Agrochemical and polychlorobyphenyl (PCB) residues in the Mekong River delta, Vietnam

An environmental survey on pesticide residues and polychlorobyphenyl compounds (PCBs), encompassing more than 70 polar and non-polar compounds quantifiable by the techniques used, was performed in the Mekong River delta based on analyses of water, sediment and bivalve mollusc samples. Few polar compounds, such as diazinon and fenotrothion, were detected in water but a high number of non-polar chlorinated compounds, such as DDT, HCH, endosulfan and PCBs, were detected in sediments and biota. The highest concentrations measured were of DDT with an average 6.3 ng g(-1) dry weight (range 0.32-67 ng g(-1)) in sediments and 38.6 ng g(-1) (range 5.5-123 ng g(-1)) in molluscs' soft tissues. Amongst chlorinated compounds, DDT concentrations were followed in decreasing order by those of PCB, endosulfan, hexachlorocyclohexane and chlordane. Residues of organochlorine compounds originate from local usage of agrochemicals although with a likely contribution also of atmospheric deposition of residues (not measured) originated elsewhere. Concentrations of PCB and pesticide residues in the aquatic environment of the Mekong River delta are lower than values reported for other regions of Vietnam and Asia. Nevertheless, current concerns about the effects of chlorinated compounds on public health advise improved control of chemical residue discharges in order to abate environmental contamination.     

Natural resource damage assessments in the United States: rules and procedures for compensation from spills of hazardous substances and oil in waterways under US jurisdiction

Natural Resource Damage Assessment (NRDA) procedures in the US involve the use of uniform federally approved rules and procedures to assess economic losses and/or address restoration of injured resources that result from spills of hazardous substances and/or oil and petroleum substances in waterways under US jurisdiction. This effort started in the 1980s and involves two federal agencies that have developed separate federally approved procedures and rules, the US Department of Interior (US DOI) and the US Department of Commerce, National Oceanographic and Atmospheric Administration (US DOC, NOAA). This paper provides a brief overview of the federal laws applicable to resource damage assessments in the US, review of NRDA rules and procedures, and progress to date regarding US cases.     

南加州的地震危险性：1994—2024年可能发生的地震

我们综合分析了大地测量、地质以及地震资料来评估南加州３类地震构造带破坏性地震的发生概率。Ａ类地震构造带的断层有充分的古地震数据用于评估发震条件概率。Ｂ类地震构造带的断层缺乏条件概率分析的数据。Ｃ类地震构造带则是转换或隐伏断层。假设在各类地震构造带的具体断层上地震加上特征地震呈随机分布，那末我们的“阶式排列”模型就能适合多种断层地震。在每一地震构造带中，假如用古登堡－里克特震级分布平滑曲线上分配地震     

倾向断层中的地震：对称性被破坏的效应

对倾向断层中地城的动力学模拟表明,不对称的近源地面运动是由这类断层不对称的几何形态引起的。在初始应力大小相同的情况下,逆（冲）断层引起的地面运动要比正断层 引起的地面运动大２倍或更多。无论是在逆（冲）断层还是正断层引起的地震中,上盘的运动都比下盘的大。地震产生的应力场与地球自由表面的相互作用导致了与时间相关的正应力的立生,从而造成了正断层与逆（冲）断层之间的不对称性。断层上、下两盘的不对称性是由于     

应用于VAN方法的地震预报评估标准

为了在做出决断上的可能应用,地震预报研究在能够被适当评估之前必须符合一定的标准。对于导致二元警报状态(有或无)的方法而言,要求包括:(1)对引起报警的可观测量的定量描述;(2)对所预报地震,包括时间、地点和震级范围的定量描述;(3)所有事先报警的文字证据;(4)完整的已预报过的地震清单;(5)完整的漏报地震的清单。VAN 技术(Varotsos and Lazaridou,1991;Varotsos et a1.,1996)还没被指定为是一种可检验的假设。由于它不满足判据(1)和(2),因此还不适宜于对之进行专门的评估。尽管电报是在自称的成功之前发出的,但是这些电报没有对所预报的事件给以详尽的说明,并且发表的所有统计评价混杂了许多事后的主观决定。一种候选的预报技术如果缺少与地震的统计验证关系,那么应当满足几项有理判据,包括:(1)候选前兆与所预报地震的地点间的合理关系;(2)对候选前兆观测量与应力、应变或与地震有关的其他量相关的某种证明;(3)有候选前兆的同震变化以及震前变化存在。VAN 技术不满足这些判据中的任何一项。     

Geochemical behavior of 210Pb and 210Po in the nearshore waters off western Taiwan

Dissolved and particulate (210)Pb and (210)Po were determined at 15 stations along the coastline off western Taiwan in April 2007. The (210)Pb activities in dissolved and particulate phases fell within a relatively small range of 2.4-5.2 dpm 100 L(-1) and 1.0-3.2 dpm 100 L(-1), respectively. The dissolved and particulate (210)Po activities also fell within a small range of 0.8-3.4 dpm 100 L(-1) and 1.1-2.9 dpm 100 L(-1), respectively. The correlation of the distribution coefficients (K(d)) of (210)Pb and (210)Po with particle concentration in turbid waters are not as evident as in the open ocean. The mass balance calculation shows that the residence times of (210)Pb and (210)Po with respect to particle removal from the nearshore waters ranges from 3 to 15 days and from 14 to 125 days, respectively. The flux of particulate organic carbon was estimated by (210)Po proxy and ranged from 4.8 to 33.7 mmol-C m(-2) d(-1).     

Upscaling of hydraulic conductivity and telescopic mesh refinement

Performance assessments of repositories for the underground disposal of nuclear fuel and waste include models of ground water flow and transport in the host rocks. Estimates of hydraulic conductivity, K, based on field measurements may require adjustment (upscaling) for use in numerical models, but the choice of upscaling approach can be complicated by the use of nested modeling, large-scale fracture zones, and a high degree of heterogeneity. Four approaches to upscaling K are examined using a reference case based on exhaustive site data and an application of nested modeling to evaluate performance assessment of a waste repository. The upscaling approaches are evaluated for their effects on the flow balance between nested modeling domains and on simple measures of repository performance. Of the upscaling approaches examined in this study, the greatest consistency of boundary flows was achieved using the observed scale dependence for the rock domains, measured values from the large-scale interference test for the conductor domain, and a semivariogram regularization based on the Moye model for packer test interpretation. Making the assumption that large fracture zones are two-dimensional media results in the greatest changes to the median of travel time and improves the flow balance between the nested models. The uncertainty of upscaling methods apparently has a small impact on median performance measures, but a significant impact on the variances and earliest arrival times.