MODERN BIOGEOCHEMISTRY: SECOND EDITION Phần 7

Figure2. GeohydrologicsectionsthroughPanocheCreekalluvialfanillustratingtheevolution of groundwater flow system and the concentration of selenium in these waters in the western SanJoanquinValley.Arrowsindicatedirectionofflow.(A)Shallowdistributionofsoilselenium saltsandprimaryhorizontaldirectionofgroundwaterflowbetweenrechargeareasintheupper part of the fan and discharge areas along the San Joaguin River during pre-irrigation time. (B) Changes in groundwater flow direction and distribution of soil salts from the 1930s through the 1960s. (C) Discontinuation of pumping in the late 1960s caused a rise in the water table. Irrigation of low-lying areas and continued irrigation of middle and upper fan areas caused further downward displacement of soil selenium-containing salts and increasing their content in ground and drainage waters (Deverel et al., 1994). CALIFORNIA CASE STUDIES 265 Figure3. Concentrationsofseleniuminshallowgroundwaterinthemiddlealluvialfandeposits (Deverel et al., 1994). Figure 4. Content of Se in fodder crops in USA, ppm: 1—low, <0.05; 2—intermediate; 3— sufficient, >0.1 ppm, and 4—high, up to 5,000 and more (Besson and Martone, 1976). 266 CHAPTER 14 Box 1. Multiple chemical agent exposure assessment (EARC, 2005) A major research area for the EARC was the development of approaches for the specification, collection and analysis of environmental exposure and job task data for the purpose of hazard surveillance/epidemiology and for informing risk assessment where there is exposure to multiple chemical agents. A major area of research is the development of an integrated theory, approach and methodology to exposure assessment and hazard surveillance which emphasizes characterization of exposure to multiple chemical and physical agents. The following ongoing research projects are elements of the overall approach to the development of methods for studying multiple chemical exposure: r The application of toxicokinetic modeling to the assessment of interactive effects between hexane, ketones and aromatic compounds. Investigation of dermal ab-sorption of polycyclic aromatic compounds (PAHs). Research indicates dermal absorption of PAHs in a number of industries including aluminum smelting, coke ovens, creosote production and others is significantly more important than previ-ously recognized. r Modeling pollutant concentration between source and worker; prediction of small-scale dispersion of contaminants using data collected with a high-resolution three-axis sonic anemometer. The ultimate goal is to convert information collected by the anemometer into eddy diffusion coefficients, which can be used to estimate contaminant concentrations at any point within indoor environments. r Short-term non-invasive biomarkers for processes producing long-term lung damage-evaluation of the feasibility of candidate measurement systems. Toxicoki-netic models have been developed to determine whether breath analysis of pentane and ethane can be used to estimate chronic lung damage from toxicants. r Optimization of the sampling of chemicals and mixtures deposited on surfaces that could be sources of human exposures. Specific collection methods have been assessed and laboratory based research work is underway to define optimization procedures for sampling. r Adverseeffectsassociatedwithmultiplechemicalexposuresassociatedwithrocket testing at a commercial defense test facility. This study evaluated the excess mor-tality of workers employed at a rocket test site over a period beginning in the 1950s. Excess lung cancer was identified in this cohort of workers and their health outcomes were possibly associated with exposure to hydrazines, nitrosamines, as-bestos, trichloroethylene, and other chemicals. 2.2. Characterization of the Composition of Personal, Indoor, and Outdoor Particulate Exposure This is a temporal study of personal exposures to particulate matter in a panel of pa-tients with chronic obstructive pulmonary disease. Fifteen subjects will be monitored CALIFORNIA CASE STUDIES 267 over 15 days (in each of two seasons) for personal, indoor and outdoor concentra-tions of particulate matter. This study explores whether a high-risk group modifies its exposure to air pollution through its activities and/or avoidance behaviors. The study will also determine the feasibility of direct exposure measurement in a panel study of acute health responses to environmental exposures (Box 2). Box 2. Controlled laboratory evaluation of acute cardiopulmonary responses to concentrated particulates (EARC, 2005) To assess the respiratory effects of concentrated ambient particles in volunteer human subjects, a two-stage fine particle concentrator was fabricated and in-stalled in a movable exposure laboratory at Rancho Los Amigos Medical Center (http://www.rancho.org). Subjects’ biomedical responses (respiratory irritation, air-ways inflammation, and alterations in cardiovascular function) to these exposures are being compared to responses under clean-air control conditions to assess the follow-inghypotheses:(1)acuteexposuretoconcentratedambientfineparticlesintheSouth CoastBasincausesacutecardiopulmonarydysfunction;(2)thenatureandmagnitude of dysfunction differ according to the age and/or health status of the person exposed; (3)thenatureand/ormagnitudeofdysfunctiondiffersaccordingtothecharacteristics of the particles inhaled. 2.3. Beryllium Exposure A new area of research concerns exposure assessment for beryllium in the production ofnuclearweaponsatnucleardefenseindustries.Asafelevelofexposuretoberyllium isstillunknown.Potentialexplanationsinclude:(1)thecurrentexposurestandardmay not be protective enough to prevent sensitization, or (2) past exposure surveillance mayhaveunderestimatedtheactualexposurelevelbecauseofalackofunderstanding of the complexity of beryllium exposures. Task-based exposure assessment provides information not directly available through conventional sampling. It directly links exposure to specific activity associated with contaminant generation and provides in-depth evaluation of the worker’s role in a specific task. In-depth task analysis is being used to examine physical, postural, and cognitive demands of various tasks. Program faculty members are developing an automated cascade impactor for collectionoftask-basedsizedistributiondataofberyllium-containingaerosols.Based on the size distribution, the fraction of beryllium-containing aerosol penetrating a respirator and the inhalation and deposition in different regions of the lungs can be estimated. 3. OCCUPATIONAL EXPOSURE 3.1. Occupational Exposure to Multiple Pesticides Agricultural production has increased substantially due to the commercialization and intensificationofagricultureindevelopingcountriessuchasMexico.Identificationof 268 CHAPTER 14 pesticide use and exposure sources, direct measures of pesticide exposure, quantifi-cation of internal dose, and variation over time present the most difficult challenges in performing pesticide exposure assessment. These factors are complicated in devel-oping countries where pesticide sales and use reports, illness reports, and regulatory oversight of applications are limited. The primary objective of this research is to quantitatively assess organophosphate (OP) pesticide exposure in agricultural workers and their families. We are study-ing children of agricultural workers living in close proximity to fields where their fathers work, pesticide applicators, and individuals in harvesting activities. Prelim-inary work in this region identified the major pesticides used in the home, use and application patterns in the field, hygiene practices during application, and storage practices. Micro-environmental, occupational, and biological monitoring of agricul-tural workers and their families is being conducted three times during the agricultural season. 3.2. Occupational Exposure to Arsenic CenterinvestigatorsarecollaboratingwithscientistsatNIEHSoninvestigationofthe mechanism of arsenic carcinogenicity. The hypothesis is that there is increased sus-ceptibility to arsenic tumorigenesis from genetic limitations in methylation capacity or as a result of nutritional deficiencies. A murine model for the induction of cancer in methyl-deficient C57Bl/6 mice is being developed. A subchronic study (funded by an SCEHSC pilot project grant) included mice fed methyl sufficient diets, methyl-deficientdiets,andfourconcentrationsofarsenicinmethyl-deficientanimals.NIEHS pathologists have completed the histopathology on the animals from the subchronic study and there is evidence of hyperplasia of the bladder in the methyl-deficient, arsenic exposed mice. This research is an outgrowth of an earlier project which sought to characterize the mechanism of arsenic metabolism in a population currently drinking arsenic-contaminated water in Taiwan. There were three parts to the study, a cohort study, a case control study for skin cancer, and a study of intra-individual variability associ-ated with chronic arsenic exposure. The latter three research projects are complete and being submitted for publication. The results of this research are highly rele-vant since they indicate that alterations in methylation capacity may affect arsenic carcinogenesis. 3.3. Air Pollutants Relationship Between Personal, Outdoor and Indoor Air Concentrations (RIOPA) The overall goal of the national multicenter (Elizabeth, NJ, Houston, TX, and Los AngelesCounty,CA)RIOPAstudyistoestablishascientificfoundationforeffective, timely, public health intervention strategies. Outdoor, indoor, and personal exposures of adults and children to PM are measured and evaluated by mass, elemental, chemi-cal,andsourceapportionmentanalysesintheotherresearchprograms.Non-smoking asthmaticandnon-asthmaticadultsandtheirchildrenareincluded.Monitoringoccurs ... - tailieumienphi.vn