FISHERY BULLETIN: VOL. 73, NO. 3 



ed-weight" basis (lO-^g of w-parafRn hydrocarbon 

 per gram of the sum of the dried residue plus the 

 solvent extractables). 



RESULTS 

 Mortality Studies 



Acute toxicity studies were not intended to be a 

 major portion of this investigation since our 

 paraffin hydrocarbon analysis techniques are used 

 primarily on surviving organisms that have taken 

 up oil pollutants at levels below that detectable by 

 sight or smell. 



The percentage of cumulative mortality 

 (Figures 2 and 3) shows an approximate doubling 

 for mussels exposed to the No. 2 fuel oil compared 

 with the mussels exposed to the No. 5 fuel oil, 

 although the duration of exposure was also greater 

 for the No. 2 fuel oil (46 h vs. 32 h). Both the 

 slick-exposed and the submerged specimens in the 

 No. 5 fuel oil had a slightly higher mortality than 

 the controls, but these differences might not be 

 significant because of the small number of or- 

 ganisms used. The No. 2 fuel oil slick-exposed 

 specimens, however, showed a mortality over 

 twice that of the controls. The submerged 

 specimens had a low initial mortality, but after 2 

 wk mortality had increased to the level of the 

 slick-exposed specimens. 



These mortality data provide a comparison of 

 the two petroleum pollutants and of the test and 

 control groups but were not further utilized to 

 compute median tolerance limits which were 

 beyond the scope and objective of these 

 preliminary qualitative studies. 



Griffith (1970) reported no mortalities in mussels 

 exposed to aged crude oil for four tidal cycles over 

 a total of 120 h. When the same mussels were 

 placed in clean seawater, their rate of recovery 

 was assessed by noting that byssal reattachment 

 required 18 h for 50% of the exposed organisms but 

 less than 12 h for the controls. No observations 

 beyond 120 h (5 days) were reported. 



No. 2 Fuel Oil Studies 



Groups of mussels were collected 1, 7, 14, and 35 

 days after their removal to clean seawater 

 medium. The n-paraffin hydrocarbon patterns for 

 one set are presented as an example (Figure 4). If 

 one assumes that the hydrocarbon pattern of the 

 "controls" represents the natural or biogenic 

 paraffin hydrocarbons and that the pattern of the 

 "test" specimens represents the biogenic plus the 

 pollutant, then by subtracting the former from the 

 latter the resulting "residual" pattern might be 

 expected to depict the pollution hydrocarbon pat- 

 tern of the petroleum product tested. The 

 "residual" paraffin patterns are shown for the No. 

 2 fuel oil bioassay study for mussels sampled 1 and 

 7 days (Figure 5) and 14 and 35 days (Figure 6) 

 after removal from the pollutant. 



The shape of the residual paraffin patterns for 

 all four sampling periods approximates that of the 

 pollutant below ?t-C27H56 and above a residual 

 content level of 0.050 ppm., although individual 

 paraffin hydrocarbons may show variation from 

 the smooth, nearly bell-shaped curve for the No. 2 

 fuel oil. The quantities of uptake and loss of n- 

 paraffin hydrocarbons from the No. 2 fuel oil by the 

 mussels are shown in Figure 7. The uptake after 



50i 



Controls 



— Eiposed - Surface slick 

 — Exposed- Submerged 



Test 

 exposure 



10 15 20 25 



DAYS AFTER REMOVAL 



30 



35 



Figure 2.-Cumulative mortalities of mussels for 35 days 

 following a 48-h exposure to a No. 2 fuel oil. 



50 



40 



30 



Ui 



> 20 



S lOi 



Controls 



Exposed - Surfoce slick 



- Exposed - Submerged 



r 





Test 

 exposure 



10 15 20 25 



DAYS AFTER REMOVAL 



30 



Figure 3.-Cumulative mortalities of mussels for 35 

 following a 32-h exposure to a No. 5 fuel oil. 



35 



days 



510 



