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

Abstract

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.

Keywords:

• Ecotoxicological screening
• solid phase
• liquid phase
• biosensor