Distributional Patterns of Arsenic Concentrations in Contaminant Plumes Offer Clues to the Source of Arsenic in Groundwater at Landfills

The distributional pattern of dissolved arsenic concentrations from landfill plumes can provide clues to the source of arsenic contamination. Under simple idealized conditions, arsenic concentrations along flow paths in aquifers proximal to a landfill will decrease under anthropogenic sources but potentially increase under in situ sources. This paper presents several conceptual distributional patterns of arsenic in groundwater based on the arsenic source under idealized conditions. An example of advanced subsurface mapping of dissolved arsenic with geophysical surveys, chemical monitoring, and redox fingerprinting is presented for a landfill site in New Hampshire with a complex flow pattern. Tools to assist in the mapping of arsenic in groundwater ultimately provide information on the source of contamination. Once an understanding of the arsenic contamination is achieved, appropriate remedial strategies can then be formulated. © 2013 Wiley Periodicals, Inc.*     

Ferrous iron oxidation rates in the pycnocline of a permanently stratified lake

Ferrous iron was found year round at 2-4 mM in the anoxic hypolimnion of the Halls Brook Holding Area (HBHA), a small lake in eastern Massachusetts. Oxygenated epilimnion waters always had total iron concentrations of <80 nanomolar, implying nearly complete oxidation of ferrous iron as it mixed upward across the lake's pycnocline. Assuming conductivity was a conservative parameter, and using data on the lake's water balance, upward advection rates (0.02-0.05 m d(-1)) and vertical eddy diffusion coefficients (0.007-0.05 m2 d(-1)) were determined for the lake's pycnocline on five dates. Using the same advection and diffusion parameters, corresponding pseudo first-order rate coefficients for ferrous iron oxidation, k(ox) (s(-1)), on those dates were calculated (0.0004-0.007 s(-1)). The values of k(ox) (s(-1)) were always too large to reflect only homogeneous solution reactions; and on at least four dates they appeared too fast to be due to heterogeneous catalysis on iron oxyhydroxides. This suggested that ferrous iron oxidation in this lake's pycnocline was primarily due to catalysis by microorganisms, and this was supported by comparison of azide-poisoned vs. untreated batch tests. As a result of their continuous production, iron oxyhydroxide precipitates and any associated sorbates/coprecipitates are most likely continuously settling back into the lake's deep water and bed sediments, except when episodic storm events flush these solids out of the pycnocline and downstream via the Aberjona River.     

A practical demonstration in modelling diclofenac and propranolol river water concentrations using a GIS hydrology model in a rural UK catchment

An existing GIS hydrology water quality model, LF2000-WQX, was applied to predict the concentrations of the pharmaceuticals diclofenac and propranalol in catchments. As a practical exercise the predominantly rural Tamar (UK) catchment was chosen. Consumption, excretion, and fate data were used to estimate the pharmaceutical input load for the model. The predicted concentrations throughout most of the catchment were 1 ng/L or less under low flow (90th percentile) conditions. However, at a few locations, downstream of small sewage treatment plants, concentrations above 25 ng/L were predicted. This exercise shows that it is relatively straightforward to predict the concentrations of new and emerging organic microcontaminants in real catchments using existing GIS hydrology water quality models. Further testing will be required to establish their accuracy.     

Effects of HMX exposure upon metabolic rate of northern bobwhite quail (Colinus virginianus) in ovo

We evaluated the use of the gas exchange rate as an ecologically relevant indicator of chemical stress in avian embryos/eggs. Northern bobwhite quail (Colinus virginianus) were exposed to octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) via feed containing nominal concentrations of 0, 12.5, 50.0, and 125.0 mg kg(-1). Metabolic rates (oxygen consumption) of developing quail eggs were then measured via respirometry to examine potential effects of HMX exposure. Metabolic rates were examined on 5, 9, and 21 d of incubation. Next, concentrations of HMX in embryos/eggs were determined by liquid chromatography-mass spectrometry. Mean (+/-SE) concentrations of HMX in eggs were 21.0+/-5.9, 1113+/-79.0, 3864+/-154.0, and 7426+/-301.1 ng g(-1) in control, low, medium and high dose groups, respectively. There were significant differences in oxygen consumption among the three embryo ages, however differences among the ages were not consistent among dose groups (age x dose group interaction p<0.0001). Oxygen consumption rates did not vary as a function of HMX in embryos (p=0.18). No evidence was observed for alterations of in ovo metabolic rates associated with HMX exposure.     

Interpretation of standard leaching test BS EN 12457-2: is your sample hazardous or inert?

A slag sample from a lead refiner has been obtained and given to two analytical laboratories to determine the release of trace elements from the sample according to BS EN 12457-2. Samples analysed by one laboratory passed waste acceptance criteria, leading it to be classified as an inert material; samples of the same material analysed by the other laboratory failed waste acceptance criteria and were classified as hazardous. It was found that the sample preparation procedure is the critical step in the leaching analysis and that the effects of particle size on leachability should be taken into account when using this standard. The purpose of this paper is to open a debate on designing a better defined standard leaching test and making current waste acceptance criteria more flexible.     

Does cannibalism in Spodoptera frugiperda (Lepidoptera: Noctuidae) reduce the risk of predation?

The incidence of cannibalism of larval Spodoptera frugiperda (Lepidoptera: Noctuidae) on maize under field conditions was investigated using field cages. Cannibalism was found to account for approximately 40% mortality when maize plants were infested with two or four fourth-instar larvae over a 3-day period. Field trials examined the effect of larval density on the prevalence of natural enemies of S. frugiperda. The abundance of predators (earwigs, staphylinids, other predatory beetles, and Chrysoperla spp.) was significantly greater on maize plants with higher levels of larval feeding damage, while the relationship between predator abundance and number of S. frugiperda larvae per plant was less clear. As larval damage is probably a more reliable indicator of previous larval density than numbers collected at an evaluation, this indicates that predation risk will be greater for larvae living in large groups. Parasitism accounted for 7.1% mortality of larvae in sorghum, and involved six species of Hymenoptera and Tachinidae. There was no effect of larval density or within-plant distribution on the probability of larval attack by parasitoids. The selective benefits of cannibalism, in relation to the risk of predation and parasitism, are discussed. Received: 23 March 2000 / Accepted: 24 June 2000     

Modelling concentrations of decamethylcyclopentasiloxane in two UK rivers using LF2000-WQX

Current regulatory environmental exposure assessments for decamethylcyclopentasiloxane (D₅), used in a range of personal care products, are based on a number of erroneous assumptions. Using an estimated D₅ flux to waste water of 11.6 mg cap⁻¹ d⁻¹, a 95.2% removal rate in Sewage Treatment Plants (STP) and a dilution factor of 10 results in modelled surface water concentrations that are up to an order of magnitude higher than concentrations observed downstream of STPs in two UK rivers. A GIS-based water quality model (LF2000-WQX) was used to predict concentrations of D₅ in two UK rivers. Assuming the STP removal rate is reasonable, a waste water flux of 2.4 mg cap⁻¹ d⁻¹ is needed in order to obtain a reasonable match between predicted and observed in-river concentrations. This flux is consistent with measured effluent concentrations. The results highlight major uncertainties in estimating chemical emission rates for volatile chemicals used in personal care products and suggest that measured concentrations in waste water are needed to refine exposure assessments.     

Tree and stand growth of mature Norway spruce and European beech under long-term ozone fumigation

In a 50- to 70-year-old mixed stand of Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica L.) in Germany, tree cohorts have been exposed to double ambient ozone (2×O₃) from 2000 through 2007 and can be compared with trees in the same stand under the ambient ozone regime (1×O₃). Annual diameter growth, allocation pattern, stem form, and stem volume were quantified at the individual tree and stand level. Ozone fumigation induced a shift in the resource allocation into height growth at the expense of diameter growth. This change in allometry leads to rather cone-shaped stem forms and reduced stem stability in the case of spruce, and even neiloidal stem shapes in the case of beech. Neglect of such ozone-induced changes in stem shape may lead to a flawed estimation of volume growth. On the stand level, 2×O₃ caused, on average, a decrease of 10.2 m³ ha⁻¹ yr⁻¹ in European beech.