Silver toxic pollutants

Concentrations of Toxic Pollutants in the Raw Wastewater of the Secondary Silver Subcategory... 

The pollutants characteristic of the industry wastewaters are summarized in Table 5.4 through Table 5.11, for both classical and toxic pollutants. The toxic pollutant data have been developed using a verification protocol established by U.S. EPA, with the exception of the following selenium, silver, thallium, and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCCD). Table 5.12 presents the minimum detection limit for the toxic pollutants. Any value below the minimum limit is listed in the summary tables as below detection limit (BDL). 

From an environmental standpoint, there are two reasons to perform chemical speciation. One reason is that the toxicity of an element varies with its chemical form. For example, mercury and silver form an amalgam that is used to fill tooth cavities. Ninety per cent of dentists use amalgam to fill cavities, and mercury in this form can be in the body for years with no toxic effects. Elemental mercury has low toxicity and, although this is not recommended, can be touched and handled with Utde chance of ill effects. However, methyl mercury, caused by industrial pollution and sometimes found in sea food, is readily adsorbed into the body and once there is extremely toxic. Pollution incidents involving mercury have shown that total metal data are insufficient and often misleading in assessing the potential hazard of this metal. 

Silver and silver compounds are regulated under Superfund, SARA 313, RCRA, Clean Water Act Toxic Pollutant, California State Superfund Hazardous Substances, CAL-OSHA Director s List of Hazardous Substances, and California HWCL Hazardous Wastes. 

Although the abundance of silver in the Earth s crust is comparatively low (0.07 pgg-1), it is considered an environmental contaminant and is toxic at the nanomolar level. As an environmental pollutant it is derived from mining and smelting wastes and, because of its use in the electrical and photographic industries, there are considerable discharges into the aquatic environment. Consequently, there have been studies on the geochemistry and structure of silver-sulfur compounds [31]. Silver, either bound to large molecules or adsorbed on to particles, is found in the colloidal phase in freshwater. In anoxic sediments Ag(I) can bind to amorphous FeS, but dissolved silver compounds are not uncommon. A more detailed study of silver speciation in wastewater effluent, surface and pore waters concluded that 33-35% was colloidal and ca. 15-20% was in the dissolved phases [32]. 

All water-soluble silver salts are toxic and ingestion can cause severe poisoning (see Silver Nitrate). Silver is listed by the US EPA as one of the priority pollutant metals in the environment. 

Of the elements in the Periodic Table more than two thirds are metals. Although many of these metals are toxic, only some metals are major environmental pollutants, because of their widespread use. U S. EPA has classified 13 metals as priority pollutants aluminum, antimony, arsenic, beryllium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, and zinc. The Resource Conservation and Recovery Act has fisted eight metals whose mobility in the soil is measured to determine the characteristic of toxic wastes. These metals include arsenic, barium, cadmium, chromium, lead, mercury, selenium, and silver—all but one from the above list of priority pollutant metals. 

The objective of another project was to evaluate the level of pollution in water and sediments in Lake Turawskie, a storage reservoir built in the 1930s on the Mala Panew River in southwestern Poland, and then to search for a correlation between the analytical chemical results and the toxicity parameters estimated from the application of biotests. Polluted waters as well as large amounts of polluted sediments enter the reservoir from the Mala Panew and its tributary, the Libawa. Industrial activities in the river basin include silver, zinc, and lead processing plants, steel and glass manufacture, and the production of cellulose and chemicals. Agriculture presents a further potential threat (e.g., fertilizer and pesticide run-off), as does the use of the reservoir s banks for recreational purposes. 

However, organic pollutants are often accompanied by heavy metal ion contaminants that can be reduced by photogenerated electrons into their less toxic, nonsoluble metallic form. Ti02-assisted photoreductive catalysis was found to be useful in the removal of certain heavy metals including mercury, silver, platinum, palladium, rhodium, and gold via their reduction followed by deposition at the catalyst surface [20-22] or photoreduction of nitroaromatic compounds [23-26]. The use of photogenerated electrons for deposition of metal layers on... 

The CerOx process avoided some of the difficulties of the Ag(II) process in that cerium is much cheaper and less toxic than silver. However, the most serious disadvantage for the CerOx process, at least at the time of the report (NRC, 2001a), was that it was found to not be as mature a technology as the Ag(II) process, and it had never been tested with any neutralents. As with the Ag(II) process, it also uses large amounts of nitric acid and thus rated poorly in terms of pollution prevention criteria. 

Abstract. Cyanides and hydrocyanic acid are one of the priority pollutants being most toxic. Therefore, it is very important to monitor cyanide concentration with specific and sensitive analytical methods. Some analytical methods for cyanide determination were presented in the last years spectrophotometer, potentiometer with silver cyanide electrode and titrimetric method. The paper presents original results concerning the spectrometric method and argentometric titration utilization for the measurement of cyanide concentration in some distilled alcoholic drinks from plums, grapes and apricots. The obtained cyanide concentrations vary between 0.0162 and 0.0970 mg/lOOmL, being under the imposed limits. 

It is also commonly used in the silver fillings of dental amalgam. Methyl mercury is a toxic global pollutant. The route of its exposure in humans is attributed to consumption of pilot whale meat, cod fish, and other sea food. 

This review considers the literature of the past years (up to 1979) that treats the preconcentration of the priority pollution metals antimony, arsenic, beryllium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, thallium, and zinc. In some cases, a brief outline is given or some discussion of the method, but in most instances, the number of methods available precludes more than a mention of their specific application or special feature. For some elements such as mercury many methods of preconcentration are available, for others such as beryllium and thallium only a few are reported. Relatively few procedures actually detail the analysis of a sample containing several species both organic and inorganic, although this area is of major concern, because of large differences in the relative toxicity of the various species. 

Although many metals are toxic, only some metals including aluminum, antimony, arsenic, beryllium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, and zinc are considered as priority pollutants in industrial effluents. Metals in general can be analyzed in industrial effluents by the following techniques ... 

As elemental pollutants, lead, mercury and cadmium are in a class by themselves and these elements have received a great deal of attention from research workers in recent years. Other elements which are frequently involved in environmental toxicity problems are arsenic, boron, chromium, copper, fluorine, molybdenum, nickel and zinc. Problems are also occasionally encountered with antimony, beryllium, selenium, silver and thallium, although dispersion of these elements in the biosphere is generally on a relatively small scale. 

The degree to which soils in the urban and industrial environment have already been contaminated with the elements, boron, cobalt, copper, cadmium, lead, mercury, nickel and zinc, is already so high that we can only speculate about some of the possible long-term consequences of this kind of environmental pollution. There is also widespread dispersion, on a large scale, of other elements, such as iron, aluminium, chromium, silver and tin in the environment, but since iron and aluminium are already major components of the-earth s crust, and since chromium, silver and tin are not often involved in toxicity problems, we are mainly concerned with the eight elements in the former group. 

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