Effect of polycyclic aromatic hydrocarbons on the pallial fluid buffering capacity of the marine mussel, Mytilus galloprovincialis.

Pallial fluid buffering capacity of the sea mussel Mytilus galloprovincialis was investigated to establish the potential of this biological parameter to serve as a biomarker. Four groups of 15 animals were used in a 72-h toxicity test. Group 1, the aerobic control group, was placed in a filtered aerated natural seawater aquarium. Groups 2-4 were subjected to hypoxic conditions by removal from water after animals were injected with a single dose of the following: group 2 (anaerobic control) was administered 10 microl of UV-treated filtered natural seawater; group 3 (anaerobic solvent control) was injected with 10 microl of acetonitrile and group 4 (PAH exposed group) with 10 microl of 2 mM anthracene. Pallial fluid was taken from all the animals following seawater immersion or air exposure. Pallial fluid from each individual was extracted, adjusted to pH 5.0 and titrated with NaOH until reaching pH 6.0. The buffering capacity index (beta), defined as the amount of mu equivalents of NaOH needed to change in one unit the pH of a 5-ml sample of pallial fluid, was calculated for each group. Values were: for group 1, beta = 3.17 (+/- 0.782); for group 2, beta=15.713 (+/-2.992); group 3 was beta=18.124 (+/-2.288); and group 4 was beta=28.109 (+/-11.398). The statistically significant increase (P<0.05) in group 4 compared with the other groups indicates that the buffering capacity index (beta) is a worthy biological parameter to be further explored as a biomarker for ecotoxicological monitoring programs. The increase in buffering capacity is discussed and a biochemical link between anaerobic metabolism and the exposure to PAH is suggested to explain changes of this biological parameter.