PERSISTENT AND TOXIC

Apart from the oxidations just mentioned, cyclodienes are rather stable chemically. It should, however, be noted that dieldrin can undergo photochemical rearrangement under the influence of sunlight to the persistent and toxic molecule photo dieldrin, which occurs as a residue following the application of this insecticide in the field. 

This process shonld be considered in the light of the preceding comments on association. Many experiments on the recoverability, persistence, and toxicity of xenobiotics have used spiked samples that do not take into acconnt the cardinal issne of alterations in the contaminant that have taken place after deposition. This is termed aging, and shonld be evalnated critically in determining persistence. Some examples are given below as illnstration for both terrestrial and aquatic systems ... 

Tanabe, S., N. Kannan, A. Subramanian, S. Watanabe, and R. Tatsukawa. 1987. Highly toxic coplanar PCBs occurrence, source, persistency and toxic implications to wildlife and humans. Environ. Pollut. 47 147-163. 

APEOs are used in domestic and industrial applications. They are applied as detergents, emulsifiers, wetting agents, dispersants or solubilisers. APEO derived from nonylphenol (NP), i.e. nonylphenol ethoxylates (NPEOs) comprises about 80% of the total market volume, while octylphenol-derived surfactants (OPEOs) account for 15-20%. Because of the persistence and toxicity of some degradation intermediates, their use has been reduced in several countries either through voluntary bans by the chemical industry or by legal regulations. However, excellent properties in combination with comparably low production costs hampers their complete replacement with other more environmentally acceptable alternatives. 

Ecotoxicological effects have been demonstrated for a number of surfactants or their metabolites, including some still currently in use, such as the nonylphenol ethoxylates [1], and as such there is a necessity to find more environmentally acceptable alternatives. Whilst the silicones are not the major surfactant type in use to date, the efficient properties and indications of low environmental persistence and toxicity demonstrate their potential for widespread use [2-4]. Relatively little is known about these new, rapidly emerging surfactants and the purpose of this chapter is thus to collate the available data, present new data, and identify the future research required in this area in order to evaluate the environmental relevance of this class of surfactants. 

Mote Probably the most newsworthy, publicized incidents have stemmed from public and industrial dumping sites, covered in this summary under landfill leachate. A class of pesticides most commonly found in groundwater is ncmatocidcs. They arc particularly difficult because manufacturers design them to be both persistent and toxic. DBCP il,2-dibromo-3-chloropropane) is a representative nematocide. 

Polychlorinated biphenyls (PCBs) have been known for sometime as persistent pollutants, which can be readily bioaccumulated through the food chain causing well-documented toxic effects in number of species including humans [191]. Consequently, PCBs are commonly routinely monitored as potential industrial pollutants. Due to their environmental persistence and toxicity, detection limits in the ng ml-1 region are generally required. Consequently, such work has generally required solvent or solid extraction and concentration steps prior to separation by GC in conjunction with electron capture detection, or mass... 

The Binational Toxics Strategy between the USA and Canada has identified 12 bioaccumulative substances (referred to as Level-1 substances) having significant persistency and toxicity to the Great Lakes system, with the goal of reducing the sources of these substances to achieve naturally occurring levels [23]. Six of the 12 Level-1 substances are OC pesticides aldrin/dieldrin, chlordane, DDT, HCB, mirex, and toxaphene. Several other OC pesticides, such as endrin, heptachlor/heptachlor epoxide, hexachloro-cyclohexanes, tetra- and penta-chlorobenzenes, and pentachlorophenol, have been identified as Level-2 substances. 

PAHs are hydrophobic compounds and their persistence in the environment is mainly due to their low water solubilities and electrochemical stability. Higher molecular weight PAHs exhibit greater environmental persistence than lower molecular weight PAHs due to an increase in hydrophobicity and an increase in stability with increasing mass. Evidence suggests that the lipophilicity, environmental persistence, and toxicity of PAHs increase as the molecular size of the PAHs increases up to four or five fused benzene rings.18 This relationship... 

Once chemical agents are fully dispersed, they do not tend to persist in the environment because of their high chemical reactivity, particularly with water (hydrolysis). However, in extremely dry desert climates, they can persist for considerable periods of time (U.S. Army, 1988). The major environmental degradation products of nerve and mustard agents have recently been assessed and their persistence and toxicity evaluated. A potential hydrolysis product of VX (S-(2-diisopropylaminoethyl) methylphosphonothioic acid [EA-2192]) is a degradation product expected to display a high level of mammalian toxicity. Some mustard partial hydrolysis products are also toxic (Munro et al., 1999). 

Bowmer, K.H. (1991). Atrazine persistence and toxicity in two irrigated soils of Australia. Aust. J. Soil Res., 29 339-350. 

Miller, G.J., Connell, D.W., Anderson, S.M., 2002. Health risk assessment of persistent toxic substances in Australia. Prepared for 2nd technical working group meeting, Region 8, GEF-UNEP project on global assessment of persistent and toxic substances, April 17-19, 2002, Penang, Malaysia. 

Davila et al. [68] reported the transformation of the pesticides bromoxynil, dichlorophen, and pentachlorophenol by the versatile peroxidase from B. adusta. For the three transformed pesticides by versatile peroxidase, an oxidative dehalo-genation was observed, a very important process since the halogenated pesticides are considered more persistent and toxic than the organophosphorus pesticides, because of the carbon-halogen bond. Enzymatic transformation of dichlorophen compound... 

Phenols of enviromnental interest are derived from a wide variety of industrial sources, or present as biodegradation products of humic substances, tannins, and lignins, and as degradation products of many chlorinated phenoxyacid herbicides and organophosphorous pesticides. Phenols, especially chlorophenols, are persistent, and toxic at a few pg/1. Therefore, phenols are hsted at the US-EPA hst of priority pollutants and the EU Directive 76/464/EEC as dangerous substances. The samples to be analysed can be surface waters or industrial effluents. 

Barra, R., Colombo, J.C., Eguren, G. and Jardim, N.G.W. (2002) Regionally based assessment of persistent and toxic substances (PTS) in South America. VII Congresso Brasileiro de Ecotoxicologia. V. Reuniao da SETAC Latino-America, October 2002, Vitoria-Espirito Santo, Brazil. 

Although the distribution, persistence, and toxicity of these halogenated compounds — such as the chlorinated grisans, chloramphenicol, 7-chlorotetracycline, and clindamycin are antibiotics — are subject to the same principles as those outlined in this book, this aspect has seldom been examined. One exception that may serve as an illustration is the debromination of naturally occurring bromophenols by bacteria under anaerobic conditions (King 1988). 

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