Seawater concentration

Thorium has a wide distribution in nature and is present as a tetravalent oxide in a large number of minerals in minor or trace amounts. Thorium is significantly more common in nature than uranium, having an average content in the earth s cmst of approximately 10 ppm. By comparison, Pb is approximately 16 ppm. Thorium has a seawater concentration of <0.5 x 10 . Thorium refined from ores free of uranium would be almost... 

Industrial Wastes. Closely related to seawater concentration is the simultaneous concentration of industrial effluents and recycle of recovered water (see Wastes, industrial). These appHcations are expected to increase as environmental restrictions increase. Examples are the concentration of blowdown from cooling towers in power plants concentration of reverse osmosis blowdown and the processing of metal treatment wastes (11) (see... 

Table 10-9 The major ions of seawater concentration at 35%o, ratio to chlorinity, and molar concentration"...

Uranium has a reasonably constant seawater concentration in both space and time, 1529-6466/00/0052-0012 05.00... 

Metal Seawater concentration (nmol/kg) Blank (nmol) Relative standard deviation at test level (average of 10 analyses %) Recovery (%)... 

The seawater concentration of rhenium is in the range from less than 3 to llng/1, compared to iridium, platinum, and gold, whose concentrations usually do not exceed 0.3 ng/1. 

Dimethyl sulfide is derived primarily from the enzymatic hydrolysis of dimethylsulfoniopropionate(CH3)2S+CH2CH2COO DMSP),an osmoregulatory compound produced by a wide variety of marine phytoplankton [313,317]. Intracellular DMSP hydrolysis has been shown in phytoplankton [318], in macro algae [319], and also in bacteria following uptake of DMSP from seawater [320]. Reported seawater concentrations of dissolved dimethyl sulfide (< 0.1-90 nM) and DMSP (1 -1000 nM) vary with increasing depth, spatially from coastal areas to the open ocean, and also temporally from winter to summer [313-316]. 

Criteria now recommended for protection of various species include the following dietary loadings, in mg/kg FW ration, of <0.05 for human health, <0.05 for livestock, <1 for honey bees, and <5 for poultry seawater concentrations <0.1 pg/L for estuarine crustacean larvae and, for all aquatic life, restricted or prohibited use of diflubenzuron in saltmarsh mosquito breeding areas and on agricultural lands less than 5 km from coastal areas. No criteria are available or proposed for protection of avian and mammalian wildlife against diflubenzuron, probably because of an incomplete toxicological database. 

Residence time and reactivity are strongly correlated through equation (7.2.9). This is true for seawater composition since Whitfield and Turner (1979) showed a rather good correlation between oceanic residence times and seawater-crustal rock partition coefficients which are taken as a measure of element reactivity in the ocean. Actually, a better estimate of reactivity is given by oceanic suspensions, so Li (1982) suggested to use pelagic clay-seawater concentration ratios as a proxy to partition coefficients. 

P is equal to the sulfate concentration C 4 deep in the sedimentary pile. It can be determined by making concentration at z=0 equal to seawater concentration... 

Ellis et al. (2003) reduced Se(Vl) with anaerobic sediment slurries in order to approximate conditions in natural wetlands. Sediments and waters from the northern reach of the San Francisco estuary, the San Luis Drain, and a man-made wetland, all in California, were used. Reduction was apparently carried out by microbes, as autoclaved control experiments exhibited little reduction. Despite differences between the sediments and concentrations of Se(Vl) used in the various experiments, ese(vi)-se(iv) varied little, from 2.6%o to 3.1%o. The starting Se(Vl) concentrations of three experiments ranged from 230 nmol/L to 430 nmol/L that of a fourth experiment was much greater, at 100 pmol/L. Thus, it appears based on these few data that signihcant Se isotope fractionations persist to very low concentrations, though extrapolation to seawater concentrations (e.g., 1 nmol/L) would be risky. 

The only significant 5 Mo variation in these samples is a small offset of 0.15%o seen between Paciflc and Atlantic crusts, just outside the 2a uncertainties of Siebert et al. (2003). A similar offset is seen in nodule data, although well within the analytical uncertainties of Barling et al. (2001). Such offsets seem unlikely to reflect variations in 8 Mo in seawater in view of the long ocean residence time and relatively invariant seawater concentrations of Mo. Systematic differences in sediment composition may play a role (Barling and Anbar 2004). 

Not all chemical reactions proceed at rates fast enough to create significant deviations from NAECs. For example, although N2 gas is consumed by nitrogen-fixing plankton and produced by denitrifying bacteria, these processes are too slow to affect the relatively high seawater concentrations established by equilibration with the atmosphere. 

Evaporite and seasalt cycling effects are not included in this estimate. This was done by subtracting out molar concentrations equivabnt to that of the chloride ion. Increment seawater concentration is rbing over time decrement seawater concentration is declining over time. 

Thus, for an element whose removal from seawater follows first-order reaction kinetics, its MORT is the inverse of its removal rate constant. This relationship predicts that reactive elements should have short residence times. As shown in Figure 21.3, the actual data do demonstrate a linear relationship (r = 0.79, p = 0.00), although a log-log plot is required to cover the several orders of magnitude diversity of MORT and concentrations exhibited by the solutes in seawater. A similar relationship exists between the MORT and the seawater-crustal rock partition coefficient (Ay). The latter is defined as the ratio of the mean seawater concentration of an element to its mean concentration in crustal rocks. Elements with high partitioning coefficients would be expected to have low seawater concentrations. As shown in Figure 21.4, this is seen in the data and... 

Mean seawater concentration versus mean oceanic residence time. Note that this is a iog-iog piot. 

Annual mean surface seawater concentrations of (a) chlorophyll (b) nitrate, (c) phosphate, (d) silicate, and (e) iron. Data from Conkright, M., et al. (2002). World Ocean Atlas 2001 Vol. 4 Nutrients. Vol. NOAA Atlas NESDIS 52. U.S. Government Printing Office. Plots from M. Vichi, et al. (2007). Journal of Marine Systems 64, 110-134. (See companion website for color version.)... 

Enrichment factor (E.F.) The degree to which a marine organism is enriched in a particular chemical with respect to the seawater concentration, e.g., E.E = [metal concentration in biogenic material]/[metal concentration in seawater]. 

The advent of the Loeb-Sourirajan asyimnetric membrane some twenty years ago gave birth to an industry now exceeding 200 million dollars in annual sales. Reverse osmosis (RO) and ultrafiltration (UP) were previously only laboratory curiosities. Today, there are many large membrane plants (up to 16 million gallons per day) in service for applications as diverse as desalinating seawater concentrating serum proteins, or the recovery of paint and other by-products from waste streams. 

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