Approved Abstracts

Determination of the effects produced by contaminated dredged sediment deposition in soils using cell and tissue level biomarkers in Eisenia fetida earthworms



Author(s): Hereng Y; García-Velasco N; Urionabarrenetxea E; Soto M; Zaldibar B;
Presenter: Manu Soto

Dredging is a common activity in harbors and estuaries consisting on the removal of sediments from the bottom of water masses in order to facilitate marine traffic. The majority of the dredged sediments are discharged into the sea, however, depending on their contamination levels they can be deposited in soils as fertilizer and material for construction, lands rehabilitation or soil filling. Sediments land disposal can lead to changes in the physico-chemical characteristics of the soils, resulting in their degradation and affecting soil living organisms. Thus, the aim of the present work was to assess the impacts of contaminated dredged sediment deployed in soils using Eisenia fetida earthworm. For that, sediments were collected in March 2019 from the Nerbioi-Ibaizabal estuary (Basque Country, Northern Spain), historically subjected to important inputs of pollutants, sampling in two sites with high metal concentrations: Udondo (UDO) and Benedicta (BEN). After air drying the sediments, mixtures of OECD artificial soil with different proportions of sediments from UDO (0.6, 3 and 15%) and BEN (0.8, 4 and 20%) were prepared. Moreover, due to the relatively high salinity present in the sediments, a saline control was also tested. The Earthworm Acute Toxicity Test was performed and a battery of biomarkers at cellular (cell number and cell viability measurements) and tissue levels (histopathological alterations and polysaccharide histochemistry) were measured on E. fetida. Overall, a higher toxicity was observed with increasing proportion of sediment in the mixtures. Higher mortality and severe weight losses were observed in earthworms exposed to soils with the highest contents of UDO and BEN sediments, being sediments from BEN more toxic than UDO under the present experimental conditions. In agreement, histopathological measurements showed significant reductions in the mucopolysaccharids relative area after exposure to saline control and soils with sediments, mainly for the highest proportions. These results indicate a relevant dehydration process in earthworms exposed to sediments that could affect the integrity of the tegument. Moreover, a decrease in the digestive epithelium thickness of earthworms maintained in soils with high sediment content (and in the saline control) was observed. At cellular level, a significant reduction in coelomocytes number and viability was observed in earthworms exposed to the highest concentration of sediments in the mixtures, especially in soils mixed with BEN sediments. Thus, the cellular endpoints measured in coelomocytes demonstrated the capacity to predict impairments caused by polluted sediments at organism levels. Data correlation indicated that among other factors, salinity was directly related with a high weight loss of earthworms and decrease in mucous cells in the integument. It can be concluded that the increasing proportion of contaminated sediments (Nerbioi-Ibaizabal provenance) in soils enhanced toxicity for E. fetida, due to increasing salinity and metal bioavailability and decreasing organic matter content. This work may contribute to render more robust sediment toxicity test for Sediment Quality and Dredged Material Characterization Guidelines. Acknowledgements: This work has been funded by Basque Government (IT1302-19) and the Spanish MINECO (SEAdimenTOX CTM2017-87766-R).

Keywords: sediment; deposition; earthworms

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