United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-92/187 October 1992
\yEPA Project Summary
Pollution Prevention Opportunity
Assessment: Histology
Laboratory Xylene Use
Fort Carson, Colorado
George Wahl, Deana Stamm, Jeffery Driver, and Joe Bob Cravens
One of the primary ongoing programs
for promotion and encouragement of
pollution prevention research is a co-
operative program between the U.S.
Environmental Protection Agency (EPA)
and the Federal community at large.
EPA's Waste Reduction Evaluations at
Federal Sites (WREAFS) Program sup-
ports pollution prevention research
through joint assessments of problem-
atic areas at selected sites. The three
primary objectives of the WREAFS
Program are to 1) conduct waste mini-
mization assessments and case stud-
ies; 2) conduct research and demon-
stration projects jointly with other Fed-
eral activities; and 3) provide technol-
ogy and information transfer of pollu-
tion prevention results.
A Pollution Prevention Opportunity
Assessment of a community hospital
undertook an evaluation of xylene and
ethanol waste streams generated as the
result of tissue processing and staining
in the hospital's histology laboratory,
and methanol waste pollutions from the
hematology laboratory.
Feasibility analyses for solvent re-
covery, materials substitution, and vol-
ume reduction also considered both
technical and economic factors. These
analyses allowed an "economic of
scale" to be constructed to illustrate
the net savings and payback periods
for these options when implemented in
histology laboratories of varying work
loads (i.e., tissue sample throughputs).
This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the research project
that is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
To promote pollution prevention activi-
ties in accordance with the national policy
objectives established under the 1984
Hazardous and Solid Waste Amendments
to the Resource Conservation and Re-
covery Act of 1976 (RCRA), the Risk Re-
duction Engineering Laboratory (RREL) of
the EPA's Office of Research and Devel-
opment is supporting the Waste Reduc-
tion Evaluations at Federal Sites
(WREAFS) Program. This program con-
sists of a series of projects for pollution
prevention conducted cooperatively by
EPA and various parts of the Department
of Defense, Department of Energy, and
other Federal agencies. The WREAFS
Program focuses on pollution prevention
research opportunities and technical as-
sessments at Federal sites. The present
project focused on a pollution prevention
opportunity assessment conducted at the
Fort Carson Evans Community Hospital
(ECH) Histology Laboratory in Colorado
Springs, CO.
Results of the pollution prevention op-
portunity assessment conducted at the
histology laboratory identified two pollution
prevention opportunities involving materi-
als used for tissue processing and slide
staining. The third opportunity that was
investigated was volume reduction. At
ECH, however, this option had been
implemented by installing and utilizing au-
tomatic tissue and staining processors, so
Printed on Recycled Pd
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the cost savings associated with volume
reduction had already been realized and
are no longer available.
Pollution Prevention
Opportunities
The pollution prevention opportunity as-
sessment was initiated by developing an
inventory of the wastes generated at the
ECH. Although the waste stream includes
small quantities of various chemicals, xy-
lene, ethanol, and methanol are the most
significant wastes, with respect to volume,
and require disposal as hazardous waste.
The Pathology Department (which in-
cludes the histology laboratory) at ECH
disposes of approximately 150, 250, and
240 L (40, 66, and 63 gal) per yr of xy-
lene, ethanol, and methanol, respectively.
The principal operations involving these
solvents include human tissue processing
and slide staining for histologic and cyto-
logic evaluations to support clinical diag-
noses. The current method of disposal is
through a local contractor who transports
and incinerates the solvent waste. Chemi-
cal Waste Management, located in
Henderson, CO, is currently under con-
tract for this purpose. Disposal costs is
approximately $160/55-gal drum, includ-
ing transportation. The generation of these
solvent wastes involve the following spe-
cific processes.
Tissue Processing
One solvent reservoir of xylene with a
volume of 1.5 L and two reservoirs of
ethanol with volumes of 3.5 and 0.7 L,
respectively, are used in the automatic
tissue processing equipment. The xylene
and ethanol baths used during tissue pro-
cessing are discarded and replaced with
fresh solvent on a weekly basis. The dis-
carded solvents are currently placed in a
hazardous waste storage container. During
this procedure, the solvents are mixed
(the three chemicals from both the histol-
ogy and hematology laboratories are not
segregated but "pooled" (mixed) in the
same drum and disposed together) in 55-
gal drums with significant volumes of
methanol from the hematology laboratory
for eventual transport by a contractor for
disposal.
Slide Staining
Two solvent reservoirs of xylene, both
with volumes of 0.7 L, and one reservoir
of ethanol with a volume of 0.7 L are used
in the automatic staining equipment. The
ethanol used during slide staining of his-
tologic or cytologic specimens is changed
on a weekly basis. Of the two xylene
reservoirs (baths), the first reservoir is dis-
carded; the second reservoir is rotated
forward; and a fresh xylene reservoir re-
places the reservoir that is rotated for-
ward. This is done on a weekly basis. In
the hematology laboratory, methanol is
used for slide staining and other purposes.
It is important to note that for the pur-
poses of implementing any solvent recov-
ery option, it would be necessary to keep
these solvents separate to maximize their
recovery and reuse. The hematology
laboratory's methanol waste can be kept
separate from the histology laboratory's
xylene and ethanol waste. Because cross-
contamination of the xylene and ethanol
baths occur during tissue processing and
slide staining, therefore, mixing of xylene
and ethanol will always occur in the pro-
cess of tissue preparation for microscopic
examination.
Two pollution prevention options were
identified and evaluated for xylene and
ethanol waste generated as the result of
tissue processing and slide staining ac-
tivities in the histology laboratory solvent
substitution and solvent recovery. These
options were also evaluated for methanol
waste resulting from staining procedures
performed in the hematology laboratory.
The technical details of these options are
discussed in the full report summarized
here.
Solvent Substitution
Example xylene substitutes include
Clear-Rite 3®*, Americlear®, Histosolv X®,
and Mediclear II®. Adequate discussions of
the toxicological profiles of these substi-
tutes are not available to be able to com-
pare their toxicity and safety to that of
xylene. A review of the Material Safety
Data Sheets shows that the primary haz-
ardous constituent of the chemical substi-
tutes are aliphatic petroleum distillates,
which are classified as a D001 (Flammable
Liquid) hazardous waste for disposal pur-
poses. Before disposal into the sanitary
sewer, the local wastewater treatment au-
thority would need to be consulted for
either discharge approval, or permitting,
or both. Sanitary sewer districts often grant
permission for such discharges for
nonbioaccumulative wastes that are in di-
lute, or low-volume solutions, or both.
When selecting a substitute, a number
of criteria must be considered. These in-
clude toxicity, physicochemical character-
istics, compatibility with other materials,
performance, availability, recycling re-
quirements, disposal requirements, and
cost.
Mention of trade names or commercial products does
not constitute endorsement or recommendation for
use.
The ECH has initiated an evaluation of
available xylene substitutes. Preliminary
results with vendor's substitutes indicated
a preference for continuing to use xylene.
The primary reason is related to xylene's
ability to provide maximum paraffin infil-
tration of tissues resulting in greater
specimen visibility and, thus, enhanced
microscopic examination. Further, some
of the available substitutes have a citrus
odor that was undesirable to laboratory
staff, and the staff believed the substitutes
did not provide equal or better specimen
visibility. The use of vacuum hoods could,
however, eliminate the undesirable odors.
Xylene substitutes are used in both open
and closed processors and have been
reported to be nondrying to skin, leave no
oily residue for faster and easier slide
cleaning, and allow for complete paraffin
infiltration rendering tissues less brittle than
xylenes. Further information is required,
however, with respect to the potential
hazards and safe use conditions of xylene
substitutes.
Methanol substitutes for use in the he-
matology laboratory were not identified.
Since methanol waste mixed with xylene
and ethanol is difficult to separate by dis-
tillation, ECH should implement a program
to keep methanol waste separate.
Solvent Recovery
Clinical laboratories in general, and his-
tology laboratories in particular, have a
large demand for organic solvents. The
ECH laboratory is no exception. The his-
tology department is a major consumer of
xylene and ethanol. In addition, the hema-
tology laboratory uses a significant vol-
ume of methanol. One method for mini-
mizing the amount of these solvents is to
recover the solvents with the use of distil-
lation techniques. The histology labora-
tory at ECH has been considering this
option as a possible means of pollution
prevention. The initial investment cost of
a sophisticated distillation system can
usually be recovered in a reasonable
amount of time (e.g., 1 yr because less
solvent is needed and disposed costs are
reduced).
The ECH laboratory mixes xylene, etha-
nol, and methanol wastes for ease of dis-
posal. The only method to effectively sepa-
rate these chemicals onsite is by distilla-
tion. In distillation, substances are heated
to their boiling temperatures when the sub-
stance with the lowest boiling point is va-
porized. This vapor rises into the con-
densing portion of the distillation column
where it reverts back to its liquid state and
is removed from the column. Efficiencies
for separating compounds in mixtures have
been achieved by using mechanisms de-
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signed to continuously mix the vapor and
liquid phases during the distillation pro-
cess. With these mechanisms, the vapor
becomes increasingly enriched with the
higher boiling compound, and essentially
complete separations can be achieved.
Two different solvent recovery tech-
niques have been developed to enhance
the efficiency of solvent separation. One
method available for distillation of labora-
tory solvents (spinning band distillation)
uses a motor-driven Teflon band in the
distillation column. Another method uti-
lizes an atomized plate technique. Al-
though these distillation methods offer ef-
ficient separation, pure ethanol cannot be
separated and recovered from xylene and
ethanol mixtures. In fact, even if ethanol
could be kept completely free of xylene
contamination during tissue processing and
slide staining, the ability of an alcohol
recovery system to produce a virgin grade
(95% +) alcohol depends on the system's
ability to deal with the azeotropic link be-
tween alcohol and water (see number 2
below for explanation of the source of the
water) as well as on effective alcohol re-
covery operational procedures. Effective
operational procedures have been recom-
mended as follows:
(1) Either ethanol or methanol (recom-
mended by the tissue processor
manufacturer) should be used be-
cause of their low azeotrope to water;
(2) All alcohol containers should be filled
at the end of each shift; discard the
contents of the flush container (nor-
mally 70% alcohol) following the for-
malin container; the alcohol in all re-
maining containers is put into a stor-
age vessel to be reclaimed later;
(3) The last alcohol container is normally
absolute; it should continue to be re-
placed with absolute alcohol; this will
be the only "make-up" solvent neces-
sary to purchase;
(4) The alcohol reclaimed using distilla-
tion methods normally has a purity of
95% or greater; this alcohol should
be used in the containers between
the flush container and the absolute
container; there will be enough re-
claimed 95% + alcohol left over after
filling the middle containers to be
blended to 70% purity for the flush
container.
Economic Feasibility Analysis
The economic feasibility evaluation in-
cludes a preliminary cost analysis of both
capital and operating costs. For this study,
capital costs include estimates of equip-
ment and materials. The operating costs
include estimates of disposal fees and
raw materials. Not included were insur-
ance and liabilities costs because they
were undetermined and utility use and
labor costs because they were consid-
ered relatively unchanged. Based on the
economic analyses, an economies of scale
was developed (i.e., the economics for
different amounts of slide production) to
illustrate the net savings and payback pe-
riods for each of the three options. Scale
Level A represents laboratories with
monthly slide sample throughput of 8,000
or more slides; Scale Level B throughput
of 1,000 to 8,000 slides; Scale Level C
throughput of less than 1,000 slides.
In Table 1 the cost analysis data for
ECH (i.e., pollution prevention cost as-
sessment factors determining technical
feasibility) are summarized: the total capi-
tal investment, the net operating cost sav-
ings, and the payback period (total capital
investment/net operating cost savings per
month) for each option, and each level of
throughputs. Payback evaluatbn worksheets
for the solvent recovery option are presented
in the final report. The payback evaluation
was based on solvent waste recovery for
xylene and ethanol only because these
two solvents can economically be recov-
ered with the use of the same solvent
waste recovery unit. Recovering methanol
would require a separate unit or the imple-
mentation of a solvent waste segregation
program. Worksheets for solvent substitu-
tion and solvent reduction were not pre-
pared. No savings are realized from the
use of solvent (material) substitutes. The
data reporting savings from volume re-
duction from the use of automated equip-
ment are presented only as a case study
since ECH already uses an automated
system, and no additional improvement is
possible.
Conclusions and
Recommendations
The technical and economic results of
the feasibility analysis phase are summa-
rized in the next column.
Solvent recovery: This option is clearly
the most beneficial to ECH, provided that
the relatively high payback (97 mo) is
attractive to their operations. It can be an
effective pollution prevention method for
xylene, ethanol, methanol, and other his-
tology solvents; however, solvent waste
segregation is important to make this op-
tion feasible.
Substitution: Although this option may
provide the use of less toxic substances,
the relatively high cost of the substitutes
and their less effective performance for
tissue cleaning (compared with xylene)
make their benefit as a waste minimiza-
tion option less significant.
Volume reduction: ECH, like most
laboratories, is currently using automated
equipment. This option may provide labo-
ratories using manual tissue processors
and slide stainers a significant savings
because solvent purchased as well as
disposal costs are reduced.
In conclusion, the economy of scale
analysis indicates that solvent recovery
can be a cost-effective and attractive pol-
lution prevention option to implement in
large throughput histology laboratories
(8,000 slides/mo or larger) as indicated by
the low payback period (11 mo). It is a
less attractive option for the smaller scale
laboratories having slide throughputs of
less than 8,000/mo (payback period 97
mo). The purchase of a solvent recovery
unit to allow the recovery of methanol
along with xylene and ethanol would in-
crease the economic feasibility of solvent
recovery. Material substitution offers the
benefits of less toxic material; however,
its higher cost (compared with current
practice) may not be justified unless con-
sidered primarily on environmental
grounds. Volume reduction from the use
of automated equipment can offer signifi-
cant savings in laboratories still using
manual processors. This option has al-
ready been implemented in most histol-
ogy laboratories, including ECH.
The full report was submitted in fulfill-
ment of EPA Contract No. 68-C8-0061 by
Science Applications International Corpo-
ration, Cincinnati, OH, under the sponsor-
ship of the U.S. Environmental Protection
Agency.
'U.S. Government Printing Office: 1992 — 648-060/60132
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Table 1. Summary of Cost Analysis Data for Pollution Prevention Options
Option Description
Capital Investment
1. Solvent Recovery
Scale Level A
Scale Level B
Scale Level C
2. Material Substitution
Scale Level A
Scale Level B
Scale Level C
Volume Reduction
Scale Level A
Scale Level B
Scale Level C
12,800-18,900
8,500-10,900
7,900-8,500
No capital investment required
No capital investment required
No capital investment required
25,500-32,750
22,200-25,500
18,300-22,200
Cost Savings/Month *
Payback Period (Months)
Up to $1,780
Up to $120
Up to $68
None, will increase operating cost
by about $384-$2,137/mo.
None, will increase operating cost
by about $72-$401/mo.
None, will increase operating cost
by about $21-$117/mo.
Up to $1,190
Up to $793
Up to $477
11
97
124
Costs cannot be recovered
Costs cannot be recovered
Costs cannot be recovered
21-28
28-32
38-47
* These savings were calculated utilizing solvent cost as follows: xylene, $7.50/gal; ethanol, $7.60/gal;andmethanol, $2.00/gal.
* Data for solvent volume reductions were provided by a major equipment vendor. The data compare total solvent cost requirements for manual tissue
processors and the same requirements for an automatic processor provided with solvent evaporation and fume control. Total savings of$274/wk was
reported for the Level A operation (based on Hacker Instruments estimation). Savings on Levels B and C operations were proportioned based on total slide
throughput capacity.
George Wahl and Deana Stamm are with Science Applications International
Corporation, Cincinnati, OH 45203; Jeffery Driver and Joe Bob Cravens are
with Versar, Inc., Springfield, VA 22151.
Kenneth R. Stone is the EPA Project Officer (see below).
The complete report, entitled "Pollution Prevention Opportunity Assessment:
Histology Laboratory Xylene Use, Fort Carson, Colorado," (Order No.
PB92-228 436/AS; Cost: $19.00, subject to change) will be available only
from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U. S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
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EPA/600/SR-92/187
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