Five field trips were conducted in the San Francisco Bay-Delta between May 2000 and October 2001 to investigate the sediment-water exchange of total mercury (Hg) and monomethyl mercury (MMHg). Solid-phase Hg averaged ϳ1 nmol g Ϫ1 and did not show any variability with depth or time or among sites. In contrast, solid-phase MMHg showed considerable vertical, temporal, and spatial variability (0.4-66 pmol g Ϫ1 ), with the highest values occurring at a peat-rich environment in May 2001, suggesting that MMHg production was largely controlled by temporal factors and habitat type. In pore water, both Hg and MMHg concentrations were generally elevated near the sediment-water interface during warm months. Sediment-water exchange flux of MMHg, determined with benthic chamber deployments, ranged from Ϫ92 to 850 pmol m Ϫ2 d Ϫ1 , with higher values occurring in May. In most cases, diffusional fluxes of Hg and MMHg, estimated with the use of interfacial concentration gradients, constituted only a minor portion of the measured fluxes, suggesting the importance of advective processes on sediment-water exchange. Surface-water transect and time series studies conducted in Franks Tract support the commonly held belief that wetland and marsh regions are major sources for MMHg within the Delta. The integrated sediment-water fluxes of Hg and MMHg in the study area were estimated to be 130 and 6 mmol d Ϫ1 , respectively, and the benthic input was as important a source of Hg and MMHg as the riverine input within the Delta during low-flow months.

Recent sediment accumulation rates are 18-230 mg cm\ yr\ (0.02-0.2 cm yr\) based on excess Pb activity profiles in the southwestern part of the East Sea (Sea of Japan). Assuming no mixing beneath surface mixed layers, Pb-derived sediment accumulation rates are 18-32 mg cm\ yr\ in the northern part of the Yamato Ridge and the Ulleung Basin, 29-136 mg cm\ yr\ in the Korea Plateau, and 230 mg cm\ yr\ in the southern shelf. These values generally agree with long-term sedimentation rates estimated from dated ash layers.

The Lower Cambrian shale is an important source rock for conventional oil and gas in northern Guizhou province (NGP), south China, but has recently been considered as a potential shale gas reservoir. In this study, characterization of this target shale was determined through a systematic series of measurements on core samples. According to total organic carbon (TOC) and Rock-Eval data, the Lower Cambrian shale is overmature but still contains high amounts of organic matter, which is composed mainly of alginite. The TOC content is enriched up to 10.4% at the base of the shale. There are two different correlation patterns between trace elements and TOC in the Lower Cambrian shale. A good correlation present in the upper part indicates a non-sulfidic anoxic sedimentary environment. However, higher enrichments of U, V, and Mo in the basal part exhibit sulfidic euxinic conditions. Brittle minerals are quite abundant and have a critical effect on artificial fracture. Gas sorption volume increases with an increasing TOC, pore volume, and surface area, indicating that pores at the microscale associated with the organic matter fraction are an important control on storage capacity. The contribution of clay minerals to the sorbed gas may be irrelevant because of the presence of moisture. Analysis of data indicates that the basal part of the Lower Cambrian shale demonstrates the greatest potential for gas content and can be explored for production.

This study investigated the UV254 photolysis of free available chlorine and bromine species in water. The intrinsic quantum yields for •OH and X• (X = Cl or Br) generation were determined by model fitting of formaldehyde formation using a tert-butanol assay to be 0.61/0.45 for HOCl/OCl– and 0.32/0.43 for HOBr/OBr–. The steady-state •OH concentration in UV/HOX was higher than that in UV/OX– by a factor of 23.3 and 7.8 for Cl and Br, respectively. This was attributed to the different •OH consumption rate by HOCl versus OCl–, while for HOBr/OBr–, both the •OH formation and consumption rates were implied. This was supported by a k of 1.4 × 108 M–1 s–1 for the •OH reaction with HOCl, which was >14 times less than the k for •OH reactions with OCl–, HOBr, and OBr–. Formation of ClO3 – and BrO3 – was found to be significant with apparent quantum yields of 0.12–0.23. A detailed mechanistic study on the formation of XO3 – including a new pathway involving XO• is presented, which has important implications as the level of XO3 – can exceed the regulation (BrO3 –) or guideline (ClO3 –) values during UV/halogen oxidant water treatment. Our new kinetic models well simulate the experimental results for the halogen oxidant decomposition, probe compound degradation, and formation of ClO3 – and BrO3 –.

No abstract

Methylmercury (MeHg) accumulation in marine organisms poses serious ecosystem and human health risk, yet the sources of MeHg in the surface and subsurface ocean remain uncertain. Here, we report the first MeHg mass budgets for the Western Pacific Ocean estimated based on cruise observations. We found the major net source of MeHg in surface water to be vertical diffusion from the subsurface layer (1.8-12 nmol m yr). A higher upward diffusion in the North Pacific (12 nmol m yr) than in the Equatorial Pacific (1.8-5.7 nmol m yr) caused elevated surface MeHg concentrations observed in the North Pacific. We furthermore found that the slope of the linear regression line for MeHg versus apparent oxygen utilization in the Equatorial Pacific was about 2-fold higher than that in the North Pacific. We suggest this could be explained by redistribution of surface water in the tropical convergence-divergence zone, supporting active organic carbon decomposition in the Equatorial Pacific Ocean. On the basis of this study, we predict oceanic regions with high organic carbon remineralization to have enhanced MeHg concentrations in both surface and subsurface waters.

A large body of literature has examined factors leading to filing for personal bankruptcy, but little is known about household borrowing after bankruptcy. This paper augments the existing literature with a comprehensive analysis of postbankruptcy borrowing using data from the Survey of Consumer Finances. We find that filers generally have more limited access to unsecured credit, but borrow more secured debt after bankruptcy, than comparable households that have never filed for bankruptcy. Filers also pay higher interest rates on all types of debt. In addition, as more time passes after filing, credit access and borrowing costs improve. However, filers remain more prone than comparable nonfilers to experience financial distress, accumulate less wealth, and use expensive credit sources like payday loans, even more than 10 years after filing.

Personal bankruptcy, fresh start, wealth effect, labor supply, J22, K35, D14,