Complex sentence: A major concern is that contaminated sewage sludge is frequently recycled onto agricultural land, though the occurrence of nonylphenol in soil is not as well studied as its presence in sediments in aquatic environments.
Split into simpler sentences: A major concern is that contaminated sewage sludge is frequently recycled onto agricultural land. The occurrence of nonylphenol in soil is not as well studied as its presence in sediments in aquatic environments.