Estimates of pesticide degradation rates in subsoils are needed to improve models predicting pesticide movement to groundwater. Biodegradation rates of the herbicide alachlor [2‐chloro‐(2,6‐diethylphenyl)‐N‐(methoxymethyl)acetamide] in surface soil, vadose zone, and aquifer samples collected from a single site near Plains, GA were determined in the laboratory under aerobic and anaerobic conditions. Degradation was described by first‐order kinetics during 126 d of incubation. Under aerobic conditions the halflife (t1/2) of alachlor in the surface soil (t1/2 = 23 d) was less than in the vadose zone (t1/2 = 73 to 285 d) and aquifer samples (t1/2 = 320 to 324 d). Alachlor in anaerobic samples degraded less rapidly in the surface (0 to 0.6 m) and the next deepest (0.6 to 2.4 m) subsoil than under aerobic conditions (t1/2 = 100 and 144 d, respectively). Degradation in anaerobic aquifer samples was very slow (t1/2 = 337 to 553 d). Addition of organic nutrients enhanced aerobic degradation in subsurface soils and one aquifer sample, indicating that nutrient availability limits biodegradation. Total aerobic microbial populations ranged from 6.6 × 103 to 2.5 × 106 cells per gram of soil in the subsoils and aquifer samples, but were not correlated with aerobic or anaerobic degradation rates. The lower degradation rates in vadose zone and aquifer materials may be due to less microbial activity or the absence of alachlor degraders.

Biolog's identification system was used to identify 39 American Type Culture Collection reference taxa and 45 gram-negative isolates from water samples. Of the reference strains, 98% were identified to genus level and 76% to species level within 4 to 24 h. Identification of some authentic strains of Enterobacter, Klebsiella, and Serratia was unreliable. A total of 93% of the water isolates were identified. Although rapid automated identification systems for identifying bacteria from clinical specimens exist, few systems that can identify environmental isolates quickly and reliably are available (3, 4, 8, 27). Traditional biochemical tests and commercial test kits used to identify nonenteric organisms are labor-intensive and slow (9, 10, 13, 14, 16, 19, 21-24, 26, 28, 29, 31). An automated ground-based system is needed for identifying archived environmental isolates obtained from the space shuttle and eventually from the U.S. space station Freedom (1, 20). Identification of isolates from the station's recycled water supply is of particular concern. Biolog Inc., (Hayward, Calif.) recently introduced an automated system designed to identify 434 species or groups of aerobic gram-negative bacteria within 4 to 24 h. Their data base includes environmental taxa that are not included in the data bases of other commercial systems (3, 4). Because the Biolog system has been available for a relatively short time, few published assessments of its accuracy and reliability are available (6, 18). To assess the system's potential to identify gramnegative aerobic rods, we tested 41 American Type Culture Collection (ATCC) organisms representing 39 taxa and 45 unknown isolates recovered from a prototype water-recycling system proposed for use on the U.S. space station Freedom. Biolog's identification system, consisting of a Microstation computer, turbidimeter (optical density at 590 nm), MicroLog software (MicroLog 2N, Release 2), microplate reader, and gram-negative microplates, was purchased from Biolog Inc. For comparative purposes, the Vitek system, turbidimeter, and gram-negative identification cards were purchased from Vitek Systems, Inc. (Hazelwood, Mo.). Petri plates (160-mm diameter) prepared with Trypticase soy agar, blood agar (Trypticase soy agar plus 5% sheep erythrocytes), plate count agar, or Emmon's Sabouraud dextrose agar were purchased from BBL Microbiology Systems (Cockeysville, Md.). Sterile saline (0.45 and 0.85%) was purchased from Baxter Healthcare Corp. (Deerfield, Ill.). Cards, microplates, and agar plates were stored at 4°C and then equilibrated at room temperature for 30 min (cards and microplates) or overnight (agar plates) before use.

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