USE OF DISPERSANTS - U.S. National Response Team (NRT)

Most aquatic organisms have the ability to metabolize and depurate petroleum hydrocarbons. Existing datademonstrate that complete depuration occurs once the source of the contamination is removed. It is unlikely thatsignificant amounts of petroleum hydrocarbons will be accumulated by pelagic organisms during a dispersantapplication because of the short duration and low concentration expected in the water column. Under suchconditions, any accumulated petroleum hydrocarbons should be rapidly eliminated. Marine food chainbiomagnification does not occur because vertebrate predators, including sea turtles and sea birds, readily metabolizeand depurate hydrocarbons from their tissues. Most marine organisms also metabolize and excrete the surfactants indispersants. Metabolism of surfactants is rapid enough that there is little likelihood of food chain transfer frommarine invertebrates and fish to predators (Neff, 1990).Marine finfish, for example, take up petroleum hydrocarbons from water and food. The compounds induce thehepatic Mixed-Function-Oxidase (MFO) system and within a few days following exposure, aromatic hydrocarbonsare oxygenated to polar metabolites and excreted. For this reason, most fish do not accumulate and retain highconcentrations of petroleum hydrocarbons and so are unlikely to transfer them to predators. The fish may be taintedwith metabolites bound to tissue macromolecules, but these metabolites are so reactive that it is unlikely that theywould be released in a toxic form during digestion by the consumer and so would not pose a serious risk (Neff,1990).Pelagic invertebrates become contaminated by assimilating hydrocarbons directly from seawater and by ingesting oildroplets and tainted food. Crustaceans can transform aromatic hydrocarbons to polar metabolites that may beexcreted or bound to tissues. For a few days or weeks, unmetabolized or metabolized hydrocarbons in crustaceansand other invertebrates could be transferred to predators. Considering the low concentrations and short duration ofexposure to dispersed oil, as described earlier, it is unlikely predators would ingest enough oil through consumptionof contaminated aquatic invertebrates to result in adverse affects.Analysis of AlternativesEmergency AuthorizationThe proposed action pre-authorizes the FOSC to use dispersants as a first-stage response technique in specifiedzones as described above. The alternative is to require the FOSC to seek CRRT authorization to use dispersants inthese areas on a case-by-case basis at the time of an oil spill emergency. The limited "window of opportunity" forthe most optimal and effective use of dispersants following an oil spill occurs very early -- usually within the firstfew hours. Without pre-authorization to permit rapid response and mobilization of the necessary equipment, thedelay for case-by-case CRRT approval would realistically eliminate dispersants as a response option. Moreover, inthe absence of pre-authorization, spill response organizations are unlikely to invest in the equipment and trainingnecessary to apply dispersants due to the low probability that authorization would be issued in time to employ thetechnique. Pre-authorization enabling timely use of dispersants under appropriate conditions in the designated zonesprovides greater protection for listed species and critical habitat than does case-by-case authorization at the time of aspill emergency.Mechanical RemovalMechanical containment and removal will remain the preferred response tool for most oil spills, which usually areclose to shore in areas where other response options are unlikely to be approved. Experience has shown, though,that mechanical response often cannot adequately deal with very large spills offshore. Performance of mechanicalmethods can be severely limited by weather and oceanic conditions and by the nature of the oil slick. Booms andskimmers are of limited use even in moderate seas and are usually effective only at slow current (less than 1 knot)and low wave heights (less than 2 meters). Consequently, mechanical recovery rates are often poor. Even undercalm conditions, use of mechanical equipment alone to deal with large spills in which oil rapidly spreads over largeareas may not be feasible. For these reasons, dispersant application is an important complementary spill responsetechnique and should be included along with other techniques as on option in developing the appropriate responsestrategy. Under this regional policy, use of dispersants will be considered when and where physical removal isimpossible or insufficient for protecting natural resources, including listed species.