The Impact of Pesticides - Academy Publish

absorbed NOEL dose was estimated. Simulated urinary amounts of thesemetabolites in 24-h collections considering an 8-h dermal exposure to a totalabsorbed dose equivalent to the daily absorbed NOEL dose were proposed as BRVs.With these considerations, BRV values of 26 and 45 nmol/kg bw were obtained,respectively, for 3,5,6-TCP and APs in 24-h urine collections (Bouchard et al.,2005).The BRVs were applied to practical situations, and hence were used to assess theimportance of exposure and potential effects in the groups of workers assessed bySamuel et al. (2002) and Fenske and Elkner (1990). In both studies, total amounts of3,5,6-TCP in 24-h urine collections were quantified in greenhouse workersfollowing the onset of an application of CPF or manipulation of treated plants(Samuel et al., 2002), or in workers exposed to CPF following structural controltreatment of houses (Fenske and Elkner, 1990). As displayed in Table 3, the workersof these studies presented 3,5,6-TCP values in 24-h urine collections lower than theproposed BRV.ParathionParathion (O,O-diethyl O-p-nitrophenyl phosphorothioate, CAS 56-38-2) is a potentnon-systemic insecticide and acaricide with some fumigant action. Like other OPinsecticides, it exerts its neurotoxic action by inhibiting nervous system AChEactivity, both in insects and humans (Sidell, 1994; Maroni et al., 2000a; Gosselin etal., 2004). Although there are now application restrictions due to its high toxicity,the use of parathion is still a concern in many countries (Denga et al., 1995;Akgur et al., 1999).The ACGIH ® and the GCIHH ® (German Commission for the Investigation ofHealth Hazards of Chemical Compounds in the Work Area) proposed a 30%inhibition of RBC-AChE activity compared to the individual’s baseline as abiological reference value. A more specific biological reference value based onurinary concentration of p-nitrophenol (p-NP) parathion metabolite in a spot urinesample has also been proposed, given that it is detectable in urine far before anyinhibition of enzymatic activity occurs (Arterberry et al., 1961; Richter et al., 1992).The ACGIH BEI ® value was set to 0.5 mg of p-NP/g of creatinine (0.34 mmol p-NP/mol creatinine) while the GCIHH BAT ® value was established at 0.5 mg of p-NP/L of urine. However, parathion is eliminated through the kidneys by glomerularfiltration or active secretion (Michalke, 1984; Jokanovic, 2001), such that its urinaryconcentration decreases with increasing urinary flow rate (Boeniger et al., 1993) andis thus subject to significant variations with time. A more reliable sampling strategythan spot urine samples is to quantify total amounts of metabolites excreted in urineover given time periods (Woollen, 1993; Ross et al., 2001). In this perspective,Gosselin et al. (2004) developed a toxicokinetic model to absorbed doses ofparathion to urinary biomarker measurements and to propose, using modelpredictions, BRVs for parathion metabolites, p-NP and APs, in the form ofcumulative amounts of urinary metabolites following the onset of an occupationalexposure (Figure 4B).Again, the model is based on knowledge on biotransformation pathways ofparathion. After systemic absorption, it is either rapidly hydrolyzed to p-NP andDETP or oxidized to paraoxon in the liver mainly, or stored in lipids. Paraoxonrepresents 20% of the biotransformation while the hydrolysis constitutes 80% of thebiotransformed parathion (Poore and Neal, 1972; Hayes, 1982; Jokanovic, 2001).AcademyPublish.org - The Impact of Pesticides113