Complex sentence: One academic suggests that cyromazine, a melamine derivative pesticide commonly used in China for a long time, is absorbed into plants as melamine; it may therefore have long been present in products such as poultry, eggs, fish, and dairy products.
Split into simpler sentences: One academic suggests it may have been part of the food chain in China for a long time, as cyromazine (a melamine derivative) is a very commonly used pesticide in China. Cyromazine is absorbed into plants as melamine, and may therefore be present in the food chain, which includes poultry, eggs, fish, and dairy products.