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  15 September2011
Volume 12 Issue 9
 

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ET&C August 2011

ET&C Journal Article Spotlight: Effects of Cyclic Changes in pH and Salinity on Metals Release from Sediments by Yong Seok Hong, Kerry A. Kinney, and Danny D. Reible

By Jane Parkin Kullmann, Haley & Aldrich, Inc.

Metals are often identified as constituents of potential concern in contaminated sediment; but assessing the risk associated with their presence can be challenging.  One challenging aspect is the complexity of metals speciation, and the resulting variability in sorption-desorption and precipitation-dissolution from sediments, which can be affected by the characteristics of the sediment and the water environments. 

In their new ET&C paper, “Effects of cyclic changes in pH and salinity on metals release from sediments,” Hong et al. report on an experimental approach that they developed to evaluate the potential effect of the type of water environment on the release of cadmium, zinc, manganese, and iron from sediment, both in total and as cations. The paper describes the experimental set-up to simulate saline, freshwater, and estuarine environments (as well as a control) and apply them to sediment material from the Anacostia River, spiked to increase the Cd content. The control environment was high pH/low salinity, saline high pH/high salinity, and freshwater was low pH/low salinity. The estuarine environment was created by cycling saline and freshwater environments.

Relative to the total aqueous concentrations of the metals in each of the environments, in general the lowest concentrations were observed in the control water, zinc was higher in the freshwater and lower in the saline, and cadmium and manganese were higher in the saline and lower in the freshwater. No conclusions were drawn relative to the actual concentration gradients of metals present in the water, since this would be more often dependent on the sediment quality than the properties inherent to the metals.

The researchers found that each metal exhibited slightly different responses, both temporally and with respect to the type of water environment. The pattern of aqueous zinc concentrations was attributed primarily to release from exchangeable solid phases rather than ZnS, such that a lower pH was associated with a greater release of zinc. For cadmium and manganese, it appeared that a higher pH and a greater saline concentration increased the release of these metals from the sediment.  This was interpreted to indicate that the most significant process driving this result is competition with cations and complexation with anions (i.e., salts) in the water.  They also found that the estuarine environments as the conditions change over time do appear to mimic the responses to fresh and saline water. 

Freely dissolved metals concentrations (M2+) were measured in each of the water environments over time.  These concentrations are thought to provide the best estimates of bioavailability and overall toxicity of the metals in each of the environments, making them most relevant for characterizing potential risk to the associated ecosystems.  The patterns of metals concentrations as freely dissolved ions differed from those observed for total aqueous concentrations.  Notably, release of zinc and cadmium ions was highest in freshwaterConcentrations of dissolved manganese were overall fairly similar in each of the steady state environments; however, in the estuarine (i.e., cyclic) environment, concentrations of manganese exhibited cyclic variations.

The authors described these results in relation to each of the metals’ tendencies for ligand complexation. For zinc, more ionic zinc is released in the low pH/low salinity freshwater environment, and zinc is found more often as a complexed species under saline conditions.  These characteristics were similar for the release of cadmium, but to an even greater extent, such that less than one percent of the cadmium released in the saline environment was freely dissolved, compared to 70 percent in the freshwater environment. For manganese, 90 percent of the manganese released to freshwater was in the freely dissolved ionic form, compared to 20 percent in the saline environment. 

In order to evaluate the effect of these environments on the quality of the sediment, the authors also conducted acid volatile sulfide (AVS) and simultaneously extracted metals (SEM) analysis of the sediment material, as well as metals analysis of the porewater for comparison. The authors found that for each environment, the AVS exceeded the measured SEM at a depth of 2 cm and below, leading them to conclude that sediments at depth would be anticipated to be non-toxic. They also noted that, relative to the concentrations of metals in porewater, some relationship to salinity was indicated, as concentrations in the saline and estuarine systems were higher and increased over time, whereas in the freshwater and control environments, concentrations decreased over time and were lower.

Overall, the sum of these experiments indicates significant variability in the behavior of metals release from sediment based on the characteristics of the water environment, and that an environment that exhibits a cyclic effect from a saline to freshwater environment (i.e., estuarine) adds a level of uncertainty to this behavior.  In addition, the characteristics of the metals as released from the sediment (i.e., ionic versus complexed forms), which could influence the assessment of their toxicity, differ from metal to metal and environment to environment. However, AVS/SEM analysis of the sediment also indicates that the material used in this experimental design is likely to be non-toxic at depth. These experiments provide additional confirmation of the necessity for careful consideration of the conditions under which a risk assessment is being conducted, including the environmental conditions, the properties of the metals potentially identified as compounds of concern, and the AVS/SEM characteristics of the sediment material.

SETAC and its members have contributed greatly to the scientific literature on metals in sediment. A title and keyword search of Wiley’s Online Library (available on the SETAC Journals web page) yields 1,668 ET&C and 126 IEAM papers.  In addition SETAC has published at least ten books on metals. Here are the sediment and metals papers that SETAC (and a few others) has published so far in 2011, and a list of books:

Metals and Sediment Papers, ET&C 2011 Year-To-Date

Baumann Zofia and Nicholas S. Fisher, Relating the sediment phase speciation of arsenic, cadmium, and chromium with their bioavailability for the deposit-feeding polychaete Nereis succinea, Environmental Toxicology and Chemistry, Volume 30, Issue 3, March 2011, Pages: 747–756.

Burgess, Robert M., Steven B. Hawthorne, Monique M. Perron, Mark G. Cantwell, Carol B. Grabanski, David J. Miller, Kay T. Ho and Marguerite A. Pelletier, Assessment of supercritical fluid extraction use in whole sediment toxicity identification evaluations, Environmental Toxicology and Chemistry, Volume 30, Issue 4, April 2011, Pages: 819–827.

Hong, Yong Seok, Kerry A. Kinney and Danny D. Reible, Acid volatile sulfides oxidation and metals (Mn, Zn) release upon sediment resuspension: Laboratory experiment and model development, Environmental Toxicology and Chemistry, Volume 30, Issue 3, March 2011, Pages: 564–575.

Strom, David, Stuart L. Simpson, Graeme E. Batley and Dianne F. Jolley, The influence of sediment particle size and organic carbon on toxicity of copper to benthic invertebrates in oxic/suboxic surface sediments, Environmental Toxicology and Chemistry, Volume 30, Issue 7, July 2011, Pages: 1599–1610.

Van Geest, Jordana L., David G. Poirier, Keith R. Solomon and Paul K. Sibley, A comparison of the bioaccumulation potential of three freshwater organisms exposed to sediment-associated contaminants under laboratory conditions, Environmental Toxicology and Chemistry, Volume 30, Issue 4, April 2011, Pages: 939–949.

Metals and Sediment Papers, Other Sample Journals 2011 Year-To-Date

Hwang, Kyung-Yup, Hong-Seok Kim and Inseong Hwang, Effect of Resuspension on the Release of Heavy Metals and Water Chemistry in Anoxic and Oxic Sediments, CLEAN – Soil, Air, Water, Article first published online : 3 August 2011, DOI: 10.1002/clen.201000417

Nedia, Ghannem, Azri Chafai, Serbaji Mohammed Moncef and Yaich Chokri, Spatial distribution of heavy metals in the coastal zone of “Sfax-Kerkennah” plateau, Tunisia, Environmental Progress & Sustainable Energy, Volume 30, Issue 2, July 2011, Pages: 221–233.

Sakakibara, Masayuki, Yuko Ohmori, Nguyen Thi Hoang Ha, Sakae Sano and Koichiro Sera, Phytoremediation of heavy metal-contaminated water and sediment by Eleocharis acicularis, CLEAN – Soil, Air, Water, Volume 39, Issue 8, August 2011, Pages: 735–741.

Tsakovski, Stefan and Vasil Simeonov, Hasse diagram technique as exploratory tool in sediment pollution assessment, Journal of Chemometrics, Volume 25, Issue 5, May 2011, Pages: 254–261.

Zimmer, Dana, Kristian Kiersch, Christel Baum, Ralph Meissner, Robert Müller, Gerald Jandl and PeterLeinweber, Scale-Dependent Variability of As and Heavy Metals in a River Elbe Floodplain, CLEAN – Soil, Air, Water, Volume 39, Issue 4, April, 2011, Pages: 328–337.

SETAC Metals Books
Adams and Chapman (eds).  2006.  Assessing the Hazard of Metals and Inorganic Metal Substances in Aquatic and Terrestrial Systems.

Herbert Allen(ed).  2002. Bioavailability of Metals in Terrestrial Ecosystems: Importance of Partitioning for Bioavailability in Invertebrates.

Harold Bergman, Elaine Dorward-King (eds).  1997.  Reassessment of Metals Criteria for Aquatic Life Protection.

S Meyer, SJ Clearwater, TA Doser, MJ Rogaczewski, JA Hansen (eds). 2007.  Effects of Water Chemistry on Bioavailability and Toxicity of Waterborne Cadmium, Copper, Nickel, Lead, and Zinc to Freshwater Organisms.

Meyer, Adams, Brix, Luoma, Stubblefield, Wood (eds).  2005.  Toxicity of Dietborne Metals to Aquatic Organisms.

Sparling, DW et al. (eds).  2010.  Ecotoxicology of Amphibians and Reptiles.  Second Edition.

Richard J. Wenning, Graeme E. Batley, Christopher G. Ingersoll, and David W. Moore (eds).  2005.  Use of Sediment Quality Guidelines & Related Tools for the Assessment of Contaminated Sediments (SQG).

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