Cadmium (Cd) and zinc (Zn) accumulation by Thai rice varieties and health risk assessment in a Cd-Zn co-contaminated paddy field: Effect of soil amendments.

Zinc mining and smelting activities result in cadmium (Cd) and zinc (Zn) contamination in rice grains, causing deleterious impacts on human health and local economies. Here, we investigated the effects of soil amendments, including mixtures of dicalcium phosphate with cattle manure (T1) and leonardite (T2), on soil physicochemical properties as well as growth performance and accumulation of Cd and Zn among three commercial Thai rice varieties: Khao Dok Mali 105 (KDML105), Phitsanulok2 (PSL2) and RD3, grown in a Cd-Zn co-contaminated paddy field. Human health risk was assessed using the health risk index (HRI) and Daily Intake of Metal (DIM). Application of the amendments, particularly T1, decreased Cd and Zn bioavailability by 60% and 39%, respectively, increased biomass production in PSL2 and RD3 varieties, and substantially reduced Cd uptake in the KDML105 variety by 47%. While levels of Zn in whole plant tissues of all treatments did not exceed maximum levels of undesirable substances in fodder, Cd contents in grain of PSL2 and RD3 exceeded the maximum allowable concentration of 0.2 mg kg-1. The HRI values for Cd of PSL2 and RD3 varieties were relatively high and are considered to pose a potential risk to human health. KDML105 in the T1 treatment had the lowest HRI value (0.05 ± 0.03), which was within acceptable limits. Our results suggest that Cd and Zn accumulation in rice and associated human health risks could be reduced by application of amendments to paddy soils, but the effectiveness depends on amendment types, rice varieties and soil physicochemical properties.