Geometric mean exposure

Normally, the geometric mean exposure value is used, with an operator weight of 65 kg and a time period of a typical work day (5 hours) in the EEC calculation. When this is done, the safety factor for application of cyromazine on potatoes is 40. For comparison, the values by the EEC method for individual operators are presented in Table 4. All operators had large safety factors. The values were a6000 by the U.S. EPA method. In the EEC method, any AOEL value greater than 1 is considered acceptable, as the actual safety factor is built into the calculation. The U.S. EPA factors followed the same pattern of high and low values as the EEC results. 

Exposure Route/Concentrations/Durations Inhalation/geometric mean exposure of <1 ppm (range, 0.01-3.3 ppm personal samplers), up to 6 ppm (area samples)/mean service years, 16.5 (Leeser et al. 1990) Inhalation/average exposure 8 ppm/5-15 y (El Ghawabi et al. 1975) Inhalation/5 ppm/unknown/(Grabois 1954 Maehly and Swensson 1970 Hardy et al. 1950). ... 

As a result of the Eleventh Circuit Court of Appeals decision (AFL-CIO versus OSHA), OSHA s permissible exposure level for tetrachloroethylene, which was lowered to 25 ppm in 1989, was returned to 100 ppm (OSHA 1993). Based on human exposure data, Stewart etal. (1981) concluded that a TLV of 100 ppm contained no safety factor for individuals more susceptible to the subjective and neurological symptoms of tetrachloroethylene. Based on human data, the ACGIH (ACGIH 1995) TLV-TWA is 25 ppm. The geometric mean exposure of dry cleaning machine operators was 22 ppm (Ludwig et al. 1983), a value close to the ACGIH TLV-TWA. 

Pesticide concentrations in earthworms displayed regional differences. Such differences are likely to be observed in other potential food items. Earthworm exposure was log-normally distributed with the highest concentration being 163 qgg which represents the 97th percentile of diazinon found in earthworms from all sites. The geometric mean diazinon concentration in earthworms from PA was 2.56 agg (CL95 = 1.62. 06qgg ), and from WA was 0.046 xgg ... 

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. 

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-... 

Table 2 summarizes the re-entry exposure data from studies with chlorpyrifos.1 There are fewer replicates for these workers which would seem to be justified by the lower variability in the data sets. There are practically no differences between the arithmetic and geometric means for these data sets. 

Table 3 Estimated Margins of Exposure for Chlorpyrifos from Biomonitoring Data Using Geometric Means (Single-Point Approach)3...

NS (children, environmental exposure) Developmental Small association between abnormal behavior and blood lead at age 3 40.9 (geometric mean) Wassermann et al. 1998... 

However, results obtained by Koo et al. (1991) indicate that low to moderate lead exposure (average lifetime PbB level range of 4.9-23.6 pg/dL, geometric mean of 9.8 pg/dL, n=105) in young children with adequate nutritional status, particularly with respect to calcium, phosphorus, and vitamin D, has no effect on vitamin D metabolism, calcium and phosphorus homeostasis, or bone mineral content. The authors attribute the difference in results from those other studies to the fact that the children in their study had lower PbB levels (only 5 children had PbB levels >60 pg/dL and all 105 children had average lifetime PbB levels <45 pg/dL at the time of assessment) and had adequate dietary intakes of calcium, phosphorus, and vitamin D. They concluded that the effects of lead on vitamin D metabolism observed in previous studies may, therefore, only be apparent in children with chronic nutritional deficiency and chronically elevated PbB levels. Similar conclusions were reached by IPCS (1995) after review of the epidemiological data. 

Hearing thresholds in children may be affected adversely by lead exposure at low blood lead levels (Robinson et al. 1985 Schwartz and Otto 1987, 1991). Robinson et al. (1985) reported that hearing thresholds increased linearly with maximum historical PbB levels of 6.2-56.0 pg/dL. In the analyses by Schwartz and Otto (1987, 1991), the probability of lead levels studied (NHANES II and HHANES data, respectively), from <4 to >50 pg/dL, with no apparent threshold. There is also some evidence suggesting that lead exposure may cause postural disequilibrium in children (Bhattacharya et al. 1993). The children evaluated in that study had a geometric mean PbB for the first 5 years of life of 11.9 pg/dL, the range was 5.1 to 28.2 pg/dL. 

A report entitled Chemical Trespass was issued in May 2004 by the Pesticide Action Network (Schafer et al., 2006). It contained detailed analysis of 2000/01 National Health and Nutrition Examination Survey (NHANES) OP urinary metabolite data and used published methods to estimate exposure levels to parent compounds from creatinine corrected urinary metabolite levels. They focused on chlorpyrifos and its metabolite 3,4,6-trichloro-2-pyridinol (TCP), and found that chlorpyrifos exposures for children ages 6-11 and 12-19 exceeded EPA s chronic population-adjusted dose (cPAD) by surprisingly wide margins. Geometric mean TCP levels were 3 to 4.6 times higher than the EPA-estimated safe dose, as shown in Fig. 14.2. The more heavily exposed children received daily doses more than ten times the safe level. 

Geometric mean values of personal samples 0.03-0.96 (range 0.01-3.3) Area samples up to 6 No clear exposure related symptoms or adverse health effects employment for 1-40 y Leeser et al. 1990... 

Toxicity end point Maehlyand Swensson 1970 No adverse effect in healthy adult humans occupationally exposed at geometric mean concentration of <1 (range 0.01-3.3 ppm, personal samplers [up to 6 ppm, area samples]) or 5 ppm mild headache in adult humans occupationally exposed at 8 ppm. The exposure duration was considered to be 8 h. 

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