Baseline Decade-long monitoring reveals a transient distortion of baseline butyltin bioaccumulation pattern in gastropods J.M. Ruiz a, * , J. Díaz b , N. Albaina a , L. Couceiro a , A. Irabien b , R. Barreiro a a Dpto. BA, BV y Ecología, Universidade da Coruña, Alejandro da Sota 1, 15008 Coruña, Spain b Dpto. Ingeniería Química y Química Inorgánica, Universidad de Cantabria, Avda. de los Castros s/n, 39005 Santander, Spain article info Keywords: Biomonitoring Butyltin Gastropods Nassarius reticulatus Nucella lapillus TBT abstract Worldwide measures to restrict tributyltin (TBT) in antifouling paints have been legislated for decades, and were upgraded to a total ban on September 2008. With a view to test the response of coastal biota to changing pollution, since 1996 we have determined the concentration of TBT and derivatives di- and mono-butyltin (DBT and MBT) in NW Spain populations of two gastropods of contrasting biology, the rock-snail Nucella lapillus (n = 18) and the mud-snail Nassarius reticulatus (n = 24). TBT pollution in the study area has decreased consistently and considerably over time. In addition, the baseline butyltin (BT) bioaccumulation patterns showed a marked but transient distortion. These field observations are consistent with BT desorption from sediments, a natural phenomenon that is now to be expected in developing countries recently subject to the global TBT ban. Ó 2010 Elsevier Ltd. All rights reserved. After several decades of research and partial regulations, the International Maritime Organization (IMO) finally prohibited the antifouling paint biocide tributyltin (TBT) in September 2008 (www.imo.org). However, it is feared that the success of this global ban might be reduced because of shipping practices (Wilson, 2008), particularly in developing countries without previous legis- lation. Furthermore, even if the IMO convention was fully effective, the recovery of coastal waters will probably be delayed because of sediments changing from pollution sink to source. Contaminant remobilisation is promoted by disturbance events such as dredg- ing, but it is also a natural phenomenon whereby some of the sed- iment-sorbed pollutants are released back to the water phase by passive diffusion (e.g. Eggleton and Thomas, 2004). For TBT, though, field examples of desorption are scarce (e.g. Langston and Pope, 1995), and its impact on resident biota has gone unde- tected so far. We have determined the concentration of TBT and derivatives di- and mono-butyltin (DBT and MBT) in tissues of biomonitoring gastropods since 1996. At that time national Spanish regulations adapting to the first European Union partial ban on TBT antifou- lants (Directive 1989/677/EC) had little success, and concentra- tions compared with those of UK specimens one decade before (Ruiz et al., 1998). By 2003–2005, as a combined result of previous and total prohibitions convened for 2003 by both IMO and the European Union (Directive 2002/62/EC), contamination had con- siderably decreased (Ruiz et al., 2008). Interestingly, a major change in the butyltin (BT) bioaccumulation pattern was also ob- served, and it was tentatively ascribed to desorption from sedi- ments (Ruiz et al., 2008). We also predicted that, as long as TBT pollution continued decreasing, a return to the original BT patterns in tissues should occur to conform with a generalised ‘‘aging effect” (see Burton et al., 2006). We have therefore conducted two new surveys which results are reported and interpreted below. We have employed two gastropod species traditionally studied for pollution biomonitoring in the Northeast Atlantic coasts: an intertidal rocky shore predator accumulating TBT mostly from water – the rock-snail Nucella lapillus (L.) (Bryan et al., 1989) –, and an infaunal detritivore known to also uptake considerable BTs from sediments – the mud-snail Nassarius reticulatus (L.) (Pope, 1998). The populations sampled are spread over the Galician coast- line (NW Spain), their habitat ranging from the open coast to well inside the main bays and estuaries. Sampling for both snails was not synchronous because of their different reproductive seasons (see below). In addition, since the sediment compartment is less responsive to pollution changes, we decided the surveys for mud-snails should lag some time behind the rock-snail ones. Populations of the rock-snail had been monitored in 1996 and 2003 (see results in Ruiz et al., 1998, 2008, respectively), and they were surveyed again in 2006 for this work. Sampling was con- ducted during the reproductive season (July–September) when the examination of genital characters for concurrent imposex stud- ies is practicable. Full details on the location of intertidal sites, sample selection, and their laboratory treatment have been pub- lished (Ruiz et al., 1998). In the first study (1996) the BT content in female tissues was determined for 20 samples. Unfortunately, 0025-326X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2010.04.005 * Corresponding author. Tel.: +34 981 167000; fax: +34 981 167065. E-mail address: jmruiz@udc.es (J.M. Ruiz). Marine Pollution Bulletin 60 (2010) 931–934 Contents lists available at ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul