Unit-iv unit-iv environmental Hygiene



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Atmospheric-pollution

In man:

  • In man:
    • Sneeze can release upto 10,000-10,00,000 droplets
    • Microbes released by animal & human sources survive in the environment for varying lengths of time
    • Some organisms may not survive for more than few minutes (Leptospira in dry atmosphere),
    • Can resist the adverse environmental conditions for as long as 28 years (spores of Bacillus anthracis in soil)
    • Brucellae can survive in soil for about one month
    • Exposure to sunlight causes destruction of many environmental microorganisms (Mycobacterium spp)
    • In soil: mycobacteria can survive for upto 6 months

Measurement of air contamination

  • The microbial load of moving air is determined
    • To assess the level of contamination within a building or given area
  • Several techniques are used
    • To collect the samples & conduct qualitative & quantitative analysis of air
    • Sedimentation
    • Impaction
    • Impingement
    • Precipitation
    • Filtration
    • Sieve cascade sampler

1. Sedimentation (settling plate method)

1. Sedimentation (settling plate method)

    • Permits settlement of atmospheric air on the surface of an agar plate for 10 min or more
    • It does not allow the settlement of suspended particles the air
    • 2. Impaction

    • Collecting the atmospheric particles on the surface of a solid/semi-solid agar medium
    • Air centrifuge is used
    • The air flow on the sides of a rotating cylinder lined with a culture medium
    • Suitable for large sized particles
    • A better known device called slit sampler is preferred by many to test air quality
    • The air is sucked through a slit onto a rotating culture plate kept underneath the device
    • The flow rate one cu ft .( 28.3 cu cm)/min
    • Rotation rate is kept at 0.5, 2 or 6 min/revolution

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