Resistance organochlorines

Insects have acquired resistance to organochlorine compounds, such as DDT and BHC, developed as agricultural and hygienic insecticides after World War II. This insect resistance was also acquired to subsequent organophosphorus compounds and carbamate insecticides. Photostable pyrethroids have been developed for outdoor use because pyrethroids were found to be effective against these resistant pests. As a matter of course, these pyrethroids are also effective against sanitary pests however, problems associated with safety and chemical residues indoors must be resolved. 

Another entry point for accumulation of organic in animal tissue and animal food products is direct ingestion of contaminated soil by grazing animals [44]. The compounds of main concern are the halogenated aromatics, including PCBs, organochlorine pesticides, PCDDs and PCDFs, which are resistant to metabolization and tend to accumulate in animal fat. The bioaccumulation factor (the ratio of the concentration of animal tissue or produce to the concentration in the diet) can be as high as 5-6 [43]. Compounds such as PAHs and phthalate esters are readily metabolised and excreted by the animals and thus do not accumulate in animal tissue or products. 

The Disposition and Biotransformation of Organochlorine Insecticides in Insecticide-Resistant and -Susceptible Mosquitofish... 

The uptake and distribution of organochlorine insecticides has been studied under a variety of conditions. Although the results indicate that further study is needed on a characterization of extraneous factors that affect disposition, the studies clearly demonstrate the presence of a membrane barrier to insecticide penetration in the R population. This membrane barrier would aid in the protection of target sites in the R fish from the insecticide. This barrier is felt to be an important factor in resistance to organochlorine insecticides in mosquitofish. 

Further, by virtue of their larger livers, the R fish have a greater xenobiotic biotransformation potential. However, the in vivo studies show few consistent differences in metabolism between the two populations. Biotransformation may be a major contributory factor in mosquitofish resistance to other pesticides, for example, organophosphorus and botanical insecticides, since the level of resistance to these chemicals is very low (4 fold or less) 08,20,21). However, biotransformation does not appear to play a major role in organochlorine insecticide resistance. 

The development of strains resistant to insecticides is an extremely widespread phenomenon that is known to have occurred in more than 200 species of insects and mites, and resistance of up to several 100-fold has been noted. The different biochemical and genetic factors involved have been studied extensively and well characterized. Relatively few vertebrate species are known to have developed pesticide resistance and the level of resistance in vertebrates is low compared to that often found in insects. Susceptible and resistant strains of pine voles exhibit a 7.4-fold difference in endrin toxicity. Similarly pine mice of a strain resistant to endrin were reported to be 12-fold more tolerant than a susceptible strain. Other examples include the occurrence of organochlorine insecticide-resistant and susceptible strains of mosquito fish, and resistance to Belladonna in certain rabbit strains. 

In the public health area, the phenomenal but short-lived successes of DDT in controlling disease vectors was noted. In 1955 the WHO had embarked on a program to eradicate malaria. However by the 70s it was evident that the resistance of anopheles to organochlorine pesticides had clearly foiled this plan. 1962 was a peak year for insecticide application in malaria control (130M DDT, 8M Dieldrin, and 1M Lindane). 

Resistance of an organic molecule to transformation by either chemical or biological processes contributing to its longevity in the environment (e.g., many organochlorine compounds are known to be persistent). Persistent organic compounds, because they are lipid-soluble, tend to accumulate in aquatic biota where they may exert adverse effects. Volume 2(1). 

Huckins et al.29 reported a 20-70% impedance in the uptake of PAHs in cases of severe biofouling on the surface of SPMDs. Their model describing the mass transfer in a biofilm indicated that it behaved like an immobilized water layer with a resistance that is independent of the biofilm/water partition coefficient. This would result in a similar mobility of compounds in the biofilm since this is independent of their hydrophobicity.19 Similarly, Richardson et al.47 observed that biofouling caused a reduction of up to 50% in the uptake of PAHs and organochlorine pesticides by SPMDs. It has been suggested by several authors that PRCs can be used to correct biofouling during deployment,42,47 but more experimental evidence is needed. 

Lee, R.F., Ryan, C. (1979) Microbial degradation of organochlorine compounds in estuarine waters and sediments. In Proceedings of the Workshop of Microbial Degradation of Pollutants in Marine Environments. EPA-600/9-79-012. Washington D.C. Lee, S., Pardue, J.H., Moe, W.M., Valsaraj, K.T. (2003) Mineralization of desorption-resistant 1,4-dichlorobenzene in wetland soils. Environ. Toxicol. Chem. 22, 2312-2322. 

The use of chlorinated hydrocarbons has declined worldwide and is banned in many countries for three main reasons (1) concern over the buildup of residues, (2) the increasing tendency of some insects to develop resistance to the materials, and (3) the advent of insecticides that can replace the organochlorine compounds. 

The cyclodiene group of organochlorines was introduced in 1948, starting with chlordane, then aldrin, dieldrin, endrin and toxaphene, and then heptachlor BHC was already available at the close of the war. The experience with housefly control in the Mediterranean countries was that DDT-resistance came in 2 years, and the substitution of BHC was followed by BHC-resistance a year... 

The pest mosquito Aedes nigromacul Ls of the vast San Joaquin valley of California went resistant to organochlorines by 1951, to parathion by 1960, to fenthion by 1965, and to chlorpyrifos (Dursban) by 1970. At present reliance is placed on larvicidal oils, the juvenile-hormone mimic methoprene (Altosid) and the insect growth regulator diflubenzuron (Dimilin), — and on better management of surplus irrigation water. Residual sprays for housefly control, at first so spectacular with the organochlorines, had to move into the OP compounds, which were then knocked out in... 

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