Agricultural task not predictive of children's exposure to OP pesticides.

Coronado et al. (2004) reported that the agricultural task of plant thinning by adults was associated with higher urinary pesticide metabolite concentrations in children. Their analysis was based on data from a 1999 study of farmworkers in the Yakima Valley of Washington State (Curl et al. 2002; Thompson et al. 2003). Their conclusion was based on a finding that one of the three dimethyl dialkylphosphate (DAP) metabolites of the organophosphorus (OP) pesticides--dimethylthiophosphate (DMTP)--was more frequently detected among children living in the same household with adult farmworkers who reported having thinned plants compared with children living in the same household with farmworkers who did not report thinning (92% vs. 81%, respectively).

We examined the same data set to determine if the actual urinary pesticide metabolite concentrations, rather than simply the frequency of metabolite detection, differed between these groups of children. We used log-transformed data and the independent t-test (equal variance assumption) to determine differences between geometric mean metabolite concentrations. We found no significant differences between children of thinners versus non-thinners for any of the three DAP metabolites. Geometric mean values for DMTP were 6.13 [micro]g/L for 136 children of thinners and 5.27 [micro]g/L for 75 children of non-thinners (p = 0.41). Furthermore, we did not find a significant difference between these groups for the sum of the dimethyl DAP metabolites (geometric means of 0.097 vs. 0.083 [micro]mol/L; p = 0.33).

Coronado et al. (2004) also suggested that children of thinners may receive higher exposures than children of pesticide handlers (mixers, loaders, applicators). We compared the children of thinners to children of handlers, excluding the 28 children for whom the corresponding adult farmworker reported both thinning and handling. No differences were observed between these groups for any of the three DAP metabolites. Geometric mean values for DMTP were 6.47 and 6.05 [micro]g/L, respectively (p = 0.81), and 0.10 and 0.096 [micro]mol/L, respectively, for the sum of the dimethyl DAP metabolites (p = 0.78). It is not surprising that the child population in this study exhibited high frequencies of detection of the DAP metabolites. The most recent study by the Centers for Disease Control and Prevention (Barr et al. 2004) found that 87% of U.S. children 6-11 years of age had one or more of the dimethyl DAP metabolites detected in their urine.

We conclude from our analysis of this data set that a) children living in households with thinners did not exhibit higher OP pesticide exposures than children living in households with workers in other agricultural task categories; and b) OP pesticide exposures did not differ between children of thinners and children of pesticide handlers. We further conclude that frequency of detection is an inadequate exposure metric for urinary pesticide metabolites that are detected with high frequency, and that its use independent of metabolite concentration data can prove misleading. We recommend that future analyses of children's pesticide exposure focus on measured metabolite concentrations rather than the simple presence or absence of metabolites in biological samples.

The authors declare they have no competing financial interests.

Richard A. Fenske

John C. Kissel 

Jeffry H. Shirai

Cynthia L. Curl

Kit Galvin

Department of Environmental and

Occupational Health Sciences

School of Public Health and

Community Medicine

University of Washington

Seattle, Washington 

E-mail: [e-mail]

REFERENCES

Barr DB, Bravo R, Weerasekera G, Caltabiano LM, Whitehead RD Jr, Olsson AO, et al. 2004. Concentrations of dialkyl phosphate metabolites of organophosphorus pesticides in the U.S. population. Environ Health Perspect 112:186-200.

Coronado GD, Thompson B. Strong L, Griffith WC, Islas I. 2004. Agricultural task and exposure to organophosphate pesticides among farmworkers. Environ Health Perspect 112:142-147.

Curl CL, Fenske RA, Kissel JC, Shirai JH, Moate TF, Griffith W, et al. 2002. Evaluation of take-home organophosphorus pesticide exposure among agricultural workers and their children. Environ Health Perspect 110:A787-792.

Thompson B, Coronado GD, Grossman JE, Puschel K, Solomon CC, Islas I, et al. 2003. Pesticide take-home pathway among children of agricultural workers: study design, methods, and baseline findings. J Occup Environ Med 45:42-53.

Children's Exposure to OP Pesticides: Response to Fenske et al.

In our article (Coronado et al. 2004), we reported a higher proportion of urine samples containing detectable levels of the organophosphate (OP) pesticide urinary metabolite dimethylthiophosphate (DMTP) from children of farmworkers who reported having thinned plants, compared with urine samples from children of non-thinners. We reported the detection frequency for individual dimethyl metabolites, not a composite score for the detection of multiple dimethyl metabolites. We thank Fenske et al. for their additional analyses showing slightly higher, though not significant, concentrations of urinary DMTP in children of thinners versus non-thinners.

We knew that assessing detection frequencies would provide only a preliminary view of a more complex pattern of exposure; thus, we specifically stated in the "Methods" section of our paper that the analysis was exploratory in nature. We examined job task as a factor possibly associated with high exposure to pesticides because job task is closely linked with regulatory policy. We understood that if substantial differences in the percentage of detectable samples existed between groups further exploration would be warranted.

This type of analysis follows the logic put forth by others in the field of exposure assessment. For example, Fenske et al. highlight that Barr et al. (2004)--in the same issue of EHP in which our article was published--provided detection frequencies of OP pesticide urinary metabolites in older children (6-11 years of age) from the general population. Barr et al, reported a detection frequency for DMTP of 69%, with a limit of detection of 0.18 [micro]g/L. In our study we matched children (2-6 years of age) with an adult agricultural worker in the same home. Among the children matched to farmworkers who reported thinning, we observed a detection frequency for urinary DMTP of 92%, with a limit of detection of 1.1 [micro]g/L.

We agree with Fenske et al. that a more in-depth analysis is warranted and thank them for their interest and recommendations.

The authors declare they have no competing financial interests.

Gloria D. Coronado

Beti Thompson

Cancer Prevention Research Program

Fred Hutchinson Cancer Research Center

Seattle, Washington

E-mail: [e-mail]

William C. Griffith

Department of Environmental and

Occupational Health Sciences

School of Public Health and Community Medicine

University of Washington

Seattle, Washington

REFERENCES

Coronado GD, Thompson B, Strong L, Griffith WC, Islas I. 2004. Agricultural task and exposure to organophosphate pesticides among farmworkers. Environ Health Perspect 112:142-147.

Barr DB, Bravo R, Weerasekera G, Caltabiano LM, Whitehead RD Jr, Olsson AO, et al. 2004. Concentrations of dialkyl phosphate metabolites of organophosphorus pesticides in the U.S. population. Environ Health Perspect 112:186-200.