Three successive generations of the marine polychaetous annelid Neanthes arenaceodentata taken from a laboratory population, were continuously exposed to one of three sublethal concentrations of No. 2 Fuel Oil water-soluble-fraction (WSFs). During each generation larvae, juvenile, and immature adult polychaetes were challenged with acute (96 hr) doses of No. 2 Fuel Oil or south Louisiana crude oil WSF to test their sensitivity to petroleum hydrocarbons (PHCs). 2. Larvae from all 3 generations, at all exposure concentrations, were no different from control (susceptible) larvae in their sensitivity to the two test oils. F1, F2, and F3 adults exhibited equally increased PHC resistance (X2) compared to control adults. 3. The only evidence of increased resistance beyond that observed in F1 animals was seen in results of bioassays with juvenile worms, wherein PHC resistance increased from slightly below control levels in F1 juveniles to slightly above control tolerance among F3 juveniles. 4. With the exception of F1 worms, removal from chronic exposure 7 or 14 days prior to challenge did not result in termination or reduction of resistance, implicating a genetic mechanism behind PHC resistance in N. arenaceodentata. 5. F3 resistant and unexposed control polychaetes accumulated, metabolized, and excreted a key diaromatic PHC (naphthalene-14C) in quantitatively identical fashion. Mechanisms responsible for resistance appeared unrelated to external permeability and/or excretion rates.
