Arsenic concentration ocean

The As (arsenic) concentration of seawater is controlled by input of rivers, sedimentation on the seafloor, weathering of the seafloor, exchange between atmosphere and seawater, volcanic gas input, and hydrothermal input. Previous studies on the geochemical cycle of As have not taken into account the hydrothermal flux of As. Therefore, hydrothermal flux of As from back-arc, island arc and midoceanic ridges to ocean is considered below. 

Tables I to III provide a summary of some representative data for total arsenic concentrations in sediments, marine algae, and marine animals. There can be considerable variation in the arsenic levels in these samples, in contrast to the levels in seawater, which are reasonably uniform in the world s oceans at about 0.5-2 /ug/liter (9,10). For sediments, there is perhaps a tendency for arsenic concentrations to be lower in samples from coastal regions and estuaries compared with deep-sea sediments. Industrial discharges of arsenic-enriched effluents can, however, result in arsenic contamination of near-shore sediments...

Table 3.7 lists some arsenic measurements for various marine waters. Arsenic concentrations in seawater are usually 1.1-1.9 pg L-1 with an average of 1.7 pg L-1 (Matschullat, 2000), 305. The typical concentration of arsenic at the surface of open ocean water is about 1.5 pg L-1 and deep waters in at least the Pacific and... 

In contrast to open ocean water, arsenic concentrations in estuary waters often significantly vary with time and location. The arsenic contents of estuary waters and sediments depend on many factors, including... 

Despite its availability and current use, coal is not as widely used today as the other fossil fuels. Coal s major weakness is that it does not burn cleanly. It often contains trace amounts of other elements, including mercury, arsenic, and sulfur, and when it burns, it releases these toxic substances into the air. Over time, coal pollution builds up in the environment. Mercury released during coal combustion, for example, settles in water and builds up in the bodies of fish and shellfish. When these fish and shellfish are eaten by humans and other animals, harmful amounts of mercury can be ingested. In 2008, bluefm tuna served in expensive New York restaurants was found to contain unacceptably high levels of mercury. These fish eat smaller organisms in the ocean, and when these small organisms contain mercury, the toxic element becomes concentrated in the body of the tuna. 

Arsenic in precipitation from unpolluted ocean air averages about 0.019 pg L 1 (Hering and Kneebone, 2002), 157 and terrestrial rainwater concentrations (at least over the USA) also have similar averages of around 0.013-0.032 pgL-1 ((Smedley and Kinniburgh, 2002), 522 Table 3.17). As the precipitation infiltrates into the subsurface, its chemistry changes as it reacts with sediments, soils, and rocks. Therefore, the arsenic chemistry of the groundwater of an area may be very different than its precipitation chemistry. 

The biological cycle of arsenic in the surface ocean involves the uptake of arsenate by plankton, the conversion of arsenate to a number of as yet unidentified organic compounds, and the release of arsenite and methylated species into the seawater. Biological de-methylation of the methylarsenicals and the oxidation of arsenite by as yet unknown mechanisms serve to regenerate arsenate. The concentrations of the arsenic species are then controlled primarily by the relative rates of biologically mediated reactions, superimposed on processes of physical transport and mixing. The... 

The arsenic content in the soil varies from trace amounts to about 40 mg kg. In low concentrations it is present in volcanic gases, on land as well as in the oceans. For this reason, it is always present in negligible amounts in all animal and plant tissues and liquids [6, 7]. In nature it occurs most frequently in the form of sulphides, arsenopyrite being the most commonly occurring mineral containing arsenic. These sulphides usually accompany sulphides of other metals. 

Se(VI), Te(IV) is the stable form as Te(OH)4. There are few data for this element in the ocean, and profiles of tellurium in the eastern North Pacific (Figures 5D and E) show that its concentrations are 1000 times less than those of selenium and both forms of tellurium show strongly scavenged behavior. It is interesting to note that the most abundant form of tellurium is Te(VI), but it is the least thermodynamically stable. Although there are numerous biological reasons to expect reduced species in oxic waters (i.e., as for arsenic and selenium), this observation is somewhat difficult to explain. The elevated concentrations of Te(VI) at the surface, relative to Te(IV), suggest that the atmospheric or riverine inputs of this element are enriched in this form, but virtually no atmospheric data are available to confirm this speculation. 

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