Remobilization of Metals from Polluted Marine ...

Remobilization of Metals from Polluted Marine sediment^',^

Can. J. Fish. Aquat. Sci. Downloaded from www.nrcresearchpress.com by Renmin University of China on 06/06/13 For personal use only.

CARLTON D. HUNTAND DEBORAH L. SMITH Marilze E~~os~ysaems Wrsenrc*hEabor6r?ory, Graduate School oj' Oc-eclnogmpbzp.,University c$Rhode Bslszrsd, Kingston, Rd 02886, USA

HUNT, C. D., AND D. L. SMITH. 1983. Remobilization of metals from polluted marine sediments. Can. J. Fish. Aqeaat. Sci. 40(Suppl. 2): 132- 142. The transition metals Cu, Pb, Fe, Mn, and Cd were examined to estimate short- and long-term release rates from highly contaminated sediments and to cornparc this release with present metal flux into an ecosystem. The concentration of Cra and Pb increased In the water colunan over contaminated marine sediments when these sediments were isolated from metal and organic carbon sources and held in large (13 m7) marine microcosms. During the summer and early fall, Cu concentrations increased by a factor of 3 relative to the concentration in microcosms containing slightly polluted and uncontanrinatcd sediments. Mass balance caIculaations indicate that 840 and 21 pmol mP2 yr-' Cu and Pb, respectively, were mobilized and exported from the microcosms with highly contaminated sediments, while less-contaminated sedinaents lost 120 pmoI Cu rn ' * yr-'. Iron and Mn were not exported from the microcosms. In the absence of high sedimentation rates and high bioturbation ratcs, the diffusive loss of Cu and Pb may be sufficient to return the upper 1 cm of sedinaent to background levels in 44 and 400 yr, respectively. This remobiliaation is a small percentage of currcnt inputs to Narragansett Bay.

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HUNT, C. D., AND D. L. S ~ ~ I I I T 1983. H . Wemobiliaation of metals from polluted marine sediments. Can. 5. Fish. Aquat. Sci. 4CdBSuppl. 2): 132- 142. Nous avons examink Bes mCtaux de transition Cu, Pb, Fe, Mn et Cd, estim6 les taux de mise en Iibert6 h court et long terme depuis des sediments fortemerat contaminis et compare cette mise en libert6 avec l'actuel flux de metarax dans un kcosystemc. La concentraticsn de Cu ct Pb augmente dans la colonne d'eau situCe au-desseas de skdiments mains contaminks quand ces dcrniers sc~ntisolCs des sources de mktaux et de carbone inorganique, et maintcnus dans de volurnineux (13 m" microcosmes marins. En kt6 el au debut de I'automnc, Ies concentrations de Cu augmentent d'un Ficteur 3 par rapport a la cc~ncentrationdans les microcosmes contenant des sediments 16ghrernent pollu6s et non contamines. Des caiculs de bilan de masse indiquent que 840 et 21 pmol. m an-' de Cu et de Pb respecf vement sont mobilises et export& des microcosmes contenant des sediments fortement eomtaminCs, tandis que les skdirnents moins contaminks perdent 120 pmol Cu m-" an-'. Le fer et Mn ne sont pas exportks des microcosmes. Il est possible qu'en l'absemce de taux 6levks de sedimentation et de bioturbation la perte de Cu et de Pb par diffusion suffise a ramener le centimktre supirieur de sediment aux niveaux de base en l'espace de 44 ct 400 ans respcctivement. Cette remobilisation ne represents qu'un faiblc pourcentage des apports actuels dans la baie de Narragansett.

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Received March 19, 1982 Accepted November 17. 1982

DISCHARGE of nutrients, metals, and anthropogcnic organic compounds during the past century have resulted in elevated levels within Narragansett Bay, pluticularly in the upper

his paper forms part of the Proceedings of the Conference on Pollution in the North Atlantic Ocean, convened at Halifax, Nova Scotia, October 19-23' 198 I . ?he contents of this article do not necessarily reflect the views and policies of the U.S. Environmental Protection Agency, nor docs the mention of trade names or commercial products constitute endorsement or recornnlendation for use. Printed in Canada (J6856) Imprime au Canada (56856)

R e p lc 19 mars 1982 Accept6 le 14 novembre 1982 region known as the hc~videnceRiver (Olsen and Lee 1949). Thc sediments in the Providence Wiver act as a repository for these compounds and influence the water column concentrations of nutrients (Bilson et al. 1980; Nixon. Kelly ct al. 1980; Nixon et al. 1976) and cerkain metals through both rcmobilization (Hunt 1983a) and depositional processes (Santschi et al. 1980a; Santschi et al. 1980b; Turskian 1977). Given the large size of the sediment reservoir and the influence of the sediments on the water column, it is not evident, a priori. if reduction in nutrient and metal loading through improved sewagc treatment would result in immediate improvement in the quality of the ecosystem.


HUNT AND SMITH: METAL REhIOBILIZATION

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Several laboratory studies suggest that contaminated sediments will release metals when maintained under oxidizing conditions (Lu and Chen 1977) and also in the presence of bioturbation (W. 8 . Davis USEPA, Narragansett. WH, perwnal communication). Even though diminished pollution sources may result in decreased metal loading in natural systems (Bothner et al. 1980; Meams 198l), the time scales for the recovery of natural systems have been estimated only for Mg (Bothner et al. 1980). To improve our ability to predict the consequences of reducing nutrient, metal, and organic discharge into presently impacted ecosystems, we studied a gradient of contaminated sediments held under uniform low discharge conditions in controlled marine ecosystems. The study was conducted at the Marine Ecosystem Research Laboratory (MERL) from August 1979 to March 1981. The focus of this paper is on the response of several transition metals to the relaxed pollution pressure. We examined short- and long-term release of metals from highly contaminated sediments and compared these releases with estimates of present metal fluxes into Narragansett Bay.

Methods

For this experiment, nine microcosms each containing 13 m3 of seawater were used. Three microcosms were used for each sediment type. The microcosms were operated with a flow through status by adding 480 L of seawater in four pulses daily (120 L *pulse-') which gave a 27-d water turnover time. Turbulence was supplied with 2 h on, 4 h off mixing cycle from mixers located 1 m above the sediments. The microcosms were outdoors, exposed to sunlight and weather. Details of the microcosm operation have been described at length (Pilson and Nixon 1980; Nixon, Alonso et al. 1980; Pilson 1978), as has been their ability to mimic natural estuarine environments typical of the lower west passage of Narragansett Bay (Pilson et al. 1980; Hunt and Smith 1982; Oviatt et al. 1988).

Sediments from three regions of Narragansett Bay (Fig. 1) were recovered in as natural a condition as feasible and placed within the MERL ecosystems to provide a contl-olled reduction in the level of organic, nutrient, and metal loading. Sediment from station II (Providence River) represents the region most strongly impacted by industrial and domestic sewage discharge and is rich in nutrients, organic material, trace metals, hydrocarbons, and other pollutants (Van Vleet and Quinn 1977, 1978; Farrington and Quinn 1973; Eisler et al. 1977). Sediment with a detectable pollutant load was collected at station I (midbay) which is the sediment source for previous MEWL experiments. Clean sediments were collected in Whode Island Sound. from station %%I Experimental results which can be related to natural systems require that the sediments retain natural characteristics such as orientation, animal populations, and pore water chemistry. This was achieved by collecting sediment from each site

FIG. 1 . Locations in Narragansett Bay (United States) from which sediments were recovered and placed in the MERL microcosms.

with a 8.25-rn' USNEL spade corer (Fig. 2). The corer with recovered sediment was placed on a frame over a sediment tray containing core retainers constructed from steel plate. The sediment was dropped -0.5 m into a retainer by carefully opening the corer spade. After all retainers were filled, they were lifted from the sediment tray, leaving the recovered sediment in its proper orientation and remarkably undisturbed. Sediments were covered in the field with wet bags and plywood. transported to the MERL facility, placed in the microcosms, and covered with seawater from the lower west passage of the bay. Three sediment trays from each location were recovered and placed in the microcosms between August 6 and 10, 1979. All microcosms were drained of seawater and simultaneously filled on August I I to initiate the experiment. No abnormal changes in sediment pH or El, resulted from the transfer operation.

Both dissolved and particulate metal concentrations in each microcosm and feed water were determined every 2 - 3 wk. Particulate Fe, Mn, and Al were studied because of their involvement in metal removal processes, and both Fe and Mn respond strongly to changes in the oxidation-rduction


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CAN. J . FISH. AQUAT. SCI.. VOL. 40(SUPP&. 21, 1983

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SURFACE SEDIMENT

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BOTTOM SEDIMENT

STEP 2 TENSION RELEASED FROM BOX CORE CABLE. SPADE RETMCTED CORE DROPS INTO RETAINER

LOCATED OVER RETAINED PLACED I N S I D E SEDIMENT CONTAINER

FILLED AFTER RETAINERS PLACE

w

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1

AS??

STEP 3 RETAINED CORES FIRST SUBDIVIDED TO FIT CONTAINER CURVATURE. W E N ALL RETAINERS ARE FILLED AND I N PLACE SPACES BETWEEN RETAINERS AND CONTAINER EDGE ARE FILLED AND RETAINERS ARE REMOVED.

OUTLINE OF RETAINERS

FIG. 2. Schematic representation of the technique developed to recover intact sediments with a 0.25-m' UNSEL spade corer.

potential in sediments (AlBer 1980). Copper, Pb, and Cd are known pollutants affecting a variety of organisms and are major contaminants in these sediments. Dissolved Fe, CU,Cd. and Pb concentrations were obtained by doubly extracting -500 mL of seawater (adjusted to pH 5) with methyl issbutyl ketone and mmsniumpyrrolidiine ditkiocarbarnate (MIBK-APDC) after filtration through 0.4-pm Nuclepore filters. The MIBK extracts were combined and back-extracted with 5.0 mL 2 M HN03 for 48 h. Metal concentrations were determined by flameless atomic absorption spectrometry (AAS) (Perkin Elmer 603 cquipped with an

HGA-2100 graphite furnace and D, arc background correction). Standard curves for metals were made in 2 M H N 0 3 adjusted to 550 p g Na.& -' with metal-free seawater. Seawater was added to standard solutions to compensate for a consistent depression in analytical absorbance resulting from entrainment of sea salt in the acid extract of the MHBK-APDC phase. All extractions were completed within 4 h of sample collection. Analytical precision was within 10% of the mean, as determined from replicated samples. Intercalibration of this method with laboratories at the Graduate School of Oceanography using the Co-APDC coprccipi-

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HLJNTAND SMITH: METAL WEMOBILIZATION

tation method gave results which agree within the analytical precision. Dissolved Mn was measured by direct injection into the graphite furnace of 0.4-pm-filtered samples after acidification (10 FL H N 0 3 * m Lseawater-'). Total Mn was obtained from unfiltered samples. acidified, and analyzed as above. Precision of the Mn analysis was