Iron, Zinc, and Cadmium Status in the Food Chain (Soil-Plant-Human) in Central Iran.
Amir Hossein Khoshgoftar1, Hossein Shariatmadari1, and Penelope Nestel2. (1) Isfahan University of Technology, Department of Soil Science, College of Agriculture,, Isfahan, Iran, (2) HarvestPlus, Wageningen, Netherlands
During the last 40 years, large amounts of P fertilizers have been used in salt-affected soils of central Iran. Enhanced Cd and reduced Fe and Zn concentration in the food chain (soil-plant-human) are probable consequences of poor management of plant nutrients. This study investigated Fe, Zn, and Cd levels in the soil, wheat grain, and hair of female subjects in Qom province, central Iran. Forty wheat crops and associated surface soils (0-25 cm), which are representative of soils used for wheat production in the region, were sampled. A complete information sheet including fertilizer management was prepared for each field. Available-P content, electrical conductivity (ECe), CaCO3 equivalent and the DTPA-extractable Zn, Fe, and Cd were measured in each soil. Grain Fe, Zn, phytic acid, and Cd concentrations were determined along with the hair Fe, Zn, and Cd levels of the female subjects. Most soils were generally heavily fertilized (typically > 600 Kg/ha), mainly with phosphate fertilizers, in which Cd is an impurity (<300 mg kg-1). Soil ECe and pH values varied widely. The mean Cd level (0.07 mg kg-1) was within the range expected for unpolluted soils. DTPA-extractable Cd levels were highly correlated (R2=0.93, P<0.05) with ECe. Soil Cd concentration was not correlated with pH or clay content, but was positively correlated with bicarbonate-extractable P. Most soils were Zn-deficient with DTPA-Zn concentrations <2.0 mg kg-1. Soil Zn concentrations were not correlated (P<0.05) with soil pH, ECe, clay content, or DTPA-extractable Cd. In contrast, the DTPA-extractable Fe was higher than its critical level in most of the soils; although Fe deficiency was observed in most grains. Grain Cd, Fe, and Zn concentrations varied greatly across sites. Grain Zn concentration was associated with wheat genotype; Zn efficient genotypes had more Zn and less Cd concentrations in their grains. Overall, grain Zn was negatively correlated with Cd concentration. Zn-efficiency and grain Fe concentration were not correlated. Likewise, grain Zn and P concentrations were negatively correlated. This study shows that the application of large amounts of P-fertilizers affected grain mineral concentrations in central Iran. Reduced Fe and Zn and enhanced Cd concentrations in the food chain are some of the consequences of the intensive application of P-fertilizers in the region. Mean hair Zn concentrations in 70 women of reproductive age were low compared to the normal range of hair Zn levels. Poorly nourished subjects (wheat bread being the staple food) had lower hair Zn levels (99 ug/g) compared with well-nourished subjects (150 ug/g). This indicates that a low grain Zn concentration is a likely to be an important cause of Zn deficiency. The typical Iranian diet, which contains <12 mg kg-1 Zn/day, does not meet the Zn requirement of young females. Hair Cd concentration was inversely correlated with hair Zn levels. Consequently, hair Cd levels were higher in the poorly nourished subjects than in the well-nourished ones (0.33 ug/g vs. 0.13 ug/g, respectively, P<0.0.05).