Contaminants can both speed and slow the rate of sexual development.
In general, it would appear from existing data that estrogen mimics speed sexual development in females, while anti-androgens slow sexual development in males. This story is far from complete. Androgen mimics should speed the onset of puberty in males. Unfortunately, the sparseness of the scientific literature indicates that most compounds have not been tested systematically for their effects. The studies that have been done, however, reveal very strong effects, suggesting that other hormonally-active compounds, not yet studied, will also have impacts.