有害

1. Origins, structure, and basic meaning

• Structure: 有害 (ゆうがい) means harmful to organisms or the environment. 有害な asserts a property; 有害かどうか leaves it under test.
• Basic usage: Harmful smoke is avoided; an experiment checks whether a component harms plants.

2. Common pitfalls and similar expressions

• Smoke treated as harmful and substance still under examination
  • The first presupposes harm; かどうか in the second keeps the outcome open. Do not assert toxicity before the experiment.