Thus, the data of Carls et al., 1997 and Carls et al., 1999 do not support the conclusion that the greater selleck products lethal and sublethal effects of the MWO effluents than the LWO effluents were caused by higher relative aqueous concentrations of HMW parent and alkylated PAH, because the measured concentrations of TPAH and different alkyl PAH congener groups in the toxic MWO doses were actually lower than in LWO doses that were not lethal and produced few sublethal effects. Because the oiled gravel columns were irrigated with unsterilized natural seawater and water flow was stopped for 13 days between the LWO and MWO studies, there was a strong potential for growth of hydrocarbon degrading microbes, resulting

in biodegradation of petroleum hydrocarbon residues on the gravel (Wang et al., 1998) and microbial fouling of the eggs with production of microbial toxins as described by Grothe and Johnson (1996) and Hansen

and Olafsen (1999). The ∼35% decrease (from 21.4 to 7.6 μg/L) in the TPAH concentration in the column effluents between the day 16 LWO-high dose and the day 0 MWO-high dose (Carls et al., 1999), shown in Fig. 1, reflects a substantial loss of hydrocarbons during the 13 days between experiments when the water flow to the columns was stopped. The relative rates of depletion of readily biodegraded n-alkanes and of the less biodegradable branched alkanes, pristane Farnesyltransferase and phytane, expressed PD0332991 as the n-C17/pristane or n-C18/phytane ratio, in the effluent from the oiled gravels are good indicators of microbial degradation of hydrocarbons ( NRC, 1985 and Kennicutt, 1988). These alkanes have extremely low aqueous solubilities, precluding depletion by dissolution from the oiled gravel columns. The n-octadecane (C18)/phytane ratio is the more

reliable indicator of oil biodegradation in marine environments because pristane is synthesized by some marine crustaceans and often is abundant in Arctic and sub-Arctic marine environments ( Blumer et al., 1964). Pritchard et al. (1992) showed that the n-C18/phytane ratio declined rapidly in weathered Exxon Valdez oil in the field in boulder/cobble sediments, even in the absence of added bioremediation fertilizer. The n-C18/phytane ratio in the LWO-high and MWO-high effluents declined rapidly during the respective experiments ( Fig. 2) ( EVOSTC, 2009; Supplementary data), indicating biodegradation of the more easily biodegraded n-C18 ( Wang et al., 1998). An oil-degrading microbial community apparently was established during the first 8 days of the LWO experiment, followed by extensive microbial degradation of oil on the columns during the remainder of the experiment ( Fig. 2), as indicated by the rapid loss of n-C18 between days 8 and 16. The ratio of n-C18/phytane in the high dose LWO and MWO effluents decreased from 0.95 at day 0 to 0.