Ed. Pellizzari et al., An assessment of the data quality for NHEXAS - Part I: exposure to metals and volatile organic chemicals in Region 5, J EXP AN EN, 11(2), 2001, pp. 140-154
Citations number
12
Categorie Soggetti
Environment/Ecology
Journal title
JOURNAL OF EXPOSURE ANALYSIS AND ENVIRONMENTAL EPIDEMIOLOGY
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.