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 ------- 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- ------- 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 ------- 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 $300 BULK RATE POSTAGE & FEES PAID EPA PERMIT No. G-35 EPA/600/SR-92/187 ------- |