PubMed · 10542838
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M Shank. 1999. Trouble with bubbles.. https://pubmed.ncbi.nlm.nih.gov/10542838/
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Laboratory studies were undertaken to evaluate the influence of fertilizers on pendimethalin volatilization and persistence in soil. Various organic fertilizers such as liquid humic substances and urea were used at doses of 100 L/ha or 170 kg of N/ha, respectively. Herbicide residues were determined in air, soil solution, and soil samples by GC-ECD; the recovery of pendimethalin from spiked fertilized or control samples was found to be 81-103%. Liquid humic fertilizers increased pendimethalin dissipation during the first part of the assay, although 4 months after application, herbicide levels were similar to those observed in unfertilized soil. Fertilization of soil with urea decreased, in general, pendimethalin volatilization but increased herbicide levels in soil solution and persistence in soil, with a pendimethalin half-life approximately 70% higher than that found in unfertilized soil.
Synchrotron X-ray studies and surface pressure versus molecular area (pi-A) isotherms of C18- and C20-sphingosines spread at air/water interfaces reveal unique interfacial properties with considerable differences between the two single hydrocarbon chain amino-alcohols. C20-sphingosine forms a crystalline monolayer with structural characteristics that are dominated by hydrogen bonding in the headgroup (common to its sphingolipid derivatives), whereas its natural counterpart C18-sphingosine forms a disordered liquidlike metastable monolayer and has to be spread in excess with a floating reservoir on the water surface to compensate for the high dissolution rate of molecules into the water subphase. The marginal affinity of C18-sphingosine to reside at the interface, the microcrystallization at very low densities, the corrugated monolayers it forms, and the strong interaction with the water surface are consistent with the roles that sphingolipids play in the life cycle of eukaryotic cells and as the building blocks of specialized membranes.
The exposure of fish to air is normally expected to interfere with the nitrogen excretion process. Hoplias malabaricus and Hoplerythrinus unitaeniatus, two teleost species, display distinct behaviors in response to decreases in natural reservoir water levels, although they may employ similar biochemical strategies. To investigate this point, plasma levels of ammonia, urea, uric acid, and the two urea cycle enzymes, ornithine carbamoyl transferase (OCT) and arginase (ARG), as well as glutamine synthetase (GS) were determined for both species after exposure to air. Plasma ammonia increased gradually during exposure to air, but only H. malabaricus showed increased concentrations of urea. Plasma uric acid remained very low in both fish. Enzymatic activities (mean +/- SD, micromol min(-1) g protein(-1)) of H. malabaricus showed significant increases (P<0.05, N = 6) in OCT from 0.84 +/- 0.05 to 1.42 +/- 0.03, in ARG from 8.07 +/- 0.47 to 9.97 +/- 0.53 and in GS from 1.15 +/- 0.03 to 2.39 +/- 0.04. The OCT and ARG enzymes remained constant in H. unitaeniatus (N = 6), but GS increased from 1.49 +/- 0.02 to 2.06 +/- 0.03. Although these species are very closely related and share the same environment, their biochemical strategies in response to exposure to air or to increased plasma ammonia are different.