Partitioning and bioaccumulation of PBDEs and PCBs in Lake Michigan

Water from Lake Michigan and fish from all five Great Lakes have been sampled and analyzed for a suite of six polybrominated diphenyl ether (PBDE) congeners and 110 polychlorinated biphenyl congeners (PCBs). The Lake Michigan dissolved phase PBDE congener concentrations (0.2 to 10 pg/L) are similar to dissolved phase PCB congener concentrations (nondetected to 13 pg/L). Partitioning of PBDEs between the particulate and dissolved phases exhibits behavior similar to that of PCBs. Organic-carbon-normalized water-particle partition coefficients (log K(OC)s) ranged from 6.2 to 6.5. Lake trout are depleted in BDE-99 relative to dissolved phase concentrations, and in contrast to what is expected from the PCB congener patterns. This reflects suspected debromination of BDE-99 in the food web of Lake Michigan. A regression of the log of the bioaccumulation factor (BAF) and the log of the octanol-water partition coefficent (K(OW)) indicated a positive relationship for both PCB congeners and PBDE congeners. BDE-99 does not appear to followthe same trend, a further indication that it is subject to biotransformation. Using the PBDE BAFs for Lake Michigan and the PBDE fish concentrations from the other Great Lakes it is expected that the dissolved phase concentrations of congeners in the other lakes would range from 0.04 to approximately 3 pg/L.     

The moisture content-equilibrium relative humidity relationships of five varieties of Canadian wheat and of candle rapeseed at different temperatures

The relationship between moisture content and equilibrium relative humidity was determined for five varieties of Canadian wheat over a range of temperatures both for adsorbing and desorbing grains. This was also done for a new variety of oilseed rape. The differences between varieties for wheat were small as were those between the Candle rapeseed and published data for older varieties. A durum variety of wheat maintained an e.r.h. of only 2% above those of the four hard red spring varieties. It seems to be adequate to examine only one or two varieties when determining moisture relationships of hard wheats.     

Fatty Acids Released from Milk Fat by Lipoprotein Lipase and Lipolytic Psychrotrophs

ABSTRACT: The ability of 13 different strains of psychrotrophs to release free fatty acids in milk was evaluated by using GC analysis. The 13 strains could be categorized into 3 groups: Group 1 consisted of bacteria that grew well and released large quantities of free fatty acids, group 2 consisted of bacteria that grew well but released low amounts of free fatty acids, and group 3 consisted of bacteria that did not grow well nor released large quantities of fatty acids. In group 1, 3 strains were determined to be highly lipolytic, releasing short‐chain fatty acids in amounts greater than reported threshold values. Group 3 consisted of 2 strains, which did not grow well in heat‐treated milk, and the subsequent release of free fatty acids was minor during the 10‐d monitoring time. The other 8 strains tested showed no specific pattern of fatty acid release and quantities of short‐chain fatty acids were not large, despite the ability to grow to high numbers in the treated milk. This work indicates that the lipolytic activity of psychrotrophs common in raw milk is specific to the species and a general prediction of free fatty acid release may not be possible.     

Estimation of heterogeneous variances using empirical Bayes methods: theoretical considerations.

Procedures are described to estimate variances when heterogeneity of genetic and residual dispersion parameters exists for some criterion. Genetic and residual variances are considered to follow distributions with either known or unknown parameters. The estimates of variances obtained are weighted averages of the corresponding parameter and of a data-based statistic. Although the techniques presented are largely inspired by Bayesian ideas, the procedures can be given a frequentist interpretation, and the parameters of the prior distributions can be estimated from the data at hand. Techniques are described and illustrated for situations in which animals are related or unrelated across herds. We conjecture that the proposed estimators have smaller mean squared error than those obtained by grouping observations in some way and then applying REML within each group.     

Nonlinear behavior of linear low-density polyethylene

To predict the response of polyethylene thin films subjected to stress for a long time, it is necessary to understand the influence of stress on either the relaxation modulus or creep compliance. Extensive testing has been conducted on 20-micron-thick samples of a particular linear low-density polyethylene film at temperatures from 23°C to −50°C. When reduced to creep compliance and compared with results from dynamic mechanical analysis (DMA), the influence of nonlinearities in the response function is apparent. However, the use of a two-step loading procedure has produced sufficient data to discriminate between the effect of stress on amplitude and time on the creep compliance. It has been found that a master curve of compliance generated by DMA equipment may be used in conjunction with certain nonlinear functions to accurately predict the response of the polyethylene. Perhaps of more importance is the observation that the principles of simple time-temperature superposition, commonly used with linear viscoelastic characterization, are insufficient for use with polyethylene films at most stress levels of interest.     

A Kinetic Model of Bacillus stearothermophilus α-Amylase under Process Conditions

A model is presented describing starch hydrolysis by Bacillus stearothermophilus α-amylase at temperatures of 90 to 115°C and substrate concentrations of 24 to 36% solids. First order kinetics adequately describe both the enzyme decay and starch hydrolysis reactions. Quantitation of temperature, pH, added calcium and substrate concentration interactive effects on the first order rate constants is aided by applying standard statistical techniques of experimental design and data analysis. A method for determining residual α-amylase activity in liquefact based on the Phadebas® dye release assay, and an osmometry method for determining degree of liquefact hydrolysis are described. Computer implementation of the model allows rapid graphical visualization as well as screening of ideas for improved starch hydrolysis processes.     

Heat degradation studies of solar heat transfer fluids

Destructive distillation of solar heat transfer fluids was conducted to determine the types of pyrolytic products which might be formed in solar collectors under conditions of stagnation or malfunction. The distillates were analyzed by gas chromatography/mass spectrometry (GC/MS) to determine the types of compounds which were present and the minor components which might be formed. Dehydration products were formed from ethylene and propylene glycols with ethylene oxide and propylene oxide being minor products. A high aromatic petroleum heat transfer fluid yielded distillation fractions enriched in quinolines or isoquinolines and methylated derivatives thereof. Fractionation of this aromatic heat transfer fluid showed that the basic fraction of unheated fluid also contained aza-arenes which exhibited mutagenic activity in the Ames' bioassay. GC/MS showed that the basic fraction from unheated heat transfer fluid also contained benzoquinolines which appeared to be lacking in heat degraded samples of the same fluid. Fractionation of heat transfer fluids, in particular petroleum-based fluids, may often be necessary in order to concentrate minor components so that they can be identified by GC/MS and in order to detect mutagenic activities without interference from cytotoxic components.