Modeling methyl isothiocyanate soil flux and emission ratio from a field following a chemigation of metam-sodium

Metam-sodium had become the most heavily used soil fumigant in recent years as the deadline approached for methyl bromide to phase out in January 2005. After application, metam-sodium decomposes rapidly to methyl isothiocyanate (MITC), a highly toxic compound capable of killing a wide spectrum of soil-borne pests. Inhalation risk of MITC ranked high among airborne agricultural pesticides in California. Information about off-gassing intensity and percentage of emission is essential for exposure risk assessment and mitigation measures, but is limited, especially for new application methods such as drip chemigation. Air concentrations of MITC were monitored around a field treated with metam-sodium through surface drip irrigation system. The field was tarped with plastic films before the chemigation. The air concentrations at receptor locations were simulated for the period of air monitoring with the Industrial Source Complex (ISC3) Dispersion Model, and soil flux density of MITC at various periods after chemigation was estimated through a back-calculation procedure. The estimated soil flux density of MITC showed a diurnal pattern, with the daytime flux stronger than nighttime. However, the average air concentration at nighttime was higher than that at daytime. Soil flux density peaked at 4.30 microg m-2 s-1 in the first 12-h period after chemigation, then declined with time. The MITC emission percentage in the first 60-h was 2.65% of applied mass, of which 57% occurred in the first 24-h after chemigation. The study indicated that the tarped bed drip application method of metam-sodium had a relatively good control of MITC emission from soil.     

Freshwater stress on small island developing states: population projections and aridity changes at 1.5 and 2 °C

Small island developing states (SIDS) face multiple threats from anthropogenic climate change, including potential changes in freshwater resource availability. Due to a mismatch in spatial scale between SIDS landforms and the horizontal resolution of global climate models (GCMs), SIDS are mostly unaccounted for in GCMs that are used to make future projections of global climate change and its regional impacts. Specific approaches are required to address this gap between broad-scale model projections and regional, policy-relevant outcomes. Here, we apply a recently developed methodology that circumvents the GCM limitation of coarse resolution in order to project future changes in aridity on small islands. These climate projections are combined with independent population projections associated with shared socioeconomic pathways (SSPs) to evaluate overall changes in freshwater stress in SIDS at warming levels of 1.5 and 2 °C above pre-industrial levels. While we find that future population growth will dominate changes in projected freshwater stress especially toward the end of the century, projected changes in aridity are found to compound freshwater stress for the vast majority of SIDS. For several SIDS, particularly across the Caribbean region, a substantial fraction (~?25%) of the large overall freshwater stress projected under 2 °C at 2030 can be avoided by limiting global warming to 1.5 °C. Our findings add to a growing body of literature on the difference in climate impacts between 1.5 and 2 °C and underscore the need for regionally specific analysis.     

A retrospective comparison of model-based forecasted PM2.5 concentrations with measurements

This study presents an assessment of the performance of the Community Multiscale Air Quality (CMAQ) photochemical model in forecasting daily PM2.5 (particulate matter < or = 2.5 microm in aerodynamic diameter) mass concentrations over most of the eastern United States for a 2-yr period from June 14, 2006 to June 13, 2008. Model predictions were compared with filter-based and continuous measurements of PM2.5 mass and species on a seasonal and regional basis. Results indicate an underprediction of PM2.5 mass in spring and summer, resulting from under-predictions in sulfate and total carbon concentrations. During winter, the model overpredicted mass concentrations, mostly at the urban sites in the northeastern United States because of overpredictions in unspeciated PM2.5 (suggesting possible overestimation of primary emissions) and sulfate. A comparison of observed and predicted diurnal profiles of PM2.5 mass at five sites in the domain showed significant discrepancies. Sulfate diurnal profiles agreed in shape across three sites in the southern portion of the domain but differed at two sites in the northern portion of the domain. Predicted organic carbon (OC) profiles were similar in shape to mass, suggesting that discrepancies in mass profiles probably resulted from the underprediction in OC. The diurnal profiles at a highly urbanized site in New York City suggested that the overpredictions at that site might be resulting from overpredictions during the morning and evening hours, displayed as sharp peaks in predicted profiles. An examination of the predicted planetary boundary layer (PBL) heights also showed possible issues in the modeling of PBL.     

Analytical Solutions to the Linearized Boussinesq Equation for Assessing the Effects of Recharge on Aquifer Discharge1

Boggs, Kevin G., Robert W. Van Kirk, Gary S. Johnson, Jerry P. Fairley, and P. Steve Porter, 2010. Analytical Solutions to the Linearized Boussinesq Equation for Assessing the Effects of Recharge on Aquifer Discharge. Journal of the American Water Resources Association (JAWRA) 46(6):1116–1132. DOI: 10.1111/j.1752-1688.2010.00479.x Abstract: There is a need to develop a general understanding of how variations in aquifer recharge are reflected in discharge. Analytical solutions to the linearized Boussinesq equation governing flow in an unconfined aquifer provide a unified mathematical framework to quantify relationships among lag time, attenuation and distance between aquifer recharge and discharge and the effect of an up-gradient no-flow boundary. We applied this framework to three types of recharge: (1) instantaneous, (2) periodic, and (3) constant rate for a finite duration. When the temporal scale of recharge exceeds the diffusive aquifer time scale, recharge will be reflected in discharge quickly and with little attenuation. When aquifer time scale is large, most recharge events are shorter in scale than that of the aquifer, resulting in large attenuation. Attenuation is more sensitive to boundary effects than lag time, and boundary effects increase as recharge time scale increases. Boundary effects can often be ignored when the recharge source is farther than 1/3 of the domain length away from the no-flow boundary. We illustrate analytical results with application to the economically critical Eastern Snake River Plain Aquifer in Idaho. In this aquifer, detectable annual and decadal cycles in discharge can result from recharge no farther than 20 and 60 km away from the discharge point, respectively. The effects of more distant, long-term recharge can be detected only after a time lag of several decades.     

Seasonal influences on PCB retention and biotransformation in fish

There is extensive evidence that fish from waters with polychlorinated biphenyls (PCB)-contaminated sediments accumulate PCBs and related chemicals and that people who eat fish from contaminated waters have higher body burdens of PCBs and PCB metabolites than those who do not. PCBs and their metabolites are potentially toxic; thus, it is important to human health to understand the uptake, biotransformation, and elimination of PCBs in fish since these processes determine the extent of accumulation. The intestinal uptake of PCBs present in the diet of fish into fish tissues is a process that is influenced by the lipid composition of the diet. Biotransformation of PCBs in fish, as in mammals, facilitates elimination, although many PCB congeners are recalcitrant to biotransformation in fish and mammals. Sequential biotransformation of PCBs by cytochrome P450 and conjugation pathways is even less efficient in fish than in mammalian species, thus contributing to the retention of PCBs in fish tissues. A very important factor influencing overall PCB disposition in fish is water temperature. Seasonal changes in water temperature produce adaptive physiological and biochemical changes in fish. While uptake of PCBs from the diet is similar in fish acclimated to winter or summer temperatures, there is evidence that elimination of PCBs occurs much more slowly when the fish is acclimated at low temperatures than at warmer temperatures. Research to date suggests that the processes of elimination of PCBs are modulated by several factors in fish including seasonal changes in water temperature. Thus, the body burden of PCBs in fish from a contaminated location is likely to vary with season.     

Preventing corruption in humanitarian assistance: perceptions, gaps and challenges

Corruption is a threat to the purpose of humanitarian assistance. Until fairly recently, humanitarian assistance has not been considered an important arena in broader efforts aimed at curbing corruption, and corruption has not always been considered a particularly important concern for humanitarian assistance despite the obviously challenging nature of the context of humanitarian emergencies. Corruption, though, is a threat to humanitarian action because it can prevent assistance from getting to the people who most need it, and because it can potentially undermine public support for such assistance. This paper examines perceptions of corruption and its affects, documents best practices, and outlines gaps in understanding. It suggests recommendations for improving the capacity of humanitarian agencies to prevent and manage the risk of corruption. Agencies have taken steps to combat corruption and improve accountability--downwards and upwards--but scope remains for improvement and for greater sharing of learning and good practice.     

Integrated Assessment Modeling of Atmospheric Pollutants in the Southern Appalachian Mountains. Part I: Hourly and Seasonal Ozone

Abstract

Recently, a comprehensive air quality modeling system was developed as part of the Southern Appalachians Mountains Initiative (SAMI) with the ability to simulate meteorology, emissions, ozone, size- and composition-resolved particulate matter, and pollutant deposition fluxes. As part of SAMI, the RAMS/EMS-95/URM-1ATM modeling system was used to evaluate potential emission control strategies to reduce atmospheric pollutant levels at Class I areas located in the Southern Appalachians Mountains. This article discusses the details of the ozone model performance and the methodology that was used to scale discrete episodic pollutant levels to seasonal and annual averages. The daily mean normalized bias and error for 1-hr and 8-hr ozone were within U.S. Environment Protection Agency guidance criteria for urban-scale modeling. The model typically showed a systematic overestimation for low ozone levels and an underestimation for high levels. Because SAMI was primarily interested in simulating the growing season ozone levels in Class I areas, daily and seasonal cumulative ozone exposure, as characterized by the W126 index, were also evaluated. The daily ozone W126 performance was not as good as the hourly ozone performance; however, the seasonal ozone W126 scaled up from daily values was within 17% of the observations at two typical Class I areas of the SAMI region. The overall ozone performance of the model was deemed acceptable for the purposes of SAMI’s assessment.     

The formation of bound residues of diazinon in four UK soils: implications for risk assessment

The behaviour of diazinon in the soil determines the likelihood of further pollution incidents, particularly leaching to water. The most significant processes in the control of the fate of diazinon in the soil are microbial degradation and the formation of bound residues. Soils from four sites in the UK were amended with diazinon and its ¹⁴C labelled analogue and incubated for 100 days. After 0, 10, 21, 50 and 100 days, the formation of bound residues was assessed by solvent extraction, and the microbial degradation of diazinon by mineralisation assay. In microbially active soils, diazinon is degraded rapidly, reducing the risk of future pollution incidents. However, where there was limited mineralisation there was also significantly lower formation of bound residues, which may lead to water pollution via leaching. The formation of bound residues was dependent on extraction type. Acetonitrile extraction identified bound residues in all soils, with the bound residue fraction increasing with increasing incubation time.     

Development of competitive immunoassays to hydroxyl containing fungicide metabolites

This paper describes the isolation of monoclonal antibodies and the development of competitive immunoassays to pesticide metabolites of the fungicides imazalil, carbendazim and thiabendazole. The metabolite specific hydroxyl residues were used as the reactive group with which to link the metabolite to the carrier proteins Keyhole Limpet Haemocyanin (KLH) and Bovine Serum Albumin (BSA). In each case immune responses in mice were raised and monoclonal antibodies were produced. Antibodies were developed into competitive ELISAs to the appropriate metabolite. The antibody raised to a metabolite of imazalil was optimised into a competitive ELISA format which had an assay IC50 of 7.5 μg/L and a limit of detection (LOD) of 1.1 μg/L. A single antibody isolated against the metabolite of carbendazim had assay IC50s of 3.2 and 2.7 μg/L for the metabolites of carbendazim and thiabendazole respectively with an LOD of 0.38 μg/L for both. These sensitive immunoassays may have application in the monitoring of human exposure to these fungicide residues either by occupational or non-occupational routes.