Low-Cost Goethite Nanorods for As (III) and Se (VI) Removal from Water

Arsenite (As(III)) and Selenate (Se(VI)) are universally touted as extremely toxic oxyanions in natural and industrial water systems. Thus, the production of low-cost adsorbents that are scalable and toxic-free is of great importance today. In this work, a large-scale goethite nanorods (α-FeOOH NRs) is synthesized using a modified rapid hydrolysis method. The obtained powder is characterized using different multidisciplinary techniques. Accordingly, the results showed uniform and straight nanorods (length ~400 nm and diameter ~40 nm) resembling cigar-like morphology while the structure is confirmed to be of orthorhombic α-FeOOH phase. The potential application of this material to adsorb As (III) and Se (VI) ions in water is explored. In particular, for initial adsorbate concentrations (~500 µg/L), the removal efficiencies are found exceptional with α-FeOOH doses of 0.33 g/L and ~0.5 g/L for As (III) and Se (VI), respectively. Attractively, the adsorption capacities were estimated using trusted isotherms and then experimentally verified at ultimately high concentrations. Besides, a pH-controlled adsorption study showed that a pH of 5–8 is a favored range for higher ionic uptake, which meets the World Health Organization (WHO) benchmarks of drinking water. To conclude, the α-FeOOH NRs are potential adsorbent for the sustainable removal of toxin ions in water systems.

Teleost fish osmoregulation: what have we learned since August Krogh, Homer Smith, and Ancel Keys

In the 1930s, August Krogh, Homer Smith, and Ancel Keys knew that teleost fishes were hyperosmotic to fresh water and hyposmotic to seawater, and, therefore, they were potentially salt depleted and dehydrated, respectively. Their seminal studies demonstrated that freshwater teleosts extract NaCl from the environment, while marine teleosts ingest seawater, absorb intestinal water by absorbing NaCl, and excrete the excess salt via gill transport mechanisms. During the past 70 years, their research descendents have used chemical, radioisotopic, pharmacological, cellular, and molecular techniques to further characterize the gill transport mechanisms and begin to study the signaling molecules that modulate these processes. The cellular site for these transport pathways was first described by Keys and is now known as the mitochondrion-rich cell (MRC). The model for NaCl secretion by the marine MRC is well supported, but the model for NaCl uptake by freshwater MRC is more unsettled. Importantly, these ionic uptake mechanisms also appear to be expressed in the marine gill MRC, for acid-base regulation. A large suite of potential endocrine control mechanisms have been identified, and recent evidence suggests that paracrines such as endothelin, nitric oxide, and prostaglandins might also control MRC function.

The interrelationships between gill chloride cell morphology and ionic uptake in four freshwater teleosts

We have investigated the role of the gill chloride cell in transbranchial Na+ and Cl− uptake in four species of freshwater teleost maintained in water of identical ionic composition. The basic experimental protocol was to determine whether interspecific variability in the rates of whole body Na+ or Cl− uptake could be accounted for by similar interspecific variability in the fractional area of branchial chloride cells exposed to the external environment. To investigate the underlying cause(s) of intraspecific variability, chronic (10 day) treatment with cortisol in each species was used as a tool to evoke variations in both the rates of ionic uptake and chloride cell morphology. Examination of transmission and scanning electron micrographs revealed distinctive chloride cell and pavement cell morphology in each species. The results of quantitative morphometry, based on analysis of scanning electron micrographs, demonstrated that European eel (Anguilla anguilla) possessed the lowest chloride cell fractional area on the filament epithelium (11 288 ± 2133 μm2/mm2) followed, in increasing order, by brown bullhead catfish (Ictalurus nebulosus; 48 341 ± 7694 μm2/mm2), tilapia (Oreochromis mossambicus; 85 194 ± 10 326 μm2/mm2), and rainbow trout (Oncorhynchus mykiss; 146 333 ± 31 356 μm2/mm2). With the exception of rainbow trout, chronic treatment with cortisol caused significant increases in the chloride cell fractional area of filament epithelium owing to enlargement of the surface area of individual chloride cells and (or) proliferation of chloride cells. Both the inter- and intra-specific differences in chloride cell fractional area were reflected by similar differences in whole body Cl− and Na+ uptake. The results of correlation analysis revealed (with the exception of whole body Na+ uptake in A. anguilla) significant correlations between chloride cell fractional area and the rates of ionic uptake within and among the four species that were examined. These data suggest that the chloride cell is a significant site of ionic uptake in freshwater teleosts and that both inter- and intra-specific differences in the rates of ionic uptake can be explained by variability in the surface area of chloride cells on the gill epithelia.

Morphometric Effects of Low pH and Limed Water on the Gills of Atlantic Salmon (Salmo salar)

Gills from adult Atlantic salmon held in water from an acid river (Westfield River, Queens County, Nova Scotia; mean pH 4.8) were compared to gills from fish held in the same water treated with limestone (mean pH 5.5) and gills from fish held in a nearby control river (Medway River; mean 5.4). Morphometric analysis showed that fish held in the acidic water had more gill chloride cells and mucous cells than those held in the limed water or the control river. The difference in chloride cell number was due to increased numbers of the cells on the primary lamellar epithelium; numbers of cells on the secondary lamellae did not increase with acid exposure. Male fish were found to have more chloride cells on their secondary lamellae than female fish. Chloride cells were larger and more nearly spherical in shape in the fish exposed to low pH water. The liming treatment was partially effective in preventing changes in gill histology. Changes in size, shape, and number of chloride cells probably represent a response of increasing ionic uptake to offset the losses of ions occurring during low pH stress.

Branchial Ionic Uptake and Acid-Base Regulation in the Rainbow Trout, Salmo Gairdneri

1. Amiloride (10−4 M) inhibited sodium uptake in rainbow trout by 78% and was associated with a pronounced acidosis and decreases in both plasma total CO2 (Tcoco2)* and [HCO3−]. 2. 4-acetamido-4′-iso-thiocyanatostilbene-2,2′ disulphonic acid (SITS) (10−4M) in the bathing medium inhibited chloride uptake by 66% and following 6 h a significant decrease in plasma [H+] and significant increases in TCOCO2 and [HCO3−] were observed. 3. Inhibition of chloride uptake (50%) with external sodium bicarbonate (12 mM) resulted in a more rapid and pronounced alkalosis than did SITS inhibition. 4. Hypercapnic acidosis had no significant effect on the rates of branchial sodium and chloride uptake. 5. Increasing the concentration of sodium in the bathing water resulted in a less pronounced acidosis and a more rapid pH recovery during hypercapnia. 6. These results are discussed with reference to the gill as an acid-base regulating structure. These findings are consistent with a gill model previously presented by Haswell, Randall & Perry (1980).