Naturally occurring hazardous substances

The modifying factor in the risk index represents any considerations of importance to waste classification other than those that are directly incorporated in the calculated risk from disposal and the specified allowable risk. The modifying factor can take into account, for example, the probability of occurrence of assumed exposure scenarios used in classifying waste, uncertainties in the assessment of risk from disposal and in the data required to evaluate the risk index, levels of naturally occurring hazardous substances in surface soil and their associated health risks to the public, and the costs and benefits of different means of waste disposal. The modifying factor is discussed further in Section 6.3.3. 

The known hazardous effects of most synthetic corrosion inhibitors are the reasons for the search of safer and environmentally friendly natural products. Plant extracts are viewed as an incredibly rich source of naturally synthesized chemical compounds that can be extracted at low costs. Naturally occurring substances such as vanillin [1], Opuntia extracts [2], lawsonia extract [3], natural honey [4] and extracts of chamomile, halfabar, black cumin and kidney bean [5] are some... 

The ambition of the OSPAR Commission, moreover, as manifested in the Objective of the Strategy aims at continuously reducing discharges, emissions and losses of hazardous substances (as defined In Annex 1) with the ultimate aim of achieving concentrations In the marine environment near background values for naturally occurring substances and close to zero for man-made synthetic substances. ... 

Describe possible mechanisms by which hazardous substances could be released from a disposal facility. A credible series of processes and events that could result in release of hazardous substances from the disposal site to a portion of the environment that is accessible to humans and the probability that these processes and events would occur, often called a release scenario, is developed. Release scenarios for waste disposal facilities generally should include considerations of inadvertent human intrusion resulting from normal activities, such as excavation or drilling, as well as releases to air and groundwater due to natural processes and events. 

Inadvertent human intrusion into hazardous waste. Inadvertent human intrusion is relevant to disposal of virtually all hazardous substances, especially in near-surface facilities. Typical scenarios assume that an unknowing individual (1) digs or drills into the waste and brings some of it to the surface where it is then available for dispersal and uptake, or (2) lives on the disposal site after waste has been exhumed or the cover removed, and consumes contaminated plant and animal products. Scenarios for inadvertent intrusion usually are assumed to occur after some period of active institutional control over the disposal site, which is typically 100 to 300 y. Intrusion scenarios are not very sensitive to site-specific parameters because the nature of intrusion (by digging or drilling) effectively bypasses the site-specific protection features, such as small amounts of groundwater,... 

Certain naturally-occurring contaminants in food (e.g., afla-toxin and N-nitroso compounds), and nonnutritive constituents (e.g., hydrazines in mushrooms) are carcinogenic in animals and pose a potential risk of cancer to humans. These and other compounds thus far shown to be carcinogenic in animals have been reported to occur in the average U.S. diet in small amounts however, there is no evidence that any of these substances individually makes a major contribution to the total risk of cancer in the United States. This lack of sufficient data should not be interpreted as an indication that these or other compounds subsequently found to be carcinogenic do not present a hazard. 

These questions contain a spatial (What are. ..) and a temporal part (are they approaching. ..), and an end goal ( ... background levels for naturally occurring substances and close to zero for manmade substances. .. ) for hazardous substances and their effects. In other words, die concentration of chemicals and their evolution has to be compared against two criteria, both redecting the natural condition, i.e. background levels and no effects. 

Mutagens alter DNA to produce inheritable trails. Although mutation is a natural process that occurs even in the absence of xenobiotic substances, most mutations are harmful (Manahan, 2000). The mechanisms of mutagenicity are similar to those of carcinogenicity and mutagens often cause birth defects as well. Therefore, mutagenic hazardous substances are of major toxicological concern. 

The soil plays a central role within ecosystems and fulfils a multitude of functions (as a habitat and with regulatory and production functions). On reaching soils, pollutants can adversely affect these functions, thus they can move to other media and cause damage to other components of the ecosystem. Soil contamination comprises either solid or liquid hazardous substances mixed with the naturally occurring soil. Usually, contaminants in the soil are physically or chemically attached to soil particles, or if they are not attached, trapped in the small spaces between soil particles. Soil contamination results when hazardous substances are either spilled or buried directly in the soil or migrate to the soil from a spill that has occurred elsewhere. Another source of soil contamination could be from water flowing near soils containing hazardous substances. 

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