Toxicants mixtures

Ammonium cyanide may be prepared in solution by passing hydrogen cyanide into aqueous ammonia at low temperatures. It may also be prepared from barium cyanide and ammonium sulfate, or calcium cyanide with ammonium carbonate. It may be prepared in the dry state by gentiy heating a mixture of potassium cyanide or ferrocyanide and ammonium chloride, and condensing the vapor in a cooled receiver. Ammonium cyanide is soluble in water or alcohol. The vapor above soHd NH CN contains free NH and HCN, a very toxic mixture. 

According to this scheme, when Al = 0, components are simply additive if Al > 0, then they are more than additive, and if Al < 0, they are less than additive. Lewis and Perry [347] applied this scheme to analyze the joint effects of equi-toxic mixtures of three compounds on bluegills and found that Al value ranged from 0.30 to -1.23. Even though several Al values in that study deviated significantly from 0, they concluded that the compounds acted by simple addition, based on the average Al of 0.05. 

Snake venoms are composed of a toxic mixture of enzymes that can kill or immobilize prey. 

The consequences a patient can experience if s/he is given no medicine, the wrong medicine, the wrong dose, or a toxic mixture of chemicals can be very serious (see Box 6). It is not surprising that many cases... 

In single-species risk prediction for individual toxicants and toxicant mixtures, the effect is expressed as the proportion of an exposed population that is likely to be somehow affected by toxic action (quantal responses), or as a reduction in performance parameters such as growth, clutch size, and juvenile period (continuous responses). Both concentration addition- and response addition-based methods are commonly applied for both response types. Assemblage-level risk prediction has only been introduced more recently (e.g., De Zwart and Posthuma 2005) and is founded on similar principles while focusing on the fraction of species that are likely affected by mixture exposure. 

SSD-based approaches are used for monitoring and trends analyses regarding toxic mixtures per se, and for the analysis of situations of multiple stressors. However, none of the SSD-based methods assumes a priori that only concentration addition or response addition would apply. Even the earliest applications recognize the relevance of both models. These uses of SSDs are described under Tier-3 methods. 

Various examples exist of the use of msPAF in multiple-stress analysis to acknowledge the relative role of toxicant mixtures in shaping ecological communities. Mulder et al. (2004) studied the decline of butterfly populations in a nature reserve in The Netherlands. It appeared difficult to establish associations between decline and the major environmental parameters, such as pH and water relationships. 

Mesman M, Posthuma L. 2003. Ecotoxicity of toxicant mixtures in soils recommendations for application in the Dutch regulatory context, as derived from a scientific review on approaches, models and data. No. 711701035. Bilthoven (The Netherlands) National Institute of Public Health and the Environment (RIVM), 70 p. 

Whole mixture approaches may also be indicated as diagnosis instruments, and are often used for site-specific, retrospective investigations, and hence often deal with complex mixtures, that is, those that have at least partly an unknown chemical composition. This may, for example, concern industrial or field samples containing a mixture of chemicals that is only partly or incompletely characterized. Whole mixture approaches may include bioassays, effect-directed analysis (EDA), and toxicity identification evaluation (TIE). Bioassays may be used to determine actual toxicity of an environmental sample, and do not necessarily bother about composition of the mixture or toxicity of the components. EDA and TIE approaches may be used to identify the (groups of) chemicals that are the main cause of toxicity. Mixture toxicity concepts may be useful to explain how chemicals present in the sample could have interacted to cause its toxicity. 

Haas CN, Kersten SP, Wright K, Frank MJ, Cidambi K. 1997. Generalization of independent response model for toxic mixtures. Chemosphere 34 699-710. 

Posthuma L, De Zwart D. 2006. Predicted effects of toxicant mixtures are confirmed by changes in fish species assemblages in Ohio, USA, rivers. Environ Toxicol Chem 25 1094-1105. 

Reisfeld B, Yang RSH. 2004. A reaction network model for CYP2E1-mediated metabolism of toxicant mixtures. Environ Toxicol Pharmacol 18 173-179. 

In addition, the line is filled with a highly toxic mixture. Therefore, safety must be paramount in the mind of the design engineer and in that of the operators. 

To solve Uiis problem, compute tlie cancer risk for each air toxic mixture by multipl> ing the average concenuation by the miit cancer risk. 

See also Common Mechanism of Toxicity Mixtures, Toxicoiogy and Risk Assessment Modifying Factors of Toxicity. 

See also Absorption Analytical Toxicology Biotransformation Distribution Exposure Mechanisms of Toxicity Mixtures, Toxicology and Risk Assessment Pharmacoki-netics/Toxicokinetics Resistance to Toxicants. 

The results of the traditional acute single-species toxicity tests conducted in the laboratory cannot be used alone to predict effects on natural populations, communities, and ecosystems. The cultural species in laboratory tests are different from those in most ecosystems. Conditions such as the size of the test species, its life stage, and nutritional state can have an effect on toxicity. Furthermore, the experimental conditions in laboratory tests cannot duplicate the complex interacting physical and chemical conditions of ecosystems, such as seasonal changes in water temperature, dissolved oxygen, and suspended solids. In addition to these environmental modifying factors, aquatic life is usually exposed simultaneously to numerous potential toxicants (mixtures). Although the toxicities of binary and ternary mixtures have been evaluated for some chemicals in laboratory toxicity tests, the resultant information has predictive limitations. 

The toxic mixture examples just presented are only a small fraction of those that are fully discussed and referenced in Parts 3 and 4 of this book. 

At times, people react acutely or chronically to unknown stimulants. In such cases, it is hypothesized that unidentified mixtures are often the causative agents. Such toxic mixtures can arise from mixtures of two or more household products as well as from the mixture of household chemicals with chemicals from foods, outdoor air pollutants, water pollutants, or industrial chemicals that are carried into the home on the clothing of workers. In many of these mixture exposure instances, the health effects cannot be attributed to any of the individual chemicals present, but produce distinct clinically defined symptoms. 

The following sections describe case studies for which the effects of single chemicals have been ruled out. These studies represent only a fraction of those demonstrating the known effects of toxic mixture exposure. They are meant to illustrate the scope of hazards faced when humans are exposed to toxic chemical mixtures. 

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