Man-Made Sources

The 30 Ci of in the hydrosphere plus the 10 Ci of in the lithosphere suggest an upper global total of about 40 Ci of naturally occurring I. 

Iodine-129 is produced in nuclear fission as a decay product of Te. The fission yields of several radioiodine isotopes from thermal neutron fission of were tabulated by Holland (1963). The I mass chain is partly reproduced below, with more recent values of radioactive half-lives and fission yields from Lederer and Shirley (1978) and Walker et al. (1977). 

The values in parentheses are cumulative yields in atoms per 100 fissions. The quantity of I present in a fission product mixture will increase slowly with time after irradiation has ceased as the I precursors decay. The peak activity is not reached for several months. 

Iodine-129 is produced in nuclear explosions of or Pu at approximate rates of 30 and 50 fiCi per kiloton (KT) TNT equivalent, respectively. The atmospheric transport and diffusion of radioiodine depend upon the initial height of the cloud and upon meteorological processes. A review of these factors was made by the United Nations Scientific Commitee on the Effects of Atomic Radiation (UNSCEAR, 1982). Fission products injected into the lower stratosphere have mean residence times of 0.5 y while those from medium altitude explosions may have residence times of 2 years. The fission products that diffuse to the lower atmosphere (troposphere) are deposited (mainly by precipitation) in a matter of weeks. Dry deposition is a significant fraction of the total only in areas of low rainfall. 

The net production of from fission in a thermal reactor is about 1 (id per megawatt-day (MWd), depending upon the neutron flux and irradiation time, which affect the transmutation of hy neutron absorption. An additional source of is fission of Pu produced in uranium fuel by neutron absorption in U. The atomic yield of in Pu fission is 1.5 percent, compared to 0.8 percent in fission (Walker et al., 1977). If, for example, 40 percent of the reactor energy comes from Pu fission (Russell and Hahn, 1971), the production will increase by about 30 percent. For the purposes of this report, total production of in light-water reactors containing slightly enriched fuel is taken as 1.3 tiCi per MWd. 

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Air pollution is principally a problem in urban and heavily industrialized areas, where the flow of clean air from surrounding areas is insufficient to disperse the accumulation. Motor vehicles account for more than 50% of the man-made emissions of carbon monoxide, hydrocarbons, and nitrogen oxides (4). More than half of the U.S. annual trillion vehicle miles are driven in urban areas (5). Nature produces much more pollutants than all man-made sources, but natural emissions are widely dispersed and do not contribute heavily to urban pollution problems (6, 7). 

There are natural sources of brominated hydrocarbons as well as man-made sources, such as the "halons , which are used in fire extinguishers. Reaction 21 is very fast and generates Cl and Br atoms directly the cycle does not require a photolytic step. Although this cycle occurs with high efficiency, it is less important than the chlorine peroxide cycle because of the much smaller concentrations of bromine compounds in the stratosphere-parts per trillion vs. parts per billion for the chlorine compounds. 

Nitrogen Dioxide (NO2) Is a major pollutant originating from natural and man-made sources. It has been estimated that a total of about 150 million tons of NOx are emitted to the atmosphere each year, of which about 50% results from man-made sources (21). In urban areas, man-made emissions dominate, producing elevated ambient levels. Worldwide, fossil-fuel combustion accounts for about 75% of man-made NOx emissions, which Is divided equally between stationary sources, such as power plants, and mobile sources. These high temperature combustion processes emit the primary pollutant nitric oxide (NO), which Is subsequently transformed to the secondary pollutant NO2 through photochemical oxidation. 

Figure 7.2 Acid rain occurs when water comes into contact with sulfur and nitrogen oxides in the atmosphere, which can come from natural sources or from man-made sources like cars or power plants. These acid rain-damaged coniferous trees live in the Karkonosze National Park in Silesia, Poland.

Dioxins are mainly by-products of industrial processes, but can also result from natural processes, such as volcanic eruptions and forest fires. Besides the anthropogenic (man-made) sources of PCDD/F discussed earher, biogenic and geogenic sources for dioxins also have been discovered recently. In natural clays of the kaohnite-type found in German mines in Westerwald, considerable levels of PCDD / F have been detected the same findings were obtained in special ball clays in the Mississippi area of the United States. The pattern (isomeric ratios) of this natural type of dioxins is different from the pattern obtained from incineration plants. 

A comparison of the aerosol sources listed in Tables III and IV suggests that the second distribution listed in Table III having a d of 0.39 wn corresponds to the second distribution listed in Table IV and represents aerosols arising from coagulation and condensation. Similarly, distribution 5 in Table III apparently coincides with the third seunple of aerosols listed by Whitby and Cantrell as arising from natural and man-made sources. It is conceivable that the first distribution listed in Table III corresponds to the first source listed in Table IV. This statement cannot be made with certainty, however, since the resolution of the SEN technique used was not high enough. 

A critical question concerning atmospheric concentrations of ozone and other photochemical oxidants is What fraction of the observed values in each locale can be controlled by reduction of emissions Some contend that natural background concentrations exceed the federal ambient air quality standard (0.08 ppm). Another point of view is that background ozone concentrations rarely exceed about 0.05-0.06 ppm at the surface and that higher concentrations are caused by man-made sources. 

The data reviewed in Chapter 4 support the second point of view. Measurements in remote areas of the Northern Hemisphere, when compared with those in the lower 48 states of the United States, support the contention that man-made sources are involved in cases where the standard is exceeded. Further measurements are needed to establish this contention with more certainty. Some of the difficulties involved in such studies become apparent when it is noted that the effect of pollution— particularly nitric oxide emission—is to reduce ozone concentrations locally. 

UNSCEAR (2000b) Annex C exposures to the public from man-made sources of radiation. 

The pollution control decision-maker must know the relative contributions of natural and specific man-made sources of toxic materials in order to establish criteria for control regulations. 

Life on earth has evolved in the presence of naturally occurring ionizing radiation, which is continuous and ubiquitous. In addition to natural background radiation exposure, mankind is now exposed also to radiation from various man-made sources. 

Exposure to radiation from man-made sources is estimated to deliver an average annual effective dose equivalent of about 0.6 mSv (60 mrem) to the general population (Thble 4.1). The largest contribution comes... 

Ames, 1983) — can be used as points of reference, they do not justify exposures from man-made sources. 

Figure 9 shows a generalized cycling pattern that metals might follow 244). The net effect of biomethylation is to open up new pathways for metal transfer through water, air, and/or food chains. Of special concern to environmentalists will be the translocation of toxic elements from natural or man-made sources through aquatic media to susceptible biota. 

Bach B, Volkhausen W (2010) The influence of natural and man-made sources on PM10 and PM2.5 concentrations at industrially influenced sites. Gefahrst Reinhalt Luft 70 488 192... 

Silver is one of the basic elements that make up our planet. Silver is rare, but occurs naturally in the environment as a soft, "silver" colored metal. Because silver is an element, there are no man-made sources of silver. People make jewelry, silverware, electronic equipment, and dental fillings with silver in its metallic form. It also occurs in powdery white (silver nitrate and silver chloride) or dark-gray to black compounds (silver sulfide and silver oxide). Silver could be found at hazardous waste sites in the form of these compounds mixed with soil and/or water. Therefore, these silver compounds will be the main topic of this profile. Throughout the profile the various silver compounds will at times be referred to simply as silver. 

In contrast, risk management for substances that cause deterministic effects must consider unavoidable exposures to the background of naturally occurring substances that cause such effects. Based on the assumption of a threshold dose-response relationship, the risk from man-made sources is not independent of the risk from undisturbed natural sources, and the total dose from all sources must be considered in evaluating deterministic risks. In the case of ionizing radiation, thresholds for deterministic responses are well above average doses from natural background radiation (see Section 3.2.2.1)... 

A negligible dose would be generally applicable to all man-made sources of radiation and would define a dose below which further control of sources by regulatory authorities is deemed to be unwarranted. If all doses were below a negligible level, no further reductions in dose using the ALARA principle would be attempted (see... 

Radiation Dose Limits. For routine exposure of individual members of the public to all man-made sources of radiation combined (i.e., excluding exposures due to natural background, indoor radon, and deliberate medical practices), NCRP currently recommends that the annual effective dose should not exceed 1 mSv for continuous or frequent exposure or 5 mSv for infrequent exposure. The quantity effective dose is a weighted sum of equivalent doses to specified organs and tissues (ICRP, 1991), which is intended to be proportional to the probability of a stochastic response for any uniform or nonuniform irradiations of the body (see Section 3.2.2.3.3). 

The recommended dose limits for the public define limits on the probability of stochastic responses that are regarded as necessary for protection of public health. Doses above the limits are regarded as intolerable and normally must be reduced regardless of cost or other circumstances, except in the case of accidents or emergencies (see Section 3.3.1). For continuous exposure over a 70 y lifetime, and assuming a nominal probability coefficient for fatal cancers (i.e., the probability of a fatal cancer per unit effective dose) of 5 X 10 2 Sv 1 (ICRP, 1991 NCRP, 1993a), the dose limit for continuous exposure corresponds to an estimated lifetime fatal cancer risk of about 4 X 10 3. However, meeting the dose limits is not sufficient to ensure that routine exposures of the public to man-made sources would be acceptable. 

NCRP (1993a) also has emphasized the importance of source constraints in radiation protection of the public. NCRP has reaffirmed a previous recommendation (NCRP, 1984b 1987a) that whenever the potential exists for routine exposure of an individual member of the public to exceed 25 percent of the limit on annual effective dose as a result of irradiation attributable to a single site, the site operator should ensure that the annual effective dose to the maximally exposed individual from all man-made sources combined does not exceed 1 mSv on a continuous basis. Alternatively, if such an assessment is not conducted, no single source or set of sources under one control should result in an individual receiving an annual effective dose of more than 0.25 mSv. 

X 10 3. Annual effective doses in the range of 0.25 to 1 mSv from all man-made sources combined are acceptable if they are ALARA. However, doses toward the upper end of this range are regarded as only barely tolerable (ICRP, 1991), and doses below this range are expected to be justifiable and achievable in most cases, based on site-specific application of the ALARA principle. Therefore, lifetime risks from routine exposure to all man-made sources combined usually should not exceed about 1 X 10 3. 

NCRP has recommended that annual effective doses to individuals from any practice or source of 10 p.Sv or less are negligible (see Section 4.1.2.5.3). This dose is one percent of the dose limit for continuous exposure to all man-made sources combined discussed in the previous section, and it also is about one percent of the dose from natural background radiation, excluding radon (NCRP, 1987b). The recommended negligible individual dose corresponds to an estimated lifetime fatal cancer risk of about 4 X 10 5. 

Application of NCRP Recommendations to Waste Classification. NCRP s recommendations on dose limits and a negligible dose for individual members of the public, and their associated cancer risks, could be used in developing a risk-based waste classification system. Specifically, the dose limits applicable to all man-made sources of exposure combined could be used in establishing concentration limits of radionuclides or hazardous chemicals in dedicated hazardous waste disposal facilities based on assumed scenarios for exposure of the public. Similarly, the negligible individual dose could be used in establishing concentration limits of radionuclides in disposal facilities for nonhazardous waste. These applications are discussed in Sections 6.2 and 6.3 where NCRP s recommendations on risk-based waste classification are presented. 

PAHs enter the environment from both natural and man-made sources, and the anthropogenic point and nonpoint sources are the major sources. The nonpoint sources are diffuse sources disseminated through the air and waterways. In aquatic systems, PAH-enriched particles or floes may settle to the lake s bottom under calm conditions and accumulate in the sediments. Once the PAH-enriched particles have accumulated in the lake s floor, they may undergo a number of changes that are mediated by chemical or microbial activities. As a result, the bound PAHs can be released from the sediment into the water phase. Once they enter the water column, they may also enter phytoplankton. The PAHs in phytoplankton may then bioaccumulate in the food web. This can cause both acute and chronic effects in fish, birds and other mammals that feed on aquatic organisms (Zhang, 1998). 

Details of the sources and individual behaviour of radionuclides within the environment are beyond the scope of this chapter and worthy accounts of these topics have previously been given by Bowen (1979) and Whicker and Schultz (1982). It is worth stressing the point that was alluded to in the previous section, however, that the two major groups of radionuclides which exist are those from natural and man-made sources. Radioecologists have primarily been concerned with the behaviour of the latter category and, as a result, the bulk of radioecological literature concerns radionuclides which have been released to the environment as a result of man s activities. The production of all these radionuclides is either a direct result of the nuclear fission process, or indirectly the result of activation of elements by neutron bombardment within reactors or decay of both fission and activation products. 

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