(1) It can not be degraded by microorganisms in water body, but can only produce mutual transformation, dispersion and enrichment among various forms.

(2) It can exist either in the form of compound or in the form of ion. Its solubility is very small and it is often deposited on the bottom.

(3) The toxic effect is fast. It enters the human body and reacts strongly with physiological macromolecular substances, making them inactive and poisoning the human body.

(4) It can be enriched in organisms and cause harm through various ways.

(5) The long-term pollution source is difficult to control, and the concentration increases in flood season.