Considerations when choosing a threshold of regulation for acute dietary exposure to pesticides.
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Diet↗
Biomedical subjects
B J Petersen
Publications and source records attributed to B J Petersen.
Pesticide residues in food: problems and data needs.
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Child↗
Probabilistic modelling: theory and practice.
Probabilistic modelling techniques allow much more realistic estimates of exposure and risk by computing the use of the full range of potential exposures rather than single 'worst case' exposures. However, these techniques require additional considerations regarding the appropriate data and models. This article reviews the theoretical aspects of probabilistic modelling and also considers some of the practical applications. The most common method, called Monte Carlo analysis, is discussed in some detail. The practical application of Monte Carlo to risk assessments is presented along with an evaluation of the input parameters. Topics also discussed include considerations of the requirements for precision and procedures for validation of assessments.
Food Contamination↗
Use of food-intake surveys to estimate exposures to nonnutrients.
Several steps must be taken in estimating intake of (or exposure to) dietary nonnutrients such as additives, drug residues, pesticide residues, toxicants, and natural nontoxicant chemicals. The first step involves consideration of relevant characteristics of the nonnutrient, including biological activity, physical/geographical sources, distribution in the food supply, typical concentrations, and the desirability of intake. After reviewing chemical characteristics, appropriate food-consumption data to use in the exposure assessment must be identified and obtained. Survey methodology must be reviewed carefully to determine compatibility with the characteristics of the chemical. The best available nonnutrient concentration data must be identified and obtained and the exposure models must be chosen. Available models include average exposure, simple distribution, joint distribution, and commodity contribution.
Adolescent↗
An alternative approach to dietary exposure assessment.
The method of dietary exposure assessment currently used by the Environmental Protection Agency (EPA), the Dietary Residue Evaluation System (DRES), combines a consumption distribution derived from the United States Department of Agriculture (USDA) 1977-1978 Nationwide Food Consumption Survey (NFCS) with a single estimate of residue level. The National Academy of Sciences recommended that EPA incorporate both the distribution of residues and the distribution of consumption into their exposure assessment methodology and proposed using a Monte Carlo approach. This paper presents an alternative method, the Joint Distributional Analysis (JDA), that combines the consumption and residue distributions, without relying on random sampling or fitting theoretical distributions like the Monte Carlo method. This method permits simultaneous analysis of the entire diet, including assessing exposure from residues in different foods.
Aldicarb↗
Coincident secretion of follicle-stimulating hormone and luteinizing hormone in early postpartum beef cows: effects of suckling and low-level increases of systemic progesterone.
The current experiment was conducted with beef cows during the first 2 weeks postpartum (PP) to determine the effects of suckling and low-level increases of systemic progesterone on secretory characteristics of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in peripheral plasma. Variables measured included mean gonadotropin concentrations, FSH/LH pulse frequencies, pulse amplitudes and synchrony of coincident release. Suckled (S) cows had lower (P less than 0.01-P less than 0.05) mean concentrations of FSH and LH in plasma, lower (P less than .05) FSH and LH pulse frequencies and a lower (P less than 0.05) pulse synchrony (21.6 vs 72.3% coincident pulses) than nonsuckled (NS) cows on Day 7 PP. Neither FSH nor LH pulse amplitude was affected by suckling. Similar differences existed for mean gonadotropin concentrations, pulse frequencies and pulse synchrony on Day 14 PP between S and NS cows. Implanting cows with progesterone implants on Day 7 PP, which chronically increased plasma progesterone to 0.5-0.6 ng/ml, increased (P less than 0.05) mean plasma FSH and LH concentrations, FSH and LH pulse frequencies and pulse synchrony (87.5 vs. 66.3%) in NS-implanted (NSI) versus NS-nonimplanted (NSNI) cows. Progesterone implants had no beneficial effect in S cows. Thus, three major findings seem pertinent: 1) associated with the suckling-induced depression of episodic gonadotropin release was a marked decline in FSH/LH pulse synchrony; 2) a high degree of FSH/LH pulse synchrony (72-88%) was restored in the absence of suckling when gonadotropin pulse frequency increased to 4-5/6 h; 3) the absence of suckling, followed by the provision of low-level progesterone stimulation for 7 days, appeared to have additive effects on FSH and LH secretion. These results provide evidence that the neuroendocrine block associated with suckling in early PP beef cows is, in addition to being associated with depressed LH release, comprised of characteristic anomalies in FSH secretion, FSH/LH pulse synchrony and failure to respond to a putative hypothalamo-hypophyseal potentiator, progesterone.
Animals↗
Alcohol dehydrogenase in cultured human skin fibroblasts. Human fibroblast alcohol dehydrogenase.
Studies of ethanol oxidation and other metabolic pathways in humans are often limited by the availability of a reproducible test material. Because of this we have tested human fibroblasts for ethanol metabolism and alcohol dehydrogenase content. Seven different cell lines have been studied and found to contain an enzymatic activity identified as alcohol dehydrogenase by the following criteria: it is NAD+-dependent, the Km for ethanol is like human liver, it is completely inhibited by 25 microM 4-pentylpyrazole. The fibroblast activity was analyzed by isoelectric focusing and found to contain several isozymes also present in the human liver sample. In addition, fibroblasts contain 2 major isozymes which migrate anodally to any isozymes previously reported in human liver. Thus, fibroblasts appear to be useful material for comparing enzymatic aspects of ethanol metabolism in alcoholics and nonalcoholics.
Acetaldehyde↗
Cardiac structure and function in vitamin B-12-deprived rats.
The effect of prolonged vitamin B-12 deprivation in rats on the histological structure of heart and on cardiac linoleic acid oxidation has been investigated. Offspring from pregnant females fed vitamin B-12-deficient diets were fed the deprivation diet for up to 16 months, and the development of B-12 deficiency was monitored by determination of urinary methylmalonic acid levels. These levels averaged 4.2 mg/day by 9 months of B-12-deprivation diet, and 142 mg/day after 16 months. The hearts of these animals were characterized by extensive fibrosis, and electron microscopy revealed cardiac mitochondria that were grossly enlarged and distorted. The metabolic defect of B-12 deprivation in heart muscle was determined in isolated hearts during recirculating perfusion of labeled propionic acid. Both the uptake and oxidation of propionic acid were markedly reduced in hearts from B-12-deprived rats (16 months) compared with controls, and the site of the metabolic block, i.e., accumulation of labeled methylmalonate, was established. Vitamin B-12 deprivation did not affect the extraction of recirculating labeled linoleic acid by perfused hearts, in contrast to the effect on propionic extraction. Furthermore, the oxidation of the extracted fatty acid was markedly increased over controls. Analysis of the circulating media after 45-minute perfusions showed no accumulation of labeled methylmalonate but did contain significantly less succinate than perfusion media from control hearts. The results are discussed with respect to cardiac structure and to the oxidative pathway(s) for polyunsaturated fatty acids.
Animals↗
Lack of effect of chronic nicotine administration on fatty acid distribution in the liver, testis, and adipose tissue of male Fischer-344 rats.
A comparison is made of the percentage compositions of major fatty acids in liver and testis phospholipids, liver and abdominal adipose tissue triglycerides, and liver sterol esters in male Fischer-344 rats administered a physiological saline control or a "smoking" dose of nicotine (1000 micro g base/kg/day, subcutaneously) for 2 or 22 months. Results indicate that there is no major trend, or significant difference, between nicotine- or saline-treated rats with respect to major fatty acid distribution. Some differences in fatty acid distribution in the various lipid fractions were found between young and old rats.
Adipose Tissue↗
Development of a Dietary Exposure Potential Model for evaluating dietary exposure to chemical residues in food.
The Dietary Exposure Potential Model (DEPM) is a computer-based model developed for estimating dietary exposure to chemical residues in food. The DEPM is based on food consumption data from the 1987-1988 Nationwide Food Consumption Survey (NFCS) administered by the United States Department of Agriculture (USDA) and on residue data from government-sponsored monitoring programs. Foods reported in the NFCS were categorized into exposure core foods (ECFs). A computer program for DOS-based personal computers was developed to link consumption of the ECFs with residue values observed in the foods. The data files utilized by the DEPM were designed in dBASE IV with FoxPro for Windows applications programs for queries and reporting. The program calculates exposure estimates for categories of core foods, such as grain dishes, fruits, or vegetables; for individual core foods, such as wheat and apple combination dishes; and for individual foods, such as apples or carrots. The program, residue summary databases, and core food consumption database permit the analyst to evaluate potential exposure of several population groups to various chemicals via the diet. The DEPM is not intended for risk assessments, but is a suitable tool for identifying data gaps and establishing priorities for research, and for identifying potentially significant foods for human exposure monitoring.
Adult↗