Effect of soil sterilization by mercuric chloride on herbicide sorption by soil

Microbial inhibitors such as mercuric chloride are frequently used to sterilize soil or soil-water slurries in experimental studies on the fate of xenobiotics in the environment. This study examined the influence of mercuric chloride additions to soil-water slurries on the sorptive behaviour of a phenoxy herbicide (2,4-D) in soil. The results demonstrated that mercuric chloride strongly decreased the capacity of the soil to retain herbicides, and that the interference of mercuric chloride with herbicide sorption increased with increasing soil organic carbon contents. Because of the competitive sorption between mercuric chloride and the phenoxy herbicide, we conclude that mercuric chloride may not be a good soil sterilization procedure for use in xenobiotic fate studies.     

Invasion patterns inferred from cytochrome oxidase I sequences in three bryozoans, Bugula neritina, Watersipora subtorquata, and Watersipora arcuata

Nucleotide variation in cytochrome c oxidase subunit I (COI) was used to examine population structure in three invasive bryozoans: Bugula neritina (Linnaeus, 1758), Watersipora subtorquata (d’Orbigny, 1852), and W. arcuata (Banta, 1969). These species are found on ship hulls and have a short (≤2 days) larval phase. Samples were collected from 1998–2001 at multiple sites in Australia, and in Hong Kong, New Zealand, Hawaii, California, Curaçao, and England. B. neritina is known to include three cryptic species, including species Type S (Davidson and Haygood in Biol Bull 196:273–280, 1999) which occurs on the east and west coasts of the USA. One haplotype recorded previously in the USA, S1, was found to be widespread, occurring throughout Australia and in Hong Kong, Curaçao, Hawaii, and England. W. subtorquata, a Caribbean–Atlantic species which has invaded southern Australia, New Zealand, and California, had low nucleotide diversity in these areas (π=0.0016±0.0014), consisting of three haplotypes connected by one or two nucleotide mutations. W. arcuata, an Eastern-Pacific native, had comparatively high diversity (π=0.0221±0.0115) in introduced populations from Australia and Hawaii. In each species, identical haplotypes were identified on separate coastlines providing evidence of widespread, rather than genetically independent, introductions. The major contrast in nucleotide diversity suggests that different propagule-source models explain introductions.     

Effects of organic acids on adsorption of lead onto montmorillonite,goethite and humic acid

Adsorption isotherms for Pb onto six soil components (quartz, feldspar, kaolinite, montmorillonite, goethite and humic acid) were studied. The influence of pH, EDTA and citric acid on the adsorption of Pb onto montmorillonite, goethite and humic acid were considered. Results indicate that the experimental data fit the Langmuir Adsorption Isotherm. The adsorption capacity for Pb at pH 6 was found to be in the order: humic acid (22.7 mg g(-1)) > goethite (11.04 mg g(-1)) > montmorillonite (10.4 mg g(-1)) > kaolinite (0.91 mg g(-1)) > feldspar (0.503 mg g(-1)) > quartz (0.148 mg g(-1)). Generally, the amount of Pb adsorbed onto montmorillonite, goethite and humic acid decreased with increasing concentrations of EDTA and citric acid and with increases in alkality. However, there were two exceptions: (1) addition of citric acid increased the amount of Pb adsorbed onto humic acid; and (2) the amount of Pb adsorbed onto goethite decreased with increasing pH in the presence of EDTA. Some mechanisms involved in the adsorption reactions are discussed.     

Automatic continuous river monitoring of nitrate using a novel ion-selective electrode

On-site continuous measurement of nitrate in the River Taw situated in Devon (UK) was performed automatically for two months using a recently developed ion-selective electrode (ISE). A non-submersible electrode support system was developed and a field instrument was constructed comprising the nitrate-ISEs, a reference electrode and a temperature probe connected through a pre-amplifier to a data-logger and battery supply. The nitrate-ISE was constructed using a commercially available electrode body with a membrane incorporated into the tip. This rubbery membrane contained the sensor molecule (N,N,N-triallylleucine betaine chloride, 6.5% m/m) covalently bound to polystyrene-block-polybutadiene-block-polystyrene, SBS, (43.5% m/m), with 2-nitrophenyloctyl ether (2-NPOE) as mediator (40% m/m). The Nernstian slope was -59.1 mV per decade over a linear range of 1400-0.07 mg L(-1) nitrate-N. The limit of detection was 0.007 mg L(-1) nitrate-N with a selectivity coefficient for nitrate against chloride (k(pot)NO3-, Cl-) of 3.4 x 10(-3). The speed of response was less than a minute over the linear Nernstian range. The lifetime in the laboratory exceeded 5 months with no potentiometric drift over the linear Nernstian range. A temperature correction algorithm was also used to accomodate the temperature changes encountered in the river. The river nitrate results obtained with the ISEs at hourly intervals compared very favourably (R2 = 0.9) with those obtained with laboratory automated chemical determinations made on contemporaneous river samples over a concentration range 0.55-2.00 mg L(-1) nitrate-N. The ISEs did not require re-calibration and no deterioration in performance or fouling of the membrane surface was observed during 40 days.     

Body mass index and serum chlorinated dibenzo-p-dioxin and dibenzofuran levels

Several studies have found that current levels of 2,3,7,8 tetrachlorodibenzo-p-dioxin in serum lipids are related to age with older persons generally having higher levels. To account for this age pattern, reference ranges based on national samples have been established in order to allow determination of background levels for regional studies. In several studies, body mass index (BMI), has also been associated with current 2,3,7,8 tetrachlorodibenzo-p-dioxin levels with increasing body mass index related to increasing levels. We measured lipid-adjusted serum levels for all 2,3,7,8-substituted dioxins and furans in 62 chemical manufacturing workers with chlorophenol exposures and 36 workers without chlorophenol exposures employed at the same location. We then assessed the impact of age and BMI on the serum levels of all these compounds in the presence of other potential confounders. We found that both factors are important independent determinants of serum levels of 2,3,7,8-substituted dioxins and furans. Specifically, age and BMI are both important factors for assessing background levels of 2,3,7,8 tetrachlorodibenzo-p-dioxin, 1,2,3,7,8 pentachlorodibenzo-p-dioxin and the calculated total toxic equivalency. BMI, but not age, is important for assessing background levels of higher chlorinated dioxins and some hexachlorofurans. We conclude that age and BMI are both important considerations when comparing a potentially exposed group to a referent group, or to national norms. Further, age and BMI may also be important in epidemiology studies where back-extrapolation from current dioxin levels is used to assess historical chlorophenol exposure.     

Understanding the Factors That Influence Headwater Stream Flows in Response to Storm Events1

Stanfield, Les W. and Don A. Jackson, 2011. Understanding the Factors That Influence Headwater Stream Flows in Response to Storm Events. Journal of the American Water Resources Association (JAWRA) 1‐22. DOI: 10.1111/j.1752‐1688.2010.00518.x Abstract: Headwater drainage features (first‐ to second‐order streams) are the capillaries of the landscape that, among other things, moderate the timing and volumes of water available to the riparian and aquatic ecosystems. How these features respond to summer rainfall is poorly understood. We studied how geology and an index of land use/land cover influenced peak flows following rainfall events in 110 headwater stream sites that were studied over a four‐month period during a drought year. Highest peak flows were observed in the most urbanized catchments and in poorly drained soils, but specific responses were variable depending on both geology and land disturbance. Redundancy analysis indicated that both surficial geology and land disturbance were important factors influencing peak flows under drought conditions. We conclude that responses of these headwater streams to individual storms during drought conditions are unpredictable from data collected using our methods, but increased peak flows were associated with increased urban and agricultural development, but mitigated by surficial geology. These findings demonstrate the challenges to accurately predict flow conditions in headwater streams during periods of extreme weather that concurrently have the greatest potential effect on biota. The combination of these challenges and importance of such events indicates the need to develop new approaches to study and manage these resources.     

Evolutionary and Conservation Biology of Cichlid Fishes as Revealed by Faunal Remnants in Northern Lake Victoria

Lake Victoria until recently harbored the world's second richest lacustrine fish assemblage, but it is now experiencing a mass extinction. Here we report on the current status of the endemic cichlid fishes from a preliminary biotic inventory conducted as part of limnological reconnaissance in Kenyan and Ugandan waters during 1989–1992. Sixty-two haplochromine taxa were recovered, half of them new. Some are local endemics, while others are more widely distributed, based on review of earlier collections. Comparison with data from 1982–1984 and 1988 suggests that some shoreline assemblages have been locally stable over the past decade. In addition to littoral rock and vegetation, four kinds of refugia for indigenous fishes are recognized: (1) schools of Rastrineobola , (2) benthic microbial mats in deep water, (3) satellite lakes, (4) the oxycline. Reconnaissance by remote operated vehicle (ROV) documented fish kills due to deoxygenation of the water column, indicating the risk of using the oxycline as a refugium. Several species formerly abundant in Lake Victoria were found only in satellite lakes, revealing the importance of these lakes in the conservation of indigenous species. Recent events in Lake Victoria shed light on mechanisms of speciation and mass extinction, insights relevant to conservation planning for the valuable remnants of the lake's indigenous fauna.