Lead exposure and blood pressure among workers in diverse industrial plants in Kenya.

The study evaluated airborne exposures and blood lead (BPb) levels in 233 production workers at six diverse industrial plants in Kenya. Blood and personal breathing zone air samples were collected and analyzed for lead (Pb) using atomic absorption spectroscopy. Blood pressure (BP) levels were measured using a standard mercury sphygmomanometer. The results indicated mean airborne Pb levels ± standard deviation (SD) as follows: 183.2 ± 53.6 µg/m(3) in battery recycling, 133.5 ± 39.6 µg/m(3) in battery manufacturing, 126.2 ± 39.9 µg/m(3) in scrap metal welding, 76.3 ± 33.2 µg/m(3) in paint manufacturing, 27.3 ± 12.1 µg/m(3) in a leather manufacturing, and 5.5 ± 3.6 µg/m(3) in a pharmaceutical plant. The mean airborne Pb levels exceeded the U.S. Occupational Safety and Health Administration (OSHA) 8-hr time-weighted average (TWA) permissible exposure limit (PEL) for Pb of 50 µg/m(3) in the battery manufacturing, battery recycling, welding, and paint manufacturing plants. Similarly, mean BPb concentrations exceeded the American Conference of Governmental Industrial Hygienists (ACGIH®) biological exposure index (BEI) for Pb of 30 µg/dl. A significant positive association was observed between BPb and breathing zone air Pb (R(2) = 0.73, P < 0.001). Approximately 30% of the production workers (N = 233) were in the hypertensive range with an average systolic and diastolic blood pressure (BP) of 134.7 ± 12.7 mmHg and 86.4 ± 8.9 mmHg, respectively. In the multivariate regression analysis, age, duration of work, airborne Pb and BPb levels were significantly associated (P < 0.05) with a change in BP. We recommend improved engineering controls, work practices, and personal hygiene to reduce Pb exposures. In addition, workers should undergo comprehensive medical surveillance to include BPb and BP testing, and airborne Pb assessments in all industries with significant lead exposures.

Air and blood lead levels in lead acid battery recycling and manufacturing plants in Kenya.

The concentration of airborne and blood lead (Pb) was assessed in a Pb acid battery recycling plant and in a Pb acid battery manufacturing plant in Kenya. In the recycling plant, full-shift area samples taken across 5 days in several production sections showed a mean value ± standard deviation (SD) of 427 ± 124 µg/m(3), while area samples in the office area had a mean ± SD of 59.2 ± 22.7 µg/m(3). In the battery manufacturing plant, full-shift area samples taken across 5 days in several production areas showed a mean value ± SD of 349 ± 107 µg/m(3), while area samples in the office area had a mean ± SD of 55.2 ± 33.2 µg/m(3). All these mean values exceed the U.S. Occupational Safety and Health Administration's permissible exposure limit of 50 µg/m(3) as an 8-hr time-weighted average. In the battery recycling plant, production workers had a mean blood Pb level ± SD of 62.2 ± 12.7 µg/dL, and office workers had a mean blood Pb level ± SD of 43.4 ± 6.6 µg/dL. In the battery manufacturing plant, production workers had a mean blood Pb level ± SD of 59.5 ± 10.1 µg/dL, and office workers had a mean blood Pb level ± SD of 41.6 ± 7.4 µg/dL. All the measured blood Pb levels exceeded 30 µg/dL, which is the maximum blood Pb level recommended by the ACGIH(®). Observations made in these facilities revealed numerous sources of Pb exposure due to inadequacies in engineering controls, work practices, respirator use, and personal hygiene.

Magnitude and direction of thermal diffusion of colloidal particles measured by thermal field-flow fractionation.

In this paper we provide experimental evidence showing that various types of submicrometer-sized particles (latexes, inorganic, and metallic), suspended in either aqueous or nonaqueous carrier liquids to which a temperature gradient dT/dx is applied, experience a force in the direction opposite to that of dT/dx. This behavior is similar to that of small particles such as soot, aerosols, and small bubbles suspended in stagnant gases across which temperature gradients are applied, a phenomenon known as "thermophoresis in gases." We report the use of a thermal field-flow fractionation (ThFFF) apparatus in two different configurations to establish the direction of particle motion subject to a temperature gradient. The first approach employed the conventional horizontal ThFFF channel orientation. In this case, small electrical potentials were applied across the narrow channel thickness either to augment or to act in opposition to the applied thermal gradient, depending on whether the accumulation wall was maintained at a positive or negative potential relative to the depletion wall. Thus, by observing the changes in the retention behavior of surface-charged latices or silica particles with changes in potential difference across the channel thickness, we were able to ascertain the direction of migration of the particles in the thermal gradient. The second approach involved the use of a ThFFF column oriented vertically in an implementation of a technique known as thermogravitational FFF. In this approach, the convective flow along the channel length (due to density gradients associated with the temperature gradient) couples with the thermal diffusion effect across the channel thickness to result in a combined particle retention mechanism. A retarded upward migration rate is indicative of accumulation of particles at the cold wall, while enhanced upward migration would indicate a hot-wall accumulation. From the results of our investigations, we conclude that submicrometer-sized particles suspended in either aqueous or nonaqueous carrier liquids and subjected to a temperature gradient migrate from the hot wall toward the cold wall of a ThFFF channel.

Practical implications of ionic strength effects on particle retention in thermal field-flow fractionation.

Modification of ionic strength of an aqueous or non-aqueous carrier solution can have profound effects on the particle retention behavior in thermal field-flow fractionation (ThFFF). These effects can be considered as either advantageous or not depending on the performance criteria under consideration. Aside from the general increase in retention time of particulate material (latexes and silica particles), our experiments indicate improvement in resolution with increases in electrolyte concentration. Absence of an electrolyte in the carrier solution causes deviations from the theoretically expected linear behavior between the retention parameter lambda (a measure of the extent of interaction between the applied field and the particle) and the reciprocal temperature drop across the channel walls. A negative interaction parameter delta(w), of about -0.170 was determined for 0.105- and 0.220-microm polystyrene (PS) latex particles suspended in either a 0.25 or a 1.0 mM TBAP-containing acetonitrile carrier and for 0.220 microm PS in 0.50 and 1.0 mM NaCl-containing aqueous medium. This work also demonstrates that optimum electrolyte concentrations can be chosen to achieve reasonable experimental run-times, good resolution separations, and shifts in the steric inversion points at lower field strengths, and that too high electrolyte concentrations can have deleterious effects such as band broadening and sample loss through adsorption to the channel accumulation surface. The advantages of using ionic strength rather than field strength to effect desired changes are lowered power consumption and possible application of ThFFF to high temperature-labile samples.

Retention behavior of metal particle dispersions in aqueous and nonaqueous carriers in thermal field-flow fractionation.

Until quite recently, theories on thermophoresis of particles predicted very low thermophoretic velocities of metal particles in liquids. This prediction was based on the understanding that the very high thermal conductivities of metals relative to most liquid media resulted in quite low temperature gradients across the metal particle thereby leading to low net force on the particle. In this paper, we report the retention behavior of submicrometer size metal particles of silver (Ag), gold (Au), palladium (Pd) and platinum (Pt) suspended in both aqueous and organic (specifically, acetonitrile and tetrahydrofuran) carrier liquids in thermal field-flow fractionation (ThFFF). The dependence of the metal particle retention on various factors such as particle composition, amount of added electrolyte, carrier liquid composition, field strength, channel thickness, and carrier flow-rate is evaluated and discussed. A comparison in particle retention behavior among equal-sized metal, latex and silica particles is also provided.

Adsorption and detection of some phenolic compounds by rice husk ash of Kenyan origin.

Rice husk ash (RHA) obtained from a rice mill in Kenya has been used as an inexpensive and effective adsorbent (and reagent) for the removal (and detection) of some phenolic compounds in water. The abundantly available rice mill waste was used in dual laboratory-scale batch experiments to evaluate its potential in: (i) the removal of phenol, 1,3-dihydroxybenzene (resorcinol) and 2-chlorophenol from water; and (ii) the detection of 1,2-dihydroxybenzene (pyrocatechol) and 1,2,3-trihydroxybenzene (pyrogallol) present in an aqueous medium. The studies were conducted using synthetic water with different initial concentrations of the phenolic compounds. The effects of different operating conditions (such as contact time, concentration of the phenolic compounds, adsorbent quantity, temperature, and pH) were assessed by evaluating the phenolic compound removal efficiency as well as the extent of their color formation reactions (where applicable). RHA exhibits reasonable adsorption capacity for the phenolic compounds and follows both Langmuir and Freundlich isotherm models. Adsorption capacities of 1.53 x 10(-4), 8.07 x 10(-5), and 1.63 x 10(-6) mol g(-1) were determined for phenol, resorcinol and 2-chlorophenol, respectively. Nearly 100% adsorption of the phenolic compounds was possible and this depended on the weight of RHA employed. For the detection experiments, pyrocatechol and pyrogallol present in water formed coloured complexes with RHA, with the rate of colour formation increasing with temperature, weight of RHA, concentration of the phenolic compounds and sonication. This study has proven that RHA is a useful agricultural waste product for the removal and detection of some phenolic compounds.