Daily Archives: September 16, 2012

UV-decomposition of chlorine solution yields perchlorate

Rao, B., Estrada, N., McGee, S. Mangold, J., Gu, B, Jackson, W.A. Perchlorate production by photo-decomposition of aqueous chlorine solutions. Environ Sci Technol. 2012 Sep 10.

Aqueous chlorine solutions (defined as chlorine solutions (Cl2,T) containing solely or a combination of molecular chlorine (Cl2) ), hypochlorous acid (HOCl) and hypochlorite (OCl-)) are known to produce toxic inorganic disinfection by-products (e.g., chlorate and chlorite) through photo-activated transformations. Recent reports of perchlorate (ClO4-) production-a well-known thyroid hormone disruptor- from stored bleach solutions indicates the presence of unexplored transformation pathway(s). The evaluation of this potential ClO4- source is important given the widespread use of aqueous chlorine as a disinfectant. In this study, we perform detailed rate analysis of ClO4- generation from aqueous chlorine under varying environmental conditions including ultra-violet (UV) light sources, intensity, solution pH, and Cl2,T)  concentrations. Our results show that ClO4- is produced upon UV exposure of aqueous chlorine solutions with yields ranging from 0.09 × 10-3 to 9.2 × 10-3 % for all experimental conditions. The amount of ClO4- produced depends on the starting concentrations of Cl2,T) , ClO3-, UV source wavelength, and solution pH but is independent of light intensity. We hypothesize a mechanistic pathway derived from known reactions of Cl2,T)  photo-decomposition that involves the reaction of Cl radicals with ClO3- to produce ClO4- with calculated rate coefficient (kClO4-) of (4-40) × 10^5 M^-1 s^-1 and (3‒250) × 10^5 M^-1 s^-1 for UV-B/C and UV-A, respectively.  The measured ClO4- concentrations for both UV-B and UV-C experiments agreed well with our model (R^2= 0.88 ‒ 0.99), except under UV-A light exposure (R^2 = 0.52 ‒ 0.93), suggesting the possible involvement of additional pathways at higher wavelengths. Based on our results photo-transformation of aqueous chlorine solutions at concentrations relevant to drinking water treatment would result in ClO4- concentrations (~ 0.1 µg L-1) much below the proposed drinking water limits. The importance of the hypothesized mechanism is discussed in relation to natural ClO4- formation by atmospheric transformations.

No effect of perchlorate found near superfund site

Gold, E.B., Blount, B.C., O’Neill, Rasor, M., Lee, J.S., Alwis, U., Srivastav, A. Kim, K. Thyroid hormones and thyroid disease in relation to perchlorate dose and residence near a superfund site. J Expo Sci Environ Epidemiol. 2012 Sep 12. doi: 10.1038/jes.2012.90.

Perchlorate is a widely occurring contaminant, which can competitively inhibit iodide uptake and thus thyroid hormone production. The health effects of chronic low dose perchlorate exposure are largely unknown. In a community-based study, we compared thyroid function and disease in women with differing likelihoods of prior and current perchlorate exposure. Residential blocks were randomly selected from areas: (1) with potential perchlorate exposure via drinking water; (2) with potential exposure to environmental contaminants; and (3) neighboring but without such exposures. Eligibility included having lived in the area for ≥6 months and aged 20-50 years during 1988-1996 (during documented drinking water well contamination). We interviewed 814 women and collected blood samples (assayed for thyroid stimulating hormone and free thyroxine) from 431 interviewed women. Daily urine samples were assayed for perchlorate and iodide for 178 premenopausal women with blood samples. We performed multivariable regression analyses comparing thyroid function and disease by residential area and by urinary perchlorate dose adjusted for urinary iodide levels. Residential location and current perchlorate dose were not associated with thyroid function or disease. No persistent effect of perchlorate on thyroid function or disease was found several years after contaminated wells were capped.

 

Arsenic and cardiovascular effects…

Moon, K., Guallar, E., Navas-Acien, A. Arsenic Exposure and Cardiovascular Disease:An Updated Systematic Review. Curr Atheroscler Res. 2012 Sep 12.

In epidemiologic studies, high-chronic arsenic exposure has been associated with cardiovascular disease, despite methodological limitations. At low-moderate arsenic levels, the evidence was inconclusive. Here, we update a previous systematic review (Am J Epidemiol 2005;162:1037-49) examining the association between arsenic exposure and cardiovascular disease. Eighteen studies published since 2005 were combined with 13 studies from the previous review. We calculated pooled relative risks by comparing the highest versus the lowest exposure category across studies. For high exposure (arsenic in drinking water > 50 μg/L), the pooled relative risks (95 % confidence interval) for cardiovascular disease, coronary heart disease, stroke, and peripheral arterial disease were 1.32 (95 % CI:1.05-1.67), 1.89 (95 % CI:1.33-2.69), 1.08 (95 % CI:0.98-1.19), and 2.17 (95 % CI:1.47-3.20), respectively. At low-moderate arsenic levels, the evidence was inconclusive. Our review strengthens the evidence for a causal association between high-chronic arsenic exposure and clinical cardiovascular endpoints. Additional high quality studies are needed at low-moderate arsenic levels.

 

Surprise! Climate models wrong again, this time on rainfall….

Climate models assume that moist soils lead to more evaporation, then more precipitation, then moist soils, then precipitation, etc…..whereas dry soils receive no precipitation…..

“The implication is that existing climate models are more likely to go into a vicious circle whereby dry soils decrease rainfall, leading to even drier soil conditions … fixing this problem is a priority for scientists developing the climate models.” (Click here for press coverage.)

Oh, so the models are not very good afterall. Then why use them for making policy decisions if you are only fooling yourself?

Taylor, C.M., de Jeu, R.A.M., Guichard, F., Harris, P.P., and Dorigo, W.A. Afternoon rain more likely over drier soils. Nature, (2012) doi:10.1038/nature11377

Land surface properties, such as vegetation cover and soil moisture, influence the partitioning of radiative energy between latent and sensible heat fluxes in daytime hours. During dry periods, soil-water deficit can limit evapotranspiration, leading to warmer and drier conditions in the lower atmosphere1, 2. Soil moisture can influence the development of convective storms through such modifications of low-level atmospheric temperature and humidity1, 3, which in turn feeds back on soil moisture. Yet there is considerable uncertainty in how soil moisture affects convective storms across the world, owing to a lack of observational evidence and uncertainty in large-scale models4. Here we present a global-scale observational analysis of the coupling between soil moisture and precipitation. We show that across all six continents studied, afternoon rain falls preferentially over soils that are relatively dry compared to the surrounding area. The signal emerges most clearly in the observations over semi-arid regions, where surface fluxes are sensitive to soil moisture, and convective events are frequent. Mechanistically, our results are consistent with enhanced afternoon moist convection driven by increased sensible heat flux over drier soils, and/or mesoscale variability in soil moisture. We find no evidence in our analysis of a positive feedback—that is, a preference for rain over wetter soils—at the spatial scale (50–100 kilometres) studied. In contrast, we find that a positive feedback of soil moisture on simulated precipitation does dominate in six state-of-the-art global weather and climate models—a difference that may contribute to excessive simulated droughts in large-scale models.

Click here for the article (fee).