Chemical mixtures synergistic effects

The effects of atmospheric pollution are chemical, and concentration, specific. However, additive, and sometimes synergistic, effects arising from mixtures are important. A sutmuary of the potential effects of common air pollutants is given in Table 16.10. 

The simultaneous determination of trimeprazine and methotrimeprazine in mixtures using the classical peroxyoxalate system based on the reaction between TCPO and hydrogen peroxide was used to validate the new methodology. The reaction was implemented by using the CAR technique, which increased nonlinearity in the chemical system studied by virtue of its second-order kinetic nature. In addition, both drugs exhibited a similar kinetic behavior and synergistic effects on each other, as can be inferred from the individual and combined (real and theoretical) CL-versus-time response curves. 

In dealing with the heterogeneous gas-liquid-solid mixture characterized as photochemical smog, it is important to realize from a chemical, as well as a biological, point of view that synergistic effects may occur. 

Environmental contamination usually consists of a mixture of pollutants and their partially degraded derivatives. Such an ill-defined chemical mixture will eventually lead to the formation of an ecosystem of microbes. The individual member species cannot survive in the toxic and hostile environment. Effective bioremediation technologies should therefore invoke a mixture of microorganisms forming synergistic consortia. Any realistic bioremediation concept is based on the recognition that it is the concerted action of various species, which may bring about the desired clean-up effect. 

There are other such scenarios that can be proposed. Evidence exists for both additive and synergistic actions. There is nothing magical about mixtures. The effects of mixtures can be explained in terms of the actions of the individual chemicals, all of which obey the usual physicochemical laws.3°... 

The use of skin permeation enhancers in combination for synergistic effects has been studied in the transdermal literature (70). Such synergistic methods can be grouped in three categories (i) combination of two physical methods, e.g., ultrasound and iontophoresis (71-75) (ii) combination of a physical method with a chemical enhancer, e.g., use of ultrasound with sodium lauryl sulfate or isopropyl myristate (76-80) and (iii) combination of two chemicals, e.g., terpenes and propylene glycol (46,81-88). Numerous studies have been published on using combination of two physical methods or use of a physical method in conjunction with a chemical enhancer. Use of a physical method, by itself or in combination with another physical method, increases application cost for delivery purposes as mentioned before. In addition, there are unexplored safety and membrane recovery issues associated with these methods. A few reports have also been published on the use of a mixture of chemical enhancers for enhancing transdermal delivery. Typically, such studies use... 

In reality, medical scientists cannot yet predict the toxic effects to individual humans from consuming low-level chemical mixtures that permeate our food. Although scientists know virtually nothing about the toxic effects of chemical mixtures, they do know that there can be synergistic effects from multiple chemical exposures.1... 

An essential oil used for aromatherapy should not be chemically altered in any way for it to be effective. A true oil is a very complex mixture containing hundreds of compounds that themselves may vary in terms of factors previously described - growth conditions and so on. The unidentified compounds contribute to the overall synergistic effect of the oil, as do the known substances. 

A classification of whole products would minimize the risk of not discovering possible additive and synergistic effect of chemical mixtures. A labelling of the risk of the whole product would be less confusing and increase the clarity of the risk communication to consumers. 

Exposure to a single PAH compound seldom occurs in situations of relevance to local law enforcement agencies or defense forces. Often, people are exposed to PAHs in combination with other toxicants such as aliphatic hydrocarbons and/or metals (NRC, 2005). Information on toxicity of chemical mixtures, of which PAHs are a constituent, is lacking. Until such studies are undertaken in animal models, it is difficult to establish whether PAHs have an additive or a synergistic effect in determining neurotoxicity. 

Traditionally, toxicologists have addressed the effects of chemical mixtures as being additive, antagonistic, potentiated, or synergistic.M To these, sequential effects are added here. 

Here, again, numerous mixtures are possible. An example of a toxic binary mixture of chemicals on this list shows a synergistic effect. When administered together, ethanol inhibits the metabolism of ethyl acetate, resulting in greater toxicity of ethyl acetate. I29l... 

In one study, leachates from a polyfiber factory, an aeronautical plant, and a municipal sludge site were all shown to induce DNA damage in human peripheral blood lymphocytes. The authors of the study conclude that synergistic effects of the mixtures of chemicals in the leachates may be responsible for the DNA damage. 38 Similar cytotoxic effects were observed in studies where animals were exposed to ISW 39 and MSW 40 leachates. These studies underscore the dangers posed to ISW and MSW workers, as well as to people who are exposed to leachates that infiltrate drinking water. 

The effects of individual substances on a wide range of species in the environment are rarely understood and, depending on the adequacy and the quality of the information, an uncertainty factor usually is applied. There are a number of limitations to this approach. It is substance specific and of the total number of listed chemicals less than 1% have sufficient information to derive a safe level. Uncertainty factors can move towards overly stringent control, the approach is unable to consider toxic effects of complex mixtures (which is the usual route of entry) and it takes no account of additive or synergistic effects. 

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