944 PCBs AND ASSOCIATED AROMATICS
Louw, et al. 96,96a have interpreted the pyrolysis of chlo-
robenzenes as a radical chain reaction involving ·C 6 H 4 Cl,Cl·
and H· as carriers. The authors discuss a radical reaction
sequence which explains the observed product pattern,
including the formation of PCBs.
The formation of polychlorinated naphthalenes (PCNs)
in Buser’s experiments (Buser^55 ) can be explained by either
invoking the formation of benzyne intermediates or the rear-
rangement of intermediates formed between an ortho-chloro
phenyl radical with a chlorobenzene.
The overall effect of radical reactions on the product
distribution in a pyrolysis reaction will be affected by both
temperature and the availability of oxygen. This is well illus-
trated in the product distributions found after accidental fires
involving PCBz/PCB filled electrical equipment (see earlier
section).
It would be ironic if a process aimed at the detoxification
of PCBs, which have been shown to be for the most part non-
toxic in humans, should inadvertently create a hazard as the
result of uncontrolled side reactions to give products with a
much greater apparent toxicity.
Analytical chemistry at the time of the “Yusho” incident
in 1968 was at a stage of development in which the determi-
nation of analytes at the ppm concentration level was con-
sidered to be the forefront of the field. Vos showed in 1970
that PCDFs could be determined in the presence of a matrix
of PCBs but it was not until about 10 years later in 1977/78
that analytical methodology had advanced to the point that
PCDFs and PCDDs could be determined, albeit laboriously,
with anything like a “standardized” method. At the present
time, EPA method 613 for the target compound 2,3,7,8-
TCDD, uses high resolution gas chromatography coupled to
low resolution mass spectrometry and is capable of detection
limits of about 10 ppb. Developments in tandem mass spec-
trometry promise to provide a very rapid screening method
for the presence of target compounds and is sensitive to
PCDDs in the ppt range.
A part of the problem in the interpretation of PCB dis-
posal methods lies in the analytical requirements of uncon-
trolled reactions. For example, even though methodology
has been developed which is able to determine compounds
which were not considered at the time of the Yusho inci-
dent, it is currently not possible to determine some of the
polychlorinated polyaromatic pyrolysis products of PCBs
because of a lack of standard compounds. The key question
which remains unanswered today is “What are the concen-
trations of compounds of concern?”(3) THE PCB REMEDIATION OF SOILSThe cost-effective remediation of PCB contaminated soils is
discussed in terms of the availability of current options and an
assessment of the best available technology. Major categories
of in-place treatment techniques are reviewed as well as a wide
range of technologies for the treatment of excavated soils.
Treatment methods are used to reduce the toxicity, mobil-
ity or volume of PCB contaminated material and fall into twodistinct groups. One group requires the use of large energy
sources and requires a significant amount of setup time. The
other group of technologies tend to be more mobile, use
much less energy and apply a decontamination process to
excavated soil.
This section focuses on the use of electrochemical meth-
ods for the treatment of soil extracts and, in particular, on
a new electrochemical technology which has been demon-
strated to be significantly superior.
The Comprehensive Environmental Response, Compen-
sation and Liability Act (CERCLA) mandates the Environ-
mental Protection Agency (EPA) to select remedial actions
which “utilize permanent solutions and alternative treatment
technologies or resource recovery technologies to the maxi-
mum extent practicable”. Also, a preferred remedial action
is one which “permanently and significantly reduces the
volume, toxicity, or mobility of hazardous substances, pol-
lutants, and contaminants as a principal element.”
The Toxic Substances Control Act (TSCA) requires that
material contaminated with PCBs at concentrations above
50 ppm should be disposed of in an incinerator approved for
the purpose or by an alternate method that achieves a level of
destruction which is equivalent to incineration.
Other applicable or relevant and appropriate require-
ments (ARARs) which can apply to a PCB contaminated
site might involve the Resource Conservation and Recovery
Act (RCRA) as well as the Clean Water Act (CWA) and Safe
Drinking Water Act (SDWA).
RCRA applies to PCBs when liquid waste that is hazard-
ous under RCRA contains PCBs at concentrations greater
than 50 ppm or non-liquid hazardous waste contains total
hazardous organic constituents at concentrations greater
than 1000 ppm. PCBs are specifically addressed under
RCRA in 40 CFR 268, which describes the prohibitions on
land disposal of various hazardous wastes. The land disposal
restrictions require that prior to placing PCB contaminated
material on the land, it must be incinerated unless a treat-
ability variance is obtained.
The National Contingency Plan (NCP) established a gen-
eral presumption that a treatability variance is warranted for
CERCLA soil and debris because when the Act was put into
effect there were no standards for disposal. Consequently,
alternate treatment levels (161) are justified according to the
treatability guidance levels set out by the EPA. To qualify
for a treatability variance for PCBs, residuals after the alter-
nate treatment should contain 0.1 to 10 ppm PCBs for initial
concentrations up to 100 ppm, and for initial concentrations
above 100 ppm, treatment should achieve 90 to 99% reduc-
tion in concentration.
Soil remediation techniques applied to hazardous waste
sites are assessed in terms of the soil processes which affect
them and the type of system to be used. Once a technology
has been selected it must be monitored for treatment effec-
tiveness until it is finally proven that decontamination has
taken place to an acceptable level of risk.
In general, contaminated soil systems must be considered
as four phases: (1) aqueous; (2) vapour or gas; (3) organic
and (4) solid. The distribution of contamination between theC016_003_r03.indd 944C016_003_r03.indd 944 11/18/2005 1:12:45 PM11/18/2005 1:12:45 PM