Anthropogenic and naturally-produced organobrominated compounds in bluefin tuna from the Mediterranean Sea

Abstract

Anthropogenic compounds, such as polybrominated diphenyl ethers (PBDEs), together with naturally-produced organobromines, such as methoxylated PBDEs (MeO-PBDEs), polybrominated hexahydroxanthene derivatives (PBHDs), 2,4,6-tribromoanisole (TBA) and a mixed halogenated monoterpene (MHC-1), were measured in muscle from 26 farmed and wild bluefin tuna (Thunnus thynnus) caught in the Mediterranean Sea. This species is ecological attractive because of the changes of geographic habitat throughout its long lifespan which affect its feeding. PBDE concentrations were similar between tuna samples of different groups (17–149 ng g⁻¹ lipid weight – lw in farmed tuna, 25–219 ng g⁻¹ lw in longline fished tuna and 26–126 ng g⁻¹ lw in net-fished tuna). However, higher concentrations of naturally-produced MeO-PBDEs and PBHDs were observed in the two types of wild tuna (longline fished and net-fished) compared to farmed tuna suggesting that wild tunas come easily in contact with sources of these compounds. In all cases PBHDs presented the highest contribution to the sum of organobromines (50% in farmed tuna and >90% in wild tuna). TBA was detected at low concentrations (<6 ng g⁻¹ lw), while MHC-1 was found at higher concentrations (up to 42 ng g⁻¹ lw) in farmed tuna. The estimated daily ingestion of PBDEs from tuna was 830 ng PBDEs day⁻¹, regardless of the origin of the tuna. While this value is approximately 600 times lower than the minimum risk level set by the US Department of Health and Human Services, it is approximately eight times higher than the total intake of PBDEs via diet, suggesting that consumption of tuna can add considerably to the total daily intake of PBDEs.

Introduction

Brominated flame retardants (BRFs), such as polybrominated diphenyl ethers (PBDEs), have been the focus of an increasing number of studies during the last decade because of their potential for bioaccumulation and contamination in the environment and food webs (de Wit, 2002, Alaee et al., 2003, Law et al., 2003) and because of their potential health effects (ATSDR, 2004, Birnbaum and Staskal, 2004). PBDEs are synthetic compounds, commercially available as mixtures with different degree of bromination (Penta-, Octa- and Deca-BDE), used in a variety of products such as plastics, textiles and electrical equipment. In 2004, the Penta- and Octa-BDE mixtures were banned by the European Union (Directive, 2003/11/EC). The Deca-BDE mixture was banned in 2008 (Betts, 2008). Recently (May 2009), the Penta- and Octa-BDE mixtures were added to the Stockholm convention list.

Several structural PBDE analogues, such as the methoxylated PBDEs (MeO-PBDEs), have recently been evidenced in fish and marine mammals (Pettersson et al., 2004, Sinkkonen et al., 2004, Valters et al., 2005, Covaci et al., 2008; Weijs et al., 2009). MeO-PBDEs are naturally-produced in the marine environment by sponges or algae (Vetter et al., 2002, Malmvarn et al., 2005). More than 4000 halogenated naturally-produced compounds have been found in the marine environment (Gribble, 2000), while only a few of them, such as MeO-PBDEs, polybrominated hexahydroxanthene derivatives (PBHDs), 2,4,6-tribromoanisole (TBA) and a mixed halogenated compound (MHC-1), have been measured at high concentrations in marine organisms, including top-predators (Vetter et al., 2001, Vetter et al., 2002, Vetter et al., 2008, Melcher et al., 2005, Hiebl et al., 2006, Melcher et al., 2007). Yet, only a few papers reported on concentrations of PBDEs and MeO-PBDEs in Mediterranean Sea organisms (Pettersson et al., 2004, Corsolini et al., 2008, Covaci et al., 2008).

The present work focuses on bluefin tuna (Thunnus thynnus) from the Mediterranean Sea, an economically and gastronomically relevant species. Tuna populations are variable according to the season, the Mediterranean area being massively populated during warmer seasons (Medina et al., 2002, Sara and Sara, 2007). Remarkably, populations have considerably decreased in the last decades (almost by 80%) most likely due to over-fishing by industrial fisheries (Chase, 2002, Corsolini et al., 2007, Sara and Sara, 2007). The bluefin tuna is a good example of a flexible species, capable of adapting to its environment which changes rapidly due to their temporal migration. Moreover, this species is also suitable for aquaculture. They feed on crustaceans, small fishes and cephalopods in their juveniles stages, and rely on large cephalopods and pelagic fishes as adults (Corsolini et al., 2007, Sara and Sara, 2007). Because of all these confounding factors, these animals may exhibit different bioaccumulation profiles, which make this species interesting from an ecotoxicological point of view.

This paper aims at assessing the presence of anthropogenic and naturally-produced organobrominated compounds in bluefin tuna from the Mediterranean Sea. Differences in concentrations and accumulation profiles of these brominated compounds between wild and farmed tuna were investigated. Moreover, the daily human intake of brominated compounds was estimated from the ingestion of Mediterranean tuna and its contribution to the total diet was evaluated.