William G. MacIntyre

GC determination of butyltins in natural waters by flame photometric detection of hexyl derivatives with mass spectrometric confirmation

Abstract Butyltin compounds in the 1–100 ng Sn/Liter range are solvent extracted from estuarine waters and derivatized with n-hexyl magnesium bromide. This forms tetraalkyltins that are quantified by gas chromatography with flame photometric detection and confirmed by gas chromatography mass spectrometry. The n-hexyl derivatives of methyltin and butyltin species are easily separated, and quantified relative to an internal standard, tripentyltin chloride.

Sorption of hydrophobic compounds on aquifer materials: analysis methods and the effect of organic carbon

Abstract Sorption studies of polynuclear aromatic hydrocarbons (PAH) on low-carbon aquifer materials are reported. Both column and batch partition coefficients (Kd) were affected by synthetic polymeric components, such as Teflon®, in commonly used experimental apparatus. These influences include incorrect (high) estimates for Kd and tailing of peaks in column studies. Both batch and column experimental methods are developed, using polymer-free systems, that allow accurate measurement of Kds for hydrophobic PAHs in low-carbon systems. Application of these methods shows that organic carbon contents below the commonly cited threshold level of 0.1% may dominate the partitioning and subsequent transport of phenanthrene in aquifer systems.

A thermodynamic study of solutions of liquid hydrocarbon mixtures in water

Abstract The hydrocarbon solution process in water was studied because it is important in environmental and geological situations. The aqueous solubility of binary hydrocarbon mixtures was determined ( n -octane + 1-methylnaphthalene at 20 and 70° C ; n -octane + ethylbenzene at 20° C and tetralin + methylcyclohexane at 20° C ). Vapor-liquid equilibrium hydrocarbon phase activity coefficients for the above mixtures were also determined. Hydrocarbon activity coefficients in the aqueous phase were found not to be measurably reduced in the presence of hydrocarbon co-solutes, in contradiction to the conclusions of Leinonen and Mackay (1973) and Leinonen (1976). This indicates that the effects of aqueous phase solute-solute interactions can not be determined within the precision of water solubility measurements. The presence of a substantial amount of water in the liquid hydrocarbon phase at 70°C did not significantly affect the hydrocarbon activity coefficients in the hydrocarbon phase. Activity coefficients estimated by the UNIFAC group-contribution method indicate that water in the hydrocarbon phase may not significantly affect hydrocarbon phase activity coefficients up to 150°C.

Zostera marina L. growth response to atrazine in root-rhizome and whole plant exposure experiments

Atrazine (2-chloro-4-[ethylamino]-6-[isopropylamino-]-s-triazine), a triazine herbicide, is one of the most widely used herbicides in the Chesapeake Bay watershed. Increased use of atrazine in the 1970s coincided with a decline in the abundance of Zostera marina L. (eelgrass). Ground-water surveys have found atrazine in concentrations that may affect eelgrass growth and survival. The effects of atrazine in groundwater discharges on the growth of eelgrass through root-rhizome exposure were examined in laboratory systems. A long term, dynamic, groundwater simulation study was conducted with atrazine concentrations ranging from 0.0 to 2.5 mg·l−1. No significant effects on chlorophyll content, growth or survival were detected. A static root-rhizome exposure experiment was conducted using split chamber exposure systems to verify these results, atrazine concentrations were increased by an order of magnitude. Neither mortality nor significant effects on plant growth were detected (maximum atrazine concentration 7.6 mg·l−1). A static, whole plant exposure experiment was conducted, and mortality was observed at atrazine concentrations of 1.9 mg·l−1 and above. This work suggests that eelgrass is not susceptible to atrazine through root-rhizome uptake, and that atrazine exposure via groundwater seepage did not cause the declines in eelgrass abundance and distribution.

Solution of hydrocarbons in a hydrocarbon-water system with changing phase composition due to evaporation.

Pure water was brought into contact with a four-component liquid hydrocarbon phase comprised of methylcyclohexane, ethylbenzene, tetralin, and 1-methyl-naphthalene. The headspace above the hydrocarbon phase was continually purged with N/sub 2/ to provide a controlled evaporative loss. Hydrocarbon concentrations in the water and hydrocarbon phases changed due to dissolution and evaporation and were measured as a function of time. A surface renewal mass transfer model is congruent with the observed hydrocarbon concentrations in the aqueous phase. Hydrocarbon-phase composition and component interactions are important in determining the time dependence of the aqueous-phase composition. The results have implications concerning the fate of components of petroleum products discharged in the aquatic environment. 12 references, 4 figures, 1 table.

Cycling of water through the sediment-water interface by passive ventilation of relict biological structures

Abstract The biogeochemical environment of benthic sediments is affected by seawater transport across the sediment-water interface and within the sediment pore spaces. Water circulation through the near surface sediments is produced by passive pumping of relict biostructures such as worm tubes and burrows. This passive ventilation results from hydrodynamic interactions between structures that protrude from the sediment surface and flowing water in the overlying boundary layer. Flow over the end of a cylindrical worm tube projecting above the sediment surface into the benthic boundary layer results in lowered pressure in the tube and in sediments around the bottom end of the tube. This induces flow of surface water through the adjacent sediment, and back to the surface through tube. A physical mechanism for this passive circulation is presented. A mathematical model of interstitial water circulation produced by passive hydrodynamic effects has been solved analytically for steady flow in homogeneous isotropic sediments. modflow , a finite difference groundwater flow model, is used to numerically determine the hydraulic gradients induced and the resulting flow through sediments near a structure under various conditions. The magnitude of passive irrigation fluxes depends on the size and position of relict structures, velocity of overlying surface water, hydraulic conductivity of the sediments, and the spatial distribution of tubes. For a typical sandy sediment, the hydraulic head in sediments near the bottom of a tube can be reduced by up to several centimeters, and the zone of reduced head can extend over several hundred square centimeters around the tube. Surface water is drawn into the sediment throughout this area with a mean influx velocity of 10 −3 cm/s or greater, yielding discharge rates on the order of tens to hundreds of milliliters per hour. These passive fluxes are of the same magnitude as active pumping rates, significantly greater than molecular diffusive fluxes, and may represent a major driving mechanism for cycling water through surface sediments.

Dissolved fatty acids in the James River estuary, Virginia, and adjacent ocean waters

The two meter depth of waters of the James River estuary and adjacent continental shelf was sampled at 34 locations. Dissolved fatty acids were analyzed by gas-liquid chromatography.

The boron-salinity relationship in estuarine sediments of the Rappahannock River, Virginia

Twelve sediment cores from the lower Rappahannock estuary in Virginia were analyzed for boron concentration, clay-silt ratio, and percent organic carbon. Clay-silt ratios and percent organic carbon, along with distance upstream in nautical miles and average water salinity, were used as independent variables in linear regression plots with boron concentration as the dependent variable. The results show a lack of correlation between boron concentration and either the clay-silt ratio or the percent organic carbon; however, both a negative correlation with distance upstream and positive correlation with salinity appear to be real. This is taken as evidence supporting the theory of boron incorporation in fine-grained sediments in amounts proportional to the salinity of the depositional environment.

Correlation between electron capture negative chemical ionization mass spectrometric fragmentation and calculated internal energies for polychlorinated biphenyls.

Correlationbse tween molecular structure and fragmentation observed in electron capture negative chemical ionization mass spectra (moderator gas = methane) of 49 selected tetrachlorinated, pentachlorinated, and hexachlorinated biphenyls have been investigated by using molecular modeling. The semiempirical general molecular orbital program MOPAC was used to calculate molecular properties for biphenyl and the 209 polychlorinated biphenyls. The mass spectrometric ionization and fragmentation processes were found to be linked to the number of chlorine atoms present on the biphenyl, and to the number of those chlorine atoms in the ortho (2, 2′, 6, and 6′) positions. The intensity of molecular ions increased with the number of chlorine atoms present, but this was counteracted by enhanced fragmentation as the number of ortho position chlorine atoms increased. The molecular parameters that were most closely linked with the number of ortho chlorine atoms were the twist angle between the phenyl rings and the energy of the lowest unoccupied molecular orbital (LUMO). It is suggested that fragmentation occurs when the energy of the ionizing electron exceeds the energy difference between the LUMO and LlJMO + 1 orbitals.

Quadricyclane hydration kinetics in natural waters

Hydration rates of quadricyclane were measured over a pH range of 3 to 8 in phosphate buffer, carbonate buffer, and nitric acid solutions. Norbornadiene was a minor impurity in the quadricyclane, and its hydration rate was also measured. Hydration products were exo-5-norbornen-2-ol (bicyclo[2.2.1]hept-5-ene-2-ol) and nortricyclyl alcohol (tricyclo[2.2.1.03,5 ]heptane-2-ol). Diol formation was not detected. Quadricyclane hydration in solutions containing chloride ions formed the alcohols and their chlorinated analogs. A mechanism consistent with observed kinetics and reaction products involving two carbocation intermediates is proposed. Comparison of reaction rates was used to determine the role of buffer catalysis and chlorination reactions in natural waters. Phosphate buffer catalysis was shown to be important, and rate constants for all phosphate species were calculated. Comparison of hydration rates in nitric acid and carbonate buffer indicated that catalysis by carbonate species for this reaction is unimportant in surface waters. Catalytic effects of other buffers in some natural waters appear possible. Proper buffer selection is important if laboratorymeasured hydration rates of quadricyclane are to be applied to natural water systems.