Journal of Pediatric Psychology Advance Access originally published online on February 27, 2008
Journal of Pediatric Psychology 2008 33(4):447-448; doi:10.1093/jpepsy/jsn015
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Response
1Centro de Estudos Superiores do Trópico Úmido (CESTU), Escola Normal Superior, 2The University of Arizona, College of Public Health, and 3The University of Arizona, Special Education Rehabilitation, and School Psychology
All correspondence concerning this article should be addressed to Patricia Sánchez Lizardi, Centro de Estudos Superiores do Trópico Úmido (CESTU), Universidade do Estado do Amazonas (UEA), Reitoria, sala 111, Avenida Djalma Batista 3578, Flores, 69050-010-Manaus-AM, Brasil. E-mail: patricia.s.lizardi{at}gmail.com
We thank Drs. Gresham and LoVecchio for their interest in our article, "The Effects of Organophosphate Pesticide Exposure on Hispanic Children's Cognitive and Behavioral Functioning" in the Jan/Feb 2008 issue of the Journal of Pediatric Psychology (Sánchez Lizardi, O’Rourke, & Morris, 2008
) and invite others to read the article and evaluate it for themselves. We are in complete agreement that low socio-economic status (SES) has an appreciable impact on the health and achievement of children (Duncan, Brooks-Gunn, & Klebanov, 1994; Duncan, Yeung, Brooks-Gunn, & Smith, 1998) and considered these factors in the description of our study participants.
We utilized the categorical income questions from the 2000 Census for both income and education completed. In our study, the income difference between exposed and nonexposed groups was nonsignificant. Our population has no high SES segment and no one in our sample exceeded the national median income. We are examining low and lower SES individuals. All participating children were derived from the same census block groups. We also agree with Drs. Gresham and LoVecchio that parental level of education is a predictor of children's achievement. In our study, the only demographic characteristic that was statistically significant between the groups was father's years of education and mother's years of education was not. Children in both groups, despite father's years of education, had on the average the same grade point average (GPA, i.e., academic achievement). We stand by our assertion that both groups had nearly identical demographic characteristics.
As stated in the article, we had selected children for the exposed and nonexposed groups based on their organophosphate pesticide (OP) metabolite levels on the Children's Pesticide Survey (CPS), but had no certainty that they would remain in the same group. Unfortunately, for all of us, there is no OP-free control group that can be identified à priori within the same community. We selected a real world population from a geographically limited area, where residents are demographically similar and virtually everyone could be exposed at one time or another to OP. Work by Lu, Knutson, Fisker-Andersen, and Fenske (2001) also indicates that urinary OP metabolite levels can vary from day to day as a function of daily diet. When urinary samples for our study were analyzed, we found that all children had detectable levels of OP metabolite, meaning that we had a single "new-exposed" group. We are in agreement that the lack of a true control group is a major limitation, as we clearly indicated in the Discussion section of our article under "Limitations of the study and suggestions for future research."
Drs. Gresham and LoVecchio's concern about adjusting a study design after the study had been undergone is well founded. However, ours is an observational study in an agricultural community; no one's activities were altered by the study design. Furthermore, given the similar characteristics of our study participants, a correlational analysis was deemed appropriate to explore the association of the OP metabolite levels and the study participants’ performance on the particular day of their cognitive assessment. That is, we considered that the half-life of the compounds is very short and that urinary metabolite values can differ within the same child over short-time periods, and looked at the association of these values to performance measures in the same short-time span. We believe that our statement that short-term OP pesticide exposure seems to have deleterious effects on specific subtests of the Wisconsin Card Sorting Test (WCST) is supported by our correlational analysis of the data. Children with greater OP metabolite levels performed less effectively in the WCST's measures of speed of attention, sequencing, mental flexibility, visual search, concept formation, and conceptual flexibility. But, as we recommended in the article, this needs to be further investigated. As stated in our article, our study is among the first attempts to investigate a complex problem. We are pleased that Drs. Gresham and LoVecchio have chosen to comment on our article and look forward to more research being conducted by the scientific community in what we consider to be a very important area of inquiry.
Conflicts of interest: None declared.
Received January 23, 2008; revision received January 23, 2008; accepted February 4, 2008
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Duncan GJ, Brooks-Gunn J, Klebanov PK. Economic deprivation and early childhood development. Child Development (1994) 65:296–318.[CrossRef][Web of Science][Medline]
Duncan GJ, Yeung WJ, Brooks-Gunn J, Smith JR. How much does childhood poverty affect the life of children? American Sociological Review (1998) 63:406–423.[CrossRef][Web of Science]
Lu C, Knutson DE, Fisker-Andersen J, Fenske RA. Biological monitoring survey of organophosphorus pesticide exposure among pre-school children in the Seattle metropolitan area. Environmental Health Perspectives (2001) 109:299–303.[Web of Science][Medline]
Sánchez Lizardi P, O’Rourke MK, Morris RJ. The effects of organophosphate pesticide exposure on Hispanic children's cognitive and behavioral functioning. Journal of Pediatric Psychology (2008) 33:91–101.
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