Environmental fate physicochemical properties

C. Tomlin, ed.. The Pesticides Manual A World Compendium, Incorporating the Agrochemicals Handbook, 10th ed.. The British Crop Protection Council and The Royal Society of Chemistry, Crop Protection PubHcations, Cambridge, U.K., 1994. Includes 725 entries by common name in alphabetic order, with chemical stmcture, chemical name(s), molecular formula, CAS Registry Number, physicochemical properties, commercialisation, mode of action, uses, trade names, analytical methods, mammalian toxicology, ecotoxicology, and environmental fate. 

It is also important to develop an understanding of the movement of chemicals through the environment by investigating their fate and behaviour. Based on a chemical s inherent physicochemical properties, it is possible to predict with some degree of certainty which environmental compartment it is likely to reside in and to what extent it is likely to be bioavailable and accumulate through the food chain. 

Because of the influence of the ligand, physicochemical properties and environmental fate modelling derived from them are often uncertain for the organotins. 

Despite the existence of several databases for certain substances, it is not possible to find physicochemical and/or toxicological parameters to assess the risk for all substances. The lack of data is one of the main problems in risk assessment. This is especially true for emerging pollutants. One solution to solve this problem is the use of QSAR or estimation tools. QSAR models correlate the structure of the substance with their activities (physicochemical properties, environmental fate, and/or toxicological properties). 

Klopffer, W., Rippen, G., Frische, R. (1982) Physicochemical properties as useful tools for predicting the environmental fate of organic chemicals. Ecotoxicol. Environ. Saf. 6, 294—301. 

The fate of trace organic compounds applied to soil is controlled by several processes volatilization, degradation, sorption, leaching and bioaccumulation. The significance of each process is affected by the physicochemical properties of the organic compound, sludge and soil properties, and environmental conditions. 

The primary processes determining the fate of crude oils and oil products after a spill are (1) dispersion, (2) dissolution, (3) emulsification, (4) evaporation, (5) leaching, (6) sedimentation, (7) spreading, and (8) wind. These processes are influenced by the spill characteristics, environmental conditions, and physicochemical properties of the material spilled. 

Environmental fate Chemicals released in the environment are suscephble to several degradahon pathways, including chemical (i.e., hydrolysis, oxidation, reduction, dealkylahon, dealkoxylation, decarboxylahon, methylation, isomerization, and conjugation), photolysis or photooxidahon and biodegradation. Compounds transformed by one or more of these processes may result in the formation of more toxic or less toxic substances. In addihon, the transformed product(s) will behave differently from the parent compound due to changes in their physicochemical properties. Many researchers focus their attention on transformahon rates rather than the transformahon products. Consequently, only limited data exist on the transitional and resultant end products. Where available, compounds that are transformed into identified products as weh as environmental fate rate constants and/or half-lives are listed. 

Initial environmental fate and effect analysis Physicochemical properties and fate assessment... 

To fill the data gaps for determining potential hazards to human health and the environment, the EPA often relies on internally developed estimation methods. These include empirical data available for structural analogs and computational methods for the estimation of physicochemical properties, which in turn are used to estimate environmental fate, bioavailability, toxicity in humans and aquatic organisms, and exposure [17]. 

Possible transformation products can be numerous and their identification and assessment are both costly and time consuming. Transformation normally causes a change in the physicochemical and (eco)toxicological properties, that is, transformation products have different environmental fates and effects. A risk assessment of such compounds is often not feasible because these chemicals are not available in the amounts needed for testing, and their identities may not even be known. 

Chemical reactivity and biological activity can be related to molecular structure and physicochemical properties. QSAR models can be established among hydrophobic-lipophilic, electronic, and steric properties, between quantum-mechanics-related parameters and toxicity and between environmental fate parameters such as sorption and tendency for bioaccumulation. The main objective of a QSAR study is to develop quantitative relationships between given properties of a set of chemicals and their molecular descriptors. To develop a valid QSAR model, the following steps are essential ... 

The search for relationships among the dynamic and equilibrium properties of related series of compounds has been a paradigm of chemists for many years. The discovery of such unifying principles and predictive relationships has practical benefits. Numerous relationships exist among the structural characteristics, physicochemical properties, and/or biological qualities of classes of related compounds. Perhaps the best-known attribute relationships are the correlations between reaction rate constants and equilibrium constants for related reactions commonly known as linear tree-energy relationships (LFERs). The LFER concept led to the broader concepts of QSARs, which seek to predict the environmental fate of related compounds based on correlations between their bioactivity or physicochemical properties and structural features. For example, therapeutic response, environmental fate, and toxicity of organic compounds have been correlated with... 

Structure-activity relationships (SARs) and quantitative structure-activity relationships (QSARs), referred to collectively as QSARs, can be used for the prediction of physicochemical properties, environmental fate parameters (e.g., accumulation and biodegradation), human health effects, and ecotoxicological effects. A SAR is a (qualitative) association between a chemical substructure and the potential of a chemical containing the substructure to exhibit a certain physical or biological effect. A QS AR is a mathematical model that relates a quantitative measure of chemical structure (e.g., a physicochemical property) to a physical property or to a biological effect (e.g., a toxicological endpoint). 

The goals of this section are to introduce methods of modeling chemical movement within and between environment compartments, to define specific translocation and transformation processes, to provide a basic understanding of the association among chemical structure, physicochemical properties, and susceptibility to specific translocation and transformation processes, and to provide methods of accessing and estimating physicochemical properties and environmental fate of chemicals. 

As indicated previously, the final disposition of a chemical in the environment is dependent on the environmental conditions, characteristics of the media involved, and the various physicochemical properties of the contaminants. Table 6.6 provides a listing of properties describing the chemical, medium, and potential for translocation and transformation. This section focuses on chemical properties that are frequently used to assess the fate of a contaminant in air, water, soil, or biota. The goals of this section are to provide brief descriptions of relevant properties of a contaminant and to directly link specific ranges of these properties to predicted fate in the environment. 

Physicochemical Properties and Their Influence on Environmental Fate and Behaviour... 

A9.6.4.4 The U.S. EPA has recently posted a draft document on its website Development of Chemical Categories in the HPV Challenge Program, that proposes the use of chemical categories to voluntarily compile a Screening Information Data Set (SIDS) on all chemicals on the US HPV list. .. [to provide] basic screening data needed for an initial assessment of the physicochemical properties, environmental fate, and human and environmental effects of chemicals (US EPA, 1999). This list consists of ...about 2,800 HPV chemicals which were reported for the Toxic Substances Control Act s 1990 Inventory Update Rule (lUR) . 

A further OECD Council Decision in 1991 focused on HPV chemicals. These decisions prompted the development of a minimum hazard data set to describe an HPV chemical - the Screening Information Data Set, or SIDS. This includes physicochemical properties (melting point, boiling point, vapor pressure, water solubility, and octanol-water partition coefficient) environmental fate (stability in water, photodegradation, biodegradation, and an estimate of distribution/transport in the environment) environmental effects (acute toxicity to aquatic vertebrates, invertebrates, and plants) and human health effects (acute toxicity, repeated-dose toxicity, toxicity to the gene and the chromosome, and reproductive and developmental toxicity). 

For information on physicochemical properties, toxic potential and potency, environmental distribution and fate, and biokinetic processes... 

In the read-across or analogue approach, endpoint information for one chemical is used to make a prediction of the endpoint for another chemical, which is considered to be similar in some way. In principle, read-across can be used to assess physicochemical properties, environmental fate, and (eco)toxicity effects, and it may be performed in a qualitative or quantitative manner. A one-to-one read-across is an ad hoc comparison based on the similarity between two chemicals. Read-across carried out between three or more chemicals can lead to the formulation of generalizations about the group, and eventually to establish that a common substructure can be associated with a SAR. Although the distinction between SAR and read-across may appear vague, the term SAR usually refers to an approach that has been subjected to some degree of statistical validation, and thus to a more formalized approach than read-across. 

One of the first steps in the risk assessment process involves the collection of available information on the physicochemical properties, ecological effects, environmental fate, and health effects for a given chemical. In a nontesting strategy, data are also essential to make predictions by means of the read-across approach. Data can be retrieved from books, Internet-based resources (free and commercial resources), or commercial databases. This is a vast and rapidly developing field, so the reader is referred elsewhere for discussions of data sources [28-31],... 

The EEC in a given matrix is a function of the estimated use rate of the chemical in the lidd and the fate and transport of the chemical in the environment. The distribution and degradation of a compound is a function of the physicochemical properties (e.g. solubility, octanol/water partition coefficient, Henry s Law constant), the environmental fate processes and the use pattern (i.e. method of application, rate, frequency of application) (Table 8.4). Aquatic EEC s are... 

Table 8.4. Physicochemical and environmental fate properties of PBO used in EXAMS modelling...

Environmental Fate. There is a paucity of experimental data regarding the environmental fate of 2-butoxyethanol and 2-butoxyethanol acetate. Fates of these two compounds estimated from their physicochemical properties indicate that a few critical areas need further elucidation. Although it has been estimated that hydrolysis of 2-butoxyethanol acetate is not an important fate process in the environment (ASTER 1995b), experimental confirmation of the rate of hydrolysis under conditions typically found in water and moist soil (pH 5-9) would be helpful. If hydrolysis of 2-butoxyethanol acetate is found to be an important fate determining process, it would be important to identify the products of hydrolysis and assess the health and environmental impacts of the degradation products. 

While these points are now understood qualitatively, there is a general lack of quantitative information on specific processes for specific pesticides. The lack of such information has hampered the development of capability for predicting the relative role of atmospheric processes in overall pesticide environmental fate, and specifically of equations correlating atmospheric processes with pesticide physicochemical properties and environmental variables. 

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