The United States Environmental Protection Agency has defined five tiers of environmental costs. Tie-2 costs are called 'hidden costs' because

they are hidden in the accounts so that stakeholders are unaware of the potential environmental risks of the firm.

they tend to be included in other accounts such as overhead and therefore are not easily identifiable.

they cannot be estimated with any degree of certainty.

it is not possible to show them in a separate account.

they may not be incurred in the future