This study looked at how rocks under farmland can put harmful metals into soil and rice. Three common rock types were studied: phosphorite, black shale, and basalt. The researchers measured the amounts of lead, arsenic, mercury, cadmium, zinc, chromium, nickel and copper in the soil and in rice grains grown there. They also used isotope fingerprints and a statistical tool called Positive Matrix Factorization to figure out where the metals were coming from.

In fields over phosphorite, soil had high levels of lead, arsenic and mercury. Rice grown there picked up a mix of cadmium, lead, arsenic, mercury and chromium, but the overall increase was moderate. Black shale soils were rich in cadmium and zinc; this meant rice from those fields contained a lot of cadmium. Basalt soils carried more chromium, nickel and copper; rice from those plots ended up with high chromium and nickel.

The analysis traced the metals to four main sources: the natural background of the rocks, farming practices, car traffic and coal burning. Metals that come from phosphorite stayed mostly in the top layer of soil and were less available for plants to absorb. In contrast, metals released from weathered black shale (cadmium and copper) and basalt (zinc, nickel and mercury) were more readily taken up by rice.

Overall the work shows which metals are most dangerous in each geological setting and how they move from rock to plant. This information can help farmers and regulators decide how best to keep rice safe in areas with different underlying rocks.

Rice Soil and Grain Risks from Different Rocks

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