“Integrated biomarker and transcriptomic assessment of the health status of mussels Mytilus galloprovincialis in the Bay of Biscay in relation with legacy contaminants and microplastics”

LANDRO S.M; CAJARAVILLE MP; ARRIGHETTI F

Workshop; 7th Workshop for PhD candidates CTA/ECT 2021; 2021

Analytical measurements of legacy pollutants such as trace metals, PAHs and PCBs are usually combined with biomarkers of contamination at different levels of biological organisation and have been widely used to study the environment health status in the Bay of Biscay. Amongst contaminants of emerging concern, microplastics (MPs) pose a great interest because of their large surface area/volume ratio that facilitates the transfer of chemical additives or hydrophobic waterborne pollutants. However, studies of the presence and/or effect of MPs in wild mussels are still scare in the Bay of Biscay. Thus, the main objectives of the present work are 1) To assess the presence of MPs in soft tissues of mussels as well as to determine the presence of trace metals (Al, Ar, Cd, Cu, Cr, Fe, Ni, Pb, Se, Zn), total PAHs (16) and total PCBs (14) in mussels and sediment; 2) To perform a transcriptomic assessment of different target genes: 2.1. To determine whether the exposure to trace metals produce changes in metallothionein gene transcription levels (MT20), 2.2. To determine whether the exposure to stressors is reflected as alterations in the transcription levels of genes related to oxidative stress (CAT, SOD), biotransformation (GST), peroxisome proliferation (AOX), and heat shock (HSP) in the digestive gland and 2.3. To determine whether the exposure to endocrine disruptors is reflected as changes in vitellogenin gene transcription levels (Vtg) in the gonadal tissue, and 3) To complement the previous objectives with several biomarkers and parameters at different levels of biological organization: 3.1. To determine peroxisome proliferation by measuring changes in the enzymatic activity of AOX, 3.2. To determine the occurrence of DNA damage by analysing the levels of DNA strand breaks through the Comet assay, and the presence of chromosomal DNA damage through the Micronuclei frequency test, 3.3. To study the general stress status of mussels through lysosomal responses (LMS and LSC), cell type composition (VVBAS), morphological alterations of the digestive tubules (MLR/MET), the integrity of the digestive gland tissue (CTD) and histopathologies in the digestive gland and, as well as alterations in gamete development and histological alterations in gonadal tissue, 3.4 To determine fitness-related responses through condition indexes (CI and CIL).Mussels M. galloprovincialis and sediment samples were collected on June 8th from the mid-intertidal rocky shore during low tide in the mouth of the Butroi estuary in Plentzia as the reference site and in the leisure harbour of Arriluze as the polluted site. Briefly, in sediment, total PAH values were higher than the limit of detection (LOD) in both sites (Plentzia 2840.67 ± 836.06, Arriluze 2681.25 ± 960.11; µg/kg), whereas total PCB was higher than the LOD only in Arriluze (40.83 ± 6.77; µg/kg). However, in mussels, total PAHs and PCBs content were under the LOD in both sites. In general, these results are not in accordance with the expected from previous reports but further analyses of individual values of PAH and PCB and/or the used LOD are necessary to understand such differences. On the other hand, as it was expected, the content of all metals in sediment was much higher in Arriluze than in Plentzia. Regarding metal bioaccumulation in mussels, Al, Cd and Pb were higher in Arriluze than in Plentzia while Ar was lower. The metals that exhibited the highest values in both sites were Al, Fe and Zn while Cu, Cr, and Ni were under the LOD in both sites. The Comet Assay revealed that the percentage of tail DNA was higher in Arriluze than in Plenztia (p< 0.05) while the Micronuclei frequency test showed no differences between sites for the micronucleated cells (p> 0.05) but the presence of nuclear buds was higher in Arriluze than in Plentzia (p< 0.05). The higher occurrence of DNA damage in Arriluze may be mainly driven by the presence of metals or other pollutants not measured. Sex ratio was 1F:1M in Plentzia and 1F:3M in Arriluze and not the expected “1:1” ratio, what may indicate an effect endocrine disruption that will be confirmed at the transcriptional level. Finally, both condition indexes of mussels were higher in Arriluze than in Plenztia (p< 0.05), this may be because of higher organic matter levels in Arriluze, which in the end plays a more important key role than pollutants in the growth and physiological status.