SynopsisPolycaprolactone is degraded by the mold P . pullulans in the presence of other nutrients. The weight loss from solid polymer films covered by a nutrient agar gel on which colonies are growing is used to establish comparative rates of degradation. There is substantial loss (16 mg/cm2 surface area) from a whole polymer of low (2,000) molecular weight in three weeks at 30°C. A high (30,000) molecular weight whole polymer degrades about 0.15 as much in the same time period. A fraction in the same range (38,000) but with a narrower molecular weight distribution shows no significant loss. This indicates that whole polymers of high molecular weight may lose only a portion of their distribution by microbial degradation in short-term tests. This hypothesis is tested by making mixtures of high (61,000) molecular weight with low (2,000) molecular weight polymer. Degradation is directly proportional to the low molecular weight content in these short-term tests with a single species of mold. Other workers have shown previously that in long-term, soil-burial tests, even a high (40,000) molecular weight polycaprolactone is essentially completely degraded after one year.

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With a new enrichment protocol, pentachlorophenol (PCP)-degrading bacteria were isolated from soil, water, and sewage. When characterized, all isolates were related and shared characteristics of the genus Arthrobacter. Growth rates for strain NC were determined for a number of substrates, including PCP and 2,4,6trichlorophenol. Changes in PCP concentration affected growth rate and length of the lag phase but not cell yield. Increasing the pH from 6.8 to 7.8 decreased the length of the lag phase for growth on PCP. Cessation of growth, upon incremental addition of PCP, was found to be related to a decrease in pH rather than to a buildup of a toxic metabolite. Degradation of PCP by strain NC was shown to be complete.

Direct inoculation of bacteria capable of degrading pentachlorophenol (PCP) into PCP-contaminated soil was investigated as a prophylactic measure to reduce the hazards of runoffs when spills occur or when wooden poles freshly treated with PCP-containing preservatives are located near streams and lakes. In laboratory tests at 30°C, the direct addition of 10 6 PCP-utilizing Arthrobacter cells per g of dry soil reduced the half-life of the pesticide from 2 weeks to <1 day. Soil inoculation also was shown to be an effective way to increase the PCP disappearance rate in a test conducted in an outdoor shed.

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