Daily Archives: January 28, 2013

QSAR models for ozone, AOP processes

Sairam Sudhakaran, Gary L. Amy. QSAR models for oxidation of organic micropollutants in water based on ozone and hydroxyl radical rate constants and their chemical classification. Water Research. Volume 47, Issue 3, 1 March 2013, Pages 1111–1122.

Ozonation is an oxidation process for the removal of organic micropollutants (OMPs) from water and the chemical reaction is governed by second-order kinetics. An advanced oxidation process (AOP), wherein the hydroxyl radicals (OH radicals) are generated, is more effective in removing a wider range of OMPs from water than direct ozonation. Second-order rate constants (kOH and kO3) are good indices to estimate the oxidation efficiency, where higher rate constants indicate more rapid oxidation. In this study, quantitative structure activity relationships (QSAR) models for O3 and AOP processes were developed, and rate constants, kOH and kO3, were predicted based on target compound properties. The kO3 and kOH values ranged from 5 * 10−4 to 105 M−1s−1 and 0.04 to 18 * (109) M−1 s−1, respectively. Several molecular descriptors which potentially influence O3 and OH radical oxidation were identified and studied. The QSAR-defining descriptors were double bond equivalence (DBE), ionisation potential (IP), electron-affinity (EA) and weakly-polar component of solvent accessible surface area (WPSA), and the chemical and statistical significance of these descriptors was discussed. Multiple linear regression was used to build the QSAR models, resulting in high goodness-of-fit, r2 (>0.75). The models were validated by internal and external validation along with residual plots.

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Modeling study examines household water treatment…

Kyle S. Enger, Kara L. Nelson, Joan B. Rose, Joseph N.S. Eisenberg, The joint effects of efficacy and compliance: A study of household water treatment effectiveness against childhood diarrhea. Water Research, Volume 47, Issue 3, 1 March 2013, Pages 1181–1190.

The effectiveness of household water treatment (HWT) at reducing diarrheal disease is related to the efficacy of the HWT method at removing pathogens, how people comply with HWT, and the relative contributions of other pathogen exposure routes. We define compliance with HWT as the proportion of drinking water treated by a community. Although many HWT methods are efficacious at removing or inactivating pathogens, their effectiveness within actual communities is decreased by imperfect compliance. However, the quantitative relationship between compliance and effectiveness is poorly understood. To assess the effectiveness of HWT on childhood diarrhea incidence via drinking water for three pathogen types (bacterial, viral, and protozoan), we developed a quantitative microbial risk assessment (QMRA) model. We examined the relationship between log10 removal values (LRVs) and compliance with HWT for scenarios varying by: baseline incidence of diarrhea; etiologic fraction of diarrhea by pathogen type; pattern of compliance within a community; and size of contamination spikes in source water. Benefits from increasing LRVs strongly depend on compliance. For perfect compliance, diarrheal incidence decreases as LRVs increase. However, if compliance is incomplete, there are diminishing returns from increasing LRVs in most of the scenarios we considered. Higher LRVs are more beneficial if: contamination spikes are large; contamination levels are generally high; or some people comply perfectly. The effectiveness of HWT interventions at the community level may be limited by imperfect compliance, such that the benefits of high LRVs are not realized. Compliance with HWT should be carefully measured during HWT field studies and HWT dissemination programs. Studies of pathogen concentrations in a variety of developing-country source waters are also needed. Guidelines are needed for measuring and promoting compliance with HWT.

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Solar impact on climate tied to ENSO?

Jianjun Xu, Alfred M. Powell Jr. What happened to surface temperature with sunspot activity in the past 130 years? Theor Appl Climatol (2013) 111:609–622. DOI 10.1007/s00704-012-0694-y

Based on composite analysis using categories of solar inactivity and activity, the responses of surface temperature to different categorized solar activity and a plausible mechanism have been discussed. The results show the increasing solar sunspot activity during solar cycles 13 to 24 (18802010) and it seemed to make a positive contribution to rising global temperature. However, the sunspots were fewer in number, if we focused on the most recent 60 years (19502010), and the decreasing solar activity did not contribute to a cooler Earth. This result indicates that the connection between sunspots and the Earths climate is sensitive to the study period. An extreme analysis was performed in an attempt to gain a better understanding of solar impacts. The extreme top 10 composite analysis demonstrated that the surface temperature response to solar activity is spatially different and is highly sensitive to El NiñoSouthern Oscillation (ENSO) events. The most sensitive areas in the Pacific sector revealed a significant difference between including and excluding ENSO years. During the solar inactive years, the tropical eastern Pacific was observed as a weak El Niño-like (strong La Niña-like) pattern in the composite including (excluding) ENSO events. Another interesting feature is the strong similarity in the composites which include or exclude ENSO events during the sunspot active years, but it differs from the La Niña-like pattern observed in previous studies. The bottom-up mechanism associated with the response of the surface dynamical circulation and the heat balance when compared to the total solar irradiance forcing partially explains the connection.

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