MERCURY CONTAMINATION STANDARDS 251 



to essentially the same degree, while inorganic mercury was concentrated 

 about 4 times less over a 74-day exposure. For organomercury com- 

 pounds, values in mg Hg/kg wet weight were about 10 at 20 days and 30 at 

 60 days (a final concentration factor of about 30,000). For inorganic 

 mercuric chloride, values were about 2 at 20 days and about 10 at 60 days. 



Mercury is also accumulated from seawater by other marine 

 organisms. In radiotracer studies, clams {Tapes decussatus) contained 

 10 times more ^^ ^Hg per unit weight than the medium within 24 hr 

 (Unlu, Heyraud, and Keckes, 1972). Two species of marine alga, 

 Chaetoceros galvestonensis and Phaeodactylum tricornutum, con- 

 tained 7.4 and 2.4 g/kg of mercury, respectively, when cultured in 

 media containing 100 /ig Hg/liter (Chaetoceros) or 50 jug Hg/liter 

 (Phaeodactylum) (Hannan et al., 1973). 



Mercury can also be accumulated through food webs. Bacteria 

 have a demonstrable effect on mercury accumulation in food chains 

 that include filter feeders. Thus whole oyster accumulation of 

 mercury more than doubled in the presence of mercury-resistant 

 strains of Pseudomonas spp. (Colwell and Nelson, 1975; Colwell 

 et al. 1976; Sayler, Nelson, and Colwell, 1975). Sarcophagous flies 

 feeding on mercury-contaminated fish muscle accumulated 3 times 

 more mercury than their food; this was especially pronounced when 

 the fish flesh contained > 0.5 mg Hg/kg wet weight (Nuorteva and 

 Hasanen, 1972). A similar pattern was noted among wild fish feeding 

 on mercury-contaminated fingerlings (Rucker and Amend, 1969). In 

 the food chain algae-detritus— worm— fish (prey)— fish (predator), 

 mercury had a long biological half-life, > 1000 days in predatory fish 

 compared with about 55 days in prey fish (Huckabee and Blaylock, 

 1972). The transfer efficiency of inorganic mercury from prey to 

 predator fish was about 40% but from worm to prey fish, only 12%; 

 worms assimilated 60% of the inorganic mercury contained in the 

 algae-detritus. Huckabee and Blaylock concluded that food-chain 

 uptake can account for a significant percentage of the mercury body 

 burden in fish. In an algae-to-copepod food link, however, the 

 Crustacea showed no impairment of egg laying or egg development 

 and no retention of mercury in tissues, eggs, or feces (Parrish and 

 Carr, 1976). No progressive mercury concentration was observed in a 

 clam-to-eel transfer (Tsuruga, 1963). When dogfish meal containing 

 up to 2.3 mg total Hg/kg, of which 1.9 mg/kg was methyl mercury, 

 replaced low-mercury fish rations used in salmon culture, the flesh of 

 the salmon contained > 0.5 mg/kg within 240 days (Spinelli and 

 Mahnken, 1976). When dogfish meal comprised less than half the 

 diet, however, mercury levels in salmon flesh were < 0.5 mg/kg. 

 Similar results were observed among sablefish fed dogfish meal 

 (Kennedy and Smith, 1972). 



