Risk assessment of nitrate and oxytetracycline addition on coastal ecosystem functions

Unravelling joint cytotoxicity of ibuprofen and oxytetracycline on Chlamydomonas reinhardtii using a programmed cell death-related biomarkers panel

Pharmaceutical active compounds (PhACs) are emerging contaminants that pose a growing concern due to their ubiquitous presence and harmful impact on aquatic ecosystems. Among PhACs, the anti-inflammatory ibuprofen (IBU) and the antibiotic oxytetracycline (OTC) are two of the most used compounds whose presence has been reported in different aquatic environments worldwide. However, there is still scarce information about the cellular and molecular alterations provoked by IBU and OTC on aquatic photosynthetic microorganisms as microalgae, even more if we refer to their potential combined toxicity. To test the cyto- and genotoxicity provoked by IBU, OTC and their binary combination on Chlamydomonas reinhardtii, a flow cytometric panel was performed after 24 h of single and co-exposure to both contaminants. Assayed parameters were cell vitality, metabolic activity, intracellular ROS levels, and other programmed cell death (PCD)-related biomarkers as cytoplasmic and mitochondrial membrane potentials and caspase-like and endonuclease activities. In addition, a nuclear DNA fragmentation analysis by comet assay was carried out. For most of the parameters analysed (vitality, metabolic activity, cytoplasmic and mitochondrial membrane potentials, and DNA fragmentation) the most severe damages were observed in the cultures exposed to the binary mixture (IBU+OTC), showing a joint cyto- and genotoxicity effect. Both PhACs and their mixture caused a remarkable decrease in cell proliferation and metabolic activity and markedly increased intracellular ROS levels, parallel to a noticeable depolarization of cytoplasmic and mitochondrial membranes. Moreover, a strong increase in both caspase and endonuclease activities as well as a PCD-related loss of nuclear DNA integrity was observed in all treatments. Results analysis showed that the PhACs caused cell death on this non-target organism, involving mitochondrial membrane depolarization, enhanced ROS production and activation of PCD process. Thus, PCD should be an applicable toxicological target for unraveling the harmful effects of co-exposure to PhACs in aquatic organisms as microalgae.

Phototransformation of p-arsanilic acid in aqueous media containing nitrogen species

The effects of co-existing nitrogen species in surface water on the phototransformation of organoarsenical p-arsanilic acid (p-ASA) have been investigated using a xenon lamp as a simulated solar light source. Significant enhancements of p-ASA phototransformation efficiency were observed in the presence of nitrate and nitrite, increasing with the concentration of these species and pH, whereas ammonia showed no obvious effect. The products, including inorganic arsenic species and organic derivatives, have been analyzed in order to reveal the phototransformation pathways. In the nitrate and nitrite systems, only small proportions of inorganic arsenic species were generated, with the majority of p-ASA being converted into other organoarsenical derivatives through hydroxylation, nitration, and nitrosation. Phototransformation of p-ASA in collected natural surface water was also observed. This work has implications for the phototransformation of p-ASA in nitrogen-contaminated surface water.

Mid-infrared spectroscopy and multivariate analysis for determination of tetracycline residues in cow's milk

Mid-infrared spectroscopy and chemometric analysis were tested to determine tetracycline's residues in cow's milk. Cow's milk samples (n = 30) were spiked with tetracycline, chlortetracycline, and oxytetracycline in the range of 10-400 µg/l. Chemometric models to quantify each of the tetracycline's residues were developed by applying Partial Components Regression and Partial Least Squares algorithms. The Soft Independent Modeling of Class Analogy model was used to differentiate between pure milk and milk sample with tetracycline residues. The best models for predicting the levels of these antibiotics were obtained using Partial Least Square 1 algorithm (coefficient of determination between 0.997-0.999 and the standard error of calibration from 1.81 to 2.95). The Soft Independent Modeling of Class Analogy model showed well-separated groups allowing classification of milk samples and milk sample with antibiotics. The obtained results demonstrate the great analytical potential of chemometrics coupled with mid-infrared spectroscopy for the prediction of antibiotic in cow's milk at a concentration of microgram per litre (µg/l). This technique can be used to verify the safety of the milk rapidly and reliably.

Rainbow trout (Oncorhynchus mykiss) pro-oxidant and genotoxic responses following acute and chronic exposure to the antibiotic oxytetracycline

Oxytetracycline (OTC), an antibacterial agent, is extensively used in aquaculture practices all over the world, but also in human and veterinary medicines. Because of its intensive use, low rates of absorption by treated animals, inadequate disposal, and low efficiency of removal in wastewater treatment plants, the potential harmful effects on aquatic organisms are of great concern. This work aimed to assess the effects of this antibiotic in rainbow trout, following both acute and chronic exposures. Catalase (CAT), total glutathione peroxidase (GPx), glutathione reductase (GRed) activities and lipid peroxidation (TBARS levels) were quantified as oxidative stress biomarkers, in gills and liver. Genotoxic endpoints, reflecting different types of genetic damage in blood cells, were also determined, by analysis of genetic damage (determination of the genetic damage index, GDI, measured by comet assay) and erythrocytic nuclear abnormalities (ENAs). The obtained results showed a mild pattern of antioxidant response, with modifications in CAT and GPx activities in gills, and lipid peroxidation in liver. These results suggest that despite the occurrence of oxidative effects, a full scenario of oxidative stress is not likely. However, exposure to OTC resulted in the establishment of genotoxic alterations with the induction of DNA strand breaks in blood cells (increase of GDI), and of chromosome breakage and/or segregational abnormalities (increase of ENAs). Considering that the oxidative response was not totally devisable, other mechanisms may be involved in the genotoxic effects reported.

Influence of acidification and eutrophication on physiological functions of Conticribra weissflogii and Prorocentrum donghaiense

Eutrophication and acidification have been the most concerned environmental problems in coastal ecosystem. However, their combined effect on coastal ecosystem function was unknown. Both diatom (Conticribra weissflogii) and dinoflagellate (Prorocentrum donghaiense) are used as coastal algal model. Seven parameters were determined for physiological function assessment, including cell density, chlorophyll a (Chl a), protein, malonaldehyde (MDA), superoxide dismutase, carbonic anhydrase (CA), and nitrate reductase (NR). The influence of nitrate (N) and phosphate (P) on MDA and CA in C. weissflogii was significant, and that on Chl a and protein in P. donghaiense were also significant. However, the influence of acidification on physiological functions was not significant. The effect of acidification could be intensified by coastal eutrophication. More importantly, the coexist influence of acidification and eutrophication on CA, NR and protein in C. weissflogii and MDA in P. donghaiense was significant. Both NR activity and Chl a content in P. donghaiense were positively correlated to N and P concentration when pH were 7.9 and 7.8, respectively. With simultaneous worsening of acidification and eutrophication, the cell growth of P. Donghaiense was accelerated more obviously than C. weissflogii, i.e., dinoflagellate was more adaptable than diatom, thus algal species distribution and abundance could be changed.

Effect of nitrate enrichment and diatoms on the bioavailability of Fe(III) oxyhydroxide colloids in seawater

The photoconversion of colloidal iron oxyhydroxides was a significant source of bioavailable iron in coastal systems. Diatoms dominate phytoplankton communities in coastal and upwelling regions. Diatoms are often exposed to eutrophication. We investigated the effects of different species of diatom, cell density, illumination period, and nitrate additions on the bioavailability of Fe(III) oxy-hydroxide colloids in seawaters. With the increase of illumination period from 1 to 4 h, the ratios of concentrations of total dissolved Fe (DFe) to colloidal iron oxyhydroxides and Fe(II) to DFe increased up to 24.3% and 23.9% for seawater without coastal diatoms, 45.6% and 30.2% for Skeletonema costatum, 44.3% and 29.7% for Thalassiosira weissflogii, respectively. The photochemical activity of coastal diatoms themselves (excluding the dissolved organic matter secreted by algae) on the species transformation of iron in seawater (including the light-induced dissolution of Fe(III) oxyhydroxide colloids and the photo-reduction of Fe(III) into Fe(II)) was confirmed for the first time. There was no significant difference of the ability of S. costatum and Thalassiosira weissflogii on the photoconversion of colloidal iron oxyhydroxides. The photoproduction of dissolved Fe(II) and DFe in the seawater with or without diatoms could be depressed by the nitrate addition.

Effect of excessive CO2 on physiological functions in coastal diatom

Rising dissolution of anthropogenic CO₂ in seawater may directly/indirectly cause ocean acidification and desalination. However, little is known about coastal physiological functions sensitivity to these processes. Here we show some links between ocean acidification/desalination and physiological functions in Thalassiosira weissflogii. Cell density (CD), protein, chlorophyll a (Chl a), malonaldehyde (MDA), superoxide dismutase (SOD), and carbonic anhydrase (CAs) were determined for the assessment of algal biomass, nutritional value, photosynthesis and respiration, lipid peroxidation, antioxidant capacity, and carbon sequestration ability. The influence of pH on the algal Chl a and MDA were extremely significant (P < 0.01). Salinity (S) on cell density and acidity (pH) on protein was significant (0.01 < P < 0.05). Additionally, a significant negative-correlation was observed between cell density and CAs. CAs and SOD had negatively correlations with CD, Chl a, protein, and MDA under pH or S influence, but positive correlation between themselves. Coastal physiological functions were affected by increasing order was acidification < acidification + desalination < desalination for Chl a and protein, desalination < acidification + desalination < acidification for SOD and CAs. Thus, the ongoing excessive CO₂-driven ocean acidification and desalination should be of high attention when assessing the risks of climate change on coastal phytoplankton.

Molecular and Cellular Effects Induced in Mytilus galloprovincialis Treated with Oxytetracycline at Different Temperatures

The present study evaluated the interactive effects of temperature (16°C and 24°C) and a 4-day treatment with the antibiotic oxytetracycline (OTC) at 1 and 100 μg/L on cellular and molecular parameters in the mussel Mytilus galloprovincialis. Lysosomal membrane stability (LMS), a sensitive biomarker of impaired health status in this organism, was assessed in the digestive glands. In addition, oxidative stress markers and the expression of mRNAs encoding proteins involved in antioxidant defense (catalase (cat) and glutathione-S-transferase (gst)) and the heat shock response (hsp90, hsp70, and hsp27) were evaluated in the gills, the target tissue of soluble chemicals. Finally, cAMP levels, which represent an important cell signaling pathway related to oxidative stress and the response to temperature challenges, were also determined in the gills. Exposure to heat stress as well as to OTC rendered a decrease in LMS and an increase in malonedialdehyde accumulation (MDA). CAT activity was not significantly modified, whereas GST activity decreased at 24°C. Cat and gst expression levels were reduced in animals kept at 24°C compared to 16°C in the presence or absence of OTC. At 16°C, treatment with OTC caused a significant increase in cat and gst transcript levels. Hsp27 mRNA was significantly up-regulated at all conditions compared to controls at 16°C. cAMP levels were increased at 24°C independent of the presence of OTC. PCA analysis showed that 37.21% and 25.89% of the total variance was explained by temperature and OTC treatment, respectively. Interestingly, a clear interaction was observed in animals exposed to both stressors increasing LMS and MDA accumulation and reducing hsp27 gene expression regulation. These interactions may suggest a risk for the organisms due to temperature increases in contaminated seawaters.

Effect of coastal eutrophication on heavy metal bioaccumulation and oral bioavailability in the razor clam, Sinonovacula constricta

As traditional seafoods, the razor clams are widely distributed from tropical to temperate areas. Coastal razor clams are often exposed to eutrophication. Heavy metal contamination is critical for seafood safety. However, how eutrophication affects bioaccumulation and oral bioavailability of heavy metals in the razor clams is unknown. After a four-month field experimental cultivation, heavy metals (Fe, Cu, Ni, V, As, and Pb) could be bioaccumulated by the razor clams (Sinonovacula constricta) through exposure to metals present in water and sediments or in the food chain, and then transferred to human via consumption of razor clams. Bionic gastrointestinal digestion and monolayer liposome extraction are used for metal oral bioavailability (OBA) assessment. The influence of eutrophication on OBA is decreased for Fe and Pb and increased for V. A significant positive linear correlation was observed between the bioaccumulation factors of Fe, Ni, V, and As in razor clams and the coastal eutrophication. These results may be due to the effect of eutrophication on metal species transformation in coastal seawater and subcellular distribution in razor clams. The maximum allowable daily intakes of razor clams are controlled by eutrophication status and the concentration of affinity-liposome As in razor clams.