Screening indices for cadmium-contaminated soil using earthworm as bioindicator

Artificial soil simulation tests were conducted to study the response of oxidative stress in different parts of Eisenia fetida under cadmium Cd) stress. Factor analysis and analytic hierarchy process were used to establish a comprehensive mathematical model to screen key monitoring indices of the Cd-contaminated soil early warning system. This paper sets the short-term group and the long-term group. The former lasted 10 days, and the latter was 30 days. Gradient solution of 0, 50, 100, 125, 250, and 500 mg kg^-1 Cd²⁺ was used in each test group. The earthworm was cut into two parts from its clitellum to determine oxidative stress indices. Results showed that during the short-term stress, TP (total protein) in the head tissues of the earthworm was the key monitoring index for 3-4 and 8-9 days of Cd stress. In addition, the TP in tail tissues was the key index for 2, 4, 6, and 8-10 days of stress. On the first and second days, the key monitoring indices in the tail tissues were both the CAT (catalase), while in the head, they were CAT and TP, respectively. On the 5th, the 7th, and the 9th days, the focus should be on monitoring POD (peroxidase) in the tail tissues, while in the head tissues, they were POD, CAT, and TP, respectively. In the long-term test after 10 days of Cd stress, the key monitoring index in head tissues was GPX (glutathione peroxidase), and in the tail, it was TP. At 20-30 days, the key monitoring indices were TP in the head and MDA (malondialdehyde) in the tail.