New Publications from the World Health Organization

New Publications from the World Health Organization

Carbon Monoxide, Environmental Health Criteria No. 213

1999, xxiv + 464 pages (English, with summaries in French and Spanish), ISBN 92-4-157213-2, CHF 96.-/USD 86.40; In developing countries: CHF 67.20, Order No. 1160213. WHO Marketing and Dissemination, CH-1211 Geneva 27, Switzerland; Tel.: +41 22 791 24 76; Fax: +41 22 791 48 57; E-mail: bookorders@who.ch.

This book evaluates the risks to human health and the environment posed by exposure to carbon monoxide, a colorless, odorless gas produced by both natural and anthropogenic processes. Concerns about the potential health effects of exposure have been addressed in extensive studies with both humans and a range of animal species. Although studies of carbon monoxide poisoning are included, the report gives major attention to possible health risks linked to the relatively low concentrations that characterize most exposures. The report also aims to identify subpopulations that may be especially susceptible to adverse health effects. Close to 1 000 references are included in this comprehensive assessment. Concerning environmental levels arising from human activities, highway vehicle emissions are considered the principal source, followed by emissions from nonhighway transportation sources, other fuel combustion sources, industrial processes, and solid waste disposal. Evidence from monitoring stations supports the conclusion that environmental concentrations are declining, reflecting the efficacy of emission control devices on newer vehicles. The report also considers the factors that contribute to indoor concentrations, with cigarette smoke singled out as a major source.

A chapter on environmental distribution and transformation summarizes what is known about the environmental fate of carbon monoxide, its contribution to ozone production in the troposphere, and its possible role in global warming. Sources of personal exposure are considered in the next chapter, which concludes that the most important exposures for the general population occur in the vehicle and indoor macroenvironments. Several occupations involving an increased risk of high exposures are also identified. Toxicokinetics and mechanisms of action are reviewed in the next chapter, which discusses the many factors that influence the concentrations of carboxyhemoglobin in blood, and summarizes what is known about the primary mechanisms by which carboxyhemoglobin formation exerts its toxic effects.

The remaining chapters consider adverse effects on health. A review of the abundant findings from animal studies helps elucidate the mechanisms of carbon monoxide toxicity, its direct effects on the blood and other tissues, and the manifestations of these effects in the form of changes in organ function. Studies of developmental toxicity provide strong evidence that material exposure produces reductions in birth weight, cardiomegaly, delays in behavioral development, and disruptions in cognitive function.

A chapter on health effects in humans considers numerous investigations of adverse effects linked to typical ambient exposure levels. Findings are summarized in terms of damage to the cardiovascular and respiratory systems, effects on neurobehavioral functions, developmental toxicity, and other systemic effects. Also considered are the effects of exposure at high altitudes, in users of psychoactive drugs, and in combination with exposure to other air pollutants.

An evaluation of high-risk groups concludes that patients with reproducible exercise-induced ischemia are a sensitive group at increased risk for experiencitig adverse health effects. The report also found evidence indicating that exposure may cause an increased risk of sudden death from arrhythmia in patients with coronary artery disease. The report further concludes that exposure during pregnancy and early childhood carries a number of important risks.

Concerning accidental exposure to high concentrations, the report concludes that carbon monoxide poisoning occurs frequently, has severe consequences (including immediate death), involves complications and late sequelae, and is often overlooked. Among its many other conclusions, the report calls for better education of the general population about the risks of exposure, especially in individuals with cardiovascular and respiratory disease, and better awareness among medical professions of the dangers of carbon monoxide exposure during pregnancy.

New Publications from the World Health Organization

Human Exposure Assessment, Environmental Health Criteria No. 214

2000, xxx + 375 pages (English, with summaries in French and Spanish), ISBN 92-4-157214-0, CHF 78.-/ USD 70.20; In developing countries: CHF 54.60, Order No. 1160214.

This book offers an up-to-date guide to the concepts, procedures, statistical methods, and models used to assess human exposure to environmental chemicals. Noting that exposure assessment is a comparatively new discipline of the environmental sciences, the book aims to encourage its use as a powerful tool for measuring actual levels of exposure and determining whether interventions are needed to protect public health. With this goal in mind, the book gives researchers expert advice on the design and conduct of studies, the interpretation of findings, and the best methods for ensuring the reliability and reproducibility of results. Throughout, emphasis is placed on the ways in which well-designed exposure assessments can enhance the practical value of findings from traditional epidemiological and toxicological investigations.

The book has twelve chapters. The first six cover conceptual and methodological issues. Chapter 1 introduces basic concepts used in exposure assessment, and describes direct and indirect methods of measuring or estimating actual exposure and determining whether intervention is required. The uses of human exposure data are covered in Chapter 2, which explains how studies of human exposure can reduce the uncertainty of estimates used in epidemiology, risk assessment, and risk management. Chapter 3 considers several generic study designs and approaches, and compares their advantages and limitations. Chapter 4, on statistical methods, discusses selective applications of descriptive and inferential statistics, using data on lead exposure as an example. Subsequent chapters review methods for the collection and application of time-use data, and introduce the principles, methods, and data requirements of exposure modeling.

Against this background, chapters in the second half of the book offer practical advice on the design and conduct of studies aimed at assessing exposure to chemicals in different environmental media. Separate chapters describe sampling methods used to analyze chemical concentrations in air, water, and food, and in soil and settled dust. Environmental allergens that can contribute to disease or alter susceptibility are considered in Chapter 9, which concentrates on methods for measuring particles from house dust mites and their feces, allergens from pets and cockroaches, and allergens or toxins from fungi, bacteria, and pollen.

Subsequent chapters describe the use of biological markers in exposure assessment, and discuss issues surrounding the quality assurance of exposure studies and results. The final chapter presents brief summaries and examples of exposure studies in order to illustrate different study designs for different objectives, target pollutants, and populations. Studies that show how exposure assessment supports epidemiology and risk management, particularly in developing countries, are also included.

New Publications from the World Health Organization

Vinyl Chloride, Environmental Health Criteria No. 215

1999, xxi + 356 pages (English, with summaries in French and Spanish), ISBN 92-4-157215-9, CHF 72.-/USD 64.80; In developing countries: CHF 50.40, Order No. 1160215.

This book evaluates the risks to human health and the environment posed by exposure to vinyl chloride, a colorless, flammable gas manufactured almost exclusively for use in the production of polyvinyl chloride (PVC). PVC is used to produce plastic materials having wide applications in the building sector, packaging, electrical appliances, medical care, agriculture, the automotive industry, and toys.

Conclusive evidence that vinyl chloride causes cancer in humans led to the lowering, in the early 1970s, of occupational exposure limits in several countries. At the same time, many countries imposed restrictions on the levels of residual vinyl chloride permitted in PVC, thus reducing the risk that residues in packaging materials might contaminate food items, pharmaceutical products, and cosmetics. A chapter on sources of human and environmental exposure covers production levels and processes, noting the recent geographical expansion of production plants to Southeast Asia, Eastern Europe, the Indian subcontinent, and oil-producing countries. Production technologies that lead to lower residual levels of PVC are also briefly described. A review of data on the environmental fate of vinyl chloride notes that environmental releases are almost entirely in the vapor phase. Vinyl chloride is rapidly volatilized and removed from surface water and soil, but is not easily biodegraded. Evidence suggests some bioaccumulation within the food chain, but no biomagnification.

Concerning human exposure, the report concludes that atmospheric concentrations in ambient air are low, resulting in very little exposure of the general population. Much higher concentrations have been recorded near industry and waste disposal sites, and following accidental spills, including spills of chlorinated solvents in dry cleaning shops. Findings confirm a reduced risk of exposure for the general population via residues in packaging materials. The report identifies inhalation as the main route for occupational exposure, which occurs primarily in plants producing vinyl chloride and PVC. A chapter on kinetics and metabolism in laboratory animals and humans concludes that vinyl chloride is rapidly absorbed and widely distributed following exposure via the inhalation and oral routes. Following inhalation, the main metabolic route involves oxidation to form chloroethylene oxide, which is rapidly transformed to chloroacetaldehyde. Effects on laboratory mammals and in vitro test systems have been extensively studied. The compound shows low acute toxicity when administered by inhalation. Long-term feeding studies in several species show significantly increased incidences of liver angiosarcoma, hepatocellular carcinoma, and tumors at several other organ sites.

An assessment of effects on humans draws on clinical findings following accidental exposures, supported by a large number of well-designed epidemiological studies of occupationally exposed workers. Apart from defining the symptoms of "vinyl chloride illness", these studies provide strong and consistent evidence that vinyl chloride causes the rare tumor, angiosarcoma of the liver. Brain tumors and hepatocellular carcinoma may also be associated with exposure, though the evidence is less conclusive.

On the basis of this analysis, the report calls for measures to minimize emissions at production sites and sanitary landfills, and to ensure low residual levels in PVC. Moreover, as vinyl chloride is a known carcinogen, the report stresses the need to keep occupational exposures as low as possible and to educate workers about the risks involved and the need for safe working procedures.

New Publications from the World Health Organization

Bacillus thuringiensis, Environmental Health Criteria No. 217

1999, xv + 105 pages (English, with summaries in French and Spanish), ISBN 92-4-157217-5, CHF 27.-/USD 24.30; In developing countries: CHF 11.20, Order No. 1160217.

This book evaluates the risks to human health and the environment posed by the use of Bacillus thuringiensis (Bt) as a microbial agent for pest control. Products containing various Bt subspecies are increasingly used worldwide to control the larvae of several insect pests that threaten major agricultural crops and forests. Bt products are also being used to control the insect vectors of malaria, onchocerciasis, and other diseases of major public health importance. The bacterium is also a key source of genes for transgenic expression to provide pest resistance in plants and microorganisms.

The report opens with an overview of the biological properties of Bt and commercial Bt products. Particular attention is given to the mechanisms by which sporulation produces inclusion bodies, containing insecticidal crystalline proteins, which are selectively toxic for insect species in the orders Coleoptera, Diptera, and Lepidoptera. Tables show the current classification of 67 Bt subspecies and the large number of genes coding for the insecticidal crystalline proteins. A review of Bt metabolites found in commercial products concludes that they pose no hazards to humans or the environment. Chapter 2 reviews data elucidating the mechanisms by which Bt exerts its toxic action on susceptible insect larvae. Data on insect populations that are resistant to Bt are also briefly considered. Chapter 3, which focuses on the survival and activity of Bt in the environment, compares habitats where Bt subspecies occur naturally with treated habitats. Particular attention is given to the ability of Bt to form endospores that are resistant to inactivation by heat and desiccation and that persist in the environment under adverse conditions. A chapter on commercial production describes methods of production and general patterns of use in agriculture and forestry, and in large-scale programs to control the vectors of malaria and onchocerciasis.

The most extensive chapter evaluates the large number of studies conducted to assess the toxicity of various preparations containing insecticidal crystalline proteins, spores, and vegetative cells. Laboratory studies in a range of species have failed to demonstrate toxic or pathogenic effects. Field studies have likewise failed to demonstrate adverse effects on birds, earthworms, fish, other aquatic vertebrates, and nontarget aquatic invertebrates. An evaluation of effects on humans draws on studies in volunteers, case reports from occupationally exposed workers, and extensive data from countries where Bt products are added to drinking water for mosquito control or used to treat rivers for blackfly control.

On the basis of this review, the report concludes that Bt products are unlikely to pose any hazard to humans or other vertebrates or to the great majority of nontarget invertebrates, provided that the commercial product is free from non-Bt microorganisms and biologically active products other than the insecticidal crystalline proteins. The report further concludes that Bt products can be safely used for the control of insect pests of agricultural and horticultural crops and forests. These products are likewise judged safe for use in aquatic environments, including drinking water reservoirs, for the control of mosquito, blackfly, and nuisance insect larvae.

The report stresses, however, that vegetative Bt has the potential to produce Bacillus cereus-like toxins whose significance as a possible cause of human gastrointestinal disease remains unknown.