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| Titel |
Sources and Spatial Distribution of Metal Pollutants in Soils near the El Paso Smelter: A Forensic Study with Pb and Pu Isotopes. |
| VerfasserIn |
Michael Ketterer, Matthew Moan, Paul Gremillion |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250041641
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| Zusammenfassung |
| Lead and copper smelting has been conducted at El Paso since the late 1800’s, and as a result,
environmental media near the smelter have become contaminated. A study has been
conducted to investigate the sources and spatial distribution of metal pollutants (Pb, Cd,
Zn, Hg, As, Cu) and concomitant tracers (Ag, In, Sb, Bi) in soils from the smelter
vicinity. Sampled locations were residential and non-residential locations in El
Paso (Texas, USA), Anapra (New Mexico, USA) and Ciudad Juarez (Chihuahua,
Mexico).
Lead isotope studies indicate that the soil Pb is derived from smelting, and is consistent
with two-component mixing between lead ores from Chihuahua (northern Mexico) having
206Pb/204Pb of 18.6 – 18.8 and ores from the Hanover, New Mexico (USA) mining district
with 206Pb/204Pb of ~ 17.6. The Pb isotope results also exclude other common
anthropogenic Pb sources such as paint and gasoline emissions as being major contributors.
Concentrations of Hg and Pb of up to 10 and 11,000 ppm were found in surface soils within 1
km of the smelter.
The metal concentration results clearly indicate that soils near the smelter (< 5 km)
exhibit much higher concentrations of smelter-related elements than do soils from control
locations (> 10 km distant). A general trend of decreasing concentrations vs. distance from
the smelter was also observed. However, the results indicate that metal concentrations vary
widely even at a fixed distance from the smelter point source. This phenomenon
results from a combination of natural and anthropogenic processes that disturb and
re-distribute soils in the surface environment. The site conditions consist of a very arid
environment with little vegetation cover that is frequently disturbed by high winds and
severe episodic rainfall. To study these effects, we have investigated stratospheric
fallout plutonium (239+240Pu) as a proxy measure of disturbed vs. undisturbed soil
conditions. The premise is that “undisturbed” locations will have high 239+240Pu
activities, and hence contain most or all of the cumulative deposition inventory
of smelter pollutants, while soils with low 239+240Pu activities can be regarded
as “disturbed”, and cannot contain the entire deposition inventory. 240Pu/239Pu
atom ratio measurements reveal that the Pu is from stratospheric fallout, precluding
other local or regional sources. Our results indicate that 239+240Pu activities are
closely correlated with concentrations of smelter pollutants within a specific distance
grouping; hence, the soil concentrations of contaminant metals are described by a
“distance” factor and a “disturbance” factor, the latter being probed using 239+240Pu as
an effective proxy measure. Linear correlations (r2 > 0.95) are observed for
metal concentrations vs. 239+240Pu activity for a given distance grouping; lines of
varying slope are observed for different distance groupings. In desert soils remote
from the smelter, the metal constituents are present from other anthropogenic and
geogenic sources, and their concentrations are uncorrelated with 239+240Pu activity. |
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