Natural background concentrations

Arsenic is a major constituent of at least 245 mineral species, of which arsenopyrite is the most common (NAS 1977). In general, background concentrations of arsenic are 0.2 to 15 mg/kg in the lithosphere, 0.005 to 0.1 pg/m3 in air, <10 pg/L in water, and <15 mg/kg in soil (NRCC 1978 ATSDR 1992). The commercial use and production of arsenic compounds have raised local concentrations in the environment far above the natural background concentrations (Table 28.1). 

Exposure to elements such as As, U and Rn may represent an increased human health risk, particularly in areas where the natural background concentrations are elevated. 

In order to ensure effective land-use planning, geochemical sampling and mapping are required to identify areas where the natural background concentrations are elevated so that... 

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 sampling locations are totally randomized and are not designed to show the lowest natural background concentrations in the European environment, but to demonstrate the current geochemistry of the surface environment. 

The evaluation at the regional scale of Pb and U natural background concentrations for 2389 stream sediment samples of Campania region (13,600 km2) (Lima et al.,... 

In Europe, the notion that it may be possible to determine a natural background concentration of a metal at most sites may be unrealistic. Many hundreds of years of industrial activity, urbanization, and widespread aerial deposition mean that it is best to consider background concentrations as those determined at sites of relatively low anthropogenic impact. These concentrations will still vary considerably from site to site due to geological influences. 

Accurate and precise identifications and measurements of specific chemical substances are fundamental to environmental studies and protection programs. Determinations are required to understand natural background concentrations of chemicals in the environment, the nature and extent of environmental pollution by anthropogenic chemicals, trends in concentrations of these substances, the transport and fate of chemical substances, and the causes of variations of concentrations intime and space. Accurate and precise determinations are also required to assess human health and ecological risks caused by exposure to natural and anthropogenic substances, establish air and water quality standards, develop pollution control strategies, evaluate the effectiveness of pollution prevention and treatment technologies, and monitor compliance with and the effectiveness... 

Volatilization of selenium from volcanoes, soils, sediments, the oceans, microorganisms, plants, animals, and industrial activity all contribute to selenium in the atmosphere. Natural background concentrations of selenium in nonvolcanic areas are only around 0.01-1 ngm , but the short residence time, usually a matter of weeks, makes the atmosphere a rapid transport route for selenium. Volatilization of selenium into the atmosphere results from microbial methylation of selenium from soil, plant, and water, and is affected by the availability of selenium, the presence of an adequate carbon source, oxygen availability, and temperature (Frankenberger and Benson, 1994 Jacobs, 1989). 

TABLE 14.5 Natural Background Concentrations of Heavy Metals in Different Basins... 

Bioavailability and natural background concentrations of metals can be taken into account when assessing the monitoring results against EQS. 

Fig. 11.2 Variation in multi-element profiles of street dust, garden soil, and house dust, sampled from 48 houses in the city of Ottawa, Canada. Total element concentrations in the 100-250 xm size fraction are normalized against natural background concentrations, using the 95 "%ile for all media (modified from Rasmussen et al., 2001).

ScANES P. R. and Roach A. C. (1999) Determining natural background concentrations of trace metals in oysters from New South Wales, Australia. Environ. Pollut 105, 437-446. 

If we assume that, according to these predictions the emission of SO2 will be about 1300 x 103 tons in 1985, the average concentration of acid (expressed as protons) will be 165 g-1", with a standard deviation of 17.. The 99 reliability interval gives pH values on a yearly basis of between 3 60 and 3 95. At an expected emission of about 2600 103 tons around the year 2000, on a yearly basis, pH values between 3.27 and 3 66 can be expected (at a 99 reliability interval), equal to proton concentrations of 220 to 530 pg-1 1 (375 ug as an average). As a comparison the natural background concentration of protons would be less than 10 pg-l 1. Table 8 gives the proton concentrations and pH values to be expected for different quantities of emitted SO2. 

Buller, W., 1972, Natural Background Concentration of Mercury in Surface Water of the Adirondack Region, New York, United States Geological Survey Professional Paper 800c, pp. C-233 to C-238. 

Airborne Radioactivity Area An area where the measured concentration of airborne radioactivity, above natural background concentrations, exceeds either (1) 10% of the derived air concentration (DAC) averaged over 8 hours or (2) a peak concentration of 1 DAC. DAC values are contained in the SNL RPPM. 

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