Genome-wide characterization of the Triplophysa dalaica slc4 gene family and expression profiles in response to salinity changes.

BACKGROUND: The solute carrier 4 (SLC4) gene family is involved in a variety of physiological processes in organisms and is essential for maintaining acid-base balance in the body. The slc4 genes have been extensively studied in mammals, and they play important roles in intracellular and extracellular pH regulation and in the secretion and uptake of HCO3- and other ions (Na+ and Cl-) between transepithelial cells in different tissues. This study identified and characterized the entire slc4 gene family of Triplophysa dalaica. RESULTS: Fifteen slc4 genes were identified in the whole genome of Triplophysa dalaica in this study, including five copies of Na+-independent Cl-/HCO3- transporters, eight members of Na+-dependent HCO3- transporters, and two genes coding Na+-coupled borate transporters. The chromosomal location information, isoelectric points, and molecular weights of the 15 slc4 genes were analyzed. The results for gene structure, domain analysis, and phylogenetic relationships of this gene family showed that the slc4 genes (except for slc4a9, which is missing in teleosts) are significantly expanded in teleosts compared to higher vertebrates. This phenomenon suggests that the slc4 gene family played an important role in the transition from aquatic to terrestrial animals. RT-PCR results showed that different slc4 genes showed diversified expression patterns in the tissues of T. dalaica. For osmotic pressure regulating organs, slc4a1b, slc4a4b, slc4a7, and slc4a11a were highly expressed in gills. In the kidney, slc4a1a, slc4a3, and slc4a10b were highly expressed, suggesting that the slc4 genes play a specific role in the salinity adaptation of T. dalaica. Our study has deciphered the biological roles of the slc4 genes in maintaining ionic and acid-base homeostasis in teleost fishes and provides a foundation for future exploration of the highly differentiated gene family in Triplophysa. CONCLUSIONS: The results are relevant for the breeding of alkali-tolerant varieties in saline-alkali areas for aquaculture. Our findings have important implications for the adaptation process of freshwater species to saline-alkali water.

Sediment organic matter properties facilitate understanding nitrogen transformation potentials in East African lakes.

East African lakes include the most productive and alkaline lake group in the world. Yet, they generally receive fewer nutrient inputs than the densely populated subtropical and temperate lakes in the northern hemisphere. In these lakes with insufficient supplies of inorganic nitrogen, the mineralization of benthic organic matter can play an important role in driving the nutrient cycle and nitrogen loss. Using a suite of stable 15N isotope dilution and tracer techniques, we examined five main processes of the sediment nitrogen cycle in 16 lakes and reservoirs of Tanzania and Kenya, East Africa: gross nitrogen mineralization, ammonium immobilization, dissimilatory nitrate reduction to ammonium (DNRA), and the dinitrogen (N2) production via denitrification and anaerobic ammonium oxidation (anammox). Gross nitrogen mineralization and ammonium immobilization showed the maximum values of 9.84 and 12.39 µmol N kg-1 h-1, respectively. Potential DNRA rates ranged from 0.22 to 8.15 µmol N kg-1 h-1 and accounted for 10 %-74 % (average 25 %) of the total dissimilatory nitrate reduction. Potential nitrate reduction rates in most lakes were dominated by denitrification with a contribution of 26 %-85 % and a mean of 65 %. We further found that the sediment nitrogen transformations were driven mainly by benthic organic matter properties and water column phosphate concentrations, reflecting microbial metabolic responses to the changing carbon and nutrients availability. For instance, autochthonous production of protein-like organic matter attributed to active sediment nitrogen mineralization, DNRA, and denitrification. In contrast, the high degree of humification caused by the inputs of terrestrial humic-like substances slowed down the sediment nitrogen transformations. The contribution of DNRA to total dissimilatory nitrate reduction was significantly positively correlated to sediment C: N ratios. These results indicate that predictions of sediment N supply and loss in East African lakes can be improved by incorporating sediment organic matter properties.

A comprehensive evaluation of organic micropollutants (OMPs) pollution and prioritization in equatorial lakes from mainland Tanzania, East Africa.

A lack of understanding the fate of highly toxic organic micropollutants (OMPs) in the equatorial lakes of Tanzania hinders public awareness for protecting these unique aquatic ecosystems, which are precious water resources and stunning wildlife habitats. To address this knowledge gap, the occurrence of 70 anthropogenically-sourced OMPs, including phthalates (PAEs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs), was investigated in the water and sediment of 18 lakes in Tanzania. Similar residue concentrations were found in both compartments, showing higher pollution of PAEs ranging from 835.0 to 13,153.1 ng/L in water and 244.6-8691.8 ng/g dw in sediment, followed by PAHs, while OCPs and PCBs were comparatively lower. According to the multi-criteria scoring method for prioritization, the final OMP priority list for the lake environment in Tanzania comprised 25 chemicals, specifically 5 PAEs (DEHP, DIBP, DBP, DCHP and DMPP), 6 PCBs (PCB153, PCB105, PCB28, PCB156, PCB157 and PCB167), 6 PAHs (BaP, BaA, BbF, Pyr, DahA and InP) and 8 OCPs (cis-chlordane, trans-chlordane, p,p'-DDD, p,p'-DDE, p,p'-DDT, endrin, methoxychlor and heptachlor epoxide), suggesting the key substances for conventional monitoring and pollution control in these equatorial lakes, with an emphasis on PAEs, especially DEHP, due to the top priority and endocrine disruptor properties.

[Historical Changes and Responses to Human Activities of Polycyclic Aromatic Hydrocarbons in Lake Sediments from Northern China During the Past 100 Years].

Polycyclic aromatic hydrocarbons (PAHs) are of concern globally because of their carcinogenic, teratogenic, mutagenic, and bio-accumulative effects. Northern China is one of the regions in China with a high density of lakes; however, the lake aquatic environment is becoming seriously deteriorated, especially from PAH pollution due to the intensification of human activities during the past 100 years. Therefore, the spatial distribution and historical changes in PAHs in lake sediments from northern China were analyzed to indicate their response to anthropogenic emissions and pollution reduction actions. The ω(PAHs) in lake sediments ranged from 18.2 to 1205.0 ng·g-1, and low molecular weight PAHs were the dominant compounds. PAH concentrations increased from the 1950s to a peak level in the 2000s, which was induced mainly by increased energy consumption and rapid economy development, with PAH levels decreasing subsequently in the last 10 years due to craft improvement of wastewater treatment plants and the promotion of new energy policies. Spatially, PAHs pollution in Northeast and North China was more serious than that in Northwest China due to the higher level of economic development and energy consumption. Source apportionment results revealed that historical PAH emissions transferred from biomass combustion to a mixture of coal and petroleum combustion. In addition, the results of ecological risk assessment showed that the synthetic sediment quality index (SeQI) of northern China ranged from 36 to 75, and North and Northeast China posed higher ecological risk than that in Northwest China, with phenanthrene (Phe), acenaphthylene (Ace), acenaphthylene (Acy), and dibenzo(a,h)anthracene (DahA) as the main risk contributors.

[Screening of Priority Pollutants and Risk Assessment for Surface Water from Shengjin Lake].

Shengjin Lake, which serves as an important National Nature Reserve, is suffering from chemical pollution due to rapid industrial and agricultural development in the circumjacent basin. Therefore, 168 anthropogenic toxic chemicals were determined to examine their spatial distribution and identify priority pollutants using a ranking system based on occurrence(O), persistence(P), bioaccumulation(B), ecological risk(E), and human health risk(H). Ecosystem and human health risks were also assessed. The spatial distribution of pollutants indicated that higher concentrations occur in the upper lake area compared to the middle and lower lake areas because of Jiang Dam. According to the derived priority pollutant list, phthalate esters(PAEs), organochlorine pesticides(OCPs), and heavy metals(HMs) are high-priority pollutants; polychlorinated biphenyls(PCBs), polycyclic aromatic hydrocarbons(PAHs), and volatile organic compounds(VOCs) are medium-priority pollutants; and antibiotics(ANTs) are low-priority pollutants. The ecology risk quotient(RQ) of the high-priority pollutants ranged from 4.3 to 15.9, indicating severe ecology risk to the aquatic organism, and higher risks were found in the upper lake areas. Additionally, the human health risk assessment revealed negligible carcinogenic risks associated with high-priority pollutants. The comprehensive ranking system established in this study can be applied to other lake basins by altering the measured concentrations to screen for priority pollutants, offering a scientific foundation for identifying priority control pollutants for watershed management.

Environmental implications from the priority pollutants screening in impoundment reservoir along the eastern route of China's South-to-North Water Diversion Project.

Screening priority pollutants from vast anthropogenic contaminants discharged into aquatic environment is urgent for protecting water quality definitely. The multi-criteria scoring method involved in the occurrence (O), persistence (P), bioaccumulation (B), ecological risk (Eco-T), and human health risk (Hum-T), was established for pollutants prioritization in waters and applied in Dongping Lake, the final impoundment reservoir along the eastern route of China's South-to-North Water Diversion Project (SNWDP). A total of 170 chemicals including heavy metals (HMs), volatile organic chemicals (VOCs), polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), phthalate esters (PAEs), and antibiotics (ANTs) were investigated as the candidates. Accordingly, 42 chemicals including 8 PAEs, 7 OCPs, 7 PCBs, 5 PAHs, 13 HMs, and 2 VOCs were made up the list of priority pollutants for Dongping Lake, suggesting the necessity of routine monitoring high priority groups and revising the existing list. Multiple risk assessment indicated higher ecological and human health risks induced by HMs than by organic pollutants. Spatial distribution of risks stressed the retention of toxic organic chemicals by the lake body and the accumulation of HMs along the transfer route, respectively, thus triggering ecosystem responses and potential effects on the water-receiving areas as expected.

Recording and response of persistent toxic substances (PTSs) in urban lake sediments to anthropogenic activities.

Owing to the intensification of human activities, urban lakes serving as important freshwater resources are becoming seriously deteriorated, especially due to persistent toxic substance (PTS) pollution. Therefore, the spatial distribution and sediment record of PTS in urban lake sediments in the middle Yangtze River Basin were investigated to indicate its response to anthropogenic emission and pollution reduction actions. Spatial distribution of typical PTSs (polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) included) showed that pollutants were concentrated in the southeast and center of the urban lake due to riverine inputs suffering from both petrochemical and municipal wastewaters. The sedimentary record of PAH concentrations indicated an increase from the 1960s to a peak level in the 2000s, which was induced mainly by increased PAH emissions, with PAH levels decreasing subsequently due to craft improvement of wastewater treatment plants (WWTPs). Source apportionment results revealed that historical PAH emissions transferred from petrogenic sources to a mixture of energy combustion and petrochemical industry. Furthermore, OCP and PCB pollutions reached peak levels in 1980s, which is consistent with their historical usage for agricultural and industrial production. From the synthetic sediment quality index (SeQI) analysis, sediment quality in nearly half of sites was poor, while the sediment record suggested that sediment quality had turned better since 2000s maybe due to the WWTP improvement. Furthermore, significant correlations (p < 0.05) between PTS levels and the ratio of PAH emissions to the number of WWTPs documented the PTS levels in response to the surrounding anthropogenic pollution and WWTPs in urban lakes.

The biological pump effects of phytoplankton on the occurrence and benthic bioaccumulation of hydrophobic organic contaminants (HOCs) in a hypereutrophic lake.

The distribution of hydrophobic organic contaminants (HOCs) in eutrophic ecosystems has been widely studied, but how phytoplankton blooms affect their occurrence and benthic bioaccumulation is poorly understood. To fill this knowledge gap, the biological pump effects of phytoplankton on the fate of organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs) in sediments and benthos (Corbicula fluminea) from Lake Taihu, a hypereutrophic lake in China, were identified. The spatial-temporal distribution of HOCs suggests that higher phytoplankton biomass, coupled with sediment organic matter (SOM) content, greatly increased the concentration of HOCs in sediments in both winter and summer seasons. This could be attributed to the biological pump effects sequestering more HOCs from water to sediments with settling phytoplankton, especially during the summer. The biological pump effects further promoted the uptake of sediment-bound HOCs by benthos. The significant positive relationships between concentrations of HOCs in sediments and benthos were observed during the winter dormancy phase of benthos. Furthermore, the benthic bioaccumulation of HOCs could be strengthened by phytoplankton, due to their contribution to SOM and the following increased bioavailability of HOCs in sediments. Further research is needed to elucidate the phytoplankton biological pump effects on the fate of HOCs in benthic food chain, especially for hypereutrophic waters.

Complete degradation of ciprofloxacin over g-C3N4-iron oxide composite via heterogeneous dark Fenton reaction.

Graphitic carbon nitride (g-C3N4) supported iron oxide (CN@IO) composite was first fabricated via synthesizing g-C3N4 in-situ onto iron oxide. The fabricated CN@IO composite was characterized by several techniques including XRD, XPS, TEM and nitrogen adsorption-desorption analysis. This composite was then used as a catalyst for the dark Fenton oxidative degradation of ciprofloxacin (CIP). Results demonstrated that the incorporation of g-C3N4 profoundly changed the structure and chemical properties of iron oxide, endowing CN@IO composites with high-efficient catalytic activity in dark Fenton system. In the synthesis process of CN@IO composites, iron oxide nanoparticles were successfully intercalated into the layers of g-C3N4, enlarging the surface area and thus providing more active sites for the reactions. Meanwhile, the existence of g-C3N4 can accelerate the Fe3+/Fe2+ redox cycle during the Fenton reaction, which further facilitated CIP degradation. In addition, the effects of reaction parameters, including pH, catalyst dosage, initial concentration of CIP and H2O2, on CIP degradation were investigated. Without any assistance of light irradiation, complete degradation and 48.5% mineralization of CIP were achieved under the best conditions of pH 3.0, 1 g/L CN@IO-2, 20 mg/L CIP and 0.0056 M H2O2. The trapping of iron oxide between g-C3N4 layers helped to stabilize iron oxide so the metal leaching problem that usually occurred in acidic media (pH = 3) can be effectively overcome. This work provides a new thought to develop environmental-friendly and high-efficient catalysts for the degradation of refractory pollutants in dark Fenton system, which is much easier to scale up for industrial application comparing with the photo-Fenton reaction.