Organochlorine compounds herbicides

Pesticides are also a major source of concern as water and soil pollutants. Because of their stability and persistence, the most hazardous pesticides are the organochlorine compounds such as DDT, aldrin, dieldrin, and chlordane. Persistent pesticides can accumulate in food chains for example, shrimp and fish can concentrate some pesticides as much as 1000- to 10,000-fold. This bioaccumulation has been well documented with the pesticide DDT, which is now banned in many parts of the world. In contrast to the persistent insecticides, the organophosphorus (OP) pesticides, such as malathion, and the carbamates, such as carbaryl, are short-lived and generally persist for only a few weeks to a few months. Thus these compounds do not usually present as serious a problem as the earlier insecticides. Herbicides, because of the large quantity used, are also of concern as potential toxic pollutants. Pesticides are discussed in more detail in Chapter 5. 

Classes of organic compounds analysed by this technique include non ionic surfactants, fatty acids, hydrocarbons (all types), organochlorine compounds, organosulphur and phosphorus compounds, substituted aromatic compounds, NT A, EDTA and insecticides and herbicides. Organometallic compounds studied include those of arsenic, lead, germanium, mercury and tin. 

Pentachlorophenol is a common organochlorine compound that is found in environmental samples. It is used as a preservative for wood and glue as well as an insecticide, herbicide and as a defoliant. It has been found in effluent from the paper industry, tanneries and textile plants. 

Some organochlorine compounds, especially chlorophenols (e.g. dichlorophenol, DCP, and trichlorophenol, TCP) have the ability to taint HDPE at veiy low levels. In fact, dichlorophenol can produce objectionable odors in HDPE at levels in the parts per bilhon range. DCP and TCP are notorious in the dairy industry for tainting milk bottles where levels as low as 5 ppb can be readily detected in milk due to their low threshold of taste detection. The typical scenario by which DCP enters the recycle stream is where post consmner beverage containers are used to store herbicides. The residue in one such container which enters the reuse stream has the ability to taint thousands of rmaffected containers. 

In 1939, the highly efficient contact insecticide DDT (an abbreviation of the technically incorrect name dichlorodiphenyl-trichloroethane) was introduced to the market. Its use, as well as the use of several other organochlorine compounds, spread worldwide in the following years. Important active substances that appeared on the market in the period after World War II include carbamate insecticides and herbicides. Also significant was the discovery of herbicidal phenoxyacetic acids, which represent the first group of the so-caUed hormonally active pesticides. Around the middle of the last century a number of other biologically active substances were discovered, many of which, such as herbicides based on substituted urea, s-triazines (1,3,5-triazines), quaternary ammonium salts or insecticidal synthetic pyrethroids and many others, are still used in many countries around the world. 

Pesticides are further subdivided into classes of compounds. Historically, insecticides included the organochlorine, methyl carbamate, and organophosphate classes of pesticides. Herbicides comprise about 10—12 principal classes of compounds. Within each class of pesticide there may be several hundred active ingredients. 

Accelerated solvent extraction is a new technique for the extraction of a range of organic pollutants from soils and related material. The technique is based on the use of a solvent or combination of solvents to extract organic pollutants at elevated pressure and temperature from a solid matrix. The range of organic pollutants for which the technique is proposed includes semivolatile compounds, organochlorine pesticides, organophosphorus pesticides, chlorinated herbicides, polychlorinated biphenyls and polycyclic aromatic hydrocarbons [53-56],... 

Highly selective to halogenated and oxygenated compounds Electron capture detector EDB, DBCP (EPA 8011) Acrylamide (EPA 8032) Phenols (EPA 8041) Phthalates (EPA 8061) Organochlorine pesticides (EPA 8081) PCBs (EPA 8082) Nitroaromatics and cyclic ketones (EPA 8091) Haloethers (EPA 8111) Chlorinated herbicides (EPA 8151) CLP SOW for organic analysis Interferences from Elemental sulfur (S8) Waxes, lipids, other high molecular weight compounds Phthalate esters, which are common laboratory contaminants Oil in PCB analysis... 

Larose and Chau [189] state that owing to the similar retention times of several common phenoxyacetic acid type herbicides the alkyl esters are subject to incorrect identification if several herbicides are present. Also, the sensitivity obtainable by means of electron capture detection of the alkyl esters by some herbicides, such as MCPA and MCPB is very poor and therefore the method is generally not suitable for the determination of these compounds in water. In addition, the methyl ester of MCPA has a very short retention time close to the solvent front and is prone to interference from sample coextractives, which usually appear in this region. In fact the MCPA methyl ester often cannot be detected even at higher levels because of overlapping with coextraction peaks when the same gas chromatographic parameters as for the determination of organochlorine pesticides are used. Hence other derivatives have been considered. 

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