Species-Specific Molybdenum Enrichment in Peanuts (Arachis hypogaea) from Natural Molybdenum-Rich Agricultural Soils: Uptake Drivers and Dietary Risk Implications

Molybdenum (Mo) is an essential plant micronutrient, and legumes may accumulate relatively high Mo because of their greater physiological demand. Field evidence for species-specific Mo transfer in naturally Mo-enriched soils remains limited. Rhizosphere soil and edible seeds/grains were collected from 18 peanut and 19 wheat fields in Xichuan County, Henan Province, China. Soil total and available Mo, grain Mo concentrations, bioaccumulation factors (BCFs), dietary intake, and target hazard quotients (THQs) were evaluated. Soil total Mo ranged from 0.58 to 6.09 mg/kg and available Mo from 0.08 to 0.88 mg/kg. Peanut seeds contained about 8-fold more Mo than wheat grains (3.36 vs. 0.40 mg/kg) and had higher BCFs (0.32–7.95 vs. 0.05–1.29). Path analysis identified total soil Mo as the dominant predictor of available Mo, while peanut seed Mo showed no significant direct association with available Mo but was strongly associated with soil pH. The maximum soil Mo geoaccumulation index (Igeo) was 2.82 (Class 3). All THQs were below 1 under national-average consumption, whereas a hypothetical high-consumption peanut scenario yielded a THQ of 2.37. These findings highlight contrasting soil-to-grain Mo relationships between the two cropping systems and the need for crop-specific dietary risk assessment.