Abstract
Increasing input of Metal Engineered Nano Particles (MeENPs) in marine ecosystems has raised concerns about their potential toxicity on phytoplankton. Given the lack of knowledge on MeENPs impact on these important primary producers, the effects of Copper Oxide (CuO) ENPs on growth, physiology, pigment profiles, fatty acid (FA) metabolism, and oxidative stress were investigated in the model diatom Pheodactylum tricornutum, to provide suitable biomarkers of CuO ENP exposure versus its ionic counterpart. Diatom growth was inhibited by CuO ENPs but not Ionic Cu, suggesting CuO ENP cytotoxicity. Pulse Modulated Amplitude (PAM) phenotyping evidenced a decrease in the electron transport energy flux, pointing to a reduction in chemical energy generation following CuO ENPs exposure, as well as an increase in the content of the non-functional Cu-substituted chlorophyll a (CuChl a). A significant decrease in eicosapentaenoic acid (C20:5) associated with a significant rise in thylakoid membranes FAs reflected the activation of counteractive measures to photosynthetic impairment. Significant increase in the omega 6/omega 3 ratio, underline expectable negative repercussions to marine food webs. Increased thiobarbituric acid reactive substances reflected heightened oxidative stress by CuO ENP. Enhanced Glutathione Reductase and Ascorbate Peroxidase activity were also more evident for CuO ENPs than ionic Cu. Overall, observed molecular changes highlighted a battery of possible suitable biomarkers to efficiently determine the harmful effects of CuO ENPs. The results suggest that the occurrence and contamination of these new forms of metal contaminants can impose added stress to the marine diatom community, which could have significant impacts on marine ecosystems, namely through a reduction of the primary productivity, oxygen production and omega 6 production, all essential to sustain heterotrophic marine life.
Highlights
Trace metal pollution poses a serious threat to marine environments
The ionic Cu form was CuSO4, whilst Cu ENPs were purchased as CuO nanoparticles with a particle size less than 50 nm and a surface area of 29 m2 g−1 (Sigma-Aldrich, Catalog number 544868) These concentrations are in accordance with the observed concentrations in estuarine and coastal systems, considering total metal concentration, and were tested in the past, using the ionic Cu form and the same model diatom species (Duarte et al, 2014; Cabrita et al, 2016, 2018)
Exposure of P. tricornutum cells to low (1 μg L−1), medium (5 μg L−1), and high (10 μg L−1) concentrations of Ionic Cu and CuO ENPs during the treatment period resulted in an overall decrease of both biomass and specific growth rate
Summary
Trace metal pollution poses a serious threat to marine environments. Poor management of anthropogenic waste and the accumulation of trace metals in sediments and seawater can lead to detrimental alterations in metabolic pathways of marine organisms, as well as in entire coastal ecosystems (Prosi, 1981; Pan and Wang, 2012). Considering that higher human population densities and associated anthropogenic activities generally occur near estuarine and coastal areas, these regions are among the most immediately affected ecosystems by human-generated waste (UNEP, 2006). New anthropogenic metal forms occur in marine environments as a consequence of increasing use of nanoparticles in a variety of industrial application (UNEP, 2006)
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