Can elements of one's environment act directly as hormones?
A hormone is defined as "a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism" (I'm just taking Wikipedia definition).

Hormones work by binding to specific receptors present on their target cells so, if there is something in the environment that mimics the hormone, by binding to the same receptor they can act as hormones: these substances are called xenohormones and can often act as endocrine disruptors compounds (EDC), by acting on various organs in the body.

Probably the most known xenohormones are xenoestrogens that are been studied as possibly harmful for human health (e.g. linked to breast cancer), and as an environmental hazards, as they can, for instance, cause reproductive problems in fish.

Xenohormones are not necessarily bad, though. Some analogs of human hormones are used in therapy, having being synthesised specifically, for instance, to have higher potency then their natural counterparts.