1. Solubility of compound in water (S)
The natural environment contains abundant water resources and a good water cycle. Water has good dissolution properties. It can dissolve almost all solid, liquid and gaseous substances. There are few substances in nature that are completely insoluble in water, except that the amount of them dissolves varies. Therefore, in the process of environmental monitoring and research on environmental effects of chemical substances, especially toxic chemicals, their solubility in water may affect the chemical in various environmental factors, such as the atmosphere, water bodies, aquatic organisms and sediments (substrate ) Is one of the most important properties of migration and transformation. Most inorganic compounds are in ionic state in water, so their solubility is relatively large, many organic substances are in non-ionic state, and their solubility in water is relatively small. The solubility of non-ionic compounds mainly depends on their polarity. Non-polar or weakly polar compounds are easily soluble in non-polar or weakly polar solvents. Conversely, strongly polar compounds are easily soluble in polar solvents , Water is one of the strong polar solvents. Therefore, non-polar compounds such as formic acid and carbon tetrachloride dissolve very little in water. Aromatic compounds are weakly polar and have little solubility in water. With the increase of substituents on aromatic rings (such as PAH), their solubility in water is getting smaller and smaller. On the contrary, strong polar alcohols, organic acids, and compounds with OH, SH, NH, and groups are in water. The degree of solvent is quite large.
2. Octanol-water partition coefficient (KOW)
KOW is the ratio of the equilibrium concentration of organic compounds in water and N-octanol in two phases. According to the research, the distribution of octanol to organic matter is very similar to the distribution of organic matter in soil, so when the distribution ratio of compound in octanol and water is KOW, Beijing Opera can successfully calculate KOC. In general, the solubility of organic matter in water can often be reflected by their affinity for the non-polar organic phase. The lipophilic organic compounds have a high partition coefficient in the octanol-water system, and the concentration in the organic phase can reach 101-106 times that in the aqueous phase. For example, common environmental pollutants PAH, PCBS and phthalate. The partition coefficient in octanol-water system is a dimensionless value. The KOW value is a useful indicator to describe the distribution of an organic compound between water and sediment, between organic matter or between aquatic biological fats. The larger the value of the partition coefficient, the greater the solubility of organic matter in the organic phase, that is, the lower the solubility in water.
3. Sediment-water partition coefficient (KOC)
KOC is the equilibrium concentration relationship of compounds in water and sediment-soil two phases. It is also the ratio of the amount of compound adsorbed per unit weight of sediment divided by the amount of the same compound dissolved in unit volume of ambient water. KOC is a quantitative parameter indicating the concentration distribution of a compound in the solid-liquid two phases. This parameter can be used to predict the concentration distribution of the compound in sediment or soil according to its concentration in water. Therefore, this parameter is in environmental science Occupies a very important position in the research.
The KOW value can be used to predict the behavior of a compound in a water environment, and the partition coefficient can be used to predict the compound's distribution in the environment. In fact, it is based on the various molecular reaction forces distributed between water, sediment and organisms, because this reaction force is very similar to the octanol-water system.
4. Vapor pressure (PV)
The vapor pressure of a compound expresses the degree of migration of the compound from the ambient water phase to the atmosphere. Generally speaking, compounds with high vapor pressure, low solubility and high activity coefficient are most volatile. The rate of volatilization is sometimes determined by wind, water flow and temperature. Generally low molecular weight compounds such as alkanes, monocyclic aromatic hydrocarbons and some organic nitrides have high vapor pressure and low water solubility, and some data also use the Henry constant HC to express the volatility of the compound (calculated in Torr / mol ). HC represents the relative equilibrium concentration of the compound in air and water at standard temperature and pressure, and the ratio of the vapor pressure to the solubility of the compound in water indicates the volatility of the compound.
5. Biotransformation and degradation coefficient (Kb)
Biotransformation refers to the catalytic conversion of compounds by biological enzymes. The possibility of biotransformation depends on the stability and toxicity of the compound, the presence of domesticated microorganisms, and environmental factors (including pH, temperature, amount of dissolved oxygen, and available nitrogen). The ease of biodegradation is often referred to as biodegradability. The biodegradable ratio is often used to represent an important indicator for the treatment of toxic organic wastewater with biochemical methods. The biochemical process is a long process. The second-order reaction rate constant for the rate of biotransformation depends on the concentration of the compound and the amount of microorganisms.
6. Bioconcentration factor (BCF)
BCF is the ratio of the concentration of compounds in biological tissue (dry weight) to the concentration dissolved in water. It can also be considered as the ratio of the rate of absorption of compounds by organisms to the rate of purification of compounds in organisms, and the bioconcentration factor is an important indicator that describes the accumulation trend of chemical substances in organisms. According to IRPTC data, the enrichment coefficient of fish living in water with PCB content of 1µg / L after 28 days is 37000 times of that in the water body, and then put back into clean water without PCB, the purification rate after 84 days 61%. The absorption and accumulation of chemicals by aquatic organisms in water bodies is often accomplished through the distribution between water and fat.
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