Sublethal effects of the antibiotic tylosin on estuarine benthic microalgal communities

Effect of cage culture on sedimentary heavy metal and water nutrient pollution: Case study in Sansha Bay, China

The aquaculture area in China's coastal waters has increased rapidly from 6000 km2 in 1990 to 22,000 km2 in 2020. Despite extensive research regarding the effect of coastal aquaculture on water and sediment pollution, evaluating the quantitative relationship between aquaculture and pollutants remains challenging. Sansha Bay, the world's largest cage aquaculture base for Pseudosciaena crocea, is a typical enclosed bay used for investigating aquaculture pollution. A cage culture database is established from 2000 to 2020 in Sansha Bay. Meanwhile, 236 sediment samples from 3 sediment cores and 67 water samples from 4 transects are obtained from the bay for experiments. The main indicators are five nutrients (NO3-, SiO32-, PO43-, NH4+, and NO2-) in the water samples, the grain size, the heavy metal (Zn, Cu, Pb, Cr, Cd, and As) content, and the 210Pb radioactivity in sediment samples. Based on data obtained and a new calculation method, the annual increment in Zn, Cu, As, Cd, Pb, and Cr contents in the cultured zone is shown to increase by 2137 %, 1881 %, 506 %, 300 %, 202 %, and 118 % in 2000-2018, respectively, as compared with the levels in a noncultured zone. The activities of the cage culture increased NO3- by 9 %, PO43- by 30 %, NH4+ by 115 %, and NO2- by 232 %, compared with natural conservative mixing processes, such as the mixing of SiO32-, in 2020. A novel quantitative approach with broad applicability is proposed to evaluate the magnitude of anthropogenically induced environmental contamination. The effectiveness of the proposed technique is demonstrated through a case study conducted in Sansha Bay, China.

Degradation of Azithromycin from aqueous solution using Chlorine-ferrous- oxidation: ANN-GA modeling and Daphnia magna biotoxicity test assessment

Azithromycin (AZM), an antibacterial considered one of the most consumed drugs, especially during the period against the Covid 19 pandemic, and it is one of the persistent contaminants that can be released into aquatic ecosystems. The purpose of this study is to determine the efficacy of a Fenton-like process (chlorine/iron) for the degradation of AZM in an aqueous medium by determining the impact of several factors (the initial concentration of (FeSO₄, NaClO, pollutant), and the initial pH) on the degradation rate. The Response Surface Methodology (RSM) based on the Box-Wilson design as well as the Artificial Neural Network (ANN) modeling combined with a genetic algorithm (GA) approaches were used to determine the optimal levels of the selected variables and the optimal rate of degradation. The quadratic model of multi-linear regression developed indicated that the optimal conditions were a concentration of chlorine of 600 μM, the concentration of AZM is 32.8 mg/L, the mass of the catalyst FeSO₄ is 3.5 mg and a pH of 2.5, these optimal values gave a predicted and experimental yield of 64.05% and 70% respectively, the lack of fit test in RSM modeling (F₀ = 3.31 which is inferior to Fcritic (0.05, 10.4) = 5.96) indicates that the true regression function is not linear therefore, the ANN-GA modeling as non-linear regression indicated that the optimal conditions were a concentration of chlorine of 256 μM, the concentration of AZM is 5 mg/L, the mass of the catalyst FeSO₄ is 9.5 mg and a pH of 2.8, these optimal values gave a predicted and experimental yield of 79.69% and close to 80% respectively, Furthermore, biotoxicity tests were conducted to confirm the performance of our process using bio-indicators called daphnia (Daphnia magna), which demonstrated the efficacy of the like-Fenton process after 4 h of degradation.

Occurrence of antibiotics in waters, removal by microalgae-based systems, and their toxicological effects: A review

Global antibiotics consumption has been on the rise, leading to increased antibiotics release into the environment, which threatens public health by selecting for antibiotic resistant bacteria and resistance genes, and may endanger the entire ecosystem by impairing primary production. Conventional bacteria-based treatment methods are only moderately effective in antibiotics removal, while abiotic approaches such as advanced oxidation and adsorption are costly and energy/chemical intensive, and may cause secondary pollution. Considered as a promising alternative, microalgae-based technology requires no extra chemical addition, and can realize tremendous CO₂ mitigation accompanying growth related pollutants removal. Previous studies on microalgae-based antibiotics removal, however, focused more on the removal performances than on the removal mechanisms, and few studies have concerned the toxicity of antibiotics to microalgae during the treatment process. Yet understanding the removal mechanisms can be of great help for targeted microalgae-based antibiotics removal performances improvement. Moreover, most of the removal and toxicity studies were carried out using environment-irrelevant high concentrations of antibiotics, leading to reduced guidance for real-world situations. Integrating the two research fields can be helpful for both improving antibiotics removal and avoiding toxicological effects to primary producers by the residual pollutants. This study, therefore, aims to build a link connecting the occurrence of antibiotics in the aquatic environment, the removal of antibiotics by microalgae-based processes, and the toxicity of antibiotics to microalgae. Distribution of various categories of antibiotics in different water environments were summarized, together with the antibiotics removal mechanisms and performances in microalgae-based systems, and the toxicological mechanisms and toxicity of antibiotics to microalgae after either short-term or long-term exposure. Current research gaps and future prospects were also analyzed. The review could provide much valuable information to the related fields, and provoke interesting thoughts on integrating microalgae-based antibiotics removal research and toxicity research on the basis of environmentally relevant concentrations.

Specific toxicity of azithromycin to the freshwater microalga Raphidocelis subcapitata

Pharmaceuticals are produced to inflict a specific physiological response in organisms. However, as only partially metabolized after administration, these types of compounds can also originate harmful side effects to non-target organisms. Additionally, there is still a lack of knowledge on the toxicological effects of legacy pharmaceuticals such as the antibiotic azithromycin. This macrolide occurs at high concentrations in the aquatic environment and can constitute a threat to aquatic organisms that are at the basis of the aquatic food chain, namely microalgae. This study established a high-throughput methodology to study the toxicity of azithromycin to the freshwater microalga Raphidocelis subcapitata. Flow cytometry and pulse amplitude modulated (PAM) fluorometry were used as screening tools. General toxicity was shown by effects in growth rate, cell size, cell complexity, cell viability and cell cycle. More specific outcomes were indicated by the analysis of mitochondrial and cytoplasmatic membrane potentials, DNA content, formation of ROS and LPO, natural pigments content and photosystem II performance. The specific mode of action (MoA) of azithromycin to crucial components of microalgae cells was revealed. Azithromycin had a negative impact on the regulation of energy dissipation at the PSII centers, along with an insufficient protection by the regulatory mechanisms leading to photodamage. The blockage of photosynthetic electrons led to ROS formation and consequent oxidative damage, affecting membranes and DNA. Overall, the used methodology exhibited its high potential for detecting the toxic MoA of compounds in microalgae and should be considered for future risk assessment of pharmaceuticals.

Tylosin toxicity in the alga Raphidocelis subcapitata revealed by integrated analyses of transcriptome and metabolome: Photosynthesis and DNA replication-coupled repair

Tylosin (TYN) is widely used in veterinary prophylactic as a macrolide and frequently detected in the surface water. Previous studies showed that exposure to TYN caused suppression of chlorophyll biosynthesis and inhibition of photosynthesis at the physiological level, associated with reduced growth performances in algae, but the molecular mechanisms remain unknown, especially at environmental exposure levels. The present study elucidated the underlying molecular mechanism(s) of TYN toxicity in a model green alga Raphidocelis subcapitata using approaches of transcriptomics and metabolomics. Following a 7-day exposure, algal growth performances were reduced by 26.3% and 58.3% in the 3 (an environmentally realistic level) and 400 μg L^-1 TYN treatment group, respectively. A total of 577 (99) and 5438 (180) differentially expressed genes (differentially accumulated metabolites) were identified in algae treated with 3 and 400 μg L^-1 TYN, respectively. Signaling pathways including photosynthesis - antenna protein, porphyrin and chlorophyll metabolism, carbon fixation in photosynthetic organisms, and DNA replication were altered in the 400 μg L^-1 TYN treatment, while photosynthesis and DNA replication were the shared pathways in both TYN treatments. The metabolomic data further suggest that molecular pathways related to photosynthesis, DNA replication-coupled repair and energy metabolism were impaired. Photosynthesis was identified as the most sensitive target of TYN toxicity in R. subcapitata, in contrast to protein synthesis inhibition caused by TYN in bacteria. This study provides novel mechanistic information of TYN toxicity in R. subcapitata.

The link between pharmaceuticals and cyanobacteria: a review regarding ecotoxicological, ecological, and sanitary aspects

Cyanobacteria are important for ecosystem functioning, but eutrophication may affect the surrounding biome by losing ecosystem services and/or through affecting the cyanotoxins production that threatens ecological and human health. Pollution is an environmental issue that affects aquatic ecosystems worldwide, and the knowledge of the role of synthetic chemicals such as pharmaceuticals is still scarce. Therefore, studies coupling these two relevant issues are essential to better understand the ecological risks and the potential threats to public health. Thus, an overview of ecotoxicological tests performed in the literature exposing cyanobacteria to pharmaceuticals and the possible consequences regarding ecological and sanitary aspects was conducted. Moreover, a risk assessment was performed to enable a better understanding of pharmaceuticals affecting cyanobacteria ecology. Most of the studies found in the literature tested isolated pharmaceuticals in laboratory conditions, while others assessed mixture effects on in situ conditions. The endpoints most assessed were growth, photosynthesis, and antioxidant enzyme activity. The studies also point out that cyanobacteria may present resistance or sensitivity depending on the concentrations and the therapeutic class, which may cause a change in the ecosystem dynamics and/or sanitary implications due to cyanotoxin production. The risk assessment highlighted that antibiotics are among the most relevant substances due to the chemical diversity and higher levels found in the environment than other therapeutic classes. This review highlighted gaps regarding cyanotoxin release into aquatic environments due to the occurrence of pharmaceuticals and the need for more realistic experiments to better understand the potential consequences for human and environmental health.

Removal of pharmaceutical and personal care products (PPCPs) from waterbody using a revolving algal biofilm (RAB) reactor

The occurrence of Pharmaceutical and Personal Care Products (PPCPs) in the aquatic environment has raised concerns due to their accumulation in the ecosystem. This study aims to explore the feasibility of using a Revolving Algal Biofilm (RAB) reactor for PPCPs removal from waterbody. Five model PPCP compounds including ibuprofen, oxybenzone, triclosan, bisphenol A and N, N-diethyl-3-methylbenzamide (DEET) were mixed and added to the culture medium. It shows that PPCP removal efficiencies of the RAB reactor ranged from 70% to 100%. The degradation of PPCPs by the RAB reactor contributed > 90% PPCP removal while < 10% PPCPs removal was due to accumulation in the algal biomass. The nutrients removal performance of the RAB reactor was not affected by exposing to the PPCPs. The extracellular polysaccharides content of the biomass increased when exposing to PPCPs, while the extracellular proteins content remained constant. The Chl a content maintained constant in the PPCPs-treated biomass, but decreased in the biomass without PPCP treatment. It was also found that the microbial consortium of the RAB reactor was enriched with PPCPs degradation microorganisms with the progressing of feeding PPCPs. Collectively, this work demonstrates that the RAB system is a promising technology for removing PPCPs from wastewater.

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.

Benthic Diatom Communities in an Alpine River Impacted by Waste Water Treatment Effluents as Revealed Using DNA Metabarcoding

Freshwater ecosystems are continuously affected by anthropogenic pressure. One of the main sources of contamination comes from wastewater treatment plant (WWTP) effluents that contain wide range of micro- and macropollutants. Chemical composition, toxicity levels and impact of treated effluents (TEs) on the recipient aquatic ecosystems may strongly differ depending on the wastewater origin. Compared to urban TEs, hospital ones may contain more active pharmaceutical substances. Benthic diatoms are relevant ecological indicators because of their high species and ecological diversity and rapid response to human pressure. They are routinely used for water quality monitoring. However, there is a knowledge gap on diatom communities’ development and behavior in treated wastewater in relation to prevailing micro- and macropollutants. In this study, we aim to (1) investigate the response of diatom communities to urban and hospital TEs, and (2) evaluate TEs effect on communities in the recipient river. Environmental biofilms were colonized in TEs and the recipient river up- and downstream from the WWTP output to study benthic diatoms using DNA metabarcoding combined with high-throughput sequencing (HTS). In parallel, concentrations of nutrients, pharmaceuticals and seasonal conditions were recorded. Diatom metabarcoding showed that benthic communities differed strongly in their diversity and structure depending on the habitat. TE sites were generally dominated by few genera with polysaprobic preferences belonging to the motile guild, while river sites favored diverse communities from oligotrophic and oligosaprobic groups. Seasonal changes were visible to lower extent. To categorize parameters important for diatom changes we performed redundancy analysis which suggested that communities within TE sites were associated to higher concentrations of beta-blockers and non-steroidal anti-inflammatory drugs in urban effluents vs. antibiotics and orthophosphate in hospital effluents. Furthermore, indicator species analysis showed that 27% of OTUs detected in river downstream communities were indicator for urban or hospital TE sites and were absent in the river upstream. Finally, biological diatom index (BDI) calculated to evaluate the ecological status of the recipient river suggested water quality decrease linked to the release of TEs. Thus, in-depth assessment of diatom community composition using DNA metabarcoding is proposed as a promising technique to highlight the disturbing effect of pollutants in Alpine rivers.

Effects of environmentally-relevant antibiotic mixtures on marine microalgal growth

As of 2008, approximately 48% of Americans use prescription drugs within any given 30-day period. Many pharmaceutical compounds are not fully metabolized by the human body, nor fully removed by wastewater treatment systems, before release into the environment. As a result, a vast array of pharmaceuticals has been detected in marine and freshwater organisms, sediments, and waters, with unintended effects on non-target organisms, and limited studies of environmental effects. The antibiotics sulfamethoxazole (SMX), and trimethoprim (TRI), often prescribed together to treat bacterial infections, have been detected worldwide in marine and estuarine environments at concentrations up to 765-870ng/L each. Little research has examined sub-lethal effects of antibiotic mixtures at environmentally-relevant concentrations on marine organisms. We examined the effects of mixtures of these two antibiotics on three marine microalgal species with wide geographic ranges: Isochrysis galbana, Chaetoceros neogracile, and Nannochloropsis oculata. In separate simulations using a temperature/light-controlled set-up, we measured the growth response for each species to environmentally-relevant levels of SMX and TRI. N. oculata growth was significantly reduced by mixture treatments of both drugs (p<0.05), by TRI (p<0.001), and by SMX (p<0.001), whereas only aggregated SMX levels significantly reduced growth for the other two species (p<0.005). The exposure time at which growth rates were affected varied across species, with significant reduction in growth focused in the latter half of the experimental period for C. neogracile and N. oculata (Days 15 and 6 respectively), and midway through the experimental period for I. galbana (by Day 3). This study finds that important marine primary producers respond to the presence of SMX and TRI in the water, offering an understanding of environmental consequences of anthropogenic pharmaceuticals contaminants, and specifically the suite of antibiotics, that are released into marine ecosystems at an ever-growing rate, and highlighting potential cascading effects through trophic levels.

Selected pharmaceuticals entering an estuary: Concentrations, temporal trends, partitioning, and fluxes

In many coastal watersheds and ecosystems, rivers discharging to estuaries receive waters from domestic wastewater-treatment plants resulting in the release and distribution of pharmaceuticals to the marine environment. In the present study, 15 active pharmaceutical ingredients were measured regularly over 1 yr in the dissolved and particulate phases as they entered Narragansett Bay from the Pawtuxet River in Cranston (Rhode Island, USA). Of the active pharmaceutical ingredients measured, 14 were consistently present in the dissolved phase, with concentrations ranging from below detection to >310 ng/L, whereas 8 were present in the particulate phase (0.2-18 ng/g). Partition coefficients (K_d s and K_OC s) were determined, and organic carbon normalization reduced variability associated with K_d s for the active pharmaceutical ingredients evaluated. Flux estimates based on river flow were calculated for both dissolved and particulate-phase active pharmaceutical ingredients, with particulate fluxes being low (1-12 g/yr) and dissolved fluxes of active pharmaceutical ingredients being 155 g/yr to 11 600 g/yr. Results indicate that the pharmaceuticals measured in the present study reside primarily in the dissolved phase and thus are likely bioavailable on entering the estuarine waters of Narragansett Bay. This long-term temporal study provides important information on seasonal and annual dynamics of pharmaceuticals in an urban estuarine watershed. Environ Toxicol Chem 2016;35:2665-2673. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US Government work and, as such, is in the public domain in the United States of America.

Ecotoxicological assessment of antibiotics: A call for improved consideration of microorganisms

Antibiotics play a pivotal role in the management of infectious disease in humans, companion animals, livestock, and aquaculture operations at a global scale. Antibiotics are produced, consumed, and released into the environment at an unprecedented scale causing concern that the presence of antibiotic residues may adversely impact aquatic and terrestrial ecosystems. Here we critically review the ecotoxicological assessment of antibiotics as related to environmental risk assessment (ERA). We initially discuss the need for more specific protection goals based on the ecosystem service concept, and suggest that the ERA of antibiotics, through the application of a mode of toxic action approach, should make more use of ecotoxicological endpoints targeting microorganisms (especially bacteria) and microbial communities. Key ecosystem services provided by microorganisms and associated ecosystem service-providing units (e.g. taxa or functional groups) are identified. Approaches currently available for elucidating ecotoxicological effects on microorganisms are reviewed in detail and we conclude that microbial community-based tests should be used to complement single-species tests to offer more targeted protection of key ecosystem services. Specifically, we propose that ecotoxicological tests should not only assess microbial community function, but also microbial diversity (‘species’ richness) and antibiotic susceptibility. Promising areas for future basic and applied research of relevance to ERA are highlighted throughout the text. In this regard, the most fundamental knowledge gaps probably relate to our rudimentary understanding of the ecological roles of antibiotics in nature and possible adverse effects of environmental pollution with subinhibitory levels of antibiotics.

Sources, impacts and trends of pharmaceuticals in the marine and coastal environment

There has been a significant investment in research to define exposures and potential hazards of pharmaceuticals in freshwater and terrestrial ecosystems. A substantial number of integrated environmental risk assessments have been developed in Europe, North America and many other regions for these situations. In contrast, comparatively few empirical studies have been conducted for human and veterinary pharmaceuticals that are likely to enter coastal and marine ecosystems. This is a critical knowledge gap given the significant increase in coastal human populations around the globe and the growth of coastal megacities, together with the increasing importance of coastal aquaculture around the world. There is increasing evidence that pharmaceuticals are present and are impacting on marine and coastal environments. This paper reviews the sources, impacts and concentrations of pharmaceuticals in marine and coastal environments to identify knowledge gaps and suggests focused case studies as a priority for future research.

Geochronologies of pharmaceuticals in a sewage-impacted estuarine urban setting (Jamaica Bay, New York)

Pharmaceuticals are active substances found in sewage effluents and can negatively impact aquatic systems even at low concentrations. A fraction of these chemicals can be attached onto suspended solids and end up in sediments. This research shows concentrations of a wide group of pharmaceuticals in sediments from an urban estuarine setting (Jamaica Bay, New York). Highest concentrations (>75 ng g(-1)) were measured in surface sediments from the inner part of the bay, directly affected by sewage discharges and where water circulation is more restricted. Only 16 out of 61 target compounds were detected, and those positively charged (e.g., metoprolol) and/or highly hydrophobic (e.g., tamoxifen) were predominant. Their sediment-pore water partition coefficients were also calculated for the first time and were in a range between 11 and 2041 L/kg depending on the compound. Analysis of dated sediment cores revealed that pharmaceuticals were well preserved along the sedimentary column, a highly reducing environment. There was an increase in the concentration of most target compounds over the last five decades correlated with the increase in their usage, with some exceptions such as sulfamethazine (now used only for veterinary purposes). Thus, overall concentration of pharmaceuticals in sediment cores showed a doubling time of 9.2 years. Vertical distribution profiles for selected compounds also allowed reconstructing the history of contamination at Jamaica Bay by pharmaceuticals. The use of some of these chemicals as sewage molecular markers was also investigated.

Occurrence, distribution and partitioning of nonionic surfactants and pharmaceuticals in the urbanized Long Island Sound Estuary (NY)

This work deals with the environmental distribution of nonionic surfactants (nonylphenol and alcohol ethoxylates), their metabolites (NP, nonylphenol; NPEC, nonylphenol ethoxycarboxylates; and PEG, polyethylene glycols) and a selection of 64 pharmaceuticals in the Long Island Sound (LIS) Estuary which receives important sewage discharges from New York City (NYC). Most target compounds were efficiently removed (>95%) in one wastewater treatment plant monitored, with the exception of NPEC and some specific drugs (e.g., hydrochlorothiazide). Concentrations of surfactants (1.4-4.5 μg L(-1)) and pharmaceuticals (0.1-0.3 μg L(-1)) in seawater were influenced by tides and sampling depth, consistent with salinity differences. Surfactants levels in suspended solids samples were higher than 1 μg g(-1), whereas only most hydrophobic or positively charged pharmaceuticals could be found (e.g., tamoxifen, clarithromycin). Maximum levels of target compounds in LIS sediments (PEG at highest concentrations, 2.8 μg g(-1)) were measured nearest NYC, sharply decreasing with distance from major sewage inputs.