CHAPTER 13 • Mercury in Marine Environments
247
(1988) to be in the range 900-62000 tonnes for the year 1983 with a mean value of
3600 tonnes. Other estimates have been 2000 tonnes yr- I (Bernard 1997) or alternatively to be about 25% of the total input to the atmosphere (WHO/IPCS 1990). Annual
emissions for Europe have been given as 726 tonnes for 1987 (Pacyna 1996) and
463 tonnes for 1990 (Berdowski et al. 1998). It has been pointed out (JernelOv and Ramel
1994) that estimates of the geogenic and anthropogenic inputs of mercury were based
on analyses of mercury in open-ocean water carried out in the 1970S, which were reported to be in the range 10-100 ng rl. These findings suggested that natural sources
were the major contributors to mercury in sea water. However, recent estimations
of total mercury concentrations in uncontaminated open oceans are in the range
0.1-1 ng rl. These revised values lead to the conclusion that the residence time for mercury in open-ocean surface waters is only decades, and therefore mercury fallout is
important for mercury levels in water and biota. It was concluded that anthropogenic
sources account for about 50% of total atmospheric mercury.
Emissions of mercury from coal combustion processes range between 20-50% elemental mercury, HgO, and 50-80% of Hg(II), which is predominantly HgCI2, while
those from waste incinerators contain 75-85% Hg(II) (Carpi 1997).
13.2.3
The Global Mercury Cycle
Hg(II) is particulate and water soluble and is removed from the atmosphere by dry
and wet deposition close to its source. Mercury, as HgO, in the atmosphere, because of
its volatility and low water solubility, follows a cycle characterized by long-range transport, and can thus be considered on the global scale. It can be deposited in remote
locations, and the concentration of mercury has been found to be greater in the recently deposited layers of the Greenland ice cap than in older layers (Weiss et al. 1971),
and has thus been increasing globally (Slemr and Langer 1992; Mason et al. 1994). Part
of the cycle is illustrated in Fig. 13.2, where elemental mercury (Hgo), emitted from
both natural and anthropogenic sources, is removed from the atmosphere by wet deposition after oxidation to water soluble Hg(II), to land and water surfaces after which
mercury can be reduced and returned to the atmosphere. Some HgO may be eventually removed from the atmosphere by dry deposition (Carpi 1997).
Concentrations of mercury in various environmental compartments were estimated
by Lindqvist et al. (1984). Representative values for total dissolved mercury, Hgr are:
open ocean, 0.5-3 ng rl; coastal sea water,2-15 ng rl; rainwater,2-25 ng rl (WHO/IPCS
1990; Lindqvist et al. 1984). Recently, Leermakers et al. (1997), reported that the concentrations of total gaseous mercury, (TGM), over the North Sea were between 0.7 and
2.6 ng m- 3 , and that the range in rainwater was between 5 and 25 ng rl; these results
are of the same order as those estimated by Lindqvist et al. (1984). More recent estimations of Hgr in uncontaminated open oceans are in the range 0.1-1 ng rl Oernelov
and Ramel 1994; Mason et al. 1995)
Mercury may be transformed by aquatic microorganisms into methyl mercury. This
is an important part of the biogeochemical cycle in the consideration of human exposure, since methyl mercury has high lipophilicity and accumulates in the food chain
(D'Itri 1991; Renzoni et al. 1998). Biological methylation by aquatic organisms was reported by Jensen and Jernelov in 1969, when they demonstrated that lake sediments,
247
(1988) to be in the range 900-62000 tonnes for the year 1983 with a mean value of
3600 tonnes. Other estimates have been 2000 tonnes yr- I (Bernard 1997) or alternatively to be about 25% of the total input to the atmosphere (WHO/IPCS 1990). Annual
emissions for Europe have been given as 726 tonnes for 1987 (Pacyna 1996) and
463 tonnes for 1990 (Berdowski et al. 1998). It has been pointed out (JernelOv and Ramel
1994) that estimates of the geogenic and anthropogenic inputs of mercury were based
on analyses of mercury in open-ocean water carried out in the 1970S, which were reported to be in the range 10-100 ng rl. These findings suggested that natural sources
were the major contributors to mercury in sea water. However, recent estimations
of total mercury concentrations in uncontaminated open oceans are in the range
0.1-1 ng rl. These revised values lead to the conclusion that the residence time for mercury in open-ocean surface waters is only decades, and therefore mercury fallout is
important for mercury levels in water and biota. It was concluded that anthropogenic
sources account for about 50% of total atmospheric mercury.
Emissions of mercury from coal combustion processes range between 20-50% elemental mercury, HgO, and 50-80% of Hg(II), which is predominantly HgCI2, while
those from waste incinerators contain 75-85% Hg(II) (Carpi 1997).
13.2.3
The Global Mercury Cycle
Hg(II) is particulate and water soluble and is removed from the atmosphere by dry
and wet deposition close to its source. Mercury, as HgO, in the atmosphere, because of
its volatility and low water solubility, follows a cycle characterized by long-range transport, and can thus be considered on the global scale. It can be deposited in remote
locations, and the concentration of mercury has been found to be greater in the recently deposited layers of the Greenland ice cap than in older layers (Weiss et al. 1971),
and has thus been increasing globally (Slemr and Langer 1992; Mason et al. 1994). Part
of the cycle is illustrated in Fig. 13.2, where elemental mercury (Hgo), emitted from
both natural and anthropogenic sources, is removed from the atmosphere by wet deposition after oxidation to water soluble Hg(II), to land and water surfaces after which
mercury can be reduced and returned to the atmosphere. Some HgO may be eventually removed from the atmosphere by dry deposition (Carpi 1997).
Concentrations of mercury in various environmental compartments were estimated
by Lindqvist et al. (1984). Representative values for total dissolved mercury, Hgr are:
open ocean, 0.5-3 ng rl; coastal sea water,2-15 ng rl; rainwater,2-25 ng rl (WHO/IPCS
1990; Lindqvist et al. 1984). Recently, Leermakers et al. (1997), reported that the concentrations of total gaseous mercury, (TGM), over the North Sea were between 0.7 and
2.6 ng m- 3 , and that the range in rainwater was between 5 and 25 ng rl; these results
are of the same order as those estimated by Lindqvist et al. (1984). More recent estimations of Hgr in uncontaminated open oceans are in the range 0.1-1 ng rl Oernelov
and Ramel 1994; Mason et al. 1995)
Mercury may be transformed by aquatic microorganisms into methyl mercury. This
is an important part of the biogeochemical cycle in the consideration of human exposure, since methyl mercury has high lipophilicity and accumulates in the food chain
(D'Itri 1991; Renzoni et al. 1998). Biological methylation by aquatic organisms was reported by Jensen and Jernelov in 1969, when they demonstrated that lake sediments,