Health risk assessment associated with heavy metal accumulation in wheat after long-term phosphorus fertilizer application.

Phosphorus (P) fertilizer is widely used to increase wheat yield. However, it remains unclear whether prolonged intake of wheat grain that received long-term P application may promote human health risks by influencing heavy metal(loid)s (HMs) accumulation. A 10-year field experiment was conducted to evaluate the effects of continuous P application (0, 25, 50, 100, 200, and 400 kg P ha) on human health risks of HMs, including zinc (Zn), copper (Cu), cadmium (Cd), lead (Pb), arsenic (As), nickel (Ni), and chromium (Cr), by ingesting wheat grain. The results showed that P application facilitated Zn, Pb, Cd, and As accumulation in the topsoil. The Zn, Cu, Pb, and Ni concentrations in grain were decreased, while Cd and As were increased by P application. All HMs concentrations of both soil and grain were in the ranges of corresponding safety thresholds at different P levels. The accumulation abilities of Zn, Cu, Pb, and Ni from soil and straw to grain were suppressed by P addition while of As was enhanced. There was no significant difference in the hazard index (HI) of the investigated HMs in all treatments except 25 kg ha. The threshold cancer risk (TCR) associated with As and Cd was enhanced, while that of Pb was alleviated as P application increased. Behaviors of Cr from soil to wheat and to humans were not affected by P application. Phosphorus application at a rate of 50 kg ha decreased total non-cancer and cancer risks by 15% and 21%, respectively, for both children and adults, compared to the highest value. In conclusion, long-term optimal application of 50 kg P ha to wheat did not result in additional adverse effects on the total non-carcinogenic or carcinogenic risk caused by the studied HMs to humans through the ingestion of wheat grain.