M.Salim Akhter

Heavy metals in street and house dust in Bahrain

A total of 106 street and household dusts have been sampled throughout Bahrain and analyzed for Pb, Zn, Cd, Ni and Cr using the atomic absorption spectrophotometric method. The sampling sites were divided into seven categories, including the control site. Results showed that dust samples contained significant levels of the metals studied compared with the control values. The mean values for Pb, Zn, Cd, Ni and Cr in street dust were 697.2, 151.8, 72.0, 125.6 and 144.4 μg g−1 respectively, whereas for household dust they were 360.0, 64.4, 37.0, 110.2 and 144.7 μg g−1. These values suggest that motor vehicles form a major source of these metals in dust samples. The values of heavy metals in dust samples in this study were compared with values found in other investigations in various countries. With respect to Ni, elevated concentration could be attributed to smoke from the burning of Kuwait oil fields. Also correlations between metal levels in dust samples for all the metals were investigated. Our results show that heavy metal levels in various sites in Bahrain are similar, which indicate that Bahrain can be considered as one big urban center with high population and traffic density.

The correlations between heavy metals in residential indoor dust and outdoor street dust in Bahrain

The lead, zinc, cadmium, chromium, and nickel contents in both indoor house dust and outdoor street dust from 76 sites in Bahrain were determined by ICP-ES. The results showed widespread heavy metal contamination, especially lead, with an overall mean value in house dust for Pb, Zn, Cd, Cr, and Ni of 517, 202, 1.9, 11, and 10, respectively. The mean values in street dust were 742, 67, 1.5, 9.6, and 12 mg/kg, respectively. The major source of metals in street dust was automobile exhaust. The major source of heavy metals indoors was also from automobile dust, i.e., lead and nickel. With respect to zinc, cadmium, and chromium, indoor sources were more important than outdoor sources. The distribution of lead both indoors and outdoors in Bahrain showed high levels of contamination occurring generally in the north and northeastern part where traffic is concentrated. The levels of these toxic metals found in indoor house dust may be a significant source of exposure, especially for children.

The effect of organic additives on critical micelle concentration of non-aqueous micellar solutions

Abstract The critical micelle concentration (c.m.c.) of various surfactants, such as sodium caprylate, sodium laurate, sodium palmitate and sodium stearate micellar solution, containing methanol, ethanol, n-propanol, n-butanol and n-pentanol in formamide has been determined using electrical conductivity and surface tension measurements at various temperatures. Both methods show that micelles are formed in formamide solution in presence of n-alkanols. Critical micelle concentrations have also been measured as a function of the concentration of alcohol added. It is suggested that alcohol addition leads to an increase in formamide penetration into the micellar interface that depends on the alcohol chain length. The results are discussed in terms of: (1) alcohol penetration of the micelles; and (2) solvent structuring. Thermodynamic parameters were evaluated for micellar systems in presence of n-alkanols to further explain the results.

Effect of acetamide on the critical micelle concentration of aqueous solutions of some surfactants

The variations of molar conductivity of various surfactants such as sodium caprylate, sodium laurate, sodium palmitate, sodium stearate, sodium oleate, sodium dodecyl sulphate, and lithium dodecyl sulphate with concentration of the surfactants for each of the solutions consisting of mixtures of varying concentrations of acetamide in water at a constant temperature of 30±0.2°C were studied. The critical micelle concentration (CMC) for each surfactant is measured. It is found that the CMC values in mixtures of acetamide and water solutions of various surfactants are lower than the CMC values in water.

Aggregation of ionic surfactants in formamide

Abstract Electrical conductivity and surface tension measurements of various ionic surfactants, such as sodium caprylate, sodium laurate, sodium palmitate and sodium stearate, in formamide has been determined at 22°C. Both methods show that micelles are formed in formamide solution. Critical micelle concentration (c.m.c.) has been determined for each of the ionic surfactants. It is suggested that amphiphilic self-assembly is a physical process that occurs in formamide and the driving force for aggregation correlates with solvophobicity. The surfactant–solvent interactions that drive amphiphilic self-organization in formamide are discussed. Thermodynamic parameters were evaluated for micellar systems to explain the results.

Influence of alcohols on the critical micelle concentration of non-aqueous micellar solutions

Abstract Electrical conductivity and surface tension measurements of various surfactants, such as sodium caprylate, sodium laurate, sodium palmitate and sodium stearate micellar solution, containing methanol, ethanol, n-propanol, n-butanol and n-pentanol in N,N-dimethyl acetamide has been determined at various temperatures. Both methods show that micelles are formed in N,N-dimethyl acetamide solution in presence of n-alkanols. Critical micelle concentration (c.m.c) has been determined for each of the surfactants. Critical micelle concentrations have also been measured as a function of the concentration of alcohol added. It is suggested that alcohol addition leads to an increase in N,N-dimethyl acetamide penetration into the micellar interface that depends on the alcohol chain length. Thermodynamic parameters were evaluated for micellar systems in presence of n-alkanols to further explain the results.

Assessment of lead in roadside vegetation in Bahrain.

Abstract Leaves from five species of trees were sampled at 18 locations in Bahrain and were analyzed for lead. Lead levels in leaves from areas with high traffic density were generally higher than lead levels in leaves from areas with low traffic density. The lead levels found in this study are in the range of 9μg/g to 420 μg/g, which is low compared to values reported for leaves of trees along busy roads in developed countries. However, the concentration of lead is increasing because of the extreme meteorological situation in Bahrain and the heavy traffic coming from other Gulf countries across King Fahad Causeway between Saudi Arabia and Bahrain.

Studies on micelle formation and enthalpy of micellization in molten acetamide

The electrical conductivity of lithium dodecylsulfate, sodium dodecylsulfate, sodium oleate and sodium stearate has been determined in molten acetamide at 90°C. Conductivity measurements show that for these surfactants, micelles are formed in molten acetamide solutions. The critical micelle concentration (CMC) of each surfactant has been calculated. Lithium dodecylsulfate has a lower CMC than sodium dodecylsulfate. Sodium oleate, which contains a double bond and has the same number of carbon atoms as sodium stearate, has a lower CMC. The enthalpy of micellization for sodium oleate in molten acetamide has been found by determining the CMC at different temperatures. The results have been explained on the basis of solvation effect and nature of micelles.

Studies on solvophobic interactions and micelle formation in non aqueous solvents

Micelle formation of various surfactants, such as sodium caprylate, sodium laurate, sodium palmitate and sodium stearate has been studied in organic solvents of various dielectric constants and intermolecular H-bonding capability, viz. molten acetamide, N-methyl acetamide (NMA) and N,N-dimethyl acetamide (DMA), at different temperatures by electrical conductivity and surface tension methods. Both methods show that micelles are formed in acetamide, NMA and DMA. Gibbs energy changes, enthalpies and entropies of micelle formation, respectively, have been determined by studying the variation of critical micelle concentration (c.m.c.) with temperature. Micelle formation in these solvents has been explained on the basis of several factors such as dielectric constant of the medium, its intermolecular H-bonding capability including solvophobic interaction.

Effect of solubilization of alcohols on critical micelle concentration of non-aqueous micellar solutions

Abstract Electrical conductivity and surface tension measurements of various surfactants, such as sodium caprylate, sodium laurate, sodium palmitate and sodium stearate micellar solution, containing methanol, ethanol, n-propanol, n-butanol and n-pentanol in N -methyl acetamide has been determined at various temperatures. Both methods show that micelles are formed in N -methyl acetamide solution in the presence of n-alkanols. Critical micelle concentration has been determined for each of the surfactants. Critical micelle concentrations have also been measured as a function of the concentration of alcohol added. It is suggested that alcohol addition leads to an increase in N-methyl acetamide penetration into the micellar interface that depends on the alcohol chain length. Thermodynamic parameters were evaluated for micellar systems in presence of n-alkanols to further explain the results.