Chlorpyrifos measuring exposure

The results from the several studies that have been conducted to measure exposures associated with the use of chlorpyrifos are summarized in Tables 1 and 2. Table 1 summarizes results from mixer-loader and applicator studies reported by Honeycutt et al.1 Listed for each work description are the number of replicates, the arithmetic mean, and the geometric mean for the replicates from both the passive dosimetry measurements and the biomonitoring tech-... 

Head, neck, and hand exposures were measured using methods outlined in the literature.4 Head patches were used to estimate dermal exposure to the neck and face of the worker. Handwashes were conducted using a 0.008% DSS solution and collected in 2-L Pyrex bowls. The handwash was repeated with distilled water, and the two handwash solutions were combined. The pooled handwash was then partitioned with ethyl acetate to remove the chlorpyrifos from the aqueous phase. An aliquot of the ethyl acetate was shipped to the analytical laboratory for analysis of chlorpyrifos. 

In order to determine the dermal exposure of volunteers to chlorpyrifos, the penetration of chlorpyrifos through the outer whole-body dosimeter (coveralls) to the inner body dosimeter (t-shirt and briefs) was measured. The penetration factor was calculated for each volunteer in the study from the experimental data by dividing the amount of chlorpyrifos on the t-shirt and brief sample by the amount of chlorpyrifos on the torso section of the coveralls. This method of calculation assumes that the surface area of the torso section of the coveralls is nearly the same as the surface area of the t-shirt and briefs worn directly under the torso section of the coveralls. A mean penetration factor for each worker type was calculated by averaging all the worker volunteer... 

The previous chapter presented results from field studies in which exposures were measured for workers involved with the use of the insecticide chlorpyrifos in several use scenarios and for persons who might re-enter treated areas. In this chapter, the results from these studies are handled by several methods to demonstrate the advantages of using probability and distributional analyses, rather than single point values, for the characterization of risks to pesticides. 

When the data in Table 4 were given full evaluation, it was recommended that the 50W formulation of chlorpyrifos no longer be marketed in bags that allowed significant exposure for mixer-loaders of this product. This product was removed from the marketplace and was replaced with one in which the wettable powder (WP) is in water-dissolvable packets. Exposure data on other active ingredients have clearly demonstrated reduced exposure with this type of packaging. The other uses were deemed to present a minimal hazard to users, and only minor protective measures have been recommended to workers. 

Doses of chlorpyrifos in human volunteers were also estimated using physical measurements. Air sampling was conducted in order to estimate the inhalation dose to each volunteer. Dislodgeable residues were also measured throughout the study to estimate the dermal contribution to total dose. Finally, hand rinses were conducted on each volunteer immediately following the 4-hr activity period to assess the potential contribution to total dose from hand exposure and to estimate an oral dose to a crawling child. 

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. 

Successive 24-hr urine specimens were provided by each volunteer. Collection in the dosimeter studies began 24 hr prior to the chlorpyrifos exposure (study day 0) and continued for 3 days based upon the 27-hr half-life of chlorpyrifos in humans (Nolan et al., 1984). Pre-exposure controls were obtained in all cases. Total urine volume was measured for each of the days, and 20- to 30-mL portions were stored frozen prior to analysis. The Sacramento collections were 48 hr and the Riverside collections were approximately 84 hr after re-entry. 

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. 

Amperometric activity of the electrodes in thiocholine before and following exposure to solutions of pesticides was measured. Sample to sample reproducibility was found to be favourable (RSD 6.6%), as was stability with electrodes being shown to be capable of being stored for up to 2 months at —18°C. Linear detection of chlorpyrifos methyl oxon by inhibition was obtained between 1 x 10 8 and 5 x 10 8M by this approach. 

Biocides are known to be tracked into the homes after a certain outdoor application (Lewis and Nishioka, 1999 Nishioka et al., 2001). Furthermore transport routes, that is, transfer from the workplace to the home (para-occupational or take-home exposure) may be relevant. Household dust concentrations of azino-phosmethyl, chlorpyrifos, parathion and phosmet were significantly lower in reference homes when compared with farmer/farmworker homes (Simcox et al., 1995). Dialkyl phosphate metabolites measured in children s urine were elevated for agrarian children compared with children whose parents did not work in agriculture (Fenske et al., 2000). 

Rigas, M.L., M.S. Okino, and J.J. Quackenboss. 2001. Use of a pharmacokinetic model to assess chlorpyrifos exposure and dose in children, based on urinary biomarker measurements. Toxicol. Sci. 61(2) 374-381. 

Chlorpyrifos provides an example of the utility of human pharmacokinetic models to estimate daily dose from biomonitoring data for a rapidly cleared pesticide. The urinary metabolite trichloro-2-pyridinol (TCP) is used in the NHANES study to monitor population exposure to chlorpyrifos (CDC 2005). Several epidemiologic studies have linked chlorpyrifos exposure to adverse birth outcomes through associations between urinary and blood biomarkers and have demonstrated maternal exposure and physiologic measurements in the neonate (Berkowitz et al. 2003, 2004 Whyatt et al. 2004 Needham 2005). 

FIGURE 4.2 Mortality of fathead minnows in relation to acetylcholinesterase activity.3 a As measured in the brain tissue following (A) a 14-day exposure to a ternary mixture of azinphos-methyl, diazinon, and chlorpyrifos in a concentration-response study and (B) a 7-day exposure to a ternary mixture of azinphos-methyl, diazinon, and chlorpyrifos applied as equipotent (toxic equivalent [TE]) mixtures. Note Dashed lines correspond to 50% reduction in AChE activity the dashed-dotted line corresponds to 50% mortality. Source Redrawn from Sibley et al. (2000). 

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. 

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). 

Recently, Olson et al. (2000) and Benschop et al. (1998) have provided reports of animal studies of effects of repeated low-level exposure to nerve CWA. In rats, Olson et al. determined the LOAEL and NOEL of subacute dosages of sarin, administered, i.m. They found that the dose of sarin (GB) needed to produce a low but measurable blood ChE inhibition was 0.75 p-g/kg once a day for 4 days. Thus, the exposure in Olson s study would be described as subclinical. GB was paired with a variety of other chemicals to include chlorpyrifos, DEET (A,A-diethyl-m-toluamide), carbaryl, and PB. No neurobehavioral or neuropathologic effects could be attributable to dosing with GB alone or in any combination with the other chemicals. Rats were also evaluated using a functional observational battery (EOB) and a Eigure 8 Activity Monitor with no significant behavioral effects reported. Benschop et al. (1998) reported on the toxicokinetics of low-level inhalation exposure to soman in... 

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