Qualitative and quantitative assessment of the risk from the exposure to fetotoxic chemical compounds

A new mathematical dose-response model for the expected probability of toxic response and also for the expected measure of the overdispersion parameter for the reproductive and developmental risk assessment is proposed. The model for the expected probability of toxic response is an improvised Weibull dose-response model incorporating the litter-size effect while the model for the overdispersion parameter is a polynomial function of the dose level. A beta-binomial distribution for the number of offspring showing toxic responses in a litter satisfactorily accounts for the extra-binomial variation and the intralitter correlation of responses of these pups. Confidence limits for low-dose extrapolation are based on the asymptotic distribution of the likelihood ratio. The safe dose for human exposure is then calculated by simple linear extrapolation. The model for overdispersion allows us to obtain the estimates of the overdispersion parameter at these dosages. This was not possible in the earlier models. The proposed model is illustrated by an application to a study on the effect of exposure to diethylhexylphthalate in mice. The results are compared with those obtained by Chen and Kodell (1989) who have applied the simple Weibull dose-response model to the same data set.This paper was prepared with partial support from the United States Environmental Protection Agency under a Cooperative Agreement Number CR-815273. The contents have not been subject to Agency review and therefore do not necessarily reflect the views or policies of the Agency and no official endorsement should be inferred.     

安徽琅琊山青檀种群数量动态

以种群生命表和生存分析理论为基础,采用胸径大小分级法和分段匀滑技术,编制琅琊山青檀（Pteroceltistatarinowii）种群静态生命表,绘制了死亡率曲线、消失率曲线、存活曲线和生存函数曲线并分析种群数量特征,结合种群动态量化方法和时间序列预测模型分析种群数量动态变化。结果表明：（1）琅琊山青檀种群属稳定增长型。种群径级结构大体呈倒“J”型分布,中、幼龄阶段个体数量较为丰富,老龄阶段个体数量相对较少,种群在发育过程中存在一定波动性,但种群数量变化动态指数Kp,i。和Kp,i（考虑外部干扰时）均大于0。（2）青檀种群死亡率曲线和消失率曲线变化趋势基本一致,均出现2个高峰,一个出现在第Ⅱ龄级,另一个出现在第XI（或Ⅻ）龄级;存活曲线经统计检验趋于Deevey-Ⅱ型。（3）青檀种群的生存率曲线单调下降,累计死亡率曲线单调上升,生存率下降趋势表现为前期高于后期,累计死亡率则相反;生存函数曲线显示,青檀种群具有前期薄弱、中期稳定和后期衰退的特点。（4）在未来2、4、6、8和10a内,青檀种群幼龄级个体数量相对丰富,种群呈稳定增长趋势。     

Estimation of birth rate and juvenile mortality from observed numbers of juveniles in a mammal population with normally dispersed reproduction

The increase in the number of juveniles in a mammal population with a normally dispersed reproduction is simulated using a computer. The effect of juvenile mortality and its age-dependency on the recruitment curve is discussed. The maximum number of juveniles is reached before all juveniles are born. The ratio of the period of time between the beginning of the reproduction period and the maximum of juveniles and of births (the coefficient of reduction of the apparent reproduction period) is related to the juvenile mortality rate and the ratio of the maximum number of juveniles to the total number of births. These relationships can be used to estimate the total number of births and the juvenile mortality rate from a series of counts of the juveniles. The simulation model used is programmed in CSMP-III.     

微板吸光法测定9种农药对斜生栅藻的抑制毒性

以斜生栅藻(Scenedesmus obliquus)为指示生物,96微孔板为暴露反应载体,SpectraMax M5酶标仪为吸光度测试设备,建立了测定毒物对藻生长抑制毒性的微板吸光法.论文系统研究了微板吸光法中斜生栅藻的可见吸收光谱和生长曲线以及pH和暴露时间对藻生长的影响,同时应用该方法成功测定了环嗪酮、阿特拉津、西草净、扑灭通、苯嗪草酮、敌草快、草甘膦7种除草剂和磷胺、甲胺磷2种杀虫剂对斜生栅藻的剂量-效应曲线(DRC).通过对剂量-效应数据进行非线性最小二乘模拟,获得了这些农药的半数效应浓度EC50及置信区间.对比标准锥形瓶栅藻毒性试验,微板吸光法具有测试简便快速,所需样品体积少,便于多次平行毒性测试等优点.     

草甘膦对旋链角毛藻和盐生杜氏藻的毒性兴奋效应(Stimulation Effect of Glyphosate on Chaetoceros curvisetus and Dunallelia salina)

为研究农药对海洋微藻的毒性兴奋效应(低剂量刺激生长效应),实验测定了不同时间点、不同剂量草甘膦(Glyphosate)对旋链角毛藻(Chaetoceros curvisetus)和盐生杜氏藻(Dunallelia salina)生长的影响,并使用Log-Logistic修正模型和三维模型对实验结果进行拟合.结果表明,草甘膦对两种海洋微藻均存在不同程度的刺激生长效应,修正的Log-Logistic生长模型和三维模型拟合结果不存在显著性差异,但由于不需编程且能得到更多参数,因此使用Log-Logistic修正模型能够更好地描述草甘膦对藻类的剂量-反应结果.     

An evaluation of environmental factors affecting species distributions

Many different models can be built to explain the distributions of species. Often there is no single model that is clearly better than the alternatives, and this leads to uncertainty over which environmental factors are limiting species’ distributions. We investigated the support for different environmental factors by determining the drop in model performance when selected predictors were excluded from the model building process. We used a paired t-test over 37 plant species so that an environmental factor was only deemed significant if it consistently improved the results for multiple species. Geology and winter minimum temperatures were found to be the environmental factors with the most support, with a significant drop in model performance when either of these factors was excluded. However, there was less support for summer maximum temperature, as other environmental factors could combine to produce similar model performance. Our method of evaluating environmental factors using multiple species will not be capable of detecting predictors that are only important for one or two species, but it is difficult to distinguish these from spurious correlations. The strength of the method is that it increases inference for factors that consistently affect the distributions of many species. We discourage the assessment of models against predefined benchmarks, such as an area under the curve (AUC) of more than 0.7, as many alternative models for the same species produce similar results. Therefore, the benchmarks do not provide any indication of how the performance of the selected model compares to alternative models, and they provide weak inference to accept any selected model.     

Assessing the parameterisation of the settling flux in a depth-integrated model of the fate of decaying and sinking particles, with application to fecal bacteria in the Scheldt Estuary

The fate of reactive tracers is often modelled by depth-averaged equations. When integrating the depth-resolved equations, it appears that the term describing the settling of particles is dependent on the concentration just above the bottom. Because in a depth-averaged framework this quantity is not available, the settling term needs to be parameterised. The most natural choice is to make the settling flux dependent on the average concentration. This approximation is acceptable if the water column is well mixed, but these conditions are not necessarily met in real applications. Therefore, this study aims at assessing and understanding the error made by using a depth-averaged model in a range of realistic conditions. For the definition of these conditions, typical values for the Scheldt Estuary and the Dutch-Belgian coast were taken. The realistic inspiration for the reactive tracer in this study is the fecal bacterium Escherichia coli, whose own dynamics are characterised by settling and gradual decay by mortality. In an attempt to understand the relative importance of several factors like settling, mortality, mixing and stratification on the error made by a depth-averaged approach, a number of simplified test cases were investigated. It follows that, as expected, the error is acceptable if the situation is mixing-dominated. However, the effect of mortality and stratification was less obvious in advance. For instance, it appeared that errors can also be significant if settling and mortality have the same characteristic timescales. Stratification often has the effect to increase the error made by the depth-averaged model.     

多组分苯胺类混合物对发光菌的抑制毒性

以淡水发光菌——青海弧菌(Q67)为指示生物,96微孔板为实验反应载体,微板光度计为发光强度测试设备,测定了苯胺、邻甲基苯胺、对甲基苯胺、邻硝基苯胺、对硝基苯胺及其混合物对发光菌的发光抑制毒性,应用非线性最小二乘拟合技术与剂量加和(DA)及独立作用(IA)原理研究了混合物的毒性规律.1)分别测定每种化合物的剂量-效应数据并进行非线性拟合.结果表明,5种苯胺类化合物的剂量-效应曲线(DRC)均可用Logit与Weibull函数有效表征,从这些模型估算的半数效应浓度负对数值(-logEC50)分别为2.11、2.35、2.49、3.60和3.88(EC50单位:mol·L-1),可知其对发光菌的毒性大小顺序为:苯胺<邻甲基苯胺<对甲基苯胺<邻硝基苯胺<对硝基苯胺.2)根据组分EC50、EC10和EC1设计3个等效应浓度比混合物进行混合物毒性实验,并对混合物剂量-效应数据进行非线性拟合得到混合物DRC.结果表明,混合物DRC可用Box-Cox-Logit与Box-Cox-Weibull函数有效表征.3)根据单一化合物DRC模型,分别应用剂量加和(DA)与独立作用(IA)模型对混合物DRC进行预测.结果表明,无论考察混合浓度比例还是效应水平,剂量加和模型都能准确预测苯胺类混合物的毒性,而独立作用模型倾向于高估混合物毒性.     

利用EIA法快速筛查垃圾焚烧飞灰和烟气中的二恶英毒性水平

基于CAPE技术公司的兔子复合克隆抗体的二恶英(PCDD/F)酶免疫分析试剂盒,建立了快速检测垃圾焚烧飞灰和烟气中PCDD/F毒性(TEQ值)的方法.试剂盒的最低检测限为3.3pg·tube-1(即3.3pgTEQ每EIA试管),线性检测范围为10～30pg·tube-1.样品经甲苯索氏抽提后过硅胶柱连接小碳柱净化处理,TCDD/F的回收率大约为50%,与原飞灰PCDD/F分布模式相比净化处理后样品中的TCDD/F含量明显降低.用净化处理后的飞灰溶液作标准溶液,绘制PCDD/F剂量-效应关系曲线,定量分析了2个飞灰样品和2个烟气样品的TEQ浓度,结果表明分析样品的TEQ实测值(HRGC/HRMS分析获得)与预测值(标准曲线计算值)的相对偏差(Rd)均小于15%,说明用该方法定量分析垃圾焚烧飞灰和烟气中PCDD/F毒性是可行的.     

南京老山国家森林公园朴树种群动态

运用相邻格子法对南京老山国家森林公园朴树(Celtis sinensis)种群(以下简称老山朴树种群)进行野外调查,以定量方法研究其种群结构特征。编制种群静态生命表,并绘制存活曲线、死亡率曲线、消失率曲线和4个生存函数曲线,同时结合时间序列预测模型研究老山朴树种群的数量动态。结果表明,种群各龄级个体数虽然存在波动,但整体呈增长趋势,存活曲线属DeeveyⅡ型,分别在第Ⅰ和第Ⅶ龄级出现2个死亡率高峰。第1个峰值的出现主要是由于种内竞争激烈,第2个峰值伴随种群进入生理死亡年龄而出现。生存分析结果表明,朴树种群至第Ⅵ龄级时,生存率仅为0.5%,累计死亡率高达99.5%;危险率曲线与死亡率和消失率曲线变化情况基本一致,反映朴树种群生长发育过程具有前期薄弱、中期稳定、后期衰退的特点。时间序列预测结果表明,在未来的2～6 a内,老山朴树种群呈增长趋势。对幼苗及幼林进行人工抚育管理将有助于老山朴树种群的天然更新。     

Inter-annual variability in somatic growth rates and mortality of coastal fishes off central Chile: an ENSO driven process?

The effects of El Niño (EN) and La Niña (LN) events upon marine organisms inhabiting the Eastern Pacific coast have been widely studied in recent years, concentrating primarily on changes in species composition and on population size. In this study, using somatic growth rates as metabolic response variables, we evaluated the mortality rates of coastal fishes inhabiting a central Chilean upwelling marine ecosystem in the South Pacific between 1990 and 2003. Four coastal fish species belonging to different trophic levels (one herbivore, one omnivore, and two carnivores) were analyzed. In all species, the estimated cohort somatic growth rates were low for those recruited during EN and high for those recruited during LN events. Annual cohort mortality rates were highest during EN events and lower during LN and transitional years. We propose that productivity (as a bottom-up driver) acts as a primary exogenous factor upon annual cohort mortality rates. We also propose that a plausible mechanism underlying this process is the negative effect the low somatic growth rates may have on fish ecological attributes such as their competitive abilities, condition factors, and predation risks, which ultimately may affect their fitness.     

Modelling the spatial population dynamics of the green oak leaf roller (Tortrix viridana) using density dependent competitive interactions: Effects of herbivore mortality and varying host-plant quality

Cyclic population dynamics of forest insects with periods of more than two generations have been discussed in relation to a variety of extrinsic and intrinsic forces. In the present study, we employed the selection pressure of density dependent competitive interactions according to Witting's equations (Witting, 2000) as driver for a discrete spatiotemporal model of the green oak leaf roller (Tortrix viridana). The model was successfully parameterised to rebuild the cyclic population dynamics of an empirical data set of a 30-year leaf roller monitoring in Russia. Our analysis focussed on the role of herbivore mortality and host plant food quality, which have a significant effect on T. viridana population dynamics. An additional egg or larvae mortality lowers population density and can lead to selection pressures that favour individuals with higher growth rate. This increased population growth rate can not only compensate the additional mortality, but also can lead to higher average moth abundances in subsequent generations. Furthermore, we analysed the effect of inter- and intraspecific variation in host plant quality on herbivore population dynamics and the spatial distribution of abundance and defoliation patterns. We found significant effects of the qualitative composition of a trees neighbourhood on the herbivore population of the respective tree. Also, the patchy damage patterns observable in reality have been reproduced by the present model. The applicability of the model approach and the putative genetic processes underlying Witting's model are discussed.     

Compositional analysis of topsoil metals and its associations with cancer mortality using spatial misaligned data

The presence of toxic metals in soil per se, and in soil impacted by mining, industry, agriculture and urbanisation in particular, is a major concern for both human health and ecotoxicology. The dual aim of this study was: to ascertain whether topsoil composition could influence the spatial distribution of mortality due to different types of cancer and to identify possible errors committed by epidemiological studies which analyse soil composition data as a closed number system. We conducted an ecological cancer mortality study, covering 861,440 cancer deaths (27 cancer sites) in 7917 Spanish mainland towns, from 1999 to 2008. Topsoil levels of Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn were determined by ICP-MS at 13,317 sampling points. We transformed the topsoil data in two ways, i.e. log transformation and centred logratio transformation. Principal factor analysis was performed to obtain independent latent factors for the transformed variables. To estimate the effect on mortality of topsoil factor loadings, we fitted Besag, York and Mollié models embedded in geostatistical-spatial models. This model included soil sample locations and town centroids (non-aligned data), fitted using the integrated nested Laplace approximation (INLA) as a tool for Bayesian inference and stochastic partial differential equations (SPDE). All results were adjusted for socio-demographic variables. The results indicated that soil composition could have an influence on the spatial distribution and mortality patterns of cancer. The analysis adjusted for socio-demographic variables showed excess male mortality due to digestive system tumours in areas with soils containing higher Cd, Pb, Zn, Mn and Cu concentrations, bladder cancer in areas with soils containing higher Cd concentrations, and brain cancer in areas with soils containing As. In both sexes, cancer of oesophagus was associated with soils containing a higher lead content, while lung cancer was associated with soils containing a higher copper content. Stress should be laid on the importance of taking into account the compositional nature of the data in this type of analysis.     

不同油类对虾蟹类幼体的胁迫效应

了解不同油类对虾蟹类幼体的急性毒性效应。曝油处理采用磁力搅拌器搅拌,一定时间的超声波乳化等操作,模拟溢油在海洋中风浪、涡动、湍流的乳化过程;设置阶梯浓度组,并在多个平行组急性试验的基础上,估算出8种油品对2种虾类和2种蟹类的半致死质量浓度LC50和安全质量浓度MPC,并运用程序编制溢油质量浓度与虾蟹类死亡率相关性的估算模型。经过分析,结果得到:各MPC值参差不齐,差距较大;燃料油普遍比原油的毒性效应大;相同生长阶段,蟹类比虾类抗油毒害性强、中国明对虾Fenneropenaeus chinensis比日本囊对虾Marsupenaeus japonicus抗油毒害性强、锯缘青蟹Scylla serrata比三疣梭子蟹Portunus trituberculatu抗油毒害性强。编制的溢油质量浓度与死亡率相关性的评估模型,简易方便直观,为渔业污染事故理赔提供了一定的参考价值,亦为海域的生态经济学评估提供了一种新的研究方法。     

Spatial elements of mortality risk in old-growth forests

For many species of long-lived organisms, such as trees, survival appears to be the most critical vital rate affecting population persistence. However, methods commonly used to quantify tree death, such as relating tree mortality risk solely to diameter growth, almost certainly do not account for important spatial processes. Our goal in this study was to detect and, if present, to quantify the relevance of such processes. For this purpose, we examined purely spatial aspects of mortality for four species, Abies concolor, Abies magnifica, Calocedrus decurrens, and Pinus lambertiana, in an old-growth conifer forest in the Sierra Nevada of California, USA. The analysis was performed using data from nine fully mapped long-term monitoring plots. In three cases, the results unequivocally supported the inclusion of spatial information in models used to predict mortality. For Abies concolor, our results suggested that growth rate may not always adequately capture increased mortality risk due to competition. We also found evidence of a facilitative effect for this species, with mortality risk decreasing with proximity to conspecific neighbors. For Pinus lambertiana, mortality risk increased with density of conspecific neighbors, in keeping with a mechanism of increased pathogen or insect pressure (i.e., a Janzen-Connell type effect). Finally, we found that models estimating risk of being crushed were strongly improved by the inclusion of a simple index of spatial proximity. Not only did spatial indices improve models, those improvements were relevant for mortality prediction. For P. lambertiana, spatial factors were important for estimation of mortality risk regardless of growth rate. For A. concolor, although most of the population fell within spatial conditions in which mortality risk was well described by growth, trees that died occurred outside those conditions in a disproportionate fashion. Furthermore, as stands of A. concolor become increasingly dense, such spatial factors are likely to become increasingly important. In general, models that fail to account for spatial pattern are at risk of failure as conditions change.     

Effects of Road Fencing on Population Persistence

Abstract:  Roads affect animal populations in three adverse ways. They act as barriers to movement, enhance mortality due to collisions with vehicles, and reduce the amount and quality of habitat. Putting fences along roads removes the problem of road mortality but increases the barrier effect. We studied this trade-off through a stochastic, spatially explicit, individual-based model of population dynamics. We investigated the conditions under which fences reduce the impact of roads on population persistence. Our results showed that a fence may or may not reduce the effect of the road on population persistence, depending on the degree of road avoidance by the animal and the probability that an animal that enters the road is killed by a vehicle. Our model predicted a lower value of traffic mortality below which a fence was always harmful and an upper value of traffic mortality above which a fence was always beneficial. Between these two values the suitability of fences depended on the degree of road avoidance. Fences were more likely to be beneficial the lower the degree of road avoidance and the higher the probability of an animal being killed on the road. We recommend the use of fences when traffic is so high that animals almost never succeed in their attempts to cross the road or the population of the species of concern is declining and high traffic mortality is known to contribute to the decline. We discourage the use of fences when population size is stable or increasing or if the animals need access to resources on both sides of the road, unless fences are used in combination with wildlife crossing structures. In many cases, the use of fences may be beneficial as an interim measure until more permanent measures are implemented.     

Combined toxic effect of airborne heavy metals on human lung cell line A549

Many studies have demonstrated that heavy metals existing as a mixture in the atmospheric environment cause adverse effects on human health and are important key factors of cytotoxicity; however, little investigation has been conducted on a toxicological study of a metal mixture from atmospheric fine particulate matter. The objective of this study was to predict the combined effects of heavy metals in aerosol by using in vitro human cells and obtain a suitable mixture toxicity model. Arsenic, nickel, and lead were selected for mixtures exposed to A549 human lung cancer cells. Cell proliferation (WST-1), glutathione (GSH), and interleukin (IL)-8 inhibition were observed and applied to the prediction models of mixture toxicity, concentration addition (CA) and independent action (IA). The total mixture concentrations were set by an IC₁₀-fixed ratio of individual toxicity to be more realistic for mortality and enzyme inhibition tests. The results showed that the IA model was statistically closer to the observed results than the CA model in mortality, indicating dissimilar modes of action. For the GSH inhibition, the results predicted by the IA and CA models were highly overestimated relative to mortality. Meanwhile, the IL-8 results were stable with no significant change in immune reaction related to inflammation. In conclusion, the IA model is a rapid prediction model in heavy metals mixtures; mortality, as a total outcome of cell response, is a good tool for demonstrating the combined toxicity rather than other biochemical responses.     

Robust trend tests with application to toxicology

In most real data situations in the one-way design both the underlying distribution and the shape of the dose-response curve are a priori unknown. The power of a trend test strongly depends on both. However, tests which are routinely used to analyze toxicological assays must be robust. We use nonparametric tests with different scores—powerful for different distributions—and different contrasts—powerful for different shapes—and use the maximum of all test statistics as a new test statistic. Simulation results indicate that this maximum test, which is a nonparametric multiple contrast test, stabilizes the power for various shapes and distributions. The investigated tests are applied to the data of a toxicological assay.     

Using and comparing two nonparametric methods (CART and MARS) to model the potential distribution of gullies

Gully erosion represents an important soil degradation process in rangelands. In order to take preventive or control measures and to reduce its environmental damages and economical costs it is useful to localize the points in the landscape where gullying takes place and to determine the importance of the different factors involved. The study is carried out in Extremadura, southwest Spain. The main objectives of this work are: (a) comparing two nonparametric schemes to model the potential distribution of gullies, (b) evaluating the importance of the different factors involved in gullying processes, (c) analyzing the role of prevalence in the success of the model and finally, (d) implementing and mapping the results with the help of a Geographical Information System (GIS). Two methods were used to model the response of a dependent variable (gullying) from a set of independent variables: Classification And Regression Trees (CART) and Multivariate Adaptive Regression Splines (MARS). Three different datasets were used; the first one for constructing the model (training dataset) and the others for validating the model (external datasets). These datasets are formed by a target variable (presence or absence of gullies) and a set of independent variables. The dependent variable was obtained by mapping the locations of gullies with the help of a GPS and high resolution aerial ortophotographs. A set of 32 independent variables reflecting topography, lithology, soil type, climate, land use and vegetation cover of each area were used. The performance of the models was evaluated using a non-dependent threshold method: the Receiver Operating Characteristic (ROC) curve. The results showed a better performance of MARS for predicting gullying with areas under the ROC curve of 0.98 and 0.97 for the validation datasets, while CART presented values of 0.96 and 0.66.     

The response of the woodpigeon (Columba palumbus) to relaxation of intraspecific competition: A hybrid modelling approach

The recent rapid growth of the woodpigeon population in the British Isles is a cause for concern for environmental managers. It is unclear what has driven their increase in abundance. Using a mathematical model, we explored two possible mechanisms, reduced intraspecific competition for food and increased reproductive success. We developed an age-structured hybrid model consisting of a system of ordinary differential equations that describes density-dependent mortality and a discrete component, which represents the birth-pulse. We investigated equilibrium population dynamics using our model. The two hypotheses predict contrasting population age profiles at equilibrium. We adapted the model to examine the impacts of control measures. We showed that an annual shooting season that follows the period of density-dependent mortality is the most effective control strategy because it simultaneously removes adult and juvenile woodpigeons. The model is a first step towards understanding the processes that influence the dynamics of woodpigeon populations.