Showing papers by "United States Environmental Protection Agency published in 1991"

Technical basis for establishing sediment quality criteria for nonionic organic chemicals using equilibrium partitioning

Abstract: The purpose of this review paper is to present the technical basis for establishing sediment quality criteria using equilibrium partitioning (EqP). Equilibrium partitioning is chosen because it addresses the two principal technical issues that must be resolved: the varying bioavailability of chemicals in sediments and the choice of the appropriate biological effects concentration. The data that are used to examine the question of varying bioavailability across sediments are from toxicity and bioaccumulation experiments utilizing the same chemical and test organism but different sediments. It has been found that if the different sediments in each experiment are compared, there is essentially no relationship between sediment chemical concentrations on a dry weight basis and biological effects. However, if the chemical concentrations in the pore water of the sediment are used (for chemicals that are not highly hydrophobic) or if the sediment chemical concentrations on an organic carbon basis are used, then the biological effects occur at similar concentrations (within a factor of two) for the different sediments. In addition, the effects concentrations are the same as, or they can be predicted from, the effects concentration determined in water- only exposures. The EqP methodology rationalizes these results by assuming that the partitioning of the chemical between sediment organic carbon and pore water is at equilibrium. In each of these phases, the fugacity or activity of the chemical is the same at equilibrium. As a consequence, it is assumed that the organism receives an equivalent exposure from a water-only exposure or from any equilibrated phase, either from pore water via respiration, from sediment carbon via ingestion; or from a mixture of the routes. Thus, the pathway of exposure is not significant. The biological effect is produced by the chemical activity of the single phase or the equilibrated system. Sediment quality criteria for nonionic organic chemicals are based on the chemical concentration in sediment organic carbon. For highly hydrophobic chemicals this is necessary because the pore water concentration is, for those chemicals, no longer a good estimate of the chemical activity. The pore water concentration is the sum of the free chemical concentration, which is bioavailable and represents the chemical activity, and the concentration of chemical complexed to dissolved organic carbon, which, as the data presented below illustrate, is not bioavailable. Using the chemical concentration in sediment organic carbon eliminates this ambiguity. Sediment quality criteria also require that a chemical concentration be chosen that is sufficiently protective of benthic organisms. The final chronic value (FCV) from the U.S. Environmental Protection Agency (EPA) water quality criteria is proposed. An analysis of the data compiled in the water quality criteria documents demonstrates that benthic species, defined as either epibenthic or infaunal species, have a similar sensitivity to water column species. This is the case if the most sensitive species are compared and if all species are compared. The results of benthic colonization experiments also support the use of the FCV. Equilibrium partitioning cannot remove all the variation in the experimentally observed sediment- effects concentration and the concentration predicted from water-only exposures. A variation of approximately a factor of two to three remains. Hence, it is recognized that a quantification of this uncertainty should accompany the sediment quality criteria. The derivation of sediment quality criteria requires the octanol/water partition coefficient of the chemical. It should be measured with modern experimental techniques, which appear to remove the large variation in reported values. The derivation of the final chronic value should also be updated to include the most recent toxicological information.

Micronuclei as an index of cytogenetic damage: Past, present, and future

Abstract: The workshop was designed to present what is known about the production of micronuclei, what protocols are now accepted or proposed internationally, what new results have been obtained, and what new methods and protocols are likely to be forthcoming. This report is designed to convey the flavour of the workshop and to provide the essence of the new information. After the workshop an effort was made to determine what single protocol would satisfy the requirements set for the micronucleus test by as many regulatory agencies as possible. The result, reported here, includes the requirements of six regulatory authorities in Canada, the European Economic Community, the Organization for Economic Co-operation and Development, Japan, and the United States.

Organochlorine pesticides and polychlorinated biphenyls in human adipose tissue.

Abstract: The U.S. Environmental Protection Agency (U.S. EPA) has estimated that approximately 750,000 chemicals are now in use in homes, industry, and agriculture. This does not include pesticides, pharmaceuticals, and food additives, nor the estimated 1,500 different ingredients used in pesticides (Geyer et al. 1986).

Effects of Enhanced Solar Ultraviolet Radiation on Aquatic Ecosystems

Abstract: The photosynthetic production of organic biomass using solar energy is the almost exclusive source of energy for life on our planet. The amount of carbon in the form of its dioxide incorporated annually into organic molecules exceeds 100 gigatons which can be visualized by the load filling 10 coal trains spanning the distance from the earth to the moon (Hader et al., 1989). However, only about one third of this enormous production is accounted for by terrestrial plants — forests, savannas, crop plants etc. — while the majority is produced by the phytoplankton organisms (primary producers) in aquatic habitats, especially in the world oceans. The marine phytoplankton communities represent by far the largest ecosystem on earth (Schneider, 1989); therefore even a small percentage decrease in the populations would result in enormous losses in the biomass productivity of these organisms, which could have dramatic effects both for the intricate ecosystem itself and for humans, who depend on this system in many ways (Hader et al., 1989).

Effects of 3,4-methylenedioxymethamphetamine on autonomic thermoregulatory responses of the rat.

Abstract: 3,4-Methylenedioxymethamphetamine (MDMA), a substituted amphetamine analogue which stimulates serotonin release in the CNS, has been shown to induce near lethal elevations in core temperature in the rat. To characterize the effects of MDMA on temperature regulation, we measured metabolic rate (MR), evaporative water loss (EWL), motor activity (MA), and colonic temperature (Tc) in male, Long-Evans rats at 60 min following 30 mg/kg (SC) MDMA or saline at ambient temperatures (Ta) of 10, 20, and 30°C. MDMA caused an elevation in MR at Ta's of 20 and 30°C but had no effect at 10°C. At a Ta of 30°C, MR of the MDMA group was double that of the saline group. EWL was elevated by MDMA, an effect which was potentiated with increasing Ta. MDMA also elicited an increase in MA at all three Ta's. MDMA led to a 3.2°C increase in Tc at 30°C, no change in Tc at 20°C, and a 2.0°C decrease in Tc at 10°C. A second study found that treatment with 20 mg/kg MDMA failed to elicit an increase in blood flow to the tail in spite of a hyperthermic core temperature of 41.4°C. Preliminary studies using radiotelemetry methodology suggested that MDMA lethality is preceded by precipitous elevations in heart rate and core temperature. The data suggest that, at relatively warm Ta's, MDMA-induced stimulation of serotonergic pathway causes an elevation in MR and peripheral vasoconstriction, thus producing life-threatening elevations in Tc. The increase in EWL following MDMA partially attenuates the hyperthermia at warm Ta's, but leads to hypothermia in the rat maintained at a cold Ta of 10°C.

An EPA program for monitoring ecological status and trends.

Abstract: Despite hundreds of millions of dollars spent annually in the United States on environmental monitoring, policy and decision makers seldom have ready access to monitoring data to aid in prioritizing reasearch and assessment efforts or to assess the extent to which current policies are meeting the desired objectives. EPA is currently conducting research to evaluate options for establishing an integrated, cooperative monitoring program, with participation by federal, state, and private entities, that could result in annual statistical reports and interpretive summaries on the status and trends in indicators of adverse disturbance and corresponding ‘health’ of the nation's ecosystem on the regional and national scale.

Multiple Imputation of Industry and Occupation Codes in Census Public-use Samples Using Bayesian Logistic Regression

Abstract: We describe methods used to create a new Census data base that can be used to study comparability of industry and occupation classification systems. This project represents the most extensive application of multiple imputation to date, and the modeling effort was considerable as well—hundreds of logistic regressions were estimated. One goal of this article is to summarize the strategies used in the project so that researchers can better understand how the new data bases were created. Another goal is to show how modifications of maximum likelihood methods were made for the modeling and imputation phases of the project. To multiply-impute 1980 census-comparable codes for industries and occupations in two 1970 census public-use samples, logistic regression models were estimated with flattening constants. For many of the regression models considered, the data were too sparse to support conventional maximum likelihood analysis, so some alternative had to be employed. These methods solve existence and ...

The Interaction of Vapour Phase Organic Compounds with Indoor Sinks

Abstract: The interaction of indoor air pollutants with interior surfaces (i.e., sinks) is a well known, but poorly understood, phenomenon. Studies have shown that re-emissions of adsorbed organic vapours can contribute to elevated concentrations of organics in indoor environments. Research is being conducted in small environmental test chambers to develop data for predicting sink behaviour. This paper reports on the development of sink models based on fundamental mass transfer theory. The results of experiments conducted to determine the magnitude and rate of adsorption and desorption of vapour phase organic compounds for several materials are presented. Five materials were evaluated: carpet, painted wallboard, ceiling tile, window glass, and upholstery. Two organic compounds were tested with each material: tetrachloroethylene (a common cleaning solvent) and ethylbenzene (a common constituent of petroleum-based solvents widely used in consumer products). The results of the experimental work are presented showing the relevant sink effect parameters for each material tested and comparing the sorptive behaviour of the two organic compounds evaluated. An indoor air quality (IAQ) model was modified to incorporate adsorption and desorption sink rates. The model was used to predict the temporal history of the concentration of total vapour phase organics in a test house after application of a wood finishing product. The predicted results are presented and compared to measured values. Suggestions for further research on indoor sinks are presented.

Acid-volatile sulfide as a factor mediating cadmium and nickel bioavailability in contaminated sediments

Abstract: The authors investigated the influence of sulfide, measured as acid-volatile sulfide (AVS), on the bioavailability of cadmium and nickel in sediments. Seventeen samples from an estuarine system heavily contaminated with cadmium and nickel were analyzed for AVS and simultaneously extracted metals (SEM) and tested in 10-d exposures with the amphipod Hyalella azteca and the oligochaete Lumbriculus variegatus. Molar SEM(cadmium + nickel)/AVS ratios in the sediments ranged from less than one to greater than 200, with several in the range of 1 to 10. Samples with SEM/AVS ratios greater than one were consistently toxic to Hyalella azteca, whereas sediments with ratios less than one were not. Lumbriculus variegatus was less sensitive to the test sediments than Hyalella azteca, which was consistent with their relative sensitivity to cadmium and nickel in water-only exposures. SEM/AVS ratios in the sediments also appeared to be important in determining bioaccumulation of metals by Lumbriculus variegatus. These results support other studies with metal-spiked samples in demonstrating the importance of AVS in determining metal bioavailability in sediments and suggest that AVS normalization is a reasonable means for assessing the hazard of some sediment-associated metals to aquatic ecosystems.

Attitudes and Stress in the Presence of Technological Risk: A Test of the Supreme Court Hypothesis

Abstract: The 1983 Supreme Court decision on Three Mile Island held it would be almost impossible to distinguish between persons suffering genuine psychological stress and those who merely opposed the facility. While this argument was treated as factual by the justices, it is merely a hypothesis. This article provides an empirical test of the hypothesis, using the only other nuclear host community known to have experienced as much opposition as Three Mile Island. If the Supreme Court hypothesis were correct, attitudes toward the facility would be almost perfectly correlated with stress symptomatology. In fact, the strongest attitude-stress correlation in this community was -.096, even though simple sociodemographic variables showed far stronger correlations with the stress measures. By contrast, the broader literature reveals growing support for the alternative hypothesis implicitly rejected by the Supreme Court, namely that the risk of technological accidents may indeed be a significant predictor of psychological stress. The findings have implications for both policy and future research. In April of 1983, the U.S. Supreme Court ruled for the first time on the role of social and psychological factors in certain federal decisions about controversial facilities. The case, Metropolitan Edison Co. v. People Against Nuclear Power (1983), dealt with the undamaged nuclear reactor at Three Mile Island, which happened to be shut down for refueling at the time of the infamous accident at the site's other reactor. People Against Nuclear Power (PANE), a local citizens' group, argued that restarting the reactor would create negative consequences for their community's psychological health and that the federal Nuclear Regulatory Commission was required to perform additional analyses before allowing the * The authors wish to thank Stephen R. Couch, Thomas E. Drabek, Riley E. Dunlap, Kai T. Erikson, William S. Jordan III, Catherine E. Ross, and anonymous Social Forces reviewersfor helpful suggestions on an earlier version of this article, which was originally developedfor the 1984 Annual Meeting of the Rural Sociological Society, College Station, Texas. Direct correspondence and requests for reprints to Dr. Freudenburg at the Department of Rural Sociology, University of Wisconsin, Madison, WI, 53706. i) The University of North Carolina Press Social Forces, June 1991, 69(4):1143-1168 This content downloaded from 207.46.13.57 on Mon, 08 Aug 2016 04:42:32 UTC All use subject to http://about.jstor.org/terms 1144 / Social Forces 69:4, June 1991 reactor to resume operation. A high court (the Washington D.C. Court of Appeals) had agreed, but the nation's highest court did not. The main thrust of the Supreme Court's reasoning was that the justices had not been shown a sufficiently close causal connection between the physical fact of starting the undamaged reactor at the site and the likelihood of increased psychological impairment (for further discussions, see Annas 1983; Jordan 1984; Llewellyn & Freudenburg 1989; Meidinger & Freudenburg 1983). A key consideration in the Supreme Court decision was the assumed relationship between attitudes toward a facility and the psychological impacts created by that same facility. The local citizens in the Three Mile Island case emphasized that their case was based on the issue of psychological health, and not merely on disliking the nearby nuclear power plant. The distinction between negative attitudes and psychological distress was vital to the citizens' case, but they failed to convince the Court that the two could be separated.' The citizens pointed to studies showing heightened stress levels in the community after the accident, with quantitative evidence of physiological symptoms such as digestive problems, headaches, and difficulty with sleeping or daily physical activity (see the summary of studies in Dohrenwend et al. 1981). The citizens were also supported by "Friend of the Court" briefs from the American Psychological Association and the American Sociological Association. They were opposed, however, by the agency that would have been required to prepare a new assessment if the court had ruled differently the Nuclear Regulatory Commission (NRC). In its arguments, the NRC emphasized the subjective rather than the physiological aspects of psychological distress, such as tension and anxiety, and it characterized psychological distress as being engendered, if at all, solely through 'public disagreement with the agency's decision" (U.S. Nuclear Regulatory Commission 1982:41). The NRC argued that, as a practical matter, these subjective responses would make it impossible to differentiate between the persons living near a reactor who suffered "genuine" psychological distress and those who reported distress merely because of their opposition to the facility. The Supreme Court justices evidently agreed in large part with the Nuclear Regulatory Commission. Writing for the Court, Justice Rehnquist noted that the D.C. Court of Appeals had previously accepted PANE's argument that the case: ... raised an issue of health damage, while [earlier] cases presented questions of fear or policy disagreement. We do not believe this line is so easily drawn. Anyone who fears or dislikes a project may find himself suffering from "anxiety, tension, fear, [and] a sense of helplessness ...." Neither the language or the history of the National Environmental Policy Act (NEPA) suggest that it was intended to give citizens a general opportunity to air their policy objections to proposed federal actions. The political process, and not [legal action], provides the appropriate forum in which to air policy disagreements. We do not mean to ... suggest that the psychological health damage [PANE] fear[s] could not, in fact, occur. Nonetheless, it is difficult for us to see the differences between someone who dislikes a government decision so much that he suffers anxiety and stress, someone who fears the effects of that decision so much that he suffers similar anxiety and stress, and someone who suffers anxiety and stress that 'flow directly' .. .from the same decision. It would be extraordinarily difficult for agencies to differentiate between 'genuine' claims of psychological health damage and claims that are grounded solely in disagreement with a democratically adopted policy. (51 LW:4374)2 This content downloaded from 207.46.13.57 on Mon, 08 Aug 2016 04:42:32 UTC All use subject to http://about.jstor.org/terms Attitudes, Stress, and Technological Risk / 1145 While Justice Rehnquist's observations were treated as findings of fact, they are clearly based on the underlying assumption that host community residents who opposed an unpopular reactor would report significantly more psychological distress than persons in the same community who favored the facility. The assumption was evidently seen as plausible by the various parties involved, but in fact it appears to be an untested hypothesis. Although the hypothesis is inherently a testable one, PANE's attorney has reported that he was unable to find any evidence to support or to refute it at the time of the case (ordan 1983). SOCIAL SCIENCE APPROACHES While all nine Supreme Court justices apparently felt negative attitudes would be strongly correlated with reported distress in the host community, at least some social scientists appear to view the question differently, suggesting that it may indeed be possible to separate stress symptomatology from negative attitudes toward a given development. Indeed, the existing literature rarely relates the two concepts, treating them instead as being both operationally and conceptually distinct. Operationally, attitudes toward a given facility tend to be dealt with in a relatively straightforward manner (e.g., "Do you favor or oppose the construction of facility X?"). Issues of psychological health are sometimes dealt with in a more complex matter, but particularly in the case of studies dealing with stress and its consequences, the most common approach is to use sets of questions about relatively distinct physical symptoms (e.g., "how often are you bothered by an upset stomach?" or "do you often have trouble with your heart beating hard?"). The PANE arguments emphasized these types of physiological measures rather than the more subjective considerations such as "anxiety, tension, fear, and a sense of helplessness," stressed by the Supreme Court (51 LW:4373). Conceptually, moreover, attitudes toward a given facility and impairments to psychological health are seen in quite different terms, although here the distinction is perhaps less clear than it is in the case of operationalization. Attitudes, of course, have been conceptualized in many different ways. Allport's classic review (1935) was able to consider over 100 definitions, and other definitions have accumulated since then. The type of attitudinal research of interest here, however, is consistent with relatively common definitions, e.g., that of Edwards (1957), 'the degree of positive or negative affect associated with some psychological object' (2), or of Hill (1981), "evaluations of objects" (352). In what is probably the most frequently employed conceptual approach, attitudes are generally seen as emerging in a relatively straightforward way from the perceived characteristics of an object (e.g., a given facility) and the individual's evaluations of what s/he perceives (see Fishbein 1963, 1967 for discussions of the additional complexities involved in measuring attitudes toward technological development and the environment; see Freudenburg 1991a; Heberlein 1981; Van Liere & Dunlap 1981 for analyses of attitudes toward nuclear power; in particular, see Brody 1984, or Rosa & Freudenburg

Non-random cell killing in cryopreservation: implications for performance of the battery of leukocyte tests (BLT), I. Toxic and immunotoxic effects.

Abstract: To eliminate between-tests error in longitudinal human studies, for specimen sharing, convenient scheduling, etc., it is necessary for us to freeze leukocytes as well as non-transformed, continuous T lymphocyte (CTL) lines. Two commonly used cryopreservation methods were compared in terms of efficacy. Isolated peripheral blood mononuclear cells and CTLs were each aliquoted into three sets of vials. Two sets each were frozen in a 1:1 mixture of 15% DMSO in Mixed Medium (MM) and 20% FBS in MM using a commonly employed styrofoam freezer insert method for liquid nitrogen refrigerators and a programmed freezer (temperature falls at an optimal rate), respectively. The remaining set was held in MM with 20% FBS at 20 degrees C during the 2-h freezing process. The cells were thawed and/or washed and assayed for viability and T helper (Th)/T suppressor (Ts) ratio. It is clear that inadequate freezing (via the styrofoam method) non-randomly damages cells of T cell subpopulations, Th being more sensitive than Ts. Further, it is shown that inadequate cryopreservation can confound results from a number of assessment methods owing to morphological and functional damages. The battery of leukocyte tests (BLT) under development in this laboratory, is designed to detect toxic, immunotoxic and genotoxic effects of in vivo mutagen exposure on human blood. It is concluded that minimization of non-random cell losses (as quantitated on the basis of morphology) and preservation of related regulatory cell function is essential if one would assess the in vivo and in vitro states of heterogeneous cells. Further, it is suggested that freezing methods should be used only after verification that selective damage to subpopulations is not occurring among cells that otherwise might wrongly be assumed to be intact.

Lead and Minor Hearing Impairment

Abstract: We examined data recorded for 3,545 subjects aged 6-19 y who participated in the Hispanic Health and Nutrition Survey We sought to confirm a relationship between blood lead levels and elevated hearing thresholds that we previously reported in a similar study in which data from the Second National Health and Nutrition Examination Survey was used Lead was associated with an increased risk of hearing thresholds that were elevated above the standard reference level at all four frequencies (ie, 500 Hz, 1,000 Hz, 2,000 Hz, and 4,000 Hz) Lead was also associated with hearing thresholds when they were treated as a continuous outcome The relationships appeared to continue at blood lead levels less than 10 micrograms/dl An increase in blood lead, from 6 micrograms/dl to 18 micrograms/dl, was associated with a 2-dB loss in hearing at all frequencies, and an additional 15% of children had hearing thresholds that were below the standard at 2,000 Hz

Pulmonary function and ambient particulate matter: epidemiological evidence from NHANES I.

Abstract: The relationship between pulmonary function and quarterly average levels of total suspended particulates (TSP) was examined for adults who resided in 49 of the locations where the First National Health and Nutrition Examination Survey (NHANES I) was conducted. Statistically significant relationships were observed between TSP levels and forced vital capacity (FVC) and forced expiratory volume at one second (FEV1.0). These relationships remained strong across several specifications and sample changes, e.g., exclusion of cities with two highest and two lowest TSP levels, restriction of sample to whites only. Anthropometric measurements and socioeconomic characteristics of the subjects were included in the analysis, and we restricted the sample to “never” smokers. The results indicate a 1 standard deviation increase (about 34 μg/m3) in TSP from the sample mean of 87 μg/m3 was associated with an average decrease in FVC of 2.25%. The results of this analysis also suggest that there is a threshold level...

The Significance and Characteristics of the Personal Activity Cloud on Exposure Assessment Measurements for Indoor Contaminants

Abstract: The influence of personal activity sources on exposure to indoor contaminants is defined and demonstrated using data from occupational and residential studies. The ratios of measurements from personal exposure monitors to those made by microenvironmental exposure monitors are summarized to be typically 3 to 10 for occupational settings and 1.2 to 3.3 for residential settings. The ratios are shown to be lognormally distributed, and dependent primarily on the proximity of the source to the receptors. Current models are reviewed for possible application to the prediction of indoor concentration gradients and future model development and validation studies are suggested. (Copyright (c) 1991 Danish Technical Press, DK-Copenhagen.)

Comparison of risks from outdoor and indoor exposure to toxic chemicals.

Abstract: Environmental Protection Agency TEAM (Total Exposure Assessment Measurement) Studies have measured exposures of about 800 persons to 25 volatile organic compounds (VOCs) and exposures of about 300 ...

The Los Angeles TEAM Study: personal exposures, indoor-outdoor air concentrations, and breath concentrations of 25 volatile organic compounds.

Abstract: The U.S. Environmental Protection Agency and the California Air Resources Board studied the exposures of 51 residents of Los Angeles, California, to 25 volatile organic chemicals (VOCs) in air and drinking water in 1987. A major goal of the study was to measure personal, indoor, and outdoor air concentrations, and breath concentrations of VOCs in persons living in households that had previously been measured in 1984. Other goals were to confirm the marked day-night and seasonal differences observed in 1984; to determine room-to-room variability within homes; to determine source emission rates by measuring air exchange rates in each home; and to extend the coverage of chemicals by employing additional sampling and analysis methods. A total of 51 homes were visited in February of 1987, and 43 of these were revisited in July of 1987. The results confirmed previous TEAM Study findings of higher personal and indoor air concentrations than outdoor concentrations of all prevalent chemicals (except carbon tetrachloride); higher personal, indoor, and outdoor air concentrations in winter than in summer; and (in winter only) higher outdoor concentrations at night than in the daytime. New findings included the following: (1) room-to-room variability of 12-hour average concentrations was very small, indicating that a single monitor may be adequate for estimating indoor concentrations over this time span; (2) "whole-house" source emission rates were relatively constant during both seasons, with higher rates for odorous chemicals such as p-dichlorobenzene and limonene (often used in room air fresheners) than for other classes of chemicals; (3) breath concentrations measured during morning and evening were similar for most participants, suggesting the suitability of breath measurements for estimating exposure in the home; (4) limited data obtained on two additional chemicals-toluene and methylene chloride-indicated that both were prevalent at fairly high concentrations and that indoor air concentrations exceeded outdoor concentrations by a factor of about three.

Lead, blood pressure, and cardiovascular disease in men and women.

Abstract: Lead has been shown to be associated with elevated blood pressure in males in the NHANES II survey and in numerous other studies. This study confirms the association in males aged 20 to 74 and docu...

Health effects of swimmers and nonpoint sources of contaminated water

Abstract: Microbiological contamination from nonpoint sources of pollution is usually related to animal faecal wastes through urban, pastureland and forest run-off of stormwater. Currently-used bacterial water quality indicators cannot discriminate between human and animal faecal contamination and, therefore, it is common practice to treat the risk associated with exposure to water polluted by animal or human wastes as equally hazardous. The purpose of this study was to determine if there is a risk of gastrointestinal illness after a swimming exposure to water contaminated with animal faecal wastes. The health status and swimming activity of volunteer study participants was followed for 49 days during June, July and August. Multiple bacterial indicators of water quality were monitored daily during the course of the study. Swimming-associated symptomatic gastrointestinal illness was observed in individuals who swam in animal nonpoint source contaminated water. Swimmer illness was not associated with high densities of common faecal indicator bacteria or high volume rainy days. Swimmer illness was associated with high numbers of swimmers per day and high densities of staphylococci. The observed illnesses appeared to be caused by a swimmer to swimmer transmission via the water.

Isotopic exchange between carbon dioxide and ozone via O(1D) in the stratosphere.

Abstract: We propose a novel mechanism for isotopic exchange between CO_2 and O_3 via O(^1D) + CO_2 → CO_3^* followed by CO_3^* → CO_2 + O(^3P). A one-dimensional model calculation shows that this mechanism can account for the enrichment in ^(18)O in the stratospheric CO_2 observed by Gamo et al. [1989], using the heavy O_3 profile observed by Mauersberger [1981]. The implications of this mechanism for other stratospheric species and as a source of isotopically heavy CO_2 in the troposphere are briefly discussed.