Toxic species

Ash particles produced in coal combustion are controlled by passing the flue gases through electrostatic precipitators. Since most of the mass of particulate matter is removed by these devices, ash received relatively little attention as an air pollutant until it was shown that the concentrations of many toxic species in the ash particles increase as particle size decreases. Particle removal techniques become less efiective as particle size decreases to the 0.1-0.5 pm range, so that particles in this size range that escape contain disproportionately high concentrations of toxic substances. 

LIF has been used in a multitude of studies to measure the concentrations of some important radicals, most frequently of OH, CH, and NO. While OH is an important contributor to the fuel degradation and oxidation pathways and an indicator of hot areas in flames, CH has often been used to trace the flame front location, whereas the direct investigation of NO formation is of importance with regard to NO, being a regulated air toxic. Species including other elements, such as sulfur, phosphorus, alkali, etc., can be detected by LIF in combustion systems, and often, an indication of their presence may already be a useful result, even if quantification is not possible. 

Marine Worms. (Platyhelminthes, Rynchocoela, Annelida, Sipunaelida.) A variety of species from worm phylla have been found to contain toxins. There are approximately 56,000 species of worms (14,000 annelids, 25,000 platyhelminthes, 15,000 nematodes, and 800 nemertines), and of these, most of the toxic species are found in the nemertines. The most well-known toxin is nereisotoxin which has been modified to form a very useful insecticide. 

The annelids include the bristle worms and blood worms in which toxicity is associated with bristle-like setae and/or biting jaws. In the order Polychaetae, toxicity is usually found in three genera (Chloeia, Eurythoe, Hemodice). The platyhelminthes are not associated with many cases of human toxicity. The only class of platyhelminthes in which toxicity can readily be found is in the Turbellaria. In the Rhynchocaela (ribbon worms), toxic species include Lineus sp. Some platyhelminthes (e.g., Planocera multitenta) have been found to contain tetrodotoxin 16). 

Approaches are required for the following stages identification of toxic species, screening techniques for detecting toxicity, techniques for purifying toxins and provisionally identifying chemical nature, and techniques for tentatively identifying mechanisms of action. 

Identification of Toxic Species. In trying to identify toxic species suitable for further studies, careful consideration should be given to zoology and, where applicable, clinical toxicology. Zoological knowledge allows the identification of the species which use toxins for purposes of offence and/or defense. For example, observations of carnivorous fish showed that many appear able to identify toxic species and avoid... 

Screening Techniques for Detecting Toxicity. Simple toxicity screening techniques are necessary to identify toxic species and to monitor the efficacy of isolation and purification procedures used to purify toxins. Atterwill and Steele 108) have recently comprehensively reviewed in vitro methods for toxicology and so much of the following is in the nature of a general overview. 

The role of the secretion from the root apex of organic acids such as citric and malic in the resistance of maize and wheat, respectively, to Al toxicity (81,82) has emerged recently as one with plausibility (83). These studies have been carried out in solution cultures, but how does the suggestion hold up in soil The first and probably greatest difficulty is that the toxic species of Al, probably hydrated Al ", must diffuse to some site in the root apex and stimulate the produc-... 

The use of copolymers is essentially a new concept free from low-MW additives. However, a random copolymer, which includes additive functions in the chain, usually results in a relatively costly solution yet industrial examples have been reported (Borealis, Union Carbide). Locking a flame-retardant function into the polymer backbone prevents migration. Organophosphorous functionalities have been incorporated in polyamide backbones to modify thermal behaviour [56]. The materials have potential for use as fire-retardant materials and as high-MW fire-retardant additives for commercially available polymers. The current drive for incorporation of FR functionality within a given polymer, either by blending or copolymerisation, reduces the risk of evolution of toxic species within the smoke of burning materials [57]. Also, a UVA moiety has been introduced in the polymer backbone as one of the co-monomers (e.g. 2,4-dihydroxybenzophenone-formaldehyde resin, DHBF). 

To facilitate biodegradation, the leachate may require modification through pH adjustment, removal or addition of oxygen, amendment with nutrients, or dilution or removal of toxic species. Microbial nutrition is complex and is better understood for aerobes than for anaerobes.34 Biological processes typically favor a pH near 7. Pretreatment processes to remove inhibitory components include coagulation and precipitation, carbon adsorption, and possibly ozonation. 

In natural waters, dissolved zinc speciates into the toxic aquo ion [Zn(H20)6]2+, other dissolved chemical species, and various inorganic and organic complexes zinc complexes are readily transported. Aquo ions and other toxic species are most harmful to aquatic life under conditions of low pH, low alkalinity, low dissolved oxygen, and elevated temperatures. Most of the zinc introduced into aquatic environments is eventually partitioned into the sediments. Zinc bioavailability from sediments is enhanced under conditions of high dissolved oxygen, low salinity, low pH, and high levels of inorganic oxides and humic substances. 

Metalls and metalloids are characterized by special ecochemical features. They are not biodegradable, but undergo a biochemical cycle during which transformations into more or less toxic species occur. They are accumulated by organisms and cause increased toxic effects in mammals and man after long term exposure [55]. 

Numerous commercial dyes are metal chelate complexes. These metals form pollutants which must be eliminated. One of the strongest points in favour of electrochemical reduction/removal of metal ions and metal complexes - the metal ions and weakly complexed ions form the toxic species - and of the metals from the metal-complex dye is that they are eliminated from the solution into the most favorable form as pure metal, either as films or powders. Polyvalent metals and metalloids can be transferred by reduction or oxidation treatment to one valency, or regenerated to the state before use, e.g. Ti(III)/Ti(IV), Sn(II)/Sn(IV), Ce(III)/Ce(IV), Cr(III)/Cr(VI), and can be recycled to the chemical process. Finally, they can be changed to a valence state better suited for separation, for instance, for accumulation on ion exchangers, etc. Parallel to the... 

Quite generally, the interphase between an organism and its environment encompasses the elements outlined in Figure 1 of Chapter 1. The scheme shows that the cell membrane, with its hydrophobic lipid bilayer core, has the most prominent function in separating the external aqueous medium from the interior of the cell. The limited and selective permeabilities of the cell membrane towards components of the medium - nutrients as well as toxic species - play a governing role in the transport of material from the medium towards the surface of the organism. 

Another factor to take into account in biouptake studies is the possibility that the organism develops strategies of eliminating toxic species by means of efflux [38,52,101]. As a first approach, the efflux rate can be set proportional to the amount of species taken up that has been internalised, thus converting the boundary condition of flux balances for two sites, equation (4), into ... 

Induction of P-450 Metabolism and Isoenzymes. When organisms are exposed to certain xenobiotics their ability to metabolize a variety of chemicals is increased. This phenomenon can produce either a transitory reduction in the toxicity of a drug or an increase (if the metabolite is the more toxic species). However, this may not be the case with compounds that require metabolic activation. The exact toxicological outcome of such increased metabolism is dependent on the specific xenobiotic and its specific metabolic pathway. Since the outcome of a xenobiotic exposure can depend on the balance between those reactions that represent detoxication and those... 

Titanium dioxide has also been involved in the photocatalysis of toxic inorganic substances to yield harmless or less-toxic species. Sterilisation of drinking water by chlorine yields potentially carcinogenic compounds so that ozone has been used as an alternative sterilising agent. Bromate... 

---