Complex sentence: Molluscs have been and still are an important food source for anatomically modern humans, but with a risk of food poisoning from toxins that accumulate in molluscs under certain conditions, and many countries have regulations to reduce this risk.
Split into simpler sentences: Molluscs have been and still are an important food source for anatomically modern humans. However there is a risk of food-poisoning from toxins that accumulate in molluscs under certain conditions, and many countries have regulations that aim to minimize this risk.