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Estrogens have a well known physiological effect on bone. Chemicals in the environment with estrogenic activity may thus influence bone during development. Methoxychlor (MXC) is a chlorinated hydrocarbon pesticide with estrogenic properties and is commonly used in the United States. This study examines early MXC exposure in 25 male Fischer 344 rats (6‐7/group) randomized to control [DMSO (CTL)], MXC [0.02 mg/kg/day, low environmentally relevant dose (M‐low)], MXC [100 mg/kg/day, high dose (M‐hi)], or E2B [positive control; 1 mg/kg/day of β‐estradiol‐3‐benzoate]. Treatments were administered in utero (days 19‐22) and postnatally (days 0‐7). Body composition, and the femur and tibia bone mineral density (BMD) and content were examined at postnatal day 84 using dual energy x‐ray absorptiometry and biomechanical properties are currently being tested. Body weight was 92‐94% (p ≤ 0.05) and 80% (p < 0.001) of CTL in the MXC and E2B groups, respectively. Only the M‐low group showed a reduced % body fat (p < 0.01) compared to CTL, whereas lean body mass was lower (p ≤ 0.01) only in the M‐hi and E2B groups compared to CTL. Whole body BMD was lower (p < 0.05) in M‐hi and E2B versus CTL, but not after correcting for body weight. Low and high dose MXC reduced femur BMD (p < 0.01). These data show that early exposure to MXC will reduce growth and bone mineral density, and may be associated with an increase in fracture risk.

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