Chlorpyrifos absorbed dose

The absorbed dose or body burden of chlorpyrifos can be estimated using urinary monitoring data as follows 3... 

Comparison of exposure levels — total absorbed dose of chlorpyrifos (passive dosimetry vs. urinary monitoring)... 

Table 7 Comparison of Exposure Estimated Levels (Total Absorbed Dose of Chlorpyrifos) Dosimetry vs. Urine Monitoring...

Assessments of risks associated with the use of chlorpyrifos insecticide products for workers have been made. The assessments are based on the results of field studies conducted in citrus groves, a Christmas tree farm, cauliflower and tomato fields, and greenhouses that utilized both passive dosimetry and biomonitoring techniques to determine exposure. The biomonitoring results likely provide the best estimate of absorbed dose of chlorpyrifos, and these have been compared to the acute and chronic no observed effect levels (NOELs) for chlorpyrifos. Standard margin-of-exposure (MOE) calculations using the geometric mean of the data are performed however, probability (Student s f-test) and distributional (Monte Carlo simulation) analyses are deemed to provide more realistic evaluations of exposure and risk to the exposed population. 

Table 1 Summary of Estimated Absorbed Doses from Mixer-Loader and Applicator Studies with Chlorpyrifos...

Table 3 shows the estimated chlorpyrifos dose stemming from absorption of chlorpyrifos from the hands. The approximate average amount of chlorpyrifos absorbed was calculated to be 0.007 pg/kg. 

This study was conducted to evaluate and compare ADD determined using whole-body dosimetry with results of two situational exposure studies conducted following use of a flea fogger under natural conditions. Chlorpy-rifos was selected due to its general availability as a fogger for indoor flea control. Chlorpyrifos is poorly absorbed by the dermal route and readily cleared from the body in urine (Nolan et al., 1984). Trichloropyridinol was measured in 24-hr urine specimens of the volunteers and was converted to chlorpyrifos equivalents as a measure of absorbed dose. The study provided an opportunity to determine the relationship between intensive, high-contact dosimetry studies and the amounts of chlorpyrifos absorbed by two sets of adults who re-entered fogger-treated homes. 

The WBDs retained an average potential dermal exposure (PDE) of 13,757 pg chlorpyrifos. If clothing penetration is assumed to be 10% and dermal absorption 9.6% per 24 hr, then the absorbed dose would be 132 pg, and the absorbed dosage would be about 1.9 pg/kg. Biological monitoring of the 13 volunteers wearing cotton dosimeters indicated that the absorbed daily dose that penetrated the WBD and was absorbed was 2 pg chlorpyrifos equivalents/kg (Table 2). 

The USEPA reviewed a number of registrant-submitted studies to assess exposure to handlers applying chlorpyrifos in agricultural and residential settings (USEPA, 2001). The biomonitoring studies measured urinary concentrations of the primary chlorpyrifos metabolite and back-calculated these to the absorbed dose of the parent. The passive dosimetry study results were corrected for 3 % dermal absorption from a human dosing study (Nolan et al 1984). The results of the studies are reported in Table 1.4 and demonstrate fairly close concordance between the two methodologies. 

Vaccaro, J.R. and R.J. Cranston (1990). Evaluation of Dislodgeable Residues and Absorbed Doses of Chlorpyrifos Following Indoor Broadcast Applications of Chlorpyrifos-based Emulsifiable Concentrate, The Dow Chemical Company, Midland, MI, USA. 

To monitor the absorbed chlorpyrifos doses in human volunteers, urine was collected before and following a 4-hr activity period on the treated grass surface(re-entry). The urine was analyzed for 3,5,6-trichloropyridinol (3,5,6-TCP), the urinary metabolite of chlorpyrifos, and creatinine, which was determined to verify completeness of urine collection by each volunteer. 

By dividing the amount of absorbed chlorpyrifos by the individual body weights, the inhalation dose for the adult volunteers was estimated. Table 1 gives the individual inhalation doses. The mean inhalation dose for the adult volunteers was 0.59 mg/kg. 

Estimation of dose from urinary metabolite analysis From the analysis of volunteer s urine for 3,5,6-TCP, the amount of absorbed chlorpyrifos was determined for each individual volunteer. Table 5 summarizes the calculated chlorpyrifos dose based on analysis of urine samples. The average chlorpyrifos dose was estimated to be 7.07 pg/kg, 182% of the dose estimated using physical techniques. 

Potential dermal exposure (PDE) was the sum of the amount of chlorpyrifos retained by the dosimeter (socks, gloves, and union suit) during the 20-min exposure period. Absorbed daily dose (ADD) was the sum of chlorpyrifos equivalents measured in urine for days 2,3, and 4. Home-use biomonitoring data are expressed as chlorpyrifos equivalents per day, as exposure continued throughout the test period. 

Fish rapidly absorb, metabolize, and excrete chlorpyrifos from the diet (Barron etal. 1991). The mechanism of action of chlorpyrifos occurs via phosphorylation of the active site of acetylcholinesterase after initial formation of chlorpyrifos oxon by oxidative desulfuration. In studies with channel catfish (Ictalurus punctatus), the oral bioavailability of chlorpyrifos was 41%, substantially higher than in mammals. Catfish muscle contained less than 5% of the oral dose with an... 

Another study monitored exposure to five workers using both passive dosimetry and biomonitoring during the application of chlorpyrifos as a termiticide. The mean absorbed chlorpyrifos dose of 4.27 mg/kg/d from the biomonitoring study was comparable to that measured in the passive dosimetry study (3.24 mg/kg/d). 

Fish rapidly absorb, metabolize, and excrete chlorpyrifos from the diet. The mechanism of action of chlorpyrifos occurs via phosphorylation of the active site of acetylcholinesterase after initial formation of chlorpyrifos oxon by oxidative desulfuration. In studies with chaimel catfish (Ictalurus punctatus), the oral hioavailability of chlorpyrifos was 41%, substantially higher than in mammals. Catfish muscle contained less than 5% of the oral dose with an elimination half-life (Tbl/2) of 3.3 days. Chlorpyrifos residues in whole catfish were more than 95% chlorpyrifos, while bile and urine primarily contained metabolites. The dephosphorylated metabolite trichloropy-ridinol (TCP) was the major metabolite in the blood while the glucuronide conjugate of TCP was the major metabolite in mine and bile. The toxic metabolite, chlorpyrifos oxon, was not detected in blood, tissues, or excreta. Extensive metabolism resulted in a low potential for chlorpyrifos to accumulate in catfish from dietary exposure. In both fish and mammals, TCP is a major biotransformation product. Chaimel catfish rapidly distribute waterborne chlorpyrifos into the blood and more slowly to peripheral tissues, with concentrations highest in fat and lowest in muscle. As was true with dietary chlorpyrifos, TCP was the major metabolite in blood and the glucuronide conjugate of TCP was the major metabolite in urine and bile. Pharmacokinetics and metabolism of waterborne chlorpyrifos in channel catfish were similar to the disposition of chlorpyrifos in other vertebrates. 

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