『Abstract
In 2004, the US Geological Survey (USGS) and the Geological Survey
of Canada sampled and chemically analyzed soils along two transects
across Canada and the USA in preparation for a planned soil geochemical
survey of North America. This effort was a pilot study to test
and refine sampling protocols, analytical methods, quality control
protocols, and field logistics for the continental survey. A total
of 220 sample sites were selected at approximately 40-km intervals
along the two transects. The ideal sampling protocol at each site
called for a sample from a depth of 0-5 cm and a composite of
each of the O, A, and C horizons. The ＜2-mm fraction of each sample
was analyzed for Al, Ca, Fe, K, Mg, Na, S, Ti, Ag, As, Ba, Be,
Bi, Cd, Ce, Co, Cr, Cs, Cu, Ga, In, La, Li, Mn, Mo, Nb, Ni, P,
Pb, Rb, Sb, Sc, Sn, Sr, Te, Th, Tl, U, V, W, Y, and Zn by inductively
coupled plasma-mass spectrometry and inductively coupled plasma-atomic
emission spectrometry following a near-total digestion in a mixture
of HCl, HNO3, HClO4,
and HF. Separate methods were used for Hg, Se, total C, and carbonate-C
on this same size fraction. Only Ag, In, and Te had a large percentage
of concentrations below the detection limit. Quality control (QC)
of the analyses was monitored at three levels: the laboratory
performing the analysis, the USGS QC officer, and the principal
investigator for the study. This level of review resulted in an
average of one QC sample foe every 20 field samples, which proved
to be minimally adequate for such a large-scale survey. Additional
QC samples should be added to monitor within-batch quality to
the extent that no more than 10 samples are analyzed between a
QC sample. Only Cr (77％), Y (82％), and Sb (80％) fell outside the
acceptable limits of accuracy (％ recovery between 85 and 115％)
because of likely residence in mineral phases resistant to the
acid digestion.
A separate sample of 0-5-cm material was collected at each site
for determination of organic compounds. A subset of 73 of these
samples was analyzed for a suite of 19 organochlorine pesticides
by gas chromatography. Only three of these samples had detectable
pesticide concentrations. A separate sample of A-horizon soil
was collected for microbial characterization by phospholipid fatty
acid analysis (PLFA), soil enzyme assays, and determination of
selected human and agricultural pathogens. Collection, preservation
and analysis of samples for both organic compounds and microbial
characterization add a great degree of complication to the sampling
and preservation protocols and a significant increase to the cost
for a continental-scale survey. Both these issues must be considered
carefully prior to adopting these parameters as part of the soil
geochemical survey of North America.』
1. Introduction
2. Site selection
3. Sample-collection protocols
3.1. Inorganic constituents
3.2. Organic compounds
3.3. Microbial characterization
4. Sample preparation protocols
4.1. Inorganic analysis
4.2. Analysis of organic compounds
5. Sample archives
6. Analytical protocols
7. Quality assurance (QA)/ quality control (QC)
7.1. Inorganic analysis
7.2. Organochlorine pesticides
8. Summary and conclusions
Acknowledgements
References