Study on the influential factors of Cd2+ on the earthworm Eisenia fetida in oxidative stress based on factor analysis approach

• Factor analysis is used in selecting biomarkers of oxidative stress induced by Cd.
• Earthworms are used to evaluate soil pollution and soil environment quality.
• Find out the key monitoring indicators in stress process caused by Cd in earthworm.
• CAT, MDA, POD, GST GSH-Px are the main bioindicators in short-term exposure.
• GSH-Px is the main bioindicators in long-term exposure.

When earthworms are exposed to pollutants, their antioxidant system will have responses immediately. Consequently earthworms are widely used to monitor various pollutants as a sensitive bio-indicator. However, there are a large number of indices associated with the oxidative stress response. Finding out the key monitoring indices in the stress process becomes a practical demand of the pollution monitoring and warning process. Factor analysis approach is a statistical method that uses a few factors to replace many original factors. This paper is aimed at analyzing and sorting factors related to Cd2+ on the earthworm Eisenia fetida in oxidative stress. We studied two groups, the short-term test and the long-term test. The former test lasted for ten days, removing an earthworm every day for analysis; The latter test lasted for 30 days, taking out an earthworm every ten days. The Cd2+ concentration was set at 0, 50, 100, 125, 250 and 500 mg kg−1, post-clitellum segments of earthworms were chosen to determine SOD, POD, GPX, GST, CAT, VE, MDA and AChE. The results showed that in the short-term group, the main bioindicator associated with oxidative stress reaction was CAT at the exposure time of 1–3 days, at 4–5 days MDA, 6–7 days POD, and GST and GPX at 8th day, CAT at 9–10 days. While with the long-term test, the main bioindicator associated with oxidative stress reaction was GPX.