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We studied the temporal variation of polycyclic aromatic hydrocarbons (PAH) levels in the wild mussel Mytilus galloprovincialis, water and sediment from 3 sampling sites on the Galician coast of Spain between the rias of Arousa and Muros, which were dramatically affected by the large oil spill from the oil tanker 'Prestige'. The samples were collected periodically, from November 22, 2002, 3 d after the tanker sank, until December 23, 2003. The total hydrocarbon content in the water and sediment samples was determined by fluorescence and expressed as concentration of chrysene. In addition, individual PAHs -analytes recommended by the US Environmental Protection Agency -were analysed in the mussel samples by HPLC using fluorimetric detection. A maximum concentration of 2.07 × 10 3 µg equiv. of chrysene l -1 was found in the water column at the sampling site of Furnas on November 29, 2002 which decreased to 0.21 µg l -1 by October 2003. Likewise, the concentrations of the sum of the 16 PAHs determined in the mussel samples collected at the sampling points were between 2.5 × 10 3 and 5.9 × 10 3 µg kg -1 dry weight in the days immediately following the oil spill and then decreased to 0.13 × 10 3 µg kg -1 in October 2003. However, no relevant information could be obtained from the PAH content of the sediment samples. A relation between parent PAHs accumulated in the mussels and their molecular weight (MW) has been found to provide an indication of hydrocarbon pollution. A good approximation was obtained when the total PAH content (ΣPAH) was represented versus the ratio of low MW PAHs to high MW PAHs (ΣLPAH:ΣHPAH). When the depuration rate r of individual PAHs by the mussels was fitted to an exponential model, 2 different values of r were found depending on the PAH concentration. The change from a slow to fast depuration rate was produced when the logarithm of the concentration was 1.0. KEY WORDS: 'Prestige' oil spill · PAH analysis · Mytilus · Mussels · Temporal variation Resale or republication not permitted without written consent of the publisher

In this study we present the early monitoring of the pollution caused by the accident of the Prestige tanker off the Galician coast. To evaluate the toxicity of sediment and water exposed to fuel, three kinds of bioassays were carried out using juvenile clams, clam embryos and microalgae. Firstly, the burrowing behaviour of Venerupis pullastra and Tappes decussatus in the sediment collected from two beaches of similar characteristics but different pollution conditions, was studied over 24 h. No significant differences were observed between the two sediments. Secondly, embryogenesis success of Venerupis rhomboideus was recorded after incubation in seawater and elutriates obtained from affected areas. In this case, fuel-polluted seawater showed a marked inhibition of embryogenesis, while sediment elutriates showed moderate toxicity. Parallel bioassays with the diatom Skeletonema costatum were carried out using sediment elutriates and filtered seawater from the sampling sites. The response variable measured was the maximum quantum yield of photosynthesis (Φpo) using a Fast Repetition Rate Fluorometer (FRRF). In the first sampling, significant differences were found in the response of S. costatum cultured in the elutriates as compared to the control after 5 h exposure. The results corresponding to the second sampling showed statistically significant lower values of Φpo in the culture incubated in M2 water as compared with the control, indicating that the water-accommodated fraction of fuel at this site was the most toxic.

An evaluation of the toxicity of seawater and sand sampled from an area of the Galician coast (NW Iberian Peninsula), highly impacted by the Prestige fuel-oil spill, was attempted by using marine invertebrate embryogenesis bioassays with bivalves and sea urchins. Water samples were frozen and toxicity testing was delayed until the reproductive season of the sea urchins. Sand samples were elutriated and tested within 13 d from sampling, using bivalves from commercial stocks. Sand elutriates were non toxic for embryos despite visual presence of small tar balls. In contrast, seawater from the most impacted site was highly toxic during the first days after the spill, with complete inhibition of embryogenesis even after 4-fold dilution. In a lower degree toxicity persisted for two months in light-exposed coastal water. These findings stress the impact to water column organisms of the less conspicuous and frequently overlooked water-accommodated fraction, rather than the more visible oil slick.

Introducción Los bioensayos con estadios embrionarios y larvarios de invertebrados marinos han sido frecuentemente utilizados para evaluar la calidad ambiental de muestras de sedimentos (Carr 1996;