The influence of time on lead toxicity and bioaccumulation determined by the OECD earthworm toxicity test

Internationally agreed standard protocols for assessing chemical toxicity of contaminants in soil to worms assume that the test soil does not need to equilibrate with the chemical to be tested prior to the addition of the test organisms and that the chemical will exert any toxic effect upon the test organism within 28 days. Three experiments were carried out to investigate these assumptions. The first experiment was a standard toxicity test where lead nitrate was added to a soil in solution to give a range of concentrations. The mortality of the worms and the concentration of lead in the survivors were determined. The LC(50)s for 14 and 28 days were 5311 and 5395 mug(Pb) g(soil)(-1) respectively. The second experiment was a timed lead accumulation study with worms cultivated in soil containing either 3000 or 5000 mug(Pb) g(soil)(-1). The concentration of lead in the worms was determined at various sampling times. Uptake at so' Sol both concentrations was linear with time. Worms in the 5000 mug g(-1) soil accumulated lead at a faster rate (3.16 mug Pb g(tissue)(-1) day(-1)) tiss than those in the 3000 mug g(-1) soil (2.21 mug Pb-tissue g(-1) day(-1)). The third experiment was a timed experiment with worms cultivated in tiss soil containing 7000 mugPb g(soil)(-1). Soil and lead nitrate solution were mixed and stored at 20 degreesC. Worms were added at various times over a 35-day period. The time to death increased from 23 h, when worms were added directly after the lead was added to the soil, to 67 It when worms were added after the soil had equilibrated with the lead for 35 days. In artificially Pb-amended soils the worms accumulate Pb over the duration of their exposure to the Pb. Thus time limited toxicity tests may be terminated before worm body load has reached a toxic level. This could result in under-estimates of the toxicity of Pb to worms. As the equilibration time of artificially amended Pb-bearing soils increases the bioavailability of Pb decreases. Thus addition of worms shortly after addition of Pb to soils may result in the over-estimate of Pb toxicity to worms. The current OECD acute worm toxicity test fails to take these two phenomena into account thereby reducing the environmental relevance of the contaminant toxicities it is used to calculate. (C) 2002 Elsevier Science Ltd. All rights reserved.

Effects of prolonged conditioning on dormancy and germination of Striga hermonthica

The impact of environment on the germination biology of Striga hermonthica was studied in the laboratory by conditioning seeds at various water potentials and urea concentrations at 17.5 to 37.5°C for up to 133 days. The experimental results presented in this research are related to the effects of temperature, water potential and urea nitrogen concentration during conditioning on subsequent germination percentage of S. hermonthica. Maximum germination in S. hermonthica seeds was observed at conditioning temperatures of 20 to 25°C within the range investigated of 17.5 to 37.5°C. Water stress and also urea during conditioning suppressed maximum germination. However, the conditioning temperature ranges at which maximum germination percentages occur vary with water stress and also urea concentration. In the presence of a high concentration of urea (3.16 mM), temperatures required for maximum germination narrowed to between 17.5 to 20°C. The optimum period of conditioning decreased with increase in water stress and also urea concentration similar to previous reports. The implications of these findings on Striga hermonthica field infestations have been investigated and being reported in another paper. Germination was greatly suppressed by conditioning environments including 3.16 mM urea and at 37.5°C. At the high concentration of 3.16 mM, temperatures required for maximum germination narrowed to between 17.5 and 20°C. Optimum conditioning period decreased with water stress and with increase in urea concentration.

To 'be', and not to 'have': auxiliary selection in unaccusative verbs in Italian

This paper investigates the characteristics of unaccusative verbs in Italian with respect to the consistency with which these verbs select the auxiliaries ‘be’ (essere) and ‘have’ (avere) in compound tense forms. The study builds on the gradient approach to split intransitivity (Sorace 2000) by exploring the behaviour of 29 intransitive Italian verbs with respect to their core-peripheral features: auxiliary selection acceptability ratings and associated variance measures. Although there is clear support for the gradient approach in relation to the general order of semantic categories along the unaccusativity gradient, the results reveal that the ordering of subclasses within the Change group conflict with that currently proposed in the literature. In addition, the findings demonstrate the aspectual and lexical semantic characteristics of internally-caused change-of-state verbs in Italian require further investigation before their auxiliary selection behaviour can be properly understood. Furthermore, contrary to the gradient account, Existence verbs, the most stative and therefore the most peripheral subclass in the unaccusativity hierarchy, exhibit behaviour more characteristic of core unaccusative verbs. This study examines a wider range of semantic subclasses of unaccusative verbs than has hitherto been reported and identifies the core-peripheral boundary for Italian.1

Linguistic interfaces and language acquisition in childhood: introduction to the special issue

Much contemporary L1 acquisition theory and empirical research are guided by the hypothesis that acquisition delays in children are often related to the integration of information across grammatical and other cognitive modules, such as syntax and discourse-pragmatics (see e.g., Grinstead, 2010). This special issue brings together cutting edge research from all relevant paradigms addressing interface issues in child language acquisition and provides a platform for the study of the interaction between different levels of linguistic knowledge. In this introduction, we present the reader with the tools needed to best understand the contributions of the individual studies and what they bring to bear on larger theoretical questions as a collective.

The drowned and the saved: shipwrecks and the 'cursus' of Latin love elegy

Throughout the corpus of Latin love elegy, the imaginary tombs envisaged by the elegists for their own personae and for other inhabitants of their poetic world display a striking tendency to take on the characteristic attributes and personalities of those interred within. The final resting-place of Propertius, for instance, that self-proclaimed acolyte of Callimachean miniaturism and exclusivity, is to be sequestered from the degrading attentions of the passing populace (Prop. 3.16.25–30) and crowned with the poet's laurel (2.13.33–4). What remains of his meagre form will rest in a ‘tiny little urn’ (paruula testa, 2.13.32) beneath a monument declaring the lover's slavery to a single passion (2.13.35–6), and the grave is to be attended, or so he hopes, by the object of that passion herself (3.16.23–4), or occasionally (though he is not so confident of this) by his patron Maecenas (2.1.71–8). Likewise the memorial designed by Ovid for Corinna's pet parrot - an imitatrix ales endowed with the most distinctive foibles of the elegiac tradition - in Amores 2.6, comprising a burial mound pro corpore magnus (2.6.59) topped with a tombstone described as exiguus (‘tiny’, 2.6.60; cf. Prop. 2.1.72, 2.13.33), exhibits an elegiac emphasis worthy of the parrot's human counterparts among Ovid's poetic predecessors.

Electronic transitions and bonding properties in a series of five-coordinate “16-electron” complexes [Mn(CO)3(L2)]− (L2=chelating redox-active π-donor ligand)

In this article we present for the first time accurate density functional theory (DFT) and time-dependent (TD) DFT data for a series of electronically unsaturated five-coordinate complexes [Mn(CO)(3)(L-2)](-), where L-2 stands for a chelating strong pi-donor ligand represented by catecholate, dithiolate, amidothiolate, reduced alpha-diimine (1,4-dialkyl-1,4-diazabutadiene (R-DAB), 2,2'-bipyridine) and reduced 2,2'-biphosphinine types. The single-crystal X-ray structure of the unusual compound [Na(BPY)][Mn(CO)(3)(BPY)]center dot Et2O and the electronic absorption spectrum of the anion [Mn(CO)(3)(BPY)](-) are new in the literature. The nature of the bidentate ligand determines the bonding in the complexes, which varies between two limiting forms: from completely pi-delocalized diamagnetic {(CO)(3)Mn-L-2}(-) for L-2 = alpha-diimine or biphosphinine, to largely valence-trapped {(CO)(3)Mn-1-L-2(2-)}(-) for L-2(2-) = catecholate, where the formal oxidation states of Mn and L-2 can be assigned. The variable degree of the pi-delocalization in the Mn(L-2) chelate ring is indicated by experimental resonance Raman spectra of [Mn(CO)(3)(L-2)](-) (L-2=3,5-di-tBu-catecholate and iPr-DAB), where accurate assignments of the diagnostically important Raman bands have been aided by vibrational analysis. The L-2 = catecholate type of complexes is known to react with Lewis bases (CO substitution, formation of six-coordinate adducts) while the strongly pi-delocalized complexes are inert. The five-coordinate complexes adopt usually a distorted square pyramidal geometry in the solid state, even though transitions to a trigonal bipyramid are also not rare. The experimental structural data and the corresponding DFT-computed values of bond lengths and angles are in a very good agreement. TD-DFT calculations of electronic absorption spectra of the studied Mn complexes and the strongly pi-delocalized reference compound [Fe(CO)(3)(Me-DAB)] have reproduced qualitatively well the experimental spectra. Analyses of the computed electronic transitions in the visible spectroscopic region show that the lowest-energy absorption band always contains a dominant (in some cases almost exclusive) contribution from a pi(HOMO) -> pi*(LUMO) transition within the MnL2 metallacycle. The character of this optical excitation depends strongly on the composition of the frontier orbitals, varying from a partial L-2 -> Mn charge transfer (LMCT) through a fully delocalized pi(MnL2) -> pi*(MnL2) situation to a mixed (CO)Mn -> L-2 charge transfer (LLCT/MLCT). The latter character is most apparent in the case of the reference complex [Fe(CO)(3)(Me-DAB)]. The higher-lying, usually strongly mixed electronic transitions in the visible absorption region originate in the three lower-lying occupied orbitals, HOMO - 1 to HOMO - 3, with significant metal-d contributions. Assignment of these optical excitations to electronic transitions of a specific type is difficult. A partial LLCT/MLCT character is encountered most frequently. The electronic absorption spectra become more complex when the chelating ligand L-2, such as 2,2'-bipyridine, features two or more closely spaced low-lying empty pi* orbitals.