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Biomedical subjects

N C Freeman

Publications and source records attributed to N C Freeman.

At least 19 recordsLinked to original sources
PubMed2001

Measurement of children's exposure to pesticides: analysis of urinary metabolite levels in a probability-based sample.

The Minnesota Children's Pesticide Exposure Study is a probability-based sample of 102 children 3-13 years old who were monitored for commonly used pesticides. During the summer of 1997, first-morning-void urine samples (1-3 per child) were obtained for 88% of study children and analyzed for metabolites of insecticides and herbicides: carbamates and related compounds (1-NAP), atrazine (AM), malathion (MDA), and chlorpyrifos and related compounds (TCPy). TCPy was present in 93% of the samples, whereas 1-NAP, MDA, and AM were detected in 45%, 37%, and 2% of samples, respectively. Measured intrachild means ranged from 1.4 microg/L for MDA to 9.2 microg/L for TCPy, and there was considerable intrachild variability. For children providing three urine samples, geometric mean TCPy levels were greater than the detection limit in 98% of the samples, and nearly half the children had geometric mean 1-NAP and MDA levels greater than the detection limit. Interchild variability was significantly greater than intrachild variability for 1-NAP (p = 0.0037) and TCPy (p < 0.0001). The four metabolites measured were not correlated within urine samples, and children's metabolite levels did not vary systematically by sex, age, race, household income, or putative household pesticide use. On a log scale, mean TCPy levels were significantly higher in urban than in nonurban children (7.2 vs. 4.7 microg/L; p = 0.036). Weighted population mean concentrations were 3.9 [standard error (SE) = 0.7; 95% confidence interval (CI), 2.5, 5.3] microg/L for 1-NAP, 1.7 (SE = 0.3; 95% CI, 1.1, 2.3) microg/L for MDA, and 9.6 (SE = 0.9; 95% CI, 7.8, 11) microg/L for TCPy. The weighted population results estimate the overall mean and variability of metabolite levels for more than 84,000 children in the census tracts sampled. Levels of 1-NAP were lower than reported adult reference range concentrations, whereas TCPy concentrations were substantially higher. Concentrations of MDA were detected more frequently and found at higher levels in children than in a recent nonprobability-based sample of adults. Overall, Minnesota children's TCPy and MDA levels were higher than in recent population-based studies of adults in the United States, but the relative magnitude of intraindividual variability was similar for adults and children.

Adolescent↗
PubMed2000

Reduction in residential chromium following site remediation.

The purpose of this study was to determine the influence of chromate production waste site remediation on residential Cr concentrations in house dust. Twenty-three homes in Jersey City, NJ, were identified as having had high (> 500 micrograms/gm, median 739 micrograms/gm), medium (100-400 micrograms/gm, median 245 micrograms/gm), or low (< 100 micrograms/gm, median 48 micrograms/gm) Cr in house dust during a study conducted in 1992-1993 prior to site remediation. House dust samples were collected on four visits from each home between November 1996 and February 1998, extracted with HNO3, and analyzed for Cr with an inductively coupled plasma-mass spectrometer. Homes that had low Cr concentrations in 1992-1993 continued to have low Cr concentrations (median 1 microgram/g). In contrast, substantial declines in Cr concentrations were found in the house dust collected from homes located near the remediated waste sites: previously high-level homes had a median of 50 micrograms/g and mid-level homes had a median of 34 micrograms/g. Site remediation had a beneficial effect on household loadings of Cr, since no differences in post-remediation house dust Cr concentrations were found among the three groups.

Air Pollution, Indoor↗
PubMed2000

Children's exposure assessment: a review of factors influencing Children's exposure, and the data available to characterize and assess that exposure.

We review the factors influencing children's exposure to environmental contaminants and the data available to characterize and assess that exposure. Children's activity pattern data requirements are demonstrated in the context of the algorithms used to estimate exposure by inhalation, dermal contact, and ingestion. Currently, data on children's exposures and activities are insufficient to adequately assess multimedia exposures to environmental contaminants. As a result, regulators use a series of default assumptions and exposure factors when conducting exposure assessments. Data to reduce uncertainty in the assumptions and exposure estimates are needed to ensure chemicals are regulated appropriately to protect children's health. To improve the database, advancement in the following general areas of research is required: identification of appropriate age/developmental benchmarks for categorizing children in exposure assessment; development and improvement of methods for monitoring children's exposures and activities; collection of activity pattern data for children (especially young children) required to assess exposure by all routes; collection of data on concentrations of environmental contaminants, biomarkers, and transfer coefficients that can be used as inputs to aggregate exposure models.

Administration, Cutaneous↗
PubMed1998

The association of chromium in household dust with urinary chromium in residences adjacent to chromate production waste sites.

Several previous studies of exposure to chromium waste in New Jersey have shown that Cr levels are elevated in household dust in homes adjacent to waste sites and that Cr levels in the urine of residents near sites are also elevated compared to control populations. It has not been possible until now, however, to examine these external and internal measures of exposure together in a large population to determine whether the external exposure is predictive of the internal exposure. We investigated the relationship between various adjusted and unadjusted measures of spot urine Cr concentration and household dust Cr from residents and residences adjacent to known Cr waste sites. Statistically significant bivariate relationships were found between log-transformed urine Cr concentration and Cr dust concentration (micrograms of Cr per gram of dust) but not Cr dust loading (nanogram Cr per square centimeter). Log-transformed urine concentration was used as the dependent variable in multiple regression analysis of the total population (n = 329), the population [less than/equal to] 10 years old (n = 67), and the population >10 years old (n = 262), with Cr dust concentration as a mandatory independent variable. Other potential direct influences on urine Cr were investigated as potential confounders of this relationship. In the final models for the entire population and those [less than/equal to] 10 years old, but not for those >10 years old, Cr dust concentration remained significant. This suggests that exposure of young children to Cr in household dust accounts for much of the relationship in the entire population.

Adolescent↗
PubMed1995

The effect of remediation of chromium waste sites on chromium levels in urine of children living in the surrounding neighborhood.

Exposure to chromium was assessed for 40 children living near chromium waste sites. Sampling was conducted in one Jersey City, New Jersey neighborhood during the summer and fall of 1991. Household dust samples from residences and urine samples from children living near chromium waste sites were collected and analyzed for chromium. During the summer and fall visits when the samples were collected, the children were also interviewed about lifestyle/activity patterns. Comparisons were made with similar samples collected from children and homes in other areas of New Jersey outside of Hudson County with no known chromium waste sites. Household dust masses and chromium loadings and concentrations in the dust showed a significant decline in this Hudson County neighborhood since the area was first sampled in 1990. Interim remediation of neighborhood sites and an active community education program in the interval between the first and second year of sampling may have contributed to the reduction in dust masses and chromium levels in dust. Children's urine chromium concentrations were consistent across the two sampling periods despite reported changes in activity patterns. Chromium concentrations in urine were found to be age-dependent and related to home location. In this sample of Jersey City children less than six years old, time spent playing outdoors was a weak secondary contributor to urine chromium levels.

Child↗
PubMed1992

Residential exposure to chromium waste--urine biological monitoring in conjunction with environmental exposure monitoring.

To determine whether a population living on or adjacent to four sites of chromate production waste was measurably exposed to environmental chromium, spot samples of urine were collected along with wipe samples of household dust and lifestyle/activity interview data. Findings were compared to those from a control population in two communities with no significant chromium use or waste sites. Urine samples were collected and analyzed, employing measures to minimize background chromium contamination. The average Cr mass in dust was 3.7 times that in control houses. The mean creatinine-corrected urine Cr (Cr/c) level of the exposed subgroup residing in households in the 75th percentile of Cr mass in wipe samples was significantly greater than that of the control population. This subgroup was primarily located at a single exposure location. Using lifestyle/activity data, significantly elevated Cr/c urine levels were identified in other exposed subgroups defined by employment location and by outside play time. These data show an association between elevated exposure to chromium in household dust and elevated urine levels of chromium, consistent with residential exposure to chromate production waste. These data also suggest an association between chromium exposure and activities outside the home which are consistent with exposure to chromate production waste.

Adolescent↗
PubMed1992

Microenvironmental analysis of residential exposure to chromium-laden wastes in and around New Jersey homes.

The purpose of this study was to identify the significant microenvironments that can lead to chromium exposure in Hudson County, New Jersey residential settings near or on soil contaminated with chromium waste. Measurements were made in indoor air, outdoor air, and house dust. Surface dust was found to be the best index of potential Cr exposure. The values of Cr in Hudson County household dust ranged from 3.25-320 ng/cm2 in wipe samples and 1.0-12 ng/cm2 in vacuum samples. Elevated Cr in household dust was found to be related to residential locations near large chromium waste sites, household cleaning habits, and house renovation activities. Outdoor Cr air levels were similar to those obtained in other urban areas at these seasons of the year, approximately 5-7 ng/m3. Comparisons with measurements of the Cr levels in urine found that the elevated Cr in dust was associated with elevated excretion of Cr. Site-specific Cr differences in household dust suggest different sources and routes of exposure. Within the total group of homes in the present study, Cr in household dust was the major influence on household exposure.

Air Pollutants↗
PubMed1991

Design and evaluation of a location and activity log used for assessing personal exposure to air pollutants.

As part of the Total Human Environmental Exposure Study (THEES), a self-administered questionnaire was developed to identify sources of exposure to BaP and PM-10. Thirteen participants in ten households completed a daily personal activity log for fourteen consecutive days during January 1988. Validation of the instrument was obtained in three ways: internal questionnaire checks, comparison with pre-sampling estimates of time/activity patterns, and comparison with earlier studies. The log was found to be easy for participants to use and reliable in most of its questions. Effectiveness of the log in identifying sources of exposure was enhanced by having most responses in the form of continuous variables. While most of personal exposure to both BaP and PM-10 could be attributed to outdoor sources, a variety of household sources and personal activities were also identified. Higher levels of PM-10 were associated with use of unvented kerosene space heaters and coalstoves, stove-top cooking, ETS, and house cleaning. Personal exposure to BaP was primarily associated with ambient levels, and secondarily with ETS, coalstove use, and cooking activities.

Adult↗
PubMed1986

Dorsal horn cells in the cat responding to stimulation of the plantar cushion.

Dorsal horn cells (DHC) in the spinal cord of cats responding to low threshold mechanical stimulation of the plantar cushion (PC), labelled with intracellular horseradish peroxidase, displayed a wide variety of anatomical and physiological characteristics, some of which were quite consistent within a given lamina. These DHC had cell bodies located medially in spinal segment L7, in laminae III, IV and VI. Dendritic fields varied greatly, for the most part conforming to patterns corresponding to their locations in the dorsal horn. Axon collaterals of most DHC ramified near their cell bodies, chiefly projecting ventral ward within the same lamina as the cell body or into more ventral laminae. Cells with the shortest central delays had cell bodies in laminae III and IV. Response latencies of DHC to PC stimulation were only slightly greater than the latencies of primary afferent fibers. Lamina IV cells had mechanical thresholds comparable to those of the primary afferents, significantly lower than the thresholds of cells of laminae III or VI. The receptive fields (RF) of the lamina IV cells were significantly larger than those of the primary afferent fibers or of the lamina VI cells. Relationships among RF area, mediolateral locations of cell bodies and dendritic spread were investigated.

Animals↗
PubMed1981

Electron microscopic observations of terminals of functionally identified afferent fibers in cat spinal cord.

Using the method of intra-axonal injection of horseradish peroxidase, functionally identified afferent fibers from three slowly adapting (Type I) receptors and one Pacinian corpuscle in the glabrous skin of the hind paw of the cat were stained. Electron microscopic observation of the terminals of these fibers revealed predominantly axodendritic asymmetric synapses containing round, clear vesicles. Multiple synapses on a single dendrite were observed, separated by as little as 900 mm from one another.

Afferent Pathways↗
PubMed1980

Morphology of spinal motoneurones mediating a cutaneous spinal reflex in the cat.

1. Intracellular injections of horseradish peroxidase were made in a functionally identified population of motoneurones in spinal cords of cats. These motoneurones were activated by tactile stimulation of the hind-limb central foot pad. 2. Cell bodies of twenty-two such motoneurones were located in the dorsolateral portion of the ventral horn in the first sacral segment. The mean diameter of the major axis of transverse sections through twelve of these cell bodies was 68 . 2 micrometer, the mean diameter of the minor axis was 48 . 7 micrometer. The major axis tended to be oriented dorsomedially-ventrolaterally. 3. In the transverse plane, the dendrites had a characteristic configuration, with a prominent group of dendrites travelling from the cell body dorsomedially into the dorsal horn, entering Rexed's lamina VI. For seventeen motoneurones with well stained dendrites, the mean medial spread of the dendrites was 960 micrometer. Though the mean lateral spread was only 508 micrometer, all of these motoneurones sent dendritic projections into the lateral white matter. The mean dorsal spread of the dendrites was 693 micrometer, the mean ventral spread, 748 micrometer. In the rostrocaudal direction, the mean spread rostrally was 911 micrometer, the mean spread caudally was 998 micrometer. The maximum dendritic spread for a single motoneurone was 2,940 micrometer, in the rostro caudal direction. The sum of dendritic lengths over an entire dendritic tree for the best-stained motoneurones exceeded 13,000 micrometer. 4. The mean diameter of the initial segment of axons of nineteen motoneurones was 4 . 3 micrometer. These axons were notable for the lack or paucity of axon collaterals. Only five of twenty-one axons possessed collaterals; of these, only one possessed more than a single collateral system. This sparseness of the collateral system was reflected in a low level of recurrent inhibition. 5. A possible relationship is discussed between the prominent dorsomedially oriented dendritic bundles of the motoneurones and the axon collaterals of dorsal horn cells mediating cutaneous stimulation which can activate these motoneurones.

Animals↗
PubMed1979

Ontogeny of maternal behavior in the laboratory rat: factors underlying changes in responsiveness from 30 to 90 days.

Male and female rats that were nonhandled or that were handled from weaning, and that had intact or impaired olfaction (intranasal zinc sulfate), were sensitized through continuous pup exposure commencing at 30, 45, 60, or 90 days of age. Nonhandled males and females were alike in latencies to become maternal at Day 30 but thereafter latencies of females became shorter and latencies of males lengthened; by 90 days males had markedly longer latencies than females and only 1/3 became maternal. Handling facilitated sensitization at 30 days among males and females but only among males at 45 and 60 days. Intranasal zinc sulfate reduced latencies of both males and females at all ages tested, but appeared most effective after 45 days of age. Gender differences in latencies persisted in adult animals even after combined treatments. Results indicate that both timidity and olfaction inhibit the onset of maternal responses to pups in virgin males and females, but they differ in relative importance by age and gender.

Aging↗
PubMed1978

The interrelationship between thermal and olfactory stimulation in the development of home orientation in newborn kittens.

The presence of a thermal gradient in the home cage and its use in home orientation was studied in kittens from shortly after birth to 2 weeks. Responses on a thermal gradient outside the home cage were also studied. With the home region and a freshly washed cage floor either cooled or warmer, kittens were placed in the adjacent corner or the home. In one study kittens chose between a cooled home and a warmed diagonal region. On a thermal gradient kittens exhibited thermotaxic turning and thermokinetic response. Kittens initially used either thermal or olfactory cues to reach the home but began to use only olfactory cues towards the end of the 1st week. Similarly, warmth in the home region caused "settling" during the 1st week but thereafter warmth and olfactory cues were most effective. Kittens chose the cooled home region more often than the warmed diagonal corner responding to olfactory over thermal cues.

Animals↗
PubMed1978

Specificity of litter odors in the control of home orientation among kittens.

The specificity of maternal-home cage odors governing home orientation was tested in 8- to 11-day-old kittens. Kittens were first tested for home orientation from the adjacent corner in their own home cages and cages of other mothers with litters of the same age. The majority of kittens oriented successfully in their own cages but not in strange mothers' cages. They then lived for 48 hr in the strange mothers' cages. At the end of this time they showed no improvement in orientation in their own home cages. Moreover, after an additional 24 hr in their own home cages they showed no improvement in their own home cages. Home orientation involves 2 odor components: 1 general to different mothers and 1 specific to each mother.

Animals↗