Toxicity organophosphates, assessing

Studies on the scaleless chicken are underway examining its suitability as a model for assessing toxicity of organophosphates. The first compound selected for field trials was the defoliant DEF (S,S,S-tributylphosphorotrithioate) used during the harvesting of cotton in California and Arizona in the fall (October-November) when air movements are frequently restricted by inversions. DEF has been the subject of sufficient complaints to place it on the pre-RPAR list, although there are no reports of acute or delayed neurotoxicity in humans when it and related chemicals are used according to recommendations. It both inhibits cholinesterases and causes delayed neurotoxicity in hens (3,6). 

Lydy MJ, Linck SL. 2003. Assessing the impact of triazine herbicides on organophosphate insecticide toxicity to the earthworm Eisenia fetida. Arch Environ Contam Toxicol 45 343-349. 

Toxicity data are available for several organophosphate ester components of hydraulic fluids, in particular tricresyl phosphate (NTP 1994). However, these components are always present in products as mixtures with other chemicals. Since insufficient information exists to assess the effect on toxicity of interactions among these mixtures, MRLs for the components were not derived. 

The purpose of this chapter is not to discuss the merits, or lack thereof, of using plasma cholinesterase inhibition as an adverse effect in quantitative risk assessments for chlorpyrifos or other organophosphate pesticides. A number of regulatory agencies consider the inhibition of plasma cholinesterase to be an indicator of exposure, not of toxicity. The U.S. Environmental Protection Agency, at this point, continues to use this effect as the basis for calculating the reference doses for chlorpyrifos, and it is thus used here for assessing risks. 

The TGD (EC 2003) contains a section on specific system/organ toxicity, which includes a section concerning guidance on investigation of neurotoxicity and EU-specific risk assessment. Eor the evaluation of organophosphate pesticides, it has been agreed to use the WHO/FAO JMPR recommendations (FAO 1998, 1999) (Section 4.7.7.3.1) as the applicability of these recommendations also can be extended to biocides and new/existing substances. 

Young, R.A., Opresko, D.M., Watson, A.P. (1999). Deriving toxicity values for organophosphate nerve agents a position paper in support of the procedures and rationale for deriving oral RfDs for chemical warfare nerve agents. Hum. Ecol. Risk Assess. 5 589-634. 

Pesticide assessment guidelines under the Federal Insecticide, Fungicide, and Rodenticide Act stipulate that organophosphates proposed for use as insecticides be tested both for their capability to cause acute toxicities due to inhibition of acetylcholinesterase and for their potential to cause inhibition of neurotoxic esterase and subsequent delayed neuropathy. Testing could be performed in laboratory rodents because they, like all species, are susceptible to acetylcholinesterase inhibition, but rodents do not develop notable ataxia, and neuropathological... 

A biological problem of concern to industrial and environmental toxicologists is the question of chronic toxicity as a consequence of continual exposure to low concentrations of organophosphates (B16, V3, V4). If it is necessary to compare exposed and nonexposed populations in order to assess relative organophosphate uptake, the determination of population averages of cholinesterase activities appears to be all that is needed. 

Our group compared in Wistar rats the acutely toxic organophosphate (OP) paraoxon with fenthion, one of the agents frequently involved in human IMS. The clinical symptoms, the occurrence of muscle fiber necrosis and histochemical assessment of neuromuscular junction AChE activity in muscle biopsies, biochemical assessment of brain AChE activity, and EMG parameters including repetitive nerve stimulation at various frequencies were studied at various lime points. 

Topical exposure to organophosphate (OP) and carbamate (CM) pesticides remains an important route for exposure to humans and animals. As in many subdisciplines in toxicology and other sciences, interpretation of pesticide deniial absorption data is highly dependent on the model systems u.sed to generate the data. This chapter discusses studies of pesticide absorption in the context of the experimental and theoretical approaches used to assess absorption, This field was reviewed by Baynes and Riviere (2001). which should be consulted for further details. This review highlighted the overarching importance of experimental design and subsequent interpretation of pesticide data reported in the literature since these factors often overshadow differences in absorption and subsequent toxicity between individual pesticides,... 

An Environmental Working Group study utilised detailed government data on food consumption patterns and pesticide residues to conduct the first comprehensive analysis of the toxic dose that infants and children receive when the entire organophosphate family of insect killers is assessed in combinations, and at levels, that actually occur in the food supply. Based on the most recent government data available on children s eating patterns, pesticides in food, and the toxicity of organophosphate insecticides, the EWG estimated that ... 

Selective behavior monitors specific toxicity and employs enzyme inhibition tests and reporter genes tests. Examples, are use of cholinesterase for organophosphates and urease for heavy metal ions detection and also transgenic microorganism for specific analyte assessment. 

Dermal dose-ChE response studies in animal models are valuable in assessing the dermal toxicity of organophosphate and carbamate pesticides to workers. The behavior of the pesticide in the body, however, cannot be determined dose-response data. Percutaneous... 

Organophosphate Induced Delayed Neuropathy (OPIDN) and other long-term problems of organophosphorus ester (OP) agricultural chemicals pose special problems for risk assessment. Procedures have been developed over the years to evaluate the dangers from acute exposures to OPs, but the Insidious effects of repeated exposures to toxic chemicals are more difficult to anticipate and to detect. 

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