Corrosion of dental burs in sterilizing and disinfecting solutions.

Potentiodynamic anodic polarization, SEM, and energy dispersive microanalysis techniques were used to determine electrochemical aggressiveness of disinfecting and sterilizing solutions on carbide and stainless steel burs. The importance of galvanic cell formation in carbide burs caused by mixed metal coupling was examined. The following conclusions were reached. 1. Anodic polarization methods are an effective means for discriminating among the relative corrosiveness of sterilizing and disinfecting agents on dental instruments, particularly dental burs. 2. The relative degree of corrosiveness on stainless steel burs shows Omni II and Omnicide solutions the best, Sterall and Sporicidin solutions the poorest, and Glutarex solution intermediate. Omnicide and Glutarex solutions show the least degree of corrosiveness on the carbide burs. 3. SEM analysis of ground, polished, and treated surfaces shows corrosion deposition over the soldered joint of the carbide burs. The stainless steel shank is a cathodic component of a three-way galvanic cell, whereas the silver soldered joint is an anodic component.

The influence of water treatment processes on the presence of organic surrogates and mutagenic compounds in water.

The effects of granular activated carbon filtration and of the combination of ozonation and GAC filtration on the quality of Rhine water were studied in a pilot plant. The scope of the study was to compare both systems in relation to the removal of organic contaminants in water, and to the reduction of the side effects of chlorination. The water quality was measured with organic surrogate parameters (organohalogen, -nitrogen, -phosphorus and -sulphur) and in bacterial mutagenicity assays. In this particular setting, the combination of ozonation and GAC filtration was superior in all points to GAC filtration alone. The effects of ozonation are sometimes quite different, depending on the type of water treated. Its positive influence should be confirmed in a local situation. As GAC treatment causes a shift towards formation of more brominated THM after chlorination, special attention was given to this item. A higher inorganic bromide/DOC ratio resulted in higher brominated THM concentrations after chlorination. However, the mutagens formed during chlorination in presence of more inorganic bromide could be inactivated more easily by rat liver homogenate than in the normal setting. The results of this study confirmed earlier findings stating a negative influence of chlorination on water quality.

Carcinogenic and mutagenic properties of chemicals in drinking water.

Isolated cases of careless handling of industrial and domestic waste has lead to a wide variety of dangerous chemicals being inadvertently introduced into drinking water. However, chemicals with established carcinogenic and mutagenic properties that occur with a high frequency and in multiple locations are limited in number. To date, the chief offenders have been chemicals of relatively low carcinogenic potency. Some of the more common chemicals are formed as by-products of disinfection. The latter process is generally regarded as essential to the production of a "microbiologically safe" drinking water. Consequently, any reductions in what may be a relatively small carcinogenic risk must be balanced against a potential for a higher frequency of waterborne infectious disease. The results of recent toxicological investigations will be reviewed to place the potential carcinogenic and mutagenic hazards frequently associated with drinking water into perspective. First, evidence for the carcinogenicity of certain volatile organic compounds such as trichloroethylene, tetrachloroethylene and carbon tetrachloride is considered. Second, the carcinogenic activity that can be ascribed to various by-products of chlorination is reviewed in some detail. Finally, recent evidence that other chemicals derived from the treatment and distribution of drinking water is highlighted as an area requiring move systematic attention.

Epidemiologic studies of organic micropollutants in drinking water.

Epidemiologic studies have been conducted in order to make a quantitative statement about associations between drinking water contaminants and disease. The basic measures of the association are a rate ratio or relative risk and rate difference or attributable risk. The appropriateness of this measure is dependent on components of study design, data collection, and the analysis of epidemiologic data, and these must be evaluated for each study to determine precision (lack of random error) and validity (lack of systematic error). Internal validity includes considerations for preventing selection bias, minimizing observation bias, and assessing, preventing, and controlling confounding bias within a particular study. No single epidemiologic study is likely to provide a definitive answer, and the results of epidemiologic studies must be interpreted in the context of other scientific information. Epidemiologic studies of organic micropollutants in drinking water have been reviewed and are summarized based on these considerations.

Drinking water and health hazards in environmental perspective.

Among the present environmental issues drinking water quality and more specifically organic micropollutants receive not the highest priority. The long tradition of potable water quality assurance and the sophisticated evaluation methodologies provide a very useful approach which has great potential for wider application in environmental research and policy making. Water consumption patterns and the relative importance of the drinking water exposure route show that inorganic water contaminants generally contribute much more to the total daily intake than organic micropollutants. An exception is chloroform and probably the group of typical chlorination by-products. Among the carcinogenic organic pollutants in drinking water only chlorination by-products may potentially increase the health risk. Treatment should therefore be designed to reduce chemical oxidant application as much as possible. It is expected that in the beginning of next century organic micropollutants will receive much less attention and that the present focus on treatment by-products will shift to distribution problems. Within the total context of water quality monitoring microbiological tests will grow in relative importance and might once again dominate chemical analysis the next century. As disinfection is the central issue of the present water treatment practice the search for the ideal disinfection procedure will continue and might result in a further reduction in the use of chemical oxidants.

Organic micropollutants in drinking water: an overview.

Biological contamination is still the most significant public health risk from drinking water even in industrialized countries. High potential for organic chemical transport to drinking water continues to exist even with source protection because of the multitude of chemical types and quantities. Drinking water is usually not a unique source nor the most significant contributor to total exposure from synthetic organic chemicals but it might be one of the most controllable. The major public concern with drinking water contamination has been possible contribution to cancer risks from organic micropollutants. Even though the actual risks are probably small in most cases it is clearly within the public interest to prevent adulteration of water supplies and to protect their quality for the future so that these concerns or risks can be avoided. A risk assessment/management decision model is suggested which may assist the process of making rational assessments of these contamination problems and control decisions that consciously consider all of the available data in a consistent manner.

Evaluation of different treatment processes with respect to mutagenic activity in drinking water.

Treatment processes which are applied in The Netherlands during the preparation of drinking water have been evaluated with regard to introduction and removal of organic mutagens as well as halogenated organics. It appeared that the most efficient processes in reducing mutagenic activity were activated carbon filtration and artificial dune recharge. In general these processes were also the most efficient in removing halogenated organics. Using low doses of chlorine dioxide (less than 1 mg C1O2/l) for safety disinfection of drinking water, no change or substantial less mutagenic activity than by chlorination (1 mg Cl/l) was found. This counts too for the formation of halogenated organics. Transport chlorination of stored river Meuse water was able to introduce or activate mutagenic nitro organics which have not been found previously. Ozone treatment under field conditions showed mostly a tendency to decrease the activity of organic mutagens. It was also shown that dependent on the water quality and treatment conditions a slight increase of mutagenic activity occurred, but this activity would be reduced by increasing the ozone dose. It seems possible to optimize the ozone treatment conditions regarding the level of ozone dose and the contact time to avoid an increase of mutagenic activity. Furthermore it was shown that when a mutagenic raw water source was used a proper combination of treatment processes is able to produce drinking water in which no mutagenic activity could be detected under the test conditions. Finally it is stated that before far-reaching decisions with respect to use mutagenicity data for a selection of water sources or treatment processes will be made, more information on the relation mutagenic activity from drinking water and effects on human health should become available.

Chloropicrin formation during oxidative treatments in the preparation of drinking water.

Chlorination of water can lead to the formation of chloropicrin. The numerous potential precursors (of various reactivities) observed during this study, confirm this hypothesis. Combination of ozonation and chlorination can also lead to the formation of this compound, dangerous to health; however, the conditions of the formation and particularly the impact of a nitration reaction in the gas phase are still not clearly defined.

Alternative methods for chlorination.

Existing disinfectants are oxidative agents which all present negative effects on subsequent treatment processes. None of them has decisive advantages over chlorine, although chlorine-dioxide and chloramines might at times be preferable. Optimum treatment practices will improve the removal of organic precursors before final disinfection which could then consist in a light chlorine addition. A philosophy of radical change in water treatment technology encompassing physical treatment without chemicals such as membrane filtration, solid disinfectants is presented.

Fractionation of mutagenic compounds formed during chlorination of humic water.

Mutagenic compounds formed during chlorination of humic water were fractionated by reversed phase high performance liquid chromatography, size exclusion chromatography and thin layer chromatography, in sequence. Following each chromatographic separation the mutagenic compounds were found in one fraction predominantly. A remarkable purification of active compounds was achieved without serious losses of activity, thus enabling further purification and mass spectrometric studies of the main mutagens.