Enrichment and risk assessment of molybdenum (Mo) in the rock-soil-maize continuum of a black shale area.

Authors

Pengfei Chen, Zijie Chen, Yongxiang Zhang, Yizhang Liu

Published in

Environmental geochemistry and health. Volume 48. Issue 11. Jul 28, 2026. Epub Jul 28, 2026.

Abstract

Soils overlying black shale commonly exhibit high molybdenum (Mo) background levels, yet Mo transfer along the rock-soil-plant continuum and its ecological implications remain unclear. This study systematically investigated Mo concentrations and associated risks in rock, soil, and maize samples from a black shale area in southwestern China. The results demonstrate that weathering of Lower Cambrian black shales (Mo: 6.14-52.59 mg/kg) results in Mo enrichment in the overlying soils (0.96-50.04 mg/kg). Along the weathering profile, Mo concentration generally increases from fresh rock to weathered rock, but shows variable trends from weathered rock to soil. Sequential extraction reveals that > 80% of soil Mo resides in the residual fraction, 15.14% in the organically bound fraction, and < 2% in other fractions. The ammonium-oxalate-extractable Mo averages 8.3% of total Mo, suggesting low bioavailability of Mo in these soils. Maize grains contain 0.55 mg Mo/kg on average, which correlates positively with total soil Mo. Moreover, Mo concentrations in different maize tissues follow the order: husk > grain > cob. The Cu/Mo ratios in cobs and husks are severely imbalanced, implying a considerable risk of Cu toxicosis in grazing ruminants. In contrast, the human health risk arising from dietary intake of Mo via maize grain consumption appears to be negligible. Collectively, these findings underscore the geogenic enrichment of Mo in soils from black shale areas and its limited translocation within the soil-maize system. This work provides guidelines for the risk management strategies in regions with similarly high geochemical backgrounds.

PMID:
42517955
Bibliographic data and abstract were imported from PubMed on 28 Jul 2026.

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