method is an alpha spectrometer. Instrument calibration: Attenuation calibration nuclide for alpha is Th-230; prior to 1994, Am-241 and U 238 were used as the calibrating nuclides. Attenuation calibration nuclide for beta is Cs-137 or Sr-90/Y-90.

BLANKS Trip Blank: Deionized water carried from laboratory to sampling location and back to the laboratory. Instrument Background: typically clean sample holder or planchet is used. Method Blank: Deionized water containing all reagents carried through sample preparation & measurement procedures Trip blanks are typically not utilized in radiological testing.

DUPLICATES Field Duplicate: Extra sample taken from same place, analyzed independently to document sampling precision. Matrix Duplicate: Intralaboratory split sample used to document method precision in a given matrix

SPIKES Spike: Known activity/nuclide addition to deionized water. Matrix Spike: Known activity/nuclide addition to sample aliquot prior to preparation to document bias in a given matrix. (Matrix interference) Matrix Spike Duplicate: Intralaboratory split sample with known additions prior to preparation to document precision and bias

OTHER QA/QC COMPONENTS Continuing Calibration Verification Evaluates instrument drift Second Source Reference Materials Different source than used for calibration Certified Reference Materials Evaluate method bias Various Sources: NIST best

QA/QC SUMMARY You cannot do too much QA Sample data w/o QA data has limited meaning Each type of QA sample evaluates a different part of the analytical process You must match reference materials to media being analyzed Labs. that do and report QA data usually produce reliable data

ISSUES TO CONSIDER Is the lab. certified to perform the specific procedure? Is the lab. using the correct preparation and analysis methods for the DQO? Can the lab. achieve the MDL? Are QA data (blanks, duplicates, spikes, reference materials, …) within defined limits?