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Effect of silver (AgNPs) and silica nanoparticles (SiO2NPs) on growth indices and photosynthetic pigments in the microalgae, Nannochloropsis oculata
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Mohammad javad Jami1   , Ali Johari , Mohamad Behzadi tayemeh , Hesamoddin Abaie , Azadeh Salehdoost2 |
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2- Department of Fisheries, Faculty of Marine Sciences and Technologies, Islamic Azad University, North Tehran Branch, Tehran, Iran |
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Abstract: (36 Views) |
Introduction
The advancement of industries and the production of various nanomaterials with different properties, as well as their widespread application in various fields, have led to the unintended introduction of these emerging compounds into aquatic ecosystems. The entry of nanomaterials into aquatic ecosystems has caused negative effects on aquatic organisms, and this issue has become one of the major concerns today (Shi et al., 2020). Silver nanoparticles, due to their antimicrobial properties, have widespread applications in medical antimicrobial products, water purification, and food packaging (Pulit-Prociak and Banach, 2016). Based on conducted studies, silver nanoparticles have varying degrees of toxicity for living organisms in aquatic ecosystems, often being classified as highly toxic substances (Kahru and Dubourguier, 2010; Ivask et al., 2014; Johari, 2014; Sohn et al., 2015; Domingo et al., 2019). Silica nanoparticles also have various industry applications (Murugadoss et al., 2017). Phytoplankton plays an important role at the first trophic level and is a potential indicator of water quality. Because of their small size and high surface-to-volume ratio, they can be significantly affected by pollutants and transfer them to the next level of the food chain (Kelly et al., 2003; Ji et al., 2011; Quigg et al., 2013). The phytoplankton Nannochloropsis oculata is unicellular, small, and non-motile, and it is used as live food for various aquatic organisms in aquaculture (Fulks and Main, 1991; Lubzens et al., 1995). Scientists believe that due to the minimal dimensions of nanomaterials, there is a possibility of their entry, accumulation, and transfer in organisms and food chains of terrestrial and aquatic ecosystems. To accurately understand the effects of these emerging materials on the environment, they should be tested at environmental concentrations as much as possible (Bathi et al., 2022). Therefore, the present study aimed to investigate the toxic effects of different concentrations, close to environmental concentrations, of silver nanoparticles and silica dioxide nanoparticles, as two highly used nanomaterials, on the phytoplankton Nannochloropsis oculata by examining several growth parameters of this organism and measuring the levels of photosynthetic pigments including chlorophyll a, chlorophyll b, total chlorophyll, and total carotenoids.
Methodology
In this study, for the cultivation of N. oculata phytoplankton cells, the Walne culture medium was used, and for lighting, LED lamps were employed with 24-hour illumination. Toxicity tests were conducted based on the OECD standard guideline number 201 and for 72 hours (OECD, 2011). To investigate the toxic effects of different concentrations of the nanomaterials under study, phytoplankton cells were exposed in triplicate to 0.005, 0.01, 0.025, 0.05, 0.075, and 0.1 milligrams per liter of silver nanoparticles or 75, 100, 150, and 200 milligrams per liter of silica dioxide nanoparticles, along with a control group. Sampling of phytoplankton cells in the treated groups and the control group was conducted every 24 hours. In each sampling to determine the biomass of the cells, 100 microliters of the sample were taken each time, and the cell count was performed using a hemocytometer (Neubauer). To measure the photosynthetic pigments, including chlorophylls a and b and carotenoids, 2 milliliters of the samples from different treatments were first centrifuged, and the precipitated cells were stored at -80 degrees Celsius. Next, to extract the pigments, 1.5 milliliters of 96% ethanol were added to the samples. Then, the samples were centrifuged, and their absorbance was measured using a spectrophotometer (SPECORD 210, AnalytikJena, Germany). For data analysis, version 26 of SPSS software and one-way ANOVA were used, and the comparison of means was conducted with 95% confidence using Duncan's statistical test.
Results
The results of the present study showed that the density of N. oculata cells in the control group increased more than 29 times by the end of the 72-hour experimental period, rising from approximately 52 cells per milliliter to over 1500 cells per milliliter. In the groups containing silver nanoparticles at concentrations of 0.005, 0.01, 0.025, 0.05, 0.075, and 0.1 milligrams per liter, the cell density increased approximately 22, 17, 15, 10, 0, and 0 times, respectively, after 72 hours. Also, at concentrations of 75, 100, 150, and 200 mg/L of silica dioxide nanoparticles, cell density increased by 23, 18, 17, and 16 times, respectively, after 72 hours. Based on the results, with the increase in the concentration of silver nanoparticles, the growth rate showed a decreasing trend, such that in the groups containing concentrations of 0.075 and 0.1 mg per liter of silver nanoparticles, the number of cells decreased from 54 to 0, and the average percentage of growth inhibition in these two groups reached 100 percent. On the other hand, in silica dioxide nanoparticles treatments, the gradual decrease was observed, and the growth inhibition percentage at the highest concentration of silica dioxide nanoparticles, namely 200 mg/L, reached 36%. Figure 1 shows the changes in phytoplankton biomass, and Figure 2 shows the changes in the average specific growth rate and the average specific growth inhibition percentage 72 hours after exposure to different concentrations of silver nanoparticles. Figure 3 shows the changes in cell biomass, and Figure 4 shows the changes in the average specific growth rate and the average specific growth inhibition percentage 72 hours after exposure to different concentrations of silica dioxide. The IC50 of silver nanoparticles and silica dioxide nanoparticles for the studied phytoplankton species were estimated to be 0.03 and 5630 mg/L, respectively. The results of measuring the photosynthetic pigments of the phytoplankton N. oculata after 72 hours of exposure to different concentrations of silver nanoparticles are shown in Figure 5. Accordingly, with the increase in the concentration of silver nanoparticles, the levels of chlorophyll a, b, total chlorophyll, and carotenoids decreased, and the lowest levels of photosynthetic pigments were observed in the groups with 0.075 and 0.1 mg per liter of silver nanoparticles. In other words, under the influence of different concentrations of silver nanoparticles, this reduction was significant and reached zero after 72 hours in the groups containing 0.075 and 0.1 mg per liter. Also, as seen in Figure 6, in the groups that were exposed to silica dioxide nanoparticles, the amount of photosynthetic pigments decreased with the increase in the concentration of this nanomaterial.
Discussion and conclusion
The results showed that the exposure of the phytoplankton Nannochloropsis oculata to different concentrations of silver nanoparticles, even at low concentrations, caused toxicity in the phytoplankton and inhibited cell division and biomass increase. The growth rate of phytoplankton in the groups exposed to silver nanoparticles decreased, indicating that the toxicity of silver nanoparticles is dependent on concentration and exposure duration. The mechanism of action of silver nanoparticles on aquatic microorganisms in aquatic ecosystems depends on the solubility of the nanoparticles and the release of silver ions from them into the environment. This mechanism can disrupt the cell division process of phytoplankton, resulting in reduced biomass density and increased growth inhibition percentage during the exposure period (Navarro et al., 2008; Oukarroum et al., 2013; Becaro et al., 2015; González et al., 2015). The study of the effects of silver nanoparticles on photosynthetic pigments showed that the levels of photosynthetic pigments decreased. The results of the study by Li et al. in 2015 on the effects of silver nanoparticles and silver ions on Euglena gracilis indicated that both of these substances, depending on the concentration, disrupt the photosynthesis mechanism and also cause changes in cell morphology. The results showed that the growth and biomass increase of phytoplankton cells exposed to different concentrations of silica dioxide nanoparticles were concentration-dependent, and with increasing concentration up to 200 mg per liter and over time, it caused an increase in the percentage of inhibition of specific growth rate. These changes indicate that the increase in the concentration of silica dioxide nanoparticles can act as a limiting factor, leading to a reduction in the growth rate of this phytoplankton. Overall, the toxicity effect of silica nanoparticles on different phytoplankton varies due to the type and shape of their cell walls and the size of their cell pores, which act as a defensive barrier against the entry of nanoparticles (Book and Backhaus, 2022). Based on the results of this study, both of these nanomaterials have toxic effects on the examined phytoplankton. Considering the higher percentage of inhibition of specific growth rate in the groups exposed to silver nanoparticles compared to the groups exposed to silica dioxide nanoparticles, it can be concluded that silver nanoparticles, at least in the short term, show greater toxicity than silica dioxide nanoparticles in N. oculata.
Conflict of interest
The authors declare that there is no conflict of interest regarding the publication of this paper.
Acknowledgment
This work is based upon research funded by Iran National Science foundation under project No 9031836.
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| Keywords: Nanotechnology, Aquatic nanotoxicology, Microalgae, Acute toxicity, Chlorophyll. |
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Full-Text [PDF 979 kb]
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Type of Study: Research |
Subject:
آلودگي محيطهاي آبي
Received: 2025/01/19 | Accepted: 2025/09/1 | Published: 2025/08/16
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jami M J, Johari A, Behzadi tayemeh M, Abaie H, Salehdoost A. Effect of silver (AgNPs) and silica nanoparticles (SiO2NPs) on growth indices and photosynthetic pigments in the microalgae, Nannochloropsis oculata. isfj 2025; 34 (3) :75-89 URL: http://isfj.ir/article-1-2857-en.html
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