Evaluation of the Uncertainty in an Oral Reference Dose for Methylmercury Due to Interindividual Variability in Pharmacokinetics

An analysis of the uncertainty in guidelines for the ingestion of methylmercury (MeHg) due to human pharmacokinetic variability was conducted using a physiologically based pharmacokinetic (PBPK) model that describes MeHg kinetics in the pregnant human and fetus. Two alternative derivations of an ingestion guideline for MeHg were considered: the U.S. Environmental Protection Agency reference dose (RfD) of 0.1 g/kg/day derived from studies of an Iraqi grain poisoning episode, and the Agency for Toxic Substances and Disease Registry chronic oral minimal risk level (MRL) of 0.5 g/kg/day based on studies of a fish-eating population in the Seychelles Islands. Calculation of an ingestion guideline for MeHg from either of these epidemiological studies requires calculation of a dose conversion factor (DCF) relating a hair mercury concentration to a chronic MeHg ingestion rate. To evaluate the uncertainty in this DCF across the population of U.S. women of child-bearing age, Monte Carlo analyses were performed in which distributions for each of the parameters in the PBPK model were randomly sampled 1000 times. The 1st and 5th percentiles of the resulting distribution of DCFs were a factor of 1.8 and 1.5 below the median, respectively. This estimate of variability is consistent with, but somewhat less than, previous analyses performed with empirical, one-compartment pharmacokinetic models. The use of a consistent factor in both guidelines of 1.5 for pharmacokinetic variability in the DCF, and keeping all other aspects of the derivations unchanged, would result in an RfD of 0.2 g/kg/day and an MRL of 0.3 g/kg/day.     

Assessing the Accuracy of Self-Reported Data: an Evaluation of the Toxics Release Inventory

Self-reported regulatory data are hard to verify. This article compares air emissions reported by plants in the Toxics Release Inventory with chemical concentration levels measured by EPA pollution monitors. We find that the large drops in air emissions reported by firms in the TRI are not always matched by similar reductions in measured concentrations from EPA monitors. When the first digits of the monitored chemical concentrations follow a monotonically decreasing distribution, we expect (via Benford's Law) a similar distribution of first digits for the TRI data. For lead and nitric acid the self-reported data do not follow the expected first digit pattern. This suggests that for these two heavily regulated chemicals plants are not reporting accurate estimates of their air emissions. JEL Classification K32, Q53     

Visualities of strategic vision: Lookout Mountain Laboratory and the deterrent state from nuclear tests to Vietnam

This article considers two visual cultures of America’s deterrent state in the Cold War, the cinematic and cybernetic, by following the history of the 600th Photographic Squadron of the United States (US) Air Force in Vietnam and its 1950s progenitor, the 1352nd Motion Picture Squadron, or Lookout Mountain Laboratory. We argue that cinematic and cybernetic visual cultures were at the heart of a Cold War visual alliance that was also a Cold War visual contest, and cameras were situated at the centre of the contest. Specifically, the cinematic and the cybernetic represent two distinct visualities of vision, as the Cold War cameras of the Air Force assumed either transcendental or transcendent positions. The former, in keeping with a cinematic visuality, was oriented towards casting America as a sight to see in the context of its war on communism, with cameras operating as a condition of possibility for the construction of the ‘image’, whereas the latter, in keeping with a cybernetic visuality, was oriented towards the American appetite to see, to monitor and survey the world over, with cameras operating as processors of ‘information’. The history of the 600th Photographic Squadron and its progenitor, Lookout Mountain Laboratory, suggests that the transition from cinematic to cybernetic visualities of vision was part of a broader transformation in the US Cold War state from a nuclear deterrent state to a supra-nuclear deterrent state.     

A value of information framework for assessing the trade-offs associated with uncertainty,duration, and cost of chemical toxicity testing

A number of investigators have explored the use of value of information (VOI) analysis to evaluate alternative information collection procedures in diverse decision-making contexts. This paper presents an analytic framework for determining the value of toxicity information used in risk-based decision making. The framework is specifically designed to explore the trade-offs between cost, timeliness, and uncertainty reduction associated with different toxicity-testing methodologies. The use of the proposed framework is demonstrated by two illustrative applications which, although based on simplified assumptions, show the insights that can be obtained through the use of VOI analysis. Specifically, these results suggest that timeliness of information collection has a significant impact on estimates of the VOI of chemical toxicity tests, even in the presence of smaller reductions in uncertainty. The framework introduces the concept of the expected value of delayed sample information, as an extension to the usual expected value of sample information, to accommodate the reductions in value resulting from delayed decision making. Our analysis also suggests that lower cost and higher throughput testing also may be beneficial in terms of public health benefits by increasing the number of substances that can be evaluated within a given budget. When the relative value is expressed in terms of return-on-investment per testing strategy, the differences can be substantial.     

U.S. Citizen Children De Facto Deported to Mexico

Between 2000 and 2015, the U.S. deported unprecedented numbers of Mexican immigrants. During the same period, the population of U.S.-born children living in Mexico doubled in size. This study estimates the number of U.S.-born children who emigrated to Mexico from the United States in order to accompany a deported parent: de facto deported children. The data come from the Mexican National Survey of Demographic Dynamics (ENADID), a national probability sample of households in Mexico collected in 2014 and 2018. About one in six U.S.-born children living in Mexico in 2014/2018, amounting to an estimated 80,000–100,000 U.S.-born children, were there because the U.S. government deported one or both of their parents. De facto deported U.S.-born children are socioeconomically disadvantaged in Mexico compared to U.S.-born children whose parents migrate to Mexico for other reasons. Women are overrepresented among deported people who bring their U.S.-born children to Mexico, and when deported mothers bring their children, they are far less likely to do so with a partner than are deported fathers. U.S. policy should consider the interests of U.S. citizen children forced to live abroad when redesigning immigration and child welfare policies.