Assessing
for the Presence of Pesticides and Polychlorinated
Biphenyls Using Passive Soil Gas Sampling
James E. Whetzel, W.L. Gore and Associates, Inc.,
Elkton, MD
Differential
reactivity of HCH Isomers Towards Nanoscale Zero-valent
Iron
Daniel W. Elliott, The Whitman Companies, Inc., East
Brunswick, NJ
Remediating
Chloroacetanilide-Contaminated Water with
Dithionite-Reduced Soil and Aquifer Sediments
Hardijeet K. Boparai, University of Nebraska,
Lincoln, NE
Assessing
Sites for the Presence of Pesticides and Polychlorinated
Biphenyls using Passive Soil Gas Sampling
James E. Whetzel, W. L. Gore and Associates,
Inc., 100 Chesapeake Blvd., Elkton, MD, 21921,
Tel: 410-506-4779, Fax: 410-506-4780, Email: jwhetzel@wlgore.com
Volatile
organic compounds (VOCs) generally have boiling points
below 200oC and vapor pressures greater than
1mm Hg. These compounds are amenable to detection in soil
gas using both active and passive sampling methods. For
compounds of less volatility, i.e. semi-volatile organic
compounds (SVOCs), site assessment using soil gas is
limited to time integrated passive collection techniques.
Because of the low volatility and therefore, low
availability in the soil gas, the range of SVOC compounds
detectable by passive soil gas is highly dependent on the
design of the collector. The design must employ materials
that do not impede vapor migration, but still provide
protection of adsorbent materials from liquid water and
soil particles. Organochlorinated pesticides and
polychlorinated biphenyls (PCBs), with vapor pressures
ranging from ~2 X 10-7 to 2 X 10-2mmHg
, are typically considered poor candidates for detection
in the soil gas by any means.
However, an advanced passive soil gas collector has been used
successfully on several sites to detect pesticides and/or
PCBs in the soil gas. Pesticides and PCB congeners up to
and including DDT and pentachlorobiphenyl have been
observed. This presentation will discuss the passive soil
gas collector design and the survey results from pesticide
and PCB site assessment programs.
Differential
Reactivity of HCH Isomers towards Nanoscale Zero-valent
Iron
Daniel W. Elliott, Senior Project Manager, The Whitman Companies Inc., 116 TiceLane, Unit
B-1, East Brunswick, NJ 08816, Tel: 732-390-5858, Fax:
732-390-9496, Email: DElliott@Whitmanco.com
Dr. Wei-xian Zhang, Associate Professor, Department of
Civil & Environmental Engineering, Lehigh University,
Fritz Engineering Laboratory, 13 Packer Avenue, Bethlehem,
PA 18015, Tel: 610-758-5318, Fax: 610-758-6405
Steven T. Spear, Research Assistant, Department of Civil
& Environmental Engineering, Lehigh University, Fritz
Engineering Laboratory, 13 Packer Avenue, Bethlehem, PA,
18015, Tel: 610-758-3283, Fax: 610:758-6405
Since 1996, researchers at Lehigh University the
efficacy of the nanoscale zero valent iron (nZVI)
technology has been tested against a variety of
environmental contaminants in both benchscale and
field-scale tests. In this study, the target contaminants
were four (4) environmentally significant isomers of
hexachlorocyclohexane (HCH): alpha-HCH, beta-HCH, gamma-HCH,
and delta-HCH. HCH (C6H6Cl6)
was heavily used as a pesticide in various technical grade
and refined formulations around the world from the 1940s
into the 1990s. Gamma-HCH, better known as lindane,
exhibited most of the pesticidinal activity. The HCHs
constitute a significant soil contamination issue due to
their toxicity and relative recalcitrance to abiotic and
biotic degradation mechanisms. The HCHs were also of
interest due to their six chlorine substituents,
non-planar cyclic structure, and the fact that the
majority of ZVI studies reported in the literature involve
relatively simple halogenated ethanes and ethenes. In this
study, high HCH concentrations ranging from 300-600 mg/L
(1-2 mM) were degraded in 95% ethanol by nZVI
concentrations of up to 35 g/L (627 mM).
The HCH isomers were removed from solution at
dramatically different rates. The most rapidly degraded
isomer was gamma-HCH followed by alpha, delta, and lastly
by beta-HCH. Using a pseudo first-order kinetic model, the
half-life of lindane in 95% in the presence of nZVI was
approximately 8-24 hours whereas the other isomers were
appreciably more stable. The degradation pathway observed
involved dihaloelimination of vicinal chlorines to yield
the corresponding tetrachlorocyclohexene. The relative
reactivity of the HCHs can be correlated to the axial
versus equatorial orientation of the chlorine substituents
around the ring. With three axial chlorines, lindane was
observed to be the most reactive isomer followed by alpha-HCH
with two axial chlorines. The delta and beta isomers, with
1 and 0 axial chlorines, respectively, were observed to be
dramatically less reactive.
Remediating
Chloroacetanilide-Contaminated Water with
Dithionite-Reduced Soil and Aquifer Sediments
Hardiljeet K. Boparai, University of Nebraska-Lincoln, 372
Plant Sciences, Lincoln, NE 68583-0915, Tel: 402-472-6540,
Fax: 402-472-7904, Email: hboparai@bigred.unl.edu
Patrick J. Shea, University of Nebraska-Lincoln, 362 Plant
Sciences, Lincoln, NE 68583-0915, Tel: 402-472-1533, Fax:
402-472-7904, Email: pshea@unlnotes.unl.edu
Steve D. Comfort, University of Nebraska-Lincoln, 255 Keim
Hall, Lincoln, NE 68583-0915, Tel: 402-472-1502, Fax:
402-472-7904, Email: scomfort@unlnotes.unl.edu
The prevalent use of chloroacetanilide herbicides has
resulted in non-point contamination of some ground and
surface waters. We found that dithionite rapidly
dechlorinates these herbicides in water with a
stoichiometric release of chloride. Structural and
kinetics analyses indicated that the chlorine is replaced
by thiosulfate (a product of dithionite decomposition).
Pretreatment of aquifer sediments and surface soils with
dithionite produced reduced solids that were capable of
herbicide dechlorination. In batch experiments,
chloroacetanilide herbicides were exposed to
dithionite-reduced aquifer sediments and surface soil.
Dechlorination kinetics were a function of the dithionite
concentration used to reduce the solids and related to the
amount of Fe(II) produced. Washing the reduced aquifer
sediments removed Fe(II) and resulted in less herbicide
transformation. In contrast, the surface soil being rich
in clay and iron, effectively degraded alachlor even after
washing. Dechlorination also occurred when the washed,
dithionite-reduced sediments were amended with Fe(II) (as
FeSO4) at pH 8.5 and continued as long as
additional Fe(II) was provided. Fe(II) alone at pH 8.5
could not dechlorinate the herbicides. Comparing
citrate-bicarbonate (C-B) and potassium carbonate (K2CO3)
buffers to maintain high pH, effective degradation of
alachlor was observed in the presence of K2CO3
while no degradation occurred in C-B buffer. The lack of
degradation in C-B buffer is likely due to extraction of
Fe(III) oxides by dithionite-citrate-bicarbonate (DCB).
The dechlorination of chloroacetanilide herbicides by
dithionite and dithionite-reduced sediments and soils
indicates a remediation option that could be employed in
natural environments when iron-bearing minerals are
abundant.
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