Disease-causing germs could remain in liquefaction silt for more than five months, a report has found.
Two reports on the impact of liquefaction after the Canterbury earthquakes were made public by Environmental Science and Research (ESR) yesterday.
It took thousands of people months to remove silt from residential streets after the quakes, but the fact no outbreaks of gastrointestinal illnesses were reported during the cleanup suggested that most silt was not heavily contaminated with sewage, the first report said.
However, it found that the risk of exposure to pathogenic micro-organisms could remain in silt that was contaminated by sewage for more than five months, regardless of how deep the silt was.
The pathogens could cause gastro-intestinal illnesses such as giardia or cryptosporidium.
Canterbury medical officer of health Alistair Humphrey said there did not seem to be any increases in giardia and cryptosporidium cases since the quakes.
However, it was important for those still removing potentially contaminated silt from under houses to take precautionary measures because it could contain pathogens.
A second report made public by ESR yesterday confirmed that liquefaction silt was made of the same elements as sand, and it looked at the effect that the ultra-fine dust particles in the silt could have on air quality and public health.
Levels of the tiny particles, known as PM10, had been decreasing in Christchurch in recent years, but dust from silt resulted in an increase last year.
Environment Canterbury believed 12 of the 34 high-pollution days recorded last year were caused by liquefaction dust and grit on roads.
The possible effects from airborne dust included respiratory problems and eye irritation, and exposure to PM10 could result in serious health effects, including premature death, the report said.
There was evidence of adverse pregnancy-related outcomes from PM10 exposure, such as low birth weight.
If more liquefaction occurred, ESR recommended removing the silt as soon as possible and preventing dust by keeping the silt wet, using barriers or coverings.
Humphrey said the report was "reassuring" and confirmed earlier health advice.