Extractability of elements in sugar maple xylem along a gradient of soil acidity

Dendrochemistry has been used for the historical dating of pollution. Its reliability is questionable due primarily to the radial mobility of elements in sapwood. In the present study, the extractability of seven elements was characterized to assess their suitability for the monitoring of environmental conditions. Nine mature sugar maple trees (Acer saccharum Marsh.), a wide-ranging species in eastern North America that has suffered decline in past decades, were sampled in three Quebec watersheds along a soil acidity gradient. Five-year groups of annual tree rings were treated by sequential chemical extractions using extractants of varying strength (deionized H2O, 0.05 M HCl, and concentrated HNO(3)) to selectively solubilize the elements into three fractions (water-soluble, acid-soluble, and residual). Monovalent K; divalent Ba, Ca, Cd, Mg, Mn; and trivalent Al cations were found mostly in the water-soluble, acid-soluble, and residual fractions, respectively. Forms more likely to be mobile within the tree (water-soluble and acid-soluble) do not seem to be suitable for temporal monitoring because of potential lateral redistribution in sapwood rings. However, certain elements (Cd, Mn) were responsive to current soil acidity and could be used in spatial variation monitoring. Extractability of Al varied according to soil acidity; at less acidic sites, up to 90% of Al was contained in the residual form, whereas on very acidic soils, as much as 45% was found in the water-soluble and acid-soluble fractions. Sequential extractions can be useful for determining specific forms of metals as key indicators of soil acidification.     

Past, current and future fire frequency in the Canadian boreal forest: implications for sustainable forest management

Over the past decades, there has been an increasing interest in the development of forest management approaches that are based on an understanding of historical natural disturbance dynamics. The rationale for such an approach is that management to favor landscape compositions and stand structures similar to those of natural ecosystems should also maintain biological diversity and essential ecological functions. In fire-dominated landscapes, this approach is possible only if current and future fire frequencies are sufficiently low, comparing to pre-industrial fire frequency, that we can substitute fire by forest management. We address this question by comparing current and future fire frequency to historical reconstruction of fire frequency from studies realized in the Canadian boreal forest. Current and simulated future fire frequencies using 2 and 3 x CO2 scenarios are lower than the historical fire frequency for many sites, suggesting that forest management could potentially be used to recreate the forest age structure of fire-controlled pre-industrial landscapes. There are however, important limitations to the current even-age management.     

Use of the ouput of a lead risk assessment model to establish soil lead cleanup levels

Three general methods to calculate soil contaminant cleanup levels are assessed: the truncated lognormal approach, Monte Carlo analysis, and the house-by-house approach. When these methods are used together with a lead risk assessment model, they yield estimated soil lead cleanup levels that may be required in an attempt to achieve specified target blood lead levels for a community. The truncated lognormal approach is exemplified by the Society for Environmental Geochemistry and Health (SEGH) model, Monte Carlo analysis is exemplified by the US EPA's LEAD Model, and the house-by-house approach is used with a structural equation model to calculate site-specific soil lead cleanup levels. The various cleanup methods can each be used with any type of lead risk assessment model. Although all examples given here are for lead, the cleanup methods can, in principle, be used as well with risk assessment models for other chemical contaminants to derive contaminant-specific soil cleanup levels.     

Role of surface chemical signals in egg cannibalism and intraguild predation in ladybirds (Coleoptera: Coccinellidae)

Summary. The eggs of some ladybirds are known to be toxic to intraguild ladybird predators. However, this defence is of little value if the eggs are killed before their toxicity becomes apparent. The results presented in this paper indicate that chemicals on the surface of the eggs of two species of ladybirds signal the relative risk of cannibalism and intraguild predation. In Adalia bipunctata and Coccinella septempunctata, 87% of the chemicals are alkanes. Each species of ladybird is less reluctant to eat their own eggs than those of the other species. This asymmetry is to be expected because there is a greater risk to ladybirds from intraguild predation than cannibalism. Similar alkanes to those on the surface of the eggs of A. bipunctata are present in tracks left by larvae and on the elytra of the adults of this species. Those in the larval tracks deter females from ovipositing in patches of prey already being attacked by their larvae and those on the elytra are used in mate recognition. That different context dependent messages could be signalled by similar chemicals is an example of semiochemical parsimony. Received 25 February 2000; accepted 22 May 2000     

Disentangling trophic relationships in a High Arctic tundra ecosystem through food web modeling

Determining the manner in which food webs will respond to environmental changes is difficult because the relative importance of top-down vs. bottom-up forces in controlling ecosystems is still debated. This is especially true in the Arctic tundra where, despite relatively simple food webs, it is still unclear which forces dominate in this ecosystem. Our primary goal was to assess the extent to which a tundra food web was dominated by plant-herbivore or predator-prey interactions. Based on a 17-year (1993-2009) study of terrestrial wildlife on Bylot Island, Nunavut, Canada, we developed trophic mass balance models to address this question. Snow Geese were the dominant herbivores in this ecosystem, followed by two sympatric lemming species (brown and collared lemmings). Arctic foxes, weasels, and several species of birds of prey were the dominant predators. Results of our trophic models encompassing 19 functional groups showed that <10% of the annual primary production was consumed by herbivores in most years despite the presence of a large Snow Goose colony, but that 20-100% of the annual herbivore production was consumed by predators. The impact of herbivores on vegetation has also weakened over time, probably due to an increase in primary production. The impact of predators was highest on lemmings, intermediate on passerines, and lowest on geese and shorebirds, but it varied with lemming abundance. Predation of collared lemmings exceeded production in most years and may explain why this species remained at low density. In contrast, the predation rate on brown lemmings varied with prey density and may have contributed to the high-amplitude, periodic fluctuations in the abundance of this species. Our analysis provided little evidence that herbivores are limited by primary production on Bylot Island. In contrast, we measured strong predator-prey interactions, which supports the hypothesis that this food web is primarily controlled by top-down forces. The presence of allochthonous resources subsidizing top predators and the absence of large herbivores may partly explain the predominant role of predation in this low-productivity ecosystem.     

Documenting lemming population change in the Arctic: Can we detect trends?

Lemmings are a key component of tundra food webs and changes in their dynamics can affect the whole ecosystem. We present a comprehensive overview of lemming monitoring and research activities, and assess recent trends in lemming abundance across the circumpolar Arctic. Since 2000, lemmings have been monitored at 49 sites of which 38 are still active. The sites were not evenly distributed with notably Russia and high Arctic Canada underrepresented. Abundance was monitored at all sites, but methods and levels of precision varied greatly. Other important attributes such as health, genetic diversity and potential drivers of population change, were often not monitored. There was no evidence that lemming populations were decreasing in general, although a negative trend was detected for low arctic populations sympatric with voles. To keep the pace of arctic change, we recommend maintaining long-term programmes while harmonizing methods, improving spatial coverage and integrating an ecosystem perspective.     

A general kinetic law for heavy metal vaporization during municipal solid waste incineration

Metal emissions from waste incineration plants become a great environmental concern because of their toxicity for both human health and environment. Metals are not destroyed by high-temperature thermal treatment and some vaporized metals may be emitted. It is thus essential to understand the release mechanism of metals during high-temperature waste treatment, in order to improve the understanding of their behavior and the control of their emission. The objective of this study is to identify the kinetic law for metal release from realistic artificial waste. The vaporization of three metals of most concern (Cd, Pb and Zn) during municipal waste incineration was studied. The vaporization rate at the particle level was determined from the experimental concentration profile in the outlet gas of a fluidized bed reactor, by using the inverse method that was previously developed and validated by our team. As a first step, the kinetic parameters were determined thanks to experiments carried out at several temperatures. Specific laws, for each studied metal, were thus obtained as a function of temperature. Nevertheless, it is very useful to identify all the experimental kinetic curves (all studied metals at all temperatures) to one single mathematical law. Therefore, a general kinetic law, expressing the solid matrix influence on the metal vaporization dynamic, was determined as a second step. It permits to predict the vaporization characteristic time and the time course of the metal concentration in the waste.     

Diffusive gradients in thin films,Rhizon soil moisture samplers,and indicator plants to predict the bioavailabilities of potentially toxic elements in contaminated technosols

The phytoavailabilities and potential remobilization of potentially toxic elements (PTEs) such as Zn, Pb, Cd, As, and Sb were assessed in contaminated technosols from former mining and smelting sites. The PTE concentrations in soil pore water (SPW) and diffusive gradients in thin films (DGT)-measured concentration (C _DGT) methods were used to assess the bioavailabilities of PTE and their remobilization in this study. Together with classical Chelex-100 DGT probes to measure Zn, Cd, and Pb, novel ferrihydrite-backed DGT were used for As and Sb measurements alongside with Rhizon soil moisture sampler method for SPW sampling. To assess the phytoavailabilities of PTE, a germination test with dwarf beans as a plant indicator was used for this purpose. Dwarf bean primary leaves showed high Zn concentrations in contrast to Pb and Cd which showed low phytoavailabilities. Despite As and Sb are present in high concentrations in the mine tailings, their phytoavailabilities indicate very low bioavailabilities. The amounts of Zn, Pb, Cd, As, and Sb extracted with DGT devices correlated well with the total dissolved PTE concentrations in the SPW. The highest R values were observed for Zn, followed by Cd and Pb, indicating the ability of the soil to sustain SPW concentrations, which decreased in that order. Good correlations were also observed between each of dissolved PTE concentrations in SPW, DGT-measured PTE concentrations (C _DGT), and the accumulation of PTE in dwarf bean primary leaves. It could be concluded that the use of Rhizon soil moisture samplers and DGT methods may be considered to be a good methods to predict the PTE bioavailabilities in contaminated technosols.     

Atmospheric concentrations of PCDD/Fs, dl-PCBs and some pesticides in northern Algeria using passive air sampling

Perfluorooctanesulfonate (PFOS) is the terminal degradation product of many commercially used perfluorinated compounds, and most of the toxicity testing to date has focused on its potential biological effects. While PFOS has been extensively studied, other PFCs including replacement chemicals such as perfluorobutanesulfonate (PFBS) and perfluorobutyric acid (PFBA), have not been well characterized. Despite the relative lack of data available on these other PFCs it has been assumed that they will cause similar or lesser effects than PFOS. This study compared the effects of 10 PFCs routinely found in the environment on mRNA abundance of 7 genes related to processes known to be affected by PFOS, such as fatty acid and cholesterol synthesis, and thyroid development. Rat H4IIE hepatoma cells were exposed and changes in mRNA abundance were quantified by real-time PCR. Significant changes in mRNA abundance were observed. The effects caused by the shorter chain replacement chemicals differed significantly from those caused by PFOS or PFOA. Furthermore, not all of the PFCs caused the same effects, and changes could not simply be attributed to chain-length or functional group. These differences could mean that these replacement chemicals do not act through the same mechanisms as the more studied PFOS and PFOA.     

Empirical relationship between precision and ultra-trace concentrations of PCDD/Fs and dioxin-like PCBs in biological matrices

Dioxin analysis in food and feed can be characterized as an analytical application where very high accuracy is required at very low levels of contamination. Gas chromatography (GC) in combination with 13C-label isotope dilution (ID) high resolution mass spectrometry (HRMS) is the reference congener-specific technique characterized by pronounced selectivity, precision and trueness at parts-per-trillion (ppt) and sub-parts-per-trillion (sub-ppt) levels. The quality of the analytical data produced routinely by a laboratory should be adequate for its intended purpose, i.e., one will seek a compromise between the cost and time needed and the consequences of incorrect decisions due to erroneous results. The requirements for reproducibility are usually dependent on the analyte concentrations and have been expressed in various empirical functions. While Horwitz or modified functions are widely useful for many purposes, it would be difficult to expect these functions to cover every analytical problem. This study reports on precision characteristics achieved by the GC-ID-HRMS reference method for polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (DL-PCBs) in food and feed in two interlaboratory method-performance studies among expert laboratories with long-standing experience in this field. Striking linear functions in log scale between reproducibility standard deviation and congener's level over a concentration range of 10(-8)-10(-14)g per g fresh weight are observed. The data fit very well to a Horwitz-type function of the form sR=0.153c0.904, where sR and c are dimensionless mass ratios expressed in pg g(-1) on fresh weight, regardless of the nature of the toxic congeners, food and feed matrices, or sample preparation methods. We demonstrate that the proposed function is suitable for use as a fitness-for-purpose criterion for proficiency assessment in interlaboratory comparisons on dioxins and related compounds in food.