rapid assessment of soil metal concentrations along the ... · field portable xrf basics • each...
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Field Portable XRF Basics
• Each element has electronic orbitals of characteristic energy
• Following removal of an inner electron by an energetic photon provided by a primary radiation source, an electron from an outer shell drops into its place
• There are a limited number of ways in which this can happen:
• L→K transition is traditionally called Kα• M→K transition is called Kβ• M→L transition is called Lα
• Each of these transitions yields a fluorescent photon with a characteristic energy equal to the difference in energy of the initial and final orbital
• The wavelength of this fluorescent radiation can be calculated from Planck's Law: E= nhv
• n=1,2,3…; h= Planck’s constant; v= frequency
• The fluorescent radiation can be analyzed either by sorting the energies of the photons (energy-dispersive analysis) or by separating the wavelengths of the radiation (wavelength-dispersive analysis)
• Intensity of each characteristic radiation is directly related to the amount of each element in the material
Field Portable XRF Basics• A battery operated, Olympus Delta series PXRF (Rh x‐ray tube
operated at 10-40 kV) • Stainless steel ‘316’ standardization clip is used to standardize
the instrument• 16.13% Cr• 1.78% Mn• 68.76% Fe• 10.42% Ni• 0.20% Cu • 2.10% Mo
• Instrument operated in either soil mode or geochem mode• Uses a scatter normalization algorithm (per EPA Method
6200) for soil, liquids, and powders allowing for sequential analysis of atomic numbers Z=15 (Phosphorus) to Z=92 (Uranium)
• Optimized tube excitation increases performance on lighter elements (Ca, K, S, P, Cl, and I)
• Samples scanned for 30 s per beam through the ~2 cm aperturePrice: ~$45,000
Allows for multiple soil science applications:• Horizonation• Gypsum/calcic/podzol horizons• Soil fertility (CEC)• Soil pH/EC
Field Portable XRF Basics
• Data processing includes reporting of the standard error on an individual element basis
• Limit of detection (LOD) is defined as three times the standard error for each element
• Varies by element, with higher atomic numbered elements generally allowing for lower detection limits
• Logged data exported to MS Excel for further statistical analyses
Potential Soil Science Applications of PXRF
• Applications:• Textural determination
• pH
• Salinity
• Cation exchange capacity
• Base saturation percentage*
• Plant essential elements
• Mineralogy
• Advantages:• Non-destructive
• Rapid
• Multi-element
• Low limits of detection and wide dynamic range
• Disadvantages:• No H, C, or Na
• Moisture effects
• Soil heterogeneity
PRXF Results Sept 1-3, 2015
Aluminum (Al)
Iron(Fe)
Copper (Cu)
Zinc (Zn)
Arsenic(As)
Lead(Pb)
Ave Range Ave Range Ave Range Ave Range Ave Range Ave Range
n Location ...................................................................Parts per million (ppm or mg/kg)………………………………………………………….
29 Not Irrigated 64087 25413-83540 28987 9047-50892 33 ND-94 117 25-330 7 ND-13 53 12-230
67 Irrigated 53541 7281-80325 28514 4430-48232 36 11-100 175 39-819 7 ND-13 67 5-271
35 Riverbank 37749 4218-80108 38302 5818-293194 77 ND-220 365 19-1068 11 ND-38 153 10-487
9 RiverbankSludge
21018 8730-38781 48355 38292-75959 137 90-176 474 277-1174 40 ND-54 637 509-859
140
Long Term Monitoring Plan (Proposed)• Element 3.0: Soils and Sediment
• Determine if elevated heavy metal concentrations presently occur in stream and irrigation ditch sediment, and in soil that has been irrigated with water diverted from the Animas River; and
• THREE SAMPLE POINTS DURING GROWING SEASON
• Monitor the migration of contaminated surface water sediment from Colorado (CO) into New Mexico (NM), as it pertains to irrigated agriculture and the river-agricultural land interface.
• ONCE PER YEAR AFTER IRRIGATION SEASON
• Element 10.5: Agricultural Crops• Determine if elevated heavy metal
concentrations occur in agricultural crops that have been irrigated with water diverted from the Animas River;
• MONITOR POTENTIAL AREAS OF CONCERN FROM SOIL AND SEDIMENT DATA
• Extent contingent upon funding
Some additional thoughts….• In the absence of
appreciable humic matter, Pb is strongly adsorbed on clay minerals and Fe oxides
• According to Chaney, Pb from sludge does not give rise to an increase in plant Pb unless the concentration is very high.
• Our soil chemistry may work in our favor (alkaline soils with variable calcium carbonate CaCO3)
pH and Plant Nutrients