Trends in spatial and temporal levels of persistent organic pollutants in Lake Erie sediments

A Lake Erie sediment survey was conducted in 1997 to characterize spatial trends in contamination, and for comparison with a 1971 survey to assess any changes in environmental quality since the advent of measures to reduce contaminant sources. Contaminant data for some contaminant classes in 1971 was based on analysis of frozen archived samples, thereby allowing a direct comparison between surficial sediment contamination in 1971 and 1997 based on modern analytical methods. Lake-wide contaminant concentrations of polychlorinated biphenyls (PCBs) and organochlorine compounds including hexachlorobenzene and the DDT compounds in 1997 were substantially lower, compared to levels in samples collected in 1971. Lake-wide average sediment PCB levels were found to have decreased roughly 70% from 136 ng/g in 1971 to 43 ng/g in 1997. Similarly, reductions in other compound classes ranged from 40% to 80%. In 1997, some individual contaminants classes including PCBs exhibited a spatial trend toward increasing sediment contamination from the eastern basin to the western basin, and from the north-central basin to the south-central basin. Levels of organic contaminants in sediments in some areas of Lake Erie still exceeded the strictest Canadian Federal and Ontario Provincial guidelines. However, exceedances of guidelines describing contaminated environments in 1997 were predominantly restricted to the western basin and near-shore sites in the southern part of the central basin.     

Application of mechanical shear in an internal-recycle for the enhancement of mesophilic anaerobic digestion.

A combination of bench- and full-scale studies were conducted to determine the effectiveness of high-intensity mechanical shear in an internal recycle loop to enhance mesophilic anaerobic digestion and the implications of this process for routine operations of a digestion system. During short-term batch digestion (56 hours), a 46% increase in biogas production was observed. However, it was found that the degree of digestion enhancement was sludge-specific, with increases in volatile solids destruction ranging from 16.6 to 110%. A full-scale demonstration showed increased total and volatile solids destruction of 22 and 21% for the primary digester and 17.2 and 11% for the secondary digester, respectively. The data also suggest that increased protein degradation is one of the major mechanisms associated with the observed increases in volatile solids destruction. The full-scale demonstration also determined that shear enhanced digestion can be operated without process upset, based on volatile fatty acid profile and headspace biogas composition (methane and carbon dioxide). Dewatering properties, as measured by polymer demand, deteriorated in the primary digester, but there was improvement in the secondary digester. High-intensity shear does not appear to enhance pathogen reduction based on total and fecal coliform bacterial enumeration.     

Effects of molluscicide baits on field populations of house mice

Two trials were carried out to test the effects of field applications of snail baits on populations of house mice (Mus domesticus) inhabiting cereal-cropping fields during a mouse plague in South Australia. In the first trial, grain based pellets containing 2% w/w active ingredient methiocarb, were laid in trails across fields before crops were sown. The second tested the effect of whole wheat grains treated with 1% w/w methiocarb when broadcast across maturing barley crops. Treatment effects were estimated by comparison with untreated control plots. In the methiocarb-treated wheat trial, comparison was also made with 0.3% w/w strychnine-treated wheat treatments. Methiocarb baiting reduced estimated mouse numbers by 0–46%. Surviving mice did not accept the excess bait material available. In contrast, strychnine-treated wheat reduced estimated mouse numbers by 86–94%. These trials indicate that methiocarb is not likely to be a useful field rodenticide. Furthermore, the consumption of bait by mice is not likely to jeopardise snail control operations. However, methiocarb baits could cause sufficient mortality to pose a threat to rare or endangered granivorous rodents inhabiting agricultural fields.     

Assessing the Response of Estuarine Intertidal Assemblages to Urbanised Catchment Discharge

Measurement of intertidal rock assemblages was investigated as a potential biological indicator to provide a quantitative estimate of the impact of urbanised catchment discharge on the estuaries of Sydney, Australia, from 1995 to 1999. Based on the presence and characteristics of adjacent human activities, sampling locations were categorised as: Bush; Urban; Urban with Sewer Overflows; and Industry with Sewer Overflows. In Sydney Harbour, variation in assemblage structure was measured between most impact categories, however differences between impact categories were not consistent for each year. Nevertheless, in years of above average rainfall (1998–1999), reference assemblages adjacent to national parks and distant from urbanisation were different to all other putatively impacted assemblages. Variability within assemblages was least at reference locations in each year and greatest at locations adjacent to stormwater canals and sewer overflows, particularly in 1998–1999. Variation in assemblage structure in Sydney estuaries was most strongly correlated with chlorophyll – a concentrations. Univariate analysis also identified highly significant differences for a number of factors, however, interactions between year, impact categories and location for numerous analyses, confounded the differentiation between impact categories. The results suggest that intertidal rock assemblages in Sydney Harbour and surrounding estuaries appear to be responding to the quality and quantity of discharge from urbanised catchments and, furthermore, that assemblages are more suitable than individual taxa to indicate the difference between Bush and anthropogenically disturbed estuarine locations.     

Convergent validity between willingness to pay elicitation methods: an application to Grand Canyon whitewater boaters

We directly compare trip willingness to pay (WTP) values between dichotomous choice contingent valuation (DCCV) and discrete choice experiment (DCE) stated preference surveys of private party Grand Canyon whitewater boaters. The consistency of DCCV and DCE estimates is debated in the literature, and this study contributes to the body of work comparing the methods. Comparisons were made of mean WTP estimates for four hypothetical Colorado River flow-level scenarios. Boaters were found to most highly value mid-range flows, with very low and very high flows eliciting lower WTP estimates across both DCE and DCCV surveys. Mean WTP precision was estimated through simulation. No statistically significant differences were detected between the two methods at three of the four hypothetical flow levels.     

Evaluation of a Slag and Portland Cement Mix to Simulate Treatment of Acidic Waste via Solidification/Stabilization in a Deep Soil Mix Application

Site investigations at an oil and gas facility identified a highly acidic waste referred to as residual acid tar that resulted in the transport of dissolved nickel toward the point of compliance at concentrations that exceeded site environmental screening levels. Solidification/stabilization (S/S) via deep soil mixing was selected as the remedial approach and a mixture of ground granulated blast furnace slag cement and Portland cement was subjected to treatability testing to evaluate the reagent mix's ability to achieve treatment objectives. Results from the treatability test showed a cement mix dose of 21 percent was sufficient to raise the pH above the target of 6.0 and reduce dissolved nickel concentrations to below site screening levels in leachate from treated samples of residual acid tar and material impacted by residual acid tar. Cement mix doses of 21 percent or greater were sufficient to achieve target strengths in the unimpacted shallow overburden. However, none of the doses tested were able to achieve target strengths in the residual acid tar or peaty material impacted by the residual acid tar. Results showed soil strengths increased significantly when the pH in leachate from the treated samples approached 12, suggesting the presence of organic acids related to the peaty soils may interfere with the cement set. Recommendations from the study include additional treatability testing to evaluate pre‐treatment with hydrated lime to satisfy acid neutralization requirements prior to dosing with the cement mix. ©2016 Wiley Periodicals, Inc.     

High-performance size exclusion chromatography with a multi-wavelength absorbance detector study on dissolved organic matter characterisation along a water distribution system

This study examined the associations between dissolved organic matter(DOM) characteristics and potential nitrification occurrence in the presence of chloramine along a drinking water distribution system. High-performance size exclusion chromatography(HPSEC) coupled with a multiple wavelength detector(200–280 nm) was employed to characterise DOM by molecular weight distribution, bacterial activity was analysed using flow cytometry, and a package of simple analytical tools, such as dissolved organic carbon, absorbance at 254 nm, nitrate,nitrite, ammonia and total disinfectant residual were also applied and their applicability to indicate water quality changes in distribution systems were also evaluated. Results showed that multi-wavelength HPSEC analysis was useful to provide information about DOM character while changes in molecule weight profiles at wavelengths less than 230 nm were also able to be related to other water quality parameters. Correct selection of the UV wavelengths can be an important factor for providing appropriate indicators associated with different DOM compositions. DOM molecular weight in the range of 0.2–0.5 k Da measured at210 nm correlated positively with oxidised nitrogen concentration(r = 0.99), and the concentrations of active bacterial cells in the distribution system(r = 0.85). Our study also showed that the changes of DOM character and bacterial cells were significant in those sampling points that had decreases in total disinfectant residual. HPSEC-UV measured at210 nm and flow cytometry can detect the changes of low molecular weight of DOM and bacterial levels, respectively, when nitrification occurred within the chloraminated distribution system.