The Wharf Roach, Ligia sp., A Novel Indicator of Polycyclic Aromatic Hydrocarbon Contamination in Coastal Areas

We investigated polycyclic aromatic hydrocarbon (PAH) pollution of the intertidal and supratidal zone using the wharf roach (Ligia sp.) as a novel environmental indicator. PAH and alkylated PAH (alkPAH) concentrations in wharf roaches collected from nine sampling sites on the central and northern coast of Japan in November 2011 were analyzed. Total alkPAH concentrations were higher than those of PAHs at all sampling sites. Seven sampling sites had relatively low total concentrations of PAHs and alkPAHs (57.7–130 and 276–770 ng/g-dry, respectively); they included sites in Miyagi Prefecture (St. 5 and 9) that were seriously damaged by the Great East Japan Earthquake and by the following Tsunami on 11 March 2011. Two sampling sites (St. 2: Kominato, Aomori Prefecture; St. 3: Usushiri, Hokkaido) had higher concentrations of total PAHs and alkPAHs (PAHs, 1025 and 591 ng/g-dry, respectively; alkPAHs, 1490 and 1160 ng/g-dry, respectively). Diagnostic ratio calculation showed that St. 2 and 3 had PAHs of pyrolytic origin, possibly from vehicle exhaust gas or industrial fuel combustion, or both. The concentrations of these pollutants in the wharf roach were similar to those in bivalves and therefore likely reflected PAH pollution at the collection sites. The wharf roach may be a suitable candidate indicator of PAH pollution, not only in the intertidal zone inhabited by the currently used bivalve indicators, but also in the supratidal zone.