Chemical substances existing chemicals

Environment As mentioned previously, a chemical product has to be produced for a particular function. Its existence is determined in the presence of the environment that it interacts with. This is to say, different from a chemical substance, the chemical product needs an environment to be defined. There is no empty space there must be a system and an environment. Therefore, this environment also needs a definition, which is established in the application field, and market for a particular chemical product. 

A gaseous chemical substance exists in the pres ce of a solid polymer, as gaseous cyanogen in the presence of solid para-cyanogen, or, again, gaseous cyanic acid with ciystaUized cyanuric acid. 

United States Environmental Protection Agency. Office of Pesticides and Toxic Substances, Existing Chemicals Assessment Division. Information packet on the OECD Screening Information Data Set (SIDS) Program for high production volume (HPV) chemicals, 1992. 

AH of the amyl alcohols are TSCA and EINECS (European Inventory of Existing Commercial Chemical Substances) registered. 

The LD q for sodium bromide taken orally by rats is 3.5 g/kg body weight, and the TD q orally in rats is 720 mg/kg (8). RTECS Hsts data on reproductive effects in male and female rats. Sodium bromide is Hsted in the TSCA Inventory, the Canadian Domestic Substances Hst (DSL), the European Inventory of Existing Commercial Chemical Substances (EINECS), the Japanese Existing and New Chemical Substances (ENCS), and the Korean Existing Chemicals Hst (ECL). It is not regulated by the U.S. Department of Transportation. 

In the European Union, coal-derived complex chemical substances, ie, those contained in the European Inventory of Existing Commercial Chemical Substances, have been classified for carcinogenicity in the twenty-first adaptation to technical progress of the European Commission (EC) Dangerous Substances Directive 1994 67/548/EEC (57). The EC Regulation 793/93 requires data sets to be submitted by producers or importers to the... 

Along with increasing evidence of health benefits from consumption of vitamins at levels much higher than RE) A recommendations comes concern over potential toxicity. This topic has been reviewed (19). Like all chemical substances, a toxic level does exist for each vitarnin. Traditionally it has been assumed that all water-soluble vitamins are safe at any level of intake and all fat-soluble vitamins are toxic, especially at intakes more than 10 times the recommended allowances. These assumptions are now known to be incorrect. Very high doses of some water-soluble vitamins, especially niacin and vitamin B, are associated with adverse effects. In contrast, evidence indicates that some fat-soluble micronutrients, especially vitamin E, are safe at doses many times higher than recommended levels of intake. Chronic intakes above the RDA for vitamins A and D especially are to be avoided, however. 

Chemicals are classed as either elements or compounds. The former are substances which cannot be split into simpler chemicals, e.g. copper. There are 90 naturally-occuiTing elements and 17 artificially produced. In nature the atoms of some elements can exist on their own, e.g. gold, whilst in others they link with other atoms of the same element to form molecules, e.g. two hydrogen atoms combine to form a molecule of hydrogen. Atoms of different elements can combine in simple numerical proportions 1 1, 1 2, 1 3, etc. to produce compounds, e.g. copper and oxygen combine to produce copper oxide hydrogen and oxygen combine to produce water. Compounds are therefore chemical substances which may be broken down to produce more than one element. Molecules are the smallest unit of a compound. 

The TLVs for airborne contaminants are based on the premise that although all chemical substances are toxic at some concentration for some period of time, a concentration exists for all substances from which no toxicity may be expected no matter how often the exposure is repeated. A similar premise holds for substances producing irritation, discomfort and nuisance. In using these limits, items such as excursion factors, ceiling values, "skin" notations, mixtures of substances, and inert material should be considered. These factors are discussed below. 

The phase rule is a mathematical expression that describes the behavior of chemical systems in equilibrium. A chemical system is any combination of chemical substances. The substances exist as gas, liquid, or solid phases. The phase rule applies only to systems, called heterogeneous systems, in which two or more distinct phases are in equilibrium. A system cannot contain more than one gas phase, but can contain any number of liquid and solid phases. An alloy of copper and nickel, for example, contains two solid phases. The rule makes possible the simple correlation of very large quantities of physical data and limited prediction of the behavior of chemical systems. It is used particularly in alloy preparation, in chemical engineering, and in geology. 

The Chemical Substances Threshold Limit Values Committee classifies certain substances found in the occupational environment as either confirmed or suspected human carcinogens. The present listing of substances that have been identified as carcinogens takes two forms those for which a TLV has b n assigned and those for which environmental and exposure conditions have not been sufficiently defined to assign a TLV. Where a TLV has been assigned, it does not necessarily imply the existence of a biological threshold however, if exposures are controlled to this level, we would not expect to see a measurable increase in cancer incidence or mortality. 

Substances listed on the European Inventory of Existing Chemical Substances (EINECS). 

There are two disadvantages to the existing vapour pressure tables. Rrst of all, like any experimental data, there is no agreement between sources. This is worsened by the decision to take only one value into account for each chemical substance. This fact may encourage the user to take on trust the figure proposed, which is sometimes unjustified. Secondly, these values are given for a temperature that does not always correspond to the thermal conditions in which the chemical substance will be handled. Some references, to overcome this difficulty, offer several values. For instance, Weka most often gives three values, 20, 30 and 50°C, and the coefficients A, B, C in Antoine s equation can thus be calculated ... 

An element is a substance that cannot be broken down into simpler substances by ordinary chemical means. A chemical compound is a substance made up of two or more elements that have been chemically bonded together. Scientists believe that solid sulfur compounds do not exist on Venus like they do on Earth because, at about 900° Fahrenheit (480° Celsius), the surface temperature on Venus is too hot for them to form in the first place. This temperature is well above the melting point of sulfur (235°F [ 113°C]). Therefore, instead of being incorporated into rocks, the sulfur on Venus continues to float around in the atmosphere in the form of the chemical compound sulfur dioxide (S02). 

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