Envlron. Sci. Technol. 1991, 25, 1137- 1142
(7) Lustre, A. 0.;Issenberg, P. J. Agric. Food Chem. 1969,17, 1387-1393. (8) Antal, M. J. Adv. Solar Energy 1983, 61-111. (9) Pouwels, A. D.; Boon, J. J. J. Anal. Appl. Pyrolysis 1990, 17, 97-126, and references therein. (10) Richards, G. N.; Shafiideh, F.; Stevenson, T. T. Carbohydr. Res. 1983, 117, 322-327. (11) Kliendienst, T. E.; Shepson, P. B.; Edney, E. 0.;Claxton, L. D.; Cupitt, L. T. Enuiron. Sci. Technol. 1986,20,493-501. (12) DeGroot, W. F.; Pan, W.-P.;Rahman, M. D.; Richards, G. N. J. Anal. Appl. Pyrolysis 1988, 13, 221-231. (13) Essig, M. G.; Richards, G. N.; Schenck, E. M. In Cellulose and Wood-Chemistry and Technology, 1st ed.; Schuerch, C., Ed.; John Wiley & Sons: New York, 1989; pp 841-862, and references therein. (14) Pettersen, R. C. In The Chemistry of Solid Wood; Rowell, R. M., Ed.; ACS Adv. Chem. Ser. 1984, No. 207,115-116.
Registry No. 1, 98-01-1; 2, 98-00-0; 3, 96-48-0; 4, 1192-62-7; 6, 100-52-7; 7,620-02-0; 8, 271-89-6; 9, 108-95-2; 10,90-02-8; 12, 95-48-7; 13, 90-05-1; 14, 108-39-4; 15, 91-20-3; 16, 93-51-6; 17, 65-85-0; 21,2785-89-9 22,7786-61-0; 24,500-99-2;25,97-53-0; 26, 121-33-5;27,22080-97-3;29,106800-34-4;30,124784-07-2;p-cresol, 106-44-5;acetic acid, 64-19-7;propionic acid, 79-09-4;formic acid, 64-18-6.
Literature Cited (1) Ward, D. E. Proceedings, 10th Conference on Fire and Forest Meteorology, Ottawa, April 1989; American Meteorological Society: Boston, MA, 1989. (2) Wilson, R. A. Combust. Sci. Technol. 1985,44, 179-193. (3) Hawthorne, S. B.; Miller, D. J.; Barkely, R. M.; Krieger, M. S. Enuiron. Sci. Technol. 1988, 22, 1191-1196. (4) Hawthorne, S. B.; Krieger, M. S.;Miller, D. J.; Mathiason, M. B. Enuiron. Sci. Technol. 1989, 23, 470-475. (5) Stuckenbruck, P.; Aquino Neto, F. R. J. High Resolut. Chromatogr. 1990, 13, 210-212. (6) Lignins; Occurrence, Formation, Structure and Reactions, 1 s t ed.; Sarkarnen, K. V., Ludwig, C. H., Eds.; Wiley-Interscience: New York, 1971; pp 43-94.
Received for review August 20,1990. Revised manuscript received January 28, 1991. Accepted February 15, 1991. The experimental assistance of J . L. Pilon, helpful discussion with D. E. Ward, and financial support of the U.S.D.A. Forest Service Intermountain Research Station are gratefully acknowedged.
Inadequacy of NASQAN Data for Assessing Metal Trends in the Nation's Rivers Herbert L. Windom,' James T. Byrd, Ralph G. Smlth, Jr., and Feng Huant
Skidaway Institute of Oceanography, P.O. Box 13687, Savannah, Georgia 31416 Results of our analyses of dissolved Cd, Cu, Pb, and Zn in east coast North American rivers are considerablylower than those reported by the US.Geological Survey, National Stream Quality Accounting Network (NASQAN) for samples collected at similar locations during a similar time period. These results along with recent literature suggest that the NASQAN dissolved trace metal data are unreliable for the purpose of establishing water quality trends in the Nation's rivers. Dissolved trace metal concentrations in east coast rivers are probably controlled more by river chemistry than by anthropogenic inputs. Trace metal concentrations on suspended particles may provide a better index of anthropogenic influences.
Introduction Over the past two decades, marine chemists have come to recognize that most, if not all, past data on the concentrations of dissolved trace metals in seawater are erroneously high. Only the most recent data, which indicate oceanographically consistent spatial variations, are considered reliable (I). The first evidence of the unreliability of seawater trace metal data emerged in the 1970s from the results of intercomparison exercises involving experienced marine scientists from a number of laboratories. Results of analyses of aliquots of carefully collected, homogeneous seawater samples by participating laboratories in these early exercises ( 2 , 3 )indicated poor comparability of results. More recently, there have been major advances in analytical instrumentation and methodology, and greater attention has been given to assuring the elimination of contamination during sampling, storage, and analysis. Because of these improvements, data produced by laboPresent address: Dept. of Ocemography, Florida Institute of Technology, Melbourne, FL, 32901. 0013-936X/91/0925-1137$02.5010
ratories participating in more recent intercomparison exercises are in better agreement and are more consistent with best recent estimates of true concentrations of trace metals in seawater (Figure 1). In the United States, a large amount of data on trace metal concentrations (both dissolved and particulate) in rivers has been reported since about 1974 by the US. Geological Survey as a part of the National Stream Quality Accounting Network (NASQAN). Recently, NASQAN data on dissolved trace metals have been used to assess temporal trends in metal levels in the Nation's rivers (4, 5 ) even though the dangers of using historic data for such purposes have been documented (6). The analytical procedures used to produce the NASQAN dissolved trace metal data are described in Methods for Determination of Inorganic Substances in Water and Fluvial Sediments, the most recent edition of which (7) describes techniques that are at least a decade outdated. Modern analytical techniques for measuring trace metals in natural waters emphasize the need for highly purified reagents, substitution of glass with Teflon and polyethylene labware, and clean laboratory environments (I, 8-10), none of which are suggested in the NASQAN methods. Given the above and the evidence thai more recently improved analytical techniques produce more reliable data, the reliability of the NASQAN data is questionable. Recently reported dissolved trace metal concentrations for the Mississippi River (11, 12) that are 1-2 orders of magnitude lower than those reported by the US. GS provide evidence that the NASQAN data are erroneous. We report here data on trace metal concentrations in east coast US.rivers which, when compared to the NASQAN data for the same rivers, cast further suspicion on their reliability. We collected samples from 17 rivers draining eastern North America from near the Georgia-Florida boundary to Nova Scotia (Figure 2). Both dissolved and particulate
0 1991 American Chemical SOC:iety
Envlron. Sci. Technol., Vol. 25, No. 6, 1991 1137
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concentrations were determined in samples collected during high and low river discharge. In this paper, we discuss the results for dissolved Cd, Cu, Pb, and Zn. Dissolved concentrations determined by us are considerably lower than those reported by the U.S. GS (NASQAN). Our results also suggest that much of the variability in dissolved concentrations is natural and indicate that metal concentrations on suspended particles may provide a better basis for evaluating anthropogenic trace metal loadings.
Methods Water samples were collected from small boats, from bridges or, in a few cases, from river banks by using silicone tubing attached to a PVC pole and a hand-powered peristaltic pump. The tubing was thoroughly cleaned by rinsing with 10% HC1 and distilled water and was flushed with river water before samples were collected. Samples for dissolved trace metal analysis were filtered through Gelman Minicapsul cartridge filters (0.45 pm), attached to the outlet end of the silicone tubing, directly into precleaned polyethylene bottles (10% HCI and distilled water). Samples were acidified in a portable clean bench with 1.0 mL of N.B.S. HNO,/L of water and were stored in plastic bags until analyzed. 1198 Envkon. Sd.Technol.. Vol. 25, No. 6, 1991
Samples for particulate trace metal analysis were pumped, unfiltered, directly into 4-L precleaned, polyethylene bottles. Within 8 h after sampling, particulate trace metals were collected on precleaned 0.4-pm Nuclepore filters held in precleaned polycarbonate filter holders. This was accomplished by using a polyethyleneTeflon Nz pressurized filtration system with all operations carried out in a portable clean bench. Before analysis, trace metals were extracted from pHadjusted (7.8 f 0.2) samples on 8-hydroxyquinoline immobilized on silica gel (13). Filters containing particulate trace metals were digested in Teflon bombs with concentrated H F and "0,. Final sample solutions, blanks, and standards were analyzed on a Perkins-Elmer &man 5ooo atomic absorption system employing a heated graphite furnace. Sample extractions and manipulations were carried out in a class 100 clean room. Dissolved and particulate trace metal concentrations were analyzed, respectively, in triplicate and duplicate. For approximately 10% of the samples, the relative standard deviation of the triplicate dissolved trace metal analyses exceeded 15%, our quality assurance objective. In these cases, two of the values were used to calculate a mean with a relative standard deviation of 15% or better. All but three of the
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was provided to us by the National Research Council (NRC) of Canada as a part of their standard certification program. Our results are compared to the final certified values for the river water standard (SLRS-2),which is now available from NRC. 005-
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Figure 2. River sampling stations. Dot, this study; triangle, NASQAN stations.
Table I. Ottawa River Sample (SLRS-2). Comparison of Reported Data with Certified Values" certified value A1 Cd co cu Fe Mn Ni Zn
84.4 f 3.4 0.028 f 0.004 0.063 f 0.012 2.76 i 0.17 129 i 7 10.1 f 0.3 1.03 i 0.10 3.33 f 0.15
direct analysesb 86.5 f 1.5 2.89 f 0.19 130 f 2.5 10.1 f 0.21
extracted analysesbpc 84.3 f 2.9 0.036 f 0.003 0.064 f 0.003 2.03 i 0.39 1.05 f 0.07 3.8 f 0.20
" All concentrations are micrograms per liter. Reported by SkIO. Extracted on 8-hydroxyquinolineimmobilized on silica gel. sets of duplicate analyses of particulate trace metal met our quality assurance objective (i-e., a relative standard deviation of 20%). These three sets of analyses were discarded. Data presented in Table I provide an indication of the accuracy of our river water dissolved trace metal analyses. These analyses were performed on an uncompromised (i.e., concentrations unknown) Ottawa River water sample that
Resu 1t s Samples were collected from rivers during May 1986 and September 1988, which generally correspond to the periods of high and low discharge, respectively. These periods also represent the extremes of suspended sediment transport with highest particle concentrations during high discharge. Although these data are insufficient to describe the temporal variability of dissolved trace metal concentrations, which are often discharge related (II), they should suffice to give a general indication of mean values since they cover extreme conditions (Figure 3). Twelve of the 17 rivers were sampled at locations near NASQAN stations (Figure 2). Thus, U.S.GS data for dissolved trace metals, collected during a similar time period, can be compared to ours (Figure 3). The US.GS values represent the mean of from 3 to 11 analyses, depending on the river, conducted between October 1985 and September 1988. Our values represent the mean of six analyses on each river; three for each of the two sampling campaigns. The mean coefficients of variation for the US. GS analyses (i.e., the sum of the coefficients of variation for each river divided by the number of rivers) are 57,70, 117, and 76% for Cd, Cu, Pb, and Zn, respectively. Our corresponding mean coefficients of variation are 17, 14, 27 and 19%. A clear discrepancy exists between these two data sets. Which is more representative of true trace metal concentrations in east coast North American rivers? We can compare our Cd, Cu, and Zn data and those from the NASQAN stations to data from other less anthropogenically disturbed rivers (Table 11). We can also compare these data to those reported for the Mississippi Environ. Scl. Technol., Vol. 25, No. 6, 1991 1138
10.0
Table 11. Comparison of Trace Metal Concentrations in East Coast Rivers with Those in Major Rivers Cd east coast rivers (this stud east coast rivers (US. GS) Mississippi (Shiller and Boyle)c Mississippi (US. GS)' Yangtzed Amazon Orinowd
0.095 2.9 0.12
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1.o
13 (60)e 0.11 222 11 3.0
140 200 18/21 0.6/1.2 0.06 24 0.313.8 0.035 19 2.0
River (11). This comparison indicates that our results from east coast rivers are similar to those reported by Shiller and Boyle (11)for the Mississippi River with the exception of Zn, which is higher in east coast rivers, but are similar to values previously reported for several east coast rivers (14). Table I1 also shows that the differences between our data and those of the US.GS are similar in magnitude to the differences between the data reported by Shiller and Boyle (11) and by the US.GS for the Mississippi River. The above comparisons suggest that our Cd, Cu, and Zn data for east coast rivers are probably more representative of true concentrations than are the NASQAN data. Although similar data comparisons for P b are not possible because of lack of data, we conclude there is sufficient reason to consider our data more representative. This conclusion is reinforced by the fact that over 60% of the results of analyses for lead by the U.S. GS are reported as below their detection limit, which varies between sampling dates. The concentrations we reported for dissolved copper in east coast rivers are similar to presumed natural levels in large undeveloped river systems (Table 11),although our values are probably low based on the results shown in Table I. The hydroxyquinoline extraction apparently does not account for a significant fraction of dissolved copper, presumably organically complexed or bound. Thus, our values may be systematically -30% low. Cadmium and zinc, on the average, appear enriched in east coast rivers. There is considerable variability, however, in observed concentrations; Cd varies from 0.01 to 0.44 nmol.kg-' and Zn from 0.8 to 59 nmol-kg-'. Shiller and Boyle (14) have shown that dissolved Zn concentrations in relatively undisturbed major rivers vary with pH, implying control by river chemistry (e.g., adsorption-desorption, solubility) rather than control by sources within the watershed. Our results for dissolved Cd and Zn also indicate a relationship between dissolved concentrations and pH (Figure 4). These relationships suggest that chemical characteristics of the river systems have a greater influence on observed dissolved Cd and Zn concentrations than do anthropogenic inputs. There are no reliable data of which we are aware for lead in large anthropogenically undisturbed rivers. The St. Mary's and Satilla watersheds in the southeastern United States, however, are relatively undeveloped and have smaller population densities and fewer upwind anthropogenic sources of lead than the watersheds of the other rivers we studied. These rivers also have the lowest lead concentrations (Figure 3). 1140 Envlron. Scl. Technol., Vol. 25, No. 6, 1991
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