Polychlorinated biphenyls (PCBs) are man-made chemicals first produced as complex mixtures in 1929 (De Voogt and Brinkman, 1989) and for nearly 50 years they were largely used with a worldwide production estimated at over 1 million metric tons (Breivik et al., 2002; WHO, 1993). The commercial utility of these synthetic halogenated aromatic hydrocarbons (e.g. transformers, capacitors, electrical equipment, hydraulic fluids, etc.) was chiefly based on their high physical and chemical stability, which is also responsible for their toxicity and persistency in the environment. In consequence, in the 1970s and 1980s, many countries restricted their marketing and use, and further in 2001, PCBs were classified as persistent organic pollutants (POPs) under the Stockholm Convention (SC) on POPs. The SC entered into force in 2004 with 90 countries agreeing to ban all production of PCBs (UNEP, 2001), to phase out all uses of these chemicals in equipment by 2025, and to ensure the destruction of remaining PCBs by 2028 (Stockholm Convention, Annex A, Part II (a), (e)). Today there are 182 parties in the SC with some relevant exceptions, including Italy and the United States, that have not ratified the Convention (Stockholm Convention, 2019).
In response to the wide ban on these chemicals, most investigations have depicted an overall slow but steady decrease in PCB environmental concentrations (Bonito et al., 2016; Hammer et al., 2016; Ross et al., 2013). Yet, in recent years some authors have focused their attention on high PCB levels still found in different marine mammal species, raising the question about the effectiveness of the current European and global mitigation efforts within a perspective of complete elimination of these harmful substances (Hens and Hens, 2017; Jepson and Law, 2016; Stuart-Smith and Jepson, 2017).
These carcinogenic and mutagenic substances tend to accumulate in fatty tissues and biomagnify along food webs, with deleterious impacts and a potential role in populations’ decline especially in species at high trophic levels (Hammond et al., 2009; Jepson et al., 2016). Impair reproduction and disruption of the endocrine and immune systems are among some of the toxic effects observed in vertebrates (Jepson et al., 2005; Kannan et al., 2000; Law et al., 2012; Letcher et al., 2010; Safe et al., 1985). PCBs seem to exert a negative impact also on species at lower levels of trophic webs such as fish. Several studies have shown the presence of these contaminants and their toxic effects on different fish species from all over the world (Brar et al., 2010; Henry, 2015; Hontela et al., 1992; Teh et al., 1997). Among those studies, some have also drawn attention on possible negative impacts on human health resulting from the consumption of contaminated fish (Jiang et al., 2005; Mozaffarian and Rimm, 2006; Sidhu, 2003). Human exposure to these harmful substances start in the early stages of life and continues throughout the entire lifespan, potentially leading to adverse health effects such as cancer (Pavuk et al., 2004), birth defects (Wigle et al., 2008) and dysfunctional immune (Kramer et al., 2012) and reproductive systems (Nicolopoulou-Stamati, 2001). This issue acquires a remarkable relevance in regions where fisheries play an important economic role and fish consumption is an integral part of people’s diet, such as the Mediterranean Sea (FAO, 2019).
It is well known that the semi-enclosed Mediterranean Sea is an area particularly susceptible to pollution and it is considered a sink for PCBs and other POPs, probably due to its geographical configuration and location, and the intense anthropogenic pressure to which it is subject (Castro-Jiménez et al., 2013; Marsili et al., 2018). In last years, most researches depicted a slow decrease of PCB levels in different fish species of this area at the same time as other authors reported high levels of these pollutants in some marine mammal populations confirming its role as a marine mammal PCB hotspot (Stuart-Smith and Jepson, 2017). PCBs are still detected in human milk (Çok et al., 2012) and blood (Ulutaş et al., 2015) of Mediterranean human populations, in some cases without a significant decrease in the last few years (Consonni et al., 2012). This picture seems to indicate potential new inputs and/or remobilization of PCBs in the Mediterranean area (Josefsson et al., 2010), which most likely also denotes inefficient mitigation measures and the ineffectiveness of global efforts towards PCB contamination. This is in concert with what is suggested by others authors (Stuart-Smith and Jepson, 2017) who point out the inability of some countries to achieve the 2025 and 2028 targets of the SC at the current rate of mitigation and reduction of PCB environmental levels.
Italian fisheries are among the most important in the whole Mediterranean region with an estimated capture production in 2014–2016 about 185,300 tons (16% of Mediterranean total landings), second only to Turkey (321,800 tons and 32% of Mediterranean total landings) (FAO, 2019). The whole catch composition of the marine Italian fisheries is very heterogeneous, but it is essentially based on two different pelagic species, namely anchovy and sardine (FAO, 2015). These two small pelagic fish species, with high ecological relevance -they transfer energy from lower to upper trophic levels (Costalago et al., 2012) – accounted for 42% (sardine) and 19% (anchovy) of the total landing volume in the central Mediterranean Sea in 2014–2016 (FAO, 2019).
Marine fish and other seafood constitute an important food source for human consumption accounting for about 17% of animal protein consumed by the global population in 2015 (FAO, 2018). Despite the beneficial effects provided by a fish-rich diet (high quality protein, minerals, essential trace elements, fat-soluble vitamins and essential fatty acids), fish consumption is considered one of the most important sources of POP exposure in humans (Pan et al., 2016), far-famed to elicit adverse health effects since early stages of life (Jacobson et al., 1990). In last years, the World Health Organization (WHO) established different toxicological reference values, in order to ensure that people are not exceeding certain body burdens that could adversely affect human health. One of the most often used is the tolerable weekly intake (TWI), recently revised by The Expert Panel on Contaminants in the Food Chain (CONTAM) of the European Food Safety Authority (EFSA). Pointing out how these pollutants remain a serious concern to human health, this panel of experts set a new TWI for dioxins and dioxin-like PCBs in food of 2 pg WHO-TEQ/Kg body weight, seven times lower than the previous TWI (14 WHO-TEQ/Kg body weight) set by the European Commission’s former Scientific Committee on food in 2001 (Knutsen et al., 2018). At European level, where attention has been placed in recent years to the ineffectiveness of the efforts towards the elimination of these pollutants, Commission Regulation (EU) No 1259/2011 established a Maximum Level (ML) of 6.5 pg/g WHO-TEQ (w.w.) for dioxins and dioxin-like PCBs in muscle meat of fish and fishery products and a ML of 75 ng/g (w.w.) for the sum of the six indicator PCB congeners (PCB 28, 52, 101, 138, 153 and 180).
This study aimed to investigate current concentrations of PCBs in three fish species of the Mediterranean Sea (anchovy, sardine and bogue) of great commercial interest in order to: 1) further provide data on PCBs in Mediterranean fish species to help understand whether or not a conspicuous decrease trend for these contaminats still holds, and 2) evaluate the potential health risk derived from PCB human intake through diet.