Arsenic (As) is a nonmetallic element that can be toxic to humans, even in small amounts. It is considered a highly undesirable impurity in water supplies and an upper concentration limit of 50 micrograms per liter was given in the 1976 drinking water standards (U. S. Environmental Protection Agency, 1976b). It has been used as a component of pesticides and thus may enter streams or ground water from lands used for waste disposal or agricultural activities.
Biochemical oxygen demand (BOD) is a measure of the quantity of dissolved oxygen necessary for the aerobic biochemical oxidation of organic substances present in water during a certain period of time. A 5-day BOD determination is commonly performed. The value of BOD is the difference between the oxygen content of the sample before and after an incubation period.
The bicarbonate ion (HCO3) concentration of natural waters generally is held within a moderate range by the effects of carbonate equilibria. Soils of humid, temperate regions may become depleted in calcium carbonate by leaching, and the pH of ground water at shallow depths may be rather low. The soil minerals in such areas may adsorb H, which could be released from time to time by addition of soil amendments or by other changes in chemical environment to reinforce the hydrogen-ion content of ground-water recharge.
Cadmium (Cd) is a trace metal that may be liberated to the environment by metallurgical processes and through the combustion of fossil fuel. Many of its uses tend to make the element available to water that comes in contact with buried wastes. The equilibrium solubility of cadmium carbonate has been was suggested as a possible limit for concentrations of cadmium in natural waters, but values observed are generally below saturation. It may be coprecipitated with manganese oxide or absorbed on mineral surfaces.
Calcium (Ca) is the most abundant of the alkaline-earth metals and is a major constituent of many common rock minerals. It is an essential element for animal and plant life forms and is a major component of the solutes in most natural water.
Dissolved carbon dioxide (CO2) and total organic carbon (C) are measurements made to obtain approximate determinations of the total concentration of organic material in a water sample. The determination of organic carbon is done by converting all carbon species present to carbon dioxide and correcting the subsequent determination of CO2 for any dissolved CO2 species that were initially present.
Chloride ion (Cl) is the only form of chlorine oxidation states of major significance in water exposed to the atmosphere. The element chlorine is the most abundant of the halogens. The geochemical behavior of chlorine reflects the volatility of the element and the fact that compounds of chlorine with common matallic elements, alkali metals, and alkaline earth metals are readily soluble in water. Chloride is present in all natural waters, but generally the concentrations are low.
Chlorine in water can be grouped into 2 classes of compounds with different reactivities. The active class is often referred to as Free Chlorine and includes dissolved chlorine gas, hypochlorous acid (HOCl), and hypochlorite (ClO-) with the latter two being the most common active species. There may be other species included with Free Chlorine like chlorine dioxide. Except for chlorine gas, the chlorine atom is in the +1 state. The amount of HOCl and ClO- depends primarily on pH as well as temperature and other factors.
Chlorine is a concern in any organic sampling plan because it oxidizes organic compounds as the chlorine(+1) is reduced to chloride(-1). The Free Chlorine is the fast acting, strong oxidizer used to kill bacteria quickly. Combined Chlorine is a weaker, slower acting oxidizer that is also added to disinfect drinking water systems. Combined chlorine is chlorine that has reacted with dissolved species (like NH3) to form molecules in which chlorine atom is in the +1 state and is the less reactive class of chlorine species. Combine chlorine includes chloramines and other compounds. Total Chlorine is Free and Combined Chlorine.
Chromium (Cr) is a transition metal. The concentrations of chromium in natural waters that have not been affected by waste disposal are usually less than 10 micrograms per liter.
Color determinations are sometimes included in water analyses to represent an evaluation of a physical property and have no direct chemical significance. The color of natural water usually results from leaching of organic debris. The color ranges from pale yellow to dark brown.
Copper (Cu) is a metal used extensively by modern industrial civilization, and many of these uses result in its dispersal in the environment. It may be dissolved from plumbing fixtures and water pipes, especially by water whose pH is below 7. Copper salts are sometimes added in small quantities to water-supply reservoirs to supress the growth of algae. Organic and inorganic compounds of copper have been used in agricultural pesticide sprays. Therefore, it is likely to be available for solution in surface and ground water than its low average abundance in rocks might imply.
Cubic foot per second (cu ft/s) is the rate of discharge representing a volume of 1 cubic foot passing a given point during 1 second and is equivalent to aproximately 7.48 gallons per second or 448.8 gallons per minute or 0.02832 cubic meters per second.
Discharge is the volume of fluid plus suspended sediment that passes a given point within a given period of time.
Fecal coliform bacteria are bacteria that are present in the intestines or feces of warm-blooded animals. They are often used as indicators of the sanitary quality of the water. In the laboratory they are defined as all organisms which produce blue colonies within 24 hours when incubated at 44.5 +/- 0.2 degrees Celsius on M-FC medium (nutrient medium for bacterial growth). Their concentrations are expressed as number of colonies per 100 milliliters of sample.
Fecal streptococcal bacteria are bacteria found also in intestines of warm-blooded animals. Their presence in water is considered to verify fecal pollution. They are characterized as grampositive, coccie bacteria which are capable of growth in brain-heart infusion broth. In the laboratory they are defined as all the organisms which produce red or pink colonies within 48 hours at 35 +/- 1.0 degrees Celsius on M-enterococcus medium (nutrient medium for bacterial growth). Their concentrations are expressed as number of colonies per 100 milliliters of sample.
Fluoride ion (F) is commonly associated with volcanic or fumarolic gases, and in some areas these may be important sources of fluoride for natural water. Fluorine is the lightest member of the halogen group of elements, and it is also the most electronegative of them all. If the concentration of fluorides is higher than 1 to 1.5 micrograms per liter, the water used for drinking presents hazards causing fluorosis of teeth. Fluorides are quite stable in natural waters.
Hardness of water (CaCO3) is a physical-chemical characteristic attributable to the presence of cations of alkaline earths (principally calcium and magnesium ions). It could be determined by a standard titration method or by atomic adsorption technique and is expressed as equivalent calcium carbonate (CaCO3). It presents one of the greatest problems in the use of water contributing to dense scale formation on heating surfaces in boilers, coating water equipment and industrial process systems. In cleaning processes, soaps, before forming a lather, reacts first with hardness salts in the waters to form insoluble calcium and magnesium stearates and oleates. The harder the water, the more soap required to react with the calcium and magnesium salts before its lathering properties are available for cleaning processes.
Iron (Fe) is the second most abundant metallic element in the Earth's outer crust, however, concentrations present in water generally are small. Iron is an essential element in the metabolism of plants and animals. It could be found in a great variety of forms: in solutions, colloids, and sus- pensions, and in organic and mineral complexes in various states of valence. If present in water in excessive amounts it forms red oxyhydroxide precipitates that stain laundry and plumbing fixtures, therefore, it is an objectionable impurity in water supplies for domestic and industrial use.
Lead (Pb) is a metal widely dispersed in sedimentary rocks. The adsorption of lead on organic and inorganic sediment surfaces and the coprecipitation of lead with manganese oxide tends to maintain low the concentration levels of lead in surface and ground water. Water that has a pH below neutrality or is poorly buffered may dissolve considerable amounts of lead from lead pipes, and may also obtain lead from solder used to join copper pipe and fittings.
Magnesium (Mg) is an alkaline-earth metal and has only one oxidation state of significance in water chemistry, Mg. It is a common element and is essential in plant and animal nutrition.
Manganese (Mn) is one of the more abundant metallic elements. It is an undesirable impurity in water supplies because of a tendency to deposit black oxide stains.
Micrograms per liter (ug/L) is a unit expressing the concentration of chemical constituents in solution as mass (micrograms) of solute per unit volume (liter) of water. One thousand micrograms per liter is equivalent to one milligram per liter.
Milligrams per liter (mg/L) is a unit for expressing the concentration of chemical constituents in solution. Milligrams per liter represent the mass of solute per unit volume (liter) of water. Concentration of suspended sediment also is expressed in mg/L, and is based on the mass of sediment per liter of water-sediment mixture.
Nickel (Ni) is an important industrial metal. Because of its extensive cultural use, it can be contributed to the environment in significant amounts by waste disposal.
Nitrogen (N) occurs in water in its anionic forms as nitrite or nitrate (NO2, NO3), in cationic form as ammonium (NH4) and at intermediate oxidation states as part of organic solutes. Nitrate and organic species are unstable in aerated water and are generally considered to be indicators of pollution through disposal of sewage or organic waste. Ammmonium ions can be formed during the anaerobic reduction of nitrates and nitrites. Its presence in unpolluted waters is connected with biochemical decomposition of proteins. An increase in ammonium is observed when aquatic organisms are dying off.
Ortho phosphate ion (PO4) is the final dissociation product of phosphoric acid (H3PO4). Phosphates belong to a group of nutrient substances which are often the limiting factor in the process of photosynthesis. The main users of organic phosphorus are zoo plankton and bacteria. During vegetation periods, the phoshates are used up rapidly by phytoplankton. Irregular concentrations of phosphates could be used as an indicator of pollutants in water.
Form of % of phosphate at pHThe oxygen content of water depends on a number of physical, chemical, biological, and microbiological processes. Oxygen is required by the higher forms of acuatic life for survival, therefore the dissolved oxygen (DO) determination is used widely in evaluations of the conditions of the habitation of the flora and fauna in a body of water. It can indicate the biological state of the body of water, the predominant processes in it , the destruction of organic substances and the intensity of self purification. The equilibrium concentration of dissolved oxygen in water in contact with air is a function of temperature and pressure, and to a lesser degree, of the concentration of dissolved salts.
Phosphate
5 6 7 8 8.5 9 10 11
H3PO4 0.10 0.01 - - - - - -
H2PO4- 97.99 83.68 33.90 4.88 1.60 0.51 0.05 -
HPO4= 1.91 16.32 66.10 95.12 98.39 99.45 99.59 96.33
PO4-= - - - - 0.01 0.04 0.36 3.47
The pH of a natural water is a useful index of the status of equilibrium reactions (acidic/basic interaction) in which the water participates. It represents the negative base-10 logarithm of the hydrogen-ion activity in moles per liter. A low pH solution has a high hydrogen ion concentration and is therefore acidic (pH < 7.0) while high pH solutions are low in hydrogen ion concentration and are alkaline ( pH > 7.0). A pH of 7.0 is considered neutral.
Phosphorus (P) is a rather common element in igneous rock. It is fairly abundant in sediments, but concentrations present in solution in natural water are normally no more than a few tenths of a milligram per liter. It is a component of sewage, as it is essential in metabolism, and it is always present in animal metabolic waste.
Potassium (K) is an essential element for both plants and animals. Maintenance of optimum soil fertility entails providing a supply of available potassium. The element is present in plant material and is lost from agricultural soil by crop harvesting and removal, leaching and runoff acting on organic residues.
Silica, meaning the oxide SIO2, is widely used in referring to silicon in natural water. Crystalline SIO2 as quartz is a major constituent of many igneous rocks and also constitutes the bulk of the grains in most sandstones. It seems probable that most of the dissolved silica observed in natural water results originally from the chemical breakdown of silicate minerals in processes of weathering. Silica is considered one of the basic nutrients in water essential to the growth of certain phytoplankton and zoo plankton species. It is sometimes measured with nitrogen and phosphorus to obtain a more complete picture of nutrients condition in water.
Sodium (Na) is one of the most abundant elements. Its salts are highly water soluble and are present in most natural waters. In igneous rocks, sodium is slightly more abundant than potassium, but in sediments, sodium is much less abundant. Sewage and industrial effluents are also sources of sodium. In irrigation waters, sodium is a problem due to its effect on soil structure, infiltration and permeability rates. A high percentage of exchangeable sodium in soil containing swelling-type clays results in a dispersion which restrict water movement and affects plant growth.
Specific conductance is a measure of the ability of water to conduct an electric current. It is expressed in microsiemens per centimeter at 25 degrees Celsius. Various surface active substances such as fats, mineral oils, tars, detergents , and specially strongly polluted water, may greatly affect the measurement. Specific conductance is related to the type and concentration of ions in solution and can be used for approximating the dissolved-solids content of the water. Commonly, the concentration of dis- solved solids (in milligrams per liter) is about 65 percent of the specific conductance (in microsiemens). This relation is not constant from stream to stream, and may vary in the same source with changes in the composition of the water.
Sulfur (S) is an essential element in the life processes of plants and animals. It is widely distributed in reduced form in igneous and sedimentary rocks as metallic sulfides. When sulfide minerals undergo weathering in contact with aerated water, sulfur is oxidized to yield sulfate ions that go into solution in the water. Sulfates also combine with alkaline earths causing non-carbonate hardness which may contribute to severe scaling in pipes, condensers, and boilers.
Suspended sediment is the sediment that at any given time is maintained in suspension by the upward components of turbulent currents or that exists in suspension as a colloid. The suspended load consists of fine sediment that usually travels at the velocity of the stream and that is held in suspension by the upward components of turbulent currents or by colloidal forces.
The temperature of water is one of the most important characteristics which determines, to a considerable extent, the trends and tendencies of changes in its quality. It is an important factor affecting ion and phase equilibria, and influencing the rates of biochemical processes which acompany the changes of concentration and of content of orgnic and mineral substances. Large streams have a small daily temperature change; shallow streams may have a daily range of several degrees and may follow closely the changes in air temperature. Some streams may be affected by waste-heat discharges.
Zinc (Zn) tends to be substantially more soluble in most types of natural water than copper or nickel. Industrial applications tend to disperse zinc widely in the environment, and its availability for solution in water has been greatly enhanced by industrial growth.
Hem, J.D., 1985 Study and interpretation of chemical characteristics of natural water: U.S. Geological Survey Water-Supply Paper 2254,