Reply: Episodic air pollution and sperm DNA fragmentation

Abstract

Sir, Dr Jafarabadi asks a valid question for which we have the following response. The actual cold season (winter) in the Teplice District of the Czech Republic, when air pollution increases, does not correspond precisely with winter as defined by the calendar. Thus cold, winter-like temperatures are encountered from at least late October through to March. The cold temperatures are associated with increased air pollution due to both increased coal usage for home heating and climate-related temperature inversions that hold the pollution in the valleys, creating episodes (several days duration) of very high pollution. This phenomenon is nicely illustrated in Sram et al. (1996), Figure 2, for an earlier year. Although not stated in our paper (Rubes et al., 2005), we intentially designed the study to obtain semen samples during the last week of the months of January, February (both years) and March. Figure 1 of our paper illustrates the average pollution levels for the 90 days preceeding each semen sampling week. This interval of time was selected precisely according to the point Dr Jararabadi makes, that spermatogenesis (including epididymal transit) in humans takes 72–90 days. Thus in Figure 1, bar 2 represents exposures averaged from late October through late January when the second semen sample was obtained; bar 3 represents exposures from late November through late February when the third semen sample was obtained, and bar 4 represents exposures averaged from late December through late March when the fourth semen sample was obtained. For the pollutants measured, the average pollution was similar when averaged for 90 days, whether starting in late October or late January. This observation formed the basis of our classifying exposures simply as ‘high’ or ‘low’. Thus, ‘winter’ pollution here includes the months of November and March. We hope this explanation clarifies that our study design adequately permitted us to examine potential associations between exposures to elevated air pollution during the entire process of spermatogenesis and changes in semen measures. Thank you for allowing us to make this important clarification.