Mercury oceanic background concentration

Mercury is a unique metal. Its oceanic background concentration (Hgx) is very low (< 1 ng/L see also Table 12-1). The risks of rapid changes in speciation, losses and contamination of samples by contact with laboratory air, materials and reagents are high. In contrast to other trace elements, seawater reference materials certified for mercury concentration are not yet available. The quality assurance with regard to accuracy of data is further hampered by the fact that most laboratories, due to the lack of alternative methods, follow almost the same analytical approach. 

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. 

Available information (23, 57) points to an annual river discharge of mercury into the ocean of 2500 to 3000 tons. Based on information from Mercury in Waters of the United States 1970-1971 (58) calculations show that these values might be low. From all the rain which falls on the continents, the amount which evaporates (7 X 10 m ) concentrates its mercury content (assumed to be 0.08 /Ltg/liter), and this excess concentration is expected to equilibrate with alluvium (3 X 10 ° tons). As a result, some of the mercury would remain on land, and only a small fraction would end up in discharge to the ocean. Thus, alluvium containing a background level of 0.07 /Ltg/gram would theoretically end up with ... 

---