Sentence Completion with Context Clues

In a remarkable display of ingenuity, the scientist devised a method to convert waste into clean energy. This technological breakthrough not only promises to reduce pollution significantly but also offers a sustainable solution for the growing energy demands of cities. Her peers were impressed by her unorthodox approach and were quick to applaud her for thinking outside the box. However, the majority of her colleagues remained skeptical, believing that the project might have ______ effects hidden beneath its surface, despite its apparent benefits.

What word best completes the sentence?