The Voice of Reason
Join Date: May 2006
* Summary of toxicology
1. Effects on Animals: Dichlorvos is an anticholinesterase agent and may cause excessive salivation, eye tearing, sweating, constricted pupils, respiratory distress, anorexia, vomiting, diarrhea, weakness, twitching, paralysis, a slow and irregular heartbeat, convulsions, coma, and death [Hathaway et al. 1991]. Dichlorvos also has reproductive effects and causes malformed offspring in rodents. The acute toxicity of dichlorvos for laboratory animals is significantly high; the dermal LD(50) for rabbits is 107 mg/kg and 80 mg/kg in rats; and the acute oral LD(50) in rats is 25 mg/kg [NIOSH 1995; ACGIH 1991; Sax and Lewis 1989]. The lowest single oral dose that causes observable behavioral changes is 10 mg/kg in calves [NLM 1995]. The neurotoxic effect of dichlorvos on the central and peripheral nervous system was investigated in acute and subchronic experiments using male rats. The acute group received a single oral dose of 88 mg/kg and the two subchronic groups received a daily oral dose of 1.6 mg/kg or 0.8 mg/kg for a period of 6 weeks. Both the acute and subchronic groups exhibited significant changes in the functions of the central nervous system, increase of EEG mean frequency, decrease of EEG amplitude, and peripheral nervous system decrease of conduction velocity, and increase of relative and absolute refractory periods. In one of two studies on the long-term effects of dichlorvos by oral exposure, an increased but not statistically significant number of squamous-cell tumors were found in mice [ACGIH 1991]. However, the International Agency for Research on Cancer (IARC) has concluded that the evidence for the carcinogenicity of dichlorvos in animals is inadequate [IARC 1987]. Administered intraperitoneally during pregnancy, dichlorvos produced developmental abnormalities in rat fetuses [NIOSH 1995]. Dichlorvos is mutagenic in bacterial and mammalian test systems [NIOSH 1995; NLM 1995].
2. Effects on Humans: Dichlorvos is an organophosphorus pesticide and is therefore a cholinesterase inhibitor. Overexposure to this substance causes symptoms that vary by route of exposure. Inhalation causes ocular and respiratory symptoms. Ingestion causes gastrointestinal effects, while skin absorption causes localized sweating and muscle twitching in the area where entry occurred. If exposure is severe, muscle weakness, twitching, fasciculation, and paralysis may occur. Paralysis of the respiratory muscles may cause death. Cardiac irregularities, including complete heart block, may also occur [Hathaway et al. 1991]. Dichlorvos is easily absorbed through the skin, gastrointestinal tract, and lungs because of its high volatility [Parmeggiani 1983]. It is rapidly inactivated by the liver, and persons with liver disease may be less tolerant of the toxic effects than normal persons [Gosselin 1984]. Human volunteers exposed for 30 minutes/hour each hour, 10 hours/day for 14 days at concentrations of 0.14 to 0.33 mg/m(3) had no changes in cholinesterase levels, airway resistance, or vision. At a concentration of 1 mg/m(3) for 7.5 to 8.5 hours, volunteers experienced a 20- to 25-percent reduction in cholinesterase levels [ACGIH 1991]. Thirteen workers exposed over a period of a year to an average concentration of 0.7 mg/m(3) showed decreases of 35 percent and 60 percent, respectively, in red blood cell and plasma cholinesterase levels [Hathaway et al. 1991]. At a level of 0.1 ppm, the plasma cholinesterase is reported to drop by 20 percent [ACGIH 1991]. Daily exposure to dichlorvos at levels insufficient to produce results on a single-dose basis may produce symptoms after several days exposure. Continuing exposure after symptoms appear can produce increasingly severe effects [Hathaway et al. 1991]. Dichlorvos has also been reported to cause allergic contact dermatitis [ACGIH 1991]. Dichlorvos causes methylation of DNA in vitro, but there is no evidence of mutagenicity in humans [Hathaway et al. 1991]. IARC has concluded that there is no adequate data for evaluating the carcinogenicity of dichlorvos in humans [IARC 1987].
* Signs and symptoms of exposure
1. Acute exposure: Symptoms and signs usually appear within minutes of exposure but they may be delayed for as long as 12 hours. After inhalation, the initial symptoms and signs are a feeling of tightness in the chest, wheezing due to bronchospasm, blurring of vision, tearing, runny nose, and frontal headache. Ingestion causes sweating, nausea, vomiting, diarrhea, cramps, urination and defecation, and anorexia within 15 minutes to 2 hours of exposure. Skin absorption can produce local sweating and muscle fasciculations within 15 minutes to 2 hours after exposure. Death is usually caused by respiratory muscle paralysis and consequent asphyxiation.
2. Chronic exposure: Continued exposure to dichlorvos may cause headache, weakness, decreased memory, easy fatigability, disturbed sleep, loss of sensation in the skin, and paralysis. Delayed neurological symptoms are reversible after exposure ceases, but recovery is low and may not be complete.
This study was designed to determine if commercial preparations of the pesticides Folpet, Captan, Guthion®, and Dichlorvos, have a significant effect on genetic recombination in maize (Zea mays L.). The pesticides were applied in aqeous solutions of 1.5% dimethyl sulfoxide with 0.04% X-77 Spreader®. Premeiotic treatment s to heterozygous females were applied as a foliar spray. Testcrosses were analyzed for changes in frequencies of recombination between loci 1g−g12 and a-et on chromosomes 2 and 3, respectively. Sib-crosses were analyzed for changes in frequencies of recombination between the 1g−g12 loci and the a2−bt loci on chromosomes 2 and 5, respectively. Between the a-et markers, significant increases in genetic recombination were produced by the 0.17 M level of Folpet, the 0.50 M level of Captan, the 0.50 M level of Guthion®, and the 0.66% v/v and 1.00% v/v levels of Dichlorvos. Between the a2−bt markers, significant increases in recombination were produced by the 0.33 and the 0.50 M levels of Guthion®. Analysis of variance for simple regression was conducted on each pesticide/marker group combination to determine possible linear dose responses. Significant increases in genetic recombination were induced linearly in the a−et linkage group with increasing levels of Captan, Guthion®, and Dichlorvos. Genetic recombination also was increased linearly in the a2−bt linkage group with increasing concentrations of Captan and Guthion®. The conclusion from this study is that commercial preparations of the pesticides Captan, Guthion®, Dichlorvos, and possibly Folpet, have the ability to increase the frequency of genetic recombination between markers of maize. This study therefore supports the consensus that certain pesticides, at abnormally high rates of application, are genetically active, environmental recombinagens.
Understanding Inorganic Salts
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– Carl Sagan
"There is rebirth of character, but no transmigration of a self. Thy thought-forms reappear, but there is no egoentity transferred. The stanza uttered by a teacher is reborn in the scholar who repeats the words. Only through ignorance and delusion do men indulge in the dream that their souls are separate and self-existent entities.""Our thinking is gone, but our thoughts continue. Reasoning ceases, but knowledge remains."