Speciation characteristics of heavy metal(loid)s in maize-wheat farmland with applying spent mushroom substrates

Spent mushroom substrates (SMS) have been increasingly applied as organic fertilizer worldwide. However, the effects of various SMS on the accumulation and speciation characteristics of soil heavy metal(loid)s (HMs) are generally overlooked. Three types of SMS, including Flammulina velutipes residue (FVR), Agaricus bisporus residue (ABR), and Auricularia auricula residue (AAR), were applied to replace 25 % and 50 % of chemical fertilizer (based on nitrogen application) used in maize-wheat farmland. Compared to chemical fertilizer, the soil Cd, Pb, and As concentrations were decreased by 20.41 %, 5.97 %, and 10.09 %, respectively. And the residual fractions of soil HMs were increased through the application of SMS, indicating a reduction in their bioavailability. Notably, 50 % ABR replacement significantly increased the proportion of residual fraction in soil Cd, Pb, and As by 23.03 %, 15.15 %, and 4.85 %, respectively (P<0.05). A significant negative correlation was observed between the concentrations of HMs in grains and the residual fractions of soil HMs. Thus, compared with chemical fertilizers, the residual fractions of soil HMs were increased by the application of SMS, thereby reducing the concentrations of HMs in grains. Ingestion of crops is the primary route for human exposure to HMs. Therefore, the application of SMS (especially ABR) reduced the accumulation and bioavailability of HMs in soil, which in turn limited the transfer of HMs to crops, resulting in lowered human health risk indices.