Photodegradation of the herbicide Norflurazon sensitised by Riboflavin. A kinetic and mechanistic study

The kinetics and mechanism of the Riboflavin (Rf)-promoted photochemical degradation with visible light of the herbicide Norflurazon (NF) has been studied by time-resolved and stationary techniques. Using light of wavelength higher than 400 nm--a region where NF is totally transparent--and with concentrations of Rf and NF of ca. 0.02 and 1 mM, respectively, only the excited triplet state of Rf ((3)Rf*) is quenched by NF, in competition with dissolved ground state triplet oxygen, O(2)((3)Sigma(g)(-)). NF degradation mainly occurs by reaction with superoxide radical anion O(2)(-) formed through two electron transfer steps: from NF to (3)Rf*, yielding Rf radical anion, and from this anion to O(2)((3)Sigma(g)(-)), regenerating ground state Rf. Although singlet molecular oxygen is also produced, NF only quenches this oxidative species in a physical mode. The global result is the photoprotection of the sensitiser and the photodegradation of NF.     

Assessment of application-rate dependent effects of a long-term fire retardant chemical (Fire Trol 934) on Typha domingensis germination

Although long-term fire retardants (LTR) gain increasingly acceptance as effective tools for wildfire management, recent studies indicate their potential harmfulness in the environment, especially in aquatic ecosystems. This study comprises a first laboratory impact assessment of LTR action in temporal Mediterranean wetlands, using seed germination of Typha domingensis as indicator of impact. Our aim was to identify application rates upon which seed germination could be significantly affected. We tested for low (1 l m(-2)) and high (3 l m(-2)) application rates of Fire Trol 934 which are recommended by the manufacturers as a function of fuel characteristics. In addition, we simulated the impact of a higher application rate of 5 l m(-2) because inhomogeneous dispersal of the LTR during fire control and prevention operations can result in locally elevated applications. Results of a microcosm experiment indicate that application rates of 1 or 3 l m(-2) can impact Typha germination rates in the short-term via indirect LTR-mediated effects on water quality, which suppressed necessary cues for germination. However, a subsequent experiment with Petri dishes, using seeds isolated from the LTR treated sediments did not show significantly different germination rates between the control and the treatments with application rates of 1 or 3 l m(-2). This suggests that retardant pre-application germination success could be recovered in nature once the retardant is eliminated. By contrast, seeds almost completely failed to germinate in the microcosm experiment and the subsequent Petri dish essay when an application rate of 5 l m(-2) was used. This suggests a critical level upon which Typha seed germination may be perpetually limited. Research should be extended to other plant species to provide fire managers with guidelines for environmentally safe use of LTR in the Mediterranean region.     

210Pb geochronology and trace metal fluxes (Cd, Cu and Pb) in the Gulf of Tehuantepec, South Pacific of Mexico

Distributions of Al, Cd, Cu, Fe, Li, Mn and Pb were analyzed in a sediment core collected in the Gulf of Tehuantepec, an important fisheries region located in the South Pacific of Mexico, where data on metal accumulation and accretion rates were previously almost nonexistent. Depth profiles of metal concentrations were converted to time-based profiles by using a 210Pb-derived vertical accretion rate, estimated to be 0.05 cm year(-1) on the average. Sediments were dated up to 8 cm depth, corresponding to a layer of ca. 140 years old. The historical changes of metal accumulation along the sediment core have shown a moderate enrichment of Cd, Cu and Pb concentrations at present, of about threefold the corresponding background concentrations. Chronological trace metal records showed that metal fluxes have increased over the last 20 years, reaching the maximum values at present of 2.5, 22.5 and 45.8 (microg cm(-2) year(-1)) for Cd, Pb and Cu, respectively. These increments in metal fluxes are likely influenced by the development of anthropogenic land-based activities since over this period of time oil production activities in the region have had a significant development.     

Sequential extraction of 226Ra in sediments from an estuary affected historically by anthropogenic inputs of natural radionuclides

Riverbed sediments from an estuary historically affected by wastes discharged by several phosphate fertiliser plants and enriched in uranium-series radionuclides were operationally speciated using a Tessier-based method. In each selective fraction the (226)Ra content was determined by alpha-particle spectrometry after radiochemical isolation and electrodeposition onto stainless steel planchets. These studies were performed in (226)Ra-polluted estuarine sediments collected one year after anthropogenic discharges had ceased in order to obtain useful information about the operational forms in which this radionuclide remains associated with the sediments at this time. The results obtained revealed that one year after (226)Ra inputs had stopped, the radionuclide was associated mostly with the more refractory forms. Consequently, it is possible to foresee little potential remobilisation of (226)Ra contamination from sediments to the aqueous phase in the future under normal environmental conditions.     

Elysia timida (Risso, 1818) (Gastropoda, Opisthobranchia): relationship and feeding deterrence to a potential predator on the south-western Mediterranean coast

The relationship between the sacoglossan Elysia timida and the ornate wrasse Thalassoma pavo was studied in two laboratory experiments using artificial models. A feeding-preference experiment was conducted to determine whether mollusc extract deterred feeding by T. pavo, by using a "realistic" mollusc model (imitating the colour pattern of E. timida) coated with mollusc extract, and a reference model (without imitation or extract), and fishes collected from two locations. It was observed that fish approached, attacked and ate more reference models than mollusc models. A second feeding-preference experiment was designed with four different coloured models: "realistic" (W), green (G), red (R) and chequered (S) pattern. Both fish populations clearly rejected the S model, and differed in their colour preferences. Although both populations seemed to prefer the R and G models equally, the W model was clearly rejected by the fish that coexist with the mollusc at one site (Mazarrón), but was not rejected by the other population of fish which does not coexist with it (Cabo de Palos). Mazarrón fishes would identify the W model with the presence of a toxic compound during their coexistence, and therefore avoid attacking conspicuously coloured E. timida models as a response to their visual signals. Therefore, it was concluded that extract of E. timida is a deterrent for T. pavo, and its effect is sufficiently noxious that the fish tend to avoid it, so that the ability of the fishes to learn to recognise colours and identify certain colour patterns associated with obnoxious prey provides the molluscs the opportunity to survive by exhibiting a conspicuous coloration.     

Distribution and mobilization of U, Th and 226Ra in the plant-soil compartments of a mineralized uranium area in south-west Spain

The activity concentrations of natural uranium isotopes (238U and 234U), thorium isotopes (232Th, 230Th and 225Th) and 226Ra were studied in soil and vegetation samples from a disused uranium mine located in the Extremadura region in the south-west of Spain. The results allowed us to characterize radiologically the area close to the installation and one affected zone was clearly manifest as being dependent on the direction of the surface water flow from the mine. The activity concentration mean values (Bq/kg) in this zone were: 10,924, 10,900, 10,075 and 5,289 for 238U, 234U, 230Th and 226Ra, respectively, in soil samples and 1,050, 1,060, 768 and 1,141 for the same radionuclides in plant samples. In an unaffected zone, the activity concentration mean values (Bq/kg) were: 184, 190, 234 and 7251 for 235U, 234U, 230Th and 226Ra, respectively, in soil samples and 28. 29, 31 and 80 in plant samples. The activity concentrations obtained for 232Th and 228Th showed that the influence of the mine was only important for the uranium series radionuclides. The relative radionuclide mobilities were determined from the activity ratios. Correlations between radionuclide activity concentrations and stable element concentrations in the soil samples helped to understand the possible distribution paths for the natural radionuclides.     

Plutonium contamination from accidental release or simply fallout: study of soils at Palomares (Spain)

The activity concentration of plutonium in an environmental sample does not usually constitute sufficient information to determine if it is due only to fallout. Alpha and gamma spectrometry are used here conjointly in the study of environmental soil samples to distinguish between samples showing plutonium contamination due to fallout exclusively, and samples contaminated with plutonium from another source. The method was applied to soil samples collected in Palomares (Spain), where an accidental release of aerosols contaminated with plutonium occurred. The two contributions (fallout and accidentally released plutonium) were separated by means of the activity ratios between various radionuclides present in the samples analyzed. The fallout level was estimated from the 239 + 240Pu/137Cs activity ratio. For samples showing contamination due to the accident, the 238Pu/239 + 240Pu and 239Pu/240Pu activity ratios were also calculated to determine the grade of plutonium of this contamination.     

Seed trait changes in dispersers' guts and consequences for germination and seedling growth

The effectiveness of a frugivore as a disperser of a plant is greatly determined by how fruits and seeds are handled in its mouth and its digestive tract. Although a number of studies have investigated the effect of avian ingestion on germination, we still know very little about the modifications to seeds during ingestion and the specific consequences on plant fitness. Here we investigate for the first time the different mechanisms by which germination patterns of seeds are modified following ingestion by frugivores. Specifically, we examine changes in seed mass, water content, permeability, seed coat thickness, texture, and resistance in two common Mediterranean fleshy-fruited plants, Phillyrea angustifolia and Myrtus communis, after ingestion by Eurasian Blackbirds, Turdus merula. We found a number of differences between the plant species: Phillyrea seeds lost mass, mainly due to water loss, and had thinner coats after gut passage, but Myrtus seeds did not. Seeds of both species showed increased permeability, while Myrtus seeds in particular became less resistant to breakage. No quantifiable changes in seed coat texture were detected in either species, although this trait was partly associated with differences in germination rate in Phillyrea. High intraspecific plant variation was found for most seed traits measured. Seed passage through birds' guts sped up germination in both species, especially in Myrtus. Increased permeability in seeds of both species following ingestion resulted in a higher germination rate. Moreover, seeds with thick coats (and in the case of Phillyrea, harder coats) germinated at a slower rate and produced seedlings that also grew more slowly, indicating a cost of coat thickness and/or hardness for seedling emergence. Results obtained here contribute to explaining the great heterogeneity in germination responses among and within plant species and the large variety of factors, both intrinsic and extrinsic to the plants, that influence such responses.     

Separating habitat invasibility by alien plants from the actual level of invasion

Habitats vary considerably in the level of invasion (number or proportion of alien plant species they contain), which depends on local habitat properties, propagule pressure, and climate. To determine the invasibility (susceptibility to invasions) of different habitats, it is necessary to factor out the effects of any confounding variables such as propagule pressure and climate on the level of invasion. We used 20 468 vegetation plots from 32 habitats in the Czech Republic to compare the invasibility of different habitats. Using regression trees, the proportion of alien plants, including archaeophytes (prehistoric to medieval invaders) and neophytes (recent invaders), was related to variables representing habitat properties, propagule pressure, and climate. The propagule pressure was expressed as the proportion of surrounding urban and industrial or agricultural land, human population density, distance from a river, and history of human colonization in the region. Urban and industrial land use had a positive effect on the proportion of both archaeophytes and neophytes. Agricultural land use, higher population density, and longer history of human impact positively affected the proportion of archaeophytes. Disturbed human-made habitats with herbaceous vegetation were most invaded by both groups of aliens. Neophytes were also relatively common in disturbed woody vegetation, such as broad-leaved plantations, forest clearings, and riverine scrub. These habitats also had the highest proportion of aliens after removing the effect of propagule pressure and climate, indicating that they are not only the most invaded, but also most invasible. These habitats experience recurrent disturbances and are rich, at least temporarily, in available nutrients, which supports the hypothesis that fluctuating resources are the major cause of habitat invasibility. The least invaded habitats were mires and alpine-subalpine grasslands and scrub. After removing the effect of propagule pressure and climate, some habitats actually invaded at an intermediate level had very low proportions of aliens. This indicates that these habitats (e.g., dry, wet, and saline grasslands, base-rich fens, and broad-leaved deciduous woodlands) are resistant to invasion.