Zobrazeno 1 - 10
of 64
pro vyhledávání: '"Dennis R. Helsel"'
Publikováno v:
Techniques and Methods.
Autor:
Jennifer A. Field, Christoph Ort, Jason Williams, Caleb J. Banta-Green, Dennis R. Helsel, Alex J. Brewer
Publikováno v:
Science of The Total Environment. 568:856-863
Analysis of wastewater samples can be used to assess population drug use, but reporting and statistical issues have limited the utility of the approach for epidemiology due to analytical results that are below the limit of quantification or detection
Autor:
Jean M. Morrison, Dennis R. Helsel, Martin B. Goldhaber, David B. Smith, Richard B. Wanty, JoAnn M. Holloway
Publikováno v:
Applied Geochemistry. 24:1482-1499
Regional-scale variations in soil geochemistry were investigated in a 20,000-km 2 study area in northern California that includes the western slope of the Sierra Nevada, the southern Sacramento Valley and the northern Coast Ranges. Over 1300 archival
Autor:
Denise M. Argue, Frederick J. McGarry, Joseph D. Ayotte, James R. Degnan, Sarah M. Flanagan, Dennis R. Helsel, Laura Hayes
Publikováno v:
Environmental Science & Technology. 42:677-684
Methyl tert-butyl ether (MTBE) concentrationsor = 0.2 /microg/L were found in samples of untreated water in 18% of public-supply wells (n = 284) and 9.1% of private domestic wells (n = 264) sampled in 2005 and 2006 in New Hampshire. In counties that
Autor:
Lopaka Lee, Dennis R. Helsel
Publikováno v:
Computers & Geosciences. 33:696-704
Analysis of low concentrations of trace contaminants in environmental media often results in left-censored data that are below some limit of analytical precision. Interpretation of values becomes complicated when there are multiple detection limits i
Autor:
Dennis R. Helsel
Publikováno v:
Chemosphere. 65:2434-2439
The most commonly used method in environmental chemistry to deal with values below detection limits is to substitute a fraction of the detection limit for each nondetect. Two decades of research has shown that this fabrication of values produces poor
Autor:
Dennis R. Helsel, Lonna M. Frans
Publikováno v:
Environmental Science & Technology. 40:4066-4073
Trends in environmental variables are often investigated within a study region at more than one site. At each site, a trend analysis determines whether a trend has occurred. Yet often also of interest is whether a consistent trend is evident througho
Autor:
Stephen J. Kalkhoff, Dennis R. Helsel, Sarah J. Stetson, Richard B. Wanty, Donald L. Macalady
Publikováno v:
Analytica Chimica Acta. 567:108-113
Perchlorate ion (ClO 4 − ) is an environmental contaminant of growing concern due to its potential human health effects, impact on aquatic and land animals, and widespread occurrence throughout the United States. The determination of perchlorate ca
Autor:
Dennis R. Helsel
Publikováno v:
Human and Ecological Risk Assessment: An International Journal. 11:1127-1137
Environmental data often include low-level concentrations below reporting limits. These data may be reported as “< RL,” where RL is one of several types of reporting limits. Some values also may be reported as a single number, but flagged with a
Autor:
Lopaka Lee, Dennis R. Helsel
Publikováno v:
Computers & Geosciences. 31:1241-1248
Trace contaminants in water, including metals and organics, often are measured at sufficiently low concentrations to be reported only as values below the instrument detection limit. Interpretation of these ''less thans'' is complicated when multiple