Sediment porewater

There are two main sources of Rn to the ocean (1) the decay of sediment-bound "Ra and (2) decay of dissolved "Ra in a water column. Radon can enter the sediment porewater through alpha recoil during decay events. Since radon is chemically inert, it readily diffuses from bottom sediments into overlying waters. The diffusion of radon from sediments to the water column gives rise to the disequilibrium (excess Rn) observed in near-bottom waters. Radon is also continuously being produced in the water column through the decay of dissolved or particulate "Ra. 

FIGURE 3.3 Pearson correlation coefficients between fish (Gambusia) Hg concentration and MeHg concentrations in various environmental media sediment, porewater, surface water, and suspended particulate matter (SPM) from the Florida Everglades (1995-1998). 

McGroddy, S.E., Farrington, J.W. (1995) Sediment porewater partitioning of polycyclic aromatic hydrocarbons in three cores from Boston Harbor, Massachusetts. Environ. Sci. Technol. 29, 1542-1550. 

Bishop [75] determined barium in seawater by direct injection Zeeman-modulated graphite furnace atomic absorption spectrometry. The V203/Si modifier added to undiluted seawater samples promotes injection, sample drying, graphite tube life, and the elimination of most seawater components in a slow char at 1150-1200 °C. Atomisation is at 2600 °C. Detection is at 553.6 nm and calibration is by peak area. Sensitivity is 0.8 absorbance s/ng (Mo = 5.6 pg 0.0044 absorbance s) at an internal argon flow of 60 ml/min. The detection limit is 2.5 pg barium in a 25 ml sample or 0.5 pg using a 135 ml sample. Precision is 1.2% and accuracy is 23% for natural seawater (5.6-28 xg/l). The method works well in organic-rich seawater matrices and sediment porewaters. 

Mayer, P Vaes, W.H.J. Wijnker, F. Legierse, K.C.H.M. Kraaij, R. Tolls, J. Hermens, J.L. 2000, Sensing dissolved sediment porewater concentrations of persistent and bioaccumula-tive pollutants using disposable solid-phase microextraction fibers. Environ. Sci. Technol. 34 5177-5183. 

Figure 10.7 Schematic illustration of uptake and depuration of chemicals by a benthic organism, a clam dwelling near the sediment-water interface. iw is the truly dis-solved compound in the water column, ipom is the compound asso-ciated with the sediment organic matter, ipw is the compound dis-solved in the sediment porewater.

Laurentian Trough estuary Canada sediment porewaters 7 sites... 

Puget Sound Washington, USA sediment porewaters 65 analyses... 

Table 3.21 Arsenic concentrations in soil and sediment porewaters... 

Azcue, J.M., Mudroch, A., Rosa, F. et al. (1995) Trace elements in water, sediments, porewater, and biota polluted by tailings from an abandoned gold mine in British Columbia, Canada. Journal of Geochemical Exploration, 52(1-2), 25-34. 

Azcue, J.M., Nriagu, J.O. and Schiff, S. (1994) Role of sediment porewater in the cycling of arsenic in a mine-polluted lake. Environment International, 20(4), 517-27. 

Massachusetts Woburn Groundwater and sediment porewaters Davis et al. (1994) Wilkin and Ford (2006)... 

PCBs that have historically accumulated in the sediments may return to the water through resuspension-desorption and through continuous diffusion from sediment porewaters. 

Diffusion of PCBs from highly contaminated surficial sediments in areas of concern may be an important net source to the Great Lakes. In fact, PCB diffusion from the porewaters of heavily contaminated coastal and riverine sediments may justify the removal of those sediments. Porewater diffusion in open lake sediments is not a major source. Diffusion of PCBs from porewater is governed by an effective diffusion or mass transfer coefficient and the... 

The general objective, principle, and scope of application of the pT-method are succinctly described in Section 1 and also reported elsewhere in this book (see Chapter 3 of this volume, Section 5.1), where readers will appreciate that this hazard assessment scheme is adaptable to both liquid and solid media. Briefly recalled here in the context of solid-media samples such as dredged material, the pT-value, which relates to a single bioassay, and the pT-index, derived from the most sensitive organism in a test battery, permit a numerical classification of environmental samples on the basis of ecotoxicological principles. Sediment from any aquatic ecosystem (freshwater, brackish, marine) and from any of its phases (whole sediment, porewaters, elutriates or organic extracts) can be appraised provided that the proper standardized toxicity tests are available. There are whole-sediment test protocols standardized for many agencies (e.g., Environment Canada, ASTM). 

Thus far, quality objectives for chemical substances are derived from the most sensitive organisms in acute and chronic toxicity test batteries that determine NOEC values for different trophic levels. The pT-method similarly determines specific sample dilution levels that are devoid of adverse effects toward (micro)organisms of a standardized test battery. Common to both approaches is the more frequent use of water-column test organisms as opposed to benthic-dwelling organism that reflect more intimate contact with sediment. This practice is primarily based on the fact that standardized bioassays capable of appraising sediment porewaters and elutriates are presently more numerous than solid-phase tests for whole-sediment assessment. As more of these latter tests become developed and standardized (see Chapters 12 and 13, volume 1 of this book on amphipod and chironomid tests), their more frequent use will contribute to a better understand of the toxic effects of sediment-bound contaminants. 

As a result, the concept of toxicity classes and management categories linked to dredged-material relocation, as presented in Tables 2 and 3, are presently based on sediment porewater and elutriate testing and may have to be adjusted in the long term. Incorporation of solid-phase tests in routine test batteries should also serve to improve sediment quality guidelines and ensure better protection of aquatic ecosystems. 

Wet sediment phase Solid phase obtained after extracting pore (or interstitial) water from whole sediment. Porewater is commonly extracted by centrifugation (e.g., at 3,000 rpm, 30 min, 15°C). Volume 2(8). 

Dissimilatory Reduction in Surficial Sediments. Porewater profiles from a number of sites throughout Little Rock Lake show that sulfate is always depleted below the sediment-water interface (Figure 3). Sulfate depletion in porewaters occurs not onlyin the soft gyttja but also in sandy, littoral sites with organic contents < 10%. The observed depletion of sulfate and the occurrence of H2S indicate that the sediments are anoxic immediately below the sediment-water interface and that sulfate reduction occurs in surficial sediments. 

A DTNP method for HPLC has recently been reported (34). The sulfur compounds are stable after derivatization and the detection limits are quite low. The major disadvantages are that the derivatized thiols are detected by absorbance, and sediment porewaters and biological samples often contain large numbers of absorbing compounds which interfere with authentic thiols. In addition, sulfide is not detected. 

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