Measuring and monitoring persistent organic pollutants in the context of risk assessment

Due to growing concerns regarding persistent organic pollutants (POPs) in the environment, extensive studies and monitoring programs have been carried out in the last two decades to determine their concentrations in water, sediment, and more recently, in biota. An extensive review and analysis of the existing literature shows that whilst the vast majority of these efforts either attempt to compare (a) spatial changes (to identify "hot spots"), or (b) temporal changes to detect deterioration/improvement occurring in the environment, most studies could not provide sufficient statistical power to estimate concentrations of POPs in the environment and detect spatial and temporal changes. Despite various national POPs standards having been established, there has been a surprising paucity of emphasis in establishing accurate threshold concentrations that indicate potential significant threats to ecosystems and public health. Although most monitoring programs attempt to check compliance through reference to certain "environmental quality objectives", it should be pointed out that many of these established standards are typically associated with a large degree of uncertainty and rely on a large number of assumptions, some of which may be arbitrary. Non-compliance should trigger concern, so that the problem can be tracked down and rectified, but non-compliance must not be interpreted in a simplistic and mechanical way. Contaminants occurring in the physical environment may not necessarily be biologically available, and even when they are bioavailable, they may not necessarily elicit adverse biological effects at the individual or population levels. As such, we here argue that routine monitoring and reporting of abiotic and biotic POPs concentrations could be of limited use, unless such data can be related directly to the assessment of public health and ecological risks. Risk can be inferred from the ratio of predicted environmental concentration (PEC) and the predicted no effect concentration (PNEC). Currently, the paucity of data does not allow accurate estimation of PNEC, and future endeavors should therefore, be devoted to determine the threshold concentrations of POPs that can cause undesirable biological effects on sensitive receivers and important biological components in the receiving environment (e.g. keystone species, populations with high energy flow values, etc.), to enable derivation of PNECs based on solid scientific evidence and reduce uncertainty. Using the threshold body burden of POPs required to elicit damages of lysosomal integrity in the green mussel (Perna virvidis) as an example, we illustrate how measurement of POPs in body tissue could be used in predicting environmental risk in a meaningful way.     

Residence time of pollutants discharged in the Gulf of Kachchh, northwestern Arabian Sea

A 2D Hydrodynamic-Particle Analysis model was applied to the Gulf of Kachchh (GoK) to estimate the residence time of pollutants. The tidal currents in the Gulf have a strong E-W component, which prevents the material in the north being transported towards south. In the regions situated very close to the open boundary, where the GoK waters exchange freely with the northern Arabian Sea, dilution takes place rapidly with the incoming waters and hence, the residence time is on the order of 1 day. Influence of eddies and a dynamic barrier across the Sikka-Mundra section on the residence time is apparent. Eastern GoK shows a relatively large residence time, on the order of 2-4 days, warranting caution while releasing industrial wastes in the northeastern Gulf. The region around location-5 behaves like a bay; the dissolved matter gets trapped in this bay and the residence time increases by 3-4 days.     

Intra- and inter-specific variability in total and methylmercury bioaccumulation by eight marine fish species from the Azores

We relate fish biological and ecological characteristics to total and organic mercury concentrations to determine whether accumulation is influenced by trophic level, Hg concentration in the diet, and vertical distribution. Levels of total mercury and methylmercury were determined in the muscle tissue of eight species of fish: Pagellus acarne, Trachurus picturatus, Phycis phycis, P. blennoides, Polyprion americanus, Conger conger, Lepidopus caudatus and Mora moro, caught in the Azores. All such fishes are commercially valuable and were selected to include species from a wide range of vertical distributions from epipelagic (<200 m) to mesopelagic (>300 m) environments. Methylmercury was the major form accumulated in all species, comprising an average of 88.1% of total mercury. Concentrations of mercury (total and methylmercury) increased with age, length and weight. Based on data from other studies, mercury concentrations in fish diet were estimated. Mercury levels in food ranged from 0.08 to 0.32 ppm, dry weight. Hg concentrations in the food and in muscle tissue from different species were positively correlated. Total Hg levels in the muscles were approximately nine times those estimated in food. Total mercury concentrations in muscle were positively correlated with both trophic level and median depth. Such enhanced mercury bioaccumulation in relation to depth appears to be determined primarily by concentrations in food and ultimately by water chemistry, which controls mercury speciation and uptake at the base of the food chain.     

航空图像与卫星图像大气圈校正的算法

本文描述了进行快速大气圈校正的一种算法。所需辐射参数储存在一个检查表格中。基本程序是把所测辐射率、波长、观察方向和照射方向、观察面高度及烟、大气微粒和气吸收的光学厚度输入一个检查表内。然后计算面辐射率、面瞬时辐照度及面反射率。同时,该程序还可以计算给定反射率,观察和照射方向、烟、大气微粒与气吸收的光学厚度等参数情况下特定高度处的上方的辐射率。     

碰撞造山带的P—T—t轨迹

压力—温度—时间(P—T—t)轨迹综合了造山作用期间变质岩石遭受的压力与温度的变化。它们为解释复杂的变质历史提供了一种简便的骨架,也提供了深入探讨碰撞造山带中控制变质作用的热因素与大地构造因素的条件。P—T—t资料是由结构观察、地质温度计、地质热时测定综合获得的,并组合构成适于地质条件的P—T—t轨迹曲线。假设瞬间变形及传导热松驰的一维P—T—t模式易于构制且对于检验大地构造模式是常用的,特别是在地质年代数据可以利用时更是如此。二维模式适于更复杂的变形几何,且容许多有对流效应的介入。根据经典楔状体理论对碰撞造山带进行的分析,可以出现反映加厚、抬升、剥离和会聚间的偶合现象的P—T—t轨迹。在剥蚀速率达到构造抬升速率时,就象目前新西兰南阿尔卑斯带中所出现的情况,那么高级变质岩可以迅速由很深处剥露出来。另一方面,迅速剥露可能反映了过陡或热软化的造山带中受重力作用出现的伸展。     

斜长石的碎裂流与半脆性变形

在温度为25～700℃、压力为500～1500MPa和应变率10~(-5)S~(-1)的条件下,对布什维尔德斜长石(An_(75),粒度350μm,5％其它物质)展开了一系列实验。在所施加的P—T范围内布什维尔德杂岩的强度都保持对压力敏感,而弱化则出现在给定压力条件下增温的情况。由粘滑向稳定滑移的转变出现在200～300℃和≥500MPa条件下。在200～300℃时强度的降低,局部出现的碎裂流及缺少晶内塑性变形的微观证据都有利地说明一种可能性,即这种转变对应于一定量随机分布的热破裂的扩展。均匀韧性流动仅出现在600℃和700℃温度,1000～1500MPa压力条件下,它与机械双晶,不均匀和带状波状消光的发育对应,这可能是由半脆性变形引起的。在这些条件下,变形持续至应变高达44％。