PAHs, PCBs, PBDEs, and OCPs trapped and remobilized in the Lake of Cavazzo (NE Italy) sediments: Temporal trends, quality, and sources in an area prone to anthropogenic and natural stressors
Introduction
As final sinks of land inputs delivered through rivers and atmospheric transport, aquatic sediments are generally considered archives of historical changes of climate and environmental conditions, as they can provide high-resolution information, from seasonal to multi-decade time-scales (e.g., Frank et al., 2002; Bellucci et al., 2012; Paquette and Gajewski, 2013; Leorri et al., 2014). This is evident when continuous and undisturbed sedimentary conditions are met, highlighting how the effects of extraordinary high-energy processes (such as earthquakes, tsunamis, and landslides) can rework and disturb the sedimentary record, and provide clear signals for the identification of the triggering mechanisms (e.g., Smedile et al., 2011; Polonia et al., 2013, 2021a; Balsamo et al., 2014; Giuliani et al., 2017).
Geochemical analyses performed on sedimentary records are then fundamental for scientific studies that aim at defining changes linked to varying natural and anthropogenic sources. These latter are generally associated to increased contamination by agricultural, industrial, and urban inputs and, in the Western developed world, are constrained in a time window of 100–150 years, encompassing the onset of industrialization/urbanization in the late 19th century, its development after the Second World War, and the first enacting of pollutant control measures in the ‘70s (e.g., Valette-Silver, 1993; Mugnai et al., 2010; Bellucci et al., 2012, 2013; Heim and Schwarzbauer, 2013; Rodgers et al., 2020). A more recent time window characterizes this pattern in Asian and other fast developing countries (e.g., Blaha et al., 2011; Ruiz-Fernández et al., 2012; Giuliani et al., 2015a, 2015b; Zhang et al., 2020), where industrialization and urban development have started later, as well as emerging contaminants (Rosenfeld and Feng, 2011), that made their first appearance or have raised new concerns on their occurrence, fate, adverse effects only in the last decades. Persistent Organic Pollutants (POPs) are among the most effective indicators of these kind of impacts because, depending on their chemical species, their anthropogenic origin can be either exclusive or can be well discriminated from natural one (Dvorska et al., 2008; Fitzgerald and Wikoff, 2014). They include classes of chemicals that persist in the environment and generally concentrate in hydrophobic sedimentary matrices. For this reason, they can transfer to and bioaccumulate through the food web via this pathway, and finally cause adverse effects also to humans (Kodavanti et al., 2014). Human and biota exposure can lead to reproductive disorders, endocrine disruption, genotoxicity, and increased birth defects, among others negative effects (World Health Organization, 2020). Therefore, the resulting biodiversity and environmental service losses can be a serious problem. Anthropogenic Polycyclic Aromatic Hydrocarbons (PAHs) can form as a result of combustion of fossil fuels, coal gasification and liquification processes, petroleum cracking, waste incineration, and spillage of fossil fuels, both unrefined and refined (McCready et al., 2000). On the other side, PAHs can also form naturally through combustion processes (e.g., forest fires) and diagenesis (Wakeham et al., 1980). As for PolyChlorinated Biphenyls (PCBs), man-made mixtures (usually called Aroclors) were used in Europe until the early ‘80s for a wide number of applications, but their current main source is linked to the phasing out of old electrical appliances or to landfills (Rodenburg et al., 2010). PCBs were rarely observed on pre-industrial sediments, but, when detected, their presence was explained with their natural formation from high-temperature combustion processes (Ruiz-Fernández et al., 2012). On the contrary, no natural sources have been clearly identified yet for PolyBrominated Diphenyl Ethers (PBDEs), flame retardants used in a wide selection of products (e.g., construction materials, electronic appliances, furniture, motor vehicles, plastics, and textiles; Romano et al., 2013; Pizzini et al., 2015), but it has been hypothesized that microbial-mediated reactions in anoxic sediments could produce low-brominated PBDEs from naturally synthesized compounds (Piazza et al., 2016). OrganoChlorine Pesticides (OCPs) are a class of chemicals of exclusively anthropogenic origin. They were widely used in agricultural production process and were subject to strong limitations in the last decades (Barr and Buckley, 2011).
Being able to discriminate the different origins of PAHs and POPs can be quite challenging but very important for studies focused on environmental pollution issues that aim at identifying the responsibility of past management choices and/or want to define the best remediation/conservation measures.
The Lake of Cavazzo (NE Italy) is a natural perialpine freshwater basin that has sustained substantial environmental changes in the last decades, principally following the urbanization of the area, and the construction of industrial and transport infrastructures. Indeed, a hydroelectric power plant (from now on referred to as the Somplago power plant) was built in 1953–1958 on the Northern shores of the lake and, since then, has discharged there its drainage waters and sediments (Pironio, 1989). Almost two decades later, in 1980, the 7-year long construction of the A23 highway Somplago viaduct was completed, which has left its mark on the lake catchment area (Pironio, 1989). In the meantime, the lake sustained a major flood of the Tagliamento River in 1966, and a sequence of large magnitude earthquakes in 1976–1977, the strongest events ever recorded in Northern Italy, causing rock falls and landslides in the lake valley (Govi, 1977).
The research presented in this paper has been preceded by a comprehensive study of the shallower lake stratigraphy, based on seismic reflection surveys and a multi-proxy analysis of sediment cores that highlighted major changes occurring in the last century at a decadal time-scale (Polonia et al., 2021a, 2021b). Its results suggested varying environmental conditions after the ‘50s as evidenced by sediment mineralogy, inputs of allochthonous clastic sediments, and recurrence of anoxic conditions at the lake floor. These latter were likely triggered by hyperpycnal flows derived from the Somplago power plant discharges. The effects of the 1976–1977 MW 6.5 seismic sequence have also been identified in core records as resedimented levels due to shaking, in situ deformation, landslides, and turbidity currents.
Results of the present work are then interpreted also in light of these findings and attempt to answer the following questions: 1) How have inputs of PAHs and specific classes of POPs (i.e. PCBs, PBDEs, and OCPs) varied in the Lake of Cavazzo since the ‘50s? 2) Do pollutant levels measured in cores depict a compromised situation of the lake's sediment quality? 3) What are the principal sources of contamination among the different anthropogenic impacts over the area? Are they diffused or local? and 4) How can the depositional dynamic of the lake affect pollutant distribution in response to anthropogenic and natural (mainly earthquakes) stressors? This study has further confirmed the importance of lacustrine sediments as reliable archives of the effects of anthropogenic and natural events, and can provide inspiration for similar studies in other impacted lacustrine areas all over the world.
Section snippets
Study area, impacts, and recent investigations
The Lake of Cavazzo is located at 195 m a.s.l. at the Southern front of the Friuli Venezia Giulia's alpine chain, not far from the national borders with Slovenia and Austria (Fig. 1a). It occupies an area of 1.4 km2 with a length of 2250 m, in a seismically active region within the Eurasia-Adria collision zone, where strong earthquakes have been recorded since medieval times (e.g., Falcucci et al., 2018; Viscolani et al., 2020), with a recurrence of 500–700 years to reload a main coseismic
Core collection and measurements for sediment parameters and chronology
Cores CAV-04 and CAV-06 were collected using a gravity corer with a 6 cm diameter plastic liner, preserving the sediment-water interface, during a first geological/geophysical survey in May 2015 (Gasperini et al., 2015). Core CAV-06 was collected close to the lake depocenter (Fig. 1d), thus potentially providing an archive of lake-scale averaged inputs for pollutants, following the preferential North-South movement of water and sediment masses (Fig. 1c). In juxtaposition, core CAV-04 was
PAHs
Total PAH concentrations in the two cores range from 13.4 to 222 ng g−1 with an average value of 103 ng g−1 (Table 1 and Fig. 2).
In core CAV-04, total concentrations below 29 cm depth do not exceed 60 ng g−1, then increase significantly moving upwards to 184 ng g−1 at 15 cm depth and remain constantly above 100 ng g−1 up to the core top (Fig. 2a). Phenanthrene (Phe) is by far the most abundant compound in all analyzed samples, with a % contribution ranging from 34 to 100% and concentrations
Recorded time frames in cores collected in the Lake of Cavazzo
According to Polonia et al. (2021a), the two analyzed cores have recorded the last 30 years of sediment deposition with different resolutions. For core CAV-04, a reliable average sedimentation rate of 0.35 cm y−1 has been defined in the upper part of Unit A, through the coupling of radiometric dating and laminae counting (Polonia et al., 2021a, 2021b), therefore assigning the first 10–11 cm of the core to materials deposited almost continuously since ‘80s (Fig. 2a). For core CAV-06, radiometric
Conclusions
In response to civil and industrial development, the Lake of Cavazzo (NE Italy) has been subject to human interventions that have interfered with its natural development since the ‘50s. Local population and experts agree in considering the construction and operativity of the Somplago hydroelectric power plant at the lake's Northern shore as the most important anthropogenic impact, together with the contemporary excavation of the artificial outlet channel on its Southern borders. The situation
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This paper is dedicated to the people of Friuli Venezia Giulia, an example of strength and resilience for the world. This is ISMAR-Bologna scientific contribution n. 2067. The authors thank Beatrice Orlando for her work.
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Current affiliation: IRBIM-CNR, Largo Fiera della Pesca 2, I-60125, Ancona, Italy.