Chapter 13
Mercury in Marine Environments
M.E. Farago
13.1
Introduction
Concentrations of elements vary depending on the compartment of the environment
that is under consideration. Thus, although the inputs of elements to the oceans are
very large in absolute terms, the dilution is extremely high, leading to very low concentrations. This situation is generalised in Fig. 13.1. The consequences oflow concentrations in the open oceans are that the possibilities for deficiency are high whereas
those for toxicity are low (Mcgrath 1997). In rivers, wetlands and closed seas, where
the dilution is lower, there can be accumulation of potentially toxic elements. Because
of the low concentrations in open oceans, analytical methods for the determination
of an element and its chemical species must have very low detection limits, and it is
only in recent years that such methods have emerged.
13.2
Mercury in the Environment
13.2.1
Chemical and Physical Properties
Elemental mercury HgO is a heavy silvery liquid at ambient temperatures, with a very
high vapour pressure. There are three oxidation states of mercury: HgO, Hg~+ (mercurous) and Hg2+ (Hg(II), mercuric). There are numerous inorganic and organic compounds, of which methyl-mercury species are important environmentally. The most
important biochemical property of Hg2+ and alkylmercurials is their affinity for sulfhydryl groups (WHO/IPCS 1991).
Lindqvist et al. (1984) have suggested the following classification of environmentally important mercury species:
• Volatile species: HgO, (CH3)zHg (dimethyl mercury, DMHg)
• Water soluble particle-borne reactive species: Hg2+; HgX2' HgX3", HgXl(where X = OH-, cr or Br-); HgO on aerosol particles; Hg2+ complexes with organic
acids
• Non-reactive species: CH3Hg +, CH3HgCl, CH30H (monomethyl-mercury species,
MMHg), and other organomercury compounds; Hg(CN)z; HgS and Hg2+ bound to
sulfur in fragments of humic matter
Mercury in Marine Environments
M.E. Farago
13.1
Introduction
Concentrations of elements vary depending on the compartment of the environment
that is under consideration. Thus, although the inputs of elements to the oceans are
very large in absolute terms, the dilution is extremely high, leading to very low concentrations. This situation is generalised in Fig. 13.1. The consequences oflow concentrations in the open oceans are that the possibilities for deficiency are high whereas
those for toxicity are low (Mcgrath 1997). In rivers, wetlands and closed seas, where
the dilution is lower, there can be accumulation of potentially toxic elements. Because
of the low concentrations in open oceans, analytical methods for the determination
of an element and its chemical species must have very low detection limits, and it is
only in recent years that such methods have emerged.
13.2
Mercury in the Environment
13.2.1
Chemical and Physical Properties
Elemental mercury HgO is a heavy silvery liquid at ambient temperatures, with a very
high vapour pressure. There are three oxidation states of mercury: HgO, Hg~+ (mercurous) and Hg2+ (Hg(II), mercuric). There are numerous inorganic and organic compounds, of which methyl-mercury species are important environmentally. The most
important biochemical property of Hg2+ and alkylmercurials is their affinity for sulfhydryl groups (WHO/IPCS 1991).
Lindqvist et al. (1984) have suggested the following classification of environmentally important mercury species:
• Volatile species: HgO, (CH3)zHg (dimethyl mercury, DMHg)
• Water soluble particle-borne reactive species: Hg2+; HgX2' HgX3", HgXl(where X = OH-, cr or Br-); HgO on aerosol particles; Hg2+ complexes with organic
acids
• Non-reactive species: CH3Hg +, CH3HgCl, CH30H (monomethyl-mercury species,
MMHg), and other organomercury compounds; Hg(CN)z; HgS and Hg2+ bound to
sulfur in fragments of humic matter