The predator-prey BMFs of HCH in ringed seals of 20 and in beluga whales of 50 exceed the BMFs of PCB 180 in those animals.
其中:
BMF是生物放大因子(是一个数字)
HCH和PCB 180是两种有毒化学物质
ringed seals是环海豹,beluga whales是白鲸
问题为:ringed seals of 20和beluga whales of 50 中的of,后面加数字代表什么意思?