Ecology of freshwater harmful euglenophytes: A review.

A diverse array of aquatic ecosystems are inhabited by the euglenophytes, a group of autotrophic and eukaryotic organisms. In inland waterbodies, the red bloom is caused by a rapid development or accumulation of euglenophytes. Recent studies have designated euglenophytes as bioindicator of organic pollution. The ecology of euglenophytes is influenced by the changes in the intensity of sunlight, temperature, nutrient cycles, and seasons. Most of the species of euglenophytes grow prolifically with the increase of water temperature. Nitrogen and phosphorus are often thought to be the main nutrients that influence the cellular growth of toxic euglenophytes. A high concentration of nutrients is required for the euglenophytes to grow and to form bloom. Heavy bloom of euglenophytes in the summer season is the characteristic of eutrophic ponds. Inland waterbodies in many countries suffer from euglenophyte blooms, which shade submerged vegetation, deplete the dissolved oxygen and disrupt the aquatic food webs. Dense bloom of euglenophytes clog the gills of fishes, cause breathing difficulties and in extreme cases results mortality. Red blooms of the deadly toxin producing Euglena sanguinea negatively affect the water quality resulting massive mortality of fishes. Consequently, aquaculture systems and fisheries are facing a serious threat from the predicted outbreak of toxic red blooms of euglenophytes worldwide. To ensure sustainability in the fisheries and aquaculture industry, it is essential to analyze the ecology of euglenophytes. Again, interesting research on euglenophycin, a Euglena-derived natural product, has shown that it can be utilized as a potential anti-cancer drug. This paper comes up with a thorough review of the latest research in this area, revealing new insights and solutions that can help mitigate the negative impact of the freshwater harmful euglenophytes. By implementing considerable management strategies, the health of the valuable aquatic ecosystems and the future of the aquaculture and fisheries can also be secured.

Microplastics pollution in the river Karnaphuli: a preliminary study on a tidal confluence river in the southeast coast of Bangladesh.

Bangladesh is a deltaic country in Asia, and its riverine systems ultimately drain into the Bay of Bengal. Plastic is a severe environmental issue for coastal-marine ecosystems due to the indiscriminate usage and discarding of plastic items in the upstream river that eventually find their route into the Bay of Bengal. Microplastics (MPs) are widespread pollutants in almost all environmental compartments, including aquatic environments. This study aimed to quantify and understand the distribution of microplastics in surface water and sediments of the river Karnaphuli, a tidal confluence river adjacent to the Chattogram seaport city of Bangladesh, a highly inhabited and industrial area on the southeast coast of the Bay of Bengal. A manta trawl net (300-µm mesh size) was used to collect surface water samples, while an Ekman dredge was used to collect sediment samples. The concentrations of microplastics in the surface water of the river Karnaphuli during late monsoon, winter, and early summer were recorded to be 120,111.11, 152,222.22, and 164,444.44 items/km2, respectively, while in sediments, those were recorded to be 103.83, 137.50, and 103.67 items/kg, respectively. A higher abundance of microplastics was observed in downstream surface water (228,888.88 items/km2) and sediments (164.17 items/kg). Smaller sizes (0.3 to 0.5 mm) of microplastics were predominant, fibers or threads were the frequent types, and black was the most common color in the river Karnaphuli. The Fourier transform infrared analysis revealed that polyethylene terephthalate (surface water: 22%, sediments: 19%), polyamide (surface water: 15%, sediments: 13%), polyethylene (surface water: 12%, sediments: 18%), polystyrene (surface water: 13%, sediments: 11%), and alkyd resin (surface water: 13%, sediments: 10%) were the most prevalent polymers in the river Karnaphuli. Moreover, there was a moderate positive correlation between MPs abundance in surface water and sediments. Therefore, improved long-term research (in different seasons with horizontal and vertical monitoring) is necessary in order to accurately determine the flux of microplastics from the river Karnaphuli to the Bay of Bengal.

Investigation of Morphological, Optical, and Dielectric Properties of RF Sputtered WOx Thin Films for Optoelectronic Applications.

Tungsten oxide (WOx) thin films were synthesized through the RF magnetron sputtering method by varying the sputtering power from 30 W to 80 W. Different investigations have been conducted to evaluate the variation in different morphological, optical, and dielectric properties with the sputtering power and prove the possibility of using WOx in optoelectronic applications. An Energy Dispersive X-ray (EDX), stylus profilometer, and atomic force microscope (AFM) have been used to investigate the dependency of morphological properties on sputtering power. Transmittance, absorbance, and reflectance of the films, investigated by Ultraviolet-Visible (UV-Vis) spectroscopy, have allowed for further determination of some necessary parameters, such as absorption coefficient, penetration depth, optical band energy gap, refractive index, extinction coefficient, dielectric parameters, a few types of loss parameters, etc. Variations in these parameters with the incident light spectrum have been closely analyzed. Some important parameters such as transmittance (above 80%), optical band energy gap (~3.7 eV), and refractive index (~2) ensure that as-grown WOx films can be used in some optoelectronic applications, mainly in photovoltaic research. Furthermore, strong dependencies of all evaluated parameters on the sputtering power were found, which are to be of great use for developing the films with the required properties.

Acute toxicity of an organophosphate insecticide sumithion to striped catfish Pangasianodon hypophthalmus.

Sumithion is widely used for crop safety and eradication of tiger bugs (Cicindela spp.) from larval rearing aquaculture ponds. To satisfy the high demand of fries and fingerlings of widely cultured species striped catfish, spawns are produced in large scale in the hatcheries through hormone induced breeding, and subsequently these spawns are reared in nursery ponds and marketed to fingerlings vendors for stocking in grow-out ponds. Considering the importance of healthy fries and fingerlings the present experiment was conducted to evaluate the toxic effects of sumithion on striped catfish fingerlings. Fish were exposed for 96 h to six concentrations of sumithion (0, 3, 4, 5, 6 and 7 mg/l) each with three replications. The 96 h LC50 value was calculated using probit analysis. After 96 h of exposure fishes were sacrificed to measure hemato-biochemical (Hemoglobin, Hb; Red blood cell, RBC; White blood cell, WBC and blood glucose) parameters. In addition, formation of micronucleus (MN) was examined in the blood erythrocytes. The 96 h LC50 value of sumithion for striped catfish was 5.886 mg/l. The values of RBCs and Hb decreased significantly in different concentrations of the toxicant compared to control, while the values of WBC and blood glucose levels showed opposite scenario. Consequently, the frequencies of formation of MN increased significantly in different concentrations of the toxicant compared to the control. The results of the current study denoted that sumithion exerts toxicity to striped catfish. It is expected that the findings of the present research will help in the development of awareness of the concerned people about the toxic effect of sumithion as well as other insecticides and pesticides in the environment.

Increased water temperature altered hemato-biochemical parameters and structure of peripheral erythrocytes in striped catfish Pangasianodon hypophthalmus.

The increase of water temperature due to global warming is a great concern of aquaculturists and fishery biologists. In the present study, we examined the effects of high temperature on hematological parameters and blood glucose levels in striped catfish, Pangasianodon hypophthalmus exposed to three temperature conditions (28, 32, and 36 °C) for 7 days. Fish were sacrificed at days 1, 3, and 7. Erythroblasts (Ebs), erythrocytic cellular abnormalities (ECA), and erythrocytic nuclear abnormalities (ENA) were assayed using peripheral erythrocytes of the sampled fishes. Hemoglobin (Hb) and red blood cell (RBC) significantly (P < 0.05) decreased at 36 °C after 3 and 7 days of exposure, whereas white blood cell (WBC) showed opposite scenario. Blood glucose levels significantly (P < 0.05) increased at 36 °C on day 3. Frequencies of Ebs, ECA, and ENA were found to be elevated at increased temperature. Differential leucocytes count showed significant increases in neutrophil and decreases in lymphocytes in the highest temperature (36 °C). Dissolved oxygen decreased and free CO2 increased significantly (P < 0.05) with increasing temperature, while the pH and total alkalinity of the water were almost unchanged throughout the study period. Therefore, the present study demonstrated that striped catfish feel better adaptation at 28 and 32 °C, while high temperature 36 °C is likely stressful to this fish species.

Study of harmful algal blooms in a eutrophic pond, Bangladesh.

The purpose of this research was to analyze the underlying mechanisms and contributing factors related to the seasonal dynamic of harmful algal blooms in a shallow eutrophic pond, Bangladesh during September 2005-July 2006. Two conspicuous events were noted simultaneously throughout the study period: high concentration of phosphate-phosphorus (>3.03; SD 1.29 mg l(-1)) and permanent cyanobacterial blooms {>3,981.88×10(3) cells l(-1) (SD 508.73)}. Cyanobacterial blooms were characterized by three abundance phases, each of which was associated with different ecological processes. High nitrate-nitrogen (>2.35; SD 0.83 mg l(-1)), for example, was associated with high cyanobacterial abundance, while low nitrate-nitrogen (0.36; SD 0.2 mg l(-1)) was recorded during moderate abundance phase. Extremely low NO3-N/PO4-P ratio (>3.55, SD 2.31) was recorded, and all blooming taxa were negatively correlated with this ratio. Cyanobacterial blooms were positively correlated with temperature (r=0.345) and pH (0.833; p=0.05) and negatively correlated with transparency (r=-0.956; p=0.01). Although Anabaena showed similar relationship with water quality parameters as cyanobacteria, the co-dominant Microcystis exhibited negative relationship with temperature (r=-0.386) and nitrate-nitrogen (r=-0.172). This was attributed to excessive growth of Anabaena that suppressed Microcystis's growth. Planktothrix was the third most dominant taxa, while Euglena was regarded as opportunistic.

Microcystins (cyanobacterial toxins) in surface waters of rural Bangladesh: pilot study.

In Bangladesh the exposure of millions of inhabitants to water from (shallow) tube wells contaminated with high geogenic loads of arsenic is a major concern. As an alternative to the costly drilling of deep wells, the return to the use of surface water as a source of drinking water is considered. In addition to the well-known hazards of water borne infectious diseases associated with the use of surface water, recently the potential public health implications of toxic cyanobacteria have been recognized. As a first step towards a risk assessment for cyanotoxins in Bangladesh surface waters, seston samples of 79 ponds were analysed in late summer 2002 for the presence of cyanobacteria and microcystins (MCYST), the most frequently detected cyanobacterial toxins worldwide. Microcystins could be detected in 39 ponds, mostly together with varying abundance of potentially microcystin-producing genera such as Microcystis, Planktothrix and Anabaena. Total microcystin concentrations ranged between <0.1 and > 1,000 microg l(-1), and more than half of the positive samples contained high concentrations of more than 10 microg l(-1). The results clearly show that concentrations of microcystins well above the provisional WHO guideline value of 1 microg l(-1) MCYST-LR can be frequently detected in Bangladesh ponds. Thus, an increasing use of surface water for human consumption introduces a risk of replacing one health hazard by another and therefore needs to be accompanied by cyanotoxin hazard assessments.

Effect of nitric oxide on H+ -efflux in presence of various nutrients in Candida albicans.

In the present study tentative link has been established between H+ -efflux and effect of NO in presence of various nutrients (glucose, 2-deoxy-D-glucose, xylose, proline, glutamic acid and lysine) in C. albicans using sodium nitroprusside (SNP) as a potent source of NO. It was observed that there was a decreasing trend in pH with time, in control, while SNP treated cells showed an initial decline in pH for 10-15 min, followed by an increase in pH up to 30 min. In presence of glucose there was an enhancement in H+ -efflux by 9-fold whereas proline, glutamic acid and lysine showed enhancement by 3, 6 and 1.5-fold respectively. Similar trends in increase in pH after 15 min in SNP treated cells of Candida was observed in presence of all nutrients used. It was demonstrated for the first time that H+ -ATPase of C. albicans was affected by NO.