Marcos A. Cheney

Mechanochemical degradation of 2,4-D adsorbed on synthetic birnessite

Abstract Mechanochemical degradation of 2,4-D (2,4-dichlorophenoxyacetic acid) adsorbed on synthetic birnessite (δ-MnO 2 ) was investigated using heat conduction calorimetry. The overall transformation kinetics of 2,4-D on birnessite after light grinding were approximately first-order, with an apparent activation energy of approximately 37 kJ mol −1 for the range of temperatures 10–50°C. The two decomposition products detected under mechanochemical degradation and incubation were 2,4-dichlorophenol and CO 2 , but no consumption of gaseous oxygen was detected. A positive correlation was found between Mn(II) produced and CO 2 evolved, suggesting that the decomposition of 2,4-dichlorophenol involves the oxide substrate as a source of oxygen and yields Mn(II).

HERBICIDE AND ESTROGEN EFFECTS ON THE METABOLIC ACTIVITY OF ELLIPTIO COMPLANATA MEASURED BY CALORESPIROMETRY

Herbicides and estrogen are important contaminants of world water systems with effects on aquatic organisms. The effects of short-time exposure to atrazine, 2,4-Dichlorophenoxyacetic acid (2,4-D), paraquat, and estrogen on the metabolic activity of gill tissue from the freshwater bivalve Elliptio complanata were investigated by isothermal calorimetry and respirometry. Metabolic heat rates were altered following short-time exposure of gill tissue to these compounds over the concentration range from 10(-6) to 10(-3) M. The effects of herbicides and estrogen on metabolic heat rates were compound specific and time and concentration dependent. Treatment of tissue with estrogen caused stimulation of metabolic heat rates. In general, treatment with herbicides at low concentration or short times of exposure caused stimulation of metabolic heat rates, possibly due to uncoupling. Longer exposures and higher concentration subsequently caused inhibition of metabolic activity and decreased metabolic heat rates. Treatment of mitochondria isolated from gill and muscle tissues showed a similar pattern of respiratory rate stimulation at concentrations of 10(-4) M 2, 4-D and inhibition at higher concentration. Analysis of CO2 and O2 from the headspace gases in the calorimeter ampule showed an increase in the respiratory quotient indicating a shift in metabolism following addition of 2,4-D or paraquat.

Mechanochemical degradation of atrazine adsorbed on four synthetic manganese oxides

Abstract Atrazine is an important contaminant of world water systems with effects on aquatic life and humans. Thus, its reactivity with soil minerals is an important issue. We have studied the mechanochemical degradation of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) adsorbed on synthetic pyrolusite (β-MnO2), birnessite (δ-MnO2), and cryptomelane types I and II (α-MnO2, α-MnO2) using differential scanning calorimetry (DSC) and spectroscopy. The overall transformation kinetics of atrazine on cryptomelane type II after light grinding does not appear to follow first order kinetics. However, first order kinetics seems to apply to birnessite at 30°C. The three decomposition products detected under mechanochemical degradation and incubation were DEA, DIA, and DDA, Mn(II) and CO2, but no consumption of gaseous oxygen was detected. A positive correlation was found between Mn(II) produced and CO2 evolved only for cryptomelane II, suggesting that the decomposition of atrazine on this mineral surface involves the oxide substrate as a source of oxygen and yields Mn(II).

ATRAZINE DEALKYLATION ON A MANGANESE OXIDE SURFACE

In this paper we report the first observation of abiotic N-dealkylation of the herbicide, atrazine[6-chloro-N-ethyl-N″-(1-methylethyl)-1,3,5-triazine-2,4-diamine], by synthetic manganese oxide (δ-MnO2). The degradation reaction of the adsorbed herbicide was quantified at 30°C by combined calorimetry, manometry, gas chromatography-mass spectrometry, liquid chromatography, and electron spin resonance spectroscopy. These combined methodologies gave clear evidence for the production of N-dealkylated forms of atrazine over a 48 h period of reaction on the surface of δ-MnO2. This surface-catalyzed, non-photochemical abiotic N-dealkylation of the herbicide differs from known microbial pathways in soils by a higher rate of reaction and a different distribution of products among N-dealkylated forms.

The Uptake of Vanadium(V) and Other Metals by the Isolated Branchial Sacs of the Ascidians Ascidia ceratodes, Ciona intestinalis, and Styela montereyensis

Abstract Isolated branchial sacs from the phlebobranch ascidian Ascidia ceratodes take up vanadium (V), to a level four times greater than the uptake by branchial sacs from the aplousobranch and stolidobranch ascidians Ciona intestinalis and Styela montereyensis , respectively. These differences in vanadium uptake may be important in the observed enhanced accumulation of vanadium in the blood cells of A. ceratodes compared to those of C. intestinalis and S. montereyensis . The uptake of iron (lll) by branchial sacs of S. montereyensis, C. intestinalis , and A. ceratodes increases in that order, but iron uptake by A. ceratodes is substantially less than that of vanadium. Branchial sacs from A. ceratodes accumulate manganese (ll) to a lesser degree than iron (lll), and mercury (ll) to a greater degree than vanadium (V).

Effects of divalent cations on amino acid and divalent cation losses from and glycine influx into gills of freshwater bivalve molluscs Anodonta californiensis and Corbicula manilensis

Abstract The losses of Ca 2+ , Mg 2+ and primary amines from excised gills of the freshwater bivalve molluscs Anodonta californiensis and Corbicula manilensis were measured as a function of the concentration of the divalent cations Ca 2+ and Mg 2+ in the medium. The rate of loss of primary amines was reduced by the presence of Mg 2+ and more effectively by Ca 2+ . This observation is consistent with the proposed role of Ca 2+ in maintaining low permeability of membranes. The losses of Ca 2+ and Mg 2+ were not affected by Mg 2+ and Ca 2+ , respectively, suggesting that these cations may bind to different sites. Glycine influx into the gills of freshwater molluscs is not an active transport process. The influx of glycine is reduced by the presence of both Ca 2+ and Mg 2+ , in contrast to the influx of glycine into gills of the marine bivalve mollusc Mytilus californianus , which is increased by Mg 2+ and unaffected by Ca 2+ . In the case of the freshwater species, the decrease in influx with increasing Ca 2+ and Mg 2+ concentrations is probably a result of changes in the permeability of gill membranes. The difference between the effect of Ca 2+ and Mg 2+ on the uptake properties of the freshwater and marine bivalve molluscs may be related to the marine species having more polar lipids than the freshwater species.