1970; Straughan, 1977; and others). The analysis of the tissues of blue 

 mussels showed extremely high concentrations (up to 3% of fresh weight) 

 of petroleum hydrocarbons to be present the first months after the 

 spill. It is noteworthy that the Tsesis oil was found to be present in 

 mussel tissues in the entire area of Svardsf jarden . Thus the contamina- 

 ted area was much larger than initially assumed, based on visual observa- 

 tions . 



The depuration of oil from contaminated bivalves is a process 

 governed by several factors, such as size of the initial spill, com- 

 position of the oil, the temperature, filtration rates and filtration 

 behavior and physiological state of the animal (Fossato and Canzonier, 

 1976; DiSalvo et al. , 1975; Stegeman, 1974; Stegeman and Teal, 1973). 

 Studies have shown that acutely acquired petroleum is fairly rapidly 

 released (Fossato and Canzonier, 1976; Anderson, 1975; Kanter, 1974; Lee 

 et al., 1972; and others). In contrast, chronically accumulated 

 hydrocarbons are retained for comparatively longer periods of time 

 (Boehm and Qumn, 1978; DiSalvo and Guard, 1975). 



The Tsesis oil was released gradually, although perhaps not com- 

 pletely, from the Mytilus tissues, during the year following the spill. 

 This agrees with observations after the West Falmouth oil spill, that 

 shellfish from the spill area continued to show a fuel oil hydrocarbon 

 pattern for several years (Blumer et al., 1970; Blumer and Sass, 1972; 

 Teal and Farrington, 1976). 



The pattern of depuration of the Tsesis oil from Mytilus indicated 

 a somewhat more rapid release of the aliphatic fraction compared to the 

 aromatic hydrocarbons. This is in general accordance with the findings 

 of Blumer et al. (1970) and Stegeman and Teal (1973). In general, the 

 chemical analysis of oil in blue mussels has proven to be a good measure 

 of the extent of the littoral insult resulting from the Tsesis spill. 



Weathered Tsesis oil sedimented to the bottom in quantity within 

 days after the spill, as shown by sediment trap data. These together 

 with the oil analysis of Macoma balthica from a number of stations, show 

 that the exposed area was much larger than originally suspected, includ- 

 ing areas which were considered clean by visual inspection or biological 

 sampling. The extent of the area where visible slicks were observed is 



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