Underestimation of Risk Due to Exposure Misclassification

Aim. Exposure misclassification constitutes a major obstacle when developing dose-response relationships for risk assessment. A non-differentional error results in underestimation of the risk. If the degree of misclassification is known, adjustment may be achieved by sensitivity analysis. The purpose of this study was to examine the full magnitude of measurement error in determining the prenatal exposure to methylmercury. Materials and methods. We used data from a prospective study of a Faroese birth cohort. Two biomarkers of methylmercury exposure were available, i.e., the mercury concentrations in cord blood and in maternal hair (sampled at the time of parturition). The laboratory imprecision on both chemical analyses was thought to be below 5% (coefficient of variation, CV). As a third exposure parameter, we used the dietary questionnaire response on frequency of whale meat dinners. Factor analysis and structural equation analysis were applied to assess the full extent of the imprecision. Results. The calculated total imprecision much exceeded the known laboratory variation: the CV was 28–30% for the cord-blood concentration and 52–55% for the maternal hair concentration. The dietary questionnaire response was even more imprecise. Conclusions. These findings illustrate that measurement error may be greatly underestimated if judged solely from reproducibility or laboratory quality data. Adjustment by sensitivity analysis is meaningful only if realistic measurement errors are applied. When exposure measurement errors are overlooked or underestimated, decisions based on the precautionary principle will not appropriately reflect the degree of precaution that was intended.     

A Historical Overview of the Ozone Exposure Problem

Ozone can be found in essentially all locations in the troposphere. Too much exposure of vegetation and humans to this potent oxidizing gas can prove toxic. Reports of human toxicity to ozone first appeared in the 1800's from accidental occupational exposures when ozone was first discovered. Ozone was recognized as damaging field vegetation with a report of altered leaf morphology in grapes in the 1950s. Ozone is the major oxidant component in photochemical smog, and is produced by reactions of volatile organic compounds and oxides of nitrogen with sunlight present. Soon after the inception of the U.S. Environmental Protection Agency (US EPA), the Agency set a general “oxidants” standard (which included ozone) in 1971. A primary standard was created to protect human health and a secondary standard to protect against agricultural losses, ecological damage, and other losses. Ozone concentrations have decreased steadily over the last two decades in some areas of the U.S., but have increased in other areas. Several aspects of ozone exposure need further characterization, including better determination of rural concentrations and the relationship of outdoor to indoor concentrations. Ozone is one of the six criteria air pollutants requiring a formal reexamination of the new findings of effects on health and vegetation on a periodic basis, a process that leads to the publication of an US EPA criteria document. As a result of further study concerning ozone effects, significant changes were made to pollution standards in 1979 and 1997. This toxicant has remained a major air pollutant of concern in the U.S. despite regulation and intense study over several decades.     

Analysis and Portrayal of Uncertainty in a Food-Web Exposure Model

The results of quantitative risk assessments are key factors in a risk manager's decision of the necessity to implement actions to reduce risk. The extent of the uncertainty in the assessment will play a large part in the degree of confidence a risk manager has in the reported significance and probability of a given risk. The two main sources of uncertainty in such risk assessments are variability and incertitude. In this paper we use two methods, a second-order two-dimensional Monte Carlo analysis and probability bounds analysis, to investigate the impact of both types of uncertainty on the results of a food-web exposure model. We demonstrate how the full extent of uncertainty in a risk estimate can be fully portrayed in a way that is useful to risk managers. We show that probability bounds analysis is a useful tool for identifying the parameters that contribute the most to uncertainty in a risk estimate and how it can be used to complement established practices in risk assessment. We conclude by promoting the use of probability analysis in conjunction with Monte Carlo analyses as a method for checking how plausible Monte Carlo results are in the full context of uncertainty.     

Distributions for Key Exposure Factors Controlling the Uptake of Xenobiotic Chemicals by Great Blue Herons (Ardea herodius) through Ingestion of Fish

A variety of exposure factors ultimately control the uptake of xenobiotic chemicals by colonial piscivorous birds, such as herons and egrets. These factors, which include feeding rate for various food sources, feeding territory size, and body weight, are critical to the implementation of models commonly used to predict ecological risks. A critical evaluation of literature on avian behavior, physiology, and ecology was conducted in order to identify those variables that most strongly influence uptake of chemicals by herons and egrets. After developing a database of such exposure factors, we identified each factor's range, central tendency, and distribution. Sufficient information was available to allow the development of statistical distributions for body weight, fraction of diet from fish, prey length, distance to foraging site, and feeding territory size for great blue herons. The five distributions presented in this paper are intended to support probabilistic assessments of potential risks to great blue herons. Distributions of exposure factors for great blue herons have not been previously published. Without such data, application of all but the most simple mechanistic models will require point estimates, most of which will be overly conservative and will not support accurate characterization of actual exposures of herons at hazardous waste sites.     

核磁共振磁场照射对子代大鼠海马突触形态的影响

研究观察了孕期磁共振磁场照射对子代大鼠海马突触超微结构的影响。SD孕鼠妊娠第12-18d给予0．35T核磁共振(magnetic resonance imaging,MRI)磁场照射。测量1、2和5月龄雌性仔鼠海马CAl区和齿状回的突触结构参数,用立体计量学方法进行定量测定。结果显示,磁场照射可引起2月龄子代大鼠海马CAl区突触间隙增宽．齿状回突触活性区长度变短、突触界面曲率和活性区面密度减小;5月龄子代大鼠CAl区突触间隙增宽,突触后致密物变薄,突触界面曲率减小,齿状回突触间隙增宽。结果提示,妊娠期接受MRI磁场照射可引起海马突触超微结构的改变。对这些结构变化与行为损害之间的关系进行了讨论。     

Development of Exposure Characterization Regions for Priority Ambient Air Pollutants

To evaluate the relationship between air pollution and morbidity and mortality in epidemiological studies, the exposure of populations must be defined. Generally, ambient air monitoring networks are the source of the exposure data for these studies. In this study, we developed methods to define population exposure regions that represent minimal variation in air pollutant concentrations. We evaluated the spatial and temporal variation in concentrations for particulate matter less than 2.5 μm (PM_2.5) and 10 μm (PM₁₀) and ozone (O₃) across New York State. The results from the PM_2.5 and ozone analysis indicate a significant degree of regional transport and showed regions of consistent concentrations of 100 and 50 miles, respectively, around each monitor. PM₁₀ analysis indicated little temporal and spatial variation for this pollutant and larger regions were adopted. The exposure characterization regions for PM_2.5, PM₁₀, and ozone have been used in ecological epidemiological investigations by the New York State Department of Health. This work was conducted under the Environmental Public Health Tracking grant from the Centers for Disease Control and Prevention.     

MicroRNAs as biomarkers of harmful environmental and occupational exposures: a systematic review

Abstract

Environmental exposure is a growing public health burden associated with several negative health effects. An estimated 4.2 million deaths occur each year from ambient air pollution alone. Biomarkers that reflect specific exposures have the potential to measure the real integrated internal dose from all routes of complex environmental exposure. MicroRNAs (miRNAs), small non-coding RNAs that regulate gene expression, have been studied as biomarkers in various diseases and have also shown potential as environmental exposure biomarkers. Here, we review the available human epidemiological and experimental evidence of miRNA expression changes in response to specific environmental exposures including airborne particulate matter. In doing so, we establish that miRNA exposure biomarker development remains in its infancy and future studies will need to carefully consider biological and analytical ‘design rules’ in order to facilitate clinical translation.     

氯烃类污染物的生态行为与毒理效应研究进展

近年来,进入到生态系统中的氯烃类有机污染物在数量和种类上迅速增加,以及由此引起的生态效应日益受到各界广泛关注,有关该类污染物的生态行为与毒理效应的研究也日益成为环境科学与污染生态学学科等相关领域的热点问题和焦点内容。为了对氯烃类有机污染物有一个较为系统的了解,首先对氯脂肪烃、氯苯和氯氟烃等三大类氯烃类污染源情况进行了分析;根据其憎水性、挥发性和稳定性的特点,对这些氯烃类有毒有机污染物在环境中的迁移行为以及在生物体内的浓缩、积累和放大行为进行了基于理论的探讨;在基于其QSARs分析的基础上,就这些化合物对鱼类的急性毒性、对视黄化合物和α-生育酚含量的影晌、可能的致畸和致突变效应以及对植物毒性效应方面的研究进行了概述,为今后氯烃类污染物相关研究工作的深入开展提供科学依据。     

Metallic Elements in Hair as a Biomarker of Human Exposure to Environmental Pollution: A Preliminary Investigation in Hubei Province

Metallic elements in hair were assessed in human subjects randomly sampled from six villages in Hubei province, PR China, known to differ in industrial pollution. Metallic elements assessed included copper, zinc, lead, and cadmium. Subjects sampled included adults and children of both sexes. Soil and rice samples from the villages were also examined for contents of metallic elements. Soil and rice contents of copper, lead, and cadmium were higher in the villages closer to the pollution source (copper smeltery). Hair contents of copper, lead, and cadmium were higher in subjects from the polluted villages compared with subjects from the nonpolluted areas. No differences were found in hair zinc content among the villagers. Cadmium contents in rice and human hair were linearly correlated. For lead and copper a logarithmic relation was found. No difference was found between the two genders with respect to hair metallic contents. With regard to age, hair cadmium content was highest in the older age groups in the polluted villages and may reflect chronic exposure. No other systematic age effects were observed. It was concluded that contents of cadmium, lead, and copper in human hair do reflect the degree of environmental pollution.     

Anogenital distance as a measure of male competitive ability in Rwenzori Angolan colobus

Anogenital distance (AGD) is positively correlated to fetal androgen exposure and developmental masculinization in mammals. Independent of overall body size, AGD shows a strong positive correlation with male fertility and in rodents, AGD is a good indicator of male competitive ability and is associated with female choice. We hypothesized that AGD will also predict male competitive ability in non-human primates. To test this, we measured AGD noninvasively with a parallel laser in a wild population of Angolan colobus monkeys (Colobus angolensis ruwenzorii) in Uganda and correlated to it to their social structure. C. angolensis ruwenzorii form a multilevel society with both one-male/multifemale units (OMUs) and multimale/multifemale units (MMUs). We compared AGD in males from five OMUs and six MMUs and related it to their fecal androgen metabolite concentrations, dominance rank and body size, and to the number of females in their unit. Males in OMUs had greater access to females, so were predicted to have longer AGDs, but this was not found. AGD also did not correlate overall with mean fecal androgen metabolites in MMUs. However, AGD was correlated with dominance rank in MMUs, demonstrating that higher-ranking males in these multimale units had longer AGDs. Body size did not show the same relationship with dominance rank, suggesting that male rank was not just a reflection of absolute male size. Our findings indicate that AGD predicts male competitive ability in this species and that it may be a useful correlate throughout the non-human primates. These results also support the idea that prenatal androgen exposure increases the likelihood of the expression of behaviors that maintain high dominance rank.     

Relationship between Measures of Exposure to PCBs/Dioxins and Behavioral Effects in Recent Developmental Studies

This paper does not reflect official EPA policy. Epidemiological studies on the neurodevelopmental effects of exposure to PCBs initiated in the last decade have had the opportunity to take advantage of modern methodologies for the analysis of congeners of PCBs, dioxins, and related orga-nochlorine compounds. Each of these studies is a longitudinal prospective study, in which women were recruited during pregnancy and the children are being followed for at least several years after birth. The study from which the largest body of data has been published to date is being performed in the Netherlands, in which exposure to PCBs and related compounds is through the general food supply. Mother-infant pairs were recruited in two cities. Half of the infants were bottle-fed and half breast-fed in each city. Four PCB congeners (118, 138, 153, 180) were assessed in maternal and cord plasma, breast milk, and plasma of the child at 3.5 years. TEQ in breast milk was calculated based on PCDDs/PCDFs and dioxin-like PCBs. Various measures of in utero exposure were associated with suboptimal neurological status during infancy, whereas maternal plasma PCB concentration was associated with cognitive deficits (Kaufman scores) at 3.5 years of age. The child's concurrent plasma PCB levels and maternal PCB plasma levels independently predicted performance on various aspects of a vigilance task, and maternal and cord plasma levels predicted impairment of complex play behavior. Poor scores on behavioral ratings were associated with concurrent blood PCB concentrations in the child. A study in Oswego in Lake Ontario fish eaters includes mothers who never ate Great Lakes fish and mothers who consumed greater than 40 PCB-equivalent pounds of Lake Ontario fish over their lifetime. Sixty-eight PCB congeners were measured in cord blood. Suboptimal neurological status during infancy was associated with maternal fish consumption and highly chlorinated cord PCB levels, whereas deficits in short-term memory at 6 months and 1 year of age were associated with total chlorinated cord PCB levels. In a study in Germany of 171 mother-infant pairs, PCB congeners 138, 153, and 180 were measured in cord plasma and milk 2 weeks after birth; both measures are considered markers of in utero exposure. Suboptimal neurological status during infancy, decrements in Bayley scores at 30 months and Kaufman scores at 42 months were associated with PCBs in milk but not cord plasma. These studies, combined with data from previous studies, reveal a consistent relationship between PCB exposure and suboptimal neurological status during infancy, and cognitive deficits associated with in utero exposure. Data from the Dutch study revealed effects on other behavioral domains associated with concurrent (postnatal) exposure. Although it is not possible to identify specific congeners or groups of congeners that may be responsible for the neurotoxic effects observed in these studies, the TEQ approach was not particularly predictive for neurotoxic outcomes.     

Human Exposure to Malathion during a Possible Vector-Control Intervention against West Nile Virus. II: Evaluation of the Toxicological Risks Using a Probabilistic Approach

In order to prevent the propagation of West Nile Virus (WNV), insecticide sprayings have been carried out in several locations in North America since 1999 with the objective of controlling the mosquito populations that transmit this pathogen. An attempt to quantitatively compare the risk of developing a health response to WNV infection with the toxicological risk of insecticides is presented here. First, the acute and subchronic environmental concentrations resulting from repeated spraying events were modeled according to a reasonable worst-case spraying sequence established in an intervention program proposed by the Government of Quebec (Canada). Second, probability density functions (PDF) were established for some exposure parameters according to the data for the concerned population, when feasible. Monte Carlo analyses were performed by incorporating these PDF into the equations used to calculate the daily absorbed doses resulting from the exposure scenarios presented in the companion article (this issue). The results showed that for a significant proportion of the population, aerial and, to a lesser extent, ground sprayings of malathion can generate acute and subchronic exposure that may exceed some levels of toxicological concern based on the USEPA's reference values. Indeed, in the case of acute exposure following aerial spraying for infants, toddlers, and children, these proportions were respectively 37.1%, 59.5%, and 32.8% of the individuals, and 27.3%, 41.3%, and 24.9% following subchronic exposure. For ground spraying, these values were 12.5%, 24.2%, 8.8%; and 9.8%, 16.5%, and 7.4%. These results allowed the comparison of the probability of exceeding a level of toxicological concern for malathion exposure with the probability of developing WNV symptoms. This comparison shows that in some circumstances, the toxicological risk of malathion may exceed the infectious risk of WNV.     

A multi-pond system as a protective zone for the management of lakes in China

A study was carried out in the small watershed of Chaohu Lake, where a scattered multi-pond system, as a part of the land-inland water ecotone, was found to be a good protective zone in the management of the lake. This multi-pond system can effectively reduce the non-point source load of nutrients, such as phosphorus and nitrogen from runoff water, and filter out sediments before they reach the lake. There are 150 artificial ponds in this small watershed, covering a surface area of 35.54 ha, which represents just under 5% of the whole catchment area. The nutrient retention in the first 9 months of the dry year 1988 was more than 90%. This multi-pond system needs low capital cost and energy consumption for maintenance, and is suitable for irrigation and drainage, while it recycles water and nutrients within the terrestrial agroecosystem. As a result of this case study, a multipond system is being proposed as part of a long term management strategy for the watershed.     

Changes in the Relative Number of Bipolar-Like Cells in the Retina of Pleurodeles waltl as a Function of Age and as a Result of Light Exposure

The study of the population of bipolar-like cells (displaced bipolars) was continued in order to establish their role in development and regeneration of the retina in lower vertebrates. The size of the population of these cells was estimated on serial semithin sections in the retina of normal eyes in adult and young newt Pleurodeles waltl, as well as in adult newts subjected to long-term bright illumination. The population of displaced bipolars was significantly increased with reference to all cells of the outer nuclear layer. In young and illuminated animals, their numbers were approximately 1.3 and 1.4 times that in the adult animals not exposed to constant light. The results obtained favor the earlier suggestion of the involvement of the displaced bipolars in growth and restoration of the outer nuclear layer in the retina of newts during development and after trauma.     

Bacterial contamination as a cause of spurious cyanide tests

Cyanogenic bacteria were common contaminants in cyanide tests of fungi. This observation demonstrated the need to ensure that the origin of hydrogen cyanide in a test is from the sample and is not microbial. This can be accomplished by recording cyanide test results after short incubation periods or by adding antibiotic solutions.     

Risk Analysis of a Farm Area Near a Lead- and Cadmium-Contaminated Industrial Site

The Asua Valley is an area on the outskirts of Bilbao where industry and small farms still coexist despite decades of serious environmental pollution. The present study was carried out to estimate the risk to which the residents of the area are exposed as a result of soil/dust ingestion and consumption of locally grown fresh produce, and, on the basis of this data, to delimit the areas that might require environmental clean-up. The relation between lead and cadmium content in soil and plant samples was assessed by multiple linear regression. The level of soil lead content for proposing intervention was determined by assessing the exposure of young children due to soil ingestion, assuming a “central-estimate” ingestion rate of 110?mg/day. Vegetable sampling was stratified according to the level of cadmium in the soil. The intervention content of cadmium was established as the midpoint of the soil sampling stratum previous to the one registering a vegetable consumption hazard quotient of 1; in this interval the intake reached 57% of the TDI.     

Ecological Risk Assessment of Radiological Exposure to Depleted Uranium in Soils at a Weapons Testing Facility

The potential for unacceptable risks to biota from radiological exposure to depleted uranium (DU) in soils was evaluated at two sites where DU weapons testing had been conducted in the past. A screening risk assessment was conducted to determine if measured concentrations of DU-associated radionuclides in site soils exceed radionuclide levels considered protective of biota. While concentrations of individual radionuclides did not exceed acceptable levels, total radionuclide concentrations could result in potentially unacceptable doses to exposed biota. Thus, a receptor-specific assessment was conducted to estimate external and internal radiological doses to vegetation and wildlife known or expected to occur at the sites. Wildlife evaluated included herbivores, omnivores, and top-level predators. Internal dose estimates to wildlife considered exposure via fugitive dust inhalation and soil and food ingestion; root uptake was the primary exposure route evaluated for vegetation. Total doses were compared with acceptable dose levels of 1.0 and 0.1 rad/day for vegetation and wildlife, respectively, with potentially unacceptable risks indicated for doses exceeding these levels. All estimated doses were below or approximated acceptable levels, typically by an order of magnitude or more. These results indicate that current levels of DU in soils do not pose unacceptable radiological risks to biota at the sites evaluated.     

土壤线虫对环境污染的指示作用

线虫作为土壤中型动物区系的一部分,在土壤生态系统中发挥着重要的作用,因其所特有的生物特性,使其广泛地应用于土壤健康状况的指示研究中．根据国内外的研究现状,分别对典型线虫在土壤污染指示与诊断中的应用和线虫群落的各种指数指标法(如成熟指数、多样性指数、相似度指数、关键种法、N／C比值和生理指标法)及其特点进行概述,论述了土壤动物线虫及其对污染环境的生物指示作用。提出土壤线虫作为一种有效的生态毒理诊断指标具有良好的发展前景．