Exposure Estimation in the Presence of Nondetectable Values: Another Look

Limited data are available on the background levels of exposure to synthetic pyrethroid (PYR) in Japan despite their frequent application for agriculture and indoor extermination and possible effects of chronic and/or low-dose PYR exposure on human health. This study was conducted to describe the level and distribution of one of the major PYR metabolites, 3-phenoxybenzoic acid (3-PBA), in urine samples collected from a general population in Japan. The subjects were 535 individuals (184 men and 351 women; 61.5 ± 9.8 years of age, mean ± S.D.) residing in a town in Hokkaido, a dairy and agricultural area. Urinary 3-PBA was found detectable in 98% of samples above the limit of detection of 0.02 μg/L. The geometric mean values of urinary 3-PBA in occupationally exposed farmers (n = 87) and the remaining general group without occupational exposure (n = 448) were 0.38 μg/L and 0.29 μg/L, respectively, ranging from < LOD to 17.09 μg/L. No significant differences in urinary 3-PBA concentrations were shown between these two groups. Moreover, 3-PBA concentrations were found comparable to those reported in some countries. The present study is, to our knowledge, the first report of a biological monitoring study of urinary 3-PBA, which elucidated the background environmental exposure level of PYR in the Japanese general population without occupational exposure. Further nationwide studies covering different seasons and age distribution are needed to monitor the urinary 3-PBA levels in Japan.

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“…Undetectable urinary 3-PBA concentrations were estimated as half the limit of detection (LOD) value (Finkelstein et al, 2001). …”

Section: Discussionmentioning

confidence: 99%

Urinary excretion of 3-phenoxybenzoic acid in middle-aged and elderly general population of Japan

Ueyama¹,

Kimata²,

Kamijima³

et al. 2009

Environmental Research

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“…Initially, 16 metrics were created from the transformed cortisol measurements to represent different aspects of the overall cortisol response. Seven metrics of biological plausibility were then selected for further analysis (Figure 1): pretest level (the first sample level), mean level (mean of all samples), area under the curve with respect to zero (AUC), 36 AUC with respect to baseline (AUC b ), variance (variance of all 4 samples), slope 12 (slope from samples 1-2), and slope 34 (slope from samples 3-4).…”

Section: Creation Of Cortisol Metricsmentioning

confidence: 99%

Associations of Salivary Cortisol With Cognitive Function in the Baltimore Memory Study

Lee¹,

Glass²,

McAtee³

et al. 2007

Arch Gen Psychiatry

230

165

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Context:The stress responses of the hypothalamicpituitary-adrenal axis can produce adverse effects on the brain. Previous studies have concluded that an elevated level of cortisol is a risk factor for cognitive dysfunction and decline in aging but have been limited by sex exclusion, restricted cognitive batteries, and small sample sizes.Objective: To examine associations among salivary cortisol metrics and cognitive domain scores in an urban adult population.Design, Setting, and Participants: A crosssectional analysis was conducted using data from a longitudinal study involving 1140 Baltimore, Maryland, residents aged 50 to 70 years. Four salivary cortisol samples were obtained from 967 participants across 1 study visit (before, during, and after cognitive testing as well as at the end of the visit) from which 7 cortisol metrics were created. We examined associations of cortisol metrics with cognitive performance using multiple linear regression. Main Outcome Measures:Performance on 20 standard cognitive tests was measured and combined to form summary measures in 7 domains (language, processing speed, eye-hand coordination, executive functioning, verbal memory and learning, visual memory, and visuoconstruction).Results: Higher levels of pretest and mean cortisol as well as the area under the curve of cortisol over the study visit were associated with worse performance (PϽ.05) in 6 domains (language, processing speed, eye-hand coordination, executive functioning, verbal memory and learning, and visual memory). For instance, an interquartile range increase in the area under the curve was equivalent to a decrease in the language score expected from an increase in 5.6 (95% confidence interval, 4.2-7.1) years of age.Conclusions: Elevated cortisol was associated with poorer cognitive function across a range of domains in this large population-based study. We believe the findings are consistent with the hypothesis that hypothalamic-pituitaryadrenal axis dysregulation may be a risk factor for poorer cognitive performance in older persons. Psychiatry. 2007;64(7):810-818 Arch Gen

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“…In the β-substitution method, the LOD is substituted with a data-dependent β-factor multiplied by the LOD (Ganser and Hewett, 2010). In the parametric ML method, the parameters are estimated by maximizing the likelihood function, which is a product of the probability density function (PDF) for the measurements greater than the LOD and the cumulative distribution function (CDF) for the measurements less than the LOD (Fisher,1925;Cohen, 1959Cohen, , 1961Finkelstein and Verma, 2001). Probability plot-based methods [also known as regression on order statistics (ROS) or log-probit regression (LPR)] computes the mean and standard deviation by fitting a linear regression of the log-transformed data versus their normal scores on a normal or lognormal probability plot (Kroll and Stedinger, 1996;Helsel and Cohen, 1988;Gilliom and Helsel, 1986).…”

Section: Introductionmentioning

confidence: 99%

A Comparison of the β-Substitution Method and a Bayesian Method for Analyzing Left-Censored Data

Huynh

Quick

Ramachandran

et al. 2015

ANNHYG

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Classical statistical methods for analyzing exposure data with values below the detection limits are well described in the occupational hygiene literature, but an evaluation of a Bayesian approach for handling such data is currently lacking. Here, we first describe a Bayesian framework for analyzing censored data. We then present the results of a simulation study conducted to compare the β-substitution method with a Bayesian method for exposure datasets drawn from lognormal distributions and mixed lognormal distributions with varying sample sizes, geometric standard deviations (GSDs), and censoring for single and multiple limits of detection. For each set of factors, estimates for the arithmetic mean (AM), geometric mean, GSD, and the 95th percentile (X 0.95 ) of the exposure distribution were obtained. We evaluated the performance of each method using relative bias, the root mean squared error (rMSE), and coverage (the proportion of the computed 95% uncertainty intervals containing the true value). The Bayesian method using non-informative priors and the β-substitution method were generally comparable in bias and rMSE when estimating the AM and GM. For the GSD and the 95th percentile, the Bayesian method with non-informative priors was more biased and had a higher rMSE than the β-substitution method, but use of more informative priors generally improved the Bayesian method's performance, making both the bias and the rMSE more comparable to the β-substitution method. An advantage of the Bayesian method is that it provided estimates of uncertainty for these parameters of interest and good coverage, whereas the β-substitution method only provided estimates of uncertainty for the AM, and coverage was not as consistent. Selection of one or the other method depends on the needs of the practitioner, the availability of prior information, and the distribution characteristics of the • 56Ann. Occup. Hyg., 2016, Vol. 60, No. 1, 56-73 doi:10.1093/annhyg/mev049 Advance Access publication 24 July 2015 measurement data. We suggest the use of Bayesian methods if the practitioner has the computational resources and prior information, as the method would generally provide accurate estimates and also provides the distributions of all of the parameters, which could be useful for making decisions in some applications.

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Exposure Estimation in the Presence of Nondetectable Values: Another Look

Cited by 90 publications

References 4 publications

Urinary excretion of 3-phenoxybenzoic acid in middle-aged and elderly general population of Japan

Urinary excretion of 3-phenoxybenzoic acid in middle-aged and elderly general population of Japan

Associations of Salivary Cortisol With Cognitive Function in the Baltimore Memory Study

A Comparison of the β-Substitution Method and a Bayesian Method for Analyzing Left-Censored Data

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