Simultaneous estimation of effective and apparent diffusion coefficients in compacted bentonite

Effective diffusion coefficients (D(e)) are usually measured by means of "through-diffusion" experiments in which steady state is reached, and the "time-lag" methods are used to estimate the apparent diffusion coefficient (D(a)). For sorbing radionuclides (as caesium), the time needed to reach steady-state conditions is very large, and the precision in D(a) determinations is not satisfactory. In this paper, a method that allows determining simultaneously effective and apparent diffusion coefficients in compacted bentonite without reaching steady-state conditions is described. Basically, this method consists of an "in-diffusion" experiment in which the concentration profile in the bentonite sample is used to estimate D(a), and the temporal evolution of the solute concentration in the reservoir is used to estimate D(e). This method has several advantages over the typical "through-diffusion" experiments, in particular: (a) experiment duration is significantly shorter, (b) D(a) values are measured with greater precision and (c) it is not necessary to maintain a constant solute concentration in the reservoir. This new method has been used to estimate the effective and apparent diffusion coefficients for caesium in FEBEX bentonite and in order to validate it, the results have been compared with results previously obtained with standard methods. Experimental results have been satisfactorily modelled using a simple model of diffusion in porewater and the measured value of D(e)(Cs) is very similar to D(e)(HTO) in the same bentonite. There is no evidence of "surface diffusion" in FEBEX bentonite for caesium.     

Comparative study of methodologies for the analysis of PCDDs and PDCFs in powdered full-fat milk. PCB, PCDD and PCDF levels in commercial samples from Spain

Feasibility of two different extraction methods involving solid-liquid extraction and Soxhlet extraction, previously used for the determination of lipid contents and PCB levels on powdered full-fat milk, are now examined for simultaneous PCDD/F analysis. The results of this study are consistent with those found for PCBs. The solid-liquid procedure provides the most efficient extraction of both labelled spiked and endogenous PCDD/Fs with the lowest variability. The average recoveries were 101% (R.S.D. = 6.9%) for 13C12-2,3,7,8-TCDD and 95% (R.S.D. = 11%) for 13C12-1,2,3,4,7,8-HxCDD. The R.S.D.s for endogenous 2,3,7,8-PCDD/Fs were in the 9.3-25% range. In addition, this methodology simplified the subsequent clean-up step as it allowed a semi-selective extraction of the apolar lipids from the milk. The proposed method was applied to simultaneous PCB and PCDD/F analyses in different brands of powdered full-fat milks commercially available in Spain. In all cases, very similar PCB and PCDD/F levels were found. Differences among batches from the same manufacturer were even lower. The total i-TEQ average for PCDDs and PCDFs in the 22 powdered full-fat milk samples analysed was 1.87 pg/g fat basis. This value was similar to those found in cow's milk from other European countries.     

Influence of industry on the geochemical urban environment of Mieres (Spain) and associated health risk

This study is concerned with the elemental composition of soils and street dust collected in an historical industrial city of approximately 27 000 inhabitants, where old Hg mining and metallurgical activities strongly affected the load of heavy metals in the urban environment. For the purpose of the study, representative samples of soils and street dust were collected at different locations in the whole urban area (3 km²). Elevated mean concentrations of As in soils and street dust (69 and 135 g g^–1, respectively), and Hg (3.07 and 4.24 g g^–1, respectively), compared to background levels and to those found in other cities, reflect the anomalous geochemical nature of these materials and the strong influence exerted by the old mining sites.     

Metals in feathers of sooty tern, white tern, gray-backed tern, and brown noddy from islands in the North Pacific

Levels of heavy metals are usuallyhigher in adult than young birds because they eatlarger, more contaminated prey, or because they havehad longer to accumulate metals in their tissues.Further, levels of contaminants are usually less inbirds nesting on remote, offshore islands than inbirds breeding closer to mainland areas that areurbanized and industrialized. We examined the featherlevels of arsenic, cadmium, chromium, lead, manganese,mercury, and selenium in adult sooty terns (Sterna fuscata), gray-backed terns (Sterna lunata), and brown noddy (Anous stolidus, and adult and young white terns (Gygis alba, fromMidway Atoll, and in adult and young sooty terns andadult brown noddy from Manana Island, Hawaii (chicksof other terns were not available). We tested andrejected the null hypotheses that metal levels are notsignificantly different among species, ages, andlocations. Despite their small size, adult white ternshad the highest levels of lead, arsenic and tin. Brownnoddies had the highest levels of cadmium, chromium,manganese, and selenium. Sooty and white terns had thehighest levels of mercury. Sooty tern adults hadsignificantly higher levels of cadmium, mercury, andselenium than young, while young had significantlyhigher levels of arsenic and manganese. White ternadults had significantly higher levels of selenium andtin than young, while young had higher levels ofcadmium and mercury than adults. Except for mercury,there were significant inter-location differenceswithin species in all heavy metals. Contrary toexpectation, where the differences were great, metalsgenerally were higher in the feathers of terns andnoddies from Midway than from Manana.     

Dissipation of fenoxycarb and pyriproxyfen in fresh and canned peach

The objective of this work was to determine the dissipation of fenoxycarb and pyriproxyfen in fresh and canned peaches in order to know the levels of residues that can reach consumers in real circumstances. Two field dissipation studies were carried out, one of them at the pre-harvest interval (PHI) with good agricultural practice (GAP) and the other one in a situation of critical agricultural practice (CAP). Two canning dissipation studies were carried out for samples from both agricultural situations in an industrial pilot plant and the dissipation was determined in each relevant step. An analytical methodology was used including acetone-dichloromethane extraction, purification and analysis by liquid chromatography and diode array detection (LC-DAD) with a limit of quantification (LOQ) of 0.05 mg/kg. It was validated under SANCO/10232/2006 Guidelines. These pesticides complied with the official maximum residue limits (MRLs) in peaches at the PHI with good agricultural practices. In hypothetical situation of a second application at the PHI, fenoxycarb and pyriproxyfen residues were above the MRLs in peaches. The canning study reduced the residues to no detectable levels in the cans for consumers.     

Inter-annual variability in the breeding performance of six tropical seabird species: influence of life-history traits and relationship with oceanographic parameters

We investigated inter-annual variability in the breeding performance of six tropical seabirds with different life histories. We further examined the extent to which presumed differences among years in food availability to seabirds were related to large-scale oceanic processes (El Niño Southern Oscillation and Indian Ocean Dipole) or local features around the colony (Sea Surface Temperature—SST, chlorophyll-a concentration, wind patterns, association with underwater predators). Two food shortages were recorded: (1) a short-term event operating at a local-scale, lacking any relationship with any measured oceanographic parameters and affecting only a few seabird species; (2) a generalized and protracted event, strikingly characterized by low SST, possibly induced by a La Niña and/or negative IOD event, and with detrimental impacts in the whole seabird community. Overall, species with inflexible feeding habits and fast chick growth rates were more affected by food shortage events than those with more plastic life-history traits.     

Hillslope terracing effects on the spatial variability of plant development as assessed by NDVI in vineyards of the Priorat region (NE Spain)

The availability of heavy machinery and the vineyard restructuring and conversion plans of the European Union Common Agricultural Policy (Commission Regulation EC no. 1227/2000 of 31 May 2000) have encouraged the restructuring of many vineyards on hillslopes of Mediterranean Europe, through the creation of terraces to favor the mechanization of agricultural work. Terrace construction requires cutting and filling operations that create soil spatial variability, which affects soil properties and plant development. In the present paper, we study the effects of hillslope terracing on the spatial variability of the normalized difference vegetation index (NDVI) in fields of the Priorat region (NE Spain) during 2004, 2005, and 2006. This index was computed from high-resolution remote sensing data (Quickbird-2). Detailed digital terrain models before and after terrace construction were used to assess the earth movements. The results indicate that terracing by heavy machinery induced high variability on the NDVI values over the years, showing significant differences as effect of the cut and fill operations.