Documents metabolic process 92 results

Beryllium is a steel-grey, brittle metal, existing naturally only as the 9Be isotope. Its compounds are divalent. Beryllium has several unique properties. It is the lightest of all solid and chemically-stable substances, with an unusually high melting point, specific heat, heat of fusion, and strength-to-weight ratio. It has excellent electrical and thermal conductivities. Because of its low atomic number, beryllium is very permeable to X-rays. Its nuclear properties include the breaking, scattering, and reflecting of neutrons, as well as the emission of neutrons on alpha-bombardment.

"Ground-level ozone is formed in complex atmospheric photochemical reactions between nitrogen oxides and hydrocarbons. The levels are highest in summertime and outside city centers. Elevated concentrations of ground-level ozone is mainly due to chemical reactions of emissions of volatile organic compounds and nitrogen oxides. The average concentrations of ground-level ozone occurring in nonurban areas in western Europe range from 40 to 70 µg m3. One-hour maximum values may reach 300 µg m3 in central Europe and 200 µg m3 in Sweden. Numerous studies, ranging from experimental studies with laboratory animals to controlled studies with humans to epidemiologic studies, have been performed on the health effects of ozone. In animal experiments, morphological effects on lung tissue, effects on host defense mechanisms, inflammation, fibrosis and tumors have all been induced by the inhalation of ozone. The lowest concentration tested that has given rise to these effects is 200 µg m3. It led to hyperplastic changes, proinflammatory changes, and sensitization to allergens.

In chamber exposure studies of 1- to 6-h duration, respiratory symptoms and pulmonary effects such as lung function decrements, increased airway responsiveness, and inflammatory reactions have all been demonstrated in humans. These effects have occurred even at the lowest concentration tested, 160 µg m3 for 6 h. Reduced lung function at 1-h maximum daily values of 160 µg m3 has also been found in epidemiologic studies, and some reports indicate effects at even lower levels. Other effects of ozone seen in epidemiologic studies include respiratory symptoms, hospital admissions, and emergency room visits for respiratory conditions, all of which correlated with daily 1-h maximum values of 240 µg m3 and lower. From these data on humans, and with the use of a safety factor of 2, a 1-h guideline value of 80 µg m3 is recommended. This level is also intended to protect against health effects in the most sensitive sections of the population. The proposed guideline level is currently exceeded and should be regarded as a goal for action to avoid adverse health effects in the future.

The experimental and epidemiologic basis for a risk assessment concerning long-term exposure is much weaker than for short-term exposure, and no explicit long-term guideline value is recommended. However, the proposed short-term guideline would probably offer some protection against potential effects of ozone following long-term exposure."

"Evaluates the risks to human health and the environment posed by 1,3-dichloropropene, 1,2-dichloropropane and mixtures of these chemicals. Since the two compounds and mixtures have been widely used in agriculture as pre-plant fumigants applied by soil injection, the report gives particular attention to studies investigating behaviour in soil, risks of leaching and groundwater contamination, uptake by food crops, residues detected in drinking-water and food, and risks to agricultural workers and the general population. Over 300 studies, including proprietary toxicological data from the manufacturers, were critically assessed.
The report concludes that, when used at the recommended rate, 1,3-dichloropropene is unlikely to attain levels of environmental significance. Risks to the general population were judged negligible. Concerning occupational hazards, the report cites evidence, largely from case reports of poisoning, underscoring the need to follow appropriate safety precautions.
The report concludes that 1,2-dichloropropane poses a negligible risk to the general population. When used at the recommended rate, the compound is unlikely to attain levels of environmental significance. For workers, the compound is judged unlikely to pose a hazard, provided good work practices, hygienic measures, and safety precautions are followed.
Data on mixtures of dichloropropenes and dichloropropane are evaluated in the final monograph. This technical mixture previously enjoyed wide use as a soil nematocide before planting. Citing evidence of a significant potential for 1,2-dichloropropane derived from this mixture to leach from soil and contaminate well water and groundwater, the report recommends that mixtures of dichloropropenes and dichloropropane should not be used as a soil fumigant. "

"Evaluates the risks to human health and the environment posed by benomyl, a fungicide registered for use in 50 countries on over 70 crops, including cereals, cotton, soybeans, tobacco, mushrooms, grapes, bananas and other fruits. One of the most widely used members of the benzimidazole family of fungicides, benomyl is effective, at low usage rates, against more than 190 different fungal diseases. Because benomyl is rapidly converted to carbendazim in the environment and is extensively metabolized to carbendazim by experimental animals, data from studies of carbendazim, which is a fungicide in its own right, are also considered when evaluating the hazards of benomyl.
Concerning hazards to environmental organisms, the report cites data from laboratory and field studies indicating that benomyl, applied at recommended rates, has little effect on soil microbial activity, but some adverse effects on groups of fungi. Benomyl is toxic to earthworms in laboratory experiments at realistic exposure concentrations and as a result of recommended usage in the field; earthworm populations may take more than two years to recover. Although high toxicity to aquatic organisms has been demonstrated in laboratory tests, the report concludes that this effect is unlikely to be seen in the field, due to the low bioavailability of sediment-bound residues.
For the general population, the main source of potential exposure is noted to be through the ingestion of food crops containing residues of benomyl and carbendazim. Though benomyl has been shown to cause contact dermatitis and dermal sensitization in some farm workers, the report found no evidence that either of these compounds can cause systemic toxic effects in occupationally exposed subjects or the general population. The report cites findings from animal studies suggesting that both compounds pose a very low risk for acute poisoning in humans."

Evaluates the risks to human health and the environment posed by trichlorfon, a broad-spectrum organophosphorus insecticide which acts as a "slow release" source of dichlorvos in the mammalian body. Marketed since the 1950s, trichlorfon is used to protect field and fruit crops, to control forest insects, and to control internal and external parasites in domestic and farm animals. Trichlorfon, formulated as metrifonate, has also been used for the pharmacological treatment of Schistosoma haematobium in millions of patients. The compound is under investigation as a treatment for Alzheimer's disease.

A review of environmental levels and human exposure concentrates on the significance of residues detected in crops, the milk of treated cows, and other food items as possible sources of exposure for the general public. Noting that detected levels are far below the established acceptable daily intake, the report concludes that trichlorfon does not constitute a health hazard for the general population. Concerning effects on environmental organisms, the report cites evidence that trichlorfon is moderately toxic for fish and birds, and moderately to highly toxic for aquatic arthropods, supporting the conclusion that this insecticide should never be sprayed over water bodies or streams.

The remaining sections evaluate data from toxicity studies in laboratory animals and in vitro test systems, from several hundred case reports of accidental or intentional human poisoning, and from studies of schistosomiasis patients treated with metrifonate. Though poisoning may have serious effects, including delayed neurotoxicity, the report concludes that, when good work practices and safety precautions are followed, trichlorfon is unlikely to present a hazard for occupationally exposed workers. The report further notes that, in the millions of schistosomiasis patients treated with metrifo-nate, reported side effects have been mild and rare.

Evaluates the vast body of evidence demonstrating serious threats to human and environmental health posed by polychlorinated biphenyls (PCBs). These chemicals, which are now ubiquitous in the environment, have been used commercially since 1930 as dielectric and heat-exchange fluids and in a variety of other applications. Over 1,300 studies were critically assessed. The book also contains a brief review of the limited data on polychlorinated terphenyls.

A section devoted to the environmental behaviour of PCBs assesses the mechanisms by which these highly persistent chemicals, previously introduced into the environment, are gradually being redistributed towards increased contamination of the marine environment. For the general population, the most important sources of exposure are identified as food items and, for babies, breast-milk. The well-documented signs of poisoning in occupationally-exposed workers are also reviewed. A section on the metabolic fate of PCBs cites evidence of accumulation in the liver and the adipose tissues of various organs, placental transport, fetal accumulation, and distribution to milk.

The most extensive section, which runs some 100 pages, evaluates findings from experimental studies of toxicity. Findings suggest that PCBs are immunosuppressive and act as tumour promoters. An assessment of effects on humans draws upon studies of two large outbreaks of poisoning from contaminated food, and of occupational exposures. Concerning risks to the environment, the report cites reproductive failure in sea mammals as the most important hazard, further concluding that the predicted redistribution of residues towards the marine environment will pose an increasing hazard for sea mammals in the future. A review of the hazards of polychlorinated terphenyls concludes the report.