 Paralytic shellfish poisoning ( PSP ) is primarily caused by the consumption of bivalves that have accumulated toxins by feeding on toxic dinoflagellates , single @-@ celled protists found naturally in the sea and inland waters . <unk> is the most virulent of these . In mild cases , PSP causes tingling , numbness , sickness and diarrhoea . In more severe cases , the muscles of the chest wall may be affected leading to paralysis and even death . In 1937 , researchers in California established the connection between blooms of these phytoplankton and PSP . The <unk> remains potent even when the shellfish are well @-@ cooked . In the United States , there is a regulatory limit of 80 µg / g of <unk> equivalent in shellfish meat . 
