Ames Power Plant for Technical assistance and to V. A. Fassel and H. J. Svec for administrative aid. Literature Cited (1) National Center for Resource Recovery Bulletin, 1979, No. 3, pp
70-6. (2) Trout, P. E. Enuzron Health Perspect 1972, I , 63-5. (3) Haney, J. S. Conf.Proc --Natl Conf.Polychlorinated Biphenyls,
1975, 1976,362-5. (4) Kuratsune, M.; Masuda, Y. Enuiron Health Perspect 1972,1, 61-2. (5) Timm, C. M. “Sampling Survey Related to Possible Emission of Polychlorinated Biphenyls from the Incineration of Domestic Refuse”, NTIS Pub. No. PB-251-285,1975. (6) Haile, C. L.; Baladi, E. “Methods for Determining the Polychlorinated Biphenyl Emission from Incineration and Capacitors and Transformer Filling Plants, NTIS Pub. No. PB-276-745, 1977. (7) Golembiewski,M.; Ananth, K.; Tricham. G.; Baladi, E. “Environmental Assessment of a Waste-To-Energy Process, Braintree Municipal Incinerator”, Midwest Research Institute Report Nos. 38216 and 4033-C, 1976. (8) Eiceman, G. A.; Clement, R. E.; Karasek, F. W. Anal Chem 1979, 51,2343-50. (9) Cowherd, C.; Marcus, M.; Guenthes, C. M.; Spigarelli, J. L. “Hazardous Emission Characteristics of Utility Boilers”, NTIS, Pub. NO. PB-245-017-19BA,1975. (10) Hall, J. L.; Severns, G. A.; Shanks, H. R.; Joensen, A. W.; Van Meter, D. B.; Olexsey, R. A. “Environmental Emissions from a Suspension Fired Boiler While Burning Refuse Derived Fuel and Coal Mixtures”, Proceedings of the IXth Biannual Conference, ASME, Washington, DC, 1980, pp 497-512. (11) Reynold, L. M. Bull Enuzron Contam Toxzcol 1969,4,12843.
(12) Buser, H. R.; Bosshardt, H. P. Chemosphere 1978,7,165. (13) Blake, D. E. “Source Assessment Sampling System: Design and Development“, EPA-600/7-78-018,1978. (14) Junk, G. A,; Richard, J. J.; Grieser, M. D.; Witiak, D.; Witiak, J. L.; Arguello, M. D.; Vick, R.; Svec, H. J.; Fritz, J. S.; Calder, G. V. J . Chromatogr. 1974,99,745-62. (15) Woolson, E. A. J . Assoc. O f f .Anal. Chem. 1974,57,604-9. (16) Armour, J. A. J. Assoc. Off. Anal. Chem. 1973,56,987-93. (17) William, D. T.; LeBel, G. L.; Furmaczyk, T. Chemosphere 1980, 9, 45-50. (18) Macheod, K. A. “Sources of Emission of Polychlorinated Biphenyls into the Ambient Atmosphere and Indoor Air”, NTIS Pub. No. PB 297122,1979. (19) Sebastian, F. P.; Kroneberger, G. F.; Lombana, L. A.; Napoleon, J. M. Proc. Am. Ind Chem. Eng. Workshop 1974,5,67-72. (20) Harvey, G. R.; Sheinhauer, W. G. Atmos Enuiron. 1974, 8, 777-82. (21) Bidleman, T. F.; Rice, C. P.; Olney, C. E. In “Marine Pollutant Transfer”; Windom, H. L., Duce, R. A., Eds; Health and Co.: Lexington, MA, 1978; pp 323-51. (22) Murphy, T. J.; Rzeszutko, C. P. “Polychlorinated Biphenyl in Precipitation in Lake Michigan Basin”, NTIS Pub. No. PB-286363,1978. (23) Bidleman, T. J.; Christensen, E. J. J . Geophys. Res. 1979,84, 7857-62. (24) Fuller, B.; Gordon, J.; Kornreich, M. “Environment Assessment of PCBs in the Atmosphere”, EPA Report No. EPA-450/3-77-045, The Mitre Corp., McLean, VA 1977.
Received for reuiew December 29,1980. Accepted April 23,1981. This research was supported by the Assistant Secretary for Enuironment, Office of Health and Enuironmental Research, WPAS-HA-02-04-01 and HA-02-03-02,
NOTES
Characterization of Copper Binding Capacity in Lake Water Harry Blutstein”7 and Roman F. Shaw Department of Inorganic and Analytical Chemistry, Latrobe University, Victoria 3083, Australia Introduction
T o assess the impact of heavy metal pollutants on aquatic biota, toxicity testing correlating total metal concentration has been shown to be misleading because it ignores metal speciation (1-4). For example, Chakoumakos e t al. ( 5 ) have shown that free copper ions and hydroxyl species are toxic forms of copper t o cutthroat trout, while carbonatocopper species are nontoxic. Particulate and organic material have also been shown t o modify the toxicity of trace metals (6). Elaborate analytical schemes have been developed t o measure different species (7, 8) by using anodic stripping voltammetry (ASV). In an untreated sample this technique detects only “labile” metal species, which are operationally defined and include ionic, and some dissociable, complexed metal species. Other fractions can be determined quantitatively by subjecting the sample to various physicochemical treatments, so as to convert other forms to labile metal. T h e released metal is determined by difference, and, depending on the sample pretreatment, it is possible to obtain estimates + Present address: Laboratory Services Branch, Environment Protection Authority, 240 Victoria Parade, East Melbourne, Victoria 3002. Australia.
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of metal associated with organic material, colloids, and particulate matter. An alternative approach is indirect, in that the concentration of complexing agents is estimated. A filtered sample is titrated with ionic copper and the labile copper is measured by differential pulse anodic stripping voltammetry (DPASV). T h e intercept of the resultant bilinear amperometric curve yields the apparent complexing capacity (9). Although this is the most frequent method used, doubts have been expressed of the accuracy of this approach ( 1 0 , l l ) . Other techniques have been used to estimate the apparent complexing capacity such as the ion-selective electrode for titration with copper(I1) ions (12, 13), solubility determinations (14),and the ion exchange equilibrium method (15).It would be useful t o be able to identify the components that make up the total binding capacity. Adsorption onto particulate matter and colloids, and chelation with organic compounds, may contribute. Smith (16) combined ultrafiltration with complexing capacity measurements so that he could determine the apparent complexing capacity of specific molecular weight fractions. However, these measurements were restricted to the filtered portion of the sample. In this work the respective binding capacities of filtered and unfiltered aliquots of a lake water sample have been measured. 0013-936X/81/0915-1100$01.25/0 @ 1981 American Chemical Society
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w The contributions to the total copper binding capacity of water from Albert Park Lake have been characterized by using
a combination of filtration, UV irradiation, and p H profile. Approximately 50% of the apparent complexing capacity is due to interaction with soluble organics in solution, while a significant proportion of the remainder is probably due to the adsorption of copper(I1) ions onto colloidal material, such as
I t has been possible from the information obtained t o differentiate the apparent complexing and adsorption capacities of the sample. By combining these measurements with a p H profile and irradiation, it should be possible to identify sources of the total binding capacity. Experimental Section
Reagents. Analytical-grade reagents were used. Ultrapure water of resistivity 18.2 m a cm-l was obtained from a Milli-Q2 system (Millipore Co.) and was further purified by using subboiling distillation. Nitric acid was sub-boiling-point distilled, and a 0.5 M sodium hydroxide solution electrolytically purified. Instrumentation. A Metrohm Polarecord Model E506 and E608 VA-controller in conjunction with a Metrohm Polarographie Stand (Model E505) was used. A three-electrode system was employed. A Metrohm E-410 hanging drop mercury electrode (drop area, 1.46 f 0.05 mm2) was used as the working electrode. Potentials were measured with reference to a saturated calomel electrode. T o minimize iR drop across the cell, a platinum wire was used as an auxiliary electrode. Procedure. Before analysis, the solution in the cell was deoxygenated by having high-purity argon passed through it for 15 min and then over its surface throughout the determination. The metals were plated into the hanging drop mercury electrode a t a potential of -0.400 V for 120 s with stirring, followed by 30 s without stirring. The anodic stripping voltammogram was then recorded a t a scan speed of 3.8 mV/s, a pulse modulation amplitude of 25 mV, and a period between pulses of 0.8 s. The cell and the platinum electrode were stored overnight in 10% nitric acid, and the working and reference electrodes stored dry. Before use the cell and the glassware were thoroughly rinsed with water and the sample. Before use, all sample containers were acid-washed with 50%nitric acid and then aged for at least 7 days by being filled with 10% nitric acid. An all-glass filtration unit was acidwashed, and the Whatman GF/C filters used were cleaned by being soaked in 1M nitric acid for at least 24 h and then rinsed with water before use. Waters, where indicated in the test, were irradiated for 24 h in quartz tubes a t a distance of 5 cm from a 1000-W Hg lamp using a La Jolla Model P0/14 photooxidation unit (La Jolla Scientific Co., La Jolla, CA). The complexing capacity was measured according to the method of Chau et al. ( 9 ) ,and the relative standard deviation was found to be 6.7% based on five replicate determinations. Sample Collection. Albert Park Lake was sampled on May 4,1978, and samples were stored in polyethylene bottles a t 4 OC. Site Description. Albert Park Lake is a small (46 ha) lake constructed on a coastal reed swamp. The lake is situated within 5 km of the center of the city of Melbourne and is primarily used for recreational activities, such as boating. R e s u l t s a n d Discussion
For the purposes of this discussion, the apparent complexing capacity corresponds t o the concentration a t the amperometric end point when a filtered sampled is titrated
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clays, silica, or manganese dioxide sols. The apparent adsorption capacity has also been measured and was only 12% of the total capacity a t natural pH. The removal of organic matter adsorbed on organic particulate matt,er by UV irradiation increased the adsorption capacity, which provides evidence for the role of organic material in inhibiting adsorption of copper onto particulates suspended in solution.
with ionic copper(I1). The end-point equivalent for an unfiltered sample will be referred to as the total binding capacity, while the difference between this quantity and the apparent complexing capacity will be defined as the apparent adsorption capacity. The apparent adsorption capacity represents the ability of particulate matter in solution to adsorb copper ions. At natural pH (7.63) the apparent complexing capacity of a sample taken from Albert Park Lake was found to be 0.36 p M of Cu/L. This value falls within the range of values obtained by Chau et al. (9) of 0-0.64 pM of Cu/L for nine lakes sampled in the Sudbury region of Ontario, Canada. The total binding capacity was determined in an unfiltered aliquot of Albert Park lake water, and, from these data and the apparent complexing capacity, the apparent adsorption capacity was calculated to be 0.050 pM of Cu/L. This represents only 12% of the total binding capacity. T o determine the contribution of organic matter to the binding capacity, we subjected filtered and unfiltered samples to UV irradiation. The results of this experiment are given in Table I. The removal of the organic carbon by irradiation was not complete, and an 86% decrease was observed for soluble carbon while particulate carbon decreased by only 73%. Ultraviolet irradiation has been used by several workers ( I 7-19) to release metals from organically bound complexes. Upon UV irradiation the apparent adsorption capacity increased from 0.050 to 0.068 pLM of Cu/L, while the particulate organic material was reduced from 1.5 to 0.4 mg of C/L. Therefore, the increase in the apparent adsorption capacity may be attributed to the destruction of the organic matter, which inhibited copper uptake on the particulate surface. This observation is in agreement with results of chemical modeling computation (20) which have shown that, in the absence of organic ligands, Cu(I1) is strongly adsorbed onto SiOz, but in their presence adsorbed copper is released. Davis and Leckie (21) studied the uptake of copper on amorphous iron oxide in the presence and the absence of organic complexing ligands. They found that copper uptake was either enhanced or reduced by organic complexing ligands, depending on whether the metal-ligand complexes formed are strongly bound by oxide surfaces or form a nonadsorbing complex in solution. Therefore, the experimental results presented in this work suggest that the naturally occurring organic compounds in Albert Park Lake effectively reduce the adsorption of copper(I1) onto particulate matter by the formation of nonadsorbing complexes in solution. Irradiation reduced the apparent complexing capacity from 0.36 to 0.18 p M of Cu/L. The corresponding percentage de-
Table l. Effect of UV Irradiation on Filtered and Unfiltered Albert Park Lake Water treatment
binding capacity, untreated sample (pM of Cu/L) binding capacity, UV-oxidized sample (pM of Cu/L) organic carbon, untreated sample (mg of C/L) organic carbon, UV-oxidized sample (mg of C/L)
unflltered tlltered
0.41
0.25 10.0 1.6
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0.36 0.18 8.5 1.2
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g-
30
0
3
L
rCI
5
6
7
8
9
1
0
I
PH Figure 1. Plot of binding capacity (pg of Cu/L) vs. pH: (A)total (unfiltered) binding capacity: ( 0 )apparent (filtered)complexing capacity; (B)apparent absorption capacity (by difference).
crease of dissolved organic carbon is 86%,whereas the decrease in the apparent complexing capacity produced by UV oxidation is only 48%. Thus, while approximately half the binding sites in the filterable fraction are associated with UV oxidizable carbon, the remaining apparent complexing capacity is associated either with refractory organic matter, such as high molecular weight humic compounds, or with colloidal material having a diameter less than the pore size of the filter used. Piro et al. (22) proposed that, by measuring the ASV “labile” metal as a function of pH, it might be possible to “fingerprint” metal forms in natural waters. This concept may be usefully applied to the binding capacities of waters to obtain information on the components contributing to the total binding capacity. The curves obtained for the binding capacity of filtered and unfiltered Albert Park Lake water are shown in Figure 1. A comparison between the pH vs. apparent complexing capacity curves obtained in this work and that obtained by Chau et al. (9) are similar in general outline but differ on several points of detail, particularly a t p H values below 5.5. I t is from an interpretation of the detailed structure of these curves that the nature of binding of metals in natural waters may be elucidated. Above p H 5.5 the apparent adsorption capacity is constant up to p H 10, but the apparent complexing capacity is p H independent only up to pH 8.5,after which it increases gradually to pH 10. This increase, which is 11%above the plateau region at p H 10, may be attributed to the formation of hydroxyl precipitates of iron, aluminium, or manganese salts, which are in turn capable of adsorbing additional Cu(I1) ions. T o confirm this mechanism, we filtered the lake water a second time, after the pH had been adjusted to 10, and determined the binding capacity. The concentration obtained was 0.37 pM of Cu/L, which is, within experimental error, the same as the apparent complexing capacity of the sample a t natural pH. The apparent adsorption capacity is constant in the pH range 5.5-10, but between p H 5.5 and 4.3 the apparent adsorption capacity decreases linearly to zero. This behavior may be due to an increase in the adsorption of aquatic humates onto particulates as the pH decreases. Gjessing (23)found that
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below pH 5 montmorillonite adsorbs humic compounds. The adsorbed organic matter can then act to inhibit metal adsorption onto particulate material as was the case in the UVirradiation experiments reported earlier in this work. An alternative explanation of this behavior is that, as the pH decreases, metal oxides and hydroxide precipitates suspended in solution dissolve, reducing the surface area available for adsorption of copper ions. From the data available, it is not possible to determine which of these mechanisms predominates. At p H values below 5.5, the apparent complexing capacity decreases in two stages-pH 5.0-5.5 and p H 4.2-4.5. Approximately 25% of the total apparent complexing capacity is removed in each of these steps. Thus mechanisms may be invoked to explain the rapid decrease observed in these two regions. These are (1) the dissociation of a copper humic compound as protons replace the complexed copper at low pH and ( 2 ) the destabilization of colloidal material with subsequent desorption of metal species. On the basis of the above experiments, it is not possible to distinguish which mechanism is operating (or to determine whether a combination of the two mechanisms is operating) in the natural water system studied in this work.
Literature Cited (1) Sunda, W. G.; Guillard, R. R. J. Mar. Res. 1976,34,511.
(2) Anderson, D. M.; Morel, F. M. Lirnnol. Oceanogr. 1978, 23, 283. (3) Anderson, D. M.; Morel, F. M.; Guillard, R. R. Nature (London) 1978,276,71. (4) McKnight, D. M.; Morel, F. M. Lirnnol. Oceanogr. 1979, 24, 823. (5) Chakoumakos, C.; Russo, R. C.; Thurston, R. V. Enuiron. Sci. Technol. 1979,13, 213. (6) Zitko, V. Toxic. Biota Met. Forms Nat. Water, Proc. Workshop, 1975, 1976, Chapter 1. (7) Florence, T. M. Water Res. 1977,11,681. (8) Hart, B. T.; Davies, S. H. R. “A Study of the Physicochemical Forms of Trace Metals in Natural Waters and Wastewaters”, Technical Report No. 6; Caulfield Institute of Technology, Water Studies Centre, 1978. (9) Chau, Y. K.; Gachter, R.; Lum-Shue-Chan, K. J. Fish. Res. Board Can. 1974,31, 1515. (10) Hanck. K. W.: Dillard. J. W. Anal. Chim. Acta 1977.89.329. (11) Greter,’F.-L.;Buffle, J.; Haerdl, W. J. ElectroanaL Chern. 1979, 101,211. (12) Buffle, J.; Greter, F.-L.; Haerdl, W. Anal. Chern. 1977, 49, 216. (13) McCrady, J. K.; Chapman, G. A. Water Res. 1979,13,143. (14) Kunkel, R.; Manahan, S. E. Anal. Chem. 1973,45,1465. (15) Crosser, M. L.; Allen, H. E. Soil Sci. 1977,123,176. (16) Smith, R. G., Jr. Anal. Chern. 1976,48,74. (17) Mancy, K. H. Prog. Water Res. 1973,3,63-72. 1181 Chau. Y. K.: Grachter. R.: Lum-Shue-Chan. K. J . Fish. Res. Board Chn. 1974,31,1515. ’ (19) Blutstein. H.: Smith, J. D. Water Res. 1978.12, 119. (20) Vuceta, J.; Morgan,’ J. J. Enuiron. Sci. ?‘echnol. 1978, 12, 1302. (21) Davis, J. A.; Leckie, J. 0. Environ. Sci. Technol. 1978, 12, 1309. 1221 Piro. A.: Bernhard. M.: Branica. M.: Verzi. M. Radioact. Contarn. Mar. Enuiron. Proc. Symp. 1972’1973,29.’ (23) Gjessing, E. T. “Physical and Chemical Characteristics of Aauatic Humus”: Ann Arbor Science Publishers: Ann Arbor, MI, 1$76; pp 77-9. ~
~
Received for review April 14,1980. Revised May 8, 1981. Accepted May 8,1981.
