risk predictor because it is based on population-wide estimates instead of single point estimates. The authors compare their approach to EPA's by analyzing 242 chemicals in the EPA's Integrated Risk Information System. [Hum. Ecol. Risk Assess. 1996, 2(1), 79-102)
TOXICITY Sunlight and PAHs Recent evidence indicates that the toxicity of PAHs to aquatic organisms may be enhanced by ultraviolet radiation. D. S. Ireland and colleagues conducted an in situ study with Ceriodaphnia dubia by placing specialized chambers containing the test organisms in sunlight and in shade within a stream environment. In general, there was a significant decrease in C. dubia survival in the sunlit test chambers but not in the shaded chambers. Survival and water turbidity also directly correlated in the sunlit test chambers The PAH concentrations were highest in the sediments and decreased toward the top of the water column The resparchers used turbidity in the water rnlumn to prevent ultraviolet radiation nenetration to thp sediment at the hottom of the watpr column whprp PAH concentrations wprp twhpst Thp authors concliiHprl rnrrpnt serliment rnntaminant •A
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guidelines were protective of aquatic hie but may be overprotective in turbid conditions. {Environ. Toxicol. Ch
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Simultaneous treatment of solvents and metals RAP. Thomas and L E. Macaskie simultaneously treated different classes of wastes, solvents, and heavy metals using a biological treatment. Bacterial cultures were isolated, immobilized, and used in a flow-through bioreactor. A combined waste stream containing uranium oxide and tributyl phosphate (TBP) was passed through the reactor. The TBP, which is used in several industries as a solvent, a complexing agent, and a defoamer, was biodegraded into butanol and phosphate. The released phosphate then precipitated uranium oxide from the waste stream into the biomass. TBP waste was the sole carbon and phosphorus source for the cultures. [Environ. Sci. Technol., ,his iisue, 2331-75)
change with time and the history of the community. [Environ. Toxicol. Chem. 1996, 15(4), 597-603)
WASTEWATER Sludge composting Increased disposal costs and tightened regulatory standards for municipal solid waste and wastewater treatment plant sludge emphasize the shortcomings of conventional management systems and demonstrate a need for innovative approaches. M. Kayhanian and D. Rich studied the biodegradable organic fraction (BOF) of municipal solid waste as an additive in an innovative co-composting process for managing sludge. They evaluated primary activated and digested wastewater sludcommingled with a simulated BOF of a municipal solid waste Results indicated that the process generated sludge that met all EPA criteria including suitability for land annlicatinn [Water Prntimn ffpc 1996 f!fl(2) 240-52)
Ultraviolet disinfection TOXICOLOGY "Community conditioning" R. A. Matthews and co-workers proposed a "community conditioning hypothesis" in which ecological communities retain information about events in their history. They studied aquatic mesocosms given single exposures of jet fuel at various levels over 70 days. In some cases, indicator species would recover from the initial effects and the community would appear to recover, only to change in a dose-dependent fashion later in the experiment. The authors caution against using predetermined indiccitor species a.s the species that best indicate community health
Municipal wastewater has been reused in agriculture and industry but is invariably subject to stringent microbiological requirements. Typically, chlorine disinfection has been used to produce activated sludge effluent that meets reuse regulations. J. L. Braunstein and colleagues evaluated the use of ultraviolet (UV) disinfection to prepare filtered activated sludge effluent for reuse. They applied a UV disinfection system to a municipal wastewater treatment plant under field conditions. Total and fecal coliform as well as MS2 coliphage criteria were used to meaperformance Results demonstrated that the most stringent EPA criteria were met consistently using
UV disinfection. Results indicate that UV disinfection represents a viable alternative to chlorine disinfection. [Water Environ. Res. 1996, 68(2), 152-61)
Nitrogen removal A significant percentage of nutrients discharged into surface water are from point sources such as municipal wastewater treatment plants. Most of these plants are designed to remove only suspended solids and biochemical oxygen demand; they would require major modifications for nitrogen removal using biological nitrification and denitrification.J. Fillos and colleagues investigated the ability of a conventional wastewater treatment plant to remove nitrogen using inexpensive operational modifications to the existing system They achieved significant nitrogen removal by controlling dissolved oxygen in aerobic and anoxic treatment zones Nitrification was observed to hp a dirprt function of dissolvpH nwppn in the aeration tank and dpnitrification was achieved hv limiting air at fppd nnints in thp apratinn tank Rp«iilt
