losses are due to adsorption rather than absorption.
regard to the type of contaminants, and it should
Sharom and Solomon (1981) concluded that pesti-
be noted that among the three solvents mentioned
cides with solubilities in the g/L range have a
only hexane is relatively nonpolar. Obviously any
tendency to be adsorbed by glass while more
organic solvent that is used as a rinsing agent
should not be one of the target analytes or inter-
soluble compounds do not.
fere with chemical analyses.
There has been relatively little study of desorp-
There are a number of problems associated
tion of hydrophobic organic contaminants from
with using organic solvents. These can include
nonpermeable surfaces. Sharom and Solomon
flammability, toxicity, disposal (although recy-
(1981) noted that the pesticide permethrin was
cling can reduce this problem), and spillage, which
much more readily desorbed from glass than from
can cause additional contamination problems on
polyvinyl chloride (PVC), polyethylene (PE), or
site. Also, many polymers (e.g., thermoplastics)
fluoropolymer (Teflon) surfaces. They were able
are degraded by various organic solvents. Infor-
to recover 94% of the lost permethrin by shaking
mation on incompatibilities between polymers and
with water for one minute. Parker (1995) pro-
organic solvents can be found in chemical resis-
posed that decontamination of nonpermeable
tance tables published by the Plastics Design
surfaces such as metals and glass should involve
Library (1994a, b) and in some of the scientific
removing only surface contaminants, such as any
supply catalogs (e.g., Nalgene Co. and Cole-
residual film (either wet or dry) that is left on the
Parmer Co.). In addition, all polymers sorb some
surface when the sampling device is removed
organic chemicals and these contaminants may
from the well, and any highly hydrophobic con-
be subsequently desorbed, thereby contaminat-
taminants that may have adsorbed to the surface.
ing a water sample.
In contrast, several studies (Barcelona et al.
1985, Reynolds and Gillham 1985, Gillham and
O'Hannesin 1990, Parker et al. 1990, Reynolds et
Factors affecting
al. 1990, Parker and Ranney 1996, 1997a) have
decontamination efficiency
Parker (1995) listed several factors that affect
shown that polymeric materials, such as well cas-
how readily a sampling device can be decontami-
ings and the tubings used in groundwater sam-
nated. These include the type of sampling device
pling pumps, sorb substantial quantities of some
(e.g., pump vs. bailer), the materials to be decon-
organic contaminants from aqueous solutions.
taminated, and physical characteristics of the
Most of these studies agree that these organic
organic contaminant, such as its aqueous solubil-
compounds have diffused into the polymer ma-
ity, volatility, and propensity to adsorb on or
trix, i.e., absorption has occurred. The rate and
absorb into materials used in the sampling de-
extent of sorption varies among analytes for a
vice. Contact time and the degree of initial con-
given material, and varies considerably among
tamination on the surface are also critical factors.
polymers for a given analyte. Generally, flexible
Cleaning a surface that has been exposed to trace-
materials tend to be much more sorptive
level organic contaminants is much different from
(Barcelona et al. 1985, Gillham and O'Hannesin
cleaning a surface exposed to neat (pure product)
1990, Reynolds et al. 1990, Parker and Ranney
hydrocarbons or organic solvents. Other types of
1996). As an example, Gillham and O'Hannesin
contaminants such as grease and oil may also
(1990) found that after only 10 minutes, sorption
affect removal.
of low-ppm levels of benzene by flexible PVC was
approximately 35%, while losses were less than
Several studies (Gillham and O'Hannesin 1990,
1% for solutions exposed to rigid PVC.
Parker et al. 1990, Reynolds et al. 1990) have shown
For polymers exposed to low concentrations of
that nonpermeable surfaces, such as glass and
organic solutes, diffusion of the organic molecule
stainless steel, do not tend to sorb more hydro-
in the polymer is considered to be concentration
philic organic solutes (with log octanolwater
partition coefficient [Kow] values less than 4). How-
independent, and at slightly higher concentra-
ever, there are reports that these surfaces sorb
tions (activities) diffusion is considered to be con-
more hydrophobic contaminants, such as poly-
centration dependent (Berens 1985, Jenkins et al.
chlorinated biphenyls (PCBs), chlorinated pesti-
1986, Holsen 1988). However, when glassy amor-
cides, and polyaromatic hydrocarbons (PAHs)
phous polymers (e.g., rigid PVC) are subjected to
(Champion and Olsen 1971, Ogan et al. 1978,
neat (undiluted) chemicals or very high concen-
Sharom and Solomon 1981, Strachan and Hess
trations (i.e., approaching the compound's aque-
1982, and Jones and Miller 1988). Most likely these
ous solubility) and the chemical is a solvent or
2
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