Occurrence, sources and transport of antibiotics in the surface water of coral reef regions in the South China Sea: Potential risk to coral growth

Unraveling individual and combined toxicity of microplastics and tetracycline at environment-related concentrations to coral holobionts

Coral holobionts constitute the foundational organisms of coral reef ecosystems. As an emerging pollutant, the projected accumulated levels of microplastics (MPs) are expected to continue increasing. Meanwhile, due to their properties, MPs can absorb multiple other marine pollutants, such as antibiotics (ATs). However, the co-toxicity mechanism of MPs and ATs to coral holobionts remains to be explored. Here, using Zoanthus sociatus as a model organism, we investigate the individual and combined toxicity of MPs and tetracycline (TC) at environment-related concentrations to coral holobionts. Microbiomics indicate that MPs and TC increase coral holobionts bacterial species richness while concurrently reducing the microbial community structure stability. The key metabolites and enzyme activity results demonstrated that the impacts of MPs and TC on corals encompassed antioxidant capacity, detoxification capability, immune function, and lipid metabolism. Transcriptomics shows that MPs and TC disrupt coral-algae relationships mainly through host nutrition limitation and inhibition of symbiotic algae carbon/nitrogen metabolism, respectively. A synergistic effect between MPs and TC has also been observed. In contrast, coral holobionts have shown adaptability through activating coral-symbiodiniaceae-bacteria interactions, mainly including: 1) enhancing the abundance of BMCs (beneficial microorganisms for corals); 2) enhancing host lipid accumulation; 3) immunoregulation; 4) symbiotic regulation. Overall, our findings provide new insights into the co-toxicity of MPs and TC, and highlight those MPs and TC at current environment concentration and predicted for most oceans in the coming decades, can ultimately cause coral bleaching.

Antibiotic type and dose variably affect microbiomes of a disease-resistant Acropora cervicornis genotype

BACKGROUND

As coral diseases become more prevalent and frequent, the need for new intervention strategies also increases to counteract the rapid spread of disease. Recent advances in coral disease mitigation have resulted in increased use of antibiotics on reefs, as their application may halt disease lesion progression. Although efficacious, consequences of deliberate microbiome manipulation resulting from antibiotic administration are less well-understood- especially in non-diseased corals that appear visually healthy. Therefore, to understand how apparently healthy corals are affected by antibiotics, we investigated how three individual antibiotics, and a mixture of the three, impact the microbiome structure and diversity of a disease-resistant Caribbean staghorn coral (Acropora cervicornis) genotype. Over a 96-hour, aquarium-based antibiotic exposure experiment, we collected and processed coral tissue and water samples for 16S rRNA gene analysis.

RESULTS

We found that antibiotic type and dose distinctively impact microbiome alpha diversity, beta diversity, and community composition. In experimental controls, microbiome composition was dominated by an unclassified bacterial taxon from the order Campylobacterales, while each antibiotic treatment significantly reduced the relative abundance of this taxon. Those taxa that persisted following antibiotic treatment largely differed by antibiotic type and dose, thereby indicating that antibiotic treatment may result in varying potential for opportunist establishment.

CONCLUSION

Together, these data suggest that antibiotics induce microbiome dysbiosis- hallmarked by the loss of a dominant bacterium and the increase in taxa associated with coral stress responses. Understanding the off-target consequences of antibiotic administration is critical not only for informed, long-term coral restoration practices, but also for highlighting the importance of responsible antibiotic dissemination into natural environments.

Coral-Symbiodiniaceae symbiotic associations under antibiotic stress: Accumulation patterns and potential physiological effects in a natural reef

Antibiotics threaten scleractinian corals, but their accumulation patterns and physiological effects on corals in natural reefs remain unclear. This study investigated antibiotic occurrence in seawater and two coral species, Galaxea fascicularis and Pocillopora damicornis, and explored the physiological effects of bioaccumulated antibiotics in a fringing reef of the South China Sea. Nineteen antibiotic components were detected in seawater, with total antibiotic concentrations (ΣABs) ranging from 17.69 to 44.22 ng L⁻¹ . Eleven antibiotic components were accumulated in the coral hosts, and five components were observed in their algal symbionts. Higher ΣABs were significantly associated with increased total antioxidant capacity in the coral hosts of P. damicornis, while G. fascicularis exhibited a significant increase in algal symbiont density. Furthermore, ofloxacin was linked to increased algal symbiont density of G. fascicularis, while several antibiotic components, including tilmicosin, sulfapyridine, ofloxacin, and lincomycin hydrochloride, were observed to reduce antioxidant levels in the algal symbionts of G. fascicularis. No significant correlations between antibiotic components and physiological activities were detected in P. damicornis. These results highlight species-specific bioaccumulation patterns and physiological responses to antibiotics, suggesting that prolonged contaminations could destabilize coral-Symbiodiniaceae symbiosis. The findings improve understanding of the ecological risks of antibiotic pollution in reefs.

Synergistic effects of ocean acidification and sulfamethoxazole on immune function, energy allocation, and oxidative stress in Trochus niloticus

Ocean acidification, a major consequence of climate change, poses significant threats to marine organisms, particularly when combined with other environmental stressors such as chemical pollution. This study investigated the physiological responses of Trochus niloticus to a 28-day exposure of ocean acidification and/or sulfamethoxazole, a commonly detected antibiotic in the South China Sea. Exposure to either acidification or sulfamethoxazole individually triggered adaptive responses through immune activation, antioxidant reactions, and metabolic adjustments. However, concurrent exposure resulted in significant adverse effects, including compromised immunity, oxidative damage, and disrupted energy budget. These findings provide new insights into how ocean acidification interacts with antibiotic pollution to synergistically impact marine gastropods, suggesting that multiple stressors may pose greater threats to T. niloticus populations than single stressors alone.

Mechanism of microplastics promoting sulfamethoxazole biodegradation in activated sludge as revealed by DNA-stable isotope probing

Microplastics (MPs) often coexist with sulfonamide antibiotics (SAs) in the activated sludge of wastewater treatment plants (WWTPs). Microbial degradation is a crucial pathway for SAs removal in the activated sludge, though its response to MPs still yet to be disclosed. Here, we combined DNA-stable isotope probing (DNA-SIP), PICRUSt and MENA techniques to explore the impact of MPs on the microbial biodegradation of sulfamethoxazole (SMX) in the activated sludge. DNA-SIP revealed 20 genera were responsible for the SMX degradation in the activated sludge, with 13 of these genera being firstly linked with sulfonamide biodegradation. The potential SMX-degrading bacteria showed complex synergistic interaction with the other microbes. Eight degradation pathways were constructed based on the nine identified SMX-related degradation genes. MPs addition enhanced the SMX biodegradation by altering the structure of degrading microbes, increasing their relative abundance and promoting the synergistic interactions between potential SMX-degrading bacteria and other microbes in activated sludge. Besides, genes related to abundant energy production and biofilm formation were involved in SMX degradation in the activated sludge with MPs. Our study reveals the MPs influence on SMX biodegradation in activated sludge, and disclose the potential underlying mechanisms, which will benefit the regulation on antibiotic removal in WWTPs.

Detection of 10 commonly used pharmaceuticals in reef-building stony corals from shallow (5-12 m) and deep (30-40 m) sites in the Red Sea

Although pharmaceutically-active compounds (PhACs) are increasingly being found to be present in marine environments, their presence in coral reefs, already under threat from various stressors, has remains unexplored. This study focused on PhAC presence in two stony-coral genera, collected from different depths and sites in the Red Sea. The findings reveal the presence of ten different PhACs, with elevated concentrations detected in corals from shallow sites and in areas with heavy human activity. Notably, all samples contained at least one PhAC, with the antibiotic sulfamethoxazole being the most prevalent compound, detected in 93% of the samples, at concentrations ranging from 1.5 to 2080 ng/g dry weight (dw) tissue, with an average concentration of 106 ng/g dw. These findings underscore the urgent need for conservation initiatives aimed at protecting coral-reef ecosystems from the escalating threat of anthropogenic contamination, including such potential risks as the development of antibiotic resistance in marine organisms and the disruption of critical spawning synchrony among coral populations.

A meta-analysis of antibiotic residues in the Beibu Gulf

Antibiotic residue stands as a significant ongoing environmental issue, with aquaculture being a major source of annual antibiotic discharge into the ocean. Nevertheless, there is still an incomplete evaluation of antibiotic residues in the Beibu Gulf, an area encompassed by two prominent aquaculture nations, China and Vietnam. The present systematic review and meta-analysis was conducted to examine the presence antibiotic residues in the Beibu Gulf based on published studies. Data were obtained through eight databases up to December 19th, 2023, and were updated on April 15th, 2024. The pooled concentration of antibiotic residues in seawater was 5.90 (ng/L), ranging from 5.73 to 6.06 (ng/L), and was 8.03 (ng/g), ranging from 7.77 to 8.28 (ng/g) in sediments. Fluoroquinolones, tetracyclines, and macrolides were identified as the main antibiotics found in both seawater and sediment samples. The Beibu Gulf showed higher antibiotic levels in its western and northeastern areas. Additionally, the nearshore mangrove areas displayed the highest prevalence of antibiotic residues. It is strongly advised to conduct regular long-term monitoring of antibiotic residues in the Beibu Gulf. Collaborative surveys covering the entire Beibu Gulf involving China and Vietnam are recommended.

Organophosphate esters (OPEs) in corals of the South China Sea: Occurrence, distribution, and bioaccumulation

Organophosphate esters (OPEs) have garnered significant attention in recent years. In view of the enormous ecosystem services value and severe degradation of coral reefs in the South China Sea, this study investigated the occurrence, distribution, and bioaccumulation of 11 OPEs in five coral regions: Daya Bay (DY), Weizhou Island (WZ), Sanya Luhuitou (LHT), Xisha (XS) Islands, and Nansha (NS) Islands. Although OPEs were detected at a high rate, their concentration in South China Sea seawater (1.56 ± 0.89 ng L-1) remained relatively low compared to global levels. All OPEs were identified in coral tissues, with Luhuitou (575 ± 242 ng g-1 dw) showing the highest pollution levels, attributed to intense human activities. Coral mucus, acting as a defense against environmental stresses, accumulated higher ∑11OPEs (414 ± 461 ng g-1 dw) than coral tissues (412 ± 197 ng g-1 dw) (nonparametric test, p < 0.05), and their compositional characteristics varied greatly. In the case of harsh aquatic environments, corals increase mucus secretion and then accumulate organic pollutants. Tissue-mucus partitioning varied among coral species. Most OPEs were found to be bioaccumulative (BAFs >5000 L kg-1) in a few coral tissue samples besides Triphenyl phosphate (TPHP). Mucus' role in the bioaccumulation of OPEs in coral shouldn't be ignored.

Typical antibiotic resistance genes and their association with driving factors in the coastal areas of Yangtze River Estuary

The massive use of antibiotics has led to the escalation of microbial resistance in aquatic environment, resulting in an increasing concern regarding antibiotic resistance genes (ARGs), posing a serious threat to ecological safety and human health. In this study, surface water samples were collected at eight sampling sites along the Yangtze River Estuary. The seasonal and spatial distribution patterns of 10 antibiotics and target genes in two major classes (sulfonamides and tetracyclines) were analyzed. The findings indicated a high prevalence of sulfonamide and tetracycline resistance genes along the Yangtze River Estuary. Kruskal-Wallis analysis revealed significant seasonal variations in the abundance of all target genes. The accumulation of antibiotic resistance genes in the coastal area of the Yangtze River Estuary can be attributed to the influence of urban instream runoff and the discharge of effluents from wastewater treatment plants. ANISOM analysis indicated significant seasonal differences in the microbial community structure. VPA showed that environmental factors contribute the most to ARG variation. PLS-PM demonstrate that environmental factors and microbial communities pose direct effect to ARG variation. Analysis of driving factors influencing ARGs in this study may shed new insights into the mechanism of the maintenance and propagation of ARGs.

Functional analyses of bacterial genomes found in Symbiodiniaceae genome assemblies

Bacterial-algal interactions strongly influence marine ecosystems. Bacterial communities in cultured dinoflagellates of the family Symbiodiniaceae have been characterized by metagenomics. However, little is known about whole-genome analysis of marine bacteria associated with these dinoflagellates. We performed in silico analysis of four bacterial genomes from cultures of four dinoflagellates of the genera Symbiodinium, Breviolum, Cladocopium and Durusdinium. Comparative analysis showed that the former three contain the alphaproteobacterial family Parvibaculaceae and that the Durusdinium culture includes the family Sphingomonadaceae. There were no large genomic reductions in the alphaproteobacteria with genome sizes of 2.9-3.9 Mb, implying they are not obligate intracellular bacteria. Genomic annotations of three Parvibaculaceae detected the gene for diacetylchitobiose deacetylase (Dac), which may be involved in the degradation of dinoflagellate cell surfaces. They also had metabolic genes for dissimilatory nitrate reduction to ammonium (DNRA) in the nitrogen (N) cycle and cobalamin (vitamin B12 ) biosynthetic genes in the salvage pathway. Those three characters were not found in the Sphingomonadaceae genome. Predicted biosynthetic gene clusters for secondary metabolites indicated that the Parvibaculaceae likely produce the same secondary metabolites. Our study suggests that the Parvibaculaceae is a major resident of Symbiodiniaceae cultures with antibiotics.

Insight into typical photo-assisted AOPs for the degradation of antibiotic micropollutants: Mechanisms and research gaps

Due to the incomplete elimination by traditional wastewater treatment, antibiotics are becoming emerging contaminants, which are proved to be ubiquitous and promote bacterial resistance in the aquatic systems. Antibiotic pollution has raised particular concerns, calling for improved methods to clean wastewater and water. Photo-assisted advanced oxidation processes (AOPs) have attracted increasing attention because of the fast reaction rate, high oxidation capacity and low selectivity to remove antibiotics from wastewater. On the basis of latest literature, we found some new breakthroughs in the degradation mechanisms of antibiotic micropollutants with respect to the AOPs. Therefore, this paper summarizes and highlights the degradation kinetics, pathways and mechanisms of antibiotics degraded by the photo-assisted AOPs, including the UV/O3 process, photo-Fenton technology, and photocatalysis. In the processes, functional groups are attacked by hydroxyl radicals, and major structures are destroyed subsequently, which depends on the classes of antibiotics. Meanwhile, their basic principles, current applications and influencing factors are briefly discussed. The main challenges, prospects, and recommendations for the improvement of photo-assisted AOPs are proposed to better remove antibiotics from wastewater.

Physiological and biochemical responses of soft coral Sarcophyton trocheliophorum to doxycycline hydrochloride exposure

In light of the rapid expansion of the marine aquaculture industry, there has been widespread and irregular usage of aquatic drugs to combat biological diseases, which significantly impact the neighboring aquatic ecosystems. This study delves into the impact of the antibiotic aquatic drug known as doxycycline hydrochloride (DOX) on offshore soft corals, providing valuable data for the responsible use and management of aquatic drugs. In this investigation, we subjected Sarcophyton trocheliophorum to acute exposure to varying concentrations of DOX (0, 1, 5, and 10 mg L-1). We meticulously assessed critical parameters and observed alterations in protein levels, superoxide dismutase (SOD) activity, catalase (CAT) activity, lipid peroxidation (LPO), malondialdehyde (MDA) levels, Acid phosphatase (ACP) activity, alkaline phosphatase (AKP) activity, glutathione (GSH) concentration, glutathione S-transferase (GST) activity, glutathione Peroxidase (GSH-Px) activity, zooxanthellae density, and chlorophyll content. Our findings reveal that in the presence of DOX-induced environmental stress, there is a significant increase in LPO, MDA, chlorophyll, carotenoid levels, and the activities of ACP, GST, and GSH-Px in soft corals. Simultaneously, there is a noteworthy decrease in zooxanthellae density. Additionally, the protein concentration and SOD activity in soft corals experience substantial reduction when exposed to 5 mg L-1 DOX. Notably, CAT activity varies significantly in environments with 1 and 10 mg L-1 DOX. Moreover, these conditions exhibit a discernible influence on AKP activity, GSH content, and chlorophyll levels. These findings suggest that DOX exposure carries the potential for toxicity in aquaculture settings, affecting protein synthesis in soft corals and influencing oxidative stress, lipid peroxidation, immunity, and detoxification processes within these organisms. There is also a risk of compromising the coral defense system, potentially leading to coral bleaching. Furthermore, this study underscores the significant impact on photosynthesis, growth, and the metabolic dynamics of the coral-zooxanthellae symbiotic system. Consequently, our research offers vital insights into the mortality and bleaching effects of aquatic drugs on marine corals, offering a foundation for the prudent use and management of such substances.

The genome of Symbiodiniaceae-associated Stutzerimonas frequens CAM01 reveals a broad spectrum of antibiotic resistance genes indicating anthropogenic drift in the Palk Bay coral reef of south-eastern India

An increase in antibiotic pollution in reef areas will lead to the emergence of antibiotic-resistant bacteria, leading to ecological disturbances in the sensitive coral holobiont. This study provides insights into the genome of antibiotics-resistant Stutzerimonas frequens CAM01, isolated from Favites-associated Symbiodiniaceae of a near-shore polluted reef of Palk Bay, India. The draft genome contains 4.67 Mbp in size with 52 contigs. Further genome analysis revealed the presence of four antibiotic-resistant genes, namely, adeF, rsmA, APH (3")-Ib, and APH (6)-Id that provide resistance by encoding resistance-nodulation-cell division (RND) antibiotic efflux pump and aminoglycoside phosphotransferase. The isolate showed resistance against 73% of the antibiotics tested, concurrent with the predicted AMR genes. Four secondary metabolites, namely Aryl polyene, NRPS-independent-siderophore, terpenes, and ectoine were detected in the isolate, which may play a role in virulence and pathogenicity adaptation in microbes. This study provides key insights into the genome of Stutzerimonas frequens CAM01 and highlights the emergence of antibiotic-resistant bacteria in coral reef ecosystems.

The Ecological Status and Change in High-Latitude Coral Assemblages at the Xuwen Coral Reef, Northern South China Sea: Insight into the Status and Causes in 2020

Taking the coral communities of the Xuwen coral reef in 2020 as the research object, we analyzed the species composition, diversity, and interspecific Spearman correlation of the scleractinian coral communities, investigated the features and spatial distribution of the scleractinian coral community, and discussed the correlation between the community composition and environmental factors to identify the affecting factors and their sources. These results showed that (1) compared with the survey in 2004, the coverage of corals in 2020 had significantly decreased, while the dominant genera were still Goniopora and Porites. The coral morphology was massive, and the diversity of the coral community (Shannon-Wiener index, H') was 2.87. The distribution of coral was uneven. The competition among some dominant species of coral was intense. (2) The mass coral bleaching event in the NSCS in August 2020 did not cause severe coral death in the short term on the Xuwen coral reef. (3) The growth of the coral community in 2020 might be greatly affected by high suspended solids and nutrient levels, which were related to the current, mariculture, and coastal erosion. (4) Anthropogenic activities such as coastal aquaculture and fishing were the major factors leading to the reduction in coral coverage on Xuwen coral reef in the past 10 years.

Bioaccumulation and trophic transfer of PAHs in tropical marine food webs from coral reef ecosystems, the South China Sea: Compositional pattern, driving factors, ecological aspects, and risk assessment

Multiple environmental pressures caused by global warming and human activities have aroused widespread concern about PAHs pollution in tropical marine coral reef regions (CRRs). However, the trophodynamics of PAHs in the food webs of the CRRs and the related influence factors have not been reported. This study investigated the occurrence, trophic amplification, and transmission of PAHs in various organisms selecting between at least representative species for each level in CRRs of the South China Sea (SCS); revealed their driving mechanisms; and explored the trophodynamics of PAHs in the food web of the coral reef ecosystem. Results showed that more PAHs can be accumulated in the mantle tissue of Tridacnidae, and the proportion of mantle tissue of Tridacnidae increases with the increase of latitude (y = 0.01x + 0.17, R² = 0.49, p < 0.05). Latitude drives the differential occurrence level and bioaccumulation of PAHs in tropical marine organisms, and also affects the trophodynamics of PAHs in aquatic ecosystem food webs. PAHs undergo trophic amplification in the food webs of tropical marine ecosystems represented by coral reefs, thus further aggravating the negative environmental impact on coral reef ecosystems. The cancer risk caused by accidental ingestion of PAHs by humans through consumption of seafood in CRRs is very low, but we should be alert to the biomagnification effect of PAHs.

Distribution and ecological risks of pharmaceuticals and personal care products with different anthropogenic stresses in a coastal watershed of China

The occurrences of pharmaceutical and personal care products (PPCPs) in both freshwater and sea have been widely reported. However, pollution control requires further information on riverine discharges with influence of land-based activities and associated risks to estuarine ecosystems. This study investigated the spatial occurrences and the relationship to sociodemographic parameters of 30 PPCPs in 67 rivers along the Bohai coastal region. The results showed that PPCPs were mainly deposited in aquatic phase, and the partitioning coefficient between water and sediment was highly determined by chemical properties. The levels of 30 PPCPs in rivers ranged from 8.33 to 894.48 ng/L, showing a large variance among regions. Caffeine, sulfamethoxazole, sulfamethazine, ofloxacin, anhydro-erythromycin, and trimethoprim were found to be the major pollutants. Multivariable analysis method was used to assess the correlation of PPCPs markers to socio-economic parameters. The results indicated that domestic emissions contributed most to the occurrences of PPCPs in the riverine water. Risk assessment result indicated that sulfamethoxazole, caffeine, tetracycline, and carbamazepine ranked top four with the highest risks to the most sensitive aquatic organisms. The results identified caffeine and carbamazepine with high detection frequency and concentration as the priority chemicals, while sulfamethoxazole and erythromycin should also be concerned due to their potential threats in specific rivers. This study provides valuable information for pollution control over PPCPs riverine discharges in estuarine regions.

Occurrence, distribution, sources, and bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) in multi environmental media in estuaries and the coast of the Beibu Gulf, China: a health risk assessment through seafood consumption

The coastal zone is a crucial transitional area between land and ocean, which is facing enormous pressure due to global climate change and anthropogenic activities. It is essential to pay close attention to the pollution caused by polycyclic aromatic hydrocarbons (PAHs) in the coastal environment and their effect on human health. The pollution status of PAHs was investigated in the Beibu Gulf, taking into consideration various environmental media. The results showed that the total concentration of 16 PAHs (Σ16PAHs) was significantly higher in winter than in summer. Compared to the coastal area, the status of PAHs in the estuarine areas was found to be more severe in summer, while the regional difference was insignificant in winter. In summer, the Σ16PAHs in estuarine waters (71.4 ± 9.58 ng/L) > coastal waters (50.4 ± 9.65 ng/L); estuarine sediment (146 ± 116 ng/g) > coastal zone (76.9 ± 108 ng/g). The source apportionment indicated that spilled oil, biomass, and coal burning were the primary sources of PAHs in the water. The predominant sources of pollution in the sediments were spilled oil, fossil fuel burning, and vehicle emissions. With regard to the status of PAHs in marine organisms in the coastal area of the Beibu Gulf, the highest average concentration of PAHs was indicated in shellfishes (183 ± 165 ng/g), followed by fishes (73.7 ± 57.2 ng/g), shrimps (42.7 ± 19.2 ng/g), and crabs (42.7 ± 19.2 ng/g) in Beibu Gulf coastal area. The calculated bioaccumulation factor indicates a low bioaccumulation capacity of PAHs in various seafood considering the ambient environment. The human health risk assessment considering multiple age groups indicates minimal health risk on accidental ingestion of PAHs through seafood. However, it is suggested that the intake of shellfish in children be controlled.

Recent Advances and Perspectives on the Sources and Detection of Antibiotics in Aquatic Environments

Water quality and safety are vital to the ecological environment, social development, and ecological susceptibility. The extensive use and continuous discharge of antibiotics have caused serious water pollution; antibiotics are widely found in freshwater, drinking water, and reservoirs; and this pollution has become a common phenomenon and challenge in global water ecosystems, as water polluted by antibiotics poses serious risks to human health and the ecological environment. Therefore, the antibiotic content in water should be identified, monitored, and eliminated. Nevertheless, there is no single method that can detect all different types of antibiotics, so various techniques are often combined to produce reliable results. This review summarizes the sources of antibiotic pollution in water, covering three main aspects: (1) wastewater discharges from domestic sewage, (2) medical wastewater, and (3) animal physiology and aquaculture. The existing analytical techniques, including extraction techniques, conventional detection methods, and biosensors, are reviewed. The electrochemical biosensors have become a research hotspot in recent years because of their rapid detection, high efficiency, and portability, and the use of nanoparticles contributes to these outstanding qualities. Additionally, the comprehensive quality evaluation of various detection methods, including the linear detection range, detection limit (LOD), and recovery rate, is discussed, and the future of this research field is also prospected.

Antibiotics in Wastewater: Baseline of the Influent and Effluent Streams in Kuwait

This study provides baseline information on the concentrations of antibiotics in influent and effluent from two wastewater treatment plants in regular operation in the State of Kuwait. Wastewater samples were collected from the influent and effluent streams of two WWTPs, over four sampling campaigns and analyzed for a broad range of antibiotics. The mean influent concentrations of sulfamethoxazole, ciprofloxacin, clarithromycin, and cefalexin were 852 ng/L, 672 ng/L, 592 ng/L), and 491 ng/L, respectively, at Umm Al Hayman WWTP. At the Kabd WWTP, the influent concentration of clarithromycin was highest with a mean of 949 ng/L, followed by ciprofloxacin (mean, 865 ng/L), cefalexin (mean, 598 ng/L), and sulfamethoxazole (mean, 520 ng/L). The dominant compounds in the effluent from Umm Al Hayman were sulfamethoxazole (mean, 212 ng/L), ciprofloxacin (mean, 153 ng/L), ofloxacin (mean, 120 ng/L), dimetridazole (mean, 96 ng/L), and metronidazole (mean, 93 ng/L). Whereas, at the Kabd WWTP, the dominant compounds were sulfamethoxazole (mean, 338 ng/L), dimetridazole (mean, 274 ng/L), cefalexin (mean, 213 ng/L), ciprofloxacin (mean, 192 ng/L), and clarithromycin (189 ng/L). The mean influent concentrations of all compounds were higher than those measured in the effluents. The concentrations of antibiotic compounds were not significantly different between the two WWTPs (p > 0.05). The removal efficiencies of the various antibiotics over the four sampling campaigns for the Kabd and Umm Hayman WWTPs ranged between 10.87 and 99.75% and also showed that they were variable and were compound dependent. The data clearly show that the concentrations of antibiotics measured in the influents of both WWTPs were highest in samples collected during the winter-summer (September samples) transition followed by the concentrations measured during the winter-summer (March samples) transition period. This is possibly linked to the increased prescription of these medications to treat infectious diseases and flu prevalent in Kuwait during these periods. This study provides the first reported concentrations of antibiotics in the dissolved aqueous influents and effluents of WWTPs in Kuwait. Additional studies are required to evaluate the environmental impact that antibiotic residues may cause since treated wastewater is used in irrigation, and often there are instances when untreated wastewater is discharged directly into the marine environment.

Semi-volatile organic compounds in fine particulate matter on a tropical island in the South China Sea

Measurements of hazardous semi-volatile organic compounds (SVOCs) in remote tropical regions are rare. In this study, polycyclic aromatic compounds (PACs) [including polycyclic aromatic hydrocarbons (PAHs), nitrated PAHs (NPAHs), and oxygenated PAHs (OPAHs)], organophosphate esters (OPEs), and phthalic acid esters (PAEs) were measured in fine particulate matter (PM_2.5) at Yongxing Island in the South China Sea (SCS). The concentrations of PACs (median = 53.5 pg/m³) were substantially low compared with previous measurements. The concentration weighted trajectory (CWT) model showed that the eastern and southern China was the main source region of PAC, occurring largely during the northeast (NE) monsoon. The PM_2.5 showed remarkably high concentrations of OPEs (median = 3231 pg/m³) and moderate concentrations of PAEs (13,013 pg/m³). Some Southeast Asian countries were largely responsible for their higher concentrations, driven by the tropical SCS monsoons. We found significant atmospheric loss of the SVOCs, which is an explanation for the low concentrations of PACs. Enhanced formation of N/OPAHs originated from tropical regions was also observed. The positive matrix factorization model was applied to apportion the SVOC sources. The results, as well as correlation analyses of the SVOC concentrations, further indicate insignificant local sources and enhanced atmospheric reactions on this island.

Occurrence, source apportionment and risk assessment of antibiotics in water and sediment from the subtropical Beibu Gulf, South China

The widespread use of antibiotics has raised global concerns, but scarce information on antibiotics in the subtropical marine environment is available. In the present study, seawater and sediment samples were collected to investigate the occurrence, spatial distribution, source, and ecological risks of 22 antibiotics in the Beibu Gulf. The total concentrations of target antibiotics (∑antibiotics) were in the range of 1.74 ng/L to 23.83 ng/L for seawater and 1.33 ng/g to 8.55 ng/g dry weight (dw) for sediment. Spatially, a decreasing trend of antibiotic levels from coast to offshore area was observed, with relatively high levels at the sites close to the Qinzhou Bay and Qiongzhou Strait. Sulfamethoxazole (SMX), trimethoprim (TMP), and norfloxacin (NOX) were predominant in seawater, while NOX, enoxacin (ENX), and enrofloxacin (ENR) were the most abundant antibiotics in sediment. In general, the sediment-water partitioning coefficients (K_d) were positively correlated with log molecular weight (MW). Salinity, particle size, and pH of water were predicted to be vital factors influencing the partition of sulfadiazine (SDZ), CIX, and ENR (p < 0.05). Livestock and aquaculture were identified as dominant sources of antibiotics in the Beibu Gulf based on PCA-MLR and Unmix model. Risk assessment revealed that SMX, CIX could pose medium risks to algae in the Beibu Gulf. Overall, our results provided paramount insights into understanding the fate and transport behaviors of antibiotics in the subtropical marine environment.

First report of organochlorine pesticides (OCPs) in coral tissues and the surrounding air-seawater system from the South China Sea: Distribution, source, and environmental fate

The levels, fate, and potential sources of 22 organochlorine pesticides (OCPs) in coral tissues and the surrounding air-seawater system from the South China Sea (SCS) were elucidated for the first time. ∑₂₂OCPs (total concentration of 22 OCPs) (16.1-223 pg L^-1) was relatively higher in coastal seawater than in offshore seawater, which may be the widespread influence of coastal pollution inputs under the western boundary current. The atmospheric ∑₂₂OCPs were predominantly distributed in the gas phase (48.0-2264 pg m^-3) and were mainly influenced by continental air mass origins. The air-seawater exchange of selected OCPs showed that OCPs tended to migrate from the atmosphere to seawater. The distribution of ∑₂₂OCPs in coral tissues (0.02-52.2 ng g^-1 dw) was significantly correlated with that in air samples, suggesting that OCPs may have a migration pattern of atmosphere-ocean corals in the SCS. Corals exhibited higher bioaccumulation ability (Log BAFs: 2.42-7.41) for OCPs. Source analysis showed that the new application of technical Chlordanes (CHLs) was primarily responsible for the current levels of CHLs in the surrounding environment over the SCS, while historical residues were the primary sources of other OCPs.

Transport and dilution of fluvial antibiotic in the Upper Gulf of Thailand

A three-dimensional hydrodynamic-antibiotic model is developed to investigate the transport and dilution of sulfamethoxazole (SMX) in the Upper Gulf of Thailand (UGoT). The simulation produced a spatially averaged annual mean SMX concentration of 0.58 μgm^-3, which varied slightly between seasons assuming a temporally constant river SMX loading observed in August. In contrast, the horizontal distribution of SMX concentrations strongly varied with season because of the changing residual currents. In addition, SMX is diluted to concentrations lower than 10% of those in river waters a short distance offshore of the estuaries. To better understand this behavior, we examined the relationship between salinity and SMX concentrations in the UGoT. The annual budget demonstrates that 98% of SMX in the UGoT is removed by natural decomposition. As the concentrations of fluvial pollutants in the UGoT depend on their river loading and decomposition rates, functions were derived to predict pollutant concentrations and flushing times based on the river input flux and half-life.

Toxicity of disinfection byproducts formed during the chlorination of sulfamethoxazole, norfloxacin, and 17β-estradiol in the presence of bromide

Brominated disinfection byproducts (Br-DBPs) are formed during the disinfection process of water containing bromine ions, such as marine aquaculture water. Little attention has been paid to Br-DBPs with anthropogenic chemicals as precursors. This study summarized the sodium hypochlorite (NaClO) oxidation of three frequently used pharmaceuticals, including two antibiotics, norfloxacin (NOR) and sulfamethoxazole (SMX), and the growth hormone estrogen 17β-estradiol (E2). Transformations of the pharmaceuticals were found to be faster in marine aquaculture water than in distilled water. Several Br-DBPs and Cl-DBPs were identified for NOR, SMX, and E2. It was shown that the carboxyl group, piperazine ring, C3, and C8 atoms were the primary reaction sites on NOR. The aniline moiety and S-N bond were identified to be the reaction sites on SMX. The C2, C4, C9, and C16 atoms were the potential reaction centers on E2. Preliminary calculation by QSAR model indicated that the value of logKow significantly increased with an increase in the number of bromine atoms in the Br-DBPs. The results of the bioconcentration factors (BCF) analysis suggested that the bioaccumulation of Br-DBPs were greater than that chlorinated DBPs (Cl-DBPs) in distilled water.

Distribution, fate and sources of polycyclic aromatic hydrocarbons (PAHs) in atmosphere and surface water of multiple coral reef regions from the South China Sea: A case study in spring-summer

Our previous study revealed PAHs' wide occurrence in corals from multiple coral reef regions (CRRs) in the South China Sea. However, little is known about their occurrence, distribution, fate, and sources in the ambient environment of these CRRs. This study aimed to resolve these research gaps. The results showed ∑₁₅PAHs (total concentrations of 15 US EPA priority controlled PAHs exclude naphthalene) in the atmosphere (gas-phase: 0.31-49.6 ng m^-3; particle-phase: 2.6-649 pg m^-3) were mainly influenced by air mass origins. Southwesterly wind caused higher ∑₁₅PAHs than the southeasterly wind. The ∑₁₅PAHs in seawater from the nearshore (462 ± 244 ng L^-1) was higher than that from offshore Zhongsha Islands (80.5 ± 72.1 ng L^-1) because of the effect of terrigenous pollution and ocean current. Source apportionment indicated that the mixed sources of spilled oil and combustion from neighboring countries were the main contributors to PAHs in these CRRs. The total deposition fluxes showed that PAHs tended to migrate from the atmosphere to seawater. Global warming may inhibit this process, but PAHs still have a migration pattern of atmosphere-ocean-corals, which will further increase the environmental pressure on coral reef ecology.

Occurrence, distribution and seasonal variation of chlorinated paraffins in coral communities from South China Sea

Our previous study revealed bioaccumulation and trophic magnification of chlorinated paraffins (CPs) in marine organisms. However, little is known about the occurrence and distribution of CPs in coral reef ecosystems. In this study, the levels of short-chain chlorinated paraffins (SCCPs) and medium-chain chlorinated paraffins (MCCPs) were determined in ten common coral species from the coastal regions of Hainan Island, South China Sea. SCCPs and MCCPs were detected in all coral species in concentrations ranging from 184 to 7,410 and 305 to 14,800 ng g^-1 lw, respectively. In most of the coral species, congener group patterns of the SCCPs and MCCPs were dominated by C₁₀Cl_6-8 and C₁₄Cl_7-8, respectively. The CP levels and congener group patterns changed slightly between the dry and wet seasons. Redundancy analyses indicated that the accumulation patterns of CPs in different corals were partly influenced by Symbiodinium densities and coral species. Significant negative correlations were found between Symbiodinium densities and CP levels. This is the first report of CP exposure in reef corals and highlights the need for CP toxicity data to evaluate the health of coral reef ecosystems.

Uranium-thorium dating of coral mortality and community shift in a highly disturbed inshore reef (Weizhou Island, northern South China Sea)

Inshore coral habitats are at high risk of loss due to a combination of climate warming and regional-scale human impacts. As a result, they have undergone significant declines. Direct evidence of acute and chronic disturbance on most inshore coral assemblages is limited. Long-term, periodical surveys and historical baseline data essential for effective management are lacking. Using high-precision uranium-thorium (UTh) dating, we reconstruct a ~100-year-long history of extensive coral loss, changes in coral community structure, and a shifting baseline. The data were collected at Weizhou Island, northern South China Sea (SCS), which has highly disturbed inshore coral habitats that are typical globally. According to our UTh dates, major coral mortalities around Weizhou Island have occurred since the 1950s, with increasing frequency and severity since the 1980s. The extensive loss of branching Acropora and collapse of coral communities with peaks around 1960, 1984, and 1998 are accompanied by a shift toward low coral cover and noncoral-dominated assemblages. Prior to this collapse, the local coral community structure sustained remarkable long-term stability over millennia. The timing of the Acropora loss and massive coral mortalities coincides with multiple acute and chronic, natural and anthropogenic disturbance events. We suggest that priority should be given to directly addressing the causes of degradation and effectively controlling chronic disturbances before attempting to restore reef ecosystems. This is probably the only way to solve the "wicked problem" of sustaining the key functions and ecosystem services of inshore coral habitats such as those of Weizhou Island, northern SCS.

Maternal exposure to environmental antibiotic mixture during gravid period predicts gastrointestinal effects in zebrafish offspring

Due to overuse, misuse, and poor absorption during treatment, antibiotics are consistently released into the environment, raising concerns about their impacts on ecological sustainability and health. In this study we performed transcriptome profiling to assess potential reproductive effects of an antibiotic mixture in gravid female zebrafish. Gravid fish (150 dpf) were exposed to a mixture of 15 commonly detected antibiotics at 0, 1, and 100 μg/L for 4 weeks. Concentrations of all the 15 antibiotics, especially chlortetracycline, were detected in the F0 ovary and F1 eggs after treatment, indicating maternal transfer of antibiotics. Impaired F0 growth (average 2.2 % and 24.3 % inductions in body length and ovary weight, respectively), and reduced F1 offspring survival (average 4.2 % reductions in survival at 120 hpf) was observed after maternal exposure to the 100 μg/L treatment. Pathway analyses of whole-transcriptome expression profiles from F0 ovaries predicted colorectal disorders. Similarly, pathways of F1 larval transcriptomes from treated females also predicted colorectal disorders along with intestinal apoptosis and oxidative stress, which may be related to growth impairment. These results show that maternal transfer of antibiotics occurs in zebrafish, resulting in transgenerational changes in F1 offspring survival and transcription that predict adverse gastrointestinal effects in offspring.

Occurrence, fate, and mass balance of selected pharmaceutical and personal care products (PPCPs) in an urbanized river

The identification and quantification of pharmaceutical and personal care products (PPCPs) in aquatic ecosystems is critical to further studies and elucidation of their fate as well as the potential threats to aquatic ecology and human health. This study used mass balances to analyse the sources, transformation, and transport of PPCPs in rivers based on the population and consumption habits of residents, the removal level of sewage treatment, the persistence and partitioning mechanisms of PPCPs, hydrological conditions, and other natural factors. Our results suggested that in an urbanized river of Guangzhou City, China, the daily consumption of PPCPs was the main reason for the variety of species and concentrations of PPCPs. Through the determination of PPCPs in the river water samples and a central composite design (CCD) methodology, the dominant elimination mechanisms of caffeine and carbamazepine from river water were photolysis and biodegradation, but that of triclosan was sorption rather than biodegradation. The mass data of 3 PPCPs were estimated and corroborated using the measured data to evaluate the accuracy of the mass balance. Finally, caffeine, carbamazepine and triclosan discharged from the Shijing River into the Pearl River accounted for 97.81%, 99.52%, and 28.00%, respectively, of the total mass of these three compounds in the surface water of Shijing River. The results suggest that photolysis are the main process of natural attenuation for selected PPCPs in surface waters of river systems, and the transfer processes of PPCPs is mainly attributed to riverine advection. In addition, the low concentration of dissolved oxygen inhibited the degradation of PPCPs in the surface water of Shijing River.

Spatial and seasonal variations of antibiotics and antibiotic resistance genes and ecological risks in the coral reef regions adjacent to two typical islands in South China Sea

Although the occurrence of antibiotics and antibiotic resistance genes (ARGs) in aquatic environmental has been widely reported, the distribution and variations of these emerging contaminants in the coral reef regions remain unclear. This study investigated the occurrence of these contaminants, and their spatial and seasonal variations in both coral reef regions and non-coral reef regions adjacent to two typical islands in the South China Sea. Eighteen antibiotics and seven ARGs were detected in the surface water with total concentrations ranging from 43.2 to 441 ng/L, and 2.11 × 10⁴ to 8.00 × 10⁶ copies/L, respectively. Erythromycin-H₂O was the most dominant antibiotic in all samples. QnrD was dominant in the dry season, whereas sul1, sul2, and floR were the most abundant in the wet season, indicating obvious seasonal variations. The distribution of ARGs was mainly influenced by changes in salinity caused by anthropogenic activities in wet season.

Comparative study of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) in corals, sediments and seawater from coral reefs of Hainan, China

This work investigated levels of PAHs and HMs in fourteen species from seven genera of scleractinian corals, adjacent sediments, and surface seawater in Hainan, China. The sources of contaminations were analyzed as well. The results showed that scleractinian corals had a relatively higher bioaccumulation capacity for PAHs from sediments than for HMs. There were inter-species differences for these contaminants enriched in corals. Pavona varians and Porites lutea could accumulate PAHs more readily. While higher concentrations of Cr, Mn and Pb occurred in Favites flexuosa, other metal levels, such as for Ni, Cu, Zn and As, were found to be elevated in Pocillopora damicornis, as well as for Cd in Acropora echinata. It was found that PAHs originated from petrogenic and pyrolytic sources, and were mainly linked to onshore and on-sea activities, such as motorboats. Mn, Ni, As and Cd were from crustal materials or natural weathering, while Cr, Cu, Zn and Pb were non-crustal origin connecting with the use of anti-fouling boat paint and agricultural and/or aquacultural chemicals. This study suggested that corals could serve as good bioindicators for two types of chemical pollution in the reef system, especially for the two species P. varians and P. lutea for PAHs contaminants.

The incidence of antibiotic resistance within and beyond the agricultural ecosystem: A concern for public health

The agricultural ecosystem creates a platform for the development and dissemination of antimicrobial resistance, which is promoted by the indiscriminate use of antibiotics in the veterinary, agricultural, and medical sectors. This results in the selective pressure for the intrinsic and extrinsic development of the antimicrobial resistance phenomenon, especially within the aquaculture‐animal‐manure‐soil‐water‐plant nexus. The existence of antimicrobial resistance in the environment has been well documented in the literature. However, the possible transmission routes of antimicrobial agents, their resistance genes, and naturally selected antibiotic‐resistant bacteria within and between the various niches of the agricultural environment and humans remain poorly understood. This study, therefore, outlines an overview of the discovery and development of commonly used antibiotics; the timeline of resistance development; transmission routes of antimicrobial resistance in the agro‐ecosystem; detection methods of environmental antimicrobial resistance determinants; factors involved in the evolution and transmission of antibiotic resistance in the environment and the agro‐ecosystem; and possible ways to curtail the menace of antimicrobial resistance.

Antibiotic resistance genes and bacterial community dynamics in the seawater environment of Dapeng Cove, South China

In recent years, the propagation of antibiotic resistance genes (ARGs) and increased antibiotic resistance in pathogens have gained serious attention. Numerous reports have investigated the influence of domestic sewage discharge, medical wastewater and aquaculture wastewater on rivers and lakes, while the dynamics of ARGs in seawater and the relationships between ARGs, bacterial community structure and environmental factors have been less thoroughly described. In this study, the abundance, distribution and source of ARGs, as well as the relationships between ARGs, bacterial community changes and environmental factors in the seawater environment and sediment of Dapeng Cove, were investigated. Real-time quantitative PCR and Illumina Miseq sequencing technology were applied to determine the effects of the production cycle of cage culture, tourism and seasonality on ARGs. Chloramphenicol resistance genes (floR, cmlA) and sulfonamide resistance genes (sul1) were the dominant resistance genes in water and sediment. Pearson's correlation analysis showed that the abundance of all ARGs and the integrase I gene intI1 was positively correlated with chemical oxygen demand and suspended solids. Class 1 integrons might facilitate the dissemination of ARGs, and intI1 was detected in all samples at high concentrations. In aqueous environments, Cyanobacteria, Proteobacteria and Bacteroidetes were the dominant phyla, among which Proteobacteria and Bacteroidetes were positively correlated with the concentration of target ARGs. In the sediment, Proteobacteria, Bacteroidetes, Chloroflexi, Acidobacteria and Planctomycetes were the dominant phyla, among which Bacteroidetes and Planctomycetes were positively correlated with most of the target ARGs and had a significant influence on changes in the abundance of ARGs. The domestic sewage was the main source of ARGs in the seawater. Our results showed that bacterial community structure and environmental factors affected the distributional dynamics of ARGs. Anthropogenic activities played significant roles in promoting ARGs abundance in the seawater environments.

Spatial and temporal variations of antibiotics in a tidal river

Estuary is an important route for the transport of terrestrial contaminants to the ocean. Its unique hydrodynamic properties may influence the fate and distribution of pollutants. Previous studies have shown that severe pollution because of antibiotics has occurred in many inland surface waterbodies; however, the behavior of antibiotic residuals remains poorly understood in estuarine environments. In this study, the occurrence and spatiotemporal distribution of seven selected antibiotics (i.e., sulfamethazine, sulfamethoxazole, trimethoprim, ofloxacin, ciprofloxacin, erythromycin, and roxithromycin) in a tidal river were investigated through one continuous and four synoptic sampling events. Results show that the concentrations of most antibiotics are in the nanogram per liter level, except for trimethoprim with the highest concentration up to 12,440 ng L^-1 during the wet season. Except for sulfamethazine, the other six antibiotics showed high concentrations (i.e., > 100 ng L^-1) in at least one sampling campaign. Different temporal distribution patterns of these antibiotics indicated that they were mainly controlled by source loading, flow condition, and discharge amounts. Spatial distribution indicated that the main pollution source of trimethoprim was located in lower reaches, while the other six antibiotics mainly came from the upstream sources. Based on the theoretical dilution line, erythromycin and roxithromycin degraded in the tidal river, whereas the other five types of antibiotics showed a conservative behavior. Tide has important effects on the spatial distribution of antibiotics, especially those with a wide concentration range, in estuarine environments. Furthermore, risk assessment based on the calculated risk quotients showed that five types of antibiotics pose high risks to aquatic organisms. These observations provided new insight into the distribution and transport of common antibiotics in estuarine environments.

Latitudinal variation in reef coral tissue thickness in the South China Sea: Potential linkage with coral tolerance to environmental stress

Coral tissue thickness (CTT) is an effective indicator of the adaptability of corals to environmental stress, but the relationships between the spatial and intergeneric variation of coral tissue across latitudes and tolerance to environmental stress are not well understood. To investigate this, the CTT of 768 specimens of 10 typical coral genera and surrounding seawater parameters were measured in six coral reef regions (CRRs) across the 9-22°N latitudes in the South China Sea (SCS). Results showed significant differences in CTT between different genera of corals and CRRs. CTTs were significantly higher in the northern SCS than in the southern SCS. There was also notable intergeneric variation, with the abundance of branching Acropora and foliaceous Pavona being significantly lower than that of massive Porites, Galaxea, Favia, Favites, Hydnophora, Platygyra, and encrusting Montipora, Psammocora across these CRRs. Redundancy analysis showed that dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP), sea surface temperature (SST), turbidity, and transparency were the main factors affecting CTT. Overall CTT, irrespective of genus, was significantly positively correlated with DIN, SRP, and latitude, but was significantly negatively correlated with transparency and SST. Further analysis suggested that corals in the southern SCS are mainly threatened by thermal stress, whereas in the northern SCS, corals have often suffered from destructive anthropogenic disturbance. Although seawater conditions were normal during on-site investigation, a large number of branching corals (e.g., Acropora corals) have been lost in the last several decades due to destructive human activity. In contrast, massive and encrusting corals may have higher energy reserves and photo-protective capacities due to their thicker tissues, and consequently have higher tolerance to environmental stress. Therefore, the coral communities of the SCS have gradually been transformed from branching corals to massive/encrusting corals.

The treatment of veterinary antibiotics in swine wastewater by biodegradation and Fenton-like oxidation

Elevated concentrations and potential toxicities of antibiotics in swine wastewater prompt the exploration of effective treatment methods to minimize the amount of antibiotics released to the environment. This study examined the technical and economic feasibility of using combined biodegradation and advanced oxidation processes for swine wastewater treatment. The up-flow anaerobic sludge blanket (UASB) reactor was mainly responsible for conventional organic pollutant removal (i.e., a COD removal rate of 75%). The subsequent sequencing batch reactor (SBR) under a short sludge retention time (SRT) of 3 days removed the biodegradable antibiotics by >95%, and hindered the nitrification process which retained NH₄⁺-N and reduced operational cost (since the treated wastewater was intended to be used as a farm fertilizer). The subsequent Fenton-like oxidation (with the aid of citric acid) achieved an average antibiotic removal efficiency of 74% under optimal reaction conditions: H₂O₂ dosage of 2.9 mM, [Fe²⁺]: [H₂O₂] = 1:3, [CA]: [Fe²⁺] = 1:1, pH 6.0, reaction time of 120 min. The superior treatment efficiency of Fenton-like compared to the conventional Fenton (74% vs 5%) under nearly neutral conditions was attributed to the chelating role of citric acid with Fe²⁺/Fe³⁺, leading to the enhanced Fe²⁺/Fe³⁺ solubility and therefore the promotion of ∙OH formation. This hybrid process of anaerobic and aerobic biodegradation and Fenton-like oxidation should be suitable and cost-effective for the treatment of wastewater with abundant conventional pollutants and persistent emerging trace contaminants.

Antibiotics in coral reef fishes from the South China Sea: Occurrence, distribution, bioaccumulation, and dietary exposure risk to human

Coral reef fishes are about 10% of commercial fishes worldwide. Their pollution is close to human's health. Antibiotics are one group of emerging organic pollutants in the marine environment. However, little data is available on the bioaccumulation and dietary risks of antibiotics in coral reef fish from the South China Sea (SCS) or any other parts of the global coral reef environment. In this study, we examined 19 antibiotics in 18 species of coral reef fish collected from coastal and offshore regions in the SCS. The results revealed that 17 antibiotics were detected in the fishes. Their average concentrations ranged from 1.3 × 10^-5 to 7.9 × 10^-1 ng/g ww, which were at the lower end of the global range about antibiotic levels in fish. The average total antibiotic concentrations (∑₁₉ABs) were significantly higher in the offshore fish (1.2 ng/g ww) than in the coastal fish (0.16 ng/g ww). Different fish species or the protection of mucus produced by coastal fish at severe environmental stress may cause the differences. Fluoroquinolones (FQs) accounted for 89% and 74% of the average ∑₁₉ABs in the offshore and coastal fish, respectively. It may relate to their relative high aqueous solubility and adsorption ability to particles. The log BAFs (bioaccumulation factors) of the antibiotics ranged from -0.34 to 4.12. Norfloxacin, dehydrated erythromycin (DETM), and roxithromycin were bioaccumulative in some offshore fish samples with their log BAFs higher than 3.7. The results of trophic magnification factors (TMFs) demonstrated that DETM underwent significant trophic dilution while enoxacin underwent trophic magnification in the food web of coral reef fishes. The estimated daily intakes of antibiotics via fish consumption by China residents ranged from 2.0 × 10^-4 to 2.7 ng/kg weight body/day, which was 3 to 8 orders of magnitude lower than the respective acceptable daily intakes.

Polycyclic aromatic hydrocarbons (PAHs) in corals of the South China Sea: Occurrence, distribution, bioaccumulation, and considerable role of coral mucus

Coral reefs have suffered degradation from climate change and water quality deterioration. Studies have shown that PAHs are present widely in some coastal seawater and coral tissues. However, no studies have focused on the PAHs in coastal coral mucus and offshore coral tissues. Targeting the South China Sea, this study for the first time investigated the occurrence, tissue-mucus partitioning, and bioaccumulation of PAHs in coastal and offshore corals. The tissue and mucus of the corals were processed separately. The results indicated that the total concentration of 15 of the 16 PAHs that are prioritized by U.S. EPA (excluding naphthalene) (∑₁₅PAHs) was significantly higher in the coastal tissues (173 ± 314 ng g^-1 dw) than in the offshore tissues (71 ± 109 ng g^-1 dw), as well as in coastal seawater (196 ± 96 ng L^-1) than in the offshore water (54 ± 9 ng L^-1). ∑₁₅PAHs is two orders of magnitude higher in the mucus (3200 ± 6470 ng g^-1 dw) than in the tissues (128 ± 43 ng g^-1 dw). By average, 29% of ∑₁₅PAHs were accumulated in the mucus. The results suggest that mucus plays an important role in the bioaccumulation of PAHs by corals from ambient seawater.

Antibiotics in coastal water and sediments of the East China Sea: Distribution, ecological risk assessment and indicators screening

The distribution of 77 antibiotics in the coastal water and sediment from 3 bays of the East China Sea was investigated. There were 43 and 25 antibiotics detected with total concentrations of 30.8-2106.1 ng/L and 2.2-99.9 ng/g in water and sediment, respectively. Approximately 83.0% and 85.4% of the individual antibiotic concentrations were lower than 5.0 ng/L in water and 1.0 ng/g in sediment. Clindamycin (1.2-1507.9 ng/L, mean 183.8 ng/L) and erythromycin (ND-45.2 ng/g, mean 3.4 ng/g) were the most abundant in water and sediment, respectively. Ecological risk assessment revealed that the joint toxicity was enhanced when multiple antibiotics were present simultaneously. A decrease in the total antibiotic concentration and the ecological risk in water was observed from nearshore to offshore. Three antibiotics (sulfamethoxypyridazine, sulfamethoxazole and cinoxacin) were selected to be prioritized based on ecological risks for antibiotics monitoring and management of the coastal water in the East China Sea.

Effects of traditional Chinese medicines on immunity and culturable gut microflora to Oncorhynchus masou

The present study was conducted to evaluate the effect of dietary traditional Chinese medicines on the growth, immunity, and composition of culturable gut microflora in Oncorhynchus masou. Diets were formulated to contain no medicine (control), antitoxic decoction (A), general antiphlogistic decoction (B), or Herbae Artemisiae Capillariae decoction (C). Fish were manually fed twice daily till apparent satiation for 30 days. Compared with that in the control group, supplementation with the three kinds of Chinese herbal medicine enhanced fish growth significantly (P < 0.05). The activities of liver superoxide dismutase and glutathione peroxidase in the treatment groups were significantly higher compared with those in the control group (P < 0.05). The quantity of intestinal microflora was higher in the treatment groups compared with that in the control group. Moreover, there were some effects of dietary Chinese herbal medicine on the composition of intestinal microflora. Microflora of Pseudomonas sp., Psychrobacter sp., Microbacterium sp., Macrococcus sp., Burkholderia sp., and Arthrobacter sp. were found in the treatment groups, whereas there were none in the control group. There was a significant increase in their amounts in the treatment groups (P < 0.05). The three kinds of traditional Chinese medicines can improve the growth and immunity of Oncorhynchus masou and affect the quantity and composition of intestinal microflora.

Organochlorines in fish from the coastal coral reefs of Weizhou Island, south China sea: Levels, sources, and bioaccumulation

Eight fish species were sampled from a coastal coral reef ecosystem near Weizhou Island, South China Sea, to investigate the composition profiles and bioaccumulation of organochlorines (OCs). The total concentrations of 18 organochlorine pesticides (OCPs) and 22 polychlorinated biphenyls (PCBs) were found to be 26.5-452 ng/g lw and 0.87-19.8 ng/g lw, respectively. The contaminant distribution pattern indicated that agrochemical sources were more important than industrial sources, and that historical residues remain the primary source of OCs in Weizhou Island. Bioaccumulation factors (BAFs) indicated that dichlorodiphenyltrichloroethanes was bioaccumulating with log BAFs ranging from 3.53 to 5.21. Some congeners diverged from the general trend predicted by the logarithm octanol-water partition coefficient (log K_ow); this was mainly attributable to differences in the bioaccumulation potentials of these congeners in the studied samples. Trophic magnification factors demonstrated that aldrin, endrin, and dieldrin undergo significant trophic dilution, while the other six OC compounds undergo trophic magnification in the food chain. The presence of OCP congeners was also probably affected by their metabolism in fish tissues. The estimated daily intakes of OCPs via fish consumption by residents ranged from 0.05 to 5.45 ng/kg body weight/day, which is below the acceptable daily intake recommended by the FAO/WHO.

Occurrence and distribution of pharmaceutical compounds in the Danshuei River Estuary and the Northern Taiwan Strait

Ten pharmaceutically active compounds (PhACs) were determined in northern Taiwan estuarine waters and Taiwan Strait (TS) seawater. The ecological risk of these PhACs was assessed using risk quotient (RQ), which is the ratio of the measured maximum concentration to the predicted no-effect concentration. Six PhACs were detected within the estuarine waters. Caffeine concentration (130-718 ng l^-1) was the highest among the analyzed PhACs. The distribution of PhACs in the Danshuei River Estuary generally exhibited addition behavior, except that caffeine showed conservative behavior. Carbamazepine, gemfibrozil, caffeine, and ketoprofen were detected in TS seawaters. Their concentrations follow the sequence: gemfibrozil > ketoprofen > caffeine > carbamazepine. The caffeine concentrations in TS seawaters were 2-3 orders of magnitude lower than those in Danshuei estuarine waters. With few exceptions for caffeine, erythromycin, and sulfadiazine posing low risk in some estuarine waters, most of the RQ values were <0.01, suggesting no adverse effects on aquatic organisms.

Photocatalytic oxidation of norfloxacin by Zn0.9Fe0.1S supported on Ni-foam under visible light irradiation

Norfloxacin (NOR) is an emerging antibiotics contaminant due to its high resistance to microbial degradation and natural weathering. In this study, Fe-doped ZnS photocatalyst (Zn_0.9Fe_0.1S) was deposited on nickel foam (Ni-foam) to improve photocatalytic activity under visible light irradiation. The mass ratio of Zn_0.9Fe_0.1S and Ni-foam was optimized to be 0.03 g catalyst versus per g Ni-foam (0.03 Zn_0.9Fe_0.1S/Ni-foam), which led to the highest removal rate of 95%. The optimal degradation condition for NOR over 0.03 Zn_0.9Fe_0.1S/Ni-foam was pH at 7.0, initial NOR concentration of 5 mg L^-1, and initial photocatalyst concentration of 11.7 g L^-1, with the highest first-order reaction rate constant of 0.025 min^-1 and mineralization rate of 63.1%. The NOR removal rate on 0.03 Zn_0.9Fe_0.1S/Ni-foam photocatalyst (95%) was approximately four times of that obtained on Zn_0.9Fe_0.1S photocatalyst (25%). The increased photocatalytic performance could be attributed to the function of Ni-foam as excellent electron collectors that provided efficient photoinduced charge separation from Zn_0.9Fe_0.1S. The reactive species responsible for the degradation of NOR were photo-generated holes, hydroxyl radical, and superoxide radicals. Nearly 90% of the photocatalytic efficiency was retained over seven cycles and the released metal ion concentrations were <0.3% of the total mass of photocatalyst, suggesting high stability of the photocatalyst during the photocatalytic reactions. The aqueous/solid mass transfer and intraparticle mass transfer for Zn_0.9Fe_0.1S/Ni-foam were not limiting factors for the degradation of NOR. Therefore the Zn_0.9Fe_0.1S/Ni-foam photocatalyst could be applied in the degradation of hazardous pollutants.

Antibiotics in corals of the South China Sea: Occurrence, distribution, bioaccumulation, and considerable role of coral mucus

Manmade antibiotics are emerging organic pollutants widely detected in the marine environment. In this study, 14 out of 19 target antibiotics were detected in corals collected from coastal and offshore regions in the South China Sea. The average total antibiotic concentrations (∑₁₉ABs) in the two regions were similar: 28 ng/g for coastal corals and 31 ng/g for offshore corals, based on dry tissue weight (dw). Fluoroquinolones (FQs) were predominant antibiotics in the coastal corals (mean ∑FQs: 18 ng/g dw), while sulfonamides (SAs) predominated in the offshore corals (mean ∑SAs: 23 ng/g dw). However, corals living in coastal regions tend to excrete more mucus than corals in offshore habitat. We found 53% by average of ∑₁₉ABs in the mucus of the coastal corals; while in offshore corals, most antibiotics (88% by average) were accumulated in the tissues. In addition, the tissue-mucus mass distribution differs among individual antibiotics. Sulfonamides were mainly accumulated in tissues while fluoroquinolones were present mainly in mucus. The results of this study suggest that mucus played an important role in the bioaccumulation of antibiotics by corals. It may resist the bioaccumulation of antibiotics by coral tissue, especially for the coastal corals. Additionally, corals were compared with other marine biotas in the study area and found to be more bioaccumulative towards antibiotics.

Radioactive level of coral reefs in the South China Sea

In this study, we examined radioactivity simultaneously in surface marine sediments and coral skeletons collected from 12 locations of the fringing and atoll reefs in the South China Sea. Radioactive level declined from the fringing reefs to atoll reefs because of input of terrigenous minerals in the fringing reefs. Radioactivity was higher in coral skeletons than in marine sediments because of the high ²²⁸Ra activity in coral skeletons. Additionally, an abnormally low ²²⁶Ra/²³⁸U activity ratio (<0.1) of marine sediments in coral reefs was attributed to the biological process of active uptake of ²²⁶Ra and ²³⁸U from seawater by coral polyps rather than the ingrowth process in the ²³⁸U-²³⁰Th-²²⁶Ra decay chain. Several radiological indices were evaluated in coral reefs and significantly lower than recommended values. Particularly, the average Ra_eq in the atoll reefs was <5% of the world's average of Ra_eq. Our results displayed typically radioactive status in coral reefs without close-in fallout of anthropogenic radionuclides.

The presence of in situ sulphamethoxazole degraders and their interactions with other microbes in activated sludge as revealed by DNA stable isotope probing and molecular ecological network analysis

Wastewater treatment plants (WWTPs) are the main hotspots for the release of antibiotics, including the widely used sulphonamides. Microbes play important roles in eliminating sulphonamides in WWTPs, and knowledge about these degraders and their interactions within the microbial community is crucial for operating and optimising WWTPs. In the present study, stable isotope probing (SIP) coupled with high-throughput sequencing as culture-independent approach revealed four operational taxonomic units (OTUs) involved in sulphamethoxazole (SMX) degradation in activated sludge. Except for the OTU affiliated with Gammaproteobacteria, the others have not been previously reported to possess the ability to metabolise SMX. The isolated SMX degrader by culture-dependent method did not participate in SMX biodegradation in situ according to the SIP analysis, and showed weak correlations with other members in the activated sludge. The complex interactions between in situ active SMX degraders and non-degrading microbes might explain our failure to isolate these degraders. In addition, sul1 genes associated with SMX resistance were also labelled with ¹³C, suggesting that they might benefit from SMX degradation and/or originate from the active SMX degraders. These findings broaden our understanding of the diversity of SMX-degrading microbes and their associated characteristics in WWTPs.

The occurrence, distribution and degradation of antibiotics by ionizing radiation: An overview

Antibiotics have been extensively applied, making them ubiquitous in aquatic environment. As emerging contaminants, the occurrence and distribution of antibiotics in the environment has received increasing attention due to their potential adverse effects on human health and ecosystem. However, antibiotics cannot be effectively removed in conventional biological treatment processes, and their natural biodegradation is also ineffective. In this review, the occurrence and distribution of antibiotics in aquatic environments, including surface water, wastewater and effluent of wastewater treatment plants, were analyzed and summarized. Recent progress of antibiotics degradation by ionizing radiation was reviewed. The various influencing factors, such as absorbed dose, initial concentration, inorganic anions and organic matters, on the removal efficiency of antibiotics were introduced and discussed. To improve their removal efficiency, several advanced oxidation processes (AOPs) such as H₂O₂, Fe²⁺, Fe²⁺/H₂O₂, as well as biological treatment processes, are combined with ionizing radiation. Some suggestions for future studies of antibiotics degradation by ionizing radiation were proposed. Ionizing radiation may be a promising technology for removal of antibiotics from water and wastewater.

Occurrence, spatial distribution, and seasonal variation of emerging trace organic pollutants in source water for Shanghai, China

The long-term low concentrations of trace "contaminants of emerging concern" (CECs) can have potential toxic effects on human health and serious risks to the ecological environment. This study investigated the occurrence, spatial distributions, and seasonal variations of 65 target CECs, including 35 pesticides, 17 antibiotics, 7 microcystins, 5 estrogens, and 1 plasticizers in Shanghai's source water. The detected pesticides and antibiotics of sulfonamides and macrolides were relatively ubiquitous in source water of Shanghai, with levels decreasing in the following order: pesticides (average (avg.) 0.0003-1.67 μg/L) > antibiotics (avg. 0.1-14.1 ng/L). While microcystins, estrogens, and plasticizers (ng/L) were non-ubiquitous, with detected species of below 50%, and detection frequencies of mostly below 50%. Pesticide concentrations did not show obvious variations in the water from the inlets of the two rivers. Compare to all other water sources of Shanghai, the much higher concentrations of antibiotics found in the Y3, H2 reservoir and H3 were mainly from roxithromycin and sulfapyridine, roxithromycin and sulfadiazine, and sulfamethazine and roxithromycin, which accounted for 69.5%, 88.1% and 70.8% of the total concentration in corresponding water source, respectively. Pesticide concentrations in the Huangpu River were higher in the wet season than in the flat season, while the concentration decreased in the Yangtze River during the wet season. In Y1, Y3 and Y4, there were relatively large differences in pesticide levels in the wet season, and flat season when the maximal contribution of the pesticide concentration was from acephate, which accounted for about 67% of the total pesticide concentration. The levels of antibiotics in the flat season were higher than those in the wet season in both water sources. Overall, improvement of raw water quality was observed after entering the reservoir except for microcystin.