Bacteria may hide in hunks of gunk
http://findarticles.com/p/articles/mi_m1200/is_n9_v153/ai_20382934/?tag=content;col1
Science News, Feb 28, 1998 by Mari N. Jensen
Processed sludge from waste treatment plants that is sold as fertilizer for home gardens may harbor disease-causing
fecal organisms, contends microbiologist David L. Lewis of the Environmental Protection Agency in Athens, Ga.
To test his suspicion that fats and petroleum products in sludge interfere with assays for bacteria, Lewis mixed
bacteria from sludge with a silicone lubricant. When he analyzed the resulting mixture for colonies of live bacteria, he
found few. However, when he dissolved the silicone with acetone and tested again, he found 100,000 times as many
colonies.
Lewis suggests that bacteria such as Salmonella get caught in clumps of gunk in the sludge. If the clumps get coated
with water-repellent substances like chicken fat, petroleum, or industrial lubricants, standard tests may significantly
underestimate the number of bacteria hidden inside them, he says. If people accidentally ingest clumps sticking to
unwashed hands or vegetables, he says, the acids and churning action of the digestive tract would expose the
bacteria.
Although EPA regulates the methods used to decontaminate and test sludge, Lewis remains "skeptical as to whether
the regulations protect us or not." Alan B. Rubin of EPA's Washington, D.C., office says sludge used as fertilizer does
not make people sick when applied according to the regulations.
The agency should use Lewis' methods to test sludge certified as free of pathogens to see whether the bacteria
indeed escape detection, says Ellen Z. Harrison of the Cornell Waste Management Institute in Ithaca, N.Y.
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