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Scavenging of particulate matter in coastal waters
Marine Chemistry, 32 ( 1991 ) 171-175
17 l
Elsevier Science Publishers B.V., Amsterdam
Scavenging of Paniculate Matter in Coastal Waters H. Weiss 1, M. Koide 2, K.K. Bertine 3 and E.D. Goldberg2. ~Naval Oceans Systems Center, San Diego, CA 92110 (U.S.A.) 2Scripps Institution of Oceanography, La Jolla, CA 92093 (U.S.A.) 3San Diego State University, San Diego, CA 92182 (U.S.A.) (Received June 20, 1989; revision accepted January 26, 1990)
ABSTRACT Weiss, H., Koide, M., Bertine, K.K. and Goldberg, E.D., 1991. Scavenging of paniculate matter in coastal waters. Mar. Chem., 32:171-175. The uptake of a suite of 19 metals from coastal seawaters upon both glass and Teflon surfaces reflected primarily the sorption of paniculate matter derived from crustal rock weathering. Uptake for all elements was greater in the light than in the dark. Based upon these and earlier results, a new definition of scavenging for environmentalsystems is proposed.
INTRODUCTION
In two earlier publications we have pointed out that surfaces exposed to coastal seawaters build up coatings of organic matter which pick up inorganic particulates (Hodge et al., 1979. Goldberg et al., 1988). Uranium, Pu, Po, Au, Pt, Mn and Cd were accumulated on different surfaces, with > 90% of these elements associated with particulate phases. With increase in depth, there were greater contributions to the coatings from the dissolved states of these metals. Further, the influence of photochemical and biological reactions in the accommodation of the metals was evident. These results bear upon what is meant by 'scavenging' in aqueous environmental systems. This term, originally taken from the vocabulary of radiochemists, was meant t6 signify the association of dissolved species with flocculent precipitates, e.g. the uptake of dissolved metals upon iron hydroxides. The metals presumably were associated with ion exchange sites of one type or another on the solid phases. However, we now argue that metals associated with surfaces in coastal waters are primarily a part of the particulate phases. *Author to whom correspondence should be addressed.
172
H WEISS ET AL.
Still, uptake of dissolved phases is not completely ruled out. Thus we propose a more general definition of scavenging in natural aqueous systems as the 'chemical or physical association of one or more components of one phase with another phase'. Herein, we report some additional results from a much broader suite of elements that were analyzed by slow neutron activation analyses. The goals of this study were to ascertain whether or not significant amounts of any of the elements come to the surface independent of the particulates and if there was preferential uptake on either of the two types of surfaces, glass or Teflon. FIELD LOGISTICS
Glass rings (0.6 c m X 0 . 6 cm o.d.) and Teflon rings (0.95 cmX0.95 cm o.d. ) were strung onto Teflon string. The total surface areas for the two types of necklaces were 4134 cm 2 for the glass rings and 1844 cm-" for the Teflon rings. The necklaces were hung on a carousel and covered with a transparent canopy (polycarbonate) and a dark canopy during the periods of deployment. The glass rings were exposed from December 12, 1987 to January 6, 1988 (22 days) and the Teflon rings from May 4, 1988 to June 1, 1988 (28 days) at a buoy situated ~ 1 km from the Scripps Institution of Oceanography Pier and at a depth of 15 m below the surface. Upon retrieval of the necklaces, they were detached from the carousel, rinsed with distilled water and transferred to large pre-cleaned Teflon beakers. These exposed necklaces and the unexposed ones, the blanks, were processed and pre-concentrated for irradiation by techniques described earlier (Goldberg et al., 1988). CHEMICAL METHODS
The chemical composition of the deposits was determined by instrumental neutron activation analysis. Irradiations were carried out at the TRIGA Reactor. University of California at Irvine, where the neutron flux was 1.2 X 1012 n c m - 2 s - i at full power. Measurements were made with high-resolution Ge(Li ) detectors coupled to microcomputer-based multi-channel analyzer systems. The sample weights ranged from 50 to 100 mg. The elements Mg, Na, Ca, Ti, A1, Mn and V were determined through production o f short-lived components. In this case, the samples were irradiated for 30 s at 10% full power. Gamma-ray emissions were measured for 10 min, following a l-rain cooldown period. The other elements were determined after a full-power irradiation of 4-7 h. The quantification of the amounts in the samples depended upon comparison of the activity of a characteristic photopeak with that induced in an elemental standard after appropriate corrections for decay and neutron flux.
SCAVENGINGOF PARTICULATEMATTERIN COASTALWATERS
173
RESULTS
The metal/aluminum ratios for the phases sorbed to the glass and Teflon surfaces are presented in Table 1. In general, the metal/aluminum ratios sorbed to the surfaces are similar to those in crustal rocks. The ratios are usually within a factor of two or so of each other. The exceptions, Sr/Al, Sb/Al and Cs/Al, were higher on both the glass and Teflon surfaces than in crustal rocks. This may reflect differences in the composition of the weathered material entering the coastal zone from that of average crustal rock, unrepresentative crustal values or the uptake of dissolved species of these elements. There are no systematic differences in the ratios between uptake on the glass and upon the Teflon rings, except for the case of thorium. The Th/A1 ratios are significantly higher on the Teflon surfaces than on the glass ones. This is unexplained at the present time. Also, there are no systematic differences between the ratios on either surface in the light and in the dark, although occasional outliers are found, such as is the case of strontium and manganese. The uptake of metals upon both.the glass and Teflon surfaces was substantially higher in the light than in the dark for all elements (Table 2). It should be emphasized that the exposures of the Teflon and of the glass rings took TABLEI
Metal/aluminum ratios sorbed to glass and Teflon tings, on a weight/weight basis Ratio × l 0 000
Mg/AI Sc/AI V/AI Mn/Al Co/Al As/A1 Rb/Al Sr/AI Zr/A1 Sb/Al Cs/A1 La/Al Ce/AI Sm/A1 Eu/Al Lu/Al Hf/Al Ta/Al Th/Al
Glass
Teflon
Crustal rock (Levinson, 1974 )
Light
Dark
Light
Dark
5600 4.4 33 87 3 2.3 16 160 41 0.27 1.1 4.6 12 1.5 0.2 0.08 0.75 0.09 2.2
5500 4.2 48 87 2.7 1.8 19 410 26 0.31 1.2 4.4 11 1.2 0.2 0.08 0.53 0.07 2.3
4100 3.4 33 89 2.6 1.5 15 170 28 0.31 1.4 4 10 1.3 0.19 0.07 0.7 0.08 6.9
7000 3.4 46 177 2.9 3.9 15 540 37 1.5 0.93 4.2 12 1.3 0.15 0.17 0.41 0.06 6.9
2 17 120 3 2.3 Il 48 20 0.025 0.375 2.5 7.5 0.75 0.15 0.06 0.38 0.13 1.3
174
H. WEISSE'I AL,
TABLE 2
Uptake of metals upon surfaces, in units ofppm sorbed solids cm -2 day Lexcept where noted Element
Glass Dark
Mg (%) AI (%) Sc Ti (%) V Mn Co As Rb Sr Zn Sb Cs La Ce Sm Eu Lu Ta Th
0.11 0.19 0.83 0.017 9 16 0.56 0.34 3.6 76.5 4.8 0.06 0.22 0.83 2 0.23 0.04 0.015 0.013 0.42
Teflon Light 0.21 0.38 1.6 12.5 33 I 0.88 6.2 60 15.5 0.1 0.41 1.8 4.6 0.56 0.08 0,03 0.033 0,85
Dark
Light
0.02 0.03 0.09 0.001 1.25 4.8 0.08 0.11 0.42 14.5 1 0.04 0.03 0.11 0.33 0:034 0.004 0,002 0.002 0.19
0.15 0.38 1.3 0.02 12.5 33.5 1 0.57 5.6 64 10.7 0. t 2 0.53 1.5 3.9 0.48 0.07 0,026 0.032 2,6
place during two separate time periods. Glass slides exposed to the light and to the dark accommodated different populations of organisms, as first noticed in the Yugoslavian experiments (Goldberg et al., 1988 ). The light-exposed surfaces were covered with diatoms and bacteria; the dark-exposed surfaces with bacteria only. It would appear that the photosynthesizing organisms are creating an environment more conducive to the uptake of the particulates by the production of more adhesive substances. The well-known association of sands, silts and clays with macrophytes supports this observation. OVERVIEW
The uptake of metals on surfaces exposed to coastal seawaters primarily involves the adherence of particles of weathered continental debris. The uptake process is enhanced by photosynthesizing organisms, most probably by their output of adhesive organic phases. The technique in this study is useful to characterize chemically and perhaps mineralogically the rock flour entering the marine system from coastal raanoff, rivers and atmosphere at a given location. It has the advantage over simple
SCAVENGINGOFPARTICULATEMA'VFERINCOASTALWATERS
175
filtration o f averaging the composition o f the particulate matter over weeks. A filtration gives the composition over a m u c h shorter time period. ACKNOWLEDGMENTS This investigation was supported by a grant from the Office o f Naval Research (USN N000-14-80-C-0440) to the University o f California at San Diego.
REFERENCES Goldberg, E.D., Koide, M., Bertine, IC, Hodge, V., Stallard, M., Martincic, D., Mika, N., Branica, M. and Abaychi,J., 1988. Appl. Geochem., 3: 561-571. Hodge, V.F., Koide, M. and Goldberg, E.D., 1979. Particulate uranium, plutonium and polonium in the biogeochemistriesof the coastal zone. Nature, 277: 206-209. Levinson, A.A., 1974. Introduction to Exploration Geochemistry. Applied Publishing, Wilmette, IL, 614 pp.
17 l
Elsevier Science Publishers B.V., Amsterdam
Scavenging of Paniculate Matter in Coastal Waters H. Weiss 1, M. Koide 2, K.K. Bertine 3 and E.D. Goldberg2. ~Naval Oceans Systems Center, San Diego, CA 92110 (U.S.A.) 2Scripps Institution of Oceanography, La Jolla, CA 92093 (U.S.A.) 3San Diego State University, San Diego, CA 92182 (U.S.A.) (Received June 20, 1989; revision accepted January 26, 1990)
ABSTRACT Weiss, H., Koide, M., Bertine, K.K. and Goldberg, E.D., 1991. Scavenging of paniculate matter in coastal waters. Mar. Chem., 32:171-175. The uptake of a suite of 19 metals from coastal seawaters upon both glass and Teflon surfaces reflected primarily the sorption of paniculate matter derived from crustal rock weathering. Uptake for all elements was greater in the light than in the dark. Based upon these and earlier results, a new definition of scavenging for environmentalsystems is proposed.
INTRODUCTION
In two earlier publications we have pointed out that surfaces exposed to coastal seawaters build up coatings of organic matter which pick up inorganic particulates (Hodge et al., 1979. Goldberg et al., 1988). Uranium, Pu, Po, Au, Pt, Mn and Cd were accumulated on different surfaces, with > 90% of these elements associated with particulate phases. With increase in depth, there were greater contributions to the coatings from the dissolved states of these metals. Further, the influence of photochemical and biological reactions in the accommodation of the metals was evident. These results bear upon what is meant by 'scavenging' in aqueous environmental systems. This term, originally taken from the vocabulary of radiochemists, was meant t6 signify the association of dissolved species with flocculent precipitates, e.g. the uptake of dissolved metals upon iron hydroxides. The metals presumably were associated with ion exchange sites of one type or another on the solid phases. However, we now argue that metals associated with surfaces in coastal waters are primarily a part of the particulate phases. *Author to whom correspondence should be addressed.
172
H WEISS ET AL.
Still, uptake of dissolved phases is not completely ruled out. Thus we propose a more general definition of scavenging in natural aqueous systems as the 'chemical or physical association of one or more components of one phase with another phase'. Herein, we report some additional results from a much broader suite of elements that were analyzed by slow neutron activation analyses. The goals of this study were to ascertain whether or not significant amounts of any of the elements come to the surface independent of the particulates and if there was preferential uptake on either of the two types of surfaces, glass or Teflon. FIELD LOGISTICS
Glass rings (0.6 c m X 0 . 6 cm o.d.) and Teflon rings (0.95 cmX0.95 cm o.d. ) were strung onto Teflon string. The total surface areas for the two types of necklaces were 4134 cm 2 for the glass rings and 1844 cm-" for the Teflon rings. The necklaces were hung on a carousel and covered with a transparent canopy (polycarbonate) and a dark canopy during the periods of deployment. The glass rings were exposed from December 12, 1987 to January 6, 1988 (22 days) and the Teflon rings from May 4, 1988 to June 1, 1988 (28 days) at a buoy situated ~ 1 km from the Scripps Institution of Oceanography Pier and at a depth of 15 m below the surface. Upon retrieval of the necklaces, they were detached from the carousel, rinsed with distilled water and transferred to large pre-cleaned Teflon beakers. These exposed necklaces and the unexposed ones, the blanks, were processed and pre-concentrated for irradiation by techniques described earlier (Goldberg et al., 1988). CHEMICAL METHODS
The chemical composition of the deposits was determined by instrumental neutron activation analysis. Irradiations were carried out at the TRIGA Reactor. University of California at Irvine, where the neutron flux was 1.2 X 1012 n c m - 2 s - i at full power. Measurements were made with high-resolution Ge(Li ) detectors coupled to microcomputer-based multi-channel analyzer systems. The sample weights ranged from 50 to 100 mg. The elements Mg, Na, Ca, Ti, A1, Mn and V were determined through production o f short-lived components. In this case, the samples were irradiated for 30 s at 10% full power. Gamma-ray emissions were measured for 10 min, following a l-rain cooldown period. The other elements were determined after a full-power irradiation of 4-7 h. The quantification of the amounts in the samples depended upon comparison of the activity of a characteristic photopeak with that induced in an elemental standard after appropriate corrections for decay and neutron flux.
SCAVENGINGOF PARTICULATEMATTERIN COASTALWATERS
173
RESULTS
The metal/aluminum ratios for the phases sorbed to the glass and Teflon surfaces are presented in Table 1. In general, the metal/aluminum ratios sorbed to the surfaces are similar to those in crustal rocks. The ratios are usually within a factor of two or so of each other. The exceptions, Sr/Al, Sb/Al and Cs/Al, were higher on both the glass and Teflon surfaces than in crustal rocks. This may reflect differences in the composition of the weathered material entering the coastal zone from that of average crustal rock, unrepresentative crustal values or the uptake of dissolved species of these elements. There are no systematic differences in the ratios between uptake on the glass and upon the Teflon rings, except for the case of thorium. The Th/A1 ratios are significantly higher on the Teflon surfaces than on the glass ones. This is unexplained at the present time. Also, there are no systematic differences between the ratios on either surface in the light and in the dark, although occasional outliers are found, such as is the case of strontium and manganese. The uptake of metals upon both.the glass and Teflon surfaces was substantially higher in the light than in the dark for all elements (Table 2). It should be emphasized that the exposures of the Teflon and of the glass rings took TABLEI
Metal/aluminum ratios sorbed to glass and Teflon tings, on a weight/weight basis Ratio × l 0 000
Mg/AI Sc/AI V/AI Mn/Al Co/Al As/A1 Rb/Al Sr/AI Zr/A1 Sb/Al Cs/A1 La/Al Ce/AI Sm/A1 Eu/Al Lu/Al Hf/Al Ta/Al Th/Al
Glass
Teflon
Crustal rock (Levinson, 1974 )
Light
Dark
Light
Dark
5600 4.4 33 87 3 2.3 16 160 41 0.27 1.1 4.6 12 1.5 0.2 0.08 0.75 0.09 2.2
5500 4.2 48 87 2.7 1.8 19 410 26 0.31 1.2 4.4 11 1.2 0.2 0.08 0.53 0.07 2.3
4100 3.4 33 89 2.6 1.5 15 170 28 0.31 1.4 4 10 1.3 0.19 0.07 0.7 0.08 6.9
7000 3.4 46 177 2.9 3.9 15 540 37 1.5 0.93 4.2 12 1.3 0.15 0.17 0.41 0.06 6.9
2 17 120 3 2.3 Il 48 20 0.025 0.375 2.5 7.5 0.75 0.15 0.06 0.38 0.13 1.3
174
H. WEISSE'I AL,
TABLE 2
Uptake of metals upon surfaces, in units ofppm sorbed solids cm -2 day Lexcept where noted Element
Glass Dark
Mg (%) AI (%) Sc Ti (%) V Mn Co As Rb Sr Zn Sb Cs La Ce Sm Eu Lu Ta Th
0.11 0.19 0.83 0.017 9 16 0.56 0.34 3.6 76.5 4.8 0.06 0.22 0.83 2 0.23 0.04 0.015 0.013 0.42
Teflon Light 0.21 0.38 1.6 12.5 33 I 0.88 6.2 60 15.5 0.1 0.41 1.8 4.6 0.56 0.08 0,03 0.033 0,85
Dark
Light
0.02 0.03 0.09 0.001 1.25 4.8 0.08 0.11 0.42 14.5 1 0.04 0.03 0.11 0.33 0:034 0.004 0,002 0.002 0.19
0.15 0.38 1.3 0.02 12.5 33.5 1 0.57 5.6 64 10.7 0. t 2 0.53 1.5 3.9 0.48 0.07 0,026 0.032 2,6
place during two separate time periods. Glass slides exposed to the light and to the dark accommodated different populations of organisms, as first noticed in the Yugoslavian experiments (Goldberg et al., 1988 ). The light-exposed surfaces were covered with diatoms and bacteria; the dark-exposed surfaces with bacteria only. It would appear that the photosynthesizing organisms are creating an environment more conducive to the uptake of the particulates by the production of more adhesive substances. The well-known association of sands, silts and clays with macrophytes supports this observation. OVERVIEW
The uptake of metals on surfaces exposed to coastal seawaters primarily involves the adherence of particles of weathered continental debris. The uptake process is enhanced by photosynthesizing organisms, most probably by their output of adhesive organic phases. The technique in this study is useful to characterize chemically and perhaps mineralogically the rock flour entering the marine system from coastal raanoff, rivers and atmosphere at a given location. It has the advantage over simple
SCAVENGINGOFPARTICULATEMA'VFERINCOASTALWATERS
175
filtration o f averaging the composition o f the particulate matter over weeks. A filtration gives the composition over a m u c h shorter time period. ACKNOWLEDGMENTS This investigation was supported by a grant from the Office o f Naval Research (USN N000-14-80-C-0440) to the University o f California at San Diego.
REFERENCES Goldberg, E.D., Koide, M., Bertine, IC, Hodge, V., Stallard, M., Martincic, D., Mika, N., Branica, M. and Abaychi,J., 1988. Appl. Geochem., 3: 561-571. Hodge, V.F., Koide, M. and Goldberg, E.D., 1979. Particulate uranium, plutonium and polonium in the biogeochemistriesof the coastal zone. Nature, 277: 206-209. Levinson, A.A., 1974. Introduction to Exploration Geochemistry. Applied Publishing, Wilmette, IL, 614 pp.