Pollution exposure and high DNA fragmentation index in human sperms: a case-control study

Study question: Could pollution exposure play a key role on sperm quality, in terms of DNA fragmentation index (DFI)? Summary answer: Patients exposed to high level of pollution show an higher percentage of sperm DNA fragmentation index in contrast with patient from control group. What is known already: Taranto area is characterized by a number of steel factories and petrochemical industries. Data about the detrimental effects of environmental pollution are alarming. Pollution coming from the industrial plants causes health and fertility risks, mainly due to the exposure to several pollutant (PM10, heavy metals, etc). Toxic substances can affect DNA directly or indirectly, through oxidative stress, impairing sperm quality: high levels of sperm DNA fragmentation index has been summoned as possible cause of male infertility; it is known, in effect, that a spermatic DFI less than 15% is physiologic, while above 30% is related to fertility issues. Study design, size, duration: Case-control study: valuation of DFI in patients exposed to different level of environmental pollutants. A. Patients from the city of Taranto leaving far from industries B. Patients working in local steel factories in Taranto C. Patients from Palermo (control group) Duration of the study: 24 months, from January 2010 to December 2012. DFI assessed by in situ TUNEL assay. The fields of fixed semen samples were analysed, by fluorescence and light microscopy. Participants/materials, setting, methods: Three different groups of patients (tot. number of pts 152), afferent to an assisted reproduction clinic in Taranto: Group A) workers of local steel factories (pt. No: 28) and B) Taranto residents (pt. No: 61) and a Control group C) (pt. No: 63) afferent to an assisted reproduction clinic in Palermo with supposed fertility issues. Main results and the role of chance: Our study analyzed sperm samples from three patients groups: A) workers of local steel factories; B) Taranto residents; C) Controls. We observed a highly statistically significant increase of spermatic DNA fragmentation Index (DFI) in the “factory workers” group, constantly exposed to environmental pollutants for professional reasons” compared with control (DFI 31% vs 16.8% P ≤ 2.685 * 10−6) as well as in comparison with the Taranto resident (DFI 31% vs 25% P ≤ 2.9 * 10−3). We have also observed a statistically significant difference between Taranto resident and control group (DFI 25% vs 16.8% P ≤ 3.681*10−6). Limitations, reasons for caution: The limitation of this study is that it is a retrospective study and the size of cohort of patients. Wider implications of the findings: Our study supports the hypothesis that the level of dioxin exposition might be positively correlated with the sperm DFI. Interrupting the sperms damaging source might bring back the DFI level to normal values. So, moving away from the damaging source, patients from A and B groups could restore spermatogenesis. Trial registration number: The trial is an observational study and no registration is needed.