Mercury oceanic

Environmental Concerns. Dyes, because they are intensely colored, present special problems in effluent discharge even a very small amount is noticeable. However, the effect is more aesthetically displeasing rather than ha2ardous, eg, red dyes discharged into rivers and oceans. Of more concern is the discharge of toxic heavy metals such as mercury and chromium. 

Exchange rates of mercury between the atmosphere and the land and between the atmosphere and the ocean are much greater... 

While the natural exchange of mercury between the land and atmosphere and the atmosphere and oceans is balanced, human activity has tipped this balance. There is now about three times more mercury in the atmosphere and fluxes of more than four times to and from the atmosphere. 

The transport rate of mercury flowing from the land to the oceans in rivers has been increased by a factor of about three by human activity. While the increased rate is still relatively less important than the total transport of Hg through the atmosphere, it can represent a significant stress on the exposed organisms, particularly since the increased flux is unevenly distributed. That is, human activity has created local environments where the transport of mercury or its concentration in a river or estuary is many tens of times higher than background levels. 

The average residence times for mercury in the atmosphere, terrestrial soils, oceans, and oceanic sediments are approximately 1 yr, 1000 yr, 3200 yr, and 2.5 x 10 yr, respectively. (See Bergan et al. (1999) for more details on atmospheric residence times.)... 

In a report from the U.S. EPA (1980), fish contained between 10,000 and 100,000 times the concentration of methyl mercury present in ambient water. In a study of methyl mercury in fish from different oceans, higher levels were reported in predators than in nonpredators (see Table 8.2). Taken overall, these data suggest that predators have some four- to eightfold higher levels of methyl mercury than do nonpredators, and it appears that there is marked bioaccumulation with transfer from prey to predator. 

Fitzgerald WF, Mason RP. 1996. The global mercury cycle oceanic and anthropogenic aspects. In Baeyens W, Ebinghaus R, Vasihev O, editors. Global and regional mercury cycles sources, fluxes and mass balances, Dordrecht, the Netherlands Kluwer Academic Publishers, p. 85-108. 

Thompson DR, Furness RW, Walsh PM. 1992. Historical changes in mercury concentrations in the marine ecosystem of the north and northeast Atlantic Ocean as indicated by seabird feathers. J Appl Ecol 29 79-84. 

Rasarnavam or, The ocean of mercury and other metals and minerals, / edited by Praphulla Chandra Ray. .. and Harischandra Kaviratna. Edited by Praphulla Chandra Ray and Hari scandra. Kaviratna. Calcutta Asiatic Society of Bengal, 1908-1910. [4], 4, 17, [1], 436, [4], 84 p. 

White, David Gordon. "The ocean of Mercury an eleventh-century alchemical text." In Religions of India in practice, ed. Donald S. Lopez, 281-287. Princeton (NJ) Princeton Univ P, 1995. 

To help prevent this, the U. S. Public Health Service has recommended a maximum limit of 0.5 ppm mercury in any food. If the fish are to have less than this level of methyl mercury and the concentration factor is 3,000, then the surrounding water in which the fish live should have less than 0.16 ppb (parts per billion). Currently the oceans have about 0.1 ppb, but it is not known whether this is in the form of organic or inorganic compounds.8 It is also not known whether fish can convert inorganic mercury into methyl mercury.8 However, a large number of microorganisms can do this, so possibly its usual form is unimportant. 

Reported mercury values in the oceans determined since 1971 span three orders of magnitude, due at least in part to errors induced by incorrect sampling [62-64]. Olasfsson [65] has attempted to establish reliable data on mercury concentrations obtained in cruises in North Atlantic water. 

Luther et al. [92] have described a procedure for the direct determination of iodide in seawater. By use of a cathodic stripping square-wave voltammetry, it is possible to determine low and sub-nanomolar levels of iodide in seawater, freshwater, and brackish water. Precision is typically 5% (la). The minimum detection limit is 0.1 - 0.2 nM (12 parts per trillion) at 180 sec deposition time. Data obtained on Atlantic Ocean samples show similar trends to previously reported iodine speciation data. This method is more sensitive than previous methods by 1-2 orders of magnitude. Triton X-100 added to the sample enhances the mercury electrode s sensitivity to iodine. 

In many applications, such as the analysis of mercury in open ocean seawater, where the mercury concentrations can be as small as 10 ng/1 [468,472-476], a preconcentration stage is generally necessary. A preliminary concentration step may separate mercury from interfering substances, and the lowered detection limits attained are most desirable when sample quantity is limited. Concentration of mercury prior to measurement has been commonly achieved either by amalgamation on a noble-metal metal [460,467, 469,472], or by dithizone extraction [462,472,475] or extraction with sodium diethyldithiocarbamate [475]. Preconcentration and separation of mercury has also been accomplished using a cold trap at the temperature of liquid nitrogen. 

Fitzgerald et al. [477 ] showed that the most significant quantities of mercury occurred in the waters of the Atlantic Ocean s continental shelf and slope (21 -78 ng/1), compared with open ocean samples (2 -11 ng/1). 

Gill and Fitzgerald [481] determined picomolar quantities of mercury in seawater using stannous chloride reduction and two-stage amalgamation with gas-phase detection. The gas flow system used two gold-coated bead columns (the collection and the analytical columns) to transfer mercury into the gas cell of an atomic absorption spectrometer. By careful control and estimation of the blank, a detection limit of 0.21 pM was achieved using 21 of seawater. The accuracy and precision of this method were checked by comparison with aqueous laboratory and National Bureau of Standards (NBS) reference materials spiked into acidified natural water samples at picomolar levels. Further studies showed that at least 88% of mercury in open ocean and coastal seawater consisted of labile species which could be reduced by stannous chloride under acidic conditions. 

Fitzgerald [53] used a cold trap to concentrate mercury from large volumes of seawater. Using this technique, he could achieve a detection limit of 0.2 ng Hg, and a coefficient of variation of 15% at the 25 ng 1 1 level. Most oceanic samples contained less than 10 ngl-1, but coastal samples could approach 50 ngl-1. 

Mercury point sources and rates of particle scavenging are key factors in atmospheric transport rates to sites of methylation and subsequent entry into the marine food chain (Rolfhus and Fitzgerald 1995). Airborne soot particles transport mercury into the marine environment either as nuclei for raindrop formation or by direct deposition on water (Rawson etal. 1995). In early 1990, both dimethylmercury and monomethylmercury were found in the subthermocline waters of the equatorial Pacific Ocean the formation of these alkylmercury species in the low oxygen zone suggests that Hg2+ is the most likely substrate (Mason and Fitzgerald 1991 Figure 5.1). 

Tunas, Indian Ocean, 1985-86, blood, total mercury vs. methylmercury Yellowfin, Thunnus albacares 0.08 (0.003-0.27) FW vs. 74... 

Mason, R.P andW.F. Fitzgerald. 1991. Mercury speciation in open ocean waters. Water Air Soil Pollut. 56 779-789. 

Monteiro, L.R., R.W. Furness, and AJ. del Novo. 1995. Mercury levels in seabirds from the Azores, midnorth Atlantic Ocean. Arch, Environ. Contam. Toxicol. 28 304-309. 

Nishimura, M., S. Konishi, K. Matsunaga, K. Hata, and T. Kosuga. 1983. Mercury concentration in the ocean. Jour. Oceanogr. Soc. Japan 39 2951-300. 

Mercury is a naturally occurring element. Natural emissions of mercury, e.g. from ore deposits and from volcanic activity, are variously estimated at amounts between 2500 and 5500 tonnes/year and are thus similar in magnitude to anthropogenic emissions, which are currently estimated at some 3600-4100 tonnes/year world-wide. Some 30000 tonnes of mercury are readily available in the environment, i.e. in the atmosphere or in the mixing zone of the oceans, with tens of millions of tonnes in the upper layers of the continental masses and still more in the deep oceans (see Table 2.1). 

Methylmercury, which we referred to in the neurotoxicity section, occurs in fish and shellfish found in both the ocean and fresh water systems. The mercury that is the source of methylmercury arises from power plant emissions and industrial processes. Some even comes from... 

Trace elements are delivered to the ocean by atmospheric, or aeolian, processes in both particulate and soluble forms. Most of the aeolian particles entering the ocean are less than 10 pm in size and are referred to as aerosols. Aeolian transport of particles occurs when winds, such as the Trades, pick up small particles from the land s surface and carry them over the ocean. Some trace elements, such as mercury, have a high enough vapor pressure that they are present as atmospheric gases. Still others are ejected during volcanic eruptions in either particulate or gaseous form. 

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