Advanced environmental chemistry 2

CHAPTER Organic Chemicals and the Environment Introduction    1962: in the South-East Asian war, a program initiated to raise some of the most heated controversy concerning the use of chemicals on the environment that continues to this day 1965: (‘Ranch Hand’ program), US forces used aircraft to spray selected areas of jungle with large amounts of defoliating agents to strip the leaves off vegetation This program of defoliation proved not to be very successful The major material used was Agent Orange that contains two herbicides Depending upon the source and the degree of quality control during the manufacture of the herbicides, AO was found to be contaminated with chemicals known as dioxins (levels ranging from 2–50 µg/g)     Dioxins caused innumerable animal deaths (Although no precise figures available) Dioxins have been blamed for the increase in prenatal deaths and in the birth of deformed Vietnamese children (because of the both deliberate and accidental delivery of AO to agricultural land), After the War, US veterans claimed that the illnesses they have experienced, including cancer and genetic disorders in their children, were caused by the presence of dioxins So far, little relationship has been determined between these claims and AO The problem has been the lack of details concerning the length of time veterans were exposed to the material and the dosage levels involved 1998: the US Institute of Medicine reported on the continuing investigations carried out to find the effects of AO on health problems (Hodgkin’s disease, lymphoma, prostate cancer, etc.) 2.1 DIOXINS AND FURANS  1960s: scientists were aware of the presence of dangerous by-products called dioxins in certain herbicides, particularly those containing or derived from 2,4,5-trichlorophenol (TCP)  Several accidental exposures of large groups of people to substances containing dioxins led to their investigation as hazardous chemicals “One of the earliest accidents occurred in 1949 when a container used for the production of TCP blew up at the Monsanto plant in West Virginia, US Exposed workers were affected by chloracne, a severe and persistent form of acne, “Incan November 1953 a runaway chemical The reaction at BASF’s which lead to permanent disfigurement culprit was in former West Germany caused a vat laterLudwigshafen identified as aplant dioxin, 2,3,7,8-tetrachlorodibenzo-pdioxin containing TCP with TCDD to boil over (TCDD), present in contaminated the reaction mixture.” Hundreds of workers were contaminated, some developing chloracne … German study would indicate that dioxins disturb the human immune system and hormonal control “Since 1979, North American studies have shown dioxins to be mechanisms.” present in many industrial wastes, paper-mill effluents being a notorious example Areas around some chemical plants are heavily contaminated and dioxins have been found in parts of the Great Lakes Dioxins have also entered the environment through the use of contaminated oil as a roadway dust suppressant” Dioxins are a group of related aromatic organic chemicals, specifically the polychlorinated dibenzo-p-dioxins (PCDDs),  Furans are the polychlorinated dibenzofurans (PCDFs)  There are 75 known compounds in the former category and 135 in the latter Both families of compounds are persistent organic pollutants (POPs)  The chemical of most concern was 2,3,7,8tetrachlorodibenzo-p-dioxin (TCDD) since this was identified as being the most toxic This compound is taken as the ‘standard’ to refer other dioxins and furans too, i.e it is given a toxic equivalence factor (TEF) of 1.0  The WHO (Van der berg et al.1998) has suggested a modification to these values to calculate the TEF for some PCDDs and PCDFs  2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) The toxic equivalence factors for some dioxins and furans International TEF WHO TEF Some dioxins 2,3,7,8 – TCDD 1,2,3,7,8 – PCDD 1,2,3,4,7,8 – HCDD 1.0 0.5 0.1 1.0 the combustion of wood and fossil fuels  The use of polychlorinated biphenyls (PCBs) is banned, but they can still be found as dielectric materials in old electrical equipment  PCBs are fat soluble and therefore can bioaccumulate They are probable carcinogens  27 PESTICIDES – THEIR NATURE AND ASSOCIATED PROBLEMS    A pesticide is any substance or mixture of substances that kills a pest, or inhibits in some way its development A pesticide is defined as ‘any substance, preparation or organism prepared or used, to protect plants or wood or other plant products from harmful organisms; to regulate the growth of plants; to give protection against harmful creatures; or to render such creatures harmless A pest is some living organism that is not required in some place because of its detrimental effects The ideal pesticide should only attack the unwanted organism, leaving the non-targeted organism unaffected Unfortunately, the ideal pesticide does not really exist, though some are much more selective than others 28 Common pesticides and their targets 29 ... PCDFs  2, 3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) The toxic equivalence factors for some dioxins and furans International TEF WHO TEF Some dioxins 2, 3,7,8 – TCDD 1 ,2, 3,7,8 – PCDD 1 ,2, 3,4,7,8... etc.) 2. 1 DIOXINS AND FURANS  1960s: scientists were aware of the presence of dangerous by-products called dioxins in certain herbicides, particularly those containing or derived from 2, 4,5-trichlorophenol... pesticide does not really exist, though some are much more selective than others 28 Common pesticides and their targets 29 Pollution of the environment by pesticides arises from both point sources