May 2001 update - compiled by Helane Shields - prepared for WWW by ESRA

In responding to Dr. Gerba, Microbiologist Dr. David Lewis notes:

"In his affidavit, Dr. Gerba states that pathogens in sludge are primarily transmitted by ingestion and not inhalation. Yet his published estimates of risks of infection ... were quantified by modeling aerosolized concentrations of microbial pathogens at a given distance from the source and the numbers inhaled over a given period of time."

"... Dr. Gerba testified that he has not been able to detect airborne, sludge-associated pathogens during application of liquid sludge (2-3% solids) and that this application method is more prone to generate airborne pathogens than chain-dragging the dried material with tractors . .
...Even without relying upon the wealth of scientific literature on transmission of pathogens by dust particles, most lay persons are familiar through personal experiences with the fact that dust from dry, non-vegetated fields is carried even great distances by strong winds and can cause respiratory illness."

"Class B sewage sludge that dries out and becomes airborne during chain dragging, or as strong winds blow over non-vegetated lands where solid sludge has been applied - especially within the previous 30 days - is more of a threat to public health than liquid aerosols."

"In any suspension, most microorganisms, by far, are attached to the surfaces of solid particles ... simply by virtue of the fact that most pathogens in sludge are attached tosolid particles

... most anyone can understand that airborne dust particles contain much higher numbers of bacteria and viruses than liquid aerosols for comparably sized particles."

"Gerba's arguments that pathogens on dust from sludge pose virtually no threat because they quickly die off neglects the fact that many of the symptoms experienced by people who inhale or ingest Class B sludge particles are actually enhanced by bacterial cell death."

"Endotoxins, which account for gastrointestinal symptoms and various effects on the respiratory system, are liberated when gram negative bacteria die. Antibiotic therapy for patients infected with gram negative bacteria sometimes carries a high risk of mortality from endotoxins released as the bacteria die away after administering antibiotics."

"When Class B sludge is not incorporated into soil, organic aggregates that form dust particles carry a double whammy: an outside coating of endotoxins from dead gram negative bacteria plus an inner core of viable pathogens. When these particles are ingested or inhaled, bodily processes break down the aggregates, releasing both endotoxins and viable pathogens."

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