Crayfish is very sensitive to heavy metals. In the water with excessive heavy metals, crayfish can't successfully shell and survive. Heavy metals can be accumulated, and the higher the food chain in nature, the more heavy metals are accumulated by organisms. Crayfish feed on aquatic plants, which are at the bottom of the food chain, and have low accumulation of heavy metals. Under normal culture, heavy metal residues will not exceed the standard.
Crayfish can survive in heavily polluted places, but most of the heavy metals it ingests are transferred to the shell. With the continuous growth and shelling, these heavy metal toxins are removed from the body, so the heavy metals in the meat may not exceed the standard. The research data show that most of the heavy metals in crayfish are concentrated in the head except the shell, and there is not much heavy metal in the tail we eat, which is unlikely to cause poisoning.