MFO induction in fish by filtrates from chlorine dioxide bleaching of wood pulp.

Spent bleaching liquors from pulp bleached with chlorine dioxide were assessed for their potency to induce hepatic mixed function oxygenase enzymes (MFO) in rainbow trout, as indicated by activity of ethoxyresorufin-o-deethyase (EROD). Filtrates were collected from two kraft mills in Central Canada to assess the potency of filtrates from hardwood and softwood bleaching. All mill-scale bleaching filtrates induced MFO activity, and filtrates from softwood pulp bleaching appeared more potent than filtrates from hardwood bleaching. Filtrates from the final bleaching stage were most potent, and filtrates from the first stage were the least potent. In laboratory bench-scale bleaching experiments, pulp from softwood and hardwood kraft mills in Eastern Canada was bleached via an industry-standard 5-stage chlorine dioxide bleaching sequence. The filtrates were collected and used in fish bioassays to assess EROD-inducing potency. Potency of bench-scale filtrates varied depending on wood furnish (i.e. softwood vs. hardwood) and the bleaching stage, with all bench-scale filtrates being much weaker EROD inducers than mill-scale filtrates. Recycled paper mill washwater is a possible source of compounds causing increased potency of the mill-scale filtrates.

Improved preparation of cholesterol calibration and control sera.

We prepared several serum batches with various cholesterol concentrations, to be used as calibrators and controls in a proficiency testing program of an organization in The Netherlands that is in charge of the standardization of cholesterol determinations for epidemiological purposes. The sera were of human origin, to avoid abnormal matrix effects. To decrease the cholesterol content in some samples, we adsorbed them onto colloidal silicic acid. To increase it, we added lipoproteins that had been precipitated from human serum with heparin and calcium ions. The precipitation method we used allowed us to dilute the serum as little as possible and to keep the final concentrations of calcium and heparin as low as possible, while maintaining a high cholesterol content. By mixing these sera having high and low cholesterol concentrations, we could prepare batches with any desired concentration. The stabilities of these sera were excellent. We used the sera to calibrate enzymic determinations of cholesterol.

Gas-chromatographic determination of cholesterol in serum: candidate reference method.

We present a candidate Reference Method for determination of total cholesterol in serum. The method is based on high-resolution capillary gas chromatography, and we took special precautions with respect to weighing, calibration, and chromatographic peak integration. Analytical recovery of added cholesterol was essentially complete (99.99%, SD 0.48%) and reproducibility was excellent (total CV 0.35-0.50%). When cholesterol was determined in a reference serum certified by means of an established candidate Definitive Method, no significant bias could be detected.