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Rebecca Z. Sokol,¹ Peter Kraft,² Ian M. Fowler,¹ Rizvan Mamet,² Elizabeth Kim,³ and Kiros T. Berhane²

¹Department of Obstetrics, Gynecology and Medicine, and ²Department of Preventive Medicine, Keck School of Medicine of the University of Southern California, Los Angeles, California, USA; ³California Cryobank, Los Angeles, California, USA

Abstract
Idiopathic male infertility may be due to exposure to environmental toxicants that alter spermatogenesis or sperm function. We studied the relationship between air pollutant levels and semen quality over a 2-year period in Los Angeles, California, by analyzing repeated semen samples collected by sperm donors. Semen analysis data derived from 5,134 semen samples from a sperm donor bank were correlated with air pollutant levels (ozone, nitrogen dioxide, carbon monoxide, and particulate matter < 10 µm in aerodynamic diameter) measured 0-9, 10-14, and 70-90 days before semen collection dates in Los Angeles between January 1996 and December 1998. A linear mixed-effects model was used to model average sperm concentration and total motile sperm count for the donation from each subject. Changes were analyzed in relationship to biologically relevant time points during spermatogenesis, 0-9, 10-14, and 70-90 days before the day of semen collection. We estimated temperature and seasonality effects after adjusting for a base model, which included donor's date of birth and age at donation. Forty-eight donors from Los Angeles were included as subjects. Donors were included if they collected repeated semen samples over a 12-month period between January 1996 and December 1998. There was a significant negative correlation between ozone levels at 0-9, 10-14, and 70-90 days before donation and average sperm concentration, which was maintained after correction for donor's birth date, age at donation, temperature, and seasonality (p < 0.01) . No other pollutant measures were significantly associated with sperm quality outcomes. Exposure to ambient ozone levels adversely affects semen quality. Key words: air pollution, epididymis, male infertility, ozone, semen analysis, sperm concentration, total motile sperm count. Environ Health Perspect 114:360-365 (2006) . doi:10.1289/ehp.8232 available via http://dx.doi.org/ [Online 5 October 2005]

Address correspondence to R.Z. Sokol, Women's and Children's Hospital, 1240 North Mission Rd., Room 8K9, Los Angeles, CA 90033 USA. Telephone: (323) 226-3091. Fax: (323) 226-2850. E-mail: rsokol@usc.edu

We thank J. Peters for his guidance and advice, F. Lurmann and Sonoma Tech Inc. for their generous provision of air quality data and advice, and S. Broder of the California Cryobank for advice.

This work was supported by National Institute of Environmental Health Sciences grants F3 ES11535 to R.Z.S. and P30 ES07048 to the University of Southern California Keck School of Medicine.

E.K. is an employee of California Cryobank.The remaining authors declare they have no competing financial interests.

Received 15 April 2005 ; accepted 27 October 2005.