Assessment of exposure to dust, gaseous pollutants and endotoxins in sewage treatment plants of Ahmedabad city, India.

BACKGROUND: Sewage treatment plant workers (STPs) are exposed to gaseous pollutants (H2S) and bioaerosols and their health is at risk. OBJECTIVE: The aim of the study was to evaluate exposures to dust, 1,3 Beta D Glucans, endotoxins and gaseous pollutants in different process plants and to provide suitable recommendations. METHODS: Gaseous pollutants and bioaerosols (inhalable dust, 1,3 beta D-glucans and endotoxins) were evaluated in two sewage treatment plants (STPs) of Ahmedabad city, India. The concentration of H2S, CO, CH4 and Cl2 were monitored in two process areas of STPs using real-time gas detectors. The dust, 1,3 beta D-glucans and endotoxins were evaluated as per standard methods. RESULTS: The mean concentration of H2S exceeded the permissible exposure limit of 10 ppm, whereas the concentration of other gaseous pollutants (CO, Cl2 and CH4) were below the permissible exposure limits of Indian Factories Act, 1948. The inhalable dust concentration was also within the permissible exposure limit of 10 mg/m3 as per Indian Factories Act, 1948. CONCLUSIONS: Significant exposures to gaseous and bioaerosols were found in the work environment of STPs. The paired t-test result showed a significant difference between two STPs for H2S, 1,3 beta D-Glucans and endotoxins. STPs were advised to reduce the exposure to H2S and bioaerosols as per CPCB guidelines applicable to India to prevent health effects.

Toxicity screening of metals with special reference to quantitative approach.

A series of metals Cr(6+), Al(3+), Cd(2+), Pb(2+), Cu(2+), Zn(2+), and Hg(2+) were tested in three systems--Microtox, Motility Test, and Growth Zone Inhibition Test. Toxicity endpoint of each metal was variable from system to system. Of the three systems, Microtox was the most sensitive system. In this system, Hg(2+) reacted as the most toxic element having EC(50) value 0.08 mg/L while Cd(2+) and Cr(6+) were least toxic with their EC(50) values 19.4 and 21.0 mg/L respectively. MEC(90) value of Motility Test was always needed more concentrations of toxicant in comparison to other systems. In comparison to Microtox, ten times more concentration of Hg(2+) (1.4 mg/L) was required to find out its MEC(90) value. Growth Zone Inhibition Test was very simple method from handling point of view. The usual practice of evaluation of toxicity screening in this system is either qualitatively or semi-qualitatively. Hence a study was designed to establish a quantitative technique, Growth Inhibition Test, as an alternative to this test using the same sensor organism B. cereus, which allows determination of MAC as well as MIC. MIC for Hg(2+) was found to be 0.03 mg/L in Growth Inhibition Test while the same element was needed more concentration (1.0 mg/L) in the case of Growth Zone Inhibition test to produce halo. However, all these systems including Growth Inhibition Test showed Hg(2+) was the most toxic element.