Chlorophenols persistence

Reductive DechIorina.tion. Such reduction of chlorinated aUphatic hydrocarbons, eg, lindane, has been known since the 1960s. More recentiy, the dechlorination of aromatic pesticides, eg, 2,4,5-T, or pesticide products, eg, chlorophenols, has also been documented (eq. 10) (20). These reactions are of particular interest because chlorinated compounds are generally persistent under aerobic conditions. 

The objectives of the soil persistence experiments were (1) to learn the effect of soil type and concentration on the TCDD degradation rate, (2) to isolate and characterize degradation products from DCDD and TCDD, and (3) to determine whether chlorodioxins could be formed from chlorophenol condensation in the soil environment. This last study was essential since quality control at the manufacturing level could reduce or eliminate the formed dioxin impurity. But the biosynthesis of chlorodioxins by chlorophenol condensation in the soil environment could not be controlled and would have connotations for all chlorophenol-de-rived pesticides if formation did occur. The same question needed to be answered for photochemical condensation reactions leading to chloro-... 

The toxicity of commercial or technical grades of PCP significantly exceeds that of analytical or purified PCP. Some of this added toxicity is attributed to impurities such as dioxins, dibenzo-furans, chlorophenols, and hexachlorobenzene. Pentachlorophenol is rapidly accumulated and rapidly excreted, and has little tendency to persist in living organisms. It acts by uncoupling oxidative... 

Although the use of organochlorinated substances has been abolished in most of the developed countries, their extensive use during the past decades and their persistence in the environment determine their actual widespread distribution. Moreover, some substances are not used or commercialized but are still important synthetic intermediates for the preparation of other substances. Thus, chlorophenols are important intermediates in the production of pesticides or other chemicals. Other substances such as PCDEs or PCDDs are... 

Many chlorophenols are harmful and persistent. It is possible that these may be produced microbiologically in nature in view of the finding that a fungal chloroperoxidase halogenates phenol to yield monochlorophenols and the latter to give dichlorophenols. The sequence continues with producing trichlorophe-nols, tetrachlorophenols, and even pentachlorophenol [208]. 

Soil. Ambrosi et al. (1977a) studied the persistence and metabolism of phosalone in both moist and flooded Matapeake loam and Monmouth fine sandy loam. Phosalone rapidly degraded (half-life 3-7 d) but mineralization to carbon dioxide accounted for only 10% of the loss. The primary degradative pathway proceeded by oxidation of phosalone to phosalone oxon. Subsequent cleavage of the 0,0-diethyl methyl phosphorodithioate linkage gave 6-chloro-2-benzoxazolinone. Although 2-amino-5-chlorophenol was not detected in this study, they postulated that the condensation of this compound yielded phenoxazinone. 

Chlorinated aromatics are primarily of interest in the liquid, rather than gas, phase and will not be covered in detail. However, chlorinated aromatic contaminants, particularly various chlorophenols, represent a significant class of water contaminants, and considerable research into the photocatalytic degradation of these materials has been conducted in recent years [29-35]. Many chlorinated aromatics are resistant to biological degradation, allowing them to accumulate in the environment and persist for long periods of time. Some are known to have significant. 

The regular use of sodium pentachlorophenate has proved successful in many instances, but it is a persistent environmental hazard and cannot be recommended. However, o -benzy 1-p -chlorophenol can often produce goods results, with low bacteria counts and clean systems. But the timing of biocide applications needs to be matched carefully with the production cycles (and process leakage periods) for optimum product effectiveness. 

Chlorinated phenols are among the most important contaminants in the environment (aqueous systems and soils) due to their widespread use in industry and agriculture and for domestic purposes for over 50 years. It is well-known that chlorophenols are toxic at low levels. The more highly chlorinated phenols such as trichlorophenols and pentachlorophenol are also persistent. Five of the chlorophenols (2-chlorophenol, 2,4-dichlorophenol, 4-chloro-3-methylphenol, 2,4,6-trichlorophenol and pentachlorophenol) have been classified as priority pollutants by the US Environmental Protection Agency (EPA). 

GC-MS and HPLC analyses of electrolyzed solutions allowed the detection of aromatic intermediates such as p-benzoquinone and nitrobenzene for aniline, 4-chlorocatechol for 4-chlorophenol, 4-chlorophenol, 4-chlorocatechol, hydroquinone, and p-benzoquinone for 4-CPA, 4-chloro-o-cresol, mehylhy-droquinone, and methyl-p-benzoquinone for MCPA, 2,4-dichlorophenol, 4,6-dichlororesorcinol, chlorohydroquinone, and chloro-p-benzoquinone for 2,4-D, and 2,4,5-trichloro-phenol, 2,5-dichlorohydroquinone, 4,6-dichlororesorcinol, and 2,5-dihydroxy-p-benzoquinone for 2,4,5-T. In general, these by-products persisted in solution while the initial pollutant was degraded. 

The substituted phenols are practically insoluble in water however, being phenols, they readily form salts with organic and inorganic bases, most of which are water-soluble. Since they must utilize water as a carrier in order to be selective and yet penetrate the leaf cuticle, they all respond to activation by buffering on the acid side of neutrality. Ammonium sulfate is the common compound used to bring about this activation. In this water-soluble form they are subject to leaching and runoff from the soil. Some, but not all, of the chlorophenols are oxidized by the soil microflora. For example, 2,6-dichlorophenol is readily destroyed while the 2,3-, 3,4-, and 3,5-dichlorophenols persist for long periods (15). 

Polychlorinated diphenyl ethers (PCDE) are common impurities in chlorophenol formulations, which were earlier used as fungicides, slimicides, and as wood preservatives. PCDEs are structurally and by physical properties similar to polychlorinated biphenyls (PCB). They have low water solubility and are lipophilic. PCDEs are quite resistant to degradation and are persistent in the environment. In the aquatic environment, PCDEs bioaccumulate. These compounds are found in sediment, mussel, fish, bird, and seal. PCDEs show biomagnification potential, since levels of PCDEs increase in species at higher trophic levels. PCDEs are also detected in human tissue. Despite the persistence and bio accumulation, the significance of PCDEs as environmental contaminants is uncertain. The acute toxicity and Ah-receptor-me-diated (aryl hydrocarbon) activity of PCDEs is low compared to those of polychlorinated di-benzo-p-dioxins (PCDD) and dibenzofurans (PCDF). Due to structural similarity to thyroid hormone, PCDEs could bind to thyroid hormone receptor and alter thyroid function. Furthermore, PCDEs might be metabolized to toxic metabolites. In the environment, it is possible that photolysis converts PCDEs to toxic PCDDs and PCDFs. 

Properties of PCDEs, including physicochemical ones, are not well known as the literature reviews of PCDEs have shown [4, 11,40,46]. PCDEs resemble PCBs structurally and in their chemical and physical properties, which, like PCDDs, PCDFs, and related compounds, are known to be stable and resistant to breakdown by heat, hydrolysis, bases, and acids. PCBs are also quite stable to oxidation under moderate conditions [3], but there is not much data about PCDEs concerning their stability. There is some evidence that PCDEs are resistant to bases and acids and the occurrence of PCDEs in the environment indicates that PCDEs are persistent and bioaccumulating compounds. The study of Firestone et al. [37] already showed that PCDEs are quite stable, since PCDEs could be measured in chlorophenol extracts after sulfuric acid treatment. Tetra- and octachlorinated PCDE congeners were later proven resistant in treatment with... 

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. 

Chlorophenols are a class of pesticide substances, e.g. fungicides, used for wood preservation, in pulp production and other miscellaneous applications. The substances were introduced in the 1930s and have been used in very large amounts. Today, the consumption has decreased and the substances are banned in many countries. The main active substance in chlorophenol products is pentachloro-phenol (PCP Figure 3.10). The substance is moderately lipophilic and persistent, yet readily absorbed and accumulated in biota and expresses a rather high acute toxicity. The metabolism and breakdown of this envirotoxicant in biota and in the environment are rather slow, resulting in successively dechlorinated metabolites. 

Acute medical consequences following exposure to dioxin-contaminated substances in industrial accidents included peripheral neuropathy, weakness, cardiovascular disease, liver dysfunction, abnormalities in liver enzymes and lipid levels. Symptoms of these medical consequences have persisted in some workers when examined in several studies conducted many years after exposure. No clear understanding yet exists of the severity or persistence of these health problems. Additionally, there is no clear information regarding medical risks for populations with low exposures to phenoxy herbicides and chlorophenols. 

Chlorinated Hydrocarbons Short-chain alkyl halides find extensive use as solvents and are common contaminants of ground water. Polychlorinated biphenyls are global contaminants as a consequence of their extensive use and persistence. Chlorinated dioxins and furans are produced as combustion by products or contaminants in reactions with chlorophenols. Consequently, there has been considerable interest in defining the physical chemical properties that determine their environmental behavior. 

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