An assessment of the data quality for NHEXAS - Part I: exposure to metals and volatile organic chemicals in Region 5

A National Human Exposure Assessment Survey (NHEXAS) was performed in U.S. Environmental Protection Agency (U.S. EPA) Region V,providing population -b ased exposure distribution data for metals and volatile organic chemicals ( VOCs) in personal, indoor, and outdoor air, drinking water, beverages, food , dust, soil, blood, and urine. One of the principal objectives of NHEXAS w as the testing of protocols for acquiring multimedia exposure measurements and developing databases for use in exposure models and assessments. Analys is of the data quality is one element in assessing the performance of the c ollection and analysis protocols used in NHEXAS. In addition, investigators must have data quality information available to guide their analyses of th e study data. At the beginning of the program quality assurance (QA) goals were established for precision, accuracy, and method quantification limits. The assessment of data quality was complicated. First, quality control ( Q C) data were not available for all analytes and media sampled, because some of the QC data, e.g., precision of duplicate sample analysis, could be der ived only if the analyte was present in the media sampled in at least four Fairs of sample duplicates. Furthermore, several laboratories were responsi ble for the analysis of the collected samples. Each laboratory provided QC data according to their protocols and standard operating procedures (SOPs). Detection limits a ere established for each analyte in each sample type. T he calculation of the method detection limits (MDLs) was different for each analytical method. Tile analytical methods for metals had adequate sensiti vity for arsenic, lead, and cadmium in most media but not for chromium. The QA goals for arsenic and lead were met for all media except arsenic icl du st and lead in air. The analytical methods for VOCs in air, water, and bloo d were sufficiently sensitive and met the QA goals, with very few exception s. Accuracy was assessed as recovery from field controls. Tile results were excellent ( greater than or equal to 98%) for metals in drinking water and acceptable ( greater than or equal to 75%) for all VOCs except o - xylene in air. The recovery of VOCs from drinking water was loner, with all analyt es except toluene (98%) in the 60-85% recovery range. Tl,e recovery of VOCs from drinking water also decreased when comparing holding times of < 8 and > 8 days. Assessment of the precision of sample collection and analysis wa s based on the percent relative standard deviation (% RSD) between the resu lts for duplicate samples. In general, the number of duplicate samples ( i. e., sample pairs) with measurable data were too few to assess the precision for cadmium and chromium in the various media. For arsenic and lead, the p recision was excellent for indoor, and outdoor air ( < 10% RSD) and, althou gh not meeting QA goals, it was acceptable for arsenic in urine and lead in blood, but showed much higher variability in dust. There were no data avai lable for metals in water and food to assess the precision of collection an d analysis.