Unit-iv unit-iv environmental Hygiene

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