Piperonyl butoxide potentiates the synaptosome ATPase inhibiting effect of pyrethrin

Pyrethrins are widely used insecticides in both agriculture and households. In many commercial formulations piperonyl butoxide (PBO) is used with pyrethrins. PBO is a well-known synergist of pyrethrins, used to intensify their effects. One of the cellular targets of pyrethrins is the sodium channel in the membrane. In the present study, the activity of the membrane-bound integral protein ATPase was studied as a biomarker for the membrane effects of pyrethrin and PBO. Cerebral synaptosomes of rat brain were used in the study. The isolation of synaptosomes was performed with the Percoll gradient method. Both total ATPase and Mg2+ activated ATPase were studied by determining inorganic phosphate. Exposure to 0.1-1000 microM of pyrethrin and to 0.4-4000 microM of PBO decreased ATPase activity dose-dependently. The most efficient mixture was the one consisting of one part of pyrethrin and four parts of PBO. The activity of total ATPase decreased 15% in concentrations of 0.1-10 microM pyrethrin, and a 50% decrease was found at 100 microM pyrethrin. The mixture of pyrethrin and PBO caused a 15-60% decrease in the total ATPase activity at 0.1-10 microM pyrethrin and 0.4-40 microM PBO. A 85% decrease was found after exposure to the mixture of 100 microM pyrethrin and 400 microM PBO. PBO alone had no effect at 0.4-40 microM concentrations, but a marked effect was seen at over 40 microM concentrations. The results indicate that PBO is an effective synergist of pyrethrin and that it is very toxic in high concentrations. The results also confirm that neuronal sodium homeostasis is one target of the neurotoxic effect of pyrethroid compounds.     

The role of copper(II) chloride in the formation of organic chlorine in fly ash

In the de-novo synthesis and formation of PCDD/PCDF, the transfer of inorganic chlorine to the carbonaceous material of fly ash plays an important role. Here, copper acts as a catalyst in the chlorination reaction. In experiments in the range of 250-350 degrees C under helium, we determined the stoichiometry of the chlorination reaction with model systems. Therefore, it was necessary to develop a method to quantify the copper(II) and copper(I) ions. In a combination of solid electron paramagnetic (spin) resonance spectroscopy (EPR) for Cu(I), and X-ray fluorescence spectroscopy (XRFA) analysis for Cu (total), we found a way for the quantification of copper(I) and (II). With these experiments, we can show that the chlorination reaction is relatively fast and comes to a stop under helium, after the copper(II) is reduced. The ratio between the organic chlorine formed and copper(II) reduced is, at the end of the reaction, 0.5, which is in agreement with the following reaction: 2CuCl2 + R-H-->2CuCl + R-Cl + HCl.     

Pyrethrins and piperonyl butoxide residues on potato leaves and in soil under field conditions.

Residues of pyrethrin-I (Py-I) and pyrethrin-II (Py-II), the major insecticidal components of the pyrethrum daisy (Tanacetum cinerariifolium) as well as residues of piperonyl butoxide (PBO, a pyrethrum synergist) were determined in soil and on potato foliage grown under field conditions. A pyrethrum formulation (Multi-Purpose Insecticide) containing the three active ingredients was sprayed twice at the rate of 6 lbs of formulated product.acre(-1) ( 5.4 and 27.2 g A.I. of pyrethrin and PBO, respectively) on potato foliage during the growing season. In soil, three management practices (yard waste compost, grass filter strips, and a no mulch treatment) were used to study the impact of surface soil characteristics on the amount of pyrethrins (Pys) and PBO retained in soil. Soil samples and potato leaves were collected at different time intervals after spraying. Samples were purified and concentrated using solid-phase extraction columns containing C18-Octadecyl bonded silica. Residues were quantified by high-performance liquid chromatograph equipped with a UV detector. The first spray resulted in mean initial deposits of 0.18, 0.40, and 0.99 microg.g(-1) potato leaves for Py-I, Py-II, and PBO, respectively. Residues in soil were higher in compost treatments compared to no mulch treatments.     

Catalytic reduction of NO on copper/MCM-41 studied by in situ EXAFS and XANES

Speciation of copper in the channels of MCM-41 during reduction of NO with CO at 473-773 K was studied by in situ extended X-ray absorption fine structural (EXAFS) and X-ray absorption near edge structural (XANES) spectroscopies in the present work. The component fitted (in situ) XANES spectra of the catalyst showed that about 72% of metallic copper (Cu(0)) in MCM-41 was oxidized to higher oxidation state coppers (Cu(II) (46%) and Cu(I) (26%)) during the NO reduction process (at 473 K). By EXAFS, we also found that in the NO reduction process, oxygen was inserted into the metallic copper matrix and led to a formation of the copper oxide species with a Cu-O bond distance of 1.93 A which was greater than that of the model compound Cu(2)O (typically 1.86 A). At 573-673 K, mainly Cu(II) was found in the channels of MCM-41. Nevertheless, at a higher temperature (e.g., 773 K), about 61% Cu(I), 31% Cu(II), and 8% Cu(O) with averaged Cu-Cu and Cu-O bond distances of 3.04 and 1.88 A, respectively were observed, that might account for the high selectivity-to-decomposition (S/D) ratios for yields of N(2) and CO(2) in the catalytic reduction of NO with CO.     

Throughfall below grassland canopies: a comparison of conventional and ion exchange methods

Sampling of canopy fluxes (throughfall and stemflow) below low structured vegetation with a small-scale, intricate canopy architecture is difficult, and representative sampling with most methods is questionable. In the present study, two sampling methods for canopy fluxes below grassland vegetation are compared. Method I sampled canopy fluxes of moisture inefficiently, because stemflow volumes were not quantitatively included. Canopy fluxes of ions calculated with method I necessitated assumptions on equal concentrations in actually sampled throughfall and non-sampled stemflow. Method II sampled canopy fluxes of ions quantitatively, because the total volume of throughfall and stemflow percolated through a mixed bed of ion exchange resins below the canopy. Ion-specific differences between the two methods were observed. For ions with foliar leaching, such as K+ and Ca2+, higher canopy fluxes were recorded with method II than with method I. In contrast, for ions with foliar uptake, such as NH4+ and NO3-, canopy fluxes were found to be less with method II than with method I. Canopy fluxes of inorganic nitrogen below Mesobrometum grassland were 2.35 and 1.52 kmol(c) ha(-1) year(-1) for methods I and II, respectively, and 2.85 and 7.90 kmol(c) ha(-1) year(-1) for K+. It is argued that these differences result from under-estimated (foliar leaching) or over-estimated (foliar uptake) concentrations in stemflow by the first method. Canopy fluxes for SO4(2-) were not statistically different, indicating that canopy exchange of SOx was quantitatively unimportant, and that both methods estimated atmospheric input equally well.     

Sustainable soil management practices and quality of potato grown on erodible lands

Land productivity can decline when top soil is lost. In Kentucky, limited resource farmers often produce vegetable crops on erodible lands. The objectives of this study were 1) to quantify the impact of three soil management practices (SMPs) on quantity of potato produced on erodible land, 2) to evaluate the impact of pyrethrin and azadirachtin insecticides on potato tuber quality, and 3) to assess the impact of yard waste compost on the chemical composition (ascorbic acid, free sugars, phenol contents) of potato tubers. Potatoes (Solanum tuberosum L. cv. Kennebec) were grown in a silty loam soil of 10% slope. Plots (n= 18) were 3.7 m wide and 22 m long (10% slope), with metal borders of 20 cm above ground level. Two botanical insecticides, Multi-Purpose Insecticide (containing pyrethrin 0.2%) and Neemix 4EC (containing 0.25% azadirachtin) were sprayed twice on potato foliage during each of two growing seasons (1997 and 1999) at the recommended rates of 6 lbs and 2 gallons.acre(-1), respectively. The SMPs were tall fescue strips (FS) intercropped between each two potato rows, soil mixed with yard waste compost (COM) and no-mulch (NM) treatment (roto-tilled bare soil). The experimental designwas a 2 x 3 x 3 factorial with main factors of two insecticides and three SMPs replicated three times. Average potato yield was lowest in NM and FS and highest in COM treatments. Yield obtained from the bottom of the plots was greater than that obtained from the top of plots. Tuber defects (rot, scab, sun green, hollow heart, necrosis, and vascular discoloration) were significantly different between the two growing seasons. The two insecticidal treatments did not have much influence on potato yield or tuber defects. Tubers obtained from tall fescue treatments had low levels of ascorbic acid and reducing sugars compared to compost treatments.     

Extraction of Sudan dyes from environmental water by hemimicelles-based magnetic titanium dioxide nanoparticles

A novel method for the extraction of Sudan dyes including Sudan I, II, III, and IV from environmental water by magnetic titanium dioxide nanoparticles (Fe₃O₄@TiO₂) coated with sodium dodecylsulfate (SDS) as adsorbent was reported. Fe₃O₄@TiO₂ was synthesized by a simple method and was characterized by transmission electron microscopy, Fourier-transform infrared spectrometry, and vibrating sample magnetometer. The magnetic separation was quite efficient for the adsorption and desorption of Sudan dyes. The effect of the amount of SDS, extraction time, pH, desorption condition, maximal extraction volume, and humic acid on the extraction process were investigated. This method was employed to analyze three environmental water samples. The results demonstrated that our proposed method had wide linear range (25–5,000 ng L^?1) with a good linearity (R ²?>?0.999) and low detection limits (2.9–7.3 ng L^?1). An enrichment factor of 1,000 was achieved. In all three spiked levels (25, 250, and 2,500 ng L^?1), the recoveries of Sudan dyes were in the range of 86.9–93.6 %. The relative standard deviations obtained were ranging from 2.5 to 9.3 %. That is to say, the new method was fast and effective for the extraction of Sudan dye from environmental water.     

Determination of chemical warfare agents

Chlorovinylannes (Lewisites) were produced and handled during WW I and WW II as chemical warfare agents. Residues of these cwa and their metabolites are still present today and continue to contaminate soil and water. A gas Chromatographic method for the detection and determination of chlorovinylarsines (Lewisites) and their metabolites is shown. Lewisite II and Lewisite III, but not Lewisite I and the metabolites of Lewisite I and Lewisite II can be detected and determined using GC/ECD. After derivatization with thiols, the sum of Lewisite I or Lewisite II and their metabolites are detected. With the proper selection of the thiol, matrix interferences can be eliminated because of the different retention times of the derivatives.     

Spectrophotometric determination of uranium with arsenazo-III in perchloric acid

A short, sensitive and reliable spectrophotometric method, which has advantages over all known "wet chemistry" methods for uranium determination with regard to tolerance to common interferences, has been developed for the determination of uranium. Selectivity, molar absorptivity and the determination range of uranium have been enhanced by using 0.07% arsenazo-III as a chromogenic reagent. The use of 3 mol dm(-3) perchloric acid as a medium of determination was found to be excellent in terms of good solvent compatibility on dilution, destruction of organic contamination and simplicity of operation. The uranium-arsenazo-III complex formed instantly, and was found to be stable for more than 3 weeks with constant absorbance. Beer's law was obeyed up to a uranium concentration of 16 microg g(-1), with a molar absorptivity at 651 nm of 1.45x10(5) mol(-1) dm(3) cm(-1) at 24+/-2 degrees C. Only phosphate and citrate at 70-fold excess over uranium interfere seriously, whereas other anions studied could be tolerated up to a 70-fold excess over uranium. Of the cations studied, only Mn(II), Co(II), Ni(II), Cu(II) and Cr(III) decreased the normal absorbance of the complex. Iron(III), Ce(III) and Y(III) enhanced the absorbance. Other cations studied did not affect the absorbance up to a 50-fold excess. The accuracy was checked by determining uranium from standard solutions in the range 10-50 microg g(-1). It was found to be accurate with a 96.0-98.6% recovery rate. The method has been successfully applied to standard reference materials and ore samples at microg g(-1) levels.     

Short-time exposure to mono-n-butyl phthalate (MBP)-induced oxidative stress associated with DNA damage and the atrophy of the testis in pubertal rats

Phthalates are widely used as plasticizer in various consumer domestic products and are known to disturb the male reproductive function in rodents. This study investigated the involvement of oxidative stress and the atrophy of the testes in pubertal rats exposed to mono-n-butyl phthalate (MBP). Four-week-old pubertal male rats were separated into three groups. In group I, 21 rats were fed rat chow containing 2 % MBP for 3 days. In group II, 21 rats were fed rat chow containing 2 % MBP for 3 days and antioxidant vitamins C (250 mg/kg/day) and E (50 mg/kg/day) were injected daily. In group III, 21 rats were fed standard rat chow and used as controls. After 3 days, each testis was weighed and the germ cell development was evaluated using the Johnsen score. The urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG) levels were measured as a biological marker of oxidative DNA damage. The mean testis weight was significantly lower for group I than groups II or III (p?<?0.05). The mean Johnsen score was significantly lower for group I than for groups II or III (p?<?0.05). Urinary 8-OHdG concentrations were higher in group I than in groups II or III. Short-time exposure to MBP may therefore induce oxidative DNA damage in rat testes, while antioxidant vitamins administered during exposure may protect against this stress.     

Studies on electrochemical recovery of silver from simulated waste water from Ag(II)/Ag(I) based mediated electrochemical oxidation process

In the Ag(II)/Ag(I) based mediated electrochemical oxidation (MEO) process, the spent waste from the electrochemical cell, which is integrated with the scrubber columns, contains high concentrations of precious silver as dissolved ions in both the anolyte and the catholyte. This work presents an electrochemical developmental study for the recovery of silver from simulated waste water from Ag(II)/Ag(I) based MEO process. Galvanostatic method of silver deposition on Ti cathode in an undivided cell was used, and the silver recovery rate kinetics of silver deposition was followed. Various experimental parameters, which have a direct bearing on the metal recovery efficiency, were optimized. These included studies with the nitric acid concentration (0.75-6M), the solution stirring rate (0-1400 rpm), the inter-electrode distance between the anode and the cathode (2-8 cm), the applied current density (29.4-88.2 mA cm(-2)), and the initial Ag(I) ion concentration (0.01-0.2M). The silver recovered by the present electrodeposition method was re-dissolved in 6M nitric acid and subjected to electrooxidation of Ag(I) to Ag(II) to ascertain its activity towards Ag(II) electrogeneration from Ag(I), which is a key factor for the efficient working of MEO process. Our studies showed that the silver metal recovered by the present electrochemical deposition method could be reused repeatedly for MEO process with no loss in its electrochemical activity. Some work on silver deposition from sulfuric acid solution of different concentrations was also done because of its promising features as the catholyte in the Ag(II) generating electrochemical cell used in MEO process, which include: (i) complete elimination of poisonous NO(x) gas liberation in the cathode compartment, (ii) reduced Ag(+) ion migration across Nafion membrane from anolyte to catholyte thereby diminished catholyte contamination, and (iii) lower cell voltage and hence lesser power consumption.     

Aquatic risk assessment of the new rice herbicide profoxydim

A tiered protocol for assessing ecological risks has been applied to the rice pesticide profoxydim. The initial assessment (Tier I) was based on toxicity exposure ratio (TER) calculations based on laboratory data using a worst-case rice scenario. The first refinement (Tier II) was based on direct toxicity assessment (DTA) of water samples collected during a field-mesocosm study. Finally, a higher-tier assessment on the in situ assessment of paddy community responses (field-mesocosm-Tier III) was performed. A successive application of three pesticides, the herbicides azimsulfuron, propanil and the insecticide malathion, was used as reference controls. The refined assessments indicated a lower risk than that predicted from TER estimations. DTA-based Tier II showed toxicity effects only for concentrations above the recommended dose of profoxydim. Effects for reference controls were observed in DTA which were not expected from Tier I. The field-mesocosm study confirmed these effects but also showed that they were transient and of low relevance.     

Catalytic degradation of Orange II by UV-Fenton with hydroxyl-Fe-pillared bentonite in water

Although homogeneous photo-Fenton system is a very efficient method for organic wastewater treatment, it suffers from costly pH adjustment as well as difficult separation of catalysts from aqueous in practical application. Through cation exchange reaction, hydroxyl-Fe-pillared bentonite (H-Fe-P-B) was successfully prepared as a solid catalyst for UV-Fenton to degrade non-biodegradable azo-dye Orange II. Compared with raw bentonite, the content of iron, interlamellar distance and external surface area of H-Fe-P-B increased remarkably. H-Fe-P-B had good photosensitivity and catalyst reactivity. And the catalytic activity of H-Fe-P-B for H(2)O(2) came from hydroxyl-Fe between sheets rather than Fe(3+) or Fe(2+) in tetrahedral or octahedral sheets of bentonite. In UVA-H(2)O(2) system, H(2)O(2) could destroy the azo bond of excited Orange II molecules but could not effectively mineralize it. After 120 min treatment, 83% discoloration was obtained while only 2% of TOC was removed. When H-Fe-P-B was used as catalyst, a significant degradation of Orange II was observed at the same condition as UVA-H(2)O(2) system. Almost 100% discoloration and more than 60% TOC removal of Orange II could be achieved after 120 min treatment. Because of the strong surface acidity and the electronegativity of H-Fe-P-B, the pH range of this catalyst in the Orange II discoloration could be extended up to 9.5. And this catalyst showed good stability during Orange II degradation in water in wide range of pH (3.0-9.5). These results indicated that the H-Fe-P-B was a promising catalyst for UV-Fenton system.     

Speciation of scandium and gallium in soil

A method for the speciation of scandium and gallium in soil has been developed. The sequential extraction scheme of Tessier et al. for heavy metals was examined for the scandium and gallium separation. The regents proposed by Tessier were used for the extraction, and only for the residual fraction the HClO(4) was replaced with H(2)SO(4). The optimum conditions for leaching scandium and gallium from the soil were chosen for each fraction. Very sensitive, spectrophotometric methods based on the mixed complexes of Sc(III) and Ga(III) with Chrome Azurol S and benzyldodecyldimethylammonium bromide were applied for the scandium and gallium determination after their separation by solvent extraction. 100% mesityl oxide and a 0.5M solution of 2-thenoyltrifluoroacetone in xylene were chosen for the extraction of scandium and butyl acetate was selected for gallium. Soil samples from two different regions of Poland were the object of this research. The content of scandium and gallium found in the individual fractions of Upper Silesia soil (industrial region) was [in mugg(-1)] Sc: I, 1.52; II, 0.53; III, 7.78; IV, 1.79; V, 0.20; Ga: I, 24.7; III, 29.2; IV, 35.4; V, 6.9. In Podlasie soil (agricultural region), the content of both elements was clearly lower. The total content of scandium and gallium in the five soil fractions was in good correlation with the total content of these elements in the soils found after HF-H(2)SO(4) digestion. Analysis using the ICP-OES method gave comparable results.     

Intercalibration of a passive wind-vane flux sampler against a continuous-flow denuder for the measurements of atmospheric ammonia concentrations and surface exchange fluxes

A passive wind-vane flux sampler is a simple low-cost device used to estimate long-term vertical fluxes of ammonia in the atmospheric surface boundary layer. The passive flux sampler measures the horizontal flux of ammonia. A vertical gradient of the horizontal flux, combined with micro-meteorological measurements of wind speed and temperature, is used to estimated the vertical flux of ammonia using a modified aerodynamic gradient technique. The passive wind-vane flux sampler gradient was calibrated against a gradient measured with fast response (6 min) continuous-flow denuders. The measurements were carried out at a heathland located in an intensive farming area in the centre of the Netherlands. A field campaign took place over 70 day period in the summer of 1996, during which the sampling periods of the passive wind-vane flux sampler varied between 3 and 9 days. The comparison clearly showed that the long-term measurements with the passive wind-vane flux samplers gave accurate average ammonia deposition values for the field campaign as a whole which deviated by only 18% from the reference flux. However, there was no significant correlation between the fluxes from the passive samplers and the reference method for the individual 10 periods which were compared. Possible explanations found for the lacking correlation were (I) a high percentage number of half-hour emission events within each period resulted in a significant large relative deviation between the fluxes, and (II) uncertainties in the reference method might also explain the lacking correlation. The passive wind-vane flux samplers proved to be a stable method for long-term measurements (months to years) due to a close to 100% optimal functioning during the field campaign.     

Spatio-temporal variability of satellite-derived aerosol optical thickness over Northeast Asia in 2004

In this study a modified Bremen aerosol retrieval (BAER) method was used to retrieve aerosol optical thickness (AOT) over both land and ocean using moderate resolution imaging spectro-radiometer (MODIS) data over Northeast Asia for a full year during 2004. Retrieved MODIS AOT data were in good agreement with data obtained from a ground-based AERONET sunphotometer (r=0.90, linear slope=0.89). Seasonal variation analysis of AOT revealed maximum values in summer (∼0.41) and minimum values in winter (∼0.25). The contribution of each aerosol type to total AOT was estimated for each pixel. A spectral shape fitting procedure was used to select the optimum aerosol model for AOT retrieval among six aerosol types: urban, rural, maritime, tropospheric, Asian dust, and biomass burning. The spatio-temporal distribution of average AOT was analyzed for the following five sectors in Northeast Asia: (I) East China, (II) Yellow Sea, (III) Korea, (IV) East Sea, and (V) South Sea plus a part of Japan. Maximum AOT values of 0.75±0.18 were measured over sector (I) in summer, while minimum values of 0.10±0.02 were recorded over sector (IV) in winter. AOT estimates over sector (I) were much higher than those of other sectors due to an increased contribution to the total AOT by fine urban aerosol, which contributed up to 56.5% of the total AOT.     

Chlorinated guaiacols and catechols bioaccumulation potential in bleaks (Alburnus alburnus, Pisces) and reproductive and toxic effects on the har-pacticoid Nitocra spinipes (Crustacea)

The bioaccumulation potential in bleaks (Alburnus alburnus, Pisces) and acute toxic and reproductive effects on Nitocra spinipes (Crustacea), of 4,5,6-trichloroguaiacol (I), tetrachloroguaiacol (II) and tetrachlorocatechol (III) was investigated. Continuous flow tests with I and II (10 μg/l) gave a rapid bi-phasic uptake in the fish with I and II reaching a level of 4 μg/g fresh weight after 14 d. An equally rapid excretion was determined with the detection limit of I and II being reached after 10 days in pure water. The 96-h LC50 values for I, II and III to N. spinipes was determined to 5.2, 3.9 and 3.3 mg/l, respectively, in static tests. The fecundity of N. spinipes was reduced to 50 % of the control values at 37±6 and 54±4 μg/l (II) per liter in static and continuous flow tests, respectively.     

Nitrogen oxide emission calculation for post-Panamax container ships by using engine operation power probability as weighting factor: A slow-steaming case

In this study, the nitrogen oxide (NO_x) emission factors and total NO_x emissions of two groups of post-Panamax container ships operating on a long-term slow-steaming basis along Euro–Asian routes were calculated using both the probability density function of engine power levels and the NO_x emission function. The main engines of the five sister ships in Group I satisfied the Tier I emission limit stipulated in MARPOL (International Convention for the Prevention of Pollution from Ships) Annex VI, and those in Group II satisfied the Tier II limit. The calculated NO_x emission factors of the Group I and Group II ships were 14.73 and 17.85 g/kWhr, respectively. The total NO_x emissions of the Group II ships were determined to be 4.4% greater than those of the Group I ships. When the Tier II certification value was used to calculate the average total NO_x emissions of Group II engines, the result was lower than the actual value by 21.9%. Although fuel consumption and carbon dioxide (CO₂) emissions were increased by 1.76% because of slow steaming, the NO_x emissions were markedly reduced by 17.2%. The proposed method is more effective and accurate than the NO_x Technical Code 2008. Furthermore, it can be more appropriately applied to determine the NO_x emissions of international shipping inventory.

Implications: The usage of operating power probability density function of diesel engines as the weighting factor and the NO_x emission function obtained from test bed for calculating NO_x emissions is more accurate and practical. The proposed method is suitable for all types and purposes of diesel engines, irrespective of their operating power level. The method can be used to effectively determine the NO_x emissions of international shipping and inventory applications and should be considered in determining the carbon tax to be imposed in the future.     

Mercury conversion processes in Amazon soils evaluated by thermodesorption analysis

This paper reports on the speciation study and the Hg redox behavior in Amazon soils not influenced by gold mining and collected near Manaus, AM, Brazil. The samples were incubated by adding Hg(0) and HgCl₂ to dry soil. Solid phase Hg speciation analysis was carried out using a Hg thermodesorption technique with the aim of distinguishing elemental Hg(0) from Hg(II) binding forms. In the first case, we observed the conversion of Hg(0) to Hg(II) binding forms in the range of 28–68% and a correlation between the percent of oxidation and OM content. Samples incubated with Hg(II) showed the formation of Hg(I) and/or Hg(0) in the range of 19–69%. The lowest values corresponded to the samples with the lowest clay contents. The kinetics of conversion of Hg(0) as well as HgCl₂ were roughly fitted to the two first order reactions, a fast one and a slow one. It was not possible to evaluate differences between sampling sites and types of soils, but the mean half-life of the first order reaction obtained by the addition of Hg(II) was slower (t_1/2 = 365 d) than the one obtained by the addition of Hg(0) (t_1/2 = 148 d). Previous studies have shown the predominance of organically bound Hg in these samples. Thus, the kinetic difference between Hg oxidation and reduction in combination with the efficient retention processes by OM may explain the high background values found in Amazon soils.     

Influence of the chemical structure on mobility of PCB congeners in female and male sardine (Sardina pilchardus) from Portuguese coast

Concentrations of 30 polychlorinated biphenyl congeners (CBs) were determined in muscle, liver and gonad tissues of female and male sardines (Sardina pilchardus) collected in February-May 2000 and September-January 2001 from purse seine vessels operating around Peniche, Portugal. The determined CBs were aggregated in four groups (I, II, III and IV), according to similarities of their chemical structures. Muscle and liver of males contained significantly higher concentrations of groups I and II than females during the final period of spawning (February-April). A less contrast was observed for the groups III and IV. This seasonal fluctuation associated with the spawning indicates that female sardines regulate the excess of CBs sequestrated during fatten period. On the contrary, levels of groups I and II were higher in males than in females indicating slower mobility of these compounds as lipids were consumed during the final period of spawning. The deficient regulation of those CBs in muscle of male sardines can not be attributed to selective transfer to gonads and subsequent excretion. Although the full explanation was not found for the different mobility of PCBs with the gender, the results provide evidence of slower elimination of group I and II congeners in male sardines.