Properties Affecting Toxicity

For nanomaterials this is especially true if the exposure scenarios used in the test system are not representative of those likely to be found in the field [91, 92]. For example, the degree of toxicity observed in aquatic invertebrates exposed to multi-walled nanotubes (MWNTs) in water and sediment was influenced by the functional groups on the MWNTs and their preparation for dispersal into the test systems [93]. As noted, even the concept of what constitutes nanomaterials is not fixed [87], so these emerging materials will likely require a rethinking of how their toxicity is assessed and the hazards and risks they might pose to ecosystems [90]. For more information on nanomaterials, including application of life-cycle concepts to their design, see Chapter 8. 

Since one of the main aims of green chemistry is to reduce the use and/or production of toxic chemicals, it is important for practitioners to be able to make informed decisions about the inherent toxicity of a compound. Where sufficient ecotoxicological data have been generated and risk assessments performed, this can allow for the selection of less toxic options, such as in the case of some surfactants and solvents [94, 95]. When toxicological data are limited, for example, in the development of new pharmaceuticals (see Section 15.4.3) or other consumer products, there are several ways in which information available from other chemicals may be helpful to estimate effect measures for a compound where data are lacking. Of these, the most likely to be used are the structure-activity relationships (SARs, or QSARs when they are quantitative). These relationships are also used to predict chemical properties and behavior (see Chapter 16). There often are similarities in toxicity between chemicals that have related structures and/or functional subunits. Such relationships can be seen in the progressive change in toxicity and are described in QSARs. When several chemicals with similar structures have been tested, the measured effects can be mathematically related to chemical structure [96-98] and QSAR models used to predict the toxicity of substances with similar structure. Any new chemicals that have similar structures can then be assumed to elicit similar responses. 

These relationships allow for screening and ranking of toxicity so that the least toxic option may be used if deemed appropriate. They are applied in many jurisdictions for regulatory use in the prediction of ecological effects (and fate) of chemicals when there are no actual toxicity data and decisions need to be made about their use [99]. QSARs have been developed, for example, to predict which chemicals may exhibit persistence, bioaccumulation, and toxicity (PBT) properties, or be very persistent and very bioaccumulative (vPvB) [99]. These methods have been applied to the prediction of chemicals that fall under the European REACH initiative and also high production volume (HPV) chemicals [99]. Currently available QSARs for predicting a compound s fall into two general classes those that have been developed for a nonspecific mode of action, and those that have been developed for specific types or classes of chemicals [99]. 

Since QSAR models for narcosis toxicity based on Kn/W are available for many endpoints and species, it has become a popular approach applied for screening the ecological risk posed by substances for which no data are available. ECOSAR itself, with 150 relationships defined for over 50 chemical classes, has been used to predict toxicity and estimate hazards for chemical warfare agents in marine environments [96], pharmaceuticals [102-104], direct and indirect food additives, and industrial chemicals [105]. Although there are several QSAR and other predictive tools currently available, this section focuses on ECOSAR as it is one of the most widely and easily used. 

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A wide variety of stmetures exist in the cyanine, merocyanine, and oxonol classes of dyes. Properties that may affect toxicity vary widely also. These include solubihty, propensity to be oxidized or reduced, aggregation tendency, and diffusion through membranes. Specific acute toxicity data are Hsted in Table 2, and the LD q data vary widely with the test used. 

Elemental bromine is a readily evaporating liquid (pBr at 1 °C = 0.23 bar) with high reactivity. Because of the good solubility of Br2 in lipids, its aggressive and toxic properties affect skin and mucous membranes (bronchi). The MAK value of elemental Br2 is defined as 0.1 ppm (0.7 mg m 3), while the sense of smell is affected at a value of 0.01 ppm. The lethal concentration (around 100-200 ppm) is reached for example, by twice the MAK value, 5 min, eight times per working unit [91, 92]. 

Microbial methylation is a reaction that affects mainly properties of toxic, inorganic hace elements, which involves the addition of a methyl group to the contaminant molecule. It occurs under aerobic or anaerobic conditions. Mercury methylation, for example, occurs under both conditions and leads to the release of mercury into the atmosphere. 

Surface water can be defined as any river, lake, stream, pond, marsh, or wetland as ice and snow and as transitional, coastal, and marine water naturally open to the atmosphere. Major matrix properties, distinguishing water types from each other, are hard and soft water, and saline and freshwater. Groundwater is typically defined as water that can be found in the saturated zone of the soil. Groundwater slowly moves from places with high elevation and pressure to places with low elevation and pressure, such as rivers and lakes. Partitioning interactions of the groundwater with the solid soil matrix is an important factor influencing the fate of toxicants. Physicochemical properties of water that may affect toxicity of chemicals in all water types are listed in Table 2.2. 

Generic chemical class data are often relevant to assessing potential toxicity and should be a part of any evaluation. The relevant information includes structure-activity relationships and physical-chemical properties, such as melting point, boiling point, solubility, and octanol-water partition coefficient. Physical-chemical properties affect an agent s absorption, tissue distribution, biotransformation, and degradation in the body. 

AES Toxicity. The effect of surfactant structure on toxicity has obvious importance. With AES, there is the tendency of decreased toxicity with increasing EO numbers, at least when comparing AES with the same hydrophobe. Also, increasing alkyl chain length in the hydrophobe will generally increase toxicity. These trends are understandable when one considers that the toxicity mechanism of surfactants, namely membrane disruption and protein denaturation, is a function of the surface-active properties of surfactants. Therefore, the alteration of surface-active properties via structure changes should affect toxicity. 

In this chapter, we present a summary of fire retardant nanoclays used in polymer blends based on the authors previous experience and the literature [15-31]. Because the main objective of this work is to study the fire retarding effects of nanoclays on polymer blends, we will focus on the properties affecting the fire performance of polymer blends (a) dispersion of nanoclay, (b) rheology, (c) thermal stability, and (d) flammability (ignition, fire spread, and toxicity), whereas the effects of nanoclays on mechanical properties and compatibilization can be found easily in references listed in Table 8.1 (e.g.. References [16, 17, 19-21] on compatibilization and [16, 18, 21, 25, 26, 29-31] on mechanical properties). A review of the mechanism by which nanoparticles organize in polymer blends is also available in [32]. 

Fillers can be crystalline or amorphous. Examples of crystalline fillers include calcium carbonate and anatase (titanium dioxide) whereas solid glass beads are amorphous. Many, but not all, fillers are extracted from the earth s crust by mining or quarrying operations examples include calcium carbonate, talc, bentonite, wollastonite (calcium metasilicate) and titanium dioxide. Some fillers are extracted along with impurities that can seriously affect the colour, electrical properties and toxicity of plastics unless they are removed. Others, such as wood flour, have organic origins. The use of wood flour itself has been rather limited because of compatibility problems. 

In addition to the resistance development, the use of Pis in the clinics is further affected by their tolerability, toxicity, and adverse effects. The Pis often interfere with lipid metabolism and trafficking pathways. The side effects might decrease the willingness of patients to undergo treatment and thus contribute indirectly to the evolution of resistance. Therefore, the need for development of novel Pis with broad specificity against Pl-resistant HIV mutants, better pharmacokinetic properties, lower toxicity, and simple dosage is still very urgent. 

Factors which may affect the cost of coal upgrading are environmental considerations such as toxicity, hazardous waste disposal, and carcinogenic properties (131). These and other environmental problems from process streams, untreated wastewaters, and raw products would figure significantly into the cost of commercialization. 

The typical acid catalysts used for novolak resins are sulfuric acid, sulfonic acid, oxaUc acid, or occasionally phosphoric acid. Hydrochloric acid, although once widely used, has been abandoned because of the possible formation of toxic chloromethyl ether by-products. The type of acid catalyst used and reaction conditions affect resin stmcture and properties. For example, oxaUc acid, used for resins chosen for electrical appHcations, decomposes into volatile by-products at elevated processing temperatures. OxaUc acid-cataly2ed novolaks contain small amounts (1—2% of the original formaldehyde) of ben2odioxanes formed by the cycli2ation and dehydration of the ben2yl alcohol hemiformal intermediates. 

Particulate emissions have their greatest impact on terrestrial ecosystems in the vicinity of emissions sources. Ecological alterations may be the result of particulate emissions that include toxic elements. Furthermore, the presence of fine particulates may cause light scattering, known as atmospheric haze, reducing visibility and adversely affecting transport safety, property values, and aesthetics. 

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