Abstract
Salinity shifts in estuarine and coastal areas are becoming a topic of concern and are one of the main factors influencing nanoparticles behaviour in the environment. For this reason, the impacts of multi-walled carbon nanotubes (MWCNTs) under different seawater salinity conditions were evaluated on the common ragworm Hediste diversicolor, a polychaete species widely used as bioindicator of estuarine environmental quality. An innovative method to assess the presence of MWCNT aggregates in the sediments was used for the first time. Biomarkers approach was used to evaluate the metabolic capacity, oxidative status and neurotoxicity of polychaetes after long-term exposure. The results revealed an alteration of energy-related responses in contaminated polychaetes under both salinity conditions, resulting in an increase of metabolism and expenditure of their energy reserves (lower glycogen and protein contents). Moreover, a concentration-dependent toxicity (higher lipid peroxidation, lower ratio between reduced and oxidized glutathione and activation of antioxidant defences and biotransformation mechanisms) was observed in H. diversicolor, especially when exposed to low salinity. Additionally, neurotoxicity was observed by inhibition of Cholinesterases activity in organisms exposed to MWCNTs at both salinities.
Highlights
Estuaries and shallow water bodies are among the most vulnerable aquatic ecosystems due to continuous influx of different contaminants commonly associated with agricultural and/or industrial activities[1,2,3,4,5,6]
The null hypotheses tested were: (i) for each biomarker and for each salinity level, no significant differences existed between multiwalled carbon nanotubes (MWCNTs) exposure concentrations or, on the contrary, there is a concentration-dependent toxicity in H. diveriscolor exposed to MWCNTs material under both salinities; (ii) for each biomarker and for each MWCNTs exposure concentration, no significant differences exist between salinity levels or, on the contrary, salinity shifts altered the toxicity of the MWCNTs material as well as the sensitivity of H. diversicolor exposed to this contaminant
dynamic light scattering (DLS) analysis of the samples taken at d7 and d28 did not evidence the presence of particles whose mean dimension was higher than that of the controls indicating the absence of materials deriving from dispersed MWCNTs
Summary
Estuaries and shallow water bodies are among the most vulnerable aquatic ecosystems due to continuous influx of different contaminants commonly associated with agricultural and/or industrial activities[1,2,3,4,5,6] These human activities can cause high environmental threats as these areas are key habitats for many ecologically relevant species including polychaetes[7]. 1776) is one of the most important and abundant species inhabiting intertidal mudflats of estuaries and shallow water bodies of the Atlantic and Indian Oceans[8] as well as the Mediterranean Sea[9], where they play an important ecological role[10,11] and represent an important economic resource[12,13] These omnivorous sediment dwelling organisms are considered key species due to the remobilization of contaminants and nutrients associated to their burrowing and dietary behaviour[14,15,16]. The range of salinity used was selected: (i) according to the environmental salinity range where specimens were collected[50,51] and (ii) the fact that salinity 21 did not have a negative impact on physiological and biochemical responses in H. diversicolor[48,49], which allowed to evaluate the hypothesis that MWCNTs toxicity could depend only on the bioavailability of the CNMs and not on polychates sensitivity to low salinity conditions
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