RT Journal Article SR Electronic T1 Sex ratio at birth and exposure to petrochemicals JF Occupational and Environmental Medicine JO Occup Environ Med FD BMJ Publishing Group Ltd SP 704 OP 704 DO 10.1136/oem.60.9.704 VO 60 IS 9 A1 W H James YR 2003 UL http://oem.bmj.com/content/60/9/704.abstract AB