The
information below was abstracted from the Remedial Investigation
for the Allied Paper/Portage Creek/Kalamazoo River Superfund
Site.
PCBs are a class of synthetic organic compounds that
includes 209 individual compounds referred to as congeners. The
various congeners differ in the number and arrangement of
chlorine atoms on the biphenyl molecule, but they all have the
same basic chemical structure and similar physical properties.
In the United States, PCBs were produced for commercial purposes
exclusively as mixtures of PCB congeners by
Monsanto Industrial Chemicals Company
under the trade name Aroclor. The average chlorine content of a
particular Aroclor product is, in most cases, evident in the
specific product name. For example, Aroclor 1242 is 42% chlorine
by weight, while Aroclor 1254 is 54% chlorine by weight.
Although most PCBs produced in the United States were used in
manufacturing electrical transformers and capacitors, some
Aroclors were also used in other applications, including
hydraulic fluids, cutting oils, heat transfer fluids, and quench
oils. From 1957 through 1971, PCBs in the form of Aroclor
1242 were used in the manufacture of carbonless copy paper.
In general, PCBs are chemically and thermally stable, fairly
inert, and have low solubility in water. In general, the lower
the water solubility of a chemical the more likely it is to be
adsorbed onto solids. The presence of other dissolved compounds
in water may affect the solubility of PCBs. For example, if
certain organic compounds are dissolved in water at sufficient
concentrations, the energy necessary to dissolve PCBs may be
reduced. This condition is referred to as cosolvency. The
solubility of PCBs in water may be increased in the presence of
codissolved non-polar chemicals, such as hydrocarbons.
PCBs have very high octanol-water partitioning
coefficient (Kow) values. The octanol-water partitioning
coefficient represents the propensity for a chemical to
partition between a polar phase (water) and a non-polar phase
(octanol) – similar to partitioning in the soil matrix between
soil organic matter and groundwater. The Kow value is determined
as the ratio of the solubility of PCBs in octanol (an organic
matter surrogate) to the solubility of PCBs in water. Thus, a
higher Kow value indicates a greater tendency for a chemical to
sorb to organic materials (e.g., peat, humic acids, and
other organic colloids) in soil.
The degree of adsorption of PCBs in soils is a function of
the soil organic content and the adsorption properties of the
specific PCB compounds that are present. Adsorption properties
are generally characterized by an organic carbon partitioning
coefficient denoted by Koc. The Koc values for PCBs are
relatively high, which means that PCBs readily adsorb to
organic material in media such as sediments and soils.
Taken together, the combination of low water solubility and
high Kow and Koc values indicates that PCBs have a strong
affinity for soils and suspended solids, especially those
high in TOC. PCBs bind to the organic matter fraction decreasing
the dissolved fraction and encouraging the transport of PCBs
sorbed to solids (i.e. particulate transport).
Other than organic content, soil or sediment
characteristics that affect the mobility of PCBs include soil
density, particle size distribution, moisture content, and
permeability. Meteorological and physical conditions such as
amount of precipitation and the presence of organic colloids
(micron-sized particles) can also affect the mobility of PCBs in
the environment. PCBs that are dissolved or sorbed to mobile
particulates (e.g., colloids) may also migrate with groundwater
in sediments and soils. PCBs can be transported by air, either
adsorbed onto airborne dust particles or in a vapor phase that
results from volatilization. The chemical characteristics that
control the adsorption of PCBs to dust particles are described
above. The Henry's Law constant of a compound provides an
indication of its tendency to volatilize, and thus provides a
means for ranking the relative volatility of chemicals. Henry's
Law constants are used to calculate the rate of volatilization
from water and can be obtained from literature or calculated by
dividing the vapor pressure value of a chemical by its water
solubility. PCBs have low Henry's Law constant values relative
to other organic compounds, which means that at equilibrium,
the fraction of PCBs found in water will be higher than the
fraction found in air.
PCBs tend to be persistent in sediments and soils, and
there is no known abiotic process that significantly degrades
PCBs in these media. Biodegradation of PCBs in soils under
aerobic or anaerobic
conditions is slow, especially in soils with high organic carbon
content. At PCB concentrations below about 50 ppm, the rate of
dechlorination is often very slow or non-quantifiable. This is
likely because PCBs are so tightly bound to the soil that at
relatively low concentrations they are not bioavailable to the
biodegrading organisms.
A number of factors may affect the migration of PCBs in
groundwater, including: (1) The chemical characteristics and
concentrations of the specific PCB congeners/Aroclors present at
the site (as described in 5.1); (2) The characteristics of the
PCB source medium (e.g., PCB-containing soils and residuals),
including physical state, mass, location, geotechnical
characteristics (e.g., bulk density, grain size and
distribution, porosity, permeability, moisture content, organic
content), heterogeneity, manner and characteristics of
containment (if any), concentration and distribution of any
cosolvents, and susceptibility to biological interaction or
disturbance; (3) The characteristics of the other (non-PCB
containing) soils above the water table, including topography,
vegetation, soil composition and heterogeneity, geotechnical
characteristics, and depth to groundwater; (4) The
hydrogeological and hydrogeochemical conditions near the source
medium, including temperature, pH, conductivity, dissolved
solids, DO, alkalinity, and ORP; groundwater velocity, presence
and composition of mobile colloidal particles; and presence and
concentration of cosolvents; and (5) The local meteorological
conditions, including daily and seasonal temperature ranges and
fluctuations, annual precipitation, barometric pressure, and
relative humidity. Dissolved PCBs are subject to a number of
different retardation processes, including sorption and various
chemical reactions.
So What Does All The Above Really Mean?
PCBs in the River - the PCBs found in carbonless
paper overwhelmingly stick to solid particles in water,
particularly organic particles. These particles could be
cellulose waste from the recycling process, soil or sediment.
Concentrations of PCBs in the Kalamazoo River are found in the
banks and areas where the water flow has deposited solid
particles. Highest concentrations are found from Kalamazoo
to the dam at Allegan because this stretch is where nearly all
the solid particles were deposited. Portage Creek and the
Kalamazoo River are where most transported PCBs from Allied Paper ended up.
PCBs in the air are only found in significant
amounts when contaminated material is at the surface and being
disturbed. Once securely covered up, PCB levels in the air are
negligible. There is currently no issue with PCBs in the
Kalamazoo air from the Allied Landfill.
PCBs in groundwater - PCBs that are dissolved in
groundwater move more slowly through aquifers than the
groundwater itself moves. PCBs will preferentially stick to soil
particles so to be mobile, these particles must be small enough
to travel through the gaps in the soil matrix. PCBs stuck to
large particles are going to stay put. Along with pumping at the
site, this sticking to solids is why Kalamazoo city well fields
were not been contaminated long ago. Transport of PCBs for long
distances via groundwater is not a significant issue in
Kalamazoo. Careful aquifer monitoring and management will ensure
that it never becomes an issue.
Here is a 2017 fact sheet for the Kalamazoo River Area of
Concern (AOC) provided by the Kalamazoo River Watershed Council
- page
1 -
page 2.
Disclaimer - The
author of this web page is not an expert on PCBs and their
pollution in the environment. He is a scientist who has read the
reports and summarized the information presented in them.