Rainwater, chemicals contained

Natural mobilization includes chemical, mechanical, and biological weathering and volcanic activity. In chemical weathering, the elements are altered to forms that are more easily transported. For example, when basic rocks are neutralized by acidic fluids (such as rainwater acidified by absorption of CO2), the minerals contained in the rocks can dissolve, releasing metals to aqueous solution. Several examples are listed below of chemical reactions that involve atmospheric gases and that lead to the mobilization of metals ... 

July 27, 1982) contained 3830 ppm EDTA. The dramatic increase in EDTA concentration may be due to the installation of the plastic cover over the waste trenches. The presence of this barrier should decrease infiltration by rainwater into the waste trenches resulting in less water accumulation in the "bathtub-like" trenches, thereby possibly resulting in a concentration of any chemical species dissolved in the contaminated groundwater. Water from waste trench 19S, near the center of the burial site, contained 1340 ppb EDTA. Of the many water samples analyzed from the experimental wells and sumps, only groundwater from inert atmosphere well W2NA contained EDTA (1088 ppm, 1009 ppm and 793 ppm on three different sampling dates, see Table IV). 

White phosphorus enters the environment when industries make it or use it to make other chemicals and when the military uses it as ammunition. It also enters the environment from spills during storage and transport. Because of the discharge of waste water, white phosphorus is likely to be found in the water and bottom deposits of rivers and lakes near facilities that make or use it. It may also be found at sites where the military uses phosphorus-containing ammunition during training exercises. Rainwater washout of these sites may contaminate nearby waterways and their bottom deposits. Hazardous waste sites that contain white phosphorus are also potential sources of exposure to people. However, because white phosphorus reacts very quickly with oxygen in the air, it may not be found far away from sources of contamination. 

Acid Hydrolysis. The water that enters soil as rain or snow is in equilibrium with CO2 in the atmosphere, which dissolves to form carbonic acid. Unpolluted rainwater has a pH of approximately 5.7, whereas water in soil pores may be exposed to air containing a higher partial pressure of CO2 than the free atmosphere, and hence soil water may be more acidic (see Section 5.4). It is the attack on soil minerals by this weak carbonic acid that is the major chemical weathering process in most soils. For example, acid hydrolysis of calcium carbonate yields calcium and bicarbonate ions ... 

When rain falls over land some drain off the surface directly into surface water courses in surface runoff. A further part of the incoming rainwater percolates into the soil and passes more slowly into either surface waters or underground reservoirs. Water held in rock below the surface is termed groundwater, and a rock formation that stores and transmits water in useful quantities is termed an aquifer. Water that passes through soil or rock on its way to a river is chemically modified during transit, generally by addition of soluble and colloidal substances washed out of the ground. Some substances are removed from the water for example, river water often contains less lead than rainwater one mechanism of removal is uptake by soil. 

DNP is not likely to build up in fish from water. We do not know how long DNP remains in water. Chemical reactions do not remove DNP from soil under natural conditions. The loss of DNP from soil to the air due to evaporation is not important. The extent that DNP seeps into soil from rainwater depends on the properties of the soil. DNP may travel deeper into certain soils than others, especially soils that are not acidic. Groundwater from a few disposal sites contains DNP. DNP in soil is destroyed primarily by microorganisms. It may take between 4 and 80 days for the level of DNP in soil to decrease by half. You will find further information about the fate and movement of DNP in the environment in Chapter 5. 

Continental water contains dissolved species that render it acidic. The acidity comes from a variety of sources from the dissociation of atmospheric C02 in rainwater—and particularly from dissociation of soil-zone C02 (Section 4.4.2)— to form H2C(and natural and anthropogenic sulphur dioxide (S02) to form H2S03 and H2S04 (see Boxes 3.7 3.8). Reaction between a mineral and acidic weathering agents is usually called acid hydrolysis. The weathering of CaCO, demonstrates the chemical principle involved ... 

Limestone, CaC03, is a water-insoluble material, whereas Ca(HC03)2 is soluble. Caves are formed when rainwater containing dissolved CO2 passes over limestone for long periods of time. Write a chemical equation for the acid-base reaction. 

The influence of acid rain on the environment is related to the various properties of different ecosystems and varies depending upon physic-chemical characteristics of soil, vegetation type, stemflow and throughfall interactions of rainwater with canopy of different botanic species. For instance, it is well known in Japan that soils close to the stems of Japanese cedar (Cryptomeria japonica) trees are strongly acidic. This is partly due to the leaching of hydrogen ions from the stems. Soil solutions close to a stem (10cm) are markedly acidic (pH 4.5) and contain 47 /zM of total Al in... 

Another example of radiometry worth mentioning is determination of a chemical species by precipitation with a radioactive reagent. For example, the amount of ions in an aqueous solution is determined by the use of Co. An excess of a standard solution of Na3[ Co(N02)e] is added to the sample solution and the precipitate of poorly soluble K2Na[ Co(N02)6] is collected by filtration. From the activity of the precipitate, is determined referring to a calibration curve obtained on samples containing known amounts of ions. This method is used, for example, to determine 0.1-0.002 mg of K ions in rainwater. 

Atmospheric corrosion requires the presence of humidity to form an electrolyte (Chapter 8). Preventing accumulation of humidity in certain spots by clever design therefore greatly reduces the risk of atmospheric corrosion. This aspect is particularly important for stmetures in civil engineering and architecture that are periodically exposed to rainwater. In a similar fashion, in the chemical industry, it is important to be able to completely empty containers when they are not in use. Figure 12.1 shows how the design of a reactor can facilitate its efficient drainage. 

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