Ecological risks of molybdenum in black shale and carbonate areas: Exposure, health effects, and relation with selenium.

Excessive molybdenum (Mo) intake poses potential health risks, particularly to liver and kidney function. Black shales are natural reservoirs of Mo and selenium (Se). Se mitigates heavy metal toxicity in humans. However, the exposure levels of Mo and its interactions with Se in black shale areas remain poorly understood. In this study, Mo exposure in Enshi, China, where clastic, carbonate, and black shales coexist, was investigated. The results revealed that the soil Mo concentration increased from clastic (1.03 μg/g) to carbonate (1.87 μg/g) to black shale (14.28 μg/g) areas. Rice provides more than 90 % of dietary Mo intake for populations that consume it as a staple food. Black shale-area residents had the highest Mo and Se intakes (907.5 and 318.2 μg/d, respectively) through local rice consumption, leading to elevated urinary Mo and Se (649.512 and 130.808 μg/L, respectively) excretion. Clastic-area residents consumed the lowest but moderate concentrations of Mo and Se (154.0 and 15.4 μg/d, respectively), and their urinary Mo and Se concentrations (89.844 and 10.153 μg/L, respectively) were the lowest. In contrast, carbonate-area residents had high Mo intake (386.8 μg/d) but insufficient Se (42.0 μg/d) to promote Mo excretion, resulting in high urinary Mo and low Se concentrations (193.164 and 14.604 μg/L, respectively), and the highest blood Mo levels. Elevated blood Mo levels in carbonate-area residents affect liver function and protein metabolism. Elevated uric acid in black shale and carbonate-area residents indicates kidney risks. These findings highlight Mo-related health concerns in black shale and carbonate rock areas.