Affected females can develop a huge penis that blocks their release of eggs. The resulting egg-engorged females eventually die. The one agent now known to trigger this excessive masculinization is tributyl tin. It's not an androgen, but a toxic compound used to retard barnacle development on ship hulls. How this pollutant masculinizes the snails remains a mystery.
Some female fish change into males in response to local sex ratio or social cues.
The chemistry behind the switch has remained elusive. The Birmingham team's report on andro and related compounds now indicates that besides natural factors, pollution can have gender bending effects. He's also impressed by the growing list of hormonal signals that have been identified in the environment. Even 5 years ago, scientists recognized only a few instances of environmental hormones, all estrogens, McLachlan notes. From Science News , Vol.