Regulation of drinking water quality regarding microbial pathogens and disinfectionby‑products set by the United States Environmental Production Agency (USEPA) has led manywater utilities to consider disinfectants and/or disinfectant schemes alternative to traditional freechlorine. This trend toward alternative disinfectants has been particularly fueled by recent andmore stringent regulation of disinfection by‑products (DBPs) (trihalomethanes [THMs] and haloaceticacids [HAAs]) and chlorine resistant pathogens (Giardia and Cryptosporidium parvum).Among the available alternative disinfection schemes, ultraviolet (UV) light sequenced with chlorinationor chloramination are considered particularly attractive because, unlike ozonation andchloramination, UV disinfection has not previously been associated with significant DBPformation. [extract from Executive Summary]
Three methods of estimating effective germicidal ultraviolet (UV) dose in a collimated beam medium pressure UV system were analyzed: (1) A bioassay; (2) a mathematical model; and (3) a chemical actinometer. The bioassay was performed with MS2 phage. The mathematical model was used to estimate incident, average, and effective germicidal intensity. The chemical actinometer used was uridine, which contains a uracil nucleobase with an absorbance spectrum similar to that of MS2 phage. The average and effective germicidal intensity, terms often equated in low pressure UV systems, differed by 27% for the medium pressure UV system used in this research. The effective germicidal dose determined mathematically was within 10% of the dose estimated with the bioassay approach. For the uridine actinometry, when the differences in the relative absorbance spectras of the uridine actinometer and MS2 phage were accounted for, the actinometry and bioassay methods resulted in similar estimations of effective germicidal dose.
BackgroundUltraviolet photodegradation products from pesticides form both in the field and during water treatment.ObjectivesWe evaluated the photolytic breakdown of the organophosphate pesticide chlorpyrifos (CPF) in terms of both the chemical entities generated by low-pressure ultraviolet C irradiation and their potential as developmental neurotoxicants.MethodsWe separated by-products using high-performance liquid chromatography and characterized them by gas chromatography/mass spectrometry. We assessed neurotoxicity in neuronotypic PC12 cells, both in the undifferentiated state and during differentiation.ResultsPhotodegradation of CPF in methanol solution generated CPF oxon and trichloropyridinol, products known to retain developmental neurotoxicant actions, as well as a series of related organophosphate and phosphorothionate derivatives. Exposure conditions that led to 50% degradation of CPF thus did not reduce developmental neurotoxicity. The degradation mixture inhibited DNA synthesis in undifferentiated cells to the same extent as native CPF. In differentiating cells, the products likewise retained the full ability to elicit shortfalls in cell number and corresponding effects on cell growth and neurite formation. When the exposure was prolonged to the point where 70% of the CPF was degraded, the adverse effects on PC12 cells were no longer evident; however, these conditions were sufficiently severe to generate toxic products from the methanol vehicle.ConclusionsOur results indicate that field conditions or remediation treatments that degrade a significant proportion of the CPF do not necessarily produce inactive products and, indeed, may elicit formation of even more toxic chemicals that are more water soluble and thus have greater field mobility than CPF itself.
