Mercury speciation in natural waters: Measurement of dissolved gaseous mercury with a field analyzer

Mercury evasion from water is commonly modeled using measurements of dissolved gaseous mercury (DGM). We developed a method using a recently available automated field-ready mercury vapor analyzer to rapidly measure the concentrations of DGM in surface waters. We summarize here results of laboratory tests of the method, field intercomparisons with a manual method, and selected data from recent sampling campaigns in Florida and Michigan. The method uses the 1.5 lpm flow of a Tekran® Model 2537A mercury analyzer to purge and analyze discrete water samples, generating near real time (5-min) data on DGM in samples and blanks. Application of the Tekran allowed for detailed analysis of DGM removal kinetics and short-term diel studies characterizing the influence of sunlight and precipitation on DGM production in surface waters. Gas removal kinetics for dozens of samples indicates a first-order rate constant, and supports a 20-min. purge time for surface water samples from Florida (40-min for Michigan samples). Blanks are measured during a second such purge. Our results indicate that DGMs determined by both automated and manual methods are generally comparable, and that DGM in Florida samples is unstable during storage (loss rate constant ∼0.1--0.2 h -1 ), probably due to oxidation. This suggests that rapid in-field analysis is preferred to storage with delayed analysis. Our data indicate that DGM at the Florida site is influenced by inputs of reactive Hg in rainwater, and by production of surface DGM during photoreduction of oxidized Hg in the water column.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42473/1/10533_2004_Article_230007.pd

Exposure to di(2-ethyl-hexyl) phthalate (DEHP) in utero and during lactation causes long-term pituitary-gonadal axis disruption in male and female mouse offspring

The present study examined the effects in mice of exposure to di(2-ethyl-hexyl) phthalate (DEHP) throughout pregnancy and lactation on the development and function of the pituitary-gonadal axis in male and female offspring once they have attained adulthood. Groups of two to three dams were exposed with the diet from gestational d 0.5 until the end of lactation, at 0, 0.05, 5, and 500 mg DEHP/kg \ub7 d. The experiment was repeated three times (total: seven to 10 dams per treatment). The 500-mg dose caused complete pregnancy failure, whereas exposure to doses of 0.05 and 5 mg did not affect pregnancy and litter size. In total, about 30 male and 30 female offspring per group were analyzed. Offspring of the DEHP-treated groups, compared with controls, at sexual maturity showed: 1) lower body weight (decrease 20-25%, P < 0.001); 2) altered gonad weight (testes were 3c13% lighter and ovaries 3c40% heavier; P < 0.001); 3) poor germ cell quality (semen was 3c50% less concentrated and 20% less viable, and 3c10% fewer oocytes reached MII stage, P < 0.001); 4) significant lower expression of steroidogenesis and gonadotropin-receptor genes in the gonads; and 5) up-regulated gonadotropin subunit gene expression in the pituitary. In conclusion, our findings suggest that, in maternally exposed male and female mice, DEHP acts on multiple pathways involved in maintaining steroid homeostasis. Specifically, in utero and lactational DEHP exposure may alter estrogen synthesis in both sexes. This, in turn, induces dysregulation of pituitary-gonadal feedback and alters the reproductive performance of exposed animals

Effects of polychlorinated biphenyls in Cd-1 mice : reproductive toxicity and intergenerational transmission

Several studies indicate that in-utero and peri-natal exposure to polychlorinated biphenyls (PCBs) induces adverse reproductive effects but it remains unclear whether such effects may be transmitted to subsequent generations. We therefore investigated the association between maternal exposure to PCBs and reproductive health in male and female offspring over three generations.Mouse dams were fed 0, 1, 10, 100 \u3bcg/kg/day of a PCB mixture (101+118) during pregnancy and lactation. PCB levels were measured in the tissues of both dams and offspring.PCB concentrations at all doses investigated were greater in the offspring than in the dams (P 640.0001) confirming that the progeny were exposed as a result of maternal exposure. In F1 offspring, exposure to PCBs resulted in reductions in: i) testis weight (P 640.05) and seminiferous tubule diameter (P 640.05); ii) sperm viability (P 640.0001) and developmental capacity (P 640.05); iii) ovary weight (P 640.05); iv) oocyte developmental capacity (P 640.05), and in v) increased follicular atresia (P 640.0001).In females, adverse effects were observed only in the F1 animals. In contrast, male offspring exhibited reduced sperm viability and altered seminiferous tubule distribution up to the third generation, showing intergenerational transmission.In summary, our data indicate that exposure to PCBs at the time of gonadal sex determination perturbed, significantly, the reproductive physiology of male and female offspring in adulthood. Furthermore, male reproductive deficiencies may be observed in at least two further generations. These findings have significant implications for reproductive health and fertility of animals and humans

Murine in vitro cellular models to better understand adipogenesis and its potential applications

Adipogenesis has been extensively studied using in vitro models of cellular differentiation, enabling long-term regulation of fat cell metabolism in human adipose tissue (AT) material. Many studies promote the idea that manipulation of this process could potentially reduce the prevalence of obesity and its related diseases. It has now become essential to understand the molecular basis of fat cell development to tackle this pandemic disease, by identifying therapeutic targets and new biomarkers. This review explores murine cell models and their applications for study of the adipogenic differentiation process in vitro. We focus on the benefits and limitations of different cell line models to aid in interpreting data and selecting a good cell line model for successful understanding of adipose biology

Nonlinear transient structural response analysis

This work presents various aspects of the analysis of nonlinear dynamical single-degree-of-freedom (SDOF) systems possessing two example polynomial-type restoring forces. The first is a lesser known purely nonlinear, single-term expression containing both the signum function and absolute-value function, thus possessing the property of becoming non-Lipschizian at specific system equilibrium points if the real but positive polynomial exponent is set to values smaller than one.  The second restoring force corresponds to the well-known Duffing-type.  For both automous conservative systems extreme values of the response and oscillation frequency are obtained in terms of exact analytical expressions.  Solutions for the phenomena of multiple harmonic frequency component are given, and nonlinear shock response spectra readily applicable to accurate response prediction in practice are presented. Time-varying exact closed-form solutions for both autonomous systems, either single or multiple term, are derived.  Employing the concept of differential transformation (DT) a set of algebraic equations is obtained that models the generalised dissipative nonautonomous time domain response behaviour.  The results obtained from both analytical approximate methods, single/multiple term solutions and DT, are compared to direct numerical integration Runge-Kutta routines.  It is shown that excellent agreement exists for both sets of results and that the newly derived methods are capable of even exceeding accuracy and computational performance of various commonly used Runge-Kutta algorithms.  Solution expressions for the transient nonconservative SDOF systems are readily applicable to multi-degree-of-freedom (MDOF) systems. A  rigorous uniqueness and stability analysis carried out for the oscillatory models considered in this work ensures that all of the obtained solutions are valid and feasible within their respective domain of definition.</p

Nonlinear transient structural response analysis

EThOS - Electronic Theses Online ServiceGBUnited Kingdo