Lead (Pb) profiles in red coral skeletons as high resolution records of pollution in the Mediterranean Sea

Abstract

Lead concentrations in long-lived Corallium species of known age, from the Mediterranean Sea, Atlantic and Pacific Oceans, were determined by laser ablation, inductively coupled plasma mass spectrometer (LA-ICPMS). Lead concentrations in a 2000-year-old sub-fossil Mediterranean C. rubrum are ca 0.09 ± 0.03 µg/g. For the period 1894-1955, lead concentrations in C. rubrum skeletons from the Mediterranean are stable within the range 0.2-0.4 µg/g; concentrations increase to about 1-1.2 µg/g during the period 1960-1978, then decrease progressively to stabilize and reach values in the range 0.2-0.4 µg/g in present-day corals. These variations can be related to the lead gasoline pollution event that (1) started in the early 1950s with the increase of the numbers of cars in the world, and (2) was mitigated by the implementation of new regulations starting in 1975, leading to a return to pre-1950 levels in 2000. In the Pacific, lead concentrations in C. japonicum and C. konojoi are lower than in the Mediterranean C. rubrum, with values close to 0.17 ± 0.03 µg/g. The lowest lead concentrations in present-day samples (0.11 µg/g) are found in C. johnsoni and C. niobe from the Azores islands in the Atlantic, and in a Mediterranean C. rubrum from Montecristo Island, one of the least accessible and most protected areas in the Mediterranean Sea. Using lead concentrations in C. rubrum and in the Mediterranean seawaters, a partition coefficient Kd = [Pb/Ca] calcite / [Pb/Ca] seawater of 13 +/-3 is estimated; it allows calculating past and present lead contents in seawater in which corals grew. Application to Corallium species indicates that values endangering human health or threatening the preservation of aquatic ecosystem on long terms were nearly reached or exceeded in Mediterranean seawaters at the maximum of the lead gasoline pollution event in the 1980s. Measurements in C. rubrum from different places in the Mediterranean indicate that present-day seawater concentrations vary between 2 40 and 200 pmol/kg. As expected, the lowest concentrations come from protected areas insulated from human activities, while the highest come from places close to lead mining or processing sites.

Why do mesophotic coral ecosystems have to be protected?

“…In addition, the offshore location of MCEs may mean that they are subject to less anthropogenic pressure from chronic pollution from coastal cities, physical effects (e.g., marine debris, anchoring, benthic infrastructure), overfishing, and high loads of sediments and turbidity (Abaya et al, 2018;Smith et al, 2019). However, in shallower continental shelves and lagoon atoll MCEs can occur close to the human populations, where they are affected by coastal runoff (e.g., plastics, microplastics and extreme floods; Soares et al, 2019;Zhang et al, 2019), abandoned fishing gears (Ballesteros et al, 2018), chemical contaminants (e.g., polycyclic aromatic hydrocarbons, organochlorine pesticides, and polychlorinated biphenyls [PCBs]; Cai et al, 2016;Jafarabadi et al, 2017Jafarabadi et al, , 2019a, labile dissolved organic carbon (Bednarz et al, 2020), metals (Ricolleau et al, 2019;Schyff et al, 2020), and fishing activities (Rocha et al, 2018;Soares et al, 2019). Furthermore, persistent organic pollutants such as PCBs can have detrimental effects on ecological systems such as MCEs owing to their high toxicity, lipophilic properties, and widespread dispersal in the marine environment (Jafarabadi et al, 2019a(Jafarabadi et al, , 2019b.…”

Identification of Precious Corals (Corallium rubrum vs C. japonicum) Using LA-ICP-MS Analysis

“…Based on unpublished data mentioned in Rajola (2012) and on further analyses of Sciacca red corals, Ricolleau et al (2019) noted that these long-dead C. rubrum corals have slightly lower concentrations of Na, slightly higher concentrations of U and Cu, and much higher concentrations of Mn and Fe than present-day (or recent) samples. We have previously proposed that reducing conditions might have existed in the organic-rich sediments surrounding the dead corals, such that the oxidation states of Mn and Fe changed, allowing these elements to enter the calcitic skeletons (Ricolleau et al 2019).…”

“…Additional specimens of P. elatius and C. japonicum of unknown origin and harvested before 2016 were obtained from a jeweller's private collection. Descriptions of these samples and their localities are provided in Vielzeuf et al (2018) and Ricolleau et al (2019). In addition, three cabochons-one each of C. rubrum, C. japonicum and Sciacca coral (Figure 3) of certified origin, were provided by the Antonino de Simone SRL coral factory in Torre del Greco, Italy.…”

“…In two previous studies by the authors' group, more than 1,000 analyses were performed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) on 36 different samples of C. rubrum, C. japonicum, P. elatius and P. konojoi (Vielzeuf et al 2018;Ricolleau et al 2019). The 2019 article focused on the variation of Pb contents in C. rubrum over several decades.…”

“…The differences in Ba and Pb concentrations in Corallium species from the Pacific Ocean and the Mediterranean Sea can be attributed to the fact that the Mediterranean Sea is a relatively small and closed sea in which concentrations of these elements are higher than in the Pacific Ocean (Lea & Boyle 1991;Ricolleau et al 2019). We carried out a similar statistical analysis on different species of precious corals from the Mediterranean Sea (C. rubrum) and Pacific Ocean (C. japonicum, P. elatius and P. konojoi; see diagram in The Journal's online data depository).…”