Fate of Explosives in Plant Tissues
Contaminated During Phytoremediation
PHILIP G. THORNE
INTRODUCTION
could contain widely different levels of contami-
The remediation of soils and groundwater
nation. It would be inefficient to waste resources
contaminated with explosives is an enormous
on remediating truckloads of excavated soil that
task facing many governments worldwide. In re-
may be, on average, below the target remediation
cent years, ex-situ bioremediation techniques
goals. Without extensive sampling and analysis,
such as composting and slurry digestion have
it is unlikely that the total mass of explosives can
gained favor as rapid and cost-effective solutions
be estimated accurately enough to provide
to the soil contamination problem (Griest et al.
design data for remediations such as composting
1993, Pennington et al. 1995, Breitung et al. 1996,
or slurry digestions. In these systems care must
Lenke et al. 1998, Shen et al. 1998). The toxicity of
be taken to protect the microbial consortia that
the finished compost and its release of toxic com-
perform the remediation from toxic overloads,
pounds during long-term weathering is accept-
while attempting to maximize the throughput of
ably low (Gunderson et al. 1997). Part of the
soil.
favorable cost benefit of ex-situ treatments results
A different approach to the cleanup of moder-
from the high degree of contamination that is
ately and heterogeneously contaminated soils is
found in waste streams from manufacturing, load
in-situ phytoremediation. In this approach, the
and pack, and washout activities. Often, deposits
cost of treatment must be low enough so that
of explosives are found in relatively small disposal
large areas can be treated without the necessity of
areas (a few acres) (Walsh et al. 1993, Jenkins et al.
detailed spatial quantification of contamination.
1996). Such soils can be efficiently excavated and
Sampling should be sufficient to define the
remediated in a nearby facility. The finished
boundaries of the suspected contamination and
remediation mixture can then be placed in a con-
proceed with a first-year treatment. It is expected
trolled landfill.
that several years might be required to remediate
The contamination at open burning/open
an entire area. Previous research has focused on
detonation (OB/OD) areas and firing ranges pre-
the effects of the explosives on plant growth and
sents a very different problem that affects the cost
transport of explosives in crop tissues (Simini et
and benefits of excavation and ex-situ remedia-
al. 1995, Thompson et al. 1998).
tion and disposal of remediated mixtures. The typi-
Treatment of groundwater contamination has
cal concentration of explosives residues in these
relied on pumping water through granular acti-
areas tends to range from hundreds to thousands
vated charcoal (GAC) beds where the explosives
of mg/kg, and the contamination is predomi-
are retained, and then reinjecting the cleaned
nantly within the top 15 cm of the soil (Jenkins et
water into the aquifer. The irrigation of plants
al. 1996, 1997). Unfortunately, the distribution of
with contaminated water is an alternative treat-
contaminants is extremely heterogeneous. There
ment to GAC removal (Harvey et al. 1991, Rivera
are "hot" spots and "non-detect" spots in close
et al. 1998, Larson et al. 1999). Although the costs
proximity (i.e., a few meters). On an operational
of pumping remain the same, savings could be
scale, this means that every bucketload excavated
realized without the capital investments in GAC
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