Published: June 14, 2011 r2011 American Chemical Society 6160 dx.doi.org/10.1021/es201234a | Environ. Sci. Technol. 2011, 45, 6160–6166 ARTICLE pubs.acs.org/est Alkylnaphthalenes: Priority Pollutants or Minor Contributors to the Poor Health of Marine Mussels? Alan G. Scarlett, † Robert Clough, † Charles West, † C. Anthony Lewis, † Andrew M. Booth, † and Steven J. Rowland* ,† † Petroleum & Environmental Geochemistry Group, Biogeochemistry Research Centre, University of Plymouth, Plymouth PL4 8AA, Devon, U.K. b S Supporting Information ’ INTRODUCTION Although oil spills from ships are in decline, pipeline bursts and sporadic blowouts continue to pose an environmental risk, as evidenced by the Deep Horizon Macondo well spill in the Gulf of Mexico in 2010. 1 Even in the absence of accidents, produced waters from both onshore and offshore oil operations provide a significant source of hydrocarbon contaminants in the environment. 2 Monitoring of hydrocarbons has largely been focused on the USEPA priority pollutant list of 16 polycyclic aromatic hydrocarbons (PAH), even though within crude oils, alkyl derivatives are much more prevalent than the parent compounds and environmental risk can be underestimated. 3 Due to the increasing hydrophobicity with alkyl carbon number, the relative contribution toward toxic effects is potentially greatly increased. For example, it was reported that C 4 isomers could contribute over 50 higher toxic units than the same concentra- tion of naphthalene in sediment pore water. 4 Naphthalene is the lowest molecular weight compound in the USEPA PAH list and due to its high volatility tends to be more rapidly lost when oil is spilled on the surface into aquatic and marine systems. However alkylnaphthalenes (AN) are less volatile and more commonly detected, and both naphthalene and AN may better survive unde- rwater discharges such as that in the Gulf spill. 1 AN are certainly major components of the water accommodated-fractions of crude oils. 5 Measured and estimated properties of selected AN are provided in Table 1. Studies by comprehensive gas chromatography  gas chro- matography  time-of-flight mass spectrometry (GC  GC- ToF-MS) of ‘unresolved’ complex mixtures (UCM) of aromatic hydrocarbons accumulated in health-impacted mussels collected from around the UK coastline revealed the presence of many isomers of branched alkylbenzenes (BABs), branched alkylin- danes (BINs), and branched alkyl tetralins (BATs). 6,7 Labora- tory studies of a commercial mixture of BABs and of synthetic BINs and BATs suggested that large numbers of isomers of such compounds were toxic to mussels. 68 Mussels are regarded as sentinel species that act as indicators for the general health of ecosystems throughout the world. 9 Beds of health-impacted mussels with large accumulations of UCM hydrocarbons have been shown to contain communities with lower species diversity. 10 Mussels are also important sources of food for many animals including humans and hence are of considerable com- mercial importance. Also detected in UK coastline mussels Received: April 12, 2011 Accepted: June 14, 2011 Revised: June 10, 2011 ABSTRACT: Alkylnaphthalenes (AN) are relatively water-soluble hydrocar- bons which, following spillages of crude oils, have been widely reported in contaminated marine organisms such as mussels. In the present report we show, by tandem-gas chromatography-time-of-flight-mass spectrometry (GC  GC- ToF-MS), that the range of AN in contaminated wild mussels from the UK extends beyond the previously GC resolved isomers to those with at least seven substituent carbon atoms. Since surprisingly little information on AN toxicity to such marine organisms has been reported we synthesized two C 8 AN and measured the toxicity of C 28 AN to mussels (clearance rate assay). C 23 AN were appreciably toxic (concentration for 50% clearance rate inhibition, 48 h IC 50 1.42.6 μmol g 1 dry weight tissue), but several C 4 , 6 and C 8 AN, including branched isomers expected to be resistant to biodegradation and more accumu- lative, were relatively nontoxic (48 h IC 50 > 10 μmol g 1 ) and longer term exposure (8 d) failed to elicit a greater toxic response. The accumulation profiles of AN in laboratory mussels exposed to oil were similar to those of the wild mussels. Moreover, laboratory oil-exposed mussels depurated toxic C 23 AN within 5 days in clean water and clearance rates recovered. The latter might imply that, in contrast with branched alkyl benzenes tested previously, AN are of less toxic concern, but such a straightforward conclusion cannot necessarily be drawn; a synthetic branched C 8 AN persisted following depuration and was as toxic to mussels as a C 3 AN (IC 50 1.3 μmol g 1 ). This indicates that the structures of AN are also important.