Species In Aquatic Environments Research Articles

Exposure to the insecticide, imidacloprid, impairs predator-recognition learning in damselfly larvae

Many aquatic organisms use chemosensory information to learn about local predation threats, but contaminants in their environment may impair such cognitive processes. Neonicotinoids are a class of water-soluble systemic insecticides that have become a major concern in aquatic systems. In this study, we explored how a 10-day exposure to various concentrations (0, 0.1, 1.0, or 10.0 μg/L) of the neonicotinoid imidacloprid affects the learned recognition of predator odour by non-target damselfly larvae (Lestes spp). Unexposed larvae and those exposed to the low concentration (0.1 μg/L) demonstrated an appropriate learned response to a novel predator odour following a conditioning with the odour paired with chemical alarm cues. However, such learning failed to occur for larvae that were exposed to imidacloprid concentrations of 1.0 and 10.0 μg/L. Thus, either the cognitive processing of the chemical information was impaired or the chemistry of one or both of the conditioning cues was altered, making them ineffective for learning. In a second experiment, we found evidence for this latter hypothesis. In the absence of background imidacloprid exposure, larvae did not show significant learned responses to the predator odour when the conditioning cues were mixed with imidacloprid (initial pulse solution of 3.0 μg/L) at the start of conditioning (reaching a final concentration of 0.01 μg/L). These findings indicate that even low levels of imidacloprid can have important implications for chemosensory cognition of non-target species in aquatic environments.

Considerations for future quantitative structure-activity relationship (QSAR) modelling for heavy metals – A case study of mercury

With increasing annual chemical development and production, safety testing demands and requirements have also increased. In addition to traditional animal testing, quantitative structure-activity relationship (QSAR) modelling can be used to predict the biological effect of a chemical structure, based on the analysis of quantitative characteristics of structure features. Whilst suitable for e.g., pharmaceuticals, other compounds can be more challenging to model. The naturally occurring heavy metal mercury speciates in the environment, with some toxic species accumulating in aquatic organisms. Although this is well known, only little data is available from (eco)toxicological studies, none of which account for this speciation behaviour. The present work highlights the current toxicity data for mercury in aquatic animals and gaps in our understanding and data for future QSAR modelling. All publicly available ecotoxicology data was obtained from databases and literature. Only few studies could be determined that assessed mercury toxicity in aquatic species. Of these, likely speciation products were determined using PHREEQc. This highlighted that the mercury exposure species was not always the predominant species in the medium. Finally, the descriptors for the modelled species were obtained from ChemDes, highlighting the limited availability of such details. Additional testing is required, accounting for speciation and biological interactions, to successfully determine the toxicity profile of different mercury species in aquatic environments. In the present work, insufficient mercury-species specific data was obtained, to conduct QSAR modelling successfully. This highlights a significant lack of data, for a heavy metal with potentially fatal repercussions.

Critical temperatures and aerobic metabolism in post-larvae of Pacific white shrimp Litopenaeus vannamei (Boone, 1931).

Increasing water temperature because of climate change decreases the oxygen concentration while increasing the oxygen requirement of species in aquatic environments. Temperature is one of the most important environmental factors affecting the physiological functions of organisms, especially poikilothermic animals, such as shrimp at all levels. In intensive shrimp culture, it is of great importance to know the tolerable temperature range of cultured species and their metabolism since this affects the physiological condition. In this study, critical temperatures (CTM: CTmin and CTmax) of Pacific white shrimp, Litopenaeus vannamei, post-larvae (PL), were determined at different acclimation temperatures of 15, 20, 25, and 30°C. Lower and upper incipient lethal temperatures (ILT: LILT and UILT) were also calculated for the PL. The thermal windows of the PL were developed using the CTM and ILT values. The standard metabolic rate (SMR) of the PL was determined based on the oxygen consumption rate (OCR) at the different acclimation temperatures mentioned above. The acclimation temperature had a subsequent effect on the thermal tolerance and SMR of the PL (P < 0.01). The PLs of Pacific white shrimp have high thermal tolerance and can survive at extreme temperatures (CTmin and CTmax: 8.2-43.8°C) with their large dynamic and static thermal window areas of 1128 and 931°C2, respectively. The optimal temperature range for Pacific white shrimp PLs is the 25-30°C range, where a decrease in SMR is determined with increasing temperature. The result of this study reveals that a range of 25-30°C is optimal for effective PL culture of Pacific white shrimp.

Ammonium changes the pathway of tetrabromobisphenol S degradation by sulfate radical oxidation

Sulfate radical (SO4•-)-based advanced oxidation processes (SR-AOPs) show great potential in the elimination of organic pollutants in wastewater treatment and groundwater remediation. Tetrabromobisphenol S (TBBPS) as an emerging contaminant can be effectively degraded in SR-AOPs. However, the present study found that SO4•- also reacted with ammonium (NH4+), a ubiquitous inorganic nitrogen species in aquatic environments, thus markedly affected the rates and pathways of TBBPS degradation in SR-AOPs. TBBPS underwent β-scission and debromination upon SO4•- attack, leading to various transformation products. The released bromide (Br-) underwent further oxidation by SO4•- to form free bromine which reacted with certain TBBPS intermediates, generating disinfection byproducts (DBPs). When NH4+ was present in such system, the abatement of TBBPS was apparently suppressed. Meanwhile, NH4+ was oxidized by SO4•- to nitrogen dioxide radical (NO2•) which coupled with certain radical intermediates of TBBPS oxidation, yielding nitrophenolic products including 2,6-dibromo-4-nitrophenol (DBNP) and mono-nitro substituted TBBPS. When 10 μM TBBPS was treated by heat activated peroxydisulfate with 1 mM NH4+, the molar yield of DBNP reached 22% in 2 h. More importantly, NH4+ scavenged the in situ formed free bromine to form monobromamine (NH2Br), decreasing regulated DBPs formation but leading to highly toxic dibromoacetonitrile (DBAN). This study broadens the understanding of interactions between the transformation of halogens and NH4+ during SO4•- oxidation. It also reveals the potential environmental risks when SR-AOPs are employed for the organohalogen pollutants degradation in realistic environments where NH4+ is present.

Yeast vacuolar enzymes as novel hatching inhibitors for aquatic organisms, Daphnia magna and Danio rerio eggs

Concerns over the spread of non-native species in aquatic environments have led to the need for effective methods to prevent and control their spread while protecting native species. This study investigated the potential of yeast vacuolar enzymes as a natural hatching inhibitor for controlling aquatic organisms. Hatching experiments with Daphnia magna eggs demonstrated that exposure to yeast vacuole enzymes inhibited hatching in a concentration-dependent manner, suggesting their potential as an effective inhibitor of egg hatching in aquatic organisms. Interestingly, the protease used for comparative purposes did not inhibit hatching, but instead increased the mortality of hatched D. magna. Additionally, chorionic changes were observed in non-hatched D. magna eggs and zebrafish eggs exposed to yeast vacuole enzymes, suggesting that the enzyme can alter the chorion and interfere with hatching. These findings suggest that yeast vacuolar enzymes may be a promising and natural management tool for controlling the spread of harmful aquatic organisms, and further research is warranted to explore their potential for species-specific control.

Mechanisms of ZnO Nanoparticles Enhancing Phototransformation of Biologically Derived Organic Phosphorus in Aquatic Environments.

Zinc oxide nanoparticles (ZnO NPs), as the highly efficient photocatalysts, could enhance the transformation of biogenic organic phosphorus (OP) to orthophosphate (PO43-) by photodegradation, accelerating eutrophication. Conversely, orthophosphate can also transform ZnO NPs and thus potentially alter their catalytic and chemical properties. Here, we investigated the transformation mechanisms of three biogenic OP compounds and ZnO NPs under ultraviolet light (UV) illumination: inositol phosphates (IHPs), nucleic acids (DNA), and aminoethylphosphonic acid (AEP). The physicochemical characteristics of the resulting products were systematically characterized. Results show that ZnO NPs accelerated the transformation of IHPs, DNA, and AEP to inorganic phosphorus with the direct photolysis efficiencies of 98.14, 87.68, and 51.76%, respectively. The main component of the precipitates remained ZnO NPs, and Zn3(PO4)2 was identified. Zinc phytate was determined in the ZnO NP-IHP system. 31P NMR and FTIR further confirmed that the aquatic phase contained orthophosphate. Photoproduced hydroxyl (·OH) and superoxide (·O2-) were proved to play a dominant role in the OP photomineralization. Furthermore, ZnO NPs significantly enhanced the intensity of ·OH and ·O2- compared to the OP and Zn2+ solution alone. This work explored the light-induced mineralization processes of OP with ZnO NPs indicating that nanophotocatalysts may play a positive role in transformation of OP species in aquatic environments to further contribute to eutrophication.

Ammonia nitrogen stress damages the intestinal mucosal barrier of yellow catfish (Pelteobagrus fulvidraco) and induces intestinal inflammation.

Nitrogen from ammonia is one of the most common pollutants toxics to aquatic species in aquatic environment. The intestinal mucosa is one of the key mucosal defenses of aquatic species, and the accumulation of ammonia nitrogen in water environment will cause irreversible damage to intestinal function. In this study, histology, immunohistochemistry, ultrastructural pathology, enzyme activity analysis and qRT-PCR were performed to reveal the toxic effect of ammonia nitrogen stress on the intestine of Pelteobagrus fulvidraco. According to histological findings, ammonia nitrogen stress caused structural damage to the intestine and reduced the number of mucous cells. Enzyme activity analysis revealed that the activity of bactericidal substances (Lysozyme, alkaline phosphatase, and ACP) had decreased. The ultrastructure revealed sparse and shortened microvilli as well as badly degraded tight junctions. Immunohistochemistry for ZO-1 demonstrated an impaired intestinal mucosal barrier. Furthermore, qRT-PCR revealed that tight junction related genes (ZO-1, Occludin, Claudin-1) were downregulated, while the pore-forming protein Claudin-2 was upregulated. Furthermore, as ammonia nitrogen concentration grew, so did the positive signal of Zap-70 (T/NK cell) and the expression of inflammation-related genes (TNF, IL-1β, IL-8, IL-10). In light of the above findings, we conclude that ammonia nitrogen stress damages intestinal mucosal barrier of Pelteobagrus fulvidraco and induces intestinal inflammation.

Assessment of a New Approach Method for Grouped Chemical Hazard Estimation: The Toxicity-Normalized Species Sensitivity Distribution (SSDn).

New approach methods are being developed to address the challenges of reducing animal testing and assessing risks to the diversity of species in aquatic environments for the multitude of chemicals with minimal toxicity data. The toxicity-normalized species sensitivity distribution (SSDn) approach is a novel method for developing compound-specific hazard concentrations using data for toxicologically similar chemicals. This approach first develops an SSDn composed of acute toxicity values for multiple related chemicals that have been normalized by the sensitivity of a common species tested with each compound. A toxicity-normalized hazard concentration (HC5n) is then computed from the fifth percentile of the SSDn. Chemical-specific HC5 values are determined by back-calculating the HC5n using the chemical-specific sensitivity of the normalization species. A comparison of the SSDn approach with the single-chemical SSD method was conducted by using data for nine transition metals to generate and compare HC5 values between the two methods. We identified several guiding principles for this method that, when applied, resulted in accurate HC5 values based on comparisons with results from single-metal SSDs. The SSDn approach shows promise for developing statistically robust hazard concentrations when adequate taxonomic representation is not available for a single chemical.

The genome of the freshwater monogonont rotifer Brachionus rubens: Identification of phase I, II, and III detoxification genes

Monogonont rotifers are common species in aquatic environments and make model species for ecotoxicology studies. Whole genomes of several species of the genus Brachionus have been assembled, but no information on the freshwater rotifer Brachionus rubens has been reported. In this study, the whole-genome sequence of B. rubens was successfully assembled using NextDenovo. The total length of the genome was 132.7 Mb (N50 = 2.51 Mb), including 122 contigs. The GC contents accounted for 29.96% of the genome. Aquatic organisms are always exposed to various external stresses, and a comprehensive genomic analysis is needed to better understand the adverse effects on organisms. This paper focuses on the ecotoxicological aspect and conducted genome analysis of representative gene families involved in detoxification mechanisms against environmental stressors. Specifically, we identified cytochrome P450 genes (CYPs) of phase I, glutathione S-transferase genes (GSTs) of phase II, and ATP-binding cassette transporter genes (ABCs) of phase III in the genome of B. rubens. Gene duplications were found in CYP, GST, and ABC genes, as is the case for other Brachionus rotifers. Our results suggest that these detoxification-related gene families have evolved in a species-specific and/or lineage-specific manner. This paper improves our understanding of how the freshwater Brachionus rotifers respond to environmental stressors in a molecular ecotoxicology context.

Water Hyacinth (Eichhornia crassipes) Detection Using Coarse and High Resolution Multispectral Data

Efficient detection and monitoring procedures of invasive plant species are required. It is of crucial importance to deal with such plants in aquatic ecosystems, since they can affect biodiversity and, ultimately, ecosystem function and services. In this study, it is intended to detect water hyacinth (Eichhornia crassipes) using multispectral data with different spatial resolutions. For this purpose, high-resolution data (&lt;0.1 m) acquired from an unmanned aerial vehicle (UAV) and coarse-resolution data (10 m) from Sentinel-2 MSI were used. Three areas with a high incidence of water hyacinth located in the Lower Mondego region (Portugal) were surveyed. Different classifiers were used to perform a pixel-based detection of this invasive species in both datasets. From the different classifiers used, the results were achieved by the random forest classifiers stand-out (overall accuracy (OA): 0.94). On the other hand, support vector machine performed worst (OA: 0.87), followed by Gaussian naive Bayes (OA: 0.88), k-nearest neighbours (OA: 0.90), and artificial neural networks (OA: 0.91). The higher spatial resolution from UAV-based data enabled us to detect small amounts of water hyacinth, which could not be detected in Sentinel-2 data. However, and despite the coarser resolution, satellite data analysis enabled us to identify water hyacinth coverage, compared well with a UAV-based survey. Combining both datasets and even considering the different resolutions, it was possible to observe the temporal and spatial evolution of water hyacinth. This approach proved to be an effective way to assess the effects of the mitigation/control measures taken in the study areas. Thus, this approach can be applied to detect invasive species in aquatic environments and to monitor their changes over time.

The Prevalence of Arcobacteraceae in Aquatic Environments: A Systematic Review and Meta-Analysis.

Members of the family Arcobacteraceae are distributed widely in aquatic environments, and some of its species have been associated with human and animal illness. However, information about the diversity and distribution of Arcobacteraceae in different water bodies is still limited. In order to better characterize the health risk posed by members in the family Arcobacteraceae, a systematic review and meta-analysis-based method was used to investigate the prevalence of Arcobacteraceae species in aquatic environments based on available data published worldwide. The database search was performed using related keywords and considering studies up to February 2021. The pooled prevalence in aquatic environments was 69.2%, ranging from 0.6 to 99.9%. These bacteria have a wide geographical distribution, being found in diverse aquatic environments with the highest prevalence found in raw sewage and wastewater treatment plants (WWTP), followed by seawater, surface water, ground water, processing water from food processing plants and water for human consumption. Assessing the effectiveness of treatments in WWTP in eliminating this contamination, it was found that the wastewater treatment may not be efficient in the removal of Arcobacteraceae. Among the analyzed Arcobacteraceae species, Al. butzleri was the most frequently found species. These results highlight the high prevalence and distribution of Arcobacteraceae in different aquatic environments, suggesting a risk to human health. Further, it exposes the importance of identifying and managing the sources of contamination and taking preventive actions to reduce the burden of members of the Arcobacteraceae family.

Clothianidin interferes with recognition of a previous encounter in rusty crayfish (Faxonius rusticus) due to a chemosensory impairment

Clothianidin, a neonicotinoid insecticide that binds to arthropod nicotinic acetylcholine receptors, is widely used to protect plants against a wide variety of agricultural pests. Little is known about how this insecticide affects non-target invertebrate species in aquatic environments. In this study, we explored the effects of aqueous exposures of clothianidin on locomotion, chemosensory-based responses, and agonistic encounters of rusty crayfish (Faxonius rusticus). Clothianidin exposures at a concentration of 1.0 μg/L (i.e., 1.0 ppb) did not alter initiations and retreats, but did increase the amount of time the crayfish interacted per interaction. In a subsequent food cue experiment with crayfish exposed to clothianidin concentrations of 0.4 μg/L and 1.0 μg/L, the test organisms demonstrated chemosensory dysfunction, but no decrease in locomotory movement. As chemosensation is essential for recognizing previous rivals in crayfish, the loss of this sense likely resulted in the exposed crayfish being unable to detect cues used to recognize a previous competitor. An inability to recognize a previous competitor (and who won or lost the previous interaction) could result in crayfish spending more time fighting and less time on foraging and reproduction. This study demonstrates that exposures of crayfish to clothianidin at concentrations found in the environment affects the behavioural ecology of these aquatic invertebrates.

Changes in physico-mechanical properties of water caltrop fruit (Trapa natans L.) during the drying process

The cosmopolitan water caltrop plant (Trapa natans L.) produces nuts, which in the maturing process develop very hard pericarps. This hardness, together with structure and shape (external spikes) of pericarp and seed, and the water contained in the fruit are responsible for their mechanical properties. This study determined the force needed to break Trapa natans nuts at various drying stages, with tests having been carried out at weekly intervals until the fruit dried completely. The amount of force necessary for cracking nuts at each of the 6 drying stages was determined, as well as the work of crushing calculated until the greatest compressive force (crushing force) was reached. The force needed to rupture the hydrated fruit in the horizontal plane was higher than that necessary for the rupture of dried fruit. The experiment showed that the maximum force needed to crush the fruit was 828.7 N and occurred when crushing the fruit after 2 weeks of drying, while the largest calculated crushing work was 2185.5 mJ for the same fruit. Other strength parameters were introduced to characterize mechanical properties of water caltrop in a more extensive scope. These are hardness defined as a ratio of compressive force increment to strain increment, specific crushing energy defined as a ratio of crushing work to water caltrop’s mass, and unit crashing force defined as a ratio of crushing force to caltrop’s thickness. All these parameters reached their highest mean values for pericarps after 2 weeks of desiccation. Mass measurements were also applied in modelling the desiccation process by the exponential function. The very dense pericarp material, after reaching maturity, slightly changes during drying. It can be used industrially as an extremely durable and biodegradable biological material. Results also suggest that the great evolutionary success of the species may result from the ability of the pericarp to protect its seeds, leading to the spread of this species in aquatic environments.

Virulence and Antibiotic Resistance Characteristics of Vibrio Isolates From Rustic Environmental Freshwaters.

The study investigated the occurrence of antimicrobial resistance genes and virulence determinants in Vibrio species recovered from different freshwater sheds in rustic milieu. A total of 118 Vibrio isolates comprising Vibrio fluvialis (n=41), Vibrio mimicus (n=40) and V. vulnificus (n=37) was identified by amplification of ToxR, vmh and hsp60 genes. The amplification of virulence genes indicated that V. mimicus (toxR, zot, ctx, VPI, and ompU) genes were detected in 12.5%, 32.5%, 45%, 37.5% and 10% respectively. V. fluvialis genes (stn, hupO and vfh) were harboured in 48.8%, 14.6% and 19.5% isolates congruently. The other virulence genes that include vcgC and vcgE were observed in 63.1% and 29% of isolates belonging to V. vulnificus. With the exceptions of imipenem, meropenem and ciprofloxacin, most isolates exhibited more than 50% resistance to antibiotics. The antimicrobial resistance was more prevalent for polymyxin B (100%), azithromycin (100%) and least in ciprofloxacin (16.1%). Multiple antibiotic resistance index range was 0.3 and 0.8 with most isolates showing MARI of 0.8. The blaTEM, AmpC, blaGES, blaIMP, blaOXA-48 and blaKPC genes were detected in 53.3%, 42%, 29.6%, 16.6%, 15%, 11.3% and 5.6% of the isolates. Non-beta lactamases such as streptomycin resistance (aadA and strA), gentamicin resistance (aphA1) and quinolone resistance gene (qnrVC) were found in 5.2%, 44.3%, 26% and 2.8%. Chloramphenicol resistance genes (cmlA1 and catII) were found in 5.2% and 44.3% among the isolates. Our findings reveal the presence of antimicrobial resistance genes and virulent Vibrio species in aquatic environment which can have potential risk to human and animal’s health.

Photochemical (UV–vis/H2O2) degradation of carotenoids: Kinetics and molecular end products

Constraining the formation mechanisms of organic matter that persists in aquatic reservoirs is important for determining the reactivity and fate of carbon and nutrients in these environments. Recent studies have linked dissolved organic matter (DOM) accumulating in the ocean to linear terpenoid structures, and carotenoid degradation products have been proposed as potential precursors. The prevalence of reactive oxygen species in aquatic environments and their potential to be quenched by carotenoids led us to examine radical-assisted photochemical degradation of carotenoids as a potential mechanism for DOM formation and transformation. Experiments were conducted with aggregates of β-carotene, astaxanthin, fucoxanthin and meso-zeaxanthin in THF:H2O under solar light irradiation assisted by hydrogen peroxide (UV–Vis/H2O2). Based on the fine structure of UV–Vis spectra, it was determined that β-carotene and meso-zeaxanthin formed J-type aggregates in experimental solutions, while astaxanthin and fucoxanthin formed H2-type aggregates, consistent with their structural characteristics. All carotenoids degraded under the combined influence of photolysis and OH scavenging, with fucoxanthin exhibiting the fastest degradation kinetics (kPO = 3.69 10−3 s−1) and meso-zeaxanthin the slowest (kPO = 4.37 10−4 s−1). The major degradation products detected by electrospray ionization (ESI) tandem mass spectrometry (MS/MS) were apo-aldehydes and apo-ketones, with the latter tending to accumulate, but epoxidation of the carotenoids also took place, and longer irradiation times resulted in lower molecular weight products. Reaction kinetics and accumulating carotenoid oxidation products identified in this study provide potential formation mechanisms and biomarkers for examining DOM cycling.

Causal relationship between alkaline phosphatase activities and phosphorus dynamics in a eutrophic coastal lagoon in Lake Michigan

Alkaline phosphatase plays an important role in regulating nutrient dynamics and algal blooms in aquatic environments, but the causal relationship between alkaline phosphatase (AP), nutrient status, and chemical speciation of phosphorus (P) in the water column remains elusive. A year-long time series (weekly to biweekly) sampling was conducted to investigate the causality between alkaline phosphatase dynamics, transformation of P species, and phytoplankton biomass in Veterans Park Lagoon, a closed lagoon with intense seasonal cyanobacterial blooms. As water temperature increased from spring to summer, depletion of dissolved inorganic P (DIP) drove increases in cell-associated AP (APcell, in nmol L−1). The elevated cell-associated alkaline phosphatase activities (APAcell, in nmol L−1 h−1) resulted in the transformation of particulate organic P (POP) into DIP, which enhanced the algal blooms. Not driven by DIP depletion, dissolved AP (APdiss) was spontaneously released during cyanobacterial blooms and the elevated dissolved APA (APAdiss) resulted in increase of DIP during the growing stage. This explains the concurrent high potential APA and high DIP concentrations in the water column observed here and other previous studies. The low-molecular-weight dissolved organic P (LMW-DOP) was found to be independent of both APAcell and APAdiss, consistent with previous results derived from isotope tracers. During the transition stage between fall and winter with lower water temperatures, APAdiss increased as a result of DIP depletion, while DOP was depleted and APAcell increased, and vice versa. The increase in both APAcell and APAdiss further resulted in the increase in concentration of particulate inorganic P through promoting the release of DIP from carbon-phosphate bonds and the adsorption of DIP onto particle surfaces especially under lower water temperature. Our results provide improved understanding of the concurrently high APA and DIP in the water column and provide new insights into the causal relationship between AP and P species in aquatic environments.

Iron oxides catalyze the hydrolysis of polyphosphate and precipitation of calcium phosphate minerals

Interfacial chemistry of phosphorus (P) is important for understanding P sequestration and bioavailability in nature. Polyphosphate is a group of important P species in aquatic environments. The geochemical behaviors of polyphosphate at the mineral-water interface play critical roles in mediating aquatic P transformation, yet remain poorly constrained. This study investigates the hydrolysis of polyphosphate in the presence of four common iron (Fe) oxide minerals (ferrihydrite, hematite, goethite, lepidocrocite) and the subsequent precipitation of calcium phosphate minerals. Batch studies are combined with microscopic and spectroscopic characterizations to reveal P speciation and complexation state under varied solution chemistry (pH 6–9, 1 mM Ca2+, and artificial seawater). All four Fe oxides can hydrolyze polyphosphate and the hydrolysis rate and extent are both enhanced in the presence of Ca2+. In the presence of 1 mM Ca2+, the apparent hydrolysis rate fitted by first-order kinetic model follows the order of lepidocrocite > hematite > ferrihydrite > goethite. After normalization by specific surface area of Fe oxides, the hydrolysis rate is in the order of lepidocrocite ≈ goethite > hematite > ferrihydrite at pH 6, regardless of Ca2+ presence. At pH 7.5 and 9, the order of area-normalized apparent hydrolysis rate is lepidocrocite > goethite ≈ hematite > ferrihydrite. A terminal-only pathway via one-by-one cleavage of terminal phosphate groups is the dominant hydrolysis mechanism. Under alkaline conditions, amorphous calcium phosphate forms in the presence of Ca2+, which transforms to crystalline hydroxyapatite after long-term aging of 70 or 150 days. This study demonstrates the importance of natural minerals in controlling polyphosphate transformation into crystalline calcium phosphate minerals, and provides new insights for understanding P cycling and sequestration in the environment.

Enantioselective Bioaccumulation of the Chiral Insecticide Indoxacarb in Zebrafish (Danio rerio)

Indoxacarb is a typical chiral insecticide widely used in agricultural pest control. In the present study, zebrafish was used as a model animal to explore the enantioselective bioaccumulation behavior of indoxacarb to nontarget species in aquatic environments. Zebrafish were exposed to 0.025 and 0.1 mg/L rac-indoxacarb solution for 12 d under the semistatic method, and the bioconcentration factor (BCF) and enantiomeric fraction of zebrafish were investigated. The results showed that the (-)-R-indoxacarb preferentially accumulated in zebrafish. The BCF values at 0.025 mg/L exposure levels were 1079.8 and 83.4 L/kg for (-)-R-indoxacarb and (+)-S-indoxacarb after 12 d, respectively. The BCF values at 0.1 mg/L exposure levels were 1752.1 and 137.0 L/kg for (-)-R-indoxacarb and (+)-S-indoxacarb after 10 d, respectively. The half-life values of (-)-R-indoxacarb and (+)-S-indoxacarb were 3.47 and 2.05 d for 0.025 mg/L concentration exposure and 4.95 and 2.66 d for 0.1 mg/L concentration exposure, respectively. The enantiomeric fraction values were in the range of 0.48 to 0.55 and 0.89 to 1.00 for water and zebrafish samples, respectively. Studies on the enantioselective bioaccumulation behavior of indoxacarb will provide data for assessing the environmental fate and potential toxic effects of indoxacarb on aquatic organisms. Environ Toxicol Chem 2021;40:1007-1016. © 2020 SETAC.

Transect sampling promotes higher detection rates compared to discrete sampling for environmental DNA applications

The use of environmental DNA (eDNA) to monitor species in aquatic environments has rapidly increased over the past decade. eDNA has consistently outperformed other methods of detection, yet eDNA relies on an indirect measure to estimate the real distribution of a species. Therefore, understanding the environmental factors that disperse eDNA is of major importance. Here we modeled the use of transect sampling for eDNA studies and also model the impact of river advection on detection radius and the expected probability of detection. Our model suggests that transect sampling: 1) increases the detection probability for both rare and common species, thus reducing the frequency of false negatives, 2) diminishes the standard deviation of the detection probability, which in most cases means higher reproducibility of eDNA studies, 3) better estimates systemwide trends of fish population distinguishing zones of multiple fishes from zones where few fishes are present, and 4) diminishes the effects of eddies and river velocity on the detection probability and detection radius. We propose the use of transect sampling as an alternative method of eDNA sampling with benefits that surpass the disadvantages of not being able to pinpoint the exact fish location. Our model also suggests that even short transects (less than 100 m) can yield considerable benefits compared to point sampling.

Are they always bad? Assessing benefits of non-indigenous species in aquatic environment and their implications

Non-indigenous species (NIS), non-native, or alien species are any organisms living and spreading outside their natural habitat. Many of NIS spread to a new environment accidentally, while some other species are intentionally introduced by humans to a new habitat in many different pathways, as follows: 1) release; 2) escape; 3) contaminant; 4) stowaway; 5) corridor; and 6) unaided. Threaten native biodiversity may be the most problematic impact of NIS. They can also disrupt food-web organizations and affect the ecosystem structures. Additionally, the problem is exacerbated by disagreements regarding whether or not NIS should be permitted for aquaculture production. The likelihood of NIS escaping, being released from aquaculture, and establishing in its native habitat poses a significant threat to the ecosystem and biodiversity. NIS also have positive impacts as ecosystem engineers which may increase the biodiversity of native communities. Other benefits of NIS include providing an alternative food source and supporting fisheries and aquaculture sectors. Understanding the introduction process and the impacts of NIS should be supported by effective policy frameworks and management approaches, including risk assessment, prevention and control, pathway and vector management, early detection and rapid response, eradication, and mitigation and restoration. Furthermore, the crucial efforts would be raising public awareness, improving scientific research, and developing strategy regarding biosecurity issues as consequences of the emergence of interactions complexity among NIS and other global ecological change drivers.