Environmental Epidemiology

A Bayesian mixture modeling approach for assessing the effects of correlated exposures in case-control studies

by Frank de Vocht

Frank de Vocht, Nicola Cherry, jon Wakefield

Predisposition to a disease is usually caused by cumulative effects of a multitude of exposures and lifestyle factors... more Predisposition to a disease is usually caused by cumulative effects of a multitude of exposures and lifestyle factors in combination with individual susceptibility. Failure to include all relevant variables may result in biased risk estimates and decreased power, whereas inclusion of all variables may lead to computational difficulties, especially when variables are correlated. We describe a Bayesian Mixture Model (BMM) incorporating a variable-selection prior and compared its performance with logistic multiple regression model (LM) in simulated case–control data with up to twenty exposures with varying prevalences and correlations. In addition, as a practical example we re analyzed data on male infertility and occupational exposures (Chaps-UK). BMM mean-squared errors (MSE) were smaller than of the LM, and were independent of the number of model parameters. BMM type I errors were minimal (less than or equal to1), whereas for the LM this increased with the number of parameters and correlation between exposures. The numbers of type II errors were comparable. Re analysis of Chaps-UK data demonstrated more convincingly than by using a LM that occupational exposure to glycol ethers and VOCs are likely risk factors for male infertility. This BMM proves an appealing alternative to standard logistic regression when dealing with the analysis of (correlated) exposures in case–control studies.

Performance of a microenviromental model for estimating personal NO2 exposure in children

by Frank de Vocht

Anna Mölter, Sarah Lindley, Frank de Vocht, Raymond Agius, Gina Kerry,
Katy Johnson, Mike Ashmore, Andrew Terry, Sani Dimitroulopoulou, Angela Simpson

A common problem in epidemiological studies on air pollution is exposure misclassification, because investigators... more A common problem in epidemiological studies on air pollution is exposure misclassification, because investigators often assume exposure is equivalent to outdoor concentrations at participants’ homes or at the nearest urban monitor.

The aims of this study were: (1) to develop a new microenvironmental exposure model (MEEM), combining time-activity data with modelled outdoor and indoor NO2 concentrations; (2) to evaluate MEEM against data collected with Ogawa™ personal samplers (OPS); (3) to compare its performance against datasets typically used in epidemiological studies.

Schoolchildren wore a personal NO2 sampler, kept a time-activity diary and completed a questionnaire. This information was used by MEEM to estimate individuals’ exposures. These were then compared against concentrations measured by OPS, modelled outdoor concentrations at the children’s home (HOME) and concentrations measured at the nearest urban monitoring station (NUM).

The mean exposure predicted by MEEM (mean = 19.6 μg m−³) was slightly lower than the mean exposure measured by OPS (mean = 20.4 μg m−³). The normalised mean bias factor (0.01) and normalised mean absolute error factor (0.25) suggested good agreement. In contrast, the HOME (mean = 31.2 μg m−³) and NUM (mean = 28.6 μg m−³) methods overpredicted exposure and showed systematic errors.

The results indicate that personal exposure can be modelled by MEEM with an acceptable level of agreement, while methods such as HOME and NUM show a poorer performance.

Reconstructing the life-time lead exposure in children using dentine in deciduous teeth.

by Wendy Dirks

Authors: Shepherd TJ, Dirks W, Manmee C, Hodgson S, Banks DA, Averley P, Pless-Mulloli T

Data are presented to demonstrate that the circumpulpal dentine of deciduous teeth can be used to reconstruct a... more Data are presented to demonstrate that the circumpulpal dentine of deciduous teeth can be used to reconstruct a detailed record of childhood exposure to lead. By combining high spatial resolution laser ablation ICP-MS with dental histology, information was acquired on the concentration of lead in dentine from in utero to several years after birth, using a true time template of dentine growth. Time corrected lead analyses for pairs of deciduous molars confirmed that between-tooth variation for the same child was negligible and that meaningful exposure histories can be obtained from a single, multi-point ablation transect on longitudinal sections of individual teeth. For a laser beam of 100 μm diameter, the lead signal for each ablation point represented a time span of 42 days. Simultaneous analyses for Sr, Zn and Mg suggest that the incorporation of Pb into dentine (carbonated apatite) is most likely controlled by nanocrystal growth mechanisms. The study also highlights the importance of discriminating between primary and secondary dentine and the dangers of translating lead analyses into blood lead estimates without determining the age or duration of dentine sampled. Further work is in progress to validate deciduous teeth as blood lead biomarkers.

Serum Perfluorooctanoate (PFOA) and Perfluorooctane Sulfonate (PFOS) Concentrations and Liver Function Biomarkers in a Population with Elevated PFOA Exposure

by Giovanni Leonardi

Gallo V, Leonardi G, Genser B, Lopez-Espinosa M-J, Frisbee SJ, Karlsson L, et al. 2012. Serum Perfluorooctanoate (PFOA) and Perfluorooctane Sulfonate (PFOS) Concentrations and Liver Function Biomarkers in a Population with Elevated PFOA Exposure. Environ Health Perspect :-. http://dx.doi.org/10.1289/ehp.1104436

Inorganic Arsenic and Basal Cell Carcinoma in Areas of Hungary, Romania, and Slovakia: A Case-Control Study.

by Giovanni Leonardi

Leonardi G, Vahter M, Clemens F, Goessler W, Gurzau E, Hemminki K, Hough R, Koppova K, Kumar R, Rudnai P, Surdu S, Fletcher T. Inorganic Arsenic and Basal Cell Carcinoma in Areas of Hungary, Romania, and Slovakia: A Case-Control Study. Environ Health Perspect:120:721–726 (2012). http://dx.doi.org/10.1289/ehp.1103534 [Online 31 January 2012]

Lessons from six years of the HPA/LSHTM course: Introduction to Environmental Epidemiology

by Giovanni Leonardi

Long-term effects of flooding on mortality in England and Wales, 1994-2005: controlled interrupted time-series analysis

by Giovanni Leonardi

Heat-Related Calls To Nhs Direct: What Relevance To the Uk Heat Wave Plan?

by Giovanni Leonardi

Self-reported neurological symptoms in relation to CO emissions due to problem gas appliance installations in London: a cross-sectional survey

by Giovanni Leonardi

Age of Puberty in Relation to Perfluorooctanoic Acid

by Giovanni Leonardi

Tony Fletcher, Giovanni Leonardi, Maria-Jose Lopez-Espinosa, and
Ben Armstrong
London School of Hygiene and Tropical Medicine, London, United Kingdom.

ISEE 22nd Annual Conference, Seoul, Korea, 28 August–1 September 2010

Epidemiology • Volume 22, Number 1, p. S122, January Supplement 2011

Background/Aims: Perfluorooctanoic acid (PFOA, also known as C8) is widespread and has been shown to affect the... more Background/Aims: Perfluorooctanoic acid (PFOA, also known as C8) is widespread and has been shown to affect the reproductive cycle in rodents. One small study has reported an association between PFOA exposure and earlier development of pubertal maturation in girls.

Methods: A survey in a group of residents from the Ohio and West Virginia communities with PFOA water contamination was conducted in 2005–2006. Approximately 69,000 participants of all ages who had consumed drinking water for at least 1 year from sources with PFOA contamination, providing demographic information by questionnaire and blood samples. Serum was analyzed for PFOA, PFOS, and many clinical markers, including testosterone and estradiol hormones. The questionnaire
included questions on pregnancy and menstruation. In analyses focused on 10—17 year olds, the proportion of teenagers who had reached puberty at each age is estimated by the concentrations of hormones, and for girls, at the onset of menses.

Results: Analyses currently underway are assessing the relationship between the odds of having reached puberty at different ages in relationship to PFOA levels in serum, from which average delay in puberty for unit PFOA increase will be estimated. The principal potential confounder for which we have data is BMI which is included in the models.

Conclusion: As the numbers studied are large and the exposure contrasts very high for PFOA in this population, this study will be very informative on any association between age of puberty and this exposure.

Estimating previous exposure to arsenic for populations living in parts of Hungary, Romania and Slovakia

by Giovanni Leonardi

Perfluorooctanoic Acid (PFOA), Clinical Parameters, and Self-Reported Disease: A Cross-sectional Study

by Giovanni Leonardi

Long-term arsenic exposure and cancer risk-sensitivity to choice of indicators based on recent and lifetime arsenic intake

by Giovanni Leonardi

Immune biomarkers in relation to exposure to particulate matter: a cross-sectional survey in 17 cities of Central Europe

by Giovanni Leonardi

The Long-Term Mortality Effects of Flooding in England and Wales, 1994 to 2005

by Giovanni Leonardi

Association of Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS) with Age of Puberty among Children Living near a Chemical Plant

by Giovanni Leonardi

Immune Markers in a Community Exposed to PFOA: Findings from the C8 Science Panel Study

by Giovanni Leonardi

Selection of controls for hospital-based case-control studies using retrospective data on the geographic distribution of cases and controls

by Giovanni Leonardi

Methodological approaches to the analysis of hierarchical studies of air pollution and respiratory health-examples from the CESAR study

by Giovanni Leonardi

2.8 The global environment

by Hilary Bambrick