Ecotoxicological screening of Kenyan tannery dust using a luminescent-based bacterial biosensor

Ecotoxicological screening of dust sampled throughout a Kenyan tannery was conducted using a luminescence (lux)-based bacterial biosensor for both solid and liquid assays. This was complemented by chemical analysis in an attempt to identify possible causative toxic components. The biosensor results showed a highly significant (p <0.001) difference in both solid and liquid phase toxicity in samples collected from various identified sampling points in the tannery. A positive correlation was observed between results of the solid and liquid phase techniques, for most of the sampling points indicating that the toxic contaminants were bioavailable both in the solid and liquid state. However, the results generally indicated toxicity associated with liquid phase except certain areas in solid phase such as chemical handling, buffing area and weighing. The most toxic tannery area identified was the weighing area (p <0.001), showing the lowest bioluminescence for both the solid (0.38 +/- 2.21) and liquid phases (0.01 +/- 0.001). Chromium was the metal present in the highest concentration indicating levels higher than the stipulated regulatory requirement of 0.5 mg Cr/m3 for total Cr (highest Cr concentration was at chemical handling at 209.24 mg l(-1)) in all dust samples. The weighing area had the highest Ni concentration (1.87 mg l(-1)) and the chemical handling area showed the highest Zn concentration (31.9 mg l(-1)). These results raise environmental health concerns, as occupational exposure to dust samples from this site has been shown to give rise to elevated concentrations (above the stipulated levels) of chromium in blood, urine and some body tissues, with inhalation being the main route. Health and Safety Executive (HSE), UK, and American Conference of Governmental Industrial Hygienist (ACGIH) and National Institute for Occupational Safety and Health (NIOSH), USA stipulates an occupational exposure limit of 0.5 mg Cr/m3 (8 h TWA) for total chromium. However, schedule 1 of Controls of substances hazardous to health (COSHH) regulations developed by HSE, indicate 0.05 mg m3 (8 h TWA reference periods) to be the limit for Cr (VI) exposure. The exposure limit for individual (e.g., Cr, Zn, Ni etc.) contaminants (homogeneity) was not exceeded, but potential impact of heterogeneity (multi-element synergistic effect) on toxicity requires application of the precautionary principle.

Assessing the occupational risk of dust particles in the Kenyan tanning industry using rapid image processing and microscopy techniques

The purpose of this study was to investigate the occupational hazards within the tanning industry caused by contaminated dust. A qualitative assessment of the risk of human exposure to dust was made throughout a commercial Kenyan tannery. Using this information, high-risk points in the processing line were identified and dust sampling regimes developed. An optical set-up using microscopy and digital imaging techniques was used to determine dust particle numbers and size distributions. The results showed that chemical handling was the most hazardous (12 mg m(-3)). A Monte Carlo method was used to estimate the concentration of the dust in the air throughout the tannery during an 8 h working day. This showed that the high-risk area of the tannery was associated with mean concentrations of dust greater than the UK Statutory Instrument 2002 No. 2677. stipulated limits (exceeding 10 mg m(-3) (Inhalable dust limits) and 4 mg m(-3) (Respirable dust limits). This therefore has implications in terms of provision of personal protective equipment (PPE) to the tannery workers for the mitigation of occupational risk.

Nonlinear dust-acoustic solitary waves in strongly coupled dusty plasmas

Dust-acoustic waves are investigated in a three-component plasma consisting of strongly coupled dust particles and Maxwellian electrons and ions. A fluid model approach is used, with the effects of strong coupling being accounted for by an effective electrostatic "pressure" which is a function of the dust number density and the electrostatic potential. Both linear and weakly nonlinear cases are considered by derivation and analysis of the linear dispersion relation and the Korteweg-de Vries equation, respectively. In contrast to previous studies using this model, this paper presents the results arising from an expansion of the dynamical form of the electrostatic pressure, accounting for the variations in its value in the vicinity of the wave. DOI: 10.1103/PhysRevE.86.066404

Strong electrostatic interaction effect on modulational stability of dust acoustic waves

The modulational instability of dust-acoustic waves is investigated, relying on a recently proposed model for strong electrostatic interactions between the highly charged dust particles. The resulting effect on the occurrence (threshold, growth rate) of modulational instability is investigated. Our results can in principle be tested experimentally.

Dust-ion-acoustic supersolitons in dusty plasmas with nonthermal electrons

Supersolitons are a recent addition to the literature on large-amplitude solitary waves in multispecies plasmas. They are distinguished from the usual solitons by their associated electric field profiles which are inherently distinct from traditional bipolar structures. In this paper, dust-ion-acoustic modes in a dusty plasma with stationary negative dust, cold fluid protons, and nonthermal electrons are investigated through a Sagdeev pseudopotential approach to see where supersolitons fit between ranges of ordinary solitons and double layers, as supersolitons always have finite amplitudes. They therefore cannot be described by reductive perturbation treatments, which rely on a weak amplitude assumption. A systematic methodology and discussion is given to distinguish the existence domains in solitary wave speed and amplitude for the different solitons, supersolitons and double layers, in terms of compositional parameters for the plasma model under consideration. © 2013 American Physical Society.

A Stubbornly Large Mass of Cold Dust in the Ejecta of Supernova 1987A

We present new Herschel photometric and spectroscopic observations of Supernova 1987A, carried out in 2012. Our dedicated photometric measurements provide new 70 mu m data and improved imaging quality at 100 and 160 mu m compared to previous observations in 2010. Our Herschel spectra show only weak CO line emission, and provide an upper limit for the 63 mu m [O-I] line flux, eliminating the possibility that line contaminations distort the previously estimated dustmass. The far-infrared spectral energy distribution (SED) is well fitted by thermal emission from cold dust. The newly measured 70 mu m flux constrains the dust temperature, limiting it to nearly a single temperature. The far-infrared emission can be fitted by 0.5 +/- 0.1M(circle dot) of amorphous carbon, about a factor of two larger than the current nucleosynthetic mass prediction for carbon. The observation of SiO molecules at early and late phases suggests that silicates may also have formed and we could fit the SED with a combination of 0.3M(circle dot) of amorphous carbon and 0.5M(circle dot) of silicates, totalling 0.8M(circle dot) of dust. Our analysis thus supports the presence of a large dust reservoir in the ejecta of SN 1987A. The inferred dust mass suggests that supernovae can be an important source of dust in the interstellar medium, from local to high-redshift galaxies.

Dust-acoustic shocks in strongly coupled dusty plasmas

Electrostatic dust-acoustic shock waves are investigated in a viscous, complex plasma consisting of dust particles, electrons, and ions. The system is modelled using the generalized hydrodynamic equations, with strong coupling between the dust particles being accounted for by employing the effective electrostatic temperature approach. Using a reductive perturbation method, it is demonstrated that this model predicts the existence of weakly nonlinear dust-acoustic shock waves, arising as solutions to Burgers's equation, in which the nonlinear forces are balanced by dissipative forces, in this case, associated with viscosity. The evolution and stability of dust-acoustic shocks is investigated via a series of numerical simulations, which confirms our analytical predictions on the shock characteristics.