Biomedical subjects

James A Calvin

Publications and source records attributed to James A Calvin.

4 recordsLinked to original sources

PubMed2006

Assessing isotropy for spatial point processes.

A common assumption while analyzing spatial point processes is direction invariance, i.e., isotropy. In this article, we propose a formal nonparametric approach to test for isotropy based on the asymptotic joint normality of the sample second-order intensity function. We derive an L(2) consistent subsampling estimator for the asymptotic covariance matrix of the sample second-order intensity function and use this to construct a test statistic with a chi(2) limiting distribution. We demonstrate the efficacy of the approach through simulation studies and an application to a desert plant data set, where our approach confirms suspected directional effects in the spatial distribution of the desert plant species.

Anisotropy↗

PubMed2005

Children's mouthing and food-handling behavior in an agricultural community on the US/Mexico border.

Children's mouthing and food-handling activities were measured during a study of nondietary ingestion of pesticides in a south Texas community. Mouthing data on 52 children, ranging in age from 7 to 53 months, were collected using questionnaires and videotaping. Data on children's play and hand-washing habits were also collected. Children were grouped into four age categories: infants (7-12 months), 1-year-olds (13-24 months), 2-year-olds (25-36 months) and preschoolers (37-53 months). The frequency and type of events prompting hand washing did not vary by age category except for hand washing after using the bathroom; this increased with increasing age category. Reported contact with grass and dirt also increased with increasing age category. The median hourly hand-to-mouth frequency for the four age groups ranged from 9.9 to 19.4, with 2-year-olds having the lowest frequency and preschoolers having the highest. The median hourly object to mouth frequency ranged from 5.5 to 18.1 across the four age categories; the frequency decreased as age increased (adjusted R(2)=0.179; P=0.003). The median hourly hand-to-food frequency for the four age groups ranged from 10.0 to 16.1, with the highest frequency being observed in the 1-year-olds. Hand-to-mouth frequency was associated with food contact frequency, particularly for children over 12 months of age (adjusted R(2)=0.291; P=0.002). The frequency and duration of hand-to-mouth, object-to-mouth and food-handling behaviors were all greater indoors than outdoors. Infants were more likely to remain indoors than children in other age groups. The time children spent playing on the floor decreased with increasing age (adjusted R(2)=0.096; P=0.031). Parental assessment was correlated with hand-to-mouth activity but not with object-to-mouth activity. The highest combined (hand and object) mouthing rates were observed among infants, suggesting that this age group has the greatest potential for exposure to environmental toxins.

Agriculture↗

PubMed2005

Biodegradation of simple chemical mixtures in soil.

Exogenous microorganisms often are used to enhance bioremediation. This study compared the capabilities of two exogenous microbial cultures and an indigenous population to detoxify a Weswood silt loam soil amended with a simple chemical mixture. The first three treatments were unamended soils inoculated with either indigenous microorganisms, Pseudomonas aeruginosa, or Phanerochaete sordida. Three additional treatments consisted of soil amended with benzo[a]pyrene, pentachlorophenol, and 2,4,6-trinitrotoluene, which were inoculated with either indigenous microorganisms, P. aeruginosa, or P. sordida. Samples were collected from the soils at several time points from 0 through 540 or 720 d, sequentially extracted with methylene chloride and methanol, and analyzed for genotoxicity (using the Salmonella/microsome assay) and chemical degradation. Although the indigenous microorganisms were effective for removal of benzo[a]pyrene, the Pseudomonas bacteria exhibited slightly greater removal rates for 2,4,6,-trinitrotoluene. The fungal cultures were significantly more effective at degrading pentachlorophenol. The day 540 extracts from all model chemical-amended treatments were genotoxic. In most cases, the day 540 extracts were more genotoxic than the day 0 extracts. The results suggest that, under appropriate conditions, enriched cultures of microorganisms may have an increased capacity to degrade individual chemicals. However, the products of degradation in some cases might be more genotoxic than the parent compounds.

Biodegradation, Environmental↗

PubMed2003

Nondietary ingestion of pesticides by children in an agricultural community on the US/Mexico border: preliminary results.

An environmental measurement and correlation study of nondietary ingestion of pesticides was carried out in a colonia in south Texas. The purpose of the study was to evaluate young children's exposure to environmental levels of organophosphate (OP) pesticides in the household. Samples were collected to measure levels of OP pesticides in housedust and on children's hands. These, in turn, were compared to levels of OP pesticide metabolites in urine. A total of 52 children, 25 boys and 27 girls, participated in the spring and summer of 2000. The children were 7-53 months of age at the time of recruitment. Univariate and multivariate regression analyses were carried out using SAS statistical software. Seventy-six percent of housedust samples and 50% of hand rinse samples contained OP pesticides. All urine samples had at least one metabolite and over 95% had at least two metabolites above the limit of detection (LOD). Total OP loadings in the housedust ranged from nondetectable (nd) to 78.03 nmol/100 cm(2) (mean=0.15 nmol/100 cm(2); median=0.07 nmol/100 cm(2)); total OP loadings on the children's hands ranged from nd to 13.40 nmol/100 cm(2) (mean=1.21 nmol/100 cm(2); median=1.41 nmol/100 cm(2)), and creatinine corrected urinary levels (nmol/mol creatinine) of total OP metabolites ranged from 3.2 to 257 nmol/mol creatinine (mean=42.6; median 27.4 nmol/mol creatinine). Urinary metabolites were inversely associated with the age of the child (in months) with the parameter estimate (pe)=-2.11, P=0.0070, and 95% confidence interval -3.60 to -0.61. The multivariate analysis observed a weak association between concentrations of OP pesticides in housedust, loadings in housedust, and concentration on hands, hand surface area, and urinary levels of OP metabolites. However, hand loadings of OP pesticides were more strongly associated (r(2)=0.28; P=0.0156) with urinary levels of OP metabolites (pe=6.39; 95% CI 0.98-11.80). This study's preliminary findings suggest that surface loadings of pesticides, on hands, are more highly correlated with urinary bioassays and, therefore, may be more useful for estimation of exposure in epidemiologic studies than levels of pesticides in housedust.

Administration, Cutaneous↗