Letter to the editor: “Review of the epidemiologic literature on residential exposure to perchloroethylene” by John A. Bukowski

Dear Sir, We read with interest the recent article by John A. Bukowski “Review of the epidemiologic literature on residential exposure to perchloroethylene” (Bukowski, 2011). We were especially interested in his review of neurobehavioral studies as we anticipated description and interpretation of our study “Tetrachloroethylene (perc) exposure and visual contrast sensitivity (VCS) test performance in adults and children residing in buildings with or without a dry cleaner” (New York State Department of Health [NYS DOH], 2010). Unfortunately, in his review, Dr. Bukowski claims that confidence in our study findings that elevated residential perc exposure may alter children’s VCS is undermined by (i) low response rates presumably leading to selection bias resulting in over representation of “exposed” subjects, (ii) “selective reporting” such that “negative” study findings that are contrary to our “positive” findings are marginalized, (iii) confounding between lower socioeconomic status and exposure limiting our ability to associate perc exposure and VCS, and (iv) inconsistency of our findings with available literature. We strongly disagree with these characterizations of our study and note in detail below why they are unfounded and do not undermine confidence in our findings. Briefly, we found that increases in residential indoor air, breath, and blood perc level were each associated with significantly increased risk for school-age children, but not adults, to have slightly altered VCS. The interested reader is encouraged to read our complete study report available at: http://www.health. ny.gov/environmental/ investigations/perc/perc_vision_report. pdf. A comprehensive description of recruitment and enrollment procedures has appeared in the scientific literature (McDermott et al., 2005); as has a comprehensive description of the influence of residential perc exposure on children’s VCS (Storm et al., 2011). The alteration in VCS was very small, limited to visual images of a specific size, and occurred only in children’s worse performing eyes. Nevertheless, because the optical components of vision were controlled during VCS testing, our results suggested that a subclincal central nervous system (CNS) effect (specifically within or affecting centrally mediated visual pathways) in schoolage children was associated with increasing perc exposure. We know of no other evidence linking residential indoor air, breath or blood perc levels to neurobehavioral effects in children, and we believe our findings are strong enough to warrant additional investigation. We do not concur that low response rates undermine confidence in our study findings. Ordinarily, low response rates are a concern because they may contribute to selection bias. This would be a concern in our study if those with elevated perc exposures and/or altered VCS or color vision were more likely to have participated than others (Aschengrau & Seage, 2008). However, selection bias was minimized by our recruitment methods. Earlier research had shown that perc exposures might be elevated in some, but not all, residential buildings where a dry cleaner using perc was colocated, and that vision in adults might be harmed by such exposures (Altmann et al., 1995; Schreiber et al., 2002). Other research suggests that children might be more affected by exposure to environmental contaminants, including perc, than adults (Needham & Sexton, 2000; Stein et al., 2002; Schwenk et al., 2003). To investigate these possibilities, we designed our study to evaluate the relationships between individual measurements of perc exposure (perc level in indoor air, exhaled breath, and blood) and vision (VCS, color vision) in matched adult–child pairs. Given past research, we anticipated that residents in buildings with colocated dry cleaners might have elevated perc exposures and that residents in buildings without a dry cleaner would not. Therefore, possibly perc “exposed” adult–child pairs were recruited from residential buildings with a dry cleaner, Letter to the editor