Comparison of four 90Sr groundwater analytical methods

Data are presented for 45 Long Island groundwater samples each measured for Sr-90 using four different analytical methods. Sr-90 levels were first established by two New York State certified laboratories, one of which used the U.S. Environmental Protection Agency Radioactive Strontium in Drinking Water Method 905.0. Three of the Sr-90 methods evaluated at Brookhaven National Laboratory can reduce analysis time by more than 50%. They were (a) an Environmental Measurements Laboratory Cerenkov technique and (b) two commercially available products that utilize strontium-specific crown-ethers supported on either a resin or membrane disk. Method independent inter-laboratory bias was <12% based on Sr-90 results obtained using both U.S, Department of Energy/Environmental Measurements Laboratory and U.S. EPA/National Environmental Radiation Laboratory samples of known activity concentration. Brookhaven National Laboratory prepared a National Institute of Standards and Technology traceable Sr-90 tap-water sample used to quantify test method biases. With gas proportional or liquid scintillation counting, minimum detectable levels (MDLs) of 37 Bq m(-3) (1 pCi L-1) were achievable for both crown-ether methods using a l-L processed sample beta counted for 1 h, The primary radiological contaminants of the Brookhaven National Laboratory groundwater samples were H-3 (14.8-518 kBq m(-3)) and Sr-90/Y (37 Bq m(-3)-18.5 kBq m(-3)). Thirty samples were above the U.S. EPA drinking water standard of 300 Bq m(-3) for beta emitting Sr-90, Regression of paired data sets show ed that both crown-ether methods quantified Sr-90 levels to within 5% of the "EPA method results" for samples greater than the drinking water standard and within 30-40% for samples less than the drinking water standard. The Cerenkov method, with a minimum detectable level of 150 Bq m(-3), was only useful for samples greater than the drinking water standard and underestimated Sr-90 levels by 13%. Precision, as measured by the relative percent difference and mean difference statistics, was acceptable for both crown-ether methods when compared to the paired "EPA method" results. Cerenkov method precision exceeded predefined acceptance criteria for 12 of 33 samples analyzed.