Stress biomarkers in juvenile Senegal Sole, Solea senegalensis, exposed to the water-accommodated fraction of the 'Prestige' fuel oil

The "Prestige" oil spill occurred in November 2002 off the Galician Coast (NW Spain). Soon after the black tide episode, that caused an ecological disaster, several monitoring programs and projects evaluating the acute and longterm toxicity of the crude oil were initiated (see monograph Marine Pollution Bulletin 2006; vol. 53). Characteristics of the "Prestige" oil are described in Albaigés and Bayona (2003). Briefly, it consists of 50% polycyclic aromatic hydrocarbons (PAHs), mostly dominated by 2–3 ringed compounds which, contrarily in contrast to the higher molecular weight PAHs, are not reported as very toxic to fish (Seruto et al. 2005). Also, due to the heavy nature of this oil and its low solubility in water, the dispersion in sea water was very low and it mostly remained in situ forming oil patches adhered to rocks and sediment.
Fish, as with all aerobic aquatic organisms, face natural stress conditions when oxygen is not fully reduced, and intermediate reactive oxygen species (ROS) are formed. Enhanced ROS formation can also take place under exposure to some toxicants such as crude oil (Livingstone 2001). In particular, the water-accommodated fraction (WAF) of some crude oils has been responsible for oxidative stress situations in aquatic organisms (Cajaraville et al. 1992). Hence, in order to evaluate if exposure to the WAF of the "Prestige" crude would interfere with the antioxidant defense system of juvenile sole, Solea senegalensis, the activities of indicative enzymes were analyzed. These included: catalase (CAT), total glutathione peroxidase (t-GPX; sum of Selenium dependent and independent forms), glutathione reductase (GR) and DT-diaphorase (DTD), as part of the antioxidant defense system. However, when this natural protective system is saturated, damage to key molecules such as DNA, proteins or lipids can occur. The latter, termed lipid peroxidation (LP), was included in the present study as a biomarker of effect, indicating damage caused by ROS. The enzyme acetylcholinesterase (AChE) regulates nerve impulse transmissions and is used as a marker of exposure to neurotoxic substances (Galloway et al. 2006). Carboxylesterases (CbE) constitute an heterogeneous group of isozymes, dominant in the liver, that play a role in the metabolism and subsequent detoxification of many xenobiotics. In marine fish AChE and CbE are biomarkers used as indicators of neurotoxicity (Lionetto et al. 2004) and enhanced hepatic metabolism (Wheelock et al. 2005). The phase II conjugating enzyme glutathione S-transferase (GST) has also been included in the present work as a measure of the detoxification metabolism.
This study is part of a project aiming to evaluate the toxicity of the water-accommodated fraction (WAF) of the "Prestige" oil in juvenile Solea senegalensis after short-term (24, 48 and 72 h) exposure to environmentally realistic PAHs levels. The choice of this species was based on (1) its high economic interest in the affected region, (2) its benthic nature and, therefore, its adequacy for pollution monitoring programs and (3) its ease to rear under laboratory conditions.