Metal associations in soils before and after EDTA extractive decontamination: implications for the effectiveness of further clean-up procedures

The distribution of Pb, Ni and Zn in two contaminated soils was determined before and after treating the soils with an EDTA solution. After the EDTA extraction, the proportion of Pb accumulated in the acid-extractable fraction considerably increased, which was related to the greater degree of metal extraction from the other fractions. EDTA was also able to extract certain amounts of Pb, Zn and Ni from the silicate matrix, which implied that these extractable amounts were not so strongly fixed to the residual fraction as previously supposed. As a consequence, after EDTA application, metal content (especially Pb) remained more weakly adsorbed to soil components (more easily leachable), potentially favouring the application of phytoremediation technologies. The extraction recoveries (for only one application) were generally low for the three metals (33-37% for Pb, 5-11% for Ni and 14-19% for Zn), although this fact is an advantage as plants would not be able to assimilate very high mobilised contents of metals.     

The role of interfacial films in the mass transfer of naphthalene from creosotes to water

Viscous, semi-rigid interfacial films that are formed at the interface of certain multi-component non-aqueous phase liquid (NAPLs) and water can significantly reduce the rates of mass transfer of solutes. Creosote-water systems were investigated for their ability to form interfacial films. The effects of these films on the creosote-water partition and on mass transfer of a representative solute, naphthalene, were investigated in a series of experiments. The area-independent mass transfer coefficient of naphthalene contained in creosote decreased by 30% over a 1-week period in systems containing creosote and water. Further aging for up to 21 days did not result in significant additional decreases in the mass transfer coefficient. The creosote-water partition coefficient, however, did not change with extended contact. The presence of viscous interfacial films in creosote-water systems was demonstrated in pendant drop tests. These interfacial films most likely caused the reduction in solute mass transfer coefficients by providing significant resistance to the diffusion of solutes through the interfacial film. Results from mass transfer experiments conducted under different system conditions suggested that hindered diffusion of naphthalene through the bulk creosote phase, changes in composition of creosote as a result of extended dissolution, or changes in creosote-water interfacial area did not contribute to the decrease in naphthalene mass transfer coefficient.     

Prospects and Constraints of Desert Agriculture: Lessons from West Omdurman

Sudan is the largest country in Africa with an area of about 2.5 million km²; the country hosts a population of about 31 million people. About two-thirds of the country area is located within arid and semi-arid regions. Recently, especially during the last half of the previous century, these regions were subject to various forms of land degradation. This paper discusses the general prospects and constraints of desert agriculture. It also presents a detailed case study of West Omdurman, which is located in a semi-desert climatic zone. The ambitious plans to utilise the area for agricultural production were initiated because of the relatively fertile soil, availability of water and the proximity of the area to marketing and export centres. The paper discusses the different land use systems experienced in the area, reasons for failure are identified and possible remedies discussed. In addition, constraints facing the proposed West Omdurman Canal Project are also discussed. Finally, the paper reviews the major research findings of Rawakeeb Dryland Research Center with regard to promoting agricultural productivity.     

Determination of Hydrocarbons in Mussels from the Egyptian Red Sea Coast

Mussels (Brachidontes Sp.) collected in April 2000 from the Red Sea coastal of Egypt in order to determine the contamination by hydrocarbons. The study included 11 sampling stations covering about 450 Km of the Egyptian Red Sea coast for the first time. Total concentrations of 20 aliphatics (average 0.105 ng g(-1) of wet weight) and sixteen polycyclic aromatic hydrocarbons (PAHs) (average 5452 ng g(-1) of wet weight) were generally lower in comparison with those reported for some of the published surveillance and monitoring studies of coastal areas from various regions. These results suggest that the coastal area in the Red Sea of Egypt might be considered as a relatively unpolluted.     

Behavior of 1,3-dichloropropene and methyl isothiocyanate in undisturbed soil columns

To develop alternatives to methyl bromide (MeBr) for soil disinfection under environmental Moroccan conditions, distribution and persistence of 1,3-dichloropropene (1,3-D) and methyl isothiocyanate (MITC) were tested in undisturbed soil columns (12 cm internal diameter, 1 m length). 1,3-D was injected at a 15 cm depth and directly followed by metam-sodium (a precursor of MITC), which was applied at the soil surface of the same column using a peristaltic pump. Concerning the distribution of these fumigants in the soil profiles, our results showed that 24 h after treatment, 1,3-D and MITC were concentrated at the 0-40 cm soil layers, and reached the deeper layers 48 h later. MITC and 1,3-D dissipation was studied and the half-life (DT50) measured were 6.5 and 8 days, respectively. Total volatilization losses reached 9% for MITC and 28% for 1,3-D. MITC and 1,3-D volatilization was found to be influence by soil water contents.The results show that by reducing volatilization, photodegradation and leaching of these fumigants a suitable alternative to MeBr use is offered.     

Impact of unleaded gasoline introduction on the concentration of lead in the air of Dhaka, Bangladesh

Airborne particulate matter (APM) samples collected at a semiresidential area in Dhaka, Bangladesh, during the periods of 1994 and 1997-2000 have been studied to assess the impact of the use of unleaded gasoline in Bangladesh. According to scanning electron microscopy/ energy-dispersive X-ray microanalyzer studies, lead (Pb) was found as Pb sulfates and Pb halides in motor-vehicle exhaust particles, whose diameters were some hundreds of nanometers. No significant changes in the annual averages of APM mass and black carbon concentrations have been observed over the period. The yearly average Pb concentration reached a maximum value of 370 ng/m3 in the particulate matter with an aerodynamic diameter < 2.5 microm fraction in 1998. In 2000, the concentration decreased to approximately one-third (106 ng/m3) of the high earlier values after the introduction of unleaded gasoline in 1999. A significant lowering of the blood Pb level of the population over next few years is expected as a result of this great decrease in Pb concentration.     

Homogeneous degradation of 1,2,9,10-tetrachlorodecane in aqueous solutions using hydrogen peroxide, iron and UV light

The homogeneous degradation of the polychlorinated n-alkane, 1,2,9,10-tetrachlorodecane (T4C10), was studied in aqueous solutions of hydrogen peroxide, including Fenton and photo-Fenton reaction conditions. All solutions were adjusted to a pH of 2.8 and an ionic strength of 0.1 M NaClO4 prior to photolysis. T4C10 (2 x 10(-6) M) was substantially degraded by the H2O2/UV system (1.0 x 10(-2) M H2O2), with 60% disappearance in 20 min of irradiation in a photoreactor equipped with 300 nm lamps of light intensity 3.6 x 10(-5) Ein L(-1) min(-1) (established by ferrioxalate actinometry). The reaction produced stoichiometric amounts of chloride ion indicating complete dechlorination of the chlorinated n-alkane. T4C10 degraded very slowly under Fenton (Fe2+/H2O2/dark) and Fenton-like (Fe3+/H2O2/dark) conditions. However, when the same solutions were irradiated, T4C10 degraded more rapidly than in the H2O2/UV system, with 61% disappearance in 10 min of exposure. The rapid degradation is related to the enhanced degradation of hydrogen peroxide to oxidizing *OH radicals under photo-Fenton conditions. Degradation was inhibited in both the H2O2/UV and photo-Fenton systems by the addition of KI and tert-butyl alcohol due to *OH scavenging.     

Biochemical enzyme activity in different tissues of rats exposed to a novel phosphorothionate (RPR-V)

The effects of a novel phosphorothionate (RPR-V) synthesized at Indian Institute of Chemical Technology, Hyderabad, was studied using three sub-chronic doses of 0.033 (low), 0.066 (medium) and 0.099 (high) mg kg(-1) in male and female rats for a period of 90 days. This long term and repeated treatment of RPR-V revealed that the membrane bound target enzymes Aspartate aminotransferase and Alanine aminotransferase increased significantly in serum and kidney, whereas these enzymes significantly decreased in liver and lung tissues when measured after 45 and 90 days of treatment. This compound also caused significant inhibition of RBC Acetylcholinesterase, target enzyme of organophosphorus compounds revealing its effect on normal synaptic transmission. Two way Anova studies disclosed that the alterations were mostly dose and time dependent, sexual dimorphism was not observed when the activities of male rats were compared with female rats. Enzyme recoveries were recorded after 28 days of post treatment, high degree positive correlation was observed with regard to these enzymes between serum versus kidney, whereas in case of serum versus liver and lung tissues high degree negative correlation was recorded. These enzyme profiles elucidates that they increased in serum but they decreased significantly in liver and lung indicating necrosis of these tissues. However, in case of kidney the level of these enzymes increased significantly with parallel to serum, which is suggestive of an increase synthesis of these enzymes, may be an adaptive mechanism due to the stress of the toxicant. These biomarker enzymes can be detected rapidly and hence may be used for the prediction and diagnosis of pesticide insults.