Heavy metals in blue mussels (Mytilus edulis) in the Bergen Harbor area, western Norway

Heavy metal discharges to the marine environment are of great concern all over the world. Both essential (e.g., Fe, Zn, Cu) and non essential (e.g., Hg, Cd, Pb) metals are toxic to living organisms when subjected to high concentrations (Underwood and Mertz 1987). Many heavy metals accumulate in organisms and some also accumulate in the food chain (Ruiter 1995). The anthropogenic heavy metal outlets can in this way both reduce marine species diversity and ecosystems. Further, by consuming seafood, humans will be exposed to the metals with a potential danger to human health. Goldberg (1975) proposed to use marine mussels to monitor contamination levels of coastal waters. Since then marine mussels, especially the blue mussel (Mytilus edulis), has been used widely as a surveillance organism (Claisse 1989; Cossa 1988). The blue mussel is regarded a suitable species for this purpose because it accumulates metals, is sessile, has a relatively long life span, is large enough for individual analysis, can tolerate a relatively wide range of temperature and salinity regimes (Phillips 1977), and can also synthesize the metal-binding protein, metallothionein, for metal detoxification (Kohler and Riisgard 1982). Furthermore, the blue mussel is a popular and tasteful food source and is suitable for culturing. The world-wide annual yield of mussels during the period 1988 to 1992 was about 1.3 million tons, of which about 0.5 million tons was Mytilus edulis. In Norway, the annual production was 77 tons in 1990 (FAG 1994). The interest of culturing mussels has increased in recent years, but the consumption of mussels has been hampered both by toxic algae and high levels of heavy metals. The latter is of special concern to those close to urban or industrial areas. The Bergen Harbor area (Byfjorden, Western Norway) is highly urbanized and has several industrial plants that discharge waste directly to the fjord. There is also heavy loading of municipal and industrial sewage to this area. It has been estimated that 9 tons of the heavy metals Zn, Cu, Pb, Hg and Cd were discharged from several small outlets to the southern part of Byfjord in 1992 Investigations have revealed that the sediments in the area are loaded with very high metal levels (Skei et al. 1994). Even though the fjord is deep (350 m) it is a rather closed water system with limited water exchange, connected to the coastal water by several narrow sounds. The present study was conducted to investigate whether blue mussels in the Bergen Harbor area were contaminated with the heavy metals Zn, Cu, Pb, Cd and Hg, thereby evaluating whether the mussels could be used for human consumption.