Rigorous uncertainty assessment in contaminant transport inverse modelling: a case study of fluoride diffusion through clay liners

Inverse methods used in assessing landfill liner design have not yet taken advantage of current developments in inverse procedures. Here, a method for inverting contaminant transport models is presented including a general error model and procedures for differentially weighted multiple response regression. General error models are employed in cases where the residuals are heteroscedastic and correlated, and lead to valid inference on model parameter and predictive uncertainty. The Shuffled Complex Evolution algorithm is used to optimise model parameters. Model parameter uncertainty is assessed by exploring the posterior probability distribution with the Metropolis algorithm, a Markov chain Monte Carlo sampling method. The inverse method is applied to simultaneously determine the sorption and diffusion parameters from laboratory diffusion cell experiments. In these experiments, fluoride migration through kaolin clays was measured by sampling the source and collector cells over time. To uniquely determine the transport model parameters, it was necessary to simultaneously fit the observed data from two independent diffusion cell experiments with different initial concentrations. The jointly fitted transport model parameters compared well with those fitted to independent batch experiments.     

PCDD/DFs and coplanar PCBs in fly ash samples from various types of incinerators in Taiwan

Polychlorinated dibenzo‐p‐dioxins and dibenzofurans (PCDD/DFs) and coplanar polychlorinated biphenyls (Co‐PCBs) were determined in fly ash samples from municipal solid waste (MSW), medical waste (MW), and electricity power plant incinerators in Taiwan. The average concentrations of PCDD/DFs and Co‐PCBs are 7.02 ng‐TEQ/g and 1.06 ng‐TEQ/g, respectively. The contributions to total TEQ are 24% from PCDDs, 64% from PCDFs, and 12% from Co‐PCBs, indicating that PCDFs generate the highest environmental impact and MSW and MW incinerators are potential Co‐PCBs contaminating sources. The levels of PCDD/DFs and Co‐PCBs found in ash samples increase from petroleum‐fired, coal‐fired, large municipal solid waste, small medical waste, to small municipal solid waste incinerators, and are generally lower than those from incinerators built earlier. All fly ash samples analyzed in this study were considered hazardous materials. More research is suggested to establish the relationship between the amounts of PCDD/DFs and Co‐PCBs in fly ash and in flue gas.     

Prenatal diagnosis and treatment of fetal long QT syndrome: a case report

We report a case of a fetus presenting with bradycardia, intermittent atrioventricular (AV) block, ventricular tachycardia (VT) and the signs of fetal congestive heart failure (ascites and scrotal hydrocele) during mid-gestation. Prenatal treatment with β-adrenergic blocker (propranolol) and digitalis glycosides was prescribed because of suspicion of long QT syndrome occurring with fetal congestive heart failure. The male baby was born at 39 weeks of gestation and showed a prolonged QT interval (QTc = 492 ms) and frequent variable AV block or alternating left and right bundle branch block, depending on the atrial rate. Prenatal administration of lidocaine failed to correct the fetal VT. Conversely, propranolol decreased the attack frequency of fetal VT. Postnatal administration of the K⁺ channel opener (nicorandil) successfully shortened the QT interval and improved the outcome. Copyright © 2002 John Wiley & Sons, Ltd.