In Pursuit of Safety: One-Hundred Years of Toxicological Risk Assessment

The publication in 1962 of Rachel Carson's Silent Spring marks the mid-point in a century that saw, in its first half, the emergence of public health concerns related to human exposures to chemicals, and, in its second half, the emergence of public policies to deal with those concerns. Those policies made it imperative that the scientific community come to grips with the problem of identifying exposure levels not likely to cause harm. This problem was not significantly discussed within the scientific community until the 1950s, and well-described methods for practical solutions to it did not appear until the 1970s. An important report from the National Academy of Sciences, published in 1983 (Risk Assessment in the Federal Government), provided an analysis of these emerging methods, and recommended a useful framework for the assessment and management of risk. This framework remains central to public health and regulatory decision-making. A high-level perspective is offered on events leading to and following the 1983 report. The article describes early thinking about chemical toxicity and the scientific path that thinking followed through the 20th century, and to the present.     

Modela-r as a Froude and Strouhal dimensionless numbers combination for dynamic similarity in running

The aim of this study was to test the hypothesis that running at fixed fractions of Froude (Nfr) and Strouhal (Str) dimensionless numbers combinations induce dynamic similarity between humans of different sizes. Nineteen subjects ran in three experimental conditions, (i) constant speed, (ii) similar speed (Nfr) and (iii) similar speed and similar step frequency (Nfr and Str combination). In addition to anthropometric data, temporal, kinematic and kinetic parameters were assessed at each stage to measure dynamic similarity informed by dimensional scale factors and by the decrease of dimensionless mechanical parameter variability. Over a total of 54 dynamic parameters, dynamic similarity from scale factors was met for 16 (mean r=0.51), 32 (mean r=0.49) and 52 (mean r=0.60) parameters in the first, the second and the third experimental conditions, respectively. The variability of the dimensionless preceding parameters was lower in the third condition than in the others. This study shows that the combination of Nfr and Str, computed from the dimensionless energy ratio at the center of gravity (Modela-r) ensures dynamic similarity between different-sized subjects. The relevance of using similar experimental conditions to compare mechanical dimensionless parameters is also proved and will highlight the study of running techniques, or equipment, and will allow the identification of abnormal and pathogenic running patterns. Modela-r may be adapted to study other abilities requiring bounces in human or animal locomotion or to conduct investigations in comparative biomechanics.     

Spring development of a Chlamydomonas population in Lake Nimetön,a small humic forest lake in southern Finland

Biomass development and vertical distribution of a Chlamydomonas population in a small humic forest lake was followed by daily sampling in May-June, 1984. Chlamydomonas dominated the phytoplankton spring bloom, forming 71% of the maximum phytoplankton biomass on 18 May. In early May the outflow rate was high and during the 24 hour period when the maximum rate of surface runoff was recorded (8–9 May), 43% of the Chlamydomonas biomass was flushed out of the lake, which delayed the onset of biomass increase. When surface runoff had slowed down Chlamydomonas biomass started increasing and during wax of the population most cells were < 10 µm in diameter. Population maximum lasted for one day (18 May) and there-after Chlamydomonas biomass decreased towards the end of the study. During wane of the population most cells were > 10 µm in diameter.     

Dynamics of soil microbial biomass N under zero and shallow tillage for spring wheat,using15N urea

Summary Field studies to determine the effect of zero and shallow (10 cm) cultivation on microbial biomass were conducted on several Chernozemic soils in western Canada. Using the CHCl₃ fumigation method, the distribution of microbial biomass N and the immobilization and subsequent release of added¹⁵N (¹⁵N-urea) from the microbial biomass were determined in the A horizon, at the 0 to 5 and 5 to 10 cm depth, during the growing season for spring wheat.Temporal variation in microbial biomass N, associated with the development of the rhizosphere, was characterized by an increase between Feekes stage 1 and 5 or 10 and decrease at Feekes stage 11.4. Over the long term, the variation in biomass N between tillage systems corresponded with crop residue distribution. Immobilization of fertilizer N was related to the increase in biomass N from Feekes stage 1, which in turn, was associated with the incorporation of recent crop residues or levels of labile organic matter in the surface soil. The study demonstrated the relatively rapid remineralization of immobilized fertilizer N under field conditions and emphasized the role of the microbial biomass N as both a sink and source of mineral N.     

Observations on populations of the horseshoe crabLimulus (=Xiphosura) polyphemus

1. Marked populations of Limulus (=Xiphosura) polyphemus reveal that in Cold Spring Harbor, New York, they consisted of 10,000–18,000 adults in 1957 and 1961. The sex ratio in 1957 was about 4 males: 1 female. Pairs may remain attached for as long as 9 days. An undisturbed female may lay as many as 12,000 eggs in one nest.
2. The Cold Spring Harbor populations appear to be rather sedentary: none of the 1,000 animals marked on the north edge of the sandspit in 1961 were detected in the outer harbor either at Laurel Hollow Beach or the peninsula adjacent to the Cold Spring Harbor Yacht Club 500–800 meters from the tagging site (see Fig. 1), nor were they found in the small beach adjacent to the Biological Laboratory in the inner harbor. Similarly, none of the 300 animals marked at this last site were found at the north edge of the sandspit.
3. The phenotype of the compound eye varies from black to pigmentless. Samples observed in Cold Spring Harbor and in the Marine Biological Laboratory, Woods Hole, Massachusetts (separated by Long Island Sound and a distance of 150 miles) differ in the frequency of the various phenotypes scored, but the mode of inheritance of eye color remains obscure.
4. The available evidence indicates Limulus has considerable phenotypic variation in regard to body size, eye color, and other characters believed to be inherited, with the result that demes or physiological races are created. It is argued that the belief that this organism is stable and has not changed since the Triassic 200 million years ago has foundation only in regard to the pattern of the body of Limulus, but not in regard to its genotype. Limulus does not seem to be different from other organisms for which considerable genetic evidence is available, and thus the statement that DNA is fairly stable and has remained so for 200 million years is open to question.

     

无机营养对春小麦抗旱适应性的影响

本文研究了无机营养对春小麦一些抗旱适应性的影响,主要包括:渗透调节的大小和变化过程、可溶性糖的积累、脯氨酸的积累、叶片导度的变化、离体叶片的失水速率、叶面积和耗水量的变化、根系生长和根/植冠值,并且分析了各个处理植株的水分利用效率(WUE)和产量的变异。认为,在干旱条件下,无机营养对于春小麦不同器官、不同生理功能,并不都具有一致的作用。有的利于提高植株的抗旱性,有的可以改变一些适应性产生的时间和发展过程,有的则不利于植株的抗旱性。通过综合分析,提出旱地施肥使作物增产的主要原因是,营养元素满足了作物生长所需,促进了根系发育,利于吸收水分、维持水分平衡和正常生理功能,但对作物自身的耐旱性并没有产生显著影响。     

冬季高温对白三叶越冬和适应春季"倒春寒"的影响

暖冬和春季"倒春寒"已严重影响着多年生植物生长发育。选择建植3a的白三叶(Trifolium repens Linn)为试验材料,在入冬采用搭建塑料大棚模拟暖冬方法,通过在建棚前、建棚后、冬季融冻胁迫、春季揭棚后和"倒春寒"过程中测定棚外和棚内白三叶植株高度和叶片抗逆生理指标的变化以揭示未来暖冬对白三叶生存和生态园林持续发展的影响。结果表明,冬季棚外气温均温低于0℃,白三叶叶片经历了冻融胁迫,棚内温度高于0℃,叶片始终未结冻。搭棚前,棚内外试验地白三叶生长势无差异。搭棚后100d棚内白三叶株高是棚外的3倍,但揭棚后3个月棚内外白三叶株高一致。另外,冬季虽然棚内外白三叶叶片细胞膜透性、丙二醛(MDA)、脯氨酸、可溶性糖含量和抗氧化酶活力(SOD、CAT、POD)均随气温下降而增高与气温变化呈负相关,但棚外白三叶叶片上述生理指标均高于棚内。在春季揭棚后2d,冬季棚内生长的白三叶不仅叶片细胞膜透性和MDA含量急剧增加并高于揭棚前和棚外白三叶,而且叶片SOD和CAT活性和可溶性糖和脯氨酸含量急剧增加也明显高于棚外白三叶。在春季"倒春寒"时,冬季棚内外不同温度下生长的白三叶叶片细胞膜透性快速升高、脯氨酸和可溶性糖含量、POD和SOD活性均上升,两处理间无显著差异。研究表明,冬季零度以上低温可延缓冬季白三叶绿叶期和单个叶片的寿命,可使白三叶安全渡过春季"倒春寒",未来暖冬不会降低白三叶抗融冻能力和其返青生长势。而这与白三叶能快速应对环境温度变化,通过调整生理代谢使叶片中快速积累渗透调节物和激活抗氧化酶防止氧自由基积累抑制膜脂过氧化,保护细胞膜的完整性有直接关系。     

奈曼地区灌溉麦田蒸散量及作物系数的确定

利用大型蒸渗仪测定了奈曼地区春小麦(Triticum aestivum L.)全生育期的蒸散量,并引用FAO Penman-Monteith等5种方法计算了相应时期的参考作物蒸散量,比较了FAO Penman-Monteith公式与其它4种方法间的关系,最后运用作物蒸散量和参考作物蒸散量计算了春小麦的作物系数．结果表明,春小麦苗期每周日平均蒸散量小于3mm·d^-1,随着叶面积系数增大,日平均蒸散量达到最大值6．49mm·d^-1(抽穗开花期),最终下降至1．94mm·d^-1(灌浆成熟期);根据试验年份的降雨分布情况,该地区的自然降水不能满足春小麦对水分需求,小麦苗期、拔节期和抽穗开花期水分亏缺比较严重,是田间水分管理的关键时期;与FAO Penman-Monteith公式的计算结果相比较,用Penman公式和FAO-24 Blaney-Criddle公式估算奈曼地区参考作物蒸散量误差较小;奈曼地区春小麦苗期、营养期、生殖期、成熟期4个生长阶段的作物系数分别为0．45、0．90、1．1l和0．52,其中成熟期的作物系数值与FAO-24给出的小麦作物系数值差异较大．     

GLM versus CCA spatial modeling of plant species distribution

Despite the variety of statistical methods available for static modeling of plant distribution, few studies directly compare methods on a common data set. In this paper, the predictive power of Generalized Linear Models (GLM) versus Canonical Correspondence Analysis (CCA) models of plant distribution in the Spring Mountains of Nevada, USA, are compared. Results show that GLM models give better predictions than CCA models because a species-specific subset of explanatory variables can be selected in GLM, while in CCA, all species are modeled using the same set of composite environmental variables (axes). Although both techniques can be readily ported to a Geographical Information System (GIS), CCA models are more readily implemented for many species at once. Predictions from both techniques rank the species models in the same order of quality; i.e. a species whose distribution is well modeled by GLM is also well modeled by CCA and vice-versa. In both cases, species for which model predictions have the poorest accuracy are either disturbance or fire related, or species for which too few observations were available to calibrate and evaluate the model. Each technique has its advantages and drawbacks. In general GLM will provide better species specific-models, but CCA will provide a broader overview of multiple species, diversity, and plant communities.