Several aromatic and chlorinated volatile hydrocarbons (VOCs) were measured in Vitoria-Gasteiz City (Spain) throughout the years 1999 and 2002 in order to find out the concentration of these pollutants in urban air. These VOCs were retained in Tenax TA, subsequently desorpted by using a thermal desorption cold trap injector (TCT), and thereafter analyzed by gas chromatography/mass spectrometry (GC/MS). This analytical methodology permits the determination of 42 VOCs at very low concentrations, although only 32 of them were found in the urban air of the city (ranging from 205.51 to 0.01 microg m(-3)), with high reproducibility (%RSD lower than 10%). Twenty-four-hour samples were taken each sampling day to ascertain their total daily concentration, and rigorous quality controls were carried out to check the representativeness of sampling. Results of this exhaustive study show that toluene (T), xylenes (X), ethylbenzene (E), and benzene (B) were, respectively, the most abundant of these VOCs in the urban area during that period. The total concentration of BTEX represented, on average, more than 72.6% of the VOC total concentration, with the highest concentrations being reached in autumn, except for benzene and derived compounds (in winter). Benzene was the minority BTEX pollutant, its yearly mean concentration being less than the maximum established by the European Directive 2000/69/CE (5 microg m(-3)).
The oil formulation of diflubenzuron (Dimilin 45 ODC) persisted for 10-12 weeks on the foliage of a conifer forest in an Atlantic-climate ecosystem. Within 22-30 days following treatment, 55-80% of the insecticide had been removed from the foliage. During this period, the concentration of diflubenzuron was higher than 370 ng g(-1). Aerial application at 56.3 g of Al ha(-1) resulted in deposition levels of the insecticide ranging from 867.5 to 1824.4 ng g(-1), depending upon forest characteristics. The results showed that aerial application is only a suitable technique for the treatment of forest areas with dense foliage and/or high tree density and no more than 15% of tree-free area. The only metabolite detected was 2,6-difluorobenzamide, and this persisted on foliage until the first rainfalls occurred. An empirical mathematical correlation was found to express the influence of meteorological variables--rainfall, solar radiation and temperature--on the persistence of the insecticide. These results suggested that degradation of diflubenzuron on foliage could be due to photodegradation. Some recommendations were made to optimize the deposition of the insecticide on foliage and to minimize its persistence and the off-site spray drift.
Solid-phase extraction or liquid-liquid extraction has been combined with adsorptive stripping voltammetry at a hanging mercury drop electrode to isolate, determine, quantify and recover trace concentrations of pyridafenthion in water, wine and soil. A systematic study of the experimental parameters affecting the stripping response was carried out by differential pulse voltammetry. By using an accumulation potential of 400 mV and an accumulation time of 540 s, the limit of detection was 0.17 microgram l-1 and the relative standard deviation (n = 10) was 1.9% at a concentration level of 8.5 micrograms l-1. Different methods are proposed which eliminate matrix interferences. These results have been applied to the systematic study of this compound in water, wine and soil. The lowest detectable concentration for pyridafenthion is 34 micrograms l-1 in water, 102 micrograms l-1 in wine and 80 micrograms kg-1 in soil. Recoveries of the pyridafenthion from supplied environmental samples were in all cases higher than 92% with a relative standard deviation lower than 3%.
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