Oxidative stress responses in two marine diatoms during sulfamethoxazole exposure and the toxicological evaluation using the IBRv2 index.

Sulfamethoxazole (SMX) is widely present in water systems, and its stable properties and poor biodegradability can result in high residues of SMX in the water environment. This, in turn, can have detrimental effects on the entire aquatic habitat and human life and health. This study aimed to investigate the toxic effects of SMX on the growth, photosynthetic pigment content, and oxidative stress of two marine microalgae species: Skeletonema costatum and Phaeodactylum tricornutum. SMX demonstrated a significant inhibitory effect on microalgae proliferation, with 96-h median effective concentration (EC50) values of 0.93 mg/L and 4.65 mg/L for S. costatum and P. tricornutum, respectively. At low concentrations, SMX significantly increased the production of Chl a in both microalgae species. However, in the higher concentration SMX treatment group, Chl a content in P. tricornutum experienced a significant decrease, whereas Chl c showed no sensitivity to SMX. The activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), along with the glutathione (GSH) content, exhibited a significant increasing trend in response to higher SMX concentrations. However, these changes effectively inhibited the accumulation of malondialdehyde (MDA) content. In the treatment group with the highest SMX concentration, MDA content in both microalgae species was significantly higher compared to the control group. The Integrated Biomarker Response Version 2 (IBRv2) index showed a significant positive correlation with SMX concentration, suggesting its potential for assessing the ecotoxicological effects of lower SMX concentrations on marine microalgae.

Effect of the molecular weight of DOM on the indirect photodegradation of fluoroquinolone antibiotics.

Dissolved organic matter (DOM) is ubiquitous and widespread in natural water and influences the transformation and removal of antibiotics. Nevertheless, the influence of DOM molecular weight (MW) on the indirect photodegradation of antibiotics has rarely been reported. This study attempted to explore the influence of the molecular weight of DOM on the indirect photodegradation of two fluoroquinolone antibiotics (FQs), ofloxacin (OFL) and norfloxacin (NOR), by using UV-vis absorption and fluorescence spectroscopy. The results showed that indirect photodegradation was considered the main photodegradation pathway of FQs in DOM fractions. Triplet-state excited organic matter (3DOM*) and singlet oxygen (1O2) were the main reactive intermediates (RIs) that affected the indirect photodegradation of FQs. The indirect photodegradation rate of FQs was significantly promoted in DOM fractions, especially in the low molecular weight DOM fractions (L-MW DOM, MW < 10 kDa). The results of excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC) showed that terrestrial humic-like substances had a higher humification degree and fluorophore content in L- MW DOM fractions, which could produce more 3DOM* and 1O2 to promote the indirect photodegradation of FQs. This study provided new insight into the effects of DOM at the molecular weight level on the indirect photodegradation of antibiotics in natural water.

Elemental sulfur-driven autotrophic denitrification process for effective removal of nitrate in mariculture wastewater: Performance, kinetics and microbial community.

To date, there is a lack of systematic investigation on the elemental sulfur-driven autotrophic denitrification (SDAD) process for removing nitrate (NO3--N) from mariculture wastewater deficient in organic carbon sources. Therefore, a packed-bed reactor was established and continuously operated for 230 days to investigate the operation performance, kinetic characteristics and microbial community of SDAD biofilm process. Results indicate that the NO3--N removal efficiencies and rates varied with the operational conditions including HRT (1-4 h), influent concentrations of NO3--N (25-100 mg L-1) and DO (0.2-7.0 mg L-1), and temperature (10oC-30 °C), in the ranges of 51.4%-98.6% and 0.054-0.546 g L-1 d-1, respectively. Limestone could partially neutralize the produced acidity. Small portions of NO3--N were converted to nitrite (<4.5%) and ammonia (<2.8%) in the reactor. Operational conditions also influenced the production of acidity, nitrite and ammonia as well as sulfate. Shortening HRT and increasing influent NO3--N concentration turned the optimal fitting model depicting the NO3--N removal along the reactor from half-order to zero-order. Furthermore, the NO3--N removal was accelerated by a higher temperature and influent NO3--N concentration and a lower HRT and influent DO concentration. Microbial richness, evenness and diversity gradually decreased during the autotrophic denitrifier enrichment cultivation and the reactor start-up and operation. Sulfurimonas constituted the predominate genus and the primary functional bacteria in the reactor. This study highlights the SDAD as a promising way to control the coastal eutrophication associated with mariculture wastewater discharge.

The characteristics of CDOM structural composition and the effect on indirect photodegradation of sulfamerazine.

Sulfamerazine (SM) is a commonly used antibiotic and have been widely used to control various bacterial infectious diseases. The structural composition of colored dissolved organic matter (CDOM) is known to be a major factor that influences the indirect photodegradation of SM, yet the influence mechanism remains unknown. In order to understand this mechanism, CDOM from different sources was fractionated using ultrafiltration and XAD resin, and characterized using UV-vis absorption and fluorescence spectroscopy. The indirect photodegradation of SM in these CDOM fractions was then investigated. Humic acid (JKHA) and Suwannee River natural organic matter (SRNOM) were used in this study. The results showed that CDOM could be divided into four components (three humic-like components and one protein-like component), and terrestrial humic-like components C1 and C2 were found to be the main components that promote SM indirect photodegradation due to their high aromaticity. The indirect photodegradation of SM was much faster in low molecular weight (MW) solutions, whose structures were dominated by greater aromaticity and terrestrial fluorophores in JKHA and higher terrestrial fluorophores in SRNOM. The HIA and HIB fractions of SRNOM contained large aromaticity and high fluorescence intensities of C1 and C2, resulting in a greater indirect photodegradation rate of SM. The HOA and HIB fractions of JKHA had abundant terrestrial humic-like components and contributed more to SM indirect photodegradation.

Organic carbon release, denitrification performance and microbial community of solid-phase denitrification reactors using the blends of agricultural wastes and artificial polymers for the treatment of mariculture wastewater.

This paper explored the possibility of heterotrophic denitrification driven by composite solid carbon sources in low carbon/nitrogen ratio marine recirculating aquaculture wastewater. In this study, two agricultural wastes, reed straw (RS), corn cob (CC) and two artificial polymers, polycaprolactone (PCL), poly3-hydroxybutyrate-hydroxypropionate (PHBV) were mixed in a 1:1 ratio to compare the carbon release characteristics of the four composite carbon sources (RS+PCL, RS+PHBV, CC+PCL, and CC+PHBV) and their effects on improving the mariculture wastewater for denitrification. Dissolved organic carbon (DOC) after carbon source release (4.96-1.07 mg/g), total organic carbon/chemical oxygen demand (1.9-0.79) and short-chain fatty acids (SCFAs) (4.23-0.21 mg/g) showed that all the four composite solid carbon sources had excellent organic carbon release ability, and the CC+PCL group had the highest release of DOC and SCFAs. Energy-dispersive X-ray spectroscopy, scanning electron microscopy, and Fourier-transform infrared spectroscopy were used to observe the changes in the surface characteristics of the composite carbon source before and after application. And results showed that the stable internal structure enabled CC+PCL group to have continuous carbon release performance and achieved the maximum denitrification efficiency (93.32 %). The NRE results were supported by the abundance of the Proteobacteria microbial community at the phylum level and Marinobacter at the genus level. Quantitative real-time PCR (q-PCR) indicated CC-containing composite carbon source groups have good nitrate reduction ability, while PCL-containing composite carbon source groups have better nitrite reduction level. In conclusion, the carbon source for agricultural wastes and artificial polymers can be used as an economic and effective solid carbon source for denitrification and treatment of marine recirculating aquaculture wastewater.

Comparative investigation on heterotrophic denitrification driven by different biodegradable polymers for nitrate removal in mariculture wastewater: Organic carbon release, denitrification performance, and microbial community.

Heterotrophic denitrification is widely studied to purify freshwater wastewater, but its application to seawater wastewater is rarely reported. In this study, two types of agricultural wastes and two types of synthetic polymers were selected as solid carbon sources in denitrification process to explore their effects on the purification capacity of low-C/N marine recirculating aquaculture wastewater (NO3 --N 30 mg/L, salinity 32‰). The surface properties of reed straw (RS), corn cob (CC), polycaprolactone (PCL) and poly3-hydroxybutyrate-hydroxypropionate (PHBV) were evaluated by Brunauer-Emmett-Teller, Scanning electron microscope and Fourier-transform infrared spectroscopy. Short-chain fatty acids, dissolved organic carbon (DOC), and chemical oxygen demand (COD) equivalents were used to analyze the carbon release capacity. Results showed that agricultural waste had higher carbon release capacity than PCL and PHBV. The cumulative DOC and COD of agricultural waste were 0.56-12.65 and 1.15-18.75 mg/g, respectively, while those for synthetic polymers were 0.07-1.473 and 0.045-1.425 mg/g, respectively. The removal efficiency of nitrate nitrogen (NO3 --N) was CC 70.80%, PCL 53.64%, RS 42.51%, and PHBV 41.35%. Microbial community analysis showed that Proteobacteria and Firmicutes were the most abundant phyla in agricultural wastes and biodegradable natural or synthetic polymers. Quantitative real-time PCR indicated the conversion from nitrate to nitrogen was achieved in all four carbon source systems, and all six genes had the highest copy number in CC. The contents of medium nitrate reductase, nitrite reductase and nitrous oxide reductase genes in agricultural wastes were higher than those in synthetic polymers. In summary, CC is an ideal carbon source for denitrification technology to purify low C/N recirculating mariculture wastewater.

Eutrophication status assessment in the Laizhou Bay, Bohai Sea: Further evidence for the ecosystem degradation.

Laizhou Bay is plagued by many environmental problems (e.g., acidification and eutrophication) that are likely to increase in the coming decades along with social and demographic trends. We thus conducted 12 cruises from July 2019 to December 2021 in the Laizhou Bay to evaluate the potential influences of human activities on its eutrophication status. The results showed that the parameters of dissolved inorganic nitrogen (DIN) and oxygen (DO) exceeded the water quality standard in some cases during the past 3 years, suggesting DIN and DO were the crucial factors controlling water quality in the bay. Meanwhile, DIN was identified as a major pollutant in the region, and played an important role in driving the phytoplankton dynamics. Furthermore, with the increases in human-related nutrient inputs (especially DIN), the bay environment reached the mild eutrophication level and was probably at risk from excessive nutrient loads at present, further evidencing the ecosystem degradation.

Occurrence and ecotoxicity of sulfonamides in the aquatic environment: A review.

Rapid population growth and increasing demand for animal protein food have led to a continuous increase in global utilization of antibiotic. Sulfonamides (SAs) are ubiquitous in aquatic environments and pose an ecological risk owing to their large consumption and strong environmental persistence. Hence, this review focuses on the recent publications on 12 different SAs and provides a detailed summary of selected antibiotic concentrations in various water systems. We evaluated the ecotoxicity of SAs on organisms at different trophic level organisms and the environmental risks regarding aquatic systems. The results indicated that SA antibiotics were ubiquitous in aquatic environments at concentrations ranging from ng/L to µg/L. According to the data using standard ecotoxicity bioassays, algae were the most susceptible aquatic organisms for selected antibiotics, followed by crustaceans and fish. The risk data suggested that some antibiotics, such as sulfadiazine (SDZ), sulfamethoxazole (SMX), and sulfamethazine (SMZ) pose a great risk to the aquatic system. Based on the present review, it is necessary to strengthen the research into their ecotoxicity to marine systems and the chronic toxicity of antibiotic mixtures.

The toxicological impact of the sunscreen active ingredient octinoxate on the photosynthesis activity of Chlorella sp.

Products designed to filter ultraviolet (UV) light are responsible for growing levels of anthropogenic environmental contamination. Octinoxate (ONT) is among the most common UV filtering active ingredients in cosmetics and sunscreens. The present study was designed to evaluate the toxicological effects of ONT on the photosynthetic activity of the Chlorella species of marine microalgae. These analyses identified ONT as a potent photo-toxicant, the effects of which were more pronounced upon light exposure relative to in the dark. Short-term ONT exposure had no effect on photosynthetic electron transport capacity in the dark but did significantly reduce the ribulose-1,5-bisphosphate carboxylase/oxygenase activity in Chlorella cells, suggesting that this compound can directly suppress the photosynthetic Calvin cycle. When cells were subsequently exposed to light, the disruption of this cycle resulted in an excess of excitation energy, in turn driving the excessive generation of reactive oxygen species (ROS). ROS-mediated disruption of cellular metabolism further aggravated this ONT-induced microalgal damage. As such, under natural light conditions, these microalgae cells are exposed to increased oxidative stress that impairs their growth and causes pigment bleaching. Restricting the utilization of ONT-containing sunscreens thus has the potential to better preserve the integrity of aquatic and terrestrial ecosystems.

Ecotoxicity of chlorpyrifos to aquatic organisms: A review.

Pesticides play an important role in promoting agricultural development, while their unreasonable use has led to environmental problems. Chlorpyrifos (CPF), a typical organophosphate pesticide, is used globally as an insecticide in agriculture. The extensive application of CPF has resulted in water contamination, and CPF has been detected in rivers, lakes, seawater, and even in rain. In the present review, CPF was selected due to its extensive use in agriculture and higher detection rate in surface waters. In this review we summarised the evidence related to CPF pollution and focused on discussing the ecotoxicity of CPF to aquatic systems and revealed the mechanism of action of CPF. The aim of this literature review was to summarise the knowledge of the toxicity to marine and freshwater organisms of CPF as well as try to select a series of sensitive biomarkers, which are suitable for ecotoxicological assessment and environmental monitoring in aquatic systems.

Impacts of polystyrene microplastics on the behavior and metabolism in a marine demersal teleost, black rockfish (Sebastes schlegelii).

After nano- (0.5 µm) or micro- (15 µm) polystyrene (PS) microplastics exposure, the behavior, metabolism and energy reserve in marine demersal fish (Sebastes schlegelii) were evaluated. The behavior of fish was accurately recorded by video behavior tracking technology. Results showed that changes in behavior (e.g. cluster, the reduction of swimming speed and range of movement) were significantly greater in 15-µm PS-exposed fish, which may affect hunting behavior and exploration competence. Oxygen consumption and ammonia excretion of fish was significantly greater in 15-µm PS treatment than in 0.5-µm PS treatment, suggesting respiration and metabolism stress. Moreover, the abnormal behavior, respiration and ammonia excretion of PS-exposed fish had recovered modestly. In addition, abnormal symptoms of bile, liver and lumen of intestine were detected in 15-µm PS exposure. Importantly, the growth and gross energy of fish were reduced in 15-µm PS exposure than 0.5-µm PS exposure. Both 0.5-µm and 15-µm PS exposures led to significantly lower protein and lipid contents, suggesting energy reserve and nutrition quality reduction of fish. Overall, microplastics had the negative impact at greater levels than nanoplastics. Altered behavior, energy reserve and nutritional quality of fish indicated the potential risk on biological functions, the development of fishery and food safety.

Ecotoxicity of phenol and cresols to aquatic organisms: A review.

With the development of industrial production and continuous demand for chemicals, a large volume of wastewater containing phenols was discharged into the aquatic environment. Moreover, chemical leakage further increased the emission of phenols into aquatic systems. Phenol and its methylated derivative (cresols) were selected due to their extensive use in industry and ecotoxicity to freshwater and marine organisms. This review focused on the ecotoxicity of phenol and m-, o-, and p-cresol on aquatic systems. The mechanism of action of phenols was also discussed. The aim of this literature review was to summarise the knowledge of the behaviour, and toxicity on marine and freshwater organisms, of phenols as well as to try to select a series of sensitive biomarkers suitable for ecotoxicological assessment and environmental monitoring in aquatic environments.

Two-stage mixotrophic cultivation for enhancing the biomass and lipid productivity of Chlorella vulgaris.

This study proposes a two-stage mixotrophic process for cultivating Chlorella vulgaris. Heterotrophic growth is the dominant step in Phase I (to increase microalgal biomass) and photoautotrophic growth occurs in Phase II (to improve biomass concentration and lipid production). The results show that the addition of the low-cost antioxidant sodium erythorbate (8 g L-1) significantly accelerates the growth of microalgae in the first stage with air aeration. Furthermore, a higher CO2 fixation rate was obtained in the second stage (at least 344.32 mg CO2 L-1 day-1) with 10% CO2 aeration. This approximately corresponds to an increase of 177% over simple photoautotrophic cultivation with 10% CO2 aeration during the whole period. The two-stage cultivation strategy achieved a maximum C. vulgaris biomass concentration of 3.45 g L-1 and lipid productivity of 43.70 mg L-1 day-1, which are 1.85 and 1.64 times those arising due to simple photoautotrophy, respectively. Moreover, an analysis of the product's fatty acid profile indicates that C. vulgaris might be an ideal candidate for two-stage mixotrophic cultivation of a renewable biomass for use in biodiesel applications. Another interesting point to note from the study is that it is an insufficiency of N and CO2 that probably limits the further growth of C. vulgaris.

[Spatial Distribution, Source and Ecological Risk Assessment of Heavy Metals in the Coastal Sediments of Northern Dongying City].

Concentrations of seven heavy metals in the coastal sediments of the northern Dongying City were measured. The spatial distribution and sources of heavy metals were discussed and the ecological risk was assessed using sediment quality guidelines (SQGs) and the potential ecological risk index (PERI). The concentration ranges of Hg, As, Pb, Cd, Cr, Cu, and Zn were calculated as 0.005-0.092, 3.44-10.41, 6.59-19.00, 0.50-1.10, 32.42-60.25, 1.72-23.78, and 31.13-69.96 mg·kg-1, respectively. Higher metal concentrations were observed at site S10, which was close to the mouth of Tiaohe River and contained plenty of organic matter, silt, and clay. Principal component analysis (PCA) indicated that As and Pb in the sediments were derived from natural weathering processes, while other metals were mainly attributed to anthropogenic sources, i.e., land-sourced pollutants transported by runoff. Concentrations of As, Cd, Cr, and Cu at some sampling sites exceeded the threshold effect level (TEL) stated in the SQGs implying occasional harmful effects on biological life. PERI showed that the sediments in this area generally had a medium risk, except sites S10, S3, and S9 posing a considerable risk, and that Cd and Hg were the major contributors to the ecological risk. It is necessary to take effective measures to control heavy metal fluxes from rivers around this area and to reduce the risk.