Environ. Sci. Technol. 1994,28, 1202-1203
of NPTOX positive materials prior to his issuance of the draft report. The data showed significant levels of NPTOX positive materials in unrelated chlorinated municipal drinking water supplies, water from wells clearly outside the zone of anthropogenic influence, and Florida blackwater streams not receiving industrial discharges. The article presents data developed by Dr. Geoffery Watts in a Florida Department of Environmental Protection (DEP) funded study. The study resulted in a draft report issued in December 1991, but the report has yet to be issued in final form. The DEP has recently acknowledged that the NPTOX parameter is not an suitable marker, and a DEP representative testifying at a September 23,1993, Environmental Regulation Commission (ERC) meeting stated that the Florida DEP has “simply los(t) all confidence in the ... NPTOX ... parameter as a suitable marker for tracking migration of the river water.” (7). This same position was confirmed by another FL DEP senior manager in an ERC meeting held November 18, 1993. In conclusion, the search for a reliable marker to trace pulp mill effluents is an important scientific objective. The article represents that the objective has been achieved with NPTOX. It has not, and it would be a disservice to all concerned to believe the task was completed. Literature Cited (1) Watts, G. B.; Locke, B. R. Enuiron. Sci. Technol. 1993,27,
2311-2317. (2) Lai, Y. 2.; Sarkanen, K. V. Lignins, Occurrence,Formation, Structure and Reactions;Sarkanen, K. V., Ludwig, C. H., Eds.; Wiley Interscience: New York, 1971; Chapter 5. (3) Kraft, F. The Pulping of Wood; MacDonald, R. G., Ed.; McGraw Hill Book Co.: New York, 1969; Chapter 11. (4) Singh, R. P. TheBleachingofPulp;TAPPIPress: Atlanta, GA, 1979; Chapter 2. ( 5 ) Watts, G. B.; Locke, B. R. Enuiron. Sci. Technol. 1993,27, 2317. ( 6 ) Florida DER Interoffice Memorandum, Feb 3, 1992. (7) Excerpted from testimony of Florida DEP official before the State of Florida Environmental Regulation Commission, Sept 23, 1993 (emphasis added).
John W. Smith’ and K. J. Schilling
Procter & Gamble Cellulose Consultants 8560 Wood Mills Drive West Cordova, Tennessee 380 18 SIR: We wish to respond to Smith and Schilling’s comments regarding our paper (1). (1)Smith and Schilling comment that we attempted to use UV spectroscopy to provide support for our conclusion that Fenextract is a chlorinated thiolignin. This was not the case since UV spectroscopy does not normally provide definitive information regarding molecular structure. Our assumption that Fenextract is a chlorinated thiolignin was based upon the elemental analysis and the fact that it was isolated from the Fenholloway River just below the outfall from a kraft mill discharge. The identical compound to Fenextract, based upon the physical and spectroscopic properties, was also isolated from the kraft mill effluent treatment pond prior to discharge to the Fenholloway River. Since chlorinated lignins are always present in kraft mill bleach liquors and alkaline extraction liquors (2),we feel confident in our 1202
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assumption that Fenextract is a chlorinated lignin. Furthermore, Fenextract cannot be isolated in a like manner from the Fenholloway River upstream of the kraft mill. (2) Smith and Schilling comment that “it is far more likely that Fenextract was created in the isolation/ purification performed by the authors. The procedure exposed the sample to multiple cycles of combined pH and elevated temperatures.” In response, we cite the work of Fricke (3). Fricke has performed extensive research on the physical properties of kraft black liquor (i.e., the kraft pulp prior to bleaching) and of the lignin isolated from black liquor. Fricke isolated the lignin from the black liquor by precipitation with sulfuric acid at pH 2 and further purified the lignin by additional cycles of pH adjustment that involved dissolution in sodium hydroxide solution and reprecipitation with sulfuric acid. Molecular weight determinations on the purified lignin were conducted using light scattering (for weight average molecular mass) and vapor pressure osmometry (for number average molecular mass) at a temperature of 80 “C. The molecular mass measurements were conducted at elevated temperatures to avoid the small potential for molecular association a t the lower temperature (3). Fricke reports that the lignin weight average molecular mass varied from 13 700 to 48 300 Da depending on the black liquor cooking conditions. The number average molecular mass ranged from 2300 to 6100 Da. Furthermore, Fricke has shown that no changes in the rheology of black liquor occurs when the liquor is stored at elevated temperatures for extended time periods. Thus, this experimental evidence does not support the notion that the isolation and purification procedure for Fenextract was responsible for its observed physical properties. (3) Smith and Schilling comment that “kraft mill effluent contains chlorinated materials which are produced by the oxidative breakdown of lignin during the kraft pulping and bleaching process. This process has been studied by other researchers who found that lignin is broken down into smaller molecules.” In our study, we reported that a direct aqueous injection of a Fenholloway River water sample (containing approximately 90% kraft mill effluent) into a particle beam liquid chromatograph/mass spectrometer (PB-LC/MS) produced no discernible peaks in the 50-1000 amu range. From this result we concluded that kraft mill effluent contains few low molecular mass lignin materials. Also in our study, we measured a range of chlorinated lignin molecular masses in a Fenholloway River/kraft mill effluent sample (a mixture of spent bleach and alkaline extraction liquors) by ultrafiltration analysis. About 30 % of the organically bound chlorine in the Fenholloway River sample was found to be in the high molecular mass fraction (Fenextract), while approximately 45 ?6 of the organically bound chlorine was relatively low molecular mass (100010 000 Da). Our reportedmolecular mass distribution does not differ significantly from that documented by Kringstad et al. (2)for the distribution of organically bound chlorine in spent chlorination and alkaline extraction liquors. In chlorination liquor, about 30% of the sample is 25 000 Da. In alkaline extraction liquor, about 5% of the sample is 25 000 Da. These results indicate that for the most part the lignin is not broken down into smaller molecules in kraft mill bleaching process but that the bleach effluent contains a range of high molecular mass materials. (4)Smith and Schilling comment that “The ability to isolate a molecule of the size the authors reported for Fenextract, viz. 1.44 X lo6 Da, from the outfall of treated effluent is inconsistent with the mechanics of the wastewater treatment system. If Fenextract were truly present in the mill waste water, its high molecular weight and water insolubility would undoubtedly result in the molecule precipitating and/or sorbing out in the settling phase of the treatment system-prior to the discharge of the effluent.” Fenextract solubility measurements conducted by US demonstrated that the material is infinitely soluble in basic aqueous solutions and cannot be reprecipitated until the pH of the aqueous solution is reduced to about pH 2. We assume that Fenextract is originally present in the kraft mill alkaline extraction liquor and remains solubilized when the solution pH is adjusted to about 7, prior to discharge of the kraft mill effluent to the Fenhollway River. Based on the Fenextract I3CCP/MAS spectrum presented in our paper, we conclude that chlorine dioxide bleaching leads to cleavage of the lignin aromatic ring and concomitant formation of mucconic acids. Increasing the proportion of carboxylic acid groups in the molecule can account for the solubility of a high molecular weight material such as Fenextract in the kraft mill effluent. (5) Smith and Schilling comment that “NPTOX is not a valid marker for tracing pulp mill effluent” and proceed to list a number of anthropogenic sources of organic halides that could produce a positive NPTOX test. We are well aware of the other potential sources of organic halides, both natural and manmade, in the environment that will produce a positive NPTOX test. The use of the NPTOX test as an indicator parameter for tracing kraft pulp mill effluent in groundwater will be the subject of a forthcoming paper to be submitted to us by Enuiron. Sci. Technol. In this paper, we will demonstrate that the NPTOX test in combination with a few other simple chemical tests may be effectively utilized to distinguish organic halides derived from pulp mill effluents from organically bound halides from (1)peat bogs and blackwater streams not receiving industrial discharges (2) domestic septic tanks, and (3) municipal drinking water supplies. (6) Smith and Schilling comment that the “NPTOX procedure employed by the authors yielded an inordinant number of false positives.” The NPTOX test is a modification of the EPA Method 9020 for Total Organic Halides (TOX), which involves the initial purging of the water sample to remove volatile organic halides from the sample prior to analysis. The
EPA Method 9020 analytical protocol is the same whether NPTOX or TOX is being analyzed. Since TOX is an EPA analytical method, it has been subjected to the rigorous method validation studies ( 4 ) . Tate reported in the method detection limit for TOX of 5 hg/L ( 4 ) . The NPTOX false positives that Smith and Schilling are referring to were obtained in a study carried out by the Florida Department of Environmental Protection (FDEP) in 1992. In this study, several blank water samples and a number of water samples spiked with different concentrations of trichlorophenol were submitted to a commercial analytical laboratory for NPTOX analysis (5). Seven of the water samples were blank samples, and six of the water samples were fortified with high levels (10 000 pg/L) of trichlorophenol. Low-level concentrations (>lo pg/L) of NPTOX were reported by the analytical laboratory in three of the seven blank water samples (5). Rather than an inherent problem with the EPA NPTOX/TOX analytical method, it is our belief that the false positives were a result of laboratory error, i.e., failure to properly clean the analytical equipment between runs leading to carryover of the high level trichlorophenol spikes to a subsequent blank water sample. The NPTOX analytical protocol employed by the commercial laboratory (5)would suggest that sample carryover was a strong possibility in this case. We hope this response has satisfied Smith and Schillings concerns regarding the issues they have raised in our paper. We maintain, and as our forthcoming paper will demonstrate, that NPTOX/TOX is a reliable indicator parameter for pulp mill effluents in groundwater and in the environment in general. Literature Cited (1) Watts, G. B.; Locke, B. R. Environ. Sci. Technol. 1993,27,
2311-2317. (2) Kringstad, K. P.; Lindstrom, K. Spent Liquors from Pulp Bleaching. Enuiron. Sci. Technol. 1984, 18, 236A.
(3) Fricke, A. L. Physical Properties of Kraft Black Liquor Summary Report-Phases Z and ZI; U.S. Department of Energy Report DOE/CE/40606-T5; Office of Industrial Programs: Washington, DC, Sep 1987. (4) Tate, C.; Chow, B. EPA Method Study 32, Method 450.1, Total Organic Halides (TOX);EPA/600/S4-85/080; US. EPA: Washington, DC, 1985. (5) Coppenger, W. Environmental Administrator, Florida Department of Environmental Protection, personal communication, June 1993.
Geoffrey B. Watts’
GeoSolutions Inc. P.O. Box 7638 Tallahassee, Florida 32314 Bruce R. Locke Department of Chemical Engineering Florida A&M University and Florida State University Tallhassee, Florida 32316-2175
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