MERCURY CONTAMINATION STANDARDS 257 



occur in livers of aquatic birds. Higher levels were observed in winter, 

 when birds were exclusively estuarine, and drastically lower levels 

 were observed in summer when birds migrate to inland Arctic and 

 sub-Arctic breeding grounds (Parslow, 1973). 



Diet is an important concentrating mechanism in marine mam- 

 mals. Gray seals and harbor seals, which feed on large fish and 

 cephalopods, contained 10 times more mercury than harp seals, 

 which feed on small pelagic fish and crustacea (Sergeant and 

 Armstrong, 1973). Age and tissue specificity also influence mercury 

 residue levels. Liver from older sea lions contained more mercury per 

 unit weight than that from younger specimens (Anas, 1974; Holden, 

 1975; Jones et al., 1976; Sergeant and Armstrong, 1973). Some adult 

 seals found dead had high levels of mercury in the brain in 

 comparison with levels in various species poisoned by exposure to 

 mercury compounds (Koeman et al., 1973). Mercury and selenium 

 concentration in livers of marine mammals seem to be positively 

 correlated (Koeman et al., 1973; 1975; Martin et al., 1976). Koeman 

 and co-workers (1973) suggested that selenium protects these species 

 against mercury poisoning by completely binding to subcellular S 

 sites, the presumed location of mercury's toxic action. 



Three points are worth emphasizing at this juncture. First, 

 mercury discharged into rivers, bays, or estuaries as metallic mercury, 

 inorganic divalent mercury, phenyl mercury, or alkoxyalkylmercury 

 can all be converted to methyl mercury compounds by natural 

 processes (Jernelov, 1969). Second, organomercury complexes are 

 rapidly accumulated in tissues with high lipid content (Wood, 1973). 

 Finally, mercury -resistant strains of bacteria which have been 

 developed or discovered may have application in mercury mobiliza- 

 tion or fixation from mercury-contaminated waters to the extent 

 that polluted areas become innocuous (Colwell and Nelson, 1975; 

 Nelson et al., 1973; Vosjan and Van der Hoek, 1972). 



Minamata 



Any review of mercury hazards in the marine environment 

 should include the Minamata Bay incident in southwestern Kyushu, 

 Japan. This extensively documented case (Fujiki, 1963; Irukayama, 

 1967; Irukayama et al., 1961; 1962a; 1962b; Kiyoura, 1963; 

 Kurland, Faro, and Siedler, 1960; Matida and Kumada, 1969; Matida 

 etal., 1972; Takevchi, 1972; Tsubaki et al., 1967) reveals effects 

 upon man of chronic discharges of low-level methyl mercury wastes 

 into coastal waters. The source of mercury was waste discharged 

 from an acetaldehyde plant into Minamata Bay beginning in 1952. 



