The combined effects of cadmium and acetochlor on an earthworm-soil-maize system

Heavy metal and pesticide pollution is a major environmental problem, and the combined effects on earthworm-soil-plant systems have not been thoroughly explored. This study investigated the individual and combined effects of cadmium (Cd) and acetochlor on earthworm physiological responses, soil physical and chemical properties, and maize growth and morphological characteristics. The results showed that superoxide dismutase (SOD) activity in earthworms decreased and then increased, whereas the opposite trend was observed with malondialdehyde (MDA) content. The earthworm distribution across soil layers increased in the compound pollution treatment, and the percentage of earthworms in the total soil layer increased by 1.34 times (on day 2) and 1.14 times (on day 50) compared with that in the control group. The soil organic matter and available phosphorus contents were unaffected by treatment time or contamination method, but alkali-hydrolyzable nitrogen content decreased and then increased with Cd + acetochlor pollution. On day 50, the maize root numbers in all treatment groups were significantly lower than those in the control group; the inhibition rates were 23.21% (30 mg·kg^-1 Cd), 42.86% (200 mg·kg^-1 acetochlor), and 50.00% (30 mg·kg^-1 Cd + 200 mg·kg^-1 acetochlor). The maize biomasses and plant heights were largest in the 30 mg·kg^-1 Cd group, followed by the 200 mg·kg^-1 acetochlor group, and were smallest in the 30 mg·kg^-1 Cd + 200 mg·kg^-1 acetochlor group. Correlation analysis showed that the interaction between Cd and acetochlor did not affect earthworm MDA content, soil nutrients, or the maize growth index, but antagonistically affected earthworm SOD activity. This study concluded that combined Cd and acetochlor pollution promoted earthworm distribution in the topsoil and inhibited maize growth by altering the soil's physical and chemical properties.